Influence of serum factors on the prevalence of "normal" and "foreign" differentiation pathways in cultures of chick embryo neuroretinal cells.

Embryonic (9-day) chick neuroretinal cells transdifferentiate extensively into lens and pigment cells during prolonged culture (4-5 weeks) in media containing foetal calf serum. Medium conditions which promote the attachment and differentiation of neural cells in other culture systems (e.g. horse serum, high glucose levels) both delay the onset and greatly reduce the extent of transdifferentiation in retinal cultures. In the presence of high glucose, horse serum (but not foetal calf serum) also favours cholinergic neuronal differentiation during the early phases of culture, as shown by the levels of choline acetyltransferase activity and accumulation of labelled choline. Substrate conditions have some effect on cholinergic differentiation (promoted by polylysine-coated dishes) but do not affect later transdifferentiation. These effects may be due in part to selective survival or growth of particular retinal cell types under the various medium conditions tested. Cultures stripped of neuronal cells contain negligible choline acetyltransferase activity, but still transdifferentiate into both lens and pigment cells, although more slowly than control cultures. Cell size distributions reveal a significant depletion of the larger cells in high glucose media with foetal calf serum, but not in those with horse serum.