Profiling L-serine Transport Throughout Growth and Meiotic Maturation in Mouse Oocytes

Abstract

With the increasing demand for assisted reproduction, more knowledge and understanding towards health requirements of oocytes and their inner workings are required. With current IVF success rates of approximately 40%, oocyte and embryo culture conditions in vitro can be improved by first understanding the finer details of oocyte function. As such, there is a need to better understand the mechanisms through which oocytes can acquire certain nutrients. This thesis focuses on the amino acid serine, which has been shown to improve outcome in developing embryos and also plays a variety of roles in the body that may carry over to oocyte health as well. Using radiolabeled [3H] serine, we measured uptake of serine as a function of time throughout growth and meiotic maturation in mouse oocytes. Serine transport appeared in oocytes during growth and became absent in mature eggs. With a competition assay using substrates diagnostic for several different amino acid transporter systems and culture with and without sodium in the external medium, I identified Na+-dependent SNAT7 of the System A/N (SLC38) family to be the most likely transporter in oocytes. Quantitative RT-PCR was consistent with this result. Transporter activity is also not activated by progression of meiotic maturation, as indicated by unperturbed transport when dbcAMP was provided to maintain meiotic arrest. However, a biological regulator of arrest, NPPC, resulted in enhanced transport activity in vitro. This may be due to signalling mechanisms of the NPPC pathway affecting regulation of serine uptake, which presents a direction for future research.