Fig. 3

Effect of light on zper2 expression during segmentation period. Embryos were kept under constant darkness (Lower) or exposed to light 10–16 hpf (Upper), sampled at 1-h intervals during 10–18 hpf, and zper2 mRNA was detected by whole-mount ISH. Shown are representative whole-mount ISH results of 10- to 18-hpf embryos, lateral view. Zebrafish per2 mRNA was undetectable in embryos kept under dark conditions (Lower), whereas exposure to light resulted in de novo transcription of zper2 (Upper). Zebrafish per2 mRNA levels remained high throughout the illumination period and declined only after lights-off. The horizontal bar at the bottom of each panel represents the lighting conditions before and during sampling; white boxes represent light and black boxes represent dark.