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R Haque, SS Chaurasia, PM Iuvone; Circadian Clock Genes in Chicken Retina: Temporal Regulation of Cryptochrome1 (cCry1) Expression . Invest. Ophthalmol. Vis. Sci. 2002;43(13):1358.
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Purpose: The molecular clock-work consists of autoregulatory transcriptional and translational feedback loops that have both positive and negative elements. Cryptochromes, blue light receptor proteins, are negative components of the feedback loop and mediate a variety of light responses, including entrainment of circadian rhythms in Arabidopsis and Drosophila. Mammalian Cry1 mRNA is expressed with circadian periodicity in the suprachiasmatic nucleus, the site of the master clock of the hypothalamus. Chicken retina contains a circadian clock that regulates melatonin biosynthesis and iodopsin expression. As an initial step to investigate the possible role of Cry1 in the chicken retina circadian clock, we examined the temporal pattern of expression of chicken Cry1 (cCry1) in retina. Methods: One day-old chickens were housed under a 12 h light- 12 h dark (LD) cycle, with lights on at zeitgeber time (ZT) 0. Subjects were entrained to this LD cycle for two weeks before the removal of neural retina at 4 hour intervals. From total RNA, a partial cDNA fragment of cCry1 mRNA was obtained by RT-PCR with primers designed from the gene bank nucleotide sequence (BI394078). The cDNA was cloned and sequenced to verify its identity. Expression of cCry1 mRNA was quantified by real-time RT-PCR. Results: Real-time RT-PCR showed high amplitude light/dark oscillations of cCry1 transcript in retinal and pineal tissues. The expression of cCry1 mRNA in retina of chicks maintained under LD is low during the early day and high at night, peaking at approximately ZT16. A similar, high-amplitude rhythm of cCry1 mRNA expression was not observed in retinas of chicks maintained for 2 days in constant darkness. Conclusion: cCry1 mRNA expression is temporally regulated in chick retina in a light-dependent manner. However, cCry1 does not appear to have its expression controlled directly by the circadian clock.
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