Chick embryo neural retinal cells transdifferentiate extensively into lens cells when cultured in Eagle's MEM containing horse and fetal calf sera (FHMEM). Such cultures express elevated levels of pp60c-src-associated tyrosine kinase activity relative to parallel cultures prevented from transdifferentiating by the addition of supplementary glucose (FHGMEM) or replacement of MEM by medium 199 (F199). Northern blotting and in vitro translation studies suggest that c-src mRNA levels are only

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... ly higher in late transdifferentiating (FHMEM) cultures as compared to parallel blocked (FHGMEM or F199) cultures. By immunocytochemical staining, we show that pp60c-src protein is largely localized in cell groups undergoing conversion into lens (i.e. expressing delta crystallin) in late FHMEM cultures. Initial studies of pp60c-src in chick lens tissues during development indicate that higher kinase activity is found in the epithelial cells relative to mature lens fibres. Thus pp60c-src may be expressed both during the differentiation of lens cells in vivo and during the transdifferentiation of neural retina cells into lens in vitro.