Notably in gene expression experiments, the expression of desat1 closely tracked Clk, indicating that desat1 may be regulated directly by an output mechanism of the cell-autonomous oenocyte clock, possibly via the transcriptional regulators of the Clk gene, VRILLE and PDP1ε ( Allada and Chung, 2010), or possibly by CLK itself. Consistent with the possibility of direct regulation, consensus binding sites or VRI, PDF1ε, and CLK are present within the desat1 locus ( Figure S2A). Genetic manipulations affecting PDF expression also affected the display of cuticular hydrocarbon compounds, including the male sex pheromones 7-T, 5-T, and 7-P. Loss of Pdf or Pdfr expression reduced sex pheromone expression,

while misexpression

Bortezomib nmr of Pdf increased these compounds. We suggest that these effects on pheromone expression reflect asynchrony between components of the circadian system, those being primarily the central pacemaker neurons and the oenocyte clock. In the absence of phase information provided by the CNS via PDF, the SCH727965 oenocyte clock and by extension the circadian expression of desat1 may become uncoupled from rhythms in other physiological and behavioral processes necessary for proper pheromonal output. In this way, seemingly subtle changes in phase may lead to a misalignment between rhythms and an amplified response in physiological output. Several studies have demonstrated daily rhythmicity in courtship and mating (Hardeland, 1972, Sakai and Ishida, 2001 and Tauber et al., 2003), thus implicating the circadian system in the regulation

of sexual behavior in Drosophila. Recently, others have shown that the PDF-expressing vLNs are involved in mediating a male sex drive C1GALT1 rhythm (MSDR), a novel activity rhythm displayed by males when individually paired with a female and allowed to interact continuously for 24 hr ( Fujii and Amrein, 2010 and Fujii et al., 2007). Our results extend these findings by demonstrating that the circadian system not only influences courtship and mating but also regulates the physiology mediating the production and display of chemical signals critically important to sexual behavior. We propose that the PDF signaling pathway and its ability to synchronize the activity of peripheral and central oscillators may couple reproductive physiology with behavior. In this regard, we suggest that the PDF signaling pathway may act at two levels: within the individual (i.e., the male fly), PDF signaling may influence both sexual characteristics (pheromone expression) and sex drive, while between individuals of the group, PDF-dependent effects on male pheromone expression may alter female mating behavior. Studies in several organisms have demonstrated that fitness benefits of the circadian system are evident in a light/dark cycle but not in constant conditions or when out of phase with environment cues (Dodd et al.