The yeast actin cytoskeleton.

REVIEW ARTICLE

The yeast actin cytoskeleton Mithilesh Mishra1, Junqi Huang1,2,3 & Mohan K. Balasubramanian1,2,3,4 1

Temasek Life Sciences Laboratory, National University of Singapore, Singapore; 2Department of Biological Sciences, National University of Singapore, Singapore; 3Mechanobiology Institute, National University of Singapore, Singapore; and 4Division of Biomedical Cell Biology, Warwick Medical School, University of Warwick, Coventry, UK

Correspondence: Mohan K. Balasubramanian, Temasek Life Sciences Laboratory, National University of Singapore, Singapore 117604, Singapore. Tel.: (65) 6872 7000; fax: (65) 6872 7007; e-mails: [email protected] or [email protected] Received 2 October 2013; revised 18 January 2014; accepted 20 January 2014. Final version published online 20 February 2014. DOI: 10.1111/1574-6976.12064 Editor: Sophie Martin

MICROBIOLOGY REVIEWS

Keywords actin; cytoskeleton; yeast; cytokinesis; polarity; endocytosis.

Abstract The actin cytoskeleton is a complex network of dynamic polymers, which plays an important role in various fundamental cellular processes, including maintenance of cell shape, polarity, cell division, cell migration, endocytosis, vesicular trafficking, and mechanosensation. Precise spatiotemporal assembly and disassembly of actin structures is regulated by the coordinated activity of about 100 highly conserved accessory proteins, which nucleate, elongate, cross-link, and sever actin filaments. Both in vivo studies in a wide range of organisms from yeast to metazoans and in vitro studies of purified proteins have helped shape the current understanding of actin dynamics and function. Molecular genetics, genome-wide functional analysis, sophisticated real-time imaging, and ultrastructural studies in concert with biochemical analysis have made yeast an attractive model to understand the actin cytoskeleton, its molecular dynamics, and physiological function. Studies of the yeast actin cytoskeleton have contributed substantially in defining the universal mechanism regulating actin assembly and disassembly in eukaryotes. Here, we review some of the important insights generated by the study of actin cytoskeleton in two important yeast models the budding yeast Saccharomyces cerevisiae and the fission yeast Schizosaccharomyces pombe.

Introduction Actin is one of the most abundant and highly conserved proteins found in eukaryotes and is essential for the survival of most eukaryotic cells (Pollard et al., 2000). It exists in two states: the globular monomeric (G-actin) and the filamentous polymeric (F-actin) forms. F-actin is a right-handed double-stranded helix with a dynamic barbed end, where ATP-bound G-actin is preferentially incorporated, and a pointed end, which is the preferred site of actin disassembly. The formation of F-actin structures in cells is limited by energetically unstable dimeric and trimeric intermediates and sequestering of G-actin by binding partners such as profilin. Dedicated filament nucleators such as Arp2/3 complex and formins overcome this inhibition and initiate actin polymerization in a spatiotemporal order inside the cell (Pollard, 2007; Chesarone & Goode, 2009; Campellone & Welch, 2010). These nucleated actin filaments elongate and organize into networks of distinct architecture and associated protein FEMS Microbiol Rev 38 (2014) 213–227

constituents (Chhabra & Higgs, 2007). Actin undergoes multiple cycles of rapid polymerization and disassembly, which allows the cells to remodel the actin cytoskeleton and provide the force for processes such as cell movement and vesicle internalization (Pollard & Borisy, 2003). Eukaryotic cells use more than 100 highly conserved accessory proteins that maintain the pool of actin monomers, promote nucleation and growth of actin filaments, stabilize and cross-link filaments into bundles and regulate the disassembly of actin filaments (Pollard et al., 2000; Pollard, 2007; Pollard & Cooper, 2009). The precise regulation and activation of these accessory proteins in space and time allows cells to organize actin filaments at specific regions of the cytoplasm where they can carry out their function in response to various stimuli. The actin filament network in yeast cells is analogous to that found in metazoans, albeit less extensive. Yeast cells assemble three distinct actin structures, cortical actin patches, actin cables, and the actomyosin ring (Fig. 1; Adams & Pringle, 1984; Kilmartin & Adams, 1984; Marks ª 2014 Federation of European Microbiological Societies. Published by John Wiley & Sons Ltd. All rights reserved

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Mitosis

Interphase

filament networks (Liu et al., 2006; Vavylonis et al., 2008; Berro et al., 2010). For these reasons, budding yeast and fission yeast have served as important cell types for the study of actin biology. Many important actin nucleators such as Arp2 (Schwob & Martin, 1992) and Arp3 (LeesMiller et al., 1992) were first identified in genetic screens performed in yeast and were subsequently found to have human homologues (Higgs & Pollard, 2001). Yeast studies have also helped to assign molecular functions to other actin cytoskeletal proteins. Role of formin as a nucleator of linear actin filaments came from analysis of its budding yeast homologues Bni1p and Bnr1p (Evangelista et al., 2002; Sagot et al., 2002a, b). In this review, we describe the three filamentous F-actin structures found in yeasts, discuss their physiological functions, and trace their formation and disassembly.

Actin patches and endocytosis F-actin cable or filament Spindle pole body

Actin patch

Actomyosin ring

Spindle

Fig. 1. Actin organization during cell cycle in budding yeast and fission yeast. In both budding yeast (left panel) and fission yeast (right panel), F-actin forms three distinct filamentous structures: actin patches, actin cables, and actin ring. Actin patches are assembled at the endocytotic sites, and their distribution is correlated with region of polarized growth. Actin patches appear at the cell growth zones during interphase and the cell division site during late mitosis. Actin cables are present in all stages of cell cycle in both yeasts, run along the length of the cell, and are involved in intracellular cargo transport. In fission yeast, actin cables also play a role in actin ring assembly. Actin ring (depicted in blue) is assembled at the division site early in mitosis, which constricts after completion of anaphase to divide the mother cell into two daughter cells. Microtubules are shown in red.

et al., 1986) as opposed to more than 15 structures found in metazoan cells (Chhabra & Higgs, 2007), thereby making the analysis of the actin filament network easier. Moreover, yeasts have only one actin isoform (Shortle et al., 1982) and a smaller number of actin regulatory proteins with little redundancy (Moseley & Goode, 2006). Genetic screens in yeast helped identify various factors important for the formation of actin filament network. Sophisticated molecular tools and a high rate of homologous recombination in yeast allow for easy genetic manipulations and expression of fluorescent-tagged proteins at their endogenous levels. This has helped in tracking the precise sequence of molecular events that drives the formation of different actin filament structures in space and time. More recently, quantitative data sets generated from studies of complex interaction networks along with theoretical modeling experiments have revealed mechanistic insights into the assembly and function of these actin ª 2014 Federation of European Microbiological Societies. Published by John Wiley & Sons Ltd. All rights reserved

Actin patches are dense dendritic networks of branched actin filaments nucleated by the Arp2/3 complex that is involved in clathrin-mediated endocytosis (CME) and localize to the polarized growth zone (Fig. 2; Kubler & Riezman, 1993; Winter et al., 1997; Kaksonen et al., 2003; Young et al., 2004; Gachet & Hyams, 2005). The link between endocytosis and actin patches was revealed when endocytic mutant screens in budding yeast identified numerous actin cytoskeletal components as proteins essential for uptake of both cell surface receptors and extracellular fluid (Kubler & Riezman, 1993; Benedetti et al., 1994; Munn & Riezman, 1994; Munn et al., 1995). Mutations in actin cytoskeletal genes, including the Arp2/ 3 complex, or treatment of budding yeast cells with drugs that inhibit actin polymerization blocked CME (Ayscough et al., 1997; Engqvist-Goldstein & Drubin, 2003; Kaksonen et al., 2003). Sophisticated live cell imaging allowed for the visualization of assembly and disassembly of endocytic and actin-associated proteins at actin patches with a high temporal resolution. Combined with genetic dependency studies, these experiments revealed the roles of various components in the process of CME (Kaksonen et al., 2003, 2005; Newpher et al., 2005; Sirotkin et al., 2010; Weinberg & Drubin, 2012). These studies have identified about 60 highly conserved proteins that localize in a strictly ordered fashion to distinct sites of the plasma membrane to coordinate membrane invagination, tubulation, and scission to form endocytic vesicles (Galletta et al., 2010; Weinberg & Drubin, 2012). Unlike in metazoan cells, actin is essential for CME in yeasts (Galletta et al., 2010). The force generated from actin polymerization has been proposed to overcome the high turgor pressure of yeast cytoplasm for plasma membrane invagination during CME (Aghamohammadzadeh & Ayscough, 2009). A recent study FEMS Microbiol Rev 38 (2014) 213–227

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Yeast F-actin structures

Plasma membrane

F-actin filament

Clathrin and adapter proteins Arp2/3 complex

Bar/F-Bar domain protein Crosslinking protein

Type I myosin

WASP

Cofilin Coronin

Capping protein

Fig. 2. A cross-section of an endocytic actin patch. Actin patch assembles at the endocytotic sites. Clathrin and adaptor proteins arrive early and mark the endocytic site. The Arp2/3 complex nucleates a dense network of branched actin filaments by generating a new branch of F-actin on a pre-existing filament at an angle of 70°. WASP and myosin 1 are the two NPFs (nucleation promoting factors) of the Arp2/3 complex present in spatially distinct regions of actin patches. Myosin 1 is localized to the neck region of the endocytic vesicle, while the WASP protein localizes to more distal region. Fimbrin cross-links the actin filaments in the actin patches. Capping proteins cap the filaments and limit their growth, and filaments are severed by cofilin. These two families of proteins along with coronin control the filament length and dynamics of the actin network in cortical patches. BAR- and F-BAR-domain-containing amphiphysin proteins cooperate with F-actin to promote membrane invagination and scission.

has uncovered an endocytic pathway in budding yeast that is mediated by the small GTPase Rho1 and is independent of clathrin and other CME components (Prosser et al., 2011; Prosser & Wendland, 2012). Actin patch proteins are recruited at the site of CME in an ordered manner (Kaksonen et al., 2003, 2005, 2006; Merrifield, 2004; Sirotkin et al., 2005, 2010). Clathrin, an endocytic protein, and its adaptors are the first to arrive at the membrane to form coated pits and assemble endocytic cargos such as membrane receptors, transporters, and v-SNAREs (Engqvist-Goldstein & Drubin, 2003; Burston et al., 2009; Conibear, 2010). These proteins remain relatively stationary at the membrane. The next wave of proteins that initiate actin assembly are recruited approximately a minute after appearance of clathrin and drive membrane invagination and assist membrane scission by amphiphysins (Kaksonen et al., 2005; Kukulski et al., 2012). Unlike in metazoan cells, dynamin is dispensable for membrane internalization although the dynamin-like protein Vps1 plays a role in budding yeast endocytosis (Galletta et al., 2010; Smaczynska-de et al., 2010). Actin patch initiation

