Cell Metabolism
Previews emphasizing the importance of this emerging research field.
Everts, B., Amiel, E., van der Windt, G.J., Freitas, T.C., Chott, R., Yarasheski, K.E., Pearce, E.L., and Pearce, E.J. (2012). Blood 120, 1422– 1431.
REFERENCES Chang, C.H., Curtis, J.D., Maggi, L.B., Jr., Faubert, B., Villarino, A.V., O’Sullivan, D., Huang, S.C., van der Windt, G.J., Blagih, J., Qiu, J., et al. (2013). Cell 153, 1239–1251. Everts, B., Amiel, E., Huang, S.C., Smith, A.M., Chang, C.H., Lam, W.Y., Redmann, V., Freitas, T.C., Blagih, J., van der Windt, G.J., et al. (2014). Nat. Immunol. 15, 323–332.
Jantsch, J., Chakravortty, D., Turza, N., Prechtel, A.T., Buchholz, B., Gerlach, R.G., Volke, M., Gla¨sner, J., Warnecke, C., Wiesener, M.S., et al. (2008). J. Immunol. 180, 4697–4705. Krawczyk, C.M., Holowka, T., Sun, J., Blagih, J., Amiel, E., DeBerardinis, R.J., Cross, J.R., Jung, E., Thompson, C.B., Jones, R.G., and Pearce, E.J. (2010). Blood 115, 4742–4749.
Miyamoto, S., Murphy, A.N., and Brown, J.H. (2008). Cell Death Differ. 15, 521–529. Ravindran, R., Khan, N., Nakaya, H.I., Li, S., Loebbermann, J., Maddur, M.S., Park, Y., Jones, D.P., Chappert, P., Davoust, J., et al. (2014). Science 343, 313–317. Stiles, B.L. (2009). Adv. Drug Deliv. Rev. 61, 1276– 1282. Tannahill, G.M., Curtis, A.M., Adamik, J., PalssonMcDermott, E.M., McGettrick, A.F., Goel, G., Frezza, C., Bernard, N.J., Kelly, B., Foley, N.H., et al. (2013). Nature 496, 238–242.
Knock, Knock to Reset the Clock: Mechanosensation and Circadian Rhythms Bart van Alphen1 and Ravi Allada1,* 1Department of Neurobiology, Northwestern University, Evanston, IL 60208, USA *Correspondence: [email protected] http://dx.doi.org/10.1016/j.cmet.2014.04.011
Circadian clocks, which underlie the daily rhythms in virtually all organisms, are entrained by diurnal changes in light, temperature, nutrients, and even sound. Simoni et al. (2014) demonstrate that diurnal variation in mechanical vibrations can reset circadian clock phase, providing a potential mechanism for integrating diverse clock-entraining stimuli. Organisms keep track of the rotation of the earth by using internal 24 hr oscillators, termed circadian clocks, which allow them to optimally deal with and even anticipate daily fluctuations in the environment. In animals, the molecular machinery driving these circadian clocks consists of a negative feedback loop in which the product of one set of genes represses its own transcription, as well as several stabilizing side loops (Allada and Chung, 2010; Buhr and Takahashi, 2013). These circadian clocks are synchronized to the environment by external cues, most notably light and temperature fluctuations, but also by other cues such as social interactions (Levine et al., 2002), feeding (Stokkan et al., 2001), and even sound (Menaker and Eskin, 1966). Using Drosophila melanogaster as a model organism, Simoni et al. now demonstrate that exposure to a 12 hr vibration:12 hr silence schedule is sufficient to synchronize daily locomotor activity patterns in the fruit fly (Simoni et al., 2014).
