Opsin gene expression and regulation in retinal transplants

In the present study we investigated the expression and regulation of the opsin gene in retinal transplants. Embryonic retinae were transplanted to intracranial locations in neonatal rodents in which they either reliably projected to the superior colliculus, or in locations (such as the cerebral cortex) in which they hid not project to subcortical visual nuclei. Our results show that, regardless of the graft location, the developmental schedule of opsin gene expression in the outer nuclear layer was similar to normal, and that it was maintained in transplants for at least 6 months. To test if ambient light affected opsin gene expression, we dark-reared rats containing a retinal transplant for up to 26 days before assaying for opsin transcripts. In situ hybridization experiments showed that opsin gene expression in the transplants of these dark-reared recipients was not different either from transplants in animals reared in cyclic light conditions, or from the retina in situ. These observations support the hypothesis that the opsin gene is activated and maintained by molecular mechanisms intrinsic to the photoreceptor.