Opsin family genes encode G protein-coupled seven-transmembrane proteins that bind a retinaldehyde chromophore in photoreception. Here, we sought potential as yet undescribed avian retinal photoreceptors, focusing on Opsin 3 homologs in the chicken. We found two Opsin 3-related genes in the chicken genome: one corresponding to encephalopsin/panopsin (Opn3) in mammals, and the other belonging to the teleost multiple tissue opsin (TMT) 2 group. Bioluminescence imaging and G protein activation assays demonstrated that the chicken TMT opsin (cTMT) functions as a blue light sensor when forced-expressed in mammalian cultured cells. We did not detect evidence of light sensitivity for the chicken Opn3 (cOpn3). In situ hybridization demonstrated expression of cTMT in subsets of differentiating cells in the inner retina and, as development progressed, predominant localization to retinal horizontal cells (HCs). Immunohistochemistry (IHC) revealed cTMT in HCs as well as in small numbers of cells in the ganglion and inner nuclear layers of the post-hatch chicken retina. In contrast, cOpn3-IR cells were found in distinct subsets of cells in the inner nuclear layer. cTMT-IR cells were also found in subsets of cells in the hypothalamus. Finally, we found differential distribution of cOpn3 and cTMT proteins in specific cells of the cerebellum. The present results suggest that a novel TMT-type opsin 3 may function as a photoreceptor in the chicken retina and brain.

Recent studies show that exposure to ultraviolet (UV) light suppresses ocular elongation, which causes myopia development. However, the specific mechanisms of this process have not been elucidated. A UV-sensor, Opsin 5 (Opn5) mRNA was shown to be present in extraretinal tissues. To test the possibility that UV-signals mediated by Opn5 would have a direct effect on the outer connective tissues of the eye, we first examined the expression patterns of a mammalian type Opn5 (Opn5m) in the late-embryonic chicken eye. Quantitative PCR showed Opn5m mRNA expression in the cornea and sclera. The anti-Opn5m antibody stained a small subset of cells in the corneal stroma and fibrous sclera. We next assessed the effect of UV-A (375 nm) irradiation on the chicken fibroblast cell line DF-1 overexpressing chicken Opn5m . UV-A irradiation for 30 min significantly increased the expression of Early growth response 1 ( Egr1 ), known as an immediate early responsive gene, and of Matrix metalloproteinase 2 ( Mmp2) in the presence of retinal chromophore 11- cis -retinal. In contrast, expression of Transforming growth factor beta 2 and Tissue inhibitor of metalloproteinase 2 was not significantly altered. These results indicate that UV-A absorption by Opn5m can upregulate the expression levels of Egr1 and Mmp2 in non-neuronal, fibroblasts. Taken together with the presence of Opn5m in the cornea and sclera, it is suggested that UV-A signaling mediated by Opn5 in the extraretinal ocular tissues could influence directly the outer connective tissues of the chicken late-embryonic eye.

Submacular exudates with serous retinal detachment can occur in cat scratch disease. Cat scratch disease should be included in the differential diagnosis of submacular exudates with central serous chorioretinopathy.