Early patch components in budding yeast include the coat protein clathrin and adaptor proteins, such as the FEMS Microbiol Rev 38 (2014) 213–227

ubiquitin-binding protein Ede1, the F-BAR protein Syp1, and Yap1810 (Weinberg & Drubin, 2012). These early patch components were thought to promote initial membrane invagination but a recent time-resolved electron tomography study in budding yeast showed that the membrane remains relatively flat during the early phase of endocytosis (Kukulski et al., 2012). One of the outstanding questions in the field of endocytosis is whether the clustering of cargo is responsible for recruiting the endocytic machinery or whether the preformed endocytic sites recruiting the cargo. A study performed with fluorescently labeled alpha factor showed that cargo arrives after the appearance of early endocytic protein at the cell surface (Toshima et al., 2006). This result suggests that some cargos enter the endocytic pathway by diffusing into preformed endocytic sites, which are formed by the stochastic interaction of adaptor proteins and lipids at the plasma membrane. Whether this order of recruitment of cargo is universal to all cargo in yeast remains to be determined. The F-BAR protein Syp1 plays an additional role in inhibiting untimely activation of Arp2/3 complex, thereby restricting premature membrane tubulation (Boettner et al., 2009). Next to arrive at the patches are the adaptor proteins, which include Sla1, End3, Pan1, Sla2, and the ENTH lipid-binding domain protein Ent1. These adaptor proteins link lipid and cargo to clathrin and actin machinery. Sla1 has been recently shown to bind to the polyproline motif of WASP protein, Las17, and to prevent its nucleation promotion factor (NPF) activity during the early stages of endocytosis (Feliciano & Di Pietro, 2012). Both Sla2 and Ent1 have phosphatidylinositol-4,5-bisphosphate-binding domain (Aguilar et al., 2003; Sun et al., 2005). Sla2 also binds to F-actin, and it has been proposed that Ent1 and Sla2 work in concert to couple the plasma membrane and actin cytoskeleton at endocytic sites (Skruzny et al., 2012). Thus, the late coat components serve as an adaptor between cargo recruiting early coat proteins and the actin filament network. Fission yeast cells express homologues of most of the coat proteins present in budding yeast and humans, which also assemble at patches in a similar temporal order (Sirotkin et al., 2005, 2010). Regulation of actin patch assembly

Actin assembly drives the inward movement of actin patches from the cortex, which is inhibited by preventing actin polymerization with latrunculin A (Kaksonen et al., 2003). Cortical actin patches are made up of branched actin filaments that are nucleated by the Arp2/3 complex (Winter et al., 1997; Young et al., 2004; Berro et al., 2010; Sirotkin et al., 2010). Arp2/3 mutants show a significant defect in actin patch formation (Winter et al., ª 2014 Federation of European Microbiological Societies. Published by John Wiley & Sons Ltd. All rights reserved

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1997). Branched actin network in endocytic patches is thought to assemble using a dendritic nucleation mechanism (Mullins et al., 1998; Pollard et al., 2000). All the components required for the dendritic nucleation mechanism including Arp2/3, capping proteins, and cofilins are required for actin patch formation in both yeasts (Lappalainen & Drubin, 1997; Winter et al., 1997; Chen & Pollard, 2013). Arp2/3 complex binds to both nucleation promoting factor (NPF) and a pre-existing actin filament to initiate new filaments. The source of such pre-existing filaments is not clear. Actin filaments from a neighboring cortical patch can serve as a source of the mother filament in fission yeast (Basu & Chang, 2011), but most of the cortical patches are initiated in regions away from a pre-existing patch. While analyzing endocytic defects in fission yeast cofilin mutants, defective in actin filament severing, Chen and Pollard observed an unexpected delay in actin filament assembly at cortical patches. These observations led them to propose that mother filaments can come from cofilin-generated actin filaments, which diffuse through the cytoplasm (Chen & Pollard, 2013). The ability of the Arp2/3 complex to drive actin assembly is stimulated by NPF. Yeast Arp2/3 complex has a high basal activity (Wen & Rubenstein, 2005) although NPFs strongly enhance its nucleation activity. Yeast has four classes of NPF, WASp (Las17 in budding yeast and Wsp1 in fission yeast), myosin I (Myo3/5 in budding yeast and Myo1 in fission yeast), Esp15-like Pan1, and Abp1. Although Abp1 and Pan1 can stimulate Arp2/3 activity in vitro they play only a minor role in actin patch nucleation in either budding yeast or fission yeast cells (Lee et al., 2000; Sirotkin et al., 2005; Sun et al., 2006; Galletta et al., 2008). WASp and myosin I play overlapping but distinct roles in actin patch formation in both yeasts (Sirotkin et al., 2005; Sun et al., 2006). Myo1 localizes to the base of the plasma membrane, which is dependent on the phosphorylation of Myo1 motor domain and its ATP-dependent motor activity in fission yeast (Lee et al., 2000; Sirotkin et al., 2005; Grosshans et al., 2006; Attanapola et al., 2009; Clayton et al., 2010). Patch internalization depends on myosin 1 motor activity in both budding and fission yeast (Lee et al., 2000; Clayton et al., 2010). WH2-domain-containing protein Vrp1 stimulates the NPF activity of myosin I in both the yeasts (Lee et al., 2000; Sirotkin et al., 2005). WASp protein is the strongest of the NPFs in budding and fission yeasts (Sun et al., 2006; Galletta et al., 2008). In budding yeast, Las17 localizes to the cortical patch about 20 s before detectable actin nucleation. Actin nucleation is inhibited in this phase by inhibition of Arp2/3 complex by Syp1 (Weinberg & Drubin, 2012). Moreover, the clathrin adaptor protein Sla1 binds to the polyproline motif of Las17 (Feliciano & Di Pietro, 2012). ª 2014 Federation of European Microbiological Societies. Published by John Wiley & Sons Ltd. All rights reserved

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The inhibition of Arp2/3 complex by Syp1 is relieved at the onset of vesicle internalization when the F-BAR protein Syp1 departs from the cortical patch and Sla1p moves inwards with the coat, thus relieving the inhibition on Arp2/3 complex (Boettner et al., 2009). The BAR and F-BAR proteins can bend membranes, sense membrane curvature, and serve as the link between membrane deformation and actin assembly (Aspenstrom, 2009). The F-BAR protein Bzz1 is recruited to cortical patches just prior to initiation of actin polymerization in budding yeast (Sun et al., 2006). The SH3 domain of Bzz1 interacts directly with Las17 and can stimulate actin polymerization that depends on Arp2/3, Las17, Vrp1, and myosin 1 (Soulard et al., 2002, 2005). It has been proposed that Bzz1 senses the membrane curvature induced by early coat F-BAR proteins such as Syp1 and initiates actin polymerization. Thus, the two F-BAR proteins can serve as on/off switches for Las17-mediated actin polymerization at the cortical patch (Galletta et al., 2010; Weinberg & Drubin, 2012). In an interesting study on budding yeast, Urbanek et al. (2013) showed that the polyproline domain of Las17 can bind actin and nucleate actin filaments in an Arp2/3 independent manner. This result also raises the possibility that the mother actin filament required for Arp2/3 nucleation may be generated by Las17 actin nucleation activity independent of its NPF function. It will be interesting to see whether the Wsp1, the fission yeast homologue of Las17, has a similar actin nucleation role. Alternatively the mother filament can be generated by severing of pre-existing actin filament by cofilin as proposed by Pollard and coworkers (Chen & Pollard, 2013). Based on in vitro studies, actin assembly by the Arp2/3 complex has been explained by the dendritic nucleation model (Pollard et al., 2000), wherein growth of the newly formed actin filament is capped by the binding of the heterotrimeric capping protein (CP) at the barbed end (Wear et al., 2003; Wear & Cooper, 2004). This, together with the actin filament severing by cofilin, ensures the maintenance of a pool of assembly-competent actin species and creates a dense network of short filaments with a constant branching frequency. Consistent with this, all the important proteins involved in the dendritic nucleation model, including Arp2/3, CP, and cofilin, localize to cortical actin patches (Weinberg & Drubin, 2012). However, in vivo studies showed that CP is not essential for endocytosis in budding yeast (Kaksonen et al., 2003) and for lamellipodium formation in metazoan cells (Iwasa & Mullins, 2007). Michelot et al. (2013) used a synthetic genome screen in combination with biochemical reconstitution to find two additional sets of proteins, Abp1/Aim3 and Aip1, that function in conjugation with CP to regulate actin filament elongation in the Arp2/3-nucleated FEMS Microbiol Rev 38 (2014) 213–227

