Expression of differentiation markers by chick embryo neuroretinal cells in vivo and in culture.

Several markers of chick neuroretinal differentiation were monitored in vivo and in culture. All increase markedly between 7 and 20 days of embryonic development in vivo. In vitro, endogenous GABA levels decrease almost immediately, while other neuronal markers increase as in vivo for 2 to 5 days before declining (choline acetyltransferase, acetyl cholinesterase, glutamic acid decarboxylase). Neuronal cell surface markers (binding sites for tetanus toxin, alpha-bungarotoxin, muscimol), however, reach maximal levels only after 8 days in vitro. Glial markers such as carbonic anhydrase and hydrocortisone-induced glutamine synthetase activities are also expressed only transiently in culture.