Adult-specific electrical silencing of pacemaker neurons uncouples the molecular oscillator from circadian outputs

CERIANI, MF

Leiden

Workshop; Workshop: How to assemble a multicellular oscillator in the brain, Lorentz Center; 2010

Circadian rhythms regulate physiology and behavior through the action of self-sustained transcriptional feedback loops of clock genes. In Drosophila, over 150 neurons in the fly brain are implicated in the circadian regulation of rest-activity cycles, but the small ventral lateral neurons (sLNvs) are clearly crucial. The preservation of molecular oscillations within the sLNvs is key to command rhythmic behavior under free running conditions. The s-LNvs transmit this time information releasing a neuropeptide known as pigment dispersing factor (PDF), and likely changing synaptic partners by remodeling their axonal terminals in a circadian fashion. Electrical activity of PDF neurons is also required for rhythmicity. Silencing PDF neurons by expressing a K+ channel (KIR) throughout lifetime leads to behavioral arrythmicity and blocks molecular oscillations in the sLNvs (Nitabach et al. Cell 2002).To gain insight into the relationship between ion conductances through the cellular membrane and molecular oscillations taking place within the nucleus/cytoplasm we developed a new tool for temporal control of gene expression in PDF neurons. Silencing the PDF circuit only during the adult stage led to behavioral arrythmicity as previously described. Surprisingly, once kir expression was shut down, flies recovered rhythmicity in a phase reminiscent to that of the initial training. PERIOD oscillations in the sLNvs showed that the molecular clock remained intact through the silenced phase, supporting that arrhythmicity is a consequence of the inability of these neurons to transmit information rather than an effect on the clock, as previously proposed. Accordingly, both the complexity of the axonal terminals as well as PDF accumulation were severely affected during the silenced phase. Interestingly, long-term silencing of PDF neurons (i.e. throughout developmental and in the adult) indeed altered molecular oscillations suggesting that long-term effects on membrane potential might trigger undesired effects on cell physiology or viability, instead of specifically drive molecular oscillations.