Figure 6.

A model for interactions between the two lateral neuron pacemaking centers in the Drosophila brain. In wild-type flies (top), the small LN_v center (s-LN_v) maintains the normal phase and amplitude of molecular rhythms in the LN_d center as well as its own synchronicity through PDF communication (possibly autocrine). Projections from the s-LN_vs and/or the LN_ds regulate premotor centers (PMC) and organize behavioral rhythms. In the absence of PDF (in pdf⁰¹ mutants, bottom), a syndrome of effects is observed: the s-LN_vs become desynchronized, but because they are effectively silenced by the pdf⁰¹ mutation, the effects of this decoupling are unlikely to influence the PMC. With the lack of PDF entrainment, the LN_ds revert to a low-amplitude, fast-running clock; however, PDF is not required for their synchronization. The loss of a strong circadian signal from the LN_d and/or the s-LN_v into the PMC leads to behavioral arrhythmicity. Shades of gray represent differences in phase and/or period. The graphs to the left represent the decreased amplitude of PER staining rhythms in LN_ds and the desynchrony of staining rhythms in the LN_vs of pdf⁰¹ mutants.