Figure 7. Expression profile of the negative feedback loop Per transcripts over a single 24 h period under distinct lighting conditions. A, C, E: RNA expression levels of Per1 in a 12h light: 12 h dark cycle (LD), in constant dark (DD) and in constant light (LL). B, D, F: RNA expression levels of Per2 in LD, DD, and LL. Each gene showed a rhythmic pattern with maximal expression at or closely following night/day transition in LD (n=3-6 per time point) and DD (n=6 per time point; A, C: Per1, B, D: Per2). LL conditions led to large phase shifts, with maxima in the early to middle night (E: Per1, F: Per2; n=4 per time point). Illumination conditions are depicted as solid white (day) and solid grey (night) areas in LD, right hatched (subjective day) and solid grey (subjective night) areas in constant dark (DD) and solid white (subjective day) and left hatched (subjective night) areas in constant light (LL). Animals were killed every 3 or 4 h across the 24 h period, and RNA extracted from retinal tissue. RNA expression levels were quantified by real time PCR. One-way analysis of variance (ANOVA) and cosinor levels of significance (P_A and P_c respectively) are given in the upper right corner of each panel.