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actin network in budding yeast. Abp1/Aim3 controls the elongation of newly generated filaments, while Aip1 inhibits elongation of old, cofilin-bound filaments (Michelot et al., 2013). Quantitative studies in fission yeast have uncovered that each patch contains about 900 molecules of the actin-bundling protein fimbrin (Sirotkin et al., 2010). Fimbrin serves to strengthen the actin filament network around endocytic vesicles, and cells lacking fimbrin fail to internalize endocytic vesicles in both fission and budding yeasts (Goodman et al., 2003; Kaksonen et al., 2005; Skau & Kovar, 2010; Skau et al., 2011). The force generated by actin polymerization is required to counter the high turgor pressure of yeast plasma membrane (Aghamohammadzadeh & Ayscough, 2009). In fission yeast, high concentration of fimbrin prevents the binding of tropomyosin to actin patches, which would block patch internalization and actin filament turnover by inhibiting Myo1 and cofilin (Clayton et al., 2010; Skau & Kovar, 2010; Skau et al., 2011). The BAR-domain-containing amphiphysin proteins, Rsv161 and Rsv167, arrive at the cortical patches at the time of membrane invagination and were shown to localize to the sites of membrane invagination by immuno-EM (Kaksonen et al., 2005; Idrissi et al., 2008; Kukulski et al., 2012). Cells lacking Rsv161 and Rsv167 show frequent retraction of endocytic proteins, consistent with their role in membrane scission (Kaksonen et al., 2005). The two FBAR-domain proteins Cdc15 and Bzz1 in fission yeast localize to the cortical patch and are critical for vesicle scission (Carnahan & Gould, 2003; Arasada & Pollard, 2011). Cdc15 is located at the cortex where it binds to and activates Myo1 (Carnahan & Gould, 2003). Bzz1 is located above the coat where it activates Wsp1 similar to its budding yeast homologue (Arasada & Pollard, 2011). Unlike metazoan cells, dynamin is not required for endocytic internalization and vesicle scission although a dynamin-like protein Vps1 plays a minor role in budding yeast endocytosis (Nannapaneni et al., 2010; Smaczynska-de et al., 2010). Once the patch is internalized, the actin network disassembles rapidly. Cofilin, Aip1, and coronin disassemble the actin filament network in budding and fission yeasts (Moon et al., 1993; Andrianantoandro & Pollard, 2006; Brieher et al., 2006; Okreglak & Drubin, 2007, 2010; Kueh et al., 2008; Chan et al., 2009; Gandhi et al., 2009; Lin et al., 2010; Chen & Pollard, 2013). Loss of such regulatory proteins slows down actin turnover and increases the lifetime of cortical patches (Lin et al., 2010; Chen & Pollard, 2013). While extensive studies on the yeast cortical patches have greatly advanced our understanding of actin dynamics and endocytosis, several outstanding questions remain. Little is known about the signals that determine endocytic FEMS Microbiol Rev 38 (2014) 213–227

site selection. What controls the strict temporal recruitment of various regulators of endocytosis to the actin patches is also poorly understood. The organization of the actin filaments around the endocytic coat and how forces generated by actin filament dynamics result in membrane invagination need further investigation. The precise mechanism behind the scission of endocytic vesicles remains unclear. Studies combining genetics, functional genomics, advanced real-time imaging, in vitro reconstitution, and ultrastructural studies in the future could help further our understanding of this complex and dynamic process.

Actin cables and cell polarity Actin cables are polarized linear bundles of parallel actin filaments that extend along the long axis of cells (Fig. 3; Adams & Pringle, 1984; Pruyne et al., 2004a, b; Moseley & Goode, 2006). Formins nucleate actin filaments and facilitate barbed end elongation (Pruyne et al., 2002; Sagot et al., 2002a, b; Kovar, 2006; Chesarone et al., 2010). Yeast cells use actin cables to direct transport and achieve polarized cell growth (Pruyne et al., 2004a, b;

Cell tip Polarisome complex

F-actin filament Tropomyosin Formin Type V myosin Crosslinking protein Cargo

Fig. 3. Schematic representation of an actin cable. The polarisome complex is recruited by upstream factors to the growing cell tips. Polarisome complex includes actin cable nucleator formins and its activators Rho-GTPase, Bud6, and Pob1. Formins are activated by the polarisome complex at the cell tips and processively nucleate actin filaments. Formins soon dissociates from the cell ends but remain bound to the barbed end of the actin filament. This actin filament is pushed inwards in the cell by the activation of a neighboring formin molecule, which assembles new actin filament, leading to a retrograde flow of actin filaments bound to forming at the barbed end. Thus, actin cable consists of short parallel actin filaments with its barbed ends facing the polarized growth zone. These short actin filaments are bundled by cross-linking proteins to form thicker actin cables, which extents along the long axis of the cells. Tropomyosin binds to and stabilizes actin filaments of the cable. Actin cables are polarized tracks used by type V myosins to deliver intracellular cargo to the growth zone of the cells.

ª 2014 Federation of European Microbiological Societies. Published by John Wiley & Sons Ltd. All rights reserved

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Martin, 2009; Pollard & Cooper, 2009; Kovar et al., 2011). In cylindrical fission yeast cells, as in metazoans, microtubules also play pivotal role in cell polarity (Siegrist & Doe, 2007). Actin cables serve as tracks for polarized transport of various cargos including secretory vesicles, actin patches, peroxisomes, golgi, mitochondria, vacuoles, and mRNAs to the site of polarized growth in both the yeasts (Feierbach & Chang, 2001; Motegi et al., 2001; Rossanese et al., 2001; Yang & Pon, 2002; Martin & Chang, 2006). Myosin V motors (Myo2 and Myo4 in budding yeast and Myo51 and Myo52 in fission yeast) translocate cargo along these tracks toward the barbed end of the actin filament (Motegi et al., 2001; Win et al., 2001; Schott et al., 2002; Darzacq et al., 2003; Grallert et al., 2007). Actin cable assembly

The Rho family of small GTPases regulates the spatiotemporal organization of actin cables at the growth zones in both yeasts (Pruyne & Bretscher, 2000a, b; Martin, 2009). Cdc42 is required for localization of a multiprotein complex termed as the polarisome, to the growth zone (Evangelista et al., 1997; Martin et al., 2007). The polarisome controls the formation of actin cables (Pruyne & Bretscher, 2000a, b; Martin et al., 2007; Martin, 2009; Minc et al., 2009). Two genetically redundant but functionally distinct formins, Bni1 and Bnr1, nucleate actin cables in budding yeast (Imamura et al., 1997; Vallen et al., 2000; Pruyne et al., 2002; Sagot et al., 2002a, b). Bni1 is recruited to the bud cortex where it nucleates thin actin cables that grow into the bud compartment (Pruyne et al., 2004a, b; Buttery et al., 2007). Bnr1 is stably tethered to the bud neck and nucleates long slow-moving thick cables that run along the cortex of the mother cell (Buttery et al., 2007; Yu et al., 2011). They are recruited and activated at the polarized cortex by the polarisome complex, which comprises of Spa2, Pea2, Bud6, Cdc42, Bin 1, and Gic2 in budding yeast (Sheu et al., 1998). The cylindrical fission yeast cells grow in a polarized fashion at the two cell ends. Interphase microtubules establish the sites for formin For3-dependent initiation of actin cables at the cell ends (Feierbach & Chang, 2001; Nakano et al., 2002; Martin & Chang, 2003; Martin et al., 2005; Martin, 2009; Minc et al., 2009; Piel & Tran, 2009). The polarity factor Tea1-Tea4 complex is carried on the plus end of the microtubules by the +TIP complex, which is made up of EB1, Mal3, CLP-170, Tip1, and Tea2, the kinesin motor. This complex is tethered to the cortex by the Mod5 receptor. The Tea1-Tea4 complex then recruits the polarisome complex that contains formin For3 (Feierbach & Chang, 2001) and its activators, Rho GTPase ª 2014 Federation of European Microbiological Societies. Published by John Wiley & Sons Ltd. All rights reserved

Cdc42, Bud6, and Pob1 (Martin et al., 2005, 2007; Rincon et al., 2009). At the cortex, the activated For3 initiates rapid actin filament assembly. For3 localizes to the cell cortex very transiently and, upon nucleation of an actin filament, moves inwards by retrograde flow with the growing actin cables (Martin & Chang, 2006). Formins nucleate the linear filaments of actin cables. Formin is a modular protein that contains formin homology 1 (FH1) domain that binds to profilin–actin complex and FH2 domain that controls actin nucleation and cable assembly (Pruyne et al., 2002; Sagot et al., 2002a, b; Kovar et al., 2003; Moseley et al., 2004; Kovar, 2006; Chesarone et al., 2010). The FH1 domain binds to profilin–actin complex and assists the FH2 domain in the nucleation and elongation of actin filaments (Kovar et al., 2003, 2005; Li & Higgs, 2003; Vavylonis et al., 2006). FH2 is processively bound to the barbed end of the actin filaments and promotes filament elongation by preventing the binding of capping proteins to the filament ends (Pruyne et al., 2002; Kovar et al., 2003, 2005; Moseley et al., 2004). In addition to FH 1 and FH2 domains, many formins also contain other regulatory domains including the diaphanous-related formin inhibitory domain (DID), diaphanous-related formin autoregulatory domain (DAD), and a Rho-binding domain (RBD). The autoinhibitory interaction between the DID and DAD domain is relieved by binding of Rho GTPase to RBD (Li & Higgs, 2003; Martin et al., 2007; Chesarone et al., 2010). Actin cable dynamics

Actin cables were first visualized in live budding yeast using an ABP-140 GFP fusion (Yang & Pon, 2002). Actin cables assemble at the buds de novo, and the cables are polarized along the mother bud axis. In fission yeast, a fusion of calponin homology domain from IQGAP Rng2 to GFP (Eng et al., 1998) or the 17 amino acid peptide Lifeact tagged to a fluorophore (Riedl et al., 2008; Huang et al., 2012) is used to follow the dynamics of actin filaments in real time. Tropomyosin and coronin associate with and stabilize actin cables (Pelham & Chang, 2001; Moseley & Goode, 2006). Myosin V transports cargo on actin cables toward the barbed end of actin. Besides transporting cargo, myosin V also plays an important role in maintaining the architecture and dynamics of actin cables (Yu et al., 2011; Lo Presti et al., 2012). Fission yeast cells lacking Myo52 often have bent and buckled actin cables, which do not orient along the long axis of the cell (Lo Presti et al., 2012). Coordinated action of tropomyosin, coronin, Aip1, cofilin, and twinfillin controls the disassembly of actin cables. What regulates the length of actin cables had remained poorly understood. FEMS Microbiol Rev 38 (2014) 213–227

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Recent studies in budding yeast have shed light on the mechanism that controls filament length. The polarity factor Bud14 can displace the formin Bnr1 from the barbed end of actin filaments, and a mutation in Bud14 leads to the formation of abnormally long actin cables that are hyperstabilized (Chesarone et al., 2009). The kinesin-like myosin passenger protein Smy1 interacts with FH2 domain of formin Bnr1 in budding yeast and decreases the rate of actin filament elongation (Chesarone-Cataldo et al., 2011). Mechanisms that regulate the length of actin cables in fission yeast are not well understood. Tea4, the fission yeast orthologue of Bud 14, also interacts with fission yeast formin, For3 (Martin et al., 2005). Fission yeast cells lacking Tea4 grow in a monopolar fashion but have normal-looking actin cables. Overexpression of Tea4, however, induces actin cable formation in For3 dependent manner (Martin et al., 2005). Mutation of ATPase domain of Klp3 the Smy1 orthologue in fission yeast leads altered cell polarity although the actin cable length remains unaffected (Rhee, et al., 2005). Thus, the two yeasts use divergent mechanisms to control actin cable length. Actin cables are highly dynamic structures with a halflife of less than a minute (Yu et al., 2011; Drake et al., 2012). Of the three F-actin structures assembled in yeast, actin cables are relatively less well understood probably because they are highly dynamic and are relatively difficult to image in real time. Hence, the list of F-actincable-associated proteins is relatively low. Also, very little is known about how the assembly, growth, and disassembly of actin cables may be controlled. Although recent studies involving advanced cellular, genomic, and mathematical modeling techniques are beginning to shed light on the assembly and dynamics of actin cables (Martin, 2009; Kovar et al., 2011; Yu et al., 2011; Drake et al., 2012), a significant amount of work is required to generate a comprehensive understanding of the assembly and dynamics of actin cables.

