Cloning and expression of cryptochrome2 cDNA in the rat.

Cryptochromes (CRY) are blue-light photoreceptors that regulate the circadian rhythm in animals and plants. In mammals, two types of CRY are involved in the regulation of circadian rhythm, but rat cryptochromes have not yet been identified. Therefore, we isolated and characterized cry2 cDNA from the rat brain. The cloned rat cry2 cDNA consists of 2,131 nucleotides and has a single open-reading frame that encodes the rat CRY2 of 594 amino acids with start and stop codons. The deduced amino acid sequence of the rat CRY2 was 97% identical with that of mice and 93% with humans, but it showed a relatively low identity of 64% with that of zebrafish. It also exhibited a high homology (about 70%) with CRY1 of mice and humans. A Northern blot analysis showed that rat cry2 was expressed in all of the tissues examined. Rat cry2 was expressed at a relatively higher level in peripheral tissues than in the brain. In situ hybridization in the whole brain indicated that the strong signal of cry2 mRNA is mainly present in the suprachiasmatic nucleus (SCN) region, but very weak in other brain regions. Therefore, present results indicate that rat cry2 may function in circadian photoreception in the rat brain.