Reconstruction of degenerate rd mouse retina by transplantation of transgenic photoreceptors

Photoreceptors from neonatal transgenic mice with normally developing retinas were transplanted to the subretinal spaces of 2-3-month-old rd mutant mice that lack photoreceptors. The transgenic mouse photoreceptors express high levels of the lac Z reporter gene product, beta-galactosidase, which facilitated tracking the transplanted cells. Two sources were used for these cells: (1) dissection of retinal microaggregates containing photoreceptors and (2) papain-dissociated photoreceptors. Host retinas were examined after transplantation. Both methods led to survival of photoreceptors for at least 2 mo after transplantation. Relatively mature outer segments were found only in transplanted microaggregates; this occurred optimally when the cells were adjacent to the retinal pigment epithelium (RPE). β-galactosidase-labeled outer segments associated closely with the apical processes of the host RPE, which, together with labeled phagosomes in the RPE cells, suggested functional interaction between the transplanted photoreceptors and the host RPE. This study is the first to the authors' knowledge to show electron microscopically that a morphologically normal-appearing photoreceptor layer can be reconstructed in an otherwise photoreceptorless retina.