Proline Transporters in the Mouse Oocyte and Embryo and Ethics of Embryo Modification

Abstract

Uptake of amino acids (AA) into the oocyte and embryo occurs via specific AA transporters (AAT) located on the cell. Embryos cultured in vitro critically rely on the composition of the embryo culture media for optimal development. The present study aimed to identify transporters of L-Proline (Pro) in the oocyte and preimplantation embryo. Embryos fertilised in medium containing Pro and/or its analogue pipecolic acid had increased development. Three transporters were identified, PROT (SLC6A7), PAT1 (SLC36A1) and PAT2 (SLC36A2). The presence of Pro and/or pipecolic acid during IVF also reduced mitochondrial activity and reactive oxygen species levels in oocytes suggesting that these AAs act as a scavenger of ROS.

The next aim was to determine the specific stages of preimplantation embryo development when Pro uptake is required. In wild-type embryos Pro increased development to the cavitation stage (day 4). In B0AT1 knockout embryos Pro induced improvement at the 4-8 cell stage (day 3) and blastocyst stage (day 6) but not at cavitation (day 4), suggesting B0AT1 is the main contributor to Pro uptake on day 4 of development. These data show that Pro transporters are present in the oocyte and at specific stages of preimplantation development.

In this study parthenogenetically-activated human oocytes did not develop to the blastocyst stage in commercial media. Activated mouse oocytes cultured in Pro had increased development compared to parthenotes cultured with no AAs or groups of AA. This study demonstrates a simplified medium can be beneficial to maintain development of parthenotes for therapeutic purposes.

Intentionally applying technology to embryos to cause developmental and heritable changes raises ethical considerations. In a first of its kind study, opinion of a segment of the Australian public was collected on the topic of embryo modification. The majority of respondents were supportive in allowing heritable changes in embryos for clinical and research purposes.