actomyosin contractility (Fig. 4). The positioning of the actomyosin ring at the division site, its assembly, and its constriction are under exquisite control by cell cycle regulatory molecules, such as cyclin dependent kinase, polo kinase, and the anaphase promoting complex, each of which ensures that events of cytokinesis are activated only at the appropriate time in the cell cycle. Several excellent recent review articles have discussed yeast cytokinesis mechanisms in detail, and therefore, the actomyosin ring and cytokinesis will only be briefly discussed (Balasubramanian et al., 2012; Lee et al., 2012; Rincon & Paoletti, 2012; Wloka & Bi, 2012). Actomyosin ring positioning

Although the actomyosin ring components are highly conserved from yeasts to human, the mechanism by which ring components are recruited to the incipient division site (thereby ensuring correct positioning of the division site) is different, even between fission and budding yeasts. In budding yeast, the septin cytoskeleton is essential for selection of the site of polarized growth and cell division. Septins function downstream of the bud-site selection genes (Chant & Herskowitz, 1991; Chant et al., 1991; Halme et al., 1996; Zahner et al., 1996). The septin cytoskeleton via the septin-binding protein Bni5 recruits Myo1 (the myosin II heavy chain in budding yeast) and its light chain Mlc2 to the future division site following entry into S phase and well before chromosome segregation (Bi et al., 1998; Lippincott & Li, 1998; Lee et al.,

F-actin filament Tropomyosin

Actomyosin ring and cytokinesis The third major structure of the actin cytoskeleton in yeast is the actomyosin ring, which plays an essential role in cytokinesis (Balasubramanian et al., 2004). The actomyosin ring assembles at the incipient division site, and besides generating the force required to divide the cell, it also functions to target secretion and cell wall assembly to the division site (Pollard & Wu, 2010; Balasubramanian et al., 2012; Lee et al., 2012; Rincon & Paoletti, 2012; Wloka & Bi, 2012). The actomyosin ring is a complex structure containing over 100 proteins, including F-actin, the motor protein myosin II, actin-filament-nucleating proteins, actin cross-linking proteins, and other modulators of FEMS Microbiol Rev 38 (2014) 213–227

Type II myosin Formin &

Crosslinking proteins

Actomyosin ring Fig. 4. Part of an actomyosin ring. Actin rings are assembled at the division site, which constricts after completion of anaphase to separate the two daughter cells. A mature actomyosin ring is composed of about 2000 short antiparallel actin filaments. These actin filaments are nucleated by formins at the barbed end and are bundled by cross-linking proteins. Tropomyosin binds to and stabilizes actin filaments in the ring. Type II myosins are believed to form dimmers and generate force during actomyosin ring assembly and constriction.


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2002; Fang et al., 2010). Interestingly, even though septins are present in fission yeast, they do not play any detectable role in division site positioning. By contrast, in fission yeast, the division site is established at G2/M by the anillin-related protein Mid1p, using the medial position of the interphase nucleus as a cue (Chang et al., 1996; Sohrmann et al., 1996; Balasubramanian et al., 1998). Mid1p assembles into a cortical band overlying the interphase nucleus and is also present within the interphase nucleus. Upon entry into mitosis, nuclear Mid1p is phosphorylated by polo kinase and is exported from the nucleus (Bahler & Pringle, 1998; Bahler et al., 1998; Paoletti & Chang, 2000). Cortical Mid1p recruits the IQGAPrelated actomyosin ring protein Rng2p, which in turn recruits other components of the actomyosin ring, such as Myo2 and Cdc15, to the division site (Almonacid et al., 2011; Laporte et al., 2011; Padmanabhan et al., 2011). It also appears that Mid1p can recruit some components of the actomyosin ring, such as the forminCdc12, to the division site in a Rng2-independent manner (Laporte et al., 2011; Padmanabhan et al., 2011). While Mid1p participates in a process that activates actomyosin ring assembly at the appropriate location, a set of cellend-localized proteins, with a key role in cell polarity, ensure that Mid1p is medially localized and also prevent actomyosin ring anchoring and septum assembly at cell ends (Celton-Morizur et al., 2006; Padte et al., 2006; Huang et al., 2007). Thus, fission yeast uses overlapping activatory and inhibitory mechanisms to correctly position the cell division site. Conversely, even though budding yeasts express a protein, Bud4, which is weakly related to fission yeast Mid1, it does not play an essential role in cytokinesis, although in haploid cells its function is required for correct bud-site positioning and indirectly therefore in division site placement (Kang et al., 2012). Actomyosin ring assembly

The two major steps in actomyosin ring assembly are 1. nucleation/accumulation of actin filaments at the division site and 2. organization of actin filaments into a cell division ring through interaction with a host of other proteins, such as myosin II, and actin cross-linking proteins IQGAP, a-actinin, and fimbrin, and filament-stabilizing proteins, such as tropomyosin. Electron microscopic studies have shown that actin filaments in the ring are linear (unbranched) in nature (Kamasaki et al., 2007). The formin class of actin filament nucleators nucleates actin filaments in the ring. In budding yeast, the formin Bni1 localizes to the division site and plays a major role in actin filament nucleation following passage through anaphase (Vallen et al., 2000; Tolliday et al., 2002; Moseley & Goode, 2006). Interestingly, as in animal cells, Bni1 is ª 2014 Federation of European Microbiological Societies. Published by John Wiley & Sons Ltd. All rights reserved

M. Mishra et al.

activated by the RhoA family GTPase Rho1 (Tolliday et al., 2002; Yoshida et al., 2006, 2009). In fission yeast, actin filaments for cytokinesis are nucleated de novo by the formin Cdc12, which localizes to a series of cortically placed node structures. In addition, speckles of Cdc12 in the rest of cell (i.e. nonmedial) also generate actin filaments (even in the absence of the formin for3), which are also incorporated into the newly assembled actomyosin ring (Chang et al., 1997; Wu et al., 2006; Vavylonis et al., 2008; Coffman et al., 2009; Huang et al., 2012). Actin nucleation during later stages of cytokinesis involves interaction between Cdc12 formin and the F-BAR protein Cdc15 (Roberts-Galbraith et al., 2010). How Cdc12 formin is regulated is unknown although currently no evidence exists to suggest that Rho GTPases are involved in Cdc12 activation. Translocation of the nonmedially nucleated actin filaments to the cell division site requires the activity of a type II myosin (Myo2) and a type V myosin (Myo51; Huang et al., 2012). Whereas one of a pair of formins (Bni1 and Bnr1) is sufficient for cell viability in budding yeast, fission yeast cytokinesis and cell viability acutely depend on Cdc12-formin. Interestingly, recent work has shown that fission yeast Cdc12 might also participate in actin bundling, and it is possible that this activity is a key to the absolute requirement for Cdc12 in cytokinesis (Bohnert et al., 2013). Other recent work has also uncovered complex interplay between the two fission yeast formins Cdc12 and For3 in actin filament assembly during cytokinesis (Coffman et al., 2013). It appears that tropomyosins might assemble onto actin cables soon after their nucleation as loss of tropomyosin function leads to instability of actin cables and the actomyosin ring (Balasubramanian et al., 1992; Arai et al., 1998; Tolliday et al., 2002). How do actin filaments (cables) at the division site get organized into the actomyosin ring? Although it is clear that actin cross-linking proteins and myosin II are involved in the organization and compaction of actin filaments into a ring (Wu et al., 2006; Vavylonis et al., 2008; Pollard & Wu, 2010), the currently proposed mechanisms do not account for all the experimental observations. It is known that myosin II and formin-Cdc12 are localized to cortical nodes. Thus, it has been proposed that, if by growth in random directions, actin filaments nucleated from one node reaches another, myosin II present in the neighboring node might capture the actin filament, thereby bringing the two nodes closer. Multiple iterations of such a process, termed search–capture–pull–release (SCPR), could lead to the condensation of the c. 60–80 nodes (containing Cdc12, Myo2 and other proteins) into a ring structure (Vavylonis et al., 2008). It is possible that such a capture mechanism also ensures that longer actin filaments, nucleated at nonmedial sites, are incorporated FEMS Microbiol Rev 38 (2014) 213–227

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into the actomyosin ring (Huang et al., 2012). Previous work has shown that actin-binding/cross-linking proteins such as Rng2-IQGAP, Ain1-a-actinin, and Fim1-Fimbrin are important for proper organization of the actomyosin ring (Wu et al., 2001; Takaine et al., 2009; Laporte et al., 2011). How the SCPR mechanism accounts for the activities of actin cross-linking proteins is not well understood. However, recent work has suggested that the actin-bundling proteins Fim1 and Ain1 stabilize F-actin interactions with myosin II (Laporte et al., 2012). Furthermore, electron microscopic studies have shown that the fission yeast actomyosin ring is initially assembled as two arcs containing c. 1000 parallel actin filaments and subsequently undergoes a transition during ring constriction to generate a structure with actin filaments of mixed polarity (Kamasaki et al., 2007). Further work is necessary to fully understand how actin filaments are organized into a ring through the action of actin cross-linking proteins. Actomyosin ring contraction, disassembly, and division septum assembly

