Meeting Abstract

P1.82  Tuesday, Jan. 4  Calcium provision in a placentotrophic lizard: structural differentiation reflects functional specialization. STINNETT, H.K.*; STEWART, J.R.; ECAY, T.W.; PYLES, R.A.; THOMPSON, M.B.; East TN State University, Johnson City; East TN State University, Johnson City; East TN State University, Johnson City; East TN State University, Johnson City; University of Sydney, NSW, AU Haley.Stinnett@gmail.com

Viviparity and placentation have evolved in more than 100 lineages of squamate reptiles, yet highly placentotrophic species are rare. Pseudemoia pagenstecheri is an Australian scincid lizard with a regionally differentiated placenta. The chorioallantoic placenta consists of an elliptical-shaped region with hypertrophied uterine and embryonic epithelial cells supported by dense vascular networks. The remainder of the chorioallantoic placenta is also highly vascularized but epithelia are thin. A yolk sac placenta with hypertrophied epithelia is located in the abembryonic hemisphere of the egg. Placental transfer of nutrients is extensive; for example, 90% of calcium in neonates is received via the placenta. Calcium uptake by extraembryonic membranes of squamates is correlated with expression of the calcium binding protein, calbindin-D28K. We used immunohistochemistry to localize calbindin-D28K in extraembryonic membranes of a developmental series of embryos to test the hypothesis that the placenta has regional functional specializations. We found support for this hypothesis because calbindin-D28K was expressed in the embryonic epithelium of the yolk sac placenta and in the chorionic epithelium of the placentome, but not in the remainder of the chorioallantoic placenta. In addition, calbindin-D28K was expressed in all embryonic stages studied, which encompassed both early and late development, suggesting that placental calcium secretion occurs over an extended interval of gestation.