Abstract
In mammals, the circadian oscillation in the suprachiasmatic nucleus (SCN) is believed to base on an autoregulatory feedback loop associated with clock gene expression and their protein products (core loop). Previously, we reported that DEC1 and DEC2, bHLH transcription factors, consist an additional feedback loop which interlocks with the core-loop. Although the expression patterns of Decs and Pers are not identical in the SCN, functional differences are not yet known. In the present experiment, we examined the circadian expression and light responsiveness of Dec1, Dec2 and Per1 in the rat SCN by in situ hybridization using Digoxigenin labeled cRNA probes, and constructed four-dimensional maps of gene expression. Photomicrographs of coronal SCN sections were sectionalized into 75×75 μm squares, and number of mRNA positive cells in each area was counted. The circadian expressions of three genes were peaked at the subjective noon, but the wide expression of Dec2 throughout the SCN was contrasted with restricted expression of Dec1 and Per1 in the medial SCN. In response to light pulse, Per1 dramatically increased only in the ventral SCN, while Dec1 induction extended more dorsally. In addition, after peaking the circadian and light-induced expressions, Per1 signals disappeared faster than Dec1. The results suggest differential roles of Dec1, Dec2 and Per1 in rhythm generation and light entrainment of the circadian clock in the SCN. [Jpn J Physiol 55 Suppl:S200 (2005)]
