SnapShot: Motile Cilia Feng Zhou1 and Sudipto Roy1,2,3 Institute of Molecular and Cell Biology, Proteos, Singapore 138673, Singapore 2 Department of Biological Sciences, National University of Singapore, Singapore 117543, Singapore 3 Department of Pediatrics, National University of Singapore, Singapore 119228, Singapore
1
Assembly of motile cilia Outer doublet microtubules Dynein arm docking complex
Radial spoke
Central sheath
Nexin-dynein regulatory complex
IDA
Central bridge
Retrograde IFT
ODA
DNAAF1
Kinesin IFT particle
Anterograde IFT
Central pair
Dynein Axonemal precursor
Recycled axonemal component
Ciliary membrane
Y fibers
Release of folded dynein protein Transport via IFT to axonemal docking sites
DNAAF3 DNAAF2
Basal foot
Basal body Striated rootlets
Association of dynein polypeptides with assembly factors
Daughter centriole
Transition fiber
Interconnecting fibers For transition zone proteins
For docking and anchorage of motility components
Transcription of ciliary genes
For cytoplasmic preassembly of motility components
FoxJ1
For IFT components For basal body docking
Rfx
Tubulins and tubulin modification enzymes for axoneme structure
For motility apparatus
Multiciliated cell differentiation
Motile cilia in locomotion Schmidtea
Chlamydomonas Mother centriole Daughter centriole
Centriole migration and docking as ciliary basal bodies
Plk4
Procentriole Mature centriole/ basal body
Paramecium Sperm Trochophore larva
Centriole release and maturation
Sas-6
Motile cilia in the mammalian embryonic node
CEP63 CEP152 DEUP1
v
Plk4, Sas-6
CCDC78
Multiple motile cilia in the mammalian airway
Transcription of: Notch signaling
MCIDAS
?
FoxJ1
Ciliary genes FoxJ1
Centriole amplification genes MCIDAS E2F
Mucus Notch signaling Multiciliated cell
224
Cell 162, July 2, 2015 ©2015 Elsevier Inc.
DOI http://dx.doi.org/10.1016/j.cell.2015.06.048
Goblet cell
See online version for legends and references
SnapShot: Motile Cilia Feng Zhou1 and Sudipto Roy1,2,3 Institute of Molecular and Cell Biology, Proteos, Singapore 138673, Singapore 2 Department of Biological Sciences, National University of Singapore, Singapore 117543, Singapore 3 Department of Pediatrics, National University of Singapore, Singapore 119228, Singapore
1
Motile cilia are hair-like organelles that protrude from the cell surface and are conserved throughout eukaryotes. Motile cilia beat rhythmically and function in cellular and organismal locomotion and in driving fluid transport over epithelia. In vertebrates, their roles are varied, and their dysfunction in humans is associated with disease. Differentiation of Mono-Motile Cilia The axoneme, the core of a motile cilium, is built from nine outer doublet microtubules together with a central pair of microtubule singlets. It is seeded by the basal body, a derivative of the mother centriole that associates with the apical cell membrane at the onset of ciliogenesis. Molecular complexes that impart or regulate motility such as the outer and inner dynein arms (ODA and IDA), radial spokes, and the nexin links are attached to the outer doublets and the central pair at regular intervals along the length of the axoneme. Assembly and disassembly of axonemal and motility components is regulated by intraflagellar transport (IFT), with anterograde transport driven by the kinesin-2 motor and retrograde transport facilitated by the cytoplasmic dynein-2 complex. Motility components, such as the dynein arms, are partially assembled with the help of specific assembly factors (DNAAFs) in the cytoplasm before being trafficked into the cilium by IFT. In addition, dedicated docking proteins function as sites for anchoring the motility proteins along the axoneme. Transcriptional control of motile ciliogenesis is mediated by members of the regulatory factor X (RFX) and the forkhead box J1 (FoxJ1) family proteins. FoxJ1 is the central transcription factor in motile ciliogenesis, and it is essential, and in many instances sufficient, to program cells to differentiate motile cilia. Expression of FoxJ1 occurs in tissues harboring motile cilia, and it activates the expression of a cohort of genes required for motile cilia differentiation and function. The RFX proteins typically control expression of genes that have functions in all types of cilia, such as those for IFT factors. There is cross talk between FoxJ1 and the RFX proteins that facilitates the unique transcriptional programs specifying the distinct identities of different kinds of motile cilia. Differentiation of Multiple Motile Cilia Central to the differentiation of multiciliated cells (MCCs) is the biogenesis of a large number of basal bodies, which subsequently migrate and dock apically to seed multiple cilia. To generate tens and even hundreds of basal bodies in non-cycling cells, differentiating MCCs co-opt molecules used by