In Drosophila, temperature-dependent entrainment of the circadian clock has been linked to chordotonal organs (Sehadova et al., 2009). These internal mechanoreceptors are located at each joint and function as stretch receptors to mediate proprioception and vibration detection (Kernan, 2007). Simoni et al. reasoned that if signaling from peripheral chordotonal organs provides sensory input to the central circadian clock, the clock can be synchronized by exciting the chordotonal organs using a rhythmic mechanical stimulus. To test this hypothesis, flies were first entrained to a 12 hr:12 hr light-dark cycle (LD) and then either placed in a control group in constant darkness, allowing their circadian clock to run free, or exposed to two consecutive vibration regimes in constant darkness (12 hr:12 hr vibration-silence). Under these conditions, vibration onset was shifted in two steps to be 12 hr out of phase with prior light onset. At the end of the vibration regime, flies were placed in free-running conditions, i.e.,
constant darkness, temperature, and silence, allowing assessments of circadian clock phase. Throughout these procedures, fly activity was measured using the classic Drosophila Activity Monitor (DAM) system, an infrared sensor that counts how often a fly crosses the center of a tube. After exposure to the two vibration regimes delivered by placing the DAM system on a bass loudspeaker, flies had synchronized their activity to the vibration cycles, where the peak of their activity in free running conditions matched the expected onset of the stimulus. Likewise, anticipatory activity before stimulus onset, a signature of circadian clock function under diurnal conditions, was also significantly increased. To test whether entrainment to vibration stimuli requires a functional clock, the experiment was also performed in arrhythmic per01 mutants that lack the core clock gene period. After exposure to the phase-shifted vibration regimes, these flies were neither able to synchronize their activity cycles
Cell Metabolism 19, May 6, 2014 ª2014 Elsevier Inc. 739
Cell Metabolism
Previews with the vibration cycles, nor did they show any anticipatory activity. per01 flies bearing a per rescue transgene were able to synchronize their free-running activity to the timing of vibration onset similar to wild-type flies, demonstrating that entrainment to mechanical stimuli requires a functional circadian clock. To explore a potential molecular pathway underlying vibration-dependent entrainment, the authors tested two genes that have been shown to be important for temperature entrainment as well as chrodotonal organ structure, function, and/or hearing: tilB (Kavlie et al., 2010) and nocte (Sehadova et al., 2009). Neither tilB nor nocte mutants are able to synchronize their activity to the vibration cycle, consistent with a role for chordotonal organs in vibration entrainment. To determine if vibration phase shifted the clock, Simoni et al. assayed the activity of a rhythmic per-luciferase fusion protein (PER-LUC) in subsets of clock neurons, subjecting flies to mechanosensory entrainment, shifting the onset and offset of vibration either 6 hr forward or 6 hr back relative to the phase of prior lightdark entrainment. While they demonstrated that vibration entrainment can shift the molecular clock, the phase shifts are counterintuitive: a phase advance in vibration onset resulted in a phase delay of PER-LUC oscillations while a delay in the phase of vibration onset resulted in a phase advance of PER-LUC. A further understanding of how mechanosensory signaling is integrated with the molecular clock could help solve this conundrum.
An interesting question raised by this work is how important mechanosensory cues are in the normal life of the fruit fly. Of note, only slightly more than half of the flies were able to synchronize their behavioral rhythm to the vibration cycles, possibly due to reduced stimulus efficacy. In addition, do the chordotonal organs respond to temperature as robustly as they do to mechanosensory stimuli, and how do thermal and mechanosensory stimuli interact? Future studies will be needed to determine the appropriate and perhaps ethologically relevant stimuli that optimally entrain clocks via the chordotonal organs. The study by Simoni et al. brings up the intriguing possibility that proprioceptive feedback—derived from an animal’s own activity—can entrain the clock. Indeed, in mice, daily restriction to access to running wheels can entrain their circadian clocks (Yamanaka et al., 2013). The authors note that many stimuli that can entrain the clock—e.g., light, temperature, and social interactions—can result in acute changes in locomotor activity. They hypothesize that these may be sensed by proprioceptors to reset circadian clocks, providing a universal mechanism for clock resetting. Indeed, the direct effects of temperature on locomotor activity could explain part of the reported role of chordotonal organs in temperature entrainment (Sehadova et al., 2009). A key test of this exciting hypothesis would be to devise a method to restrict the locomotor effects in response to phase-resetting sensory stimuli to determine how
