title: Three cryptochromes are rhythmically expressed in Xenopus laevis retinal photoreceptors.
abstract: OBJECTIVE
  To clone Xenopus laevis cryptochromes (crys) and to understand their role in the Xenopus retinal clock.
  
  
  METHODS
  We designed degenerate PCR primers based on homology between mouse and human crys. 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 cry homologs from Xenopus laevis retina. We named them xcry1, xcry2a, and xcry2b based on their high homology to the mouse crys. Sequence analysis shows that these Xenopus CRYs have more than 85% identity to mouse CRYs at the amino acid level. Northern blot analysis demonstrated that all three xcrys are rhythmically expressed in the retina with peaks at different times of the day. The xcrys are expressed in a variety of tissues. In retina, they are expressed predominantly in photoreceptor cells.
  
  
  CONCLUSIONS
  Our finding of cry expression in Xenopus photoreceptor cells further supports the idea of independent circadian oscillators being present in these cells. The sequence similarities to mouse crys suggest similar functions in the circadian clock. However, their distinct temporal expression patterns suggest some unique role for xCRY in the Xenopus retina.
authors.affiliation: NSF Center for Biological Timing, Department of Biology, University of Virginia, Charlottesville, VA 22904, USA. hz8r@virginia.edu
authors.forename: H
authors.initials: H
authors.lastname: Zhu
authors.forename: C B
authors.initials: CB
authors.lastname: Green
mesh_terms: D000595:Amino Acid Sequence; D000818:Animals; D001483:Base Sequence; D015152:Blotting, Northern; D001921:Brain / Q000378:metabolism; D002940:Circadian Rhythm / Q000502:physiology*; D056931:Cryptochromes; D017931:DNA Primers / Q000737:chemistry; D029721:Drosophila Proteins; D005136:Eye Proteins; D005420:Flavoproteins / Q000096:biosynthesis* / Q000235:genetics; D015870:Gene Expression; D006801:Humans; D017403:In Situ Hybridization; D008099:Liver / Q000378:metabolism; D008297:Male; D051379:Mice; D008969:Molecular Sequence Data; D009206:Myocardium / Q000378:metabolism; D017956:Photoreceptor Cells, Invertebrate; D020419:Photoreceptor Cells, Vertebrate / Q000378:metabolism*; D012333:RNA, Messenger / Q000096:biosynthesis; D043562:Receptors, G-Protein-Coupled; D020133:Reverse Transcriptase Polymerase Chain Reaction; D017386:Sequence Homology, Amino Acid; D013154:Spleen / Q000378:metabolism; D013737:Testis / Q000378:metabolism; D014982:Xenopus laevis / Q000378:metabolism*
chemical_list: D056931:Cryptochromes; D017931:DNA Primers; D029721:Drosophila Proteins; D005136:Eye Proteins; D005420:Flavoproteins; D012333:RNA, Messenger; D043562:Receptors, G-Protein-Coupled; C119828:cry protein, Drosophila