dividing cells for duplication of their centrioles, including centrosomal proteins Cep63 and Cep152, the kinase Plk4, and the structural protein Sas-6. Although a mother centriole-dependent (MCD) pathway contributes to centriole amplification, the majority of basal bodies are synthesized via a mother centriole-independent pathway that takes place in a cytoplasmic structure termed the deuterosome, which is enriched in molecules employed by the MCD pathway such as Cep152, Plk4, and Sas-6, and a deuterosome-specific paralog of Cep63, Deup1. Current view posits that the deuterosome is nucleated by the daughter centriole. MCC differentiation is antagonized by Notch signaling, and in tetrapods, it is transcriptionally programmed by MCIDAS (also called Multicilin), which associates with the E2F transcription factors to activate centriole amplification genes like Ccno and Deup1. MCIDAS also induces the expression of FoxJ1 in MCC progenitors. Function of Motile Cilia in Cellular and Organismal Locomotion Motile cilia are used for locomotion in many aquatic protozoan species. For example, they manifest as a pair of long flagella on the green algae Chlamydomonas and as short cilia on the external surface of various species of Paramecium. The flatworm Schmidtea possesses MCCs on the ventral surface for gliding motion, and free-swimming aquatic larval forms (such as trocophore) of several invertebrate species display several bands of motile cilia. Spermatozoa also use flagella to swim. Function of Mono-Motile Cilia in Fluid Flow In organs of laterality of various vertebrates, such as the mammalian embryonic node, Xenopus gastrocoel roof plate, and Kupffer’s vesicle of teleost fishes, mono-motile cilia establish left-right asymmetry of visceral organs. In the mouse node, these cilia display a unique ultrastructure (no central pair) and establish a leftward-directed fluid flow (nodal flow) within the node cavity. This is thought to generate a mechanical signal or transport a morphogen or both. In teleost fishes, mono-motile cilia affect deposition of otoliths, calcium carbonate particles, on sensory hair cells of the inner ear. Function of Multiple Motile Cilia in Fluid Flow MCCs populate some mammalian epithelia and facilitate directional fluid flow. The airway epithelium harbors MCCs that are intercalated with the mucus-secreting goblet cells and facilitate mucus clearance. Likewise, ependymal cells within the ventricles of the brain are important for cerebrospinal fluid flow, and MCCs that line the female reproductive tract facilitate egg transport. MCCs present on the epidermis of amphibian embryos (for clearing mucus) and within kidney tubules of teleost fishes (for urine flow) are useful models for our understanding of MCC formation and function. Human Diseases Arising from Defects in Motile Cilia Mutations in genes encoding components common to mono-, as well as multiple, motile cilia cause primary ciliary dyskinesia (PCD), characterized by recurrent airway infections and male fertility defects. In addition, a subset of PCD patients presents situs inversus (abnormal disposition of viscera), a condition called Kartagener syndrome, due to motility defects in the nodal cilia. Emerging evidence indicates situs abnormalities that arise independent of respiratory problems ensue from defects in ciliary proteins that function exclusively in the nodal cilia, whereas mutations in genes required for the generation of multiple motile cilia, such as MCIDAS and CCNO, cause reduced generation of multiple motile cilia (RGMC) without affecting fertility or situs. Motile cilia may also play a role in the pathogenesis of acquired respiratory conditions like chronic obstructive pulmonary disorder (COPD). Acknowledgments The authors gratefully acknowledge funding provided by the Agency for Science, Technology, and Research (A*STAR) of Singapore. References Al Jord, A., Lemaître, A.I., Delgehyr, N., Faucourt, M., Spassky, N., and Meunier, A. (2014). Nature 516, 104–107. Babu, D., and Roy, S. (2013). Open Biol. 3, 130052. Brooks, E.R., and Wallingford, J.B. (2014). Curr. Biol. 24, R973–R982. Choksi, S.P., Lauter, G., Swoboda, P., and Roy, S. (2014). Development 141, 1427–1441. Fliegauf, M., Benzing, T., and Omran, H. (2007). Nat. Rev. Mol. Cell Biol. 8, 880–893. Ishikawa, H., and Marshall, W.F. (2011). Nat. Rev. Mol. Cell Biol. 12, 222–234. Narasimhan, V., Hjeij, R., Vij, S., Loges, N.T., Wallmeier, J., Koerner-Rettberg, C., Werner, C., Thamilselvam, S.K., Boey, A., Choksi, S.P., et al. (2015). Hum. Mutat. 36, 307–318. Riley, B.B., Zhu, C., Janetopoulos, C., and Aufderheide, K.J. (1997). Dev. Biol. 191, 191–201. Wallmeier, J., Al-Mutairi, D.A., Chen, C.T., Loges, N.T., Pennekamp, P., Menchen, T., Ma, L., Shamseldin, H.E., Olbrich, H., Dougherty, G.W., et al. (2014). Nat. Genet. 46, 646–651.
