Temporal gradient in the clock gene and cell-cycle checkpoint kinase Wee1 expression along the gut.

Circadian clocks were recently discovered in the rat and mouse colon as well as mouse stomach and jejunum. The aim of this study was to determine whether clocks in the upper part of the gut are synchronized with those in the lower part, or whether there is a difference in their circadian phases. Moreover, the profiles of core clock-gene expression were compared with the profiles of the clock-driven Wee1 gene expression in the upper and lower parts of the gut. Adult rats were transferred to constant darkness on the day of sampling. 24 h expression profiles of the clock genes Per1, Per2, Rev-erbalpha, and Bmal1 and the cell-cycle regulator Wee1 were examined by a reverse transcriptase-polymerase chain reaction within the epithelium of the rat duodenum, ileum, jejunum, and colon. In contrast to the duodenum, the rhythms in expression of all genes but Rev-erbalpha and Bmal1 in the colon exhibited non-sinusoidal profiles. Therefore, a detailed analysis of the gene expression every 1 h within the 12 h interval corresponding to the previous lights-on was performed. The data demonstrate that rhythmic profiles of the clock gene Per1, Per2, Bmal1, Rev-erbalpha, and clock-driven Wee1 expression within the epithelium from different parts of the rat gut exhibited a difference in phasing, such that the upper part of the gut, as represented by the duodenum, was phase-advanced to the lower part, as represented by the distal colon. Our data demonstrate that the circadian clocks within each part of the gut are mutually synchronized with a phase delay in the cranio-caudal axis. Moreover, they support the view that the individual circadian clocks may control the timing of cell cycle within different regions of the gut.