740 Cell Metabolism 19, May 6, 2014 ª2014 Elsevier Inc.
much of their clock resetting effects are through direct behavior activation and thus potentially via proprioceptors. Alternatively, one could transiently activate locomotion to see if this is sufficient to phase-shift rhythms. The authors have discovered a novel pathway for resetting circadian clocks in flies, opening up the study of mechanosensory entrainment to neurogenetic analyses in this model system. Whether or not this will overturn our current view of how sensory cues entrain circadian clocks, time will tell. REFERENCES Allada, R., and Chung, B.Y. (2010). Annu. Rev. Physiol. 72, 605–624. Buhr, E.D., and Takahashi, J.S. (2013). Handbook Exp. Pharmacol., 3–27. Kavlie, R.G., Kernan, M.J., and Eberl, D.F. (2010). Genetics 185, 177–188. Kernan, M.J. (2007). Pflugers Arch. 454, 703–720. Levine, J.D., Funes, P., Dowse, H.B., and Hall, J.C. (2002). Science 298, 2010–2012. Menaker, M., and Eskin, A. (1966). Science 154, 1579–1581. Sehadova, H., Glaser, F.T., Gentile, C., Simoni, A., Giesecke, A., Albert, J.T., and Stanewsky, R. (2009). Neuron 64, 251–266. Simoni, A., Wolfgang, W., Topping, M.P., Kavlie, R.G., Stanewsky, R., and Albert, J.T. (2014). Science 343, 525–528. Stokkan, K.A., Yamazaki, S., Tei, H., Sakaki, Y., and Menaker, M. (2001). Science 291, 490–493. Yamanaka, Y., Honma, S., and Honma, K. (2013). Am. J. Physiol. Regul. Integr. Comp. Physiol. 305, R1367–R1375.
Previews emphasizing the importance of this emerging research field.
Everts, B., Amiel, E., van der Windt, G.J., Freitas, T.C., Chott, R., Yarasheski, K.E., Pearce, E.L., and Pearce, E.J. (2012). Blood 120, 1422– 1431.
REFERENCES Chang, C.H., Curtis, J.D., Maggi, L.B., Jr., Faubert, B., Villarino, A.V., O’Sullivan, D., Huang, S.C., van der Windt, G.J., Blagih, J., Qiu, J., et al. (2013). Cell 153, 1239–1251. Everts, B., Amiel, E., Huang, S.C., Smith, A.M., Chang, C.H., Lam, W.Y., Redmann, V., Freitas, T.C., Blagih, J., van der Windt, G.J., et al. (2014). Nat. Immunol. 15, 323–332.
Jantsch, J., Chakravortty, D., Turza, N., Prechtel, A.T., Buchholz, B., Gerlach, R.G., Volke, M., Gla¨sner, J., Warnecke, C., Wiesener, M.S., et al. (2008). J. Immunol. 180, 4697–4705. Krawczyk, C.M., Holowka, T., Sun, J., Blagih, J., Amiel, E., DeBerardinis, R.J., Cross, J.R., Jung, E., Thompson, C.B., Jones, R.G., and Pearce, E.J. (2010). Blood 115, 4742–4749.
Miyamoto, S., Murphy, A.N., and Brown, J.H. (2008). Cell Death Differ. 15, 521–529. Ravindran, R., Khan, N., Nakaya, H.I., Li, S., Loebbermann, J., Maddur, M.S., Park, Y., Jones, D.P., Chappert, P., Davoust, J., et al. (2014). Science 343, 313–317. Stiles, B.L. (2009). Adv. Drug Deliv. Rev. 61, 1276– 1282. Tannahill, G.M., Curtis, A.M., Adamik, J., PalssonMcDermott, E.M., McGettrick, A.F., Goel, G., Frezza, C., Bernard, N.J., Kelly, B., Foley, N.H., et al. (2013). Nature 496, 238–242.