224.e1 Cell 162, July 2, 2015 ©2015 Elsevier Inc. DOI http://dx.doi.org/10.1016/j.cell.2015.06.048
1
Assembly of motile cilia Outer doublet microtubules Dynein arm docking complex
Radial spoke
Central sheath
Nexin-dynein regulatory complex
IDA
Central bridge
Retrograde IFT
ODA
DNAAF1
Kinesin IFT particle
Anterograde IFT
Central pair
Dynein Axonemal precursor
Recycled axonemal component
Ciliary membrane
Y fibers
Release of folded dynein protein Transport via IFT to axonemal docking sites
DNAAF3 DNAAF2
Basal foot
Basal body Striated rootlets
Association of dynein polypeptides with assembly factors
Daughter centriole
Transition fiber
Interconnecting fibers For transition zone proteins
For docking and anchorage of motility components
Transcription of ciliary genes
For cytoplasmic preassembly of motility components
FoxJ1
For IFT components For basal body docking
Rfx
Tubulins and tubulin modification enzymes for axoneme structure
For motility apparatus
Multiciliated cell differentiation
Motile cilia in locomotion Schmidtea
Chlamydomonas Mother centriole Daughter centriole
Centriole migration and docking as ciliary basal bodies
Plk4
Procentriole Mature centriole/ basal body
Paramecium Sperm Trochophore larva
Centriole release and maturation
Sas-6
Motile cilia in the mammalian embryonic node
CEP63 CEP152 DEUP1
v
Plk4, Sas-6
CCDC78
Multiple motile cilia in the mammalian airway
Transcription of: Notch signaling
MCIDAS
?
FoxJ1
Ciliary genes FoxJ1
Centriole amplification genes MCIDAS E2F
Mucus Notch signaling Multiciliated cell
224
Cell 162, July 2, 2015 ©2015 Elsevier Inc.
DOI http://dx.doi.org/10.1016/j.cell.2015.06.048
Goblet cell
See online version for legends and references
SnapShot: Motile Cilia Feng Zhou1 and Sudipto Roy1,2,3 Institute of Molecular and Cell Biology, Proteos, Singapore 138673, Singapore 2 Department of Biological Sciences, National University of Singapore, Singapore 117543, Singapore 3 Department of Pediatrics, National University of Singapore, Singapore 119228, Singapore
1
Motile cilia are hair-like organelles that protrude from the cell surface and are conserved throughout eukaryotes. Motile cilia beat rhythmically and function in cellular and organismal locomotion and in driving fluid transport over epithelia. In vertebrates, their roles are varied, and their dysfunction in humans is associated with disease. Differentiation of Mono-Motile Cilia The axoneme, the core of a motile cilium, is built from nine outer doublet microtubules together with a central pair of microtubule singlets. It is seeded by the basal body, a derivative of the mother centriole that associates with the apical cell membrane at the onset of ciliogenesis. Molecular complexes that impart or regulate motility such as the outer and inner dynein arms (ODA and IDA), radial spokes, and the nexin links are attached to the outer doublets and the central pair at regular intervals along the length of the axoneme. Assembly and disassembly of axonemal and motility components is regulated by intraflagellar transport (IFT), with anterograde transport driven by the kinesin-2 motor and retrograde transport facilitated by the cytoplasmic dynein-2 complex. Motility components, such as the dynein arms, are partially assembled with the help of specific assembly factors (DNAAFs) in the cytoplasm before being trafficked into the cilium by IFT. In addition, dedicated docking proteins function as sites for anchoring the motility proteins along the axoneme. Transcriptional control of motile ciliogenesis is mediated by members of the regulatory factor X (RFX) and the forkhead box J1 (FoxJ1) family proteins. FoxJ1 is the central transcription factor in motile ciliogenesis, and it is essential, and in many instances sufficient, to program cells to differentiate motile cilia. Expression of FoxJ1 occurs in tissues harboring motile cilia, and it activates the expression of a cohort of genes required for motile cilia differentiation and function. The RFX proteins typically control expression of genes that have functions in all types of cilia, such as those for IFT factors. There is cross talk between FoxJ1 and the RFX proteins that facilitates the unique transcriptional programs specifying the distinct identities of different kinds of motile cilia. Differentiation of Multiple Motile Cilia Central to the differentiation of multiciliated cells (MCCs) is the biogenesis of a large number of basal bodies, which subsequently migrate and dock apically to seed multiple cilia. To generate tens and even hundreds of basal bodies in non-cycling cells, differentiating MCCs co-opt molecules used by dividing cells for duplication of their centrioles, including centrosomal proteins Cep63 and Cep152, the kinase Plk4, and the structural protein Sas-6. Although a