P-109: Using SMAD2/3 Inhibitor to Investigate the Importance of GDF9 Signaling on Ovine Cumulus Expansion and Subsequent Embryonic Development

Background: Oocyte in vitro maturation success rate is still low in compareision to oocyte in vivo maturation. Thus prediction and improvement of oocyte competency are two critical issues in assisted reproductive technology. New insights into oocyte-cumulus cell regulatory loop may assist our optimization of in vitro maturation technique. Maturation and developmental competency of cumulus oocyte complexes (COCs) are the result of cross talk between two pathways including endocrine hormones and paracrine growth factors (also known as oocyte secreted factors). The contribution of these factors in oocyte maturation and development is an active area of research. The objective of this research was to investigate whether growth differentiation factor 9 (GDF9) secreted by oocyte affects cumulus expansion and oocyte development in sheep. Materials and Methods: Immature ovine COCs were cultured in presence of recombinant GDF9, denuded oocytes, SB-431542, a specific inhibitor of activin like kinase 4/5/7; or a combination of these factors. Routine in vitro maturation of COCs and denuded oocytes were considered as external controls. Cultured COCs were used for assessment of i. cumulus expansion and ii. yield and quality of embryo development. Results: It was observed that cumulus expansion was not affected by any of these treatments. In the presence of exogenous GDF9, cleavage rate was reduced; blastocyst rate did not differ from other groups while trophectoderm cell number significantly increased. Conclusion: This suggests that exogenous GDF9 could improve embryo quality. This study provides evidence that GDF9 signaling has a minor influence on ovine cumulus expansion and oocyte development; it appears that other signaling pathway have dominant role.