RETINAL PIGMENTED EPITHELIUM DOES NOT TRANSDIFFERENTIATE IN ADULT GOLDFISH

The neural retina of adult goldfish can regenerate from an intrinsic s ource of proliferative neuronal progenitor cells, but it is not known whether the retina can regenerate by transdifferentiation of the retin al pigmented epithelium (RPE), a phenomenon demonstrated in adult newt s. In this study, we asked whether following surgical removal of the n eural retina in adult goldfish the RPE was capable of autonomously tra nsdifferentiating and generating new neural retina. The retina was pre labeled by injecting the fluorescent dye Fluoro-Gold (FG) into the eye prior to surgical removal; this procedure ensured that residual retin a was labeled with FG and could therefore be distinguished from unlabe led, regenerated retina. To examine the time course of retinal regener ation, and to identify regenerated retinal neurons, the thymidine anal ogue bromodeoxyuridine was injected intraocularly, and retinas were ex amined up to 2 months later. We found that the RPE did not transdiffer entiate; instead, retinas regenerated only when pieces of residual neu ral retina were left intact. Under these circumstances, newly regenera ted cells derived from proliferating cells intrinsic to the residual n eural retina. When retinas were completely removed, as was evident fro m a lack of FG labeling, there was no retinal regeneration. (C) 1995 J ohn Wiley and Sons, Inc.