Carbonic anhydrase C in the neural retina: transition from generalized to glia-specific cell localization during embryonic development.

The developmental profile and cellular localization of carbonic anhydrase C (carbonate dehydratase; carbonate hydro-lyase, EC 4.2.1.1) in the neural retina of chicken embryos and adults were investigated by immunochemical and immunohistochemical methods. Carbonic anhydrase C is present in the retina by the 3rd day of embryonic development. In the undifferentiated retina, it is detectable in virtually all the cells; however, as cell specialization progresses, its level declines rapidly in the emerging neurons and increases in Müller glia cells. An exception is certain amacrine neurons that contain carbonic anhydrase C to about the 16th day of development. In the adult retina, the enzyme is confined exclusively to Müller cells (the only gliocytes in the retina). Their identification was confirmed by immunostaining for glutamine synthase, an established Müller cell "marker." The presence in the mature retina of both these enzymes in Müller cells indicates that retinal gliocytes combine functional features that, in the brain, are segregated in astrocytes and oligodendrocytes. In the embryonic retina, carbonic anhydrase C and glutamine synthase differ markedly in their developmental profiles, cellular distribution, and susceptibility to regulation by cortisol and by cell interactions. Such differences make these two enzymes an attractive "marker team" for studying developmental mechanisms in embryonic retina and specific functions of Müller cells.