Analysis of melanopsin gene expression in the rabbit retina at different ages

Melanopsin is the photopigment of intrinsically photosensitive retinal ganglion cells that mediate non-visual responses to light. The aim of this study was to describe and analyze melanopsin gene expression in the rabbit retina at different ages and compare its expression with the prototypic gene of retinal ganglion cells (Thy-1 gene). Expression levels of OPN4, Thy-1, and GADPH genes were measured by real-time PCR at 3, 4, 8, 11, 12, 17, 19, 20, 23, 27, 32, and 47 postnatal days. We also regrouped the days before and after day 12 of life (pre-photic and post-photic stage, respectively). Average expression of the OPN4 gene between days was similar (P = 0.713), but was statistically different in the Thy-1 gene (P = 0.004). Also, no significant differences were found in OPN4 gene expression pre-photic and post-photic stage (P = 0.629); however, Thy-1 expression was higher in the pre-photic stage, almost double, than in the post-photic stage, with significant differences (P = 0.001). This is the first report describing OPN4 gene expression in the rabbit retina at different ages. We demonstrated that the OPN4 gene is constantly expressed at all early stages, even before the onset of photoentrainment by the pups and that Thy-1 and OPN4 gene expressions are out of phase.