Retinal degeneration in transgenic mice with photoreceptor-specific expression of a dominant-negative fibroblast growth factor receptor

Mutant cDNAs coding for dominant-negative forms of the fibroblast growth factor receptors 1 (FGFR-1) and 2 (FGFR-2) that lack tyrosine kinase activity were ligated to a 2.2 kb DNA fragment containing the bovine rhodopsin promoter and used to generate transgenic mice. Six independent lines were generated with the FGFR-1 construct, and five were generated with the FGFR-2 construct. Five of the six FGFR-1 mutant lines and all five FGFR-2 mutant lines showed transgene expression in the retina by reverse transcription- PCR. By both in situ hybridization and immunohistochemistry, mutant FGFRs were found to be expressed specifically in photoreceptors of transgene- positive FGFR-1 and FGFR-2 mice. Lines expressing the FGFR-2 mutant showed progressive photoreceptor degeneration; the retinas showed minimal or no abnormalities at 1 month, but by 2 months they showed focal areas of thinning of the outer nuclear layer and disruption of photoreceptors. By 2-4 months, areas of complete loss of photoreceptors were seen. These abnormalities were not seen in control littermates not expressing the transgene. Mice from two FGFR-1 mutant lines showed focal areas of thinning of the outer nuclear layer and numerous photoreceptors with fragmented chromatin, whereas the other FGFR-1 lines showed minimal or no abnormalities. These data indicate that perturbation of FGF signaling in photoreceptors is associated with progressive photoreceptor degeneration, suggesting that one or more of the FGFs may act as a survival factor for photoreceptor cells.