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Sumathi Sekaran, Philip Moseley, Sarah Regan, Christie K Campla, Suzanne Broadgate, Anand Swaroop, Stephanie Halford; Expression of an opsin protein in developing starburst amacrine cells.. Invest. Ophthalmol. Vis. Sci. 2018;59(9):583. doi: https://doi.org/.
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© ARVO (1962-2015); The Authors (2016-present)
Opn3 is an orphan opsin. It shares key amino acid motifs with other opsin proteins but its function in the mammalian retina is unknown. In the adult retina Opn3 protein expression has been primarily identified in the ganglion cell layer and inner plexiform layer. Preliminary evidence suggested that Opn3 mRNA expression was higher in early development relative to adult. Thus we hypothesized that there would be a differential expression pattern of Opn3 protein in the developing retina relative to adult.
Opn3 and choline acetyl-transferase (ChAT) expression were assessed immunohistochemically in retinal sections from C57BL/6 mice, at embryonic day (E) 11, E14, postnatal day (P) 0, P4, P8, P12, P16 and adult. Using western blotting it was confirmed that the Opn3 antibody recognized a protein of approximately 44KDa.
Opn3 was identified in a subset of neurons in the embryonic retina (E11 and E14) at the inner margin of the retina and in migrating cells. At P0, the expression pattern was primarily localized to the inner plexiform layer region and to the ganglion cell layer. At P4, a distinct pattern of expression was observed either side of the inner plexiform layer at regularly spaced intervals. By P16, Opn3 was found primarily in the ganglion cell layer with some expression in the inner plexiform layer, similar to the adult expression pattern. As Opn3 expression at P4 demonstrated similarities to the expression pattern of ChAT in amacrine cells in the retina, we colocalised Opn3 and ChAT from P0. At this age 95±2% of ChAT positive cells expressed Opn3 and a similar pattern of co-localisation was observed until P8. After this point there was a steady decline in Opn3 expression in ChAT ACs. At P12, 55±5% of ChAT cells expressed Opn3 and at P16 this had reduced to 44±3%. In the adult retina only 11±4% of the ChAT cells expressed Opn3. There was a highly significant difference in the number of ChAT cells expressing Opn3, between P0 and adult (p < 0.0001).
ChAT ACs are perhaps the most striking neuron in the retina, characterized by the distinctive “starburst” shape of their dendritic arbor. ChAT ACs play distinct but important roles in the developing and mature retina. We have found that the orphan opsin Opn3 is expressed in developing ChAT ACs in a temporally restricted manner. The results suggest a distinct role for Opn3 in the development of starburst amacrine cells.
This is an abstract that was submitted for the 2018 ARVO Annual Meeting, held in Honolulu, Hawaii, April 29 - May 3, 2018.
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