Intracellular Ca2+ oscillations at fertilization are responsible for triggering egg activation. The aim of this study was to examine the effect of the age of the oocyte donor and in-vitro maturation on the generation of Ca2+ transients at fertilization. The results show that <10% of in-vivo and in-vitro matured oocytes from 19-day old mice develop to the blastocyst stage in vitro. In contrast, 43% of in-vivo and 25% of in-vitro matured oocytes from 24-day old mice developed to the blastocyst stage. In parallel experiments, intracellular Ca2+ was monitored at fertilization. Oocytes from 19-day old mice generate significantly fewer transients than oocytes from 24-day old mice. In-vitro maturation significantly decreased the ability of oocytes from 19-day old mice but not 24-day old mice to generate Ca2+ transients in response to spermatozoa. Furthermore, we investigated the effect of oocyte maturation on Ca2+ signalling. Immature oocytes generated fewer Ca2+ oscillations and ceased oscillating earlier than mature oocytes. These studies suggest that the ability to generate Ca2+ transients in response to spermatozoa increases in the final stages of oocyte development and during oocyte maturation. This may contribute to the acquisition of developmental competence in the final stages of oogenesis.
- In vitro