Developmental expression of carbonic anyhdrase II in the extraembryonic membranes of the corn snake, Pantherophis guttatus

The eggshell provides 28% of the calcium in a hatchling corn snake, with the remainder coming from yolk. The chorioallantois contributes to calcium homeostasis during embryogenesis by mediating the transport of shell calcium to the embryo. Our objective is to understand how the embryo regulates dissolution of mineralized shell calcium and its transport during development. We hypothesize that cells of the chorioallantois secrete acid onto the eggshell thereby dissolving calcium carbonate crystals. Acid production is catalyzed by carbonic anhydrase II (CA II). Immunoblotting demonstrates an increase in CAII expression throughout development in the chorioallantois but no detectable expression in the yolk sack. Increased CAII expression is coincident with increased calbindin‐D28K expression, a marker for calcium transport. Histochemical staining identifies CA positive cells at the outer surface of the chorioallantois adjacent to the eggshell. CAII and calbindin‐D28K immunohistochemisty are being used to determine if acid secretion and calcium transport occurs in the same or different cells of the chorioallantois. (Supported by the NSF and an APS Undergraduate Summer Research Fellowship.)