The process of cytokinesis is achieved by constriction of the actomyosin ring, its coupling to the assembly of new membranes, and the intercellular cell wall. Three mechanisms appear to be capable and involved in actomyosin ring constriction and disassembly. The first of these involves myosin II function. Myosin II is essential for cytokinesis in fission yeast and is important (although nonessential) for cytokinesis in budding yeast. It is a component of the constricting actomyosin ring in both yeasts (Kitayama et al., 1997; Balasubramanian et al., 1998; Bi et al., 1998; Lord & Pollard, 2004; Lord et al., 2005). This observation has led to the suggestion that myosin IImotor-based movement of actin filaments (whose plus ends are potentially anchored to cell membranes) powers ring constriction and cytokinesis. The recent establishment of a permeabilized cell ghost system to study actomyosin ring constriction has revealed that myosin II motor activity alone can support ring constriction in vitro (Mishra et al., 2013). Also consistent with a role for myosin II motor activity in cytokinesis is the fact that the commonly used temperature-sensitive mutant in fission yeast myosin II, myo2-E1, shows a marked decrease in actin translocation in vitro (Lord & Pollard, 2004). A stable fraction of actomyosin-ring-associated myosin II has been shown to be key for proper completion of cytokinesis, although the role it plays in myosin II contractility remains unclear (Wloka & Bi, 2012). Notwithstanding these observations, it has also been found that myosin II lacking its motor domain can support cytokinesis with high efficiency in budding yeast (Lord et al., 2005; Mendes Pinto et al., 2012). Furthermore, it is also known that although myosin II mutants in budding FEMS Microbiol Rev 38 (2014) 213–227

yeast are strongly defective for cytokinesis, they are indeed viable, suggesting that other mechanisms can also participate in actomyosin ring constriction and disassembly (Mendes Pinto et al., 2012). Stabilization of actin filaments has been found to be deleterious in myosin II mutants in budding yeast (Mendes Pinto et al., 2012), and genetic interactions have also been uncovered between cofilin adf11 mutants and myosin II mutants in fission yeast (Nakano & Mabuchi, 2006). These observations have led to the idea that disassembly of actin filaments, cross-linked by dynamic end-tracking cross-linkers, can support cytokinetic ring constriction (Mendes Pinto et al., 2012). In this scenario, the identity of such dynamic end-tracking cross-linkers needs to be established. Finally, primary septum-defective mutants have been shown to be defective in actomyosin ring constriction and disassembly in budding and fission yeasts (Liu et al., 1999; Schmidt et al., 2002), suggesting either that cell wall growth pushes the actomyosin ring or that failure to assemble the primary septum activates a feedback (checkpoint) mechanism that causes prolonged retention of the actomyosin ring. Recent work has shown that cells devoid of detectable actin cytoskeleton can divide potentially through cell wall growth (Proctor et al., 2012). A Brownian ratchet-like mechanism has been proposed, which suggests that addition of cell wall monomers leads to pushing of the plasma membrane and the actomyosin ring, which is attached to the inner leaflet of the plasma membrane, thereby leading to ring closure and disassembly. While there is evidence for each of these three mechanisms, much work needs to be performed to establish the precise mechanism of actomyosin ring constriction and what fraction of contractile forces arise from each of these mechanisms.

Concluding remarks Despite recent advances, several aspects of actin organization and dynamics remain poorly understood. A more complete inventory of ABPs that regulate the actin cytoskeleton and how their dynamics affect their physiological role would continue to be important. Actin patches, actin cables, and the actomyosin ring each associate with a unique subset of actin-binding proteins, which confers a definite arrangement, and influences the dynamics of actin filaments. Actin patches are made of short and branched actin filaments, which are highly dynamic and have a lifespan of 1–2 min. Actin cables are made up of cross-linked linear bundles, which persist for longer periods of time. Myosin I only associates with actin patches, whereas myosin II exclusively localizes to the actin rings and myosin V only associates with actin cables (Michelot & Drubin, 2011). Actin filaments in these three structures are bound by partially overlapping sets of actin-binding proteins, ª 2014 Federation of European Microbiological Societies. Published by John Wiley & Sons Ltd. All rights reserved

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which give them their unique properties. How the cell generates these functionally diverse actin filament structures in the same cytoplasm is a very interesting question, answers to which are beginning to emerge. Acetylation of tropomyosin influences its localization to different actin structures and regulates myosin motors (Skoumpla et al., 2007). Interestingly, the actin-filament-bundling proteins fimbrin (Fim1) and tropomyosin (Cdc8) antagonize each other, thus confining their distribution to distinct actin structures (Skau & Kovar, 2010; Skau et al., 2011). Fim1 accumulates in high concentrations at actin patches, where it inhibits the binding of Cdc8 to the patches. This relieves Myo1 from Cdc8-mediated inhibition (Clayton et al., 2010) and allows for binding of cofilin to actin patches to promote rapid turnover of actin patches (Skau & Kovar, 2010). It would be interesting to know whether others ABPs can have similar effects on differential regulation of actin filament structures. Given that the study of the yeast actin cytoskeleton has led the entire field in many instances, it is likely that further studies in yeast will continue to lead the way in understanding many types of actin structures and their physiological roles.

Acknowledgements We wish to thank Dr. Ramanujam Srinivasan for helping with the references and endnote, and Dr. Naweed Naqvi, Dr. Ramanujam Srinivasan, Dr. Sarada Bulchand and Ms. Dhivya Subramaniam for critical reading of the article. We apologize to authors whose work has not been discussed inadvertently. This work was supported by research funds from Temasek Life Sciences Laboratory, Singapore Millennium Foundation, and the Mechanobiology Institute. The authors declare no conflict of interest.

References Adams AE & Pringle JR (1984) Relationship of actin and tubulin distribution to bud growth in wild-type and morphogenetic-mutant Saccharomyces cerevisiae. J Cell Biol 98: 934–945. Aghamohammadzadeh S & Ayscough KR (2009) Differential requirements for actin during yeast and mammalian endocytosis. Nat Cell Biol 11: 1039–1042. Aguilar RC, Watson HA & Wendland B (2003) The yeast Epsin Ent1 is recruited to membranes through multiple independent interactions. J Biol Chem 278: 10737–10743. Almonacid M, Celton-Morizur S, Jakubowski JL et al. (2011) Temporal control of contractile ring assembly by Plo1 regulation of myosin II recruitment by Mid1/anillin. Curr Biol 21: 473–479. Andrianantoandro E & Pollard TD (2006) Mechanism of actin filament turnover by severing and nucleation at different concentrations of ADF/cofilin. Mol Cell 24: 13–23. ª 2014 Federation of European Microbiological Societies. Published by John Wiley & Sons Ltd. All rights reserved

M. Mishra et al.

Arai R, Nakano K & Mabuchi I (1998) Subcellular localization and possible function of actin, tropomyosin and actin-related protein 3 (Arp3) in the fission yeast Schizosaccharomyces pombe. Eur J Cell Biol 76: 288–295. Arasada R & Pollard TD (2011) Distinct roles for F-BAR proteins Cdc15p and Bzz1p in actin polymerization at sites of endocytosis in fission yeast. Curr Biol 21: 1450–1459. Aspenstrom P (2009) Roles of F-BAR/PCH proteins in the regulation of membrane dynamics and actin reorganization. Int Rev Cell Mol Biol 272: 1–31. Attanapola SL, Alexander CJ & Mulvihill DP (2009) Ste20-kinase-dependent TEDS-site phosphorylation modulates the dynamic localisation and endocytic function of the fission yeast class I myosin, Myo1. J Cell Sci 122: 3856–3861. Ayscough KR, Stryker J, Pokala N, Sanders M, Crews P & Drubin DG (1997) High rates of actin filament turnover in budding yeast and roles for actin in establishment and maintenance of cell polarity revealed using the actin inhibitor latrunculin-A. J Cell Biol 137: 399–416. Bahler J & Pringle JR (1998) Pom1p, a fission yeast protein kinase that provides positional information for both polarized growth and cytokinesis. Genes Dev 12: 1356–1370. Bahler J, Steever AB, Wheatley S, Wang Y, Pringle JR, Gould KL & McCollum D (1998) Role of polo kinase and Mid1p in determining the site of cell division in fission yeast. J Cell Biol 143: 1603–1616. Balasubramanian MK, Helfman DM & Hemmingsen SM (1992) A new tropomyosin essential for cytokinesis in the fission yeast S. pombe. Nature 360: 84–87. Balasubramanian MK, McCollum D, Chang L et al. (1998) Isolation and characterization of new fission yeast cytokinesis mutants. Genetics 149: 1265–1275. Balasubramanian MK, Bi E & Glotzer M (2004) Comparative analysis of cytokinesis in budding yeast, fission yeast and animal cells. Curr Biol 14: R806–R818. Balasubramanian MK, Srinivasan R, Huang Y & Ng KH (2012) Comparing contractile apparatus-driven cytokinesis mechanisms across kingdoms. Cytoskeleton (Hoboken) 69: 942–956. Basu R & Chang F (2011) Characterization of dip1p reveals a switch in Arp2/3-dependent actin assembly for fission yeast endocytosis. Curr Biol 21: 905–916. Benedetti H, Raths S, Crausaz F & Riezman H (1994) The END3 gene encodes a protein that is required for the internalization step of endocytosis and for actin cytoskeleton organization in yeast. Mol Biol Cell 5: 1023–1037. Berro J, Sirotkin V & Pollard TD (2010) Mathematical modeling of endocytic actin patch kinetics in fission yeast: disassembly requires release of actin filament fragments. Mol Biol Cell 21: 2905–2915. Bi E, Maddox P, Lew DJ, Salmon ED, McMillan JN, Yeh E & Pringle JR (1998) Involvement of an actomyosin contractile ring in Saccharomyces cerevisiae cytokinesis. J Cell Biol 142: 1301–1312.

