Optimisation of oocyte in vitro maturation using oocyte secreted factors.

Abstract

During follicular development, oocyte and somatic cells communicate by producing signals such as proteins, growth factors, hormones that interact in complex harmony. The oocyte plays an active role in this communication by secreting soluble oocyte secreted factors (OSFs) including growth differentiation factor 9 (GDF9) and bone morphogenetic factor 15 (BMP15). Those two growth factors have been implicated in follicular development and are related to female fertility. In vitro matured oocytes have aberrant gene expression and altered matrix protein profiles in cumulus cells compared to their in vivo mature counterparts, which leads to a decrease in oocyte quality and embryo development post fertilisation. The first aim of this study was to determine the effect of exogenous native OSFs from denuded oocytes (DOs) on mouse in vitro maturation (IVM). In a series of experiments, native OSFs were used in various ways to observe the role of FSH, cumulus cells, and temporal effects, on production of native OSFs. Overall, co-culture of COCs with DOs improved mouse embryo development. The highest improvement in embryo development and embryo quality post co-culture of COCs with DOs was when COCs were matured in separate IVM media in the presence of FSH, then denuded at 3h to produce DOs, which were used in co-culture with COCs for another 14-15 h. Unfortunately, it is not practical to generate such large numbers of DOs in a clinical scenario. Therefore the next step was to find the functional bioactive forms of pure recombinant proteins that could improve IVM outcomes. The above concept led to the main hypothesis of this thesis that the developmental competence of IVM oocytes can be improved by novel variants of purified recombinant GDF9 and BMP15. In these studies, GDF9 and BMP15 from various sources and forms were tested in cattle and mouse IVM. Two different forms of proteins: pro-mature complex and mature domain of GDF9 and BMP15, were used in cattle and mouse IVM. In this study, pro-mature complex of human BMP15 (hBMP15) improved cattle blastocyst development, which may, in part, be due to an increased in nicotinamide adenine diphosphate [NAD(P)H] and reduced glutathione (GSH) levels. Mature region of BMP15 had a moderate, albeit non-significant, effect on cattle embryo developmental outcomes, whilst mature region of GDF9 was ineffective. Similar results were observed using pro-mature hBMP15, which improved the developmental competence of in vitro matured mouse oocytes, where a combination of mouse GDF9 (mGDF9) and hBMP15 (both in pro-mature complex form) produces the highest blastocyst rate. The work presented in this thesis has provided evidence that exogenous native OSFs, and recombinant hBMP15 in its pro-mature complex form, are important for oocyte developmental programming and prove useful for improving mouse and cattle IVM oocyte developmental competence. Moreover, the source, doses and form of recombinant proteins play an important role in improving developmental competence of IVM oocytes. These results may contribute and translate to improve the success rate of in vitro matured human oocytes.