Separate Sets of Cerebral Clock Neurons Are Responsible for Light and Temperature Entrainment of Drosophila Circadian Locomotor Rhythms

Abstract

The fruit fly Drosophila melanogaster shows a bimodal circadian locomotor rhythm with peaks at lights-on and before lights-off, which are regulated by multiple clocks in the brain. Even under light-dark cycles, the timing of the evening peak is highly dependent on temperature, starting earlier under lower ambient temperature but terminating almost at the same time. In the present study, using behavioral and immunohistochemical assays, the authors show that separate groups of clock neurons, either light-entrainable or temperature-entrainable, form a functional system driving the locomotor rhythm. When subjected to a light cycle combined with a temperature cycle advanced by 6 h relative to the light cycle, the dorsally located neurons (DNs) and lateral posterior neurons (LPNs) shifted their phase of TIMELESS expression, but the laterally located protocerebral neurons (LNs) basically maintained their original phase. Thus, the LNs seem to be preferentially light-entrainable and the DNs and LPNs to be primarily temperature-entrainable. In pdf(01) mutant flies that lack the neuropeptide PDF in the ventral groups of LNs, the onset of the evening peak was greatly advanced even under synchronized light and temperature cycles and was shifted even more than in wild-type flies in response to a 6-h phase shift of the temperature cycle, suggesting that ventral LNs have a strong impact on the phase of the other cells. It seems likely that the 2 sets of clock cells with different entrainability to light and temperature, and the coupling between them, enable Drosophila to keep a proper phase relationship of circadian activity with respect to the daily light and temperature cycles.

Synchronization of theDrosophilaCircadian Clock by Temperature Cycles

“…They were found to exhibit only weakly synchronized behavioral rhythms and also exhibited synchronized PER expression in LPN and DN cells (Yoshii et al 2005), suggesting that these neurons mediate at least some aspects of temperature-entrained behavior. These initial observations were confirmed by a recent study, in which Tim expression was analyzed in flies that were exposed to a combined LD and a 6-hour advanced temperature cycle (25°C:20°C) (Miyasako et al 2007). Tim expression in the LPNs and DNs was mainly synchronized to the temperature cycle, whereas it followed the LD schedule in the two groups of LN cells.…”

“…Nevertheless, robust behavioral synchronization and oscillations of per and tim gene products are observed in LL and temperature cycles (Glaser and Stanewsky 2005;Matsumoto et al 1998;Miyasako et al 2007;Yoshii et al 2002Yoshii et al , 2005. Moreover, it has been repeatedly observed that temperature cycles are a stronger zeitgeber when they are applied in LL compared to DD.…”

Pigment Dispersing Factor-Dependent and -Independent Circadian Locomotor Behavioral Rhythms

“…Electrophysiological measurements of NaChBac expressing flies have shown that lLNv show giant action potentials, which may likely trigger downstream neurons to release, signals that can compensate for the lack of PDF. Together, the results of our experiments along with those of others that have examined the relationship between activity and the pattern of phase distribution among the different pacemaker components (Veleri et al, 2003;Yoshii et al, 2004;Nitabach et al, 2006;Rieger et al, 2006;Miyasako et al, 2007) suggests that different genetic manipulations and environmental conditions place the architecture of the pacemaker circuit to unique steady states, each of which is able to use different components of the circadian pacemaker circuit to generate distinct circadian patterns in behavior.…”

“…The level of clock proteins Period (PER) and Timeless (TIM) oscillate with a daily rhythm, such that highest levels occur around the end of the night or early morning and lowest levels during mid-day (for review, see Yu and Hardin, 2006). Interestingly this pattern of clock protein oscillation is synchronous in almost all subgroups of pacemaker neurons in the adult fly when entrained by time cues such as light/dark (LD) cycles or temperature cycles (Kaneko et al, 1997;Miyasako et al, 2007). Based on measurements of molecular oscillations in the different subgroups in pdf 01 null flies (Peng et al, 2003;Lin et al, 2004) and phase shifts in locomotor activity rhythm by peptide injection in the cockroach brain (Petri and Stengl, 1997) it has been postulated that PDF is responsible for the synchrony in molecular oscillations both within and among pacemaker neuronal subgroups.…”

Behavioral Dissection of the Drosophila Circadian Multioscillator System that Regulates Locomotor Rhythms

“…For activity recordings, male flies 1 to 5 days old were used. The method for locomotor activity recordings was as described previously (Miyasako et al, 2007). Light intensity at the animal's level was approximately 900 lx, but varied slightly with proximity to the lamp.…”