FEMS Microbiol Rev 38 (2014) 213–227


Boettner DR, D’Agostino JL, Torres OT et al. (2009) The F-BAR protein Syp1 negatively regulates WASp-Arp2/3 complex activity during endocytic patch formation. Curr Biol 19: 1979–1987. Bohnert KA, Grzegorzewska AP, Willet AH, Vander Kooi CW, Kovar DR & Gould KL (2013) SIN-dependent phosphoinhibition of formin multimerization controls fission yeast cytokinesis. Genes Dev 27: 2164–2177. Brieher WM, Kueh HY, Ballif BA & Mitchison TJ (2006) Rapid actin monomer-insensitive depolymerization of Listeria actin comet tails by cofilin, coronin, and Aip1. J Cell Biol 175: 315–324. Burston HE, Maldonado-Baez L, Davey M, Montpetit B, Schluter C, Wendland B & Conibear E (2009) Regulators of yeast endocytosis identified by systematic quantitative analysis. J Cell Biol 185: 1097–1110. Buttery SM, Yoshida S & Pellman D (2007) Yeast formins Bni1 and Bnr1 utilize different modes of cortical interaction during the assembly of actin cables. Mol Biol Cell 18: 1826–1838. Campellone KG & Welch MD (2010) A nucleator arms race: cellular control of actin assembly. Nat Rev Mol Cell Biol 11: 237–251. Carnahan RH & Gould KL (2003) The PCH family protein, Cdc15p, recruits two F-actin nucleation pathways to coordinate cytokinetic actin ring formation in Schizosaccharomyces pombe. J Cell Biol 162: 851–862. Celton-Morizur S, Racine V, Sibarita JB & Paoletti A (2006) Pom1 kinase links division plane position to cell polarity by regulating Mid1p cortical distribution. J Cell Sci 119: 4710– 4718. Chan C, Beltzner CC & Pollard TD (2009) Cofilin dissociates Arp2/3 complex and branches from actin filaments. Curr Biol 19: 537–545. Chang F, Woollard A & Nurse P (1996) Isolation and characterization of fission yeast mutants defective in the assembly and placement of the contractile actin ring. J Cell Sci 109(Pt 1): 131–142. Chang F, Drubin D & Nurse P (1997) cdc12p, a protein required for cytokinesis in fission yeast, is a component of the cell division ring and interacts with profilin. J Cell Biol 137: 169–182. Chant J & Herskowitz I (1991) Genetic control of bud site selection in yeast by a set of gene products that constitute a morphogenetic pathway. Cell 65: 1203–1212. Chant J, Corrado K, Pringle JR & Herskowitz I (1991) Yeast BUD5, encoding a putative GDP-GTP exchange factor, is necessary for bud site selection and interacts with bud formation gene BEM1. Cell 65: 1213–1224. Chen Q & Pollard TD (2013) Actin filament severing by cofilin dismantles actin patches and produces mother filaments for new patches. Curr Biol 23: 1154–1162. Chesarone MA & Goode BL (2009) Actin nucleation and elongation factors: mechanisms and interplay. Curr Opin Cell Biol 21: 28–37. Chesarone M, Gould CJ, Moseley JB & Goode BL (2009) Displacement of formins from growing barbed ends by


223

bud14 is critical for actin cable architecture and function. Dev Cell 16: 292–302. Chesarone MA, DuPage AG & Goode BL (2010) Unleashing formins to remodel the actin and microtubule cytoskeletons. Nat Rev Mol Cell Biol 11: 62–74. Chesarone-Cataldo M, Guerin C, Yu JH, Wedlich-Soldner R, Blanchoin L & Goode BL (2011) The myosin passenger protein Smy1 controls actin cable structure and dynamics by acting as a formin damper. Dev Cell 21: 217–230. Chhabra ES & Higgs HN (2007) The many faces of actin: matching assembly factors with cellular structures. Nat Cell Biol 9: 1110–1121. Clayton JE, Sammons MR, Stark BC, Hodges AR & Lord M (2010) Differential regulation of unconventional fission yeast myosins via the actin track. Curr Biol 20: 1423–1431. Coffman VC, Nile AH, Lee IJ, Liu H & Wu JQ (2009) Roles of formin nodes and myosin motor activity in Mid1p-dependent contractile-ring assembly during fission yeast cytokinesis. Mol Biol Cell 20: 5195–5210. Coffman VC, Sees JA, Kovar DR & Wu JQ (2013) The formins Cdc12 and For3 cooperate during contractile ring assembly in cytokinesis. J Cell Biol 203: 101–114. Conibear E (2010) Converging views of endocytosis in yeast and mammals. Curr Opin Cell Biol 22: 513–518. Darzacq X, Powrie E, Gu W, Singer RH & Zenklusen D (2003) RNA asymmetric distribution and daughter/mother differentiation in yeast. Curr Opin Microbiol 6: 614–620. Drake T, Yusuf E & Vavylonis D (2012) A systems-biology approach to yeast actin cables. Adv Exp Med Biol 736: 325–335. Eng K, Naqvi NI, Wong KC & Balasubramanian MK (1998) Rng2p, a protein required for cytokinesis in fission yeast, is a component of the actomyosin ring and the spindle pole body. Curr Biol 8: 611–621. Engqvist-Goldstein AE & Drubin DG (2003) Actin assembly and endocytosis: from yeast to mammals. Annu Rev Cell Dev Biol 19: 287–332. Evangelista M, Blundell K, Longtine MS et al. (1997) Bni1p, a yeast formin linking cdc42p and the actin cytoskeleton during polarized morphogenesis. Science 276: 118–122. Evangelista M, Pruyne D, Amberg DC, Boone C & Bretscher A (2002) Formins direct Arp2/3-independent actin filament assembly to polarize cell growth in yeast. Nat Cell Biol 4: 260–269. Fang X, Luo J, Nishihama R et al. (2010) Biphasic targeting and cleavage furrow ingression directed by the tail of a myosin II. J Cell Biol 191: 1333–1350. Feierbach B & Chang F (2001) Roles of the fission yeast formin for3p in cell polarity, actin cable formation and symmetric cell division. Curr Biol 11: 1656–1665. Feliciano D & Di Pietro SM (2012) SLAC, a complex between Sla1 and Las17, regulates actin polymerization during clathrin-mediated endocytosis. Mol Biol Cell 23: 4256–4272. Gachet Y & Hyams JS (2005) Endocytosis in fission yeast is spatially associated with the actin cytoskeleton during polarised cell growth and cytokinesis. J Cell Sci 118: 4231– 4242.


224

Galletta BJ, Chuang DY & Cooper JA (2008) Distinct roles for Arp2/3 regulators in actin assembly and endocytosis. PLoS Biol 6: e1. Galletta BJ, Mooren OL & Cooper JA (2010) Actin dynamics and endocytosis in yeast and mammals. Curr Opin Biotechnol 21: 604–610. Gandhi M, Achard V, Blanchoin L & Goode BL (2009) Coronin switches roles in actin disassembly depending on the nucleotide state of actin. Mol Cell 34: 364–374. Goodman A, Goode BL, Matsudaira P & Fink GR (2003) The Saccharomyces cerevisiae calponin/transgelin homolog Scp1 functions with fimbrin to regulate stability and organization of the actin cytoskeleton. Mol Biol Cell 14: 2617–2629. Grallert A, Martin-Garcia R, Bagley S & Mulvihill DP (2007) In vivo movement of the type V myosin Myo52 requires dimerisation but is independent of the neck domain. J Cell Sci 120: 4093–4098. Grosshans BL, Grotsch H, Mukhopadhyay D et al. (2006) TEDS site phosphorylation of the yeast myosins I is required for ligand-induced but not for constitutive endocytosis of the G protein-coupled receptor Ste2p. J Biol Chem 281: 11104–11114. Halme A, Michelitch M, Mitchell EL & Chant J (1996) Bud10p directs axial cell polarization in budding yeast and resembles a transmembrane receptor. Curr Biol 6: 570–579. Higgs HN & Pollard TD (2001) Regulation of actin filament network formation through ARP2/3 complex: activation by a diverse array of proteins. Annu Rev Biochem 70: 649–676. Huang Y, Chew TG, Ge W & Balasubramanian MK (2007) Polarity determinants Tea1p, Tea4p, and Pom1p inhibit division-septum assembly at cell ends in fission yeast. Dev Cell 12: 987–996. Huang J, Huang Y, Yu H et al. (2012) Nonmedially assembled F-actin cables incorporate into the actomyosin ring in fission yeast. J Cell Biol 199: 831–847. Idrissi FZ, Grotsch H, Fernandez-Golbano IM, Presciatto-Baschong C, Riezman H & Geli MI (2008) Distinct acto/myosin-I structures associate with endocytic profiles at the plasma membrane. J Cell Biol 180: 1219–1232. Imamura H, Tanaka K, Hihara T et al. (1997) Bni1p and Bnr1p: downstream targets of the Rho family small G-proteins which interact with profilin and regulate actin cytoskeleton in Saccharomyces cerevisiae. EMBO J 16: 2745–2755. Iwasa JH & Mullins RD (2007) Spatial and temporal relationships between actin-filament nucleation, capping, and disassembly. Curr Biol 17: 395–406. Kaksonen M, Sun Y & Drubin DG (2003) A pathway for association of receptors, adaptors, and actin during endocytic internalization. Cell 115: 475–487. Kaksonen M, Toret CP & Drubin DG (2005) A modular design for the clathrin- and actin-mediated endocytosis machinery. Cell 123: 305–320. Kaksonen M, Toret CP & Drubin DG (2006) Harnessing actin dynamics for clathrin-mediated endocytosis. Nat Rev Mol Cell Biol 7: 404–414.


M. Mishra et al.

Kamasaki T, Osumi M & Mabuchi I (2007) Three-dimensional arrangement of F-actin in the contractile ring of fission yeast. J Cell Biol 178: 765–771. Kang PJ, Angerman E, Jung CH & Park HO (2012) Bud4 mediates the cell-type-specific assembly of the axial landmark in budding yeast. J Cell Sci 125: 3840–3849. Kilmartin JV & Adams AE (1984) Structural rearrangements of tubulin and actin during the cell cycle of the yeast Saccharomyces. J Cell Biol 98: 922–933. Kitayama C, Sugimoto A & Yamamoto M (1997) Type II myosin heavy chain encoded by the myo2 gene composes the contractile ring during cytokinesis in Schizosaccharomyces pombe. J Cell Biol 137: 1309–1319. Kovar DR (2006) Molecular details of formin-mediated actin assembly. Curr Opin Cell Biol 18: 11–17. Kovar DR, Kuhn JR, Tichy AL & Pollard TD (2003) The fission yeast cytokinesis formin Cdc12p is a barbed end actin filament capping protein gated by profilin. J Cell Biol 161: 875–887. Kovar DR, Wu JQ & Pollard TD (2005) Profilin-mediated competition between capping protein and formin Cdc12p during cytokinesis in fission yeast. Mol Biol Cell 16: 2313–2324. Kovar DR, Sirotkin V & Lord M (2011) Three’s company: the fission yeast actin cytoskeleton. Trends Cell Biol 21: 177–187. Kubler E & Riezman H (1993) Actin and fimbrin are required for the internalization step of endocytosis in yeast. EMBO J 12: 2855–2862. Kueh HY, Charras GT, Mitchison TJ & Brieher WM (2008) Actin disassembly by cofilin, coronin, and Aip1 occurs in bursts and is inhibited by barbed-end cappers. J Cell Biol 182: 341–353. Kukulski W, Schorb M, Kaksonen M & Briggs JA (2012) Plasma membrane reshaping during endocytosis is revealed by time-resolved electron tomography. Cell 150: 508–520. Laporte D, Coffman VC, Lee IJ & Wu JQ (2011) Assembly and architecture of precursor nodes during fission yeast cytokinesis. J Cell Biol 192: 1005–1021. Laporte D, Ojkic N, Vavylonis D & Wu JQ (2012) alpha-Actinin and fimbrin cooperate with myosin II to organize actomyosin bundles during contractile-ring assembly. Mol Biol Cell 23: 3094–3110. Lappalainen P & Drubin DG (1997) Cofilin promotes rapid actin filament turnover in vivo. Nature 388: 78–82. Lee WL, Bezanilla M & Pollard TD (2000) Fission yeast myosin-I, Myo1p, stimulates actin assembly by Arp2/3 complex and shares functions with WASp. J Cell Biol 151: 789–800. Lee PR, Song S, Ro HS et al. (2002) Bni5p, a septin-interacting protein, is required for normal septin function and cytokinesis in Saccharomyces cerevisiae. Mol Cell Biol 22: 6906–6920. Lee IJ, Coffman VC & Wu JQ (2012) Contractile-ring assembly in fission yeast cytokinesis: recent advances and new perspectives. Cytoskeleton (Hoboken) 69: 751–763. Lees-Miller JP, Helfman DM & Schroer TA (1992) A vertebrate actin-related protein is a component of a



