Calcium availability regulates calcium transport by the chorioallantoic membrane of an oviparous squamate (1100.8)

Abstract

Embryos of Pantherophis guttatus (the corn snake) develop within calcareous eggshells. Together, the yolk and eggshell provide all the calcium needed to support development through hatching. Hatchlings receive 25% of their calcium from the eggshell and removing shell calcium by physically peeling off the outer calcareous layers retards embryonic growth (length and mass) and reduces expression of calcium transport proteins by the chorioallantois, the epithelial tissue that catalyzes shell calcium transport. We hypothesize that chorioallantois calcium transport is regulated by calcium availability and predict that supplementing peeled eggs with external calcium will increased calcium transport protein expression and reverse the effects of shell peeling on hatchling growth. Paired peeled and intact eggs were incubated in either distilled water or water plus calcium chloride (2mM, 5mM, or 20mM) and incubated to the last developmental stage prior to hatching. At that time, the chorioallantois was assayed for expression of carbonic anhydrase II (CAII) and calbindin‐D28K by immunoblotting. Preliminary data show that expression of calbindin‐D28K is positively correlated with calcium supplementation in peeled eggs. CAII expression also increased, but not with the same linear concentration dependence. We conclude that chorioallantois expression of CAII and calbindin‐D28K is regulated by shell calcium but with different sensitivities. Further, 20mM calcium supplementation in peeled eggs yields calbindin‐D28K expression levels comparable to intact eggs. However, calcium supplementation did not reverse the growth effects of eggshell peeling suggesting that additional eggshell properties impact embryonic growth. (AJJ supported by an NSF‐REU fellowship)