Neuropsin (OPN5): A Non-visual UV Sensitive Photoreceptor Gene Expression Pattern Among Mega and Micro Bats

Abstract

Bats are nocturnal animals with functional eyes and M/L and S opsin genes in the majority of the species. These genes are prerequisite for daylight, UV and dichromatic colour vision. Several studies suggest that other non-visual light-sensitive pigments are also involved in the UV light perception in animals. Recent behavioural, molecular and immunohistochemical evidence supports that the opsin-like gene, neuropsin (OPN5), is identified in humans, mice and birds, where it serves as a G protein-coupled UV-sensitive photoreceptor. Based on its low sequence homology with other opsin groups, OPN5 is classified as an independent group. While the roles of non-visual light-sensitive pigment OPN5 in bats remain an open question, here we report that bat’s neuropsin (OPN5) encoded by OPN5 gene shares 89-96% amino acid identity and similar domain organization with human and mouse OPN5. By PCR amplification, we confirm that all the mega and micro bats express the OPN5 gene in their genome. The expression of OPN5 is detectable only in the brain, eye and retina and not in the heart, kidney, liver, lungs and testis. This result suggests that OPN5 gene expression is neural specific in bats. OPN5 gene expression level is significantly higher in tree-roosting bats compared to cave-roosting bats. Since, the tree-roosting bats received slightly more sunlight every day when compared to cave-roosting bats. In captive conditions, the expression levels of OPN5 in the neural tissues are significantly lower than those of wild bats. Our preliminary results suggest that the opsin-like gene, neuropsin (OPN5) is involved in UV light perception in bats.