Cellular src Gene Expression Associated with Lentoidogenesis in Transdifferentiating Cultures.: (pp60

We have shown (9) that elevated pp60c-src kinase activity accompanies the transdifferentiation of chick embryo neuroretinal (NR) cells into lens in vitro; moreover, most immunologically-detectable pp60c-src protein is confined to lentoid bodies in permissive cultures (FH; 6). By contrast, pp60c-src expression is low in non-permissive cultures where lentoid formation is blocked by high glucose (FHG; 6) or medium 199 (11). We now extend these findings in several respects. Firstly, glial-enriched cultures in both FH and FHG media form small but sparse lentoid bodies at around 20 days, accompanied by increases in both δ crystallin and pp60c-src expression. In later FHG cultures, these lentoids increase neither in number/size nor in δ/pp60c-src expression, in contrast to permissive (FH) cultures. Thus the high glucose block on transdifferentiation is only partly mediated by neuronal influences (19). Secondly, transdifferentiating cultures of tapetal cells show higher levels of pp60c-src relative to redifferentiated or dedifferentiated (16, 17) cultures of these cells. Thirdly, we find no evidence that c-src oncogene expression directly signals transdifferentiation. Thus v-src expression in RSV-transformed NR cells inhibits δ crystallin accumulation (29; this study), while a c-src-substituted RSV variant has little effect on NR transdifferentiation. Late cultures of NR cells in medium 199 fail to accumulate pp60c-src protein or c-src transcripts, even though previous studies (2) showed that δ crystallin transcripts are localised within the nuclei of many cells in such cultures.