Circadian regulation of cryptochrome genes in the mouse

Cryptochromes are non-opsin photoactive pigments which have been recently i mplicated in circadian photoentrainment. In humans and mice, two cryptochro mes, called CRY1 and CRY2, have been identified. Previously, it was shown t hat the expression of mCry1 oscillates with circadian periodicity in the su prachiasmatic nucleus (SCN) of the mouse. Herein, we have investigated the expression patterns of both mCry1 and mCry2 in various tissues and the effe ct of Cry2 knockout on Cry1 expression. First, the expression of Cry1 in th e SCN, in contrast to mPer1 and other immediate early genes, is not inducib le by acute light pulses. Second, we found that Cry1 transcription follows a circadian pattern in the liver and skeletal muscle. Third, mutation in Cr y2 causes a phase delay in Cry1 and mPer1 expression both in the SCN and in ternal organs relative to wild-type animals. Finally, no obvious periodicit y in mCry2 expression was seen in all tissues tested. (C) 1999 Elsevier Sci ence B.V. All rights reserved.