multisubunit complex involved in microtubule-based vesicle motility. Nature 359: 244–246. Li F & Higgs HN (2003) The mouse Formin mDia1 is a potent actin nucleation factor regulated by autoinhibition. Curr Biol 13: 1335–1340. Lin MC, Galletta BJ, Sept D & Cooper JA (2010) Overlapping and distinct functions for cofilin, coronin and Aip1 in actin dynamics in vivo. J Cell Sci 123: 1329–1342. Lippincott J & Li R (1998) Sequential assembly of myosin II, an IQGAP-like protein, and filamentous actin to a ring structure involved in budding yeast cytokinesis. J Cell Biol 140: 355–366. Liu J, Wang H, McCollum D & Balasubramanian MK (1999) Drc1p/Cps1p, a 1,3-beta-glucan synthase subunit, is essential for division septum assembly in Schizosaccharomyces pombe. Genetics 153: 1193–1203. Liu J, Kaksonen M, Drubin DG & Oster G (2006) Endocytic vesicle scission by lipid phase boundary forces. P Natl Acad Sci USA 103: 10277–10282. Lo Presti L, Chang F & Martin SG (2012) Myosin Vs organize actin cables in fission yeast. Mol Biol Cell 23: 4579–4591. Lord M & Pollard TD (2004) UCS protein Rng3p activates actin filament gliding by fission yeast myosin-II. J Cell Biol 167: 315–325. Lord M, Laves E & Pollard TD (2005) Cytokinesis depends on the motor domains of myosin-II in fission yeast but not in budding yeast. Mol Biol Cell 16: 5346–5355. Marks J, Hagan IM & Hyams JS (1986) Growth polarity and cytokinesis in fission yeast: the role of the cytoskeleton. J Cell Sci Suppl 5: 229–241. Martin SG (2009) Microtubule-dependent cell morphogenesis in the fission yeast. Trends Cell Biol 19: 447–454. Martin SG & Chang F (2003) Cell polarity: a new mod(e) of anchoring. Curr Biol 13: R711–R713. Martin SG & Chang F (2006) Dynamics of the formin for3p in actin cable assembly. Curr Biol 16: 1161–1170. Martin SG, McDonald WH, Yates JR 3rd & Chang F (2005) Tea4p links microtubule plus ends with the formin for3p in the establishment of cell polarity. Dev Cell 8: 479–491. Martin SG, Rincon SA, Basu R, Perez P & Chang F (2007) Regulation of the formin for3p by cdc42p and bud6p. Mol Biol Cell 18: 4155–4167. Mendes Pinto I, Rubinstein B, Kucharavy A, Unruh JR & Li R (2012) Actin depolymerization drives actomyosin ring contraction during budding yeast cytokinesis. Dev Cell 22: 1247–1260. Merrifield CJ (2004) Seeing is believing: imaging actin dynamics at single sites of endocytosis. Trends Cell Biol 14: 352–358. Michelot A & Drubin DG (2011) Building distinct actin filament networks in a common cytoplasm. Curr Biol 21: R560–R569. Michelot A, Grassart A, Okreglak V, Costanzo M, Boone C & Drubin DG (2013) Actin filament elongation in Arp2/ 3-derived networks is controlled by three distinct mechanisms. Dev Cell 24: 182–195.


225

Minc N, Bratman SV, Basu R & Chang F (2009) Establishing new sites of polarization by microtubules. Curr Biol 19: 83–94. Mishra M, Kashiwazaki J, Takagi T, Srinivasan R, Huang Y, Balasubramanian MK & Mabuchi I (2013) In vitro contraction of cytokinetic ring depends on myosin II but not on actin dynamics. Nat Cell Biol 15: 853–859. Moon AL, Janmey PA, Louie KA & Drubin DG (1993) Cofilin is an essential component of the yeast cortical cytoskeleton. J Cell Biol 120: 421–435. Moseley JB & Goode BL (2006) The yeast actin cytoskeleton: from cellular function to biochemical mechanism. Microbiol Mol Biol Rev 70: 605–645. Moseley JB, Sagot I, Manning AL, Xu Y, Eck MJ, Pellman D & Goode BL (2004) A conserved mechanism for Bni1- and mDia1-induced actin assembly and dual regulation of Bni1 by Bud6 and profilin. Mol Biol Cell 15: 896–907. Motegi F, Arai R & Mabuchi I (2001) Identification of two type V myosins in fission yeast, one of which functions in polarized cell growth and moves rapidly in the cell. Mol Biol Cell 12: 1367–1380. Mullins RD, Heuser JA & Pollard TD (1998) The interaction of Arp2/3 complex with actin: nucleation, high affinity pointed end capping, and formation of branching networks of filaments. P Natl Acad Sci USA 95: 6181–6186. Munn AL & Riezman H (1994) Endocytosis is required for the growth of vacuolar H(+)-ATPase-defective yeast: identification of six new END genes. J Cell Biol 127: 373–386. Munn AL, Stevenson BJ, Geli MI & Riezman H (1995) end5, end6, and end7: mutations that cause actin delocalization and block the internalization step of endocytosis in Saccharomyces cerevisiae. Mol Biol Cell 6: 1721–1742. Nakano K & Mabuchi I (2006) Actin-depolymerizing protein Adf1 is required for formation and maintenance of the contractile ring during cytokinesis in fission yeast. Mol Biol Cell 17: 1933–1945. Nakano K, Imai J, Arai R, Toh EA, Matsui Y & Mabuchi I (2002) The small GTPase Rho3 and the diaphanous/formin For3 function in polarized cell growth in fission yeast. J Cell Sci 115: 4629–4639. Nannapaneni S, Wang D, Jain S et al. (2010) The yeast dynamin-like protein Vps1:vps1 mutations perturb the internalization and the motility of endocytic vesicles and endosomes via disorganization of the actin cytoskeleton. Eur J Cell Biol 89: 499–508. Newpher TM, Smith RP, Lemmon V & Lemmon SK (2005) In vivo dynamics of clathrin and its adaptor-dependent recruitment to the actin-based endocytic machinery in yeast. Dev Cell 9: 87–98. Okreglak V & Drubin DG (2007) Cofilin recruitment and function during actin-mediated endocytosis dictated by actin nucleotide state. J Cell Biol 178: 1251–1264. Okreglak V & Drubin DG (2010) Loss of Aip1 reveals a role in maintaining the actin monomer pool and an in vivo oligomer assembly pathway. J Cell Biol 188: 769–777. Padmanabhan A, Bakka K, Sevugan M et al. (2011) IQGAP-related Rng2p organizes cortical nodes and ensures


226

position of cell division in fission yeast. Curr Biol 21: 467–472. Padte NN, Martin SG, Howard M & Chang F (2006) The cell-end factor pom1p inhibits mid1p in specification of the cell division plane in fission yeast. Curr Biol 16: 2480–2487. Paoletti A & Chang F (2000) Analysis of mid1p, a protein required for placement of the cell division site, reveals a link between the nucleus and the cell surface in fission yeast. Mol Biol Cell 11: 2757–2773. Pelham RJ Jr & Chang F (2001) Role of actin polymerization and actin cables in actin-patch movement in Schizosaccharomyces pombe. Nat Cell Biol 3: 235–244. Piel M & Tran PT (2009) Cell shape and cell division in fission yeast. Curr Biol 19: R823–R827. Pollard TD (2007) Regulation of actin filament assembly by Arp2/3 complex and formins. Annu Rev Biophys Biomol Struct 36: 451–477. Pollard TD & Borisy GG (2003) Cellular motility driven by assembly and disassembly of actin filaments. Cell 112: 453– 465. Pollard TD & Cooper JA (2009) Actin, a central player in cell shape and movement. Science 326: 1208–1212. Pollard TD & Wu JQ (2010) Understanding cytokinesis: lessons from fission yeast. Nat Rev Mol Cell Biol 11: 149– 155. Pollard TD, Blanchoin L & Mullins RD (2000) Molecular mechanisms controlling actin filament dynamics in nonmuscle cells. Annu Rev Biophys Biomol Struct 29: 545–576. Proctor SA, Minc N, Boudaoud A & Chang F (2012) Contributions of turgor pressure, the contractile ring, and septum assembly to forces in cytokinesis in fission yeast. Curr Biol 22: 1601–1608. Prosser DC & Wendland B (2012) Conserved roles for yeast Rho1 and mammalian RhoA GTPases in clathrin-independent endocytosis. Small GTPases 3: 229– 235. Prosser DC, Drivas TG, Maldonado-Baez L & Wendland B (2011) Existence of a novel clathrin-independent endocytic pathway in yeast that depends on Rho1 and formin. J Cell Biol 195: 657–671. Pruyne D & Bretscher A (2000a) Polarization of cell growth in yeast. J Cell Sci 113(Pt 4): 571–585. Pruyne D & Bretscher A (2000b) Polarization of cell growth in yeast. I. Establishment and maintenance of polarity states. J Cell Sci 113(Pt 3): 365–375. Pruyne D, Evangelista M, Yang C, Bi E, Zigmond S, Bretscher A & Boone C (2002) Role of formins in actin assembly: nucleation and barbed-end association. Science 297: 612–615. Pruyne D, Gao L, Bi E & Bretscher A (2004a) Stable and dynamic axes of polarity use distinct formin isoforms in budding yeast. Mol Biol Cell 15: 4971–4989. Pruyne D, Legesse-Miller A, Gao L, Dong Y & Bretscher A (2004b) Mechanisms of polarized growth and organelle segregation in yeast. Annu Rev Cell Dev Biol 20: 559–591. Rhee DK, Cho BA & Kim HB (2005) ATP-binding motifs play key roles in Krp1p, kinesin-related protein 1, function for


