Figure 2.

Liver clock is rapidly synchronized to the same circadian time as behavior in LL→DD mice. A, Immunoblotting for mPERs in liver. Representative results are shown from three independent experiments. DD control mice (top panel of each pair) were killed at 4 h intervals on the first day in DD after transfer from LD. CT 0 is subjective dawn and CT 12 is subjective dusk. LL mice were killed at 6 h intervals on the last day in at least 10 d of LL before the LL→DD transition. Two other independent experiments showed similar near steady-state mPER rhythms in LL (data not shown). LL→DD mice were collected at 4 h intervals. The first time point (4 h) in LL→DD mice was collected 4 h after the transfer. B, Quantitative real-time PCR analysis of mPer1 and 2 mRNA levels. Each point represents mean ± SEM from 3 mice. For each transcript, LL→DD, and control mice were aligned at time 0 h and CT 16, respectively, to show that the starting phase (0 h) is consistent with behavior (∼CT 15). The control CT 16 and 20 data were plotted twice to compare with the 24 and 28 h samples of LL→DD mice. The gray graphs (with triangles) and black graphs (with squares) represent LL→DD and LD→DD control mice, respectively. AU, Arbitrary unit.