Poor Embryo Development in Mouse Oocytes Aged In Vitro Is Associated with Impaired Calcium Homeostasis1

We examined whether impairment of intracellular Ca2+ homeostasis is related to poor embryo development in in vitro-aged oocytes. We found that in vitro aging of mouse oocytes affected the patterns of Ca2+ oscillations at fertilization: these Ca2+ oscillations were lower in amplitude and higher in frequency compared with oocytes without in vitro aging. We also observed that the intracellular Ca2+ store was decreased in in vitro-aged oocytes. A decrease in the Ca2+ store induced by thapsigargin, a specific endoplasmic reticulum (ER) membrane Ca2+-ATPase inhibitor, resulted in a lower fertilization rate and in poorer embryo development. The frequency of Ca2+ oscillations was significantly increased at fertilization, whereas their amplitude was decreased in thapsigargin-treated oocytes. These results suggest that impairment of intracellular Ca2+ homeostasis (such as a decrease in the ER Ca2+ store) caused an alteration in Ca2+ oscillations and the poor embryo development in in vitro-aged oocytes. Bec...