Cryptochrome genes are highly expressed in the ovary of the African clawed frog, Xenopus tropicalis

• Published in: PloS one Vol. 5; no. 2; p. e9273
• Main Authors: Kubo, Yoko, Takeuchi, Takahiro, Okano, Keiko, Okano, Toshiyuki
• Format: Journal Article
• Language: English
• Published: United States Public Library of Science 17.02.2010; Public Library of Science (PLoS)
• Subjects: Amphibians; Analysis; Animal tissues; Animals; ARNTL Transcription Factors - genetics; Cell division; Cell Line; Cell Nucleus - metabolism; Circadian rhythm; Circadian rhythms; CLOCK Proteins - genetics; Clockwork; Control theory; Cryptochromes; Cryptochromes - classification; Cryptochromes - genetics; Cryptochromes - metabolism; Cycle protein; Drosophila; E-Box Elements - genetics; Electrical engineering; Estrus; Evolutionary Biology/Animal Genetics; Feedback loops; Female; Flavoproteins; Frogs; Functional analysis; Gene expression; Gene Expression Profiling; Gene regulation; Genes; Genomics; Green Fluorescent Proteins - genetics; Green Fluorescent Proteins - metabolism; Homology; Hormones; Humans; Insects; Kidney - metabolism; Kidneys; Light; Magnetic fields; Male; Mathematical models; Microscopy, Fluorescence; Neuroscience/Behavioral Neuroscience; Neuroscience/Sensory Systems; Ovary - metabolism; Period Circadian Proteins - genetics; Photoreception; Phylogeny; Physiological aspects; Protein Isoforms - genetics; Protein Isoforms - metabolism; Proteins; Recombinant Fusion Proteins - genetics; Recombinant Fusion Proteins - metabolism; Reproductive status; Retina; Retina - metabolism; Reverse Transcriptase Polymerase Chain Reaction; RNA; Science; Steroid hormones; Transcription; Transcriptional Activation; Vertebrates; Xenopus; Xenopus - genetics; Xenopus - metabolism; Xenopus laevis; Xenopus Proteins - classification; Xenopus Proteins - genetics; Xenopus Proteins - metabolism; Japan
• ISSN: 1932-6203; 1932-6203
• DOI: 10.1371/journal.pone.0009273

Cryptochromes (CRYs) are flavoproteins sharing high homology with photolyases. Some of them have function(s) including transcription regulation in the circadian clock oscillation, blue-light photoreception for resetting the clock phase, and light-dependent magnetoreception. Vertebrates retain multiple sets of CRY or CRY-related genes, but their functions are yet unclear especially in the lower vertebrates. Although CRYs and the other circadian clock components have been extensively studied in the higher vertebrates such as mice, only a few model species have been studied in the lower vertebrates. In this study, we identified two CRYs, XtCRY1 and XtCRY2 in Xenopus tropicalis, an excellent experimental model species. Examination of tissue specificity of their mRNA expression by real-time PCR analysis revealed that both the XtCRYs showed extremely high mRNA expression levels in the ovary. The mRNA levels in the ovary were about 28-fold (XtCry1) and 48-fold (XtCry2) higher than levels in the next abundant tissues, the retina and kidney, respectively. For the functional analysis of the XtCRYs, we cloned circadian positive regulator XtCLOCK and XtBMAL1, and found circadian enhancer E-box in the upstream of XtPer1 gene. XtCLOCK and XtBMAL1 exhibited strong transactivation from the XtPer1 E-box element, and both the XtCRYs inhibited the XtCLOCK:XtBMAL1-mediated transactivation, thereby suggesting this element to drive the circadian transcription. These results revealed a conserved main feedback loop in the X. tropicalis circadian clockwork and imply a possible physiological importance of CRYs in the ovarian functions such as synthesis of steroid hormones and/or control of estrus cycles via the transcription regulation.