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E.E. Tarttelin, R.G. Foster, R.J. Lucas; Expression of the Novel Opsin Gene Opn5 in the Developing Eye . Invest. Ophthalmol. Vis. Sci. 2006;47(13):811.
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The onsets of expression of the non–rod and non–cone opsins have been shown to be much earlier than those of the classical visual opsins in the developing mammalian eye (Tarttelin et al., 2003, Exp. Eye Res. 76, 393). Opn5 is a novel opsin gene identified in the retina and brain of both mammals and other vertebrates (Tarttelin et al., 2003, FEBS Letters 554, 410; Tarttelin et al., 2004, IOVS 45: E–abstract 3637). We set out to investigate the onset of expression of the Opn5 gene in the eyes of both mammals and the zebrafish, Danio rerio.
Gene specific primers were designed to both the mouse and human Opn5 coding sequences, and tested by reverse transcription polymerase chain reaction (RT–PCR) on a well characterised panel of RNAs from mouse and human developmental eye stages (Bibb et al. 2001, Hum. Mol. Genet. 10, 1571). RT–PCR with gene specific primers was also used to analyse the onset of expression of Opn5 in the developing zebrafish. In situ hybridisation was carried out using DIG–labelled riboprobes to further analyse the expression pattern in zebrafish embryos.
Expression of the Opn5 gene in the developing mouse eye was observed from E10.5 onwards, which is the earliest time point examined in this study. Similarly, early expression of Opn5 was detected in the developing human eye, at 8.6 weeks post conception. In zebrafish, the Opn5 gene was found to be expressed in embryonic tissue by day 4 post fertilisation. Data from wholemount in situ hybridisation experiments on zebrafish embryos confirmed the early onset of expression of Opn5 in neural tissues.
The novel opsin gene Opn5 is expressed early in the developing eye in mammals, at a timepoint when differentiation of the earliest cell types in the retina is occurring. This data is consistent with our previous work demonstrating embryonic expression of non–rod and non–cone opsins, in comparison to the post–natal expression of the visual opsins. Similarly, we have also observed expression of the Opn5 gene in the developing zebrafish embryo. The functional significance of the early expression of Opn5 remains to be determined.
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