Gliogenesis in the embryonic avian optic tectum: neuronal-glial interactions influence astroglial phenotype maturation.

We have analyzed the development of neuroglial cells in the chick optic tectum under 3 sets of developmental conditions to assess the role of heterotypic cell-cell interactions in gliogenesis. Immunochemical and biochemical methods were employed to measure and localize the expression of the glial markers glutamine synthetase, glial fibrillary acidic protein, S-100 protein, carbonic anhydrase-C and myelin basic protein as functions of development in situ and in aggregation and monolayer cultures of dissociated embryonic tissue. The results showed that certain astroglial cells can be recognized as early as day 9 of development in situ. Oligodendroglial development manifests several days later and the full range of glial subtypes are not evident until nearly the time of hatching. Culture of 7-day embryonic tectum cells either in aggregates or in monolayer cultures failed to yield definitive oligodendroglia. Fibrous astroglia, as defined by glutamine synthetase and glial fibrillary acidic protein, developed well in both culturing systems. However, as previously noted in the embryonic neural retina system, glutamine synthetase expression was marked dependent on neuronal-glial associations.