Grant: Operating Grant

Increasingly, infertile couples are treated by assisted reproduction technologies that include in vitro fertilization and the extended culture of eggs and embryos outside the woman's body. Recently, this is being extended to "in vitro maturation" (IVM) of eggs. In IVM, immature eggs are taken from the ovary and matured to fertilizable eggs in the clinic. IVM would avoid the serious side effects and expense of using hormones to stimulate egg production in women. However, it is still experimental, and there are serious concerns about safety and success rates. Early embryos are extremely sensitive to perturbations of their cells' size, indicating that cell volume regulation is critical to early embryo development. We previously found, using the mouse as our model, that early embryos have a unique mechanism for maintaining cell size that relies on accumulation of the amino acid glycine inside embryonic cells. We propose that what glycine does is to replace some of the salts that the embryos, like other cells, routinely take up to quickly correct deviations from their preferred size. Embryos appear to be very sensitive to having too much salt inside them, and need to replace it with something more benign like glycine. This implies that embryos have mechanisms that import ions in response to decreased cell volume, which must be carefully regulated to allow glycine to replace salts. In this project, using the mouse model, we will determine their identity, how they are regulated during embryo development, and when they develop during the growth of the egg in the ovary. Finally, we will investigate how the egg switches to the mechanism that uses glycine, and turns off the ones that use salts, during egg maturation. We propose that dysregulation of this process is one major reasons for problems with current IVM. Therefore, finally, we will use our findings to improve the conditions for IVM, with the aim of making it safer and more effective.