Meeting Abstract
Calcium nutrition of embryos of the European common lizard is highly dependent on transport across the chorioallantoic placenta and embryonic uptake of calcium is correlated with expression of the calcium transporting protein, calbindin-D28K, in the chorioallantoic membrane. Maintenance of calcium homeostasis is a critical physiological property of intrauterine gestation. We manipulated calcium in incubation media of embryos removed from females to test two hypotheses: 1) embryos cannot conserve calcium in the absence of exogenous calcium, and 2) low calcium availability promotes expression of calbindin-D28K in the chorioallantoic membrane. Embryos were removed from six females prior to the phase of greatest embryonic growth and sampled immediately or incubated for 11 days in either calcium-free saline or saline + 2 mM calcium. We monitored calcium concentration in incubation media and analyzed calcium content of egg compartments. For embryos incubated in calcium-free saline, calcium flux between the incubation media and eggs remained low and calcium in eggs at the termination of the experiment did not differ from that of eggs in the initial sample. Embryonic calcium content of eggs incubated in media with 2 mM calcium was significantly higher than embryos from the calcium-free saline treatment and expression of calbindin-D28K was higher in the chorioallantoic membrane of these embryos. Our results suggest embryos have: 1) the capacity to protect against calcium loss in the absence of exogenous calcium and, 2) a mechanism for detection of exogenous calcium that initiates transcription of intracellular calcium transporting proteins in the chorioallantoic membrane.