Knock, Knock to Reset the Clock: Mechanosensation and Circadian Rhythms Bart van Alphen1 and Ravi Allada1,* 1Department of Neurobiology, Northwestern University, Evanston, IL 60208, USA *Correspondence: [email protected] http://dx.doi.org/10.1016/j.cmet.2014.04.011
Circadian clocks, which underlie the daily rhythms in virtually all organisms, are entrained by diurnal changes in light, temperature, nutrients, and even sound. Simoni et al. (2014) demonstrate that diurnal variation in mechanical vibrations can reset circadian clock phase, providing a potential mechanism for integrating diverse clock-entraining stimuli. Organisms keep track of the rotation of the earth by using internal 24 hr oscillators, termed circadian clocks, which allow them to optimally deal with and even anticipate daily fluctuations in the environment. In animals, the molecular machinery driving these circadian clocks consists of a negative feedback loop in which the product of one set of genes represses its own transcription, as well as several stabilizing side loops (Allada and Chung, 2010; Buhr and Takahashi, 2013). These circadian clocks are synchronized to the environment by external cues, most notably light and temperature fluctuations, but also by other cues such as social interactions (Levine et al., 2002), feeding (Stokkan et al., 2001), and even sound (Menaker and Eskin, 1966). Using Drosophila melanogaster as a model organism, Simoni et al. now demonstrate that exposure to a 12 hr vibration:12 hr silence schedule is sufficient to synchronize daily locomotor activity patterns in the fruit fly (Simoni et al., 2014).
In Drosophila, temperature-dependent entrainment of the circadian clock has been linked to chordotonal organs (Sehadova et al., 2009). These internal mechanoreceptors are located at each joint and function as stretch receptors to mediate proprioception and vibration detection (Kernan, 2007). Simoni et al. reasoned that if signaling from peripheral chordotonal organs provides sensory input to the central circadian clock, the clock can be synchronized by exciting the chordotonal organs using a rhythmic mechanical stimulus. To test this hypothesis, flies were first entrained to a 12 hr:12 hr light-dark cycle (LD) and then either placed in a control group in constant darkness, allowing their circadian clock to run free, or exposed to two consecutive vibration regimes in constant darkness (12 hr:12 hr vibration-silence). Under these conditions, vibration onset was shifted in two steps to be 12 hr out of phase with prior light onset. At the end of the vibration regime, flies were placed in free-running conditions, i.e.,
constant darkness, temperature, and silence, allowing assessments of circadian clock phase. Throughout these procedures, fly activity was measured using the classic Drosophila Activity Monitor (DAM) system, an infrared sensor that counts how often a fly crosses the center of a tube. After exposure to the two vibration regimes delivered by placing the DAM system on a bass loudspeaker, flies had synchronized their activity to the vibration cycles, where the peak of their activity in free running conditions matched the expected onset of the stimulus. Likewise, anticipatory activity before stimulus onset, a signature of circadian clock function under diurnal conditions, was also significantly increased. To test whether entrainment to vibration stimuli requires a functional clock, the experiment was also performed in arrhythmic per01 mutants that lack the core clock gene period. After exposure to the phase-shifted vibration regimes, these flies were neither able to synchronize their activity cycles
Cell Metabolism 19, May 6, 2014 ª2014 Elsevier Inc. 739
Cell Metabolism
Previews with the vibration cycles, nor did they show any anticipatory activity. per01 flies bearing a per rescue transgene were able to synchronize their free-running activity to the timing of vibration onset similar to wild-type flies, demonstrating that entrainment to mechanical stimuli requires a functional circadian clock. To explore a potential molecular pathway underlying vibration-dependent entrainment, the authors tested two genes that have been shown to be important for temperature entrainment as well as chrodotonal organ structure, function, and/or hearing: tilB (Kavlie et al., 2010) and nocte (Sehadova et al., 2009). Neither tilB nor nocte mutants are able to synchronize their activity to the vibration cycle, consistent with a role for chordotonal organs in vibration entrainment. To determine if vibration phase shifted the clock, Simoni et al. assayed the activity of a rhythmic per-luciferase fusion protein (PER-LUC) in subsets of clock neurons, subjecting flies to mechanosensory entrainment, shifting the onset and offset of vibration either 6 hr forward or 6 hr back relative to the phase of prior lightdark entrainment. While they demonstrated that vibration entrainment can shift the molecular clock, the phase shifts are counterintuitive: a phase advance in vibration onset resulted in a phase delay of PER-LUC oscillations while a delay in the phase of vibration onset resulted in a phase advance of PER-LUC. A further understanding of how mechanosensory signaling is integrated with the molecular clock could help solve this conundrum.
