STEWART, J.R.*; THOMPSON, M.B.; ATTAWAY, M.B.; HERBERT, J.F.; MURPHY, C.R.; East TN State Univ; Univ of Sydney; East TN State Univ; Univ of Sydney; Univ of Sydney: Uptake of Dextran-FITC by Placental Membranes of the Placentotrophic Lizard, Pseudemoia entrecasteauxii

Placental nutrient provision has evolved in multiple lineages of squamate reptiles and although possible structural specializations for placentotrophy have been described in a variety of species, neither the pathways nor the mechanisms of placental transfer are known. Lizards of the Australian genus Pseudemoia are placentotrophic and have a suite of derived characters that are likely to enhance nutrient transfer. The chorioallantoic placenta, which occupies the embryonic hemisphere of the egg, is regionally diversified into a large area with low epithelial height and a smaller placentome with cuboidal or columnar epithelia. Both regions are underlain by an extensive vascular bed. The abembryonic hemisphere of the egg is covered by an omphaloplacenta, which is similar to the placentome in having cuboidal or columnar epithelia but with a different embryonic vascular supply. We tested the hypothesis that embryonic epithelial cells of the placentome and the omphaloplacenta of P. entrecasteauxii are capable of endocytosis. Embryos (stages 34 – 39) with intact extraembryonic membranes were surgically removed from the uterus and incubated at 27 – 28 o C for 30-60 minutes in a solution containing fluorescein isothiocyanate-dextran (77, 000 MW). Extraembryonic membranes were dissected free of the embryo, washed in ringers, coated with cryoprotectant and frozen in iso-Pentane in liquid nitrogen. Frozen tissues were sectioned (8 &mum) on a cryostat. The fluorescent label was present in the cytoplasm of scattered populations of epithelial cells in both placental regions of all embryonic stages tested. We conclude that both the placentome and the omphaloplacenta of P. entrecasteauxii are sites of histotrophic exchange.