Age of differentiation determines rat retinal germinal cell phenotype: induction of differentiation by dissociation.

We are interested in the mechanisms that control cell phenotype during the development of the CNS. Since different neuronal types arise at different times during neurogenesis in the retina, we predicted that the factors that determine cell type must be developmentally regulated as well. To test this hypothesis, we induced retinal germinal cells to differentiate at different ages by dissociating the retina into single cells and culturing them on a variety of substrates. Prior to dissociation, the S-phase germinal cells were labeled with 3H-thymidine so that their fate could be specifically followed. We found that our culture conditions promoted the differentiation of the majority of the germinal cells and that these cells differentiated into different neuronal types depending on the age of the animal from which the retina had been taken; embryonic day 14 germinal cells differentiated primarily into ganglion cells, and never produced rods, while germinal cells from postnatal day 1 retina differentiated into rods, but not ganglion cells. These results are consistent with the hypothesis that temporally regulated factors determine cell phenotype during the development of the retina.