Figure 6. Ambient light-intensity is encoded in Hr38-dependent Pdf transcription.

(A) Expression of the active-zone marker BRP (BRUCHPILOT) (left) or the transcription-based CaLexA-GFP reporter (right) in the s-LNvs under low and high light intensities at ZT13–14. (B) Comparison of the levels of PDF peptide in the axon terminals and cell bodies of the s-LNvs under different light intensities at ZT13–14 indicates that the physiological output from the s-LNv neurons is promoted by high light. The column plot shows mean ± s.e.m of the slope of a linear regression fitted on the last four hours of activity prior to the evening peak. (C) Light-induction of PDF levels in s-LNv terminals in wild type flies or flies with downregulated Hr38 in the LNvs (left). Light-induction of a Tomato-based transcriptional reporter of Pdf in the s-LNv nuclei of wild-type flies and flies with downregulated Hr38 in the LNvs. % changes are from low-to-high light. Labelings are done at ZT13–14. (D) High light LD activity profiles of flies with a functional oscillator in the evening DN1ps in a wild type (1) or downregulated Hr38 (2) background. (E) Scheme showing that visually estimated ambient light-intensity changes PDF levels in the s-LNv cells. PDF suppresses the output of the CRY(−) DN1ps that produce evening activity. Each column in immunostaining experiments of (d), (e), and (f) represents mean ± s.e.m. of at least 8 brain hemispheres. *** p<0.0001 by unpaired two-tailed Student’s t-test, Fisher’s exact test was used for comparing % changes in (f). Representative stained images are pseudocolored, such that red-shifted colors denote stronger signal intensity. The number on the top-right corner of the activity plots shows the sample size of analyzed flies for a single run of the behavioral experiment. See also Figure S6.