M. Mishra et al.

bi-polar growth control in fission yeast. Biochem Biophys Res Commun 331: 658–668. Riedl J, Crevenna AH, Kessenbrock K et al. (2008) Lifeact: a versatile marker to visualize F-actin. Nat Methods 5: 605– 607. Rincon SA & Paoletti A (2012) Mid1/anillin and the spatial regulation of cytokinesis in fission yeast. Cytoskeleton (Hoboken) 69: 764–777. Rincon SA, Ye Y, Villar-Tajadura MA, Santos B, Martin SG & Perez P (2009) Pob1 participates in the Cdc42 regulation of fission yeast actin cytoskeleton. Mol Biol Cell 20: 4390–4399. Roberts-Galbraith RH, Ohi MD, Ballif BA et al. (2010) Dephosphorylation of F-BAR protein Cdc15 modulates its conformation and stimulates its scaffolding activity at the cell division site. Mol Cell 39: 86–99. Rossanese OW, Reinke CA, Bevis BJ, Hammond AT, Sears IB, O’Connor J & Glick BS (2001) A role for actin, Cdc1p, and Myo2p in the inheritance of late Golgi elements in Saccharomyces cerevisiae. J Cell Biol 153: 47–62. Sagot I, Klee SK & Pellman D (2002a) Yeast formins regulate cell polarity by controlling the assembly of actin cables. Nat Cell Biol 4: 42–50. Sagot I, Rodal AA, Moseley J, Goode BL & Pellman D (2002b) An actin nucleation mechanism mediated by Bni1 and profilin. Nat Cell Biol 4: 626–631. Schmidt M, Bowers B, Varma A, Roh DH & Cabib E (2002) In budding yeast, contraction of the actomyosin ring and formation of the primary septum at cytokinesis depend on each other. J Cell Sci 115: 293–302. Schott DH, Collins RN & Bretscher A (2002) Secretory vesicle transport velocity in living cells depends on the myosin-V lever arm length. J Cell Biol 156: 35–39. Schwob E & Martin RP (1992) New yeast actin-like gene required late in the cell cycle. Nature 355: 179–182. Sheu YJ, Santos B, Fortin N, Costigan C & Snyder M (1998) Spa2p interacts with cell polarity proteins and signaling components involved in yeast cell morphogenesis. Mol Cell Biol 18: 4053–4069. Shortle D, Haber JE & Botstein D (1982) Lethal disruption of the yeast actin gene by integrative DNA transformation. Science 217: 371–373. Siegrist SE & Doe CQ (2007) Microtubule-induced cortical cell polarity. Genes Dev 21: 483–496. Sirotkin V, Beltzner CC, Marchand JB & Pollard TD (2005) Interactions of WASp, myosin-I, and verprolin with Arp2/3 complex during actin patch assembly in fission yeast. J Cell Biol 170: 637–648. Sirotkin V, Berro J, Macmillan K, Zhao L & Pollard TD (2010) Quantitative analysis of the mechanism of endocytic actin patch assembly and disassembly in fission yeast. Mol Biol Cell 21: 2894–2904. Skau CT & Kovar DR (2010) Fimbrin and tropomyosin competition regulates endocytosis and cytokinesis kinetics in fission yeast. Curr Biol 20: 1415–1422. Skau CT, Courson DS, Bestul AJ, Winkelman JD, Rock RS, Sirotkin V & Kovar DR (2011) Actin filament bundling by



fimbrin is important for endocytosis, cytokinesis, and polarization in fission yeast. J Biol Chem 286: 26964–26977. Skoumpla K, Coulton AT, Lehman W, Geeves MA & Mulvihill DP (2007) Acetylation regulates tropomyosin function in the fission yeast Schizosaccharomyces pombe. J Cell Sci 120: 1635–1645. Skruzny M, Brach T, Ciuffa R, Rybina S, Wachsmuth M & Kaksonen M (2012) Molecular basis for coupling the plasma membrane to the actin cytoskeleton during clathrin-mediated endocytosis. P Natl Acad Sci USA 109: E2533–E2542. Smaczynska-de R II, Allwood EG, Aghamohammadzadeh S, Hettema EH, Goldberg MW & Ayscough KR (2010) A role for the dynamin-like protein Vps1 during endocytosis in yeast. J Cell Sci 123: 3496–3506. Sohrmann M, Fankhauser C, Brodbeck C & Simanis V (1996) The dmf1/mid1 gene is essential for correct positioning of the division septum in fission yeast. Genes Dev 10: 2707– 2719. Soulard A, Lechler T, Spiridonov V, Shevchenko A, Li R & Winsor B (2002) Saccharomyces cerevisiae Bzz1p is implicated with type I myosins in actin patch polarization and is able to recruit actin-polymerizing machinery in vitro. Mol Cell Biol 22: 7889–7906. Soulard A, Friant S, Fitterer C, Orange C, Kaneva G, Mirey G & Winsor B (2005) The WASP/Las17p-interacting protein Bzz1p functions with Myo5p in an early stage of endocytosis. Protoplasma 226: 89–101. Sun Y, Kaksonen M, Madden DT, Schekman R & Drubin DG (2005) Interaction of Sla2p’s ANTH domain with PtdIns (4,5)P2 is important for actin-dependent endocytic internalization. Mol Biol Cell 16: 717–730. Sun Y, Martin AC & Drubin DG (2006) Endocytic internalization in budding yeast requires coordinated actin nucleation and myosin motor activity. Dev Cell 11: 33–46. Takaine M, Numata O & Nakano K (2009) Fission yeast IQGAP arranges actin filaments into the cytokinetic contractile ring. EMBO J 28: 3117–3131. Tolliday N, VerPlank L & Li R (2002) Rho1 directs formin-mediated actin ring assembly during budding yeast cytokinesis. Curr Biol 12: 1864–1870. Toshima JY, Toshima J, Kaksonen M, Martin AC, King DS & Drubin DG (2006) Spatial dynamics of receptor-mediated endocytic trafficking in budding yeast revealed by using fluorescent alpha-factor derivatives. P Natl Acad Sci USA 103: 5793–5798. Urbanek AN, Smith AP, Allwood EG, Booth WI & Ayscough KR (2013) A novel actin-binding motif in Las17/WASP nucleates actin filaments independently of Arp2/3. Curr Biol 23: 196–203. Vallen EA, Caviston J & Bi E (2000) Roles of Hof1p, Bni1p, Bnr1p, and myo1p in cytokinesis in Saccharomyces cerevisiae. Mol Biol Cell 11: 593–611.


227

Vavylonis D, Kovar DR, O’Shaughnessy B & Pollard TD (2006) Model of formin-associated actin filament elongation. Mol Cell 21: 455–466. Vavylonis D, Wu JQ, Hao S, O’Shaughnessy B & Pollard TD (2008) Assembly mechanism of the contractile ring for cytokinesis by fission yeast. Science 319: 97–100. Wear MA & Cooper JA (2004) Capping protein: new insights into mechanism and regulation. Trends Biochem Sci 29: 418–428. Wear MA, Yamashita A, Kim K, Maeda Y & Cooper JA (2003) How capping protein binds the barbed end of the actin filament. Curr Biol 13: 1531–1537. Weinberg J & Drubin DG (2012) Clathrin-mediated endocytosis in budding yeast. Trends Cell Biol 22: 1–13. Wen KK & Rubenstein PA (2005) Acceleration of yeast actin polymerization by yeast Arp2/3 complex does not require an Arp2/3-activating protein. J Biol Chem 280: 24168–24174. Win TZ, Gachet Y, Mulvihill DP, May KM & Hyams JS (2001) Two type V myosins with non-overlapping functions in the fission yeast Schizosaccharomyces pombe: Myo52 is concerned with growth polarity and cytokinesis, Myo51 is a component of the cytokinetic actin ring. J Cell Sci 114: 69–79. Winter D, Podtelejnikov AV, Mann M & Li R (1997) The complex containing actin-related proteins Arp2 and Arp3 is required for the motility and integrity of yeast actin patches. Curr Biol 7: 519–529. Wloka C & Bi E (2012) Mechanisms of cytokinesis in budding yeast. Cytoskeleton (Hoboken) 69: 710–726. Wu JQ, Bahler J & Pringle JR (2001) Roles of a fimbrin and an alpha-actinin-like protein in fission yeast cell polarization and cytokinesis. Mol Biol Cell 12: 1061–1077. Wu JQ, Sirotkin V, Kovar DR, Lord M, Beltzner CC, Kuhn JR & Pollard TD (2006) Assembly of the cytokinetic contractile ring from a broad band of nodes in fission yeast. J Cell Biol 174: 391–402. Yang HC & Pon LA (2002) Actin cable dynamics in budding yeast. P Natl Acad Sci USA 99: 751–756. Yoshida S, Kono K, Lowery DM, Bartolini S, Yaffe MB, Ohya Y & Pellman D (2006) Polo-like kinase Cdc5 controls the local activation of Rho1 to promote cytokinesis. Science 313: 108–111. Yoshida S, Bartolini S & Pellman D (2009) Mechanisms for concentrating Rho1 during cytokinesis. Genes Dev 23: 810– 823. Young ME, Cooper JA & Bridgman PC (2004) Yeast actin patches are networks of branched actin filaments. J Cell Biol 166: 629–635. Yu JH, Crevenna AH, Bettenbuhl M, Freisinger T & Wedlich-Soldner R (2011) Cortical actin dynamics driven by formins and myosin V. J Cell Sci 124: 1533–1541. Zahner JE, Harkins HA & Pringle JR (1996) Genetic analysis of the bipolar pattern of bud site selection in the yeast Saccharomyces cerevisiae. Mol Cell Biol 16: 1857–1870.


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