FIG. 6.

Circadian oscillations of P-CREB in Xenopus retina. Retina sections were collected every 4 h during a 24-h LD (A and B) or DD (C) cycle. The retina sections were immunolabeled to detect the expression of P-CREB. (A) Fluorescent images of retina sections at different times of day during an LD cycle. The arrow points to the layer of photoreceptor cell nuclei (ONL). (B and C) Higher-magnification images of the photoreceptor nuclei at different times in the LD (B) and DD (C) cycles show that P-CREB levels fluctuate in a circadian rhythm. CT 0 defines the beginning of subjective day, and CT 12 defines the beginning of subjective night. Five sections were analyzed for each time point. Sections stained with secondary antibody alone (without primary antibody) showed no signal (not shown).