An interesting question raised by this work is how important mechanosensory cues are in the normal life of the fruit fly. Of note, only slightly more than half of the flies were able to synchronize their behavioral rhythm to the vibration cycles, possibly due to reduced stimulus efficacy. In addition, do the chordotonal organs respond to temperature as robustly as they do to mechanosensory stimuli, and how do thermal and mechanosensory stimuli interact? Future studies will be needed to determine the appropriate and perhaps ethologically relevant stimuli that optimally entrain clocks via the chordotonal organs. The study by Simoni et al. brings up the intriguing possibility that proprioceptive feedback—derived from an animal’s own activity—can entrain the clock. Indeed, in mice, daily restriction to access to running wheels can entrain their circadian clocks (Yamanaka et al., 2013). The authors note that many stimuli that can entrain the clock—e.g., light, temperature, and social interactions—can result in acute changes in locomotor activity. They hypothesize that these may be sensed by proprioceptors to reset circadian clocks, providing a universal mechanism for clock resetting. Indeed, the direct effects of temperature on locomotor activity could explain part of the reported role of chordotonal organs in temperature entrainment (Sehadova et al., 2009). A key test of this exciting hypothesis would be to devise a method to restrict the locomotor effects in response to phase-resetting sensory stimuli to determine how
740 Cell Metabolism 19, May 6, 2014 ª2014 Elsevier Inc.
much of their clock resetting effects are through direct behavior activation and thus potentially via proprioceptors. Alternatively, one could transiently activate locomotion to see if this is sufficient to phase-shift rhythms. The authors have discovered a novel pathway for resetting circadian clocks in flies, opening up the study of mechanosensory entrainment to neurogenetic analyses in this model system. Whether or not this will overturn our current view of how sensory cues entrain circadian clocks, time will tell. REFERENCES Allada, R., and Chung, B.Y. (2010). Annu. Rev. Physiol. 72, 605–624. Buhr, E.D., and Takahashi, J.S. (2013). Handbook Exp. Pharmacol., 3–27. Kavlie, R.G., Kernan, M.J., and Eberl, D.F. (2010). Genetics 185, 177–188. Kernan, M.J. (2007). Pflugers Arch. 454, 703–720. Levine, J.D., Funes, P., Dowse, H.B., and Hall, J.C. (2002). Science 298, 2010–2012. Menaker, M., and Eskin, A. (1966). Science 154, 1579–1581. Sehadova, H., Glaser, F.T., Gentile, C., Simoni, A., Giesecke, A., Albert, J.T., and Stanewsky, R. (2009). Neuron 64, 251–266. Simoni, A., Wolfgang, W., Topping, M.P., Kavlie, R.G., Stanewsky, R., and Albert, J.T. (2014). Science 343, 525–528. Stokkan, K.A., Yamazaki, S., Tei, H., Sakaki, Y., and Menaker, M. (2001). Science 291, 490–493. Yamanaka, Y., Honma, S., and Honma, K. (2013). Am. J. Physiol. Regul. Integr. Comp. Physiol. 305, R1367–R1375.