mother centriole-dependent (MCD) pathway contributes to centriole amplification, the majority of basal bodies are synthesized via a mother centriole-independent pathway that takes place in a cytoplasmic structure termed the deuterosome, which is enriched in molecules employed by the MCD pathway such as Cep152, Plk4, and Sas-6, and a deuterosome-specific paralog of Cep63, Deup1. Current view posits that the deuterosome is nucleated by the daughter centriole. MCC differentiation is antagonized by Notch signaling, and in tetrapods, it is transcriptionally programmed by MCIDAS (also called Multicilin), which associates with the E2F transcription factors to activate centriole amplification genes like Ccno and Deup1. MCIDAS also induces the expression of FoxJ1 in MCC progenitors. Function of Motile Cilia in Cellular and Organismal Locomotion Motile cilia are used for locomotion in many aquatic protozoan species. For example, they manifest as a pair of long flagella on the green algae Chlamydomonas and as short cilia on the external surface of various species of Paramecium. The flatworm Schmidtea possesses MCCs on the ventral surface for gliding motion, and free-swimming aquatic larval forms (such as trocophore) of several invertebrate species display several bands of motile cilia. Spermatozoa also use flagella to swim. Function of Mono-Motile Cilia in Fluid Flow In organs of laterality of various vertebrates, such as the mammalian embryonic node, Xenopus gastrocoel roof plate, and Kupffer’s vesicle of teleost fishes, mono-motile cilia establish left-right asymmetry of visceral organs. In the mouse node, these cilia display a unique ultrastructure (no central pair) and establish a leftward-directed fluid flow (nodal flow) within the node cavity. This is thought to generate a mechanical signal or transport a morphogen or both. In teleost fishes, mono-motile cilia affect deposition of otoliths, calcium carbonate particles, on sensory hair cells of the inner ear. Function of Multiple Motile Cilia in Fluid Flow MCCs populate some mammalian epithelia and facilitate directional fluid flow. The airway epithelium harbors MCCs that are intercalated with the mucus-secreting goblet cells and facilitate mucus clearance. Likewise, ependymal cells within the ventricles of the brain are important for cerebrospinal fluid flow, and MCCs that line the female reproductive tract facilitate egg transport. MCCs present on the epidermis of amphibian embryos (for clearing mucus) and within kidney tubules of teleost fishes (for urine flow) are useful models for our understanding of MCC formation and function. Human Diseases Arising from Defects in Motile Cilia Mutations in genes encoding components common to mono-, as well as multiple, motile cilia cause primary ciliary dyskinesia (PCD), characterized by recurrent airway infections and male fertility defects. In addition, a subset of PCD patients presents situs inversus (abnormal disposition of viscera), a condition called Kartagener syndrome, due to motility defects in the nodal cilia. Emerging evidence indicates situs abnormalities that arise independent of respiratory problems ensue from defects in ciliary proteins that function exclusively in the nodal cilia, whereas mutations in genes required for the generation of multiple motile cilia, such as MCIDAS and CCNO, cause reduced generation of multiple motile cilia (RGMC) without affecting fertility or situs. Motile cilia may also play a role in the pathogenesis of acquired respiratory conditions like chronic obstructive pulmonary disorder (COPD). Acknowledgments The authors gratefully acknowledge funding provided by the Agency for Science, Technology, and Research (A*STAR) of Singapore. References Al Jord, A., Lemaître, A.I., Delgehyr, N., Faucourt, M., Spassky, N., and Meunier, A. (2014). Nature 516, 104–107. Babu, D., and Roy, S. (2013). Open Biol. 3, 130052. Brooks, E.R., and Wallingford, J.B. (2014). Curr. Biol. 24, R973–R982. Choksi, S.P., Lauter, G., Swoboda, P., and Roy, S. (2014). Development 141, 1427–1441. Fliegauf, M., Benzing, T., and Omran, H. (2007). Nat. Rev. Mol. Cell Biol. 8, 880–893. Ishikawa, H., and Marshall, W.F. (2011). Nat. Rev. Mol. Cell Biol. 12, 222–234. Narasimhan, V., Hjeij, R., Vij, S., Loges, N.T., Wallmeier, J., Koerner-Rettberg, C., Werner, C., Thamilselvam, S.K., Boey, A., Choksi, S.P., et al. (2015). Hum. Mutat. 36, 307–318. Riley, B.B., Zhu, C., Janetopoulos, C., and Aufderheide, K.J. (1997). Dev. Biol. 191, 191–201. Wallmeier, J., Al-Mutairi, D.A., Chen, C.T., Loges, N.T., Pennekamp, P., Menchen, T., Ma, L., Shamseldin, H.E., Olbrich, H., Dougherty, G.W., et al. (2014). Nat. Genet. 46, 646–651.
224.e1 Cell 162, July 2, 2015 ©2015 Elsevier Inc. DOI http://dx.doi.org/10.1016/j.cell.2015.06.048
