Modulation of retinal differentiation by oncogenes: effect of the v-src gene on expression of choline acetyltransferase and glutamine synthetase.

Expression of the protooncogene c-src in chick neural retina is developmentally regulated and associated with neural differentiation. In the present study, chick neural retina (NR) cell cultures from 7 day embryos were exposed to the exogenous src oncogene, the c-src counterpart, to establish the effect of expression of v-src on specific retinal cellular differentiation. NR cells from 7 day chick embryos were placed in monolayer or rotation culture and infected with Rous sarcoma virus (RSV) containing a single transforming gene. Other cultures were infected with a transforming defective mutant of RSV which still possesses mitogenic activity for NR cells. While control cultures showed typical neuronal and Muller cell morphologies at the light and electron microscopic level, NR cells infected with RSV exhibited dramatic morphological alterations in monolayer culture and cell aggregates. However, the mutant src gene induced mitosis without accompanying transforming properties. When aggregate cultures were treated with hydrocortisone to induce glutamine synthetase (GS) expression in Muller cells, control cultures showed the typical immunofluorescence pattern of GS staining, while RSV infected cultures showed no GS fluorescence. Cultures infected with mutant RSV showed some staining for GS. In contrast, choline acetyltransferase activity was shown to increase in both monolayer and aggregate cultures of retinal cells following v-src expression. These data indicate that the presence of excess v-src in differentiating cultures of NR inhibits the expression of some neural specific enzymes and enhances the presence of other specific proteins. Moreover, continually growing cultures of oncogene-altered retinal cells may be useful as models to study gene expression in development of the nervous system.