Circadian regulation of cryptochrome genes in the mouse

Cryptochromes are non-opsin photoactive pigments which have been recently implicated in circadian photoentrainment. In humans and mice, two cryptochromes, called CRY1 and CRY2, have been identified. Previously, it was shown that the expression of mCry1 oscillates with circadian periodicity in the suprachiasmatic nucleus (SCN) of the mouse. Herein, we have investigated the expression patterns of both mCry1 and mCry2 in various tissues and the effect of Cry2 knockout on Cry1 expression. First, the expression of Cry1 in the SCN, in contrast to mPer1 and other immediate early genes, is not inducible by acute light pulses. Second, we found that Cry1 transcription follows a circadian pattern in the liver and skeletal muscle. Third, mutation in Cry2 causes a phase delay in Cry1 and mPer1 expression both in the SCN and internal organs relative to wild-type animals. Finally, no obvious periodicity in mCry2 expression was seen in all tissues tested.