
<ArticleTitle>Three <prot>cryptochromes</prot> are rhythmically expressed in Xenopus laevis retinal photoreceptors.</ArticleTitle>
<AbstractText>PURPOSE: To clone Xenopus laevis <prot>cryptochromes</prot> (<prot>crys</prot>) and to understand their role in the Xenopus retinal clock. METHODS: We designed degenerate PCR primers based on homology between mouse and human <prot>crys</prot>. DNA fragments generated from these PCR reactions were used to screen a Xenopus retinal cDNA library. Three independent clones were identified and sequenced. The temporal and spatial expression of these genes in retina were studied by Northern blot analysis and in situ hybridization. RESULTS: We cloned three <prot>cry</prot> homologs from Xenopus laevis retina. We named them <prot>xcry1</prot>, <prot>xcry2a</prot>, and <prot>xcry2b</prot> based on their high homology to the mouse <prot>crys</prot>. Sequence analysis shows that these Xenopus <prot>CRYs</prot> have more than 85% identity to mouse <prot>CRYs</prot> at the amino acid level. Northern blot analysis demonstrated that all three <prot>xcrys</prot> are rhythmically expressed in the retina with peaks at different times of the day. The <prot>xcrys</prot> are expressed in a variety of tissues. In retina, they are expressed predominantly in photoreceptor cells. CONCLUSIONS: Our finding of <prot>cry</prot> expression in Xenopus photoreceptor cells further supports the idea of independent circadian oscillators being present in these cells. The sequence similarities to mouse <prot>crys</prot> suggest similar functions in the circadian clock. However, their distinct temporal expression patterns suggest some unique role for <prot>xCRY</prot> in the Xenopus retina.</AbstractText>
