Specialised cell types in the chorioallantoic membrane express carbonic anhydrase during chick embryogenesis

The expression of carbonic anhydrase in the chorioallantoic membrane (CAM) of the chick embryo was investigated by means of the histochemical localisa tion of the enzyme catalytic sites and the immunohistochemical identificati on of its isoenzymatic forms. The results show that carbonic anhydrase is d evelopmentally expressed in a subset of cells both in the ectodermal and th e endodermal epithelium. The distribution patterns from both methodological approaches indicated that carbonic anhydrase is a marker of the villus cav ity cells and the mitochondria-rich cells in the ectodermal and the endoder mal epithelium, respectively. Such a cell-specific pattern of the enzyme ex pression provides a further contribution to characterising the heterogeneou s cell population of the chick CAM and supports specific functional involve ment for the distinct cell types in CAM-mediated processes, such as calcium transport, maintenance of acid-base balance and water and electrolyte reab sorption, during chick embryogenesis.