Co-culturing or conditioned medium of Sertoli cells: Which one supports in vitro maturation of bovine oocytes and developmental competency of resulting embryos?

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Sertoli cells (SCs) as supportive cells in the seminiferous tubule play an essential role in the nutrition and development of adjacent cells by secreting several beneficial growth factors, stimulators and cytokines which can be conceived to improve the developmental competency of oocyte or embryo in the co-culture system. This study aimed to improve the maturation of bovine oocytes and consequently the development of resulting embryos in co-culture with SCs and their conditioned medium (CM). The retrieved cumulus-oocyte complexes (COCs) from the abattoir-derived ovaries were matured in maturation medium alone (control group), in co-culture with ovine SCs (co-culture group), and in presence of 10% CM prepared in 33°C and 39°C (CM33 and CM39 groups). The nuclear maturation competency and subsequent embryo development rate of cultured COCs in all groups were evaluated. The results of this study showed that SCs and CM increased meiosis resumption from GV to the MII compared to the control group, significantly (p < 0.05). Besides, the degenerated oocytes in the co-culture group were significantly higher than those in the control, CM33 and CM39 groups (p < 0.05), and the lowest cleavage rate belonged to the co-culture group (p < 0.05). The blastocyst rate was also lower in the co-culture group than other groups and there was a significant difference between the control and two CM groups (p < 0.05). The Sertoli cells can be suitable for co-culturing with oocytes during IVM but detrimental for subsequent embryo development. In turn, Sertoli cell-derived conditioned medium (SC-CM) can provide sufficient bioactive materials for COCs to enhancing oocyte competence and embryo development.