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S.S. Chaurasia, I. Provencio, G. Jiang, W.P. Hayes, R. Haque, A. Natesan, M. Zatz, M.D. Rollag, P.M. Iuvone; Differential circadian regulation of melanopsin mRNA expression in the avian retina and pineal gland . Invest. Ophthalmol. Vis. Sci. 2004;45(13):4648.
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Purpose: The chicken retina and pineal gland contain autonomous circadian oscillators and photo–entrainment pathways. Melanopsin is a novel opsin that has been implicated in entrainment of circadian rhythms in mammals. The goal of the present study was to examine the expression of melanopsin mRNA in chicken retina and pineal gland.Methods: A fragment of Xenopus laevis melanopsin cDNA (911 bp) was used to screen a chicken cDNA library and isolate chicken melanopsin cDNA. One day old chicks were housed for two weeks on a 12 hr light / 12 hr dark (LD) cycle with light on at zeitgeber time (ZT) 0. The localization and distribution of melanopsin mRNA was examined by in situ hybridization and laser capture microdissection (LCM) with RT–PCR. Quantitative RT–PCR was used to analyze the temporal expression patterns of melanopsin mRNA in retina and pineal gland.Results: A partial cDNA encoding chicken melanopsin was isolated. The deduced amino acid sequence of chicken melanopsin is 60% identical and 71% similar to Xenopus melanopsin. In situ hybridization of retinas showed high melanopsin transcript levels in outer third of the inner nuclear layer (INL) and in a few widely dispersed ganglion cells. In pineal gland, expression was strong in parafollicular pinealocytes but was present throughout the gland. The retina and pineal gland showed distinct circadian expression patterns. In whole retina, melanopsin mRNA levels were highest during the early hours of the day (ZT 0–4) and low during the late hours of the night (ZT 16) in LD and constant darkness. In contrast, transcript levels in the pineal reached their highest levels at night (ZT 16–20) and were low during the day (ZT 4–8). However, further analysis of melanopsin expression in retinal layers isolated by LCM revealed different patterns in different layers. There was diurnal expression in all–retinal layers except the ganglion cell layer, where expression was very low. Expression of melanopsin peaked during the daytime in the RPE and INL but like pineal, peaked at night in photoreceptor cells.Conclusions: Melanopsin is widely expressed in the chicken retina and pineal gland. The temporal patterns of expression are similar in retinal and pineal photoreceptors, but opposite to those in RPE and INL, indicative of differential circadian regulation in different cell types of retina.
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