Abstract
The retina and the first optic neuropil (lamina) of Drosophila show circadian rhythms in various processes. To learn about the regulation of circadian rhythms in the retina and lamina and in two cell types, glial and the lamina L2 interneurons, we examined expression of the following clock genes; per, tim, clk, and cry and clock-controlled genes (ccgs); Atpα, nrv2, brp, Pdfr. We found that the expression of gene studied is specific for the retina and lamina. The rhythms of per and tim expression in the retina and glial cells are similar to that observed in the whole head and in clock neurons, while they differ in the lamina and L2 cells. In both the retina and lamina, CRY seems to be a repressor of clk expression. In L2 interneurons per expression is not cyclic indicating the other function of PER in those cells than in the circadian molecular clock. In contrast to per and tim, the pattern of clk and cry expression is similar in both the retina and lamina. The retina holds the autonomous oscillators but the expression of cry and ccgs, Atpα and nrv2, is also regulated by inputs from the pacemaker transmitted by PDF and ITP neuropeptides.
Highlights
The circadian clock is a self-sustaining generator of endogenous oscillations with a period of about a day that generates rhythmicity in biochemical and physiological processes of most organisms and in the behavior of animals
Animals The following strains of D. melanogaster were used: wild-type Canton S, cry01—a null mutant of the circadian photoreceptor gene cryptochrome (Dolezelova et al, 2007), Pdf 0—a null mutant of the clock neuropeptide Pigment dispersing factor gene, per01—null mutant of the clock gene period, cry-GAL4.39 expressing the yeast transcription factor GAL4 under control of cry promoter, 21D-GAL4/MKRS expressing GAL4 in L2 interneurons, repo-GAL4 expressing GAL4 under control of repo promoter, a specific marker of glial cells, UAS-dicer2; UAS-itp-RNAi/MKRS, expressing interfering RNA for itp (ITP gene) and dicer2 which catalyses the first step of RNA interference, under control of the UAS sequence, and UASgfp expressing Green Fluorescent Protein (GFP) under control of the UAS sequence
Gene Expression in the Retina In the retina of wild-type flies maintained in LD 12:12, the expression of both core clock genes, per and tim, was cyclical with a peak reached at ZT16 but higher level of both gene mRNAs than in other time points was detected at ZT13 (Figures 1A,B)
Summary
The circadian clock is a self-sustaining generator of endogenous oscillations with a period of about a day that generates rhythmicity in biochemical and physiological processes of most organisms and in the behavior of animals. It maintains the homeostasis of organisms in time, anticipates daily changes of light in the environment and its function continues in constant darkness (DD). Under day/night or light/dark (LD) conditions the circadian clock is synchronized by light and the period of the rhythm is equal to 24 h.
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