Theca cell-conditioned medium added to in vitro maturation enhances embryo developmental competence of buffalo (Bubalus bubalis) oocytes after parthenogenic activation

Theca cells (TCs) play a key role in follicular growth and atresia. TCs synthesize androgens that act as substrate for granulosa cells (GCs) aromatization to estrogens needed for oocyte maturation. However, the effects of TCs in the form of conditioned medium on in vitro maturation (IVM) and developmental competence of buffalo oocytes remain unclear. In the present study, we examined the impacts of TC-conditioned medium (TCCM) on maturation efficiency and embryo development of buffalo oocytes after parthenogenic activation (PA). Our results showed that TCCM that was collected on day 2 and added to IVM medium at a 20% proportional level (2 days & 20%) exerted no significant effect on IVM rate (43.06% vs. 44.71%), but significantly (p < .05) enhanced embryo development (oocyte cleavage, 80.93% vs. 69.66%; blastocyst formation, 39.85% vs. 32.84%) of buffalo oocytes after PA compared with the control group. However, monolayer TC significantly (p < .05) promoted both maturation efficiency (48.84% vs. 44.53%) and embryo development (oocyte cleavage, 80.39% vs. 69.32%; blastocyst formation, 35.38% vs. 29.25%) of buffalo oocytes after PA compared to that in the control group. Furthermore, TCs secreted some testosterone into the conditioned medium, which significantly (p < .05) promoted the expression levels of oestrogen synthesis-related genes (CYP11A1, CYP19A1 and 17 beta-HSD) in buffalo cumulus-oocyte complexes (COCs). Our study indicated that TCCM (2 days & 20%) did not significantly affect IVM efficiency, but enhanced embryo developmental competence of oocytes after PA principally by stimulating the secretion of testosterone and facilitating estradiol synthesis of buffalo COCs.