Growth differentiation factor 9 (GDF9) and bone morphogenetic protein 15 (BMP15) are oocyte-specific growth factors that regulate many critical processes involved in early folliculogenesis and oocyte maturation. In this study, effects of GDF9 and BMP15 treatment during in vitro maturation of porcine oocytes upon development after parthenogenetic activation were investigated. Neither GDF, BMP15 alone nor in combination affects the number and viability of cumulus cells or the rates of oocyte maturation and blastocyst development. However, the treatment of GDF9 on porcine oocytes increased the number of trophectodermal (TE) cells of blastocysts derived from activated oocytes (P<0.05). The treatment of BMP15 increased the cell numbers of both inner cell mass (ICM) and TE cells (P<0.05). The treatment with the combination of GDF9 and BMP15 further increased the numbers of ICM and TE cells, compared with GDF9 or BMP15 treatment alone (P<0.05). In conclusion, the treatment of GDF9 or BMP15 (or both) enhanced the quality of blastocysts via the increased number of ICM and/or TE cells.

It is well established that mammalian cumulus cell (CC) expansion requires BMP15 (bone morphogenetic protein bone morphogenetic protein 15) and GDF9 (growth differentiation factor 9). However, the mechanisms of the factors in CC expansion are largely unclear. This study was conducted to examine the two paracrine factors and their receptor SMAD intracellular signaling mechanism of mediating porcine CC expansion and oocyte maturation, and to compare COCs (Cumulus–oocyte complexes) maturation to DOs (Denuded oocytes). COCs and DOs were in vitro matured in medium with FSH, LH and TGFB superfamily antagonists. Our results showed that the expansion of COCs was unaffected by addition of GDF9 and BMP15 recombinant protein, but cumulus cell proliferation and DOs maturation rate were enhanced. The mRNA expressions of SMAD receptor confirmed that oocytes secreted factors that activate SMAD3,4 and SMAD1 in granulosa cells and oocytes, but unaffected SMAD2. Treatment of COCs with a SMAD2/3 phosphorylation inhibitor (SB431542) inhibited CC expansion and expression of TNFAIP6. SB431542 also was revealed to inhibit DOs maturation. The activation of CC SMAD signaling by oocytes, and the requirement of SMAD2/3 signaling for expansion and oocyte maturation were studied in pig. Nonetheless, porcine oocyte maturation without SMAD2/3 signaling is likely to be needed for optimal matrix formation, but also BMP15 and GDF9 is likely to be needed in oocyte.