JCJC - Jeunes chercheuses & jeunes chercheurs

Mécanismes de couplage dans le système circadien multi-oscillant – Clock-coupling

Submission summary

Circadian rhythmicity is a fundamental regulatory principle in living organisms. This temporal regulation is under the control not of a single, central circadian clock but of a circadian network comprising different oscillatory units organized in three levels: a suprachiasmatic clock (SCN), still considered as the master clock (its lesion leads to arrhythmicity and is the only component that can be synchronized by light), other brain clocks such as the food-entrainable clock (FEC), and numerous peripheral clocks, including endocrine glands. The emerging multi-oscillatory nature of the circadian system raises fundamental questions on how this system adjusts its multi-level rhythmicity in vivo. Our hypothesis is that, at most levels, synchronization of each oscillating component is controlled by feed-back signals to its synchronizing structure. To test this hypothesis with an integrative approach that will combine tools of molecular biology and physiology, we will investigate coupling (i.e., reciprocal synchronization) at the three clearly identified levels: between the two SCN regions, between SCN and FEC, and between SCN or FEC and peripheral clocks. First, to assess the synchronizing role of the ventral SCN neurons (VIP) to the dorsal neurons (with vasopressin, VP), we will lesion chemically the ventral neurons and analyze in vivo circadian responses in entrained, jet-lag and free-running conditions. This damage to ventral SCN neurons is expected to yield marked phase changes of circadian rhythms in entrained conditions, but not in free-running conditions, thus suggesting the ventral SCN is critical for synchronization of the dorsal SCN, but not for circadian oscillations. To test that VP plays a feed-back role between the two subdivisions of the SCN, we will follow in vivo the effects of VP or V1 antagonists on the circadian rhythms. These treatments are expected to potentiate or reduce, respectively, the amplitude of circadian rhythms. Moreover, the role of VP will be assessed in SCN slices and SCN cultured neurons by multi-microelectrode arrays and conventional patch-clamp recordings. VP in vitro may also increase the number of cells oscillating in synchrony and/or the amplitude of the oscillations. These data would demonstrate that VP projections mediate an intra-SCN feedback loop to achieve full entrainment of the whole SCN clock. Second, we will identify the neural circuit underlying food-entrainable oscillations by assessing which extra-SCN brain regions display cyclic variations of clock genes in food-restricted rats with or without intact SCN. Lesions of candidate brain structures will be used to characterize the network underlying food-entrainable oscillations. To characterize the molecular mechanisms of the FEC, circadian food anticipation will be studied in mice mutant for clock genes to find genes critically involved in FEC's clockwork. Once the site of the FEC identified, we will assess the phase-shifting responses to reduced food availability in rats with SCNX or FECX in order to reveal coupling mechanisms between the SCN and FEC. Third, we will study outputs of peripheral tissues by repeated blood sampling in the same rat rendered arrhythmic by SCN lesions (SCNX) and fed ad libitum to demonstrate the occurrence of in vivo oscillations of peripheral clocks. Individual profiles of plasma metabolites and hormones will be used as phase and period markers of peripheral organs to determine their respective endogenous period and phase-relationships and how their timing is controlled. Then we propose to expose behaviorally arrhythmic SCNX rats to daily restricted feeding with the assumption that this paradigm may restore time-giving cues as if the SCN were intact in rats synchronized to light. Next, we will dissect at what level of the circadian system a restricted feeding provides time-giving signals in SCNX animals. Finally, we will investigate whether output signals from peripheral tissues can feed-back to the SCN and FEC by determining resetting cues of hormones and their direct effects on the firing rate rhythm of SCN or FEC slices. The completion of the proposed experiments will show to what extent coupling between circadian clocks is important for the regulation of the multi-oscillatory circadian system.

Project coordination

Etienne CHALLET (Organisme de recherche)

The author of this summary is the project coordinator, who is responsible for the content of this summary. The ANR declines any responsibility as for its contents.

Partner

Help of the ANR 200,000 euros
Beginning and duration of the scientific project: - 48 Months

Useful links

Explorez notre base de projets financés

 

 

ANR makes available its datasets on funded projects, click here to find more.

Sign up for the latest news:
Subscribe to our newsletter