Figure 4.

Circadian gene expression changes gradually during restricted feeding. (A) Mice kept under a LD regimen (lights on at 6 a.m., lights off at 6 p.m.) were fed exclusively during the day for 1 d, 3 d, or 1 wk. The animals were then sacrificed at 2 and 10 p.m. to prepare whole-cell liver RNA. Transcript levels for Cry1 and Rev-erbα were determined as described in Figure 1. (B) Mice were fed exclusively during the day for seven consecutive days and, after a starvation of 24 h, switched to nighttime feeding by offering food during the night of the eighth day (from 6 p.m. to 6 a.m.). Animals were sacrificed at 4-h intervals (starting at 6 p.m. of the eighth day) for the analysis of mRNAs. Note that Per2 mRNA, Rev-erbα mRNA, and Cry1 mRNA are still at levels intermediate between those observed for mice fed during the night or during the day.