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 transpla nted to intracranial locations in neonatal rodents in which they eithe r reliably projected to the superior colliculus, or in locations (such as the cerebral cortex) in which they did 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 nuc lear layer was similar to normal, and that it was maintained in transp lants for at least 6 months. To test if ambient light affected opsin g ene expression, we dark-reared rats containing a retinal transplant fo r up to 26 days before assaying for opsin transcripts. In situ hybridi zation experiments showed that opsin gene expression in the transplant s of these dark-reared recipients was not different either from transp lants in animals reared in cyclic light conditions, or form the retina in situ. These observations support the hypothesis that the opsin gen e is activated and maintained by molecular mechanisms intrinsic to the photoreceptor.