The metanephros of the quail embryo. Developmental expression of carbonic anhydrase investigated by multiple approaches

The expression of carbonic anhydrase (CA) in the quail metanephros was inve stigated during embryonic development. The immunohistochemical localisation of the isoenzymes CAII and CAIII was compared with the distribution of enz yme activity visualised by a histochemical cobalt-precipitation procedure. The developmental profile of CA activity was also evaluated by means of a b iochemical method. The occurrence of a moderate and diffuse CAII immunostai ning from the first developmental appearance of the metanephros anlage test ified to an early expression of carbonic anhydrase. This finding is discuss ed in I-elation to the involvement of the enzyme in the morphogenetic mecha nisms leading to the establishment both of cell polarity and epithelial phe notype. CA expression in the renal sites that are positive in adults proved to be developmentally regulated. In the collecting duct system, enzyme act ivity could not be identified until the time of hatching. No CA was detecte d at any stage examined at the sites where, in adults, enzyme occurrence ha s previously been interpreted as a membrane-associated CA isoform. The diff erentiating renal tubules displayed no CAIII immunoreactivity. It can be ar gued that the bulk of the enzyme activity in the embryonic metanephros is d ue to the cytosolic isoenzyme CAII.