The overall objective of this application is to understand the regulation of embryonic calcium metabolism with specific emphasis on the process of transplacental calcium transport. The system chosen for the proposed studies is the chick embryonic chorioallantoic membrane (CAM) which represents the avian equivalent of the placental unit and is responsible for the translocation of eggshell calcium into the embryonic circulation during development. The projects described in this proposal aim to elucidate the biochemical, cellular, and molecular mechanisms regulating the CAM calcium transport function. Our approach is to study the transport-associated proteins (e.g. calcium-binding protein, CaBP; and Ca2+-ATPase) previously identified in this laboratory as functional marker molecules for the calcium transport process. Specifically, we plan to first characterize and localize at a subcellular level these components and analyze their functional involvement and mechanistic role(s) in CAM calcium transport. Secondly, we will study the cellular, biochemical, and molecular events leading to the regulation of CaBP expression during normal embryonic development and under experimentally induced conditions of vitamin K and/or calcium deficiency. We believe that the experiments proposed here will define the functional roles of these marker molecules in CAM calcium transport and provide fundamental information on the mechanisms regulating an important physiological function, transplacental calcium transport, of the developing vertebrate embryo.