REGULATION OF CELL-DIVISION AND ROD DIFFERENTIATION IN THE TELEOST RETINA

We tested the effects of several growth factors on the proliferation a nd differentiation of cells in the teleost retina which typically beco me rod photoreceptors to understand their regulation. Using organotypi c slice cultures of differentiated teleost fish retinal tissue, we fou nd that insulin and insulin-like growth factor I(IGF-I) stimulate prol iferation of rod precursor cells whereas basic fibroblast growth facto r (bFGF) does not. In the presence of bFGF, however, a greater proport ion of the cells that had divided expressed a rod photoreceptor-specif ic phenotype than did control slices. This suggests insulin and the re lated IGF-I can influence the regulation of neuronal cell division whe reas bFGF promotes the differentiation of neuronal stem cells into rod photoreceptors in retinal slice culture. These results support the id ea that cell division and differentiation are differentially regulated and diffusible factors play a role in this process.