Successful piglet production in a chemically defined system for in-vitro production of porcine embryos: dibutyryl cyclic amp and epidermal growth factor-family peptides support in-vitro maturation of oocytes in the absence of gonadotropins

To induce meiotic resumption of porcine oocytes, it is thought to be necessary to expose the cumulus-oocyte complexes (COCs) to gonadotropins during in-vitro maturation (IVM). However, the detailed mechanism of meiotic resumption by gonadotropins is still unknown, and successful piglet production has not been reported by using oocytes matured in gonadotropin-free media and fertilized in vitro. The present study was undertaken to examine the combinational effects of epidermal growth factor (EGF)-family members and dibutyryl cyclic AMP (cAMP) in a chemically defined medium on IVM of porcine oocytes and the developmental competence following in vitro fertilization (IVF). The basic IVM medium was a chemically defined medium, modified porcine oocyte medium (mPOM). Supplementation of the IVM medium with 10 or 1000 ng/ml EGF, amphiregulin and betacellulin during the whole IVM period, except for 10 ng/ml amphiregulin, increased the percentage of oocytes maturing to the metaphase-II stage. When COCs were exposed to both dibutyryl cAMP and EGF-family members during the first 20-h of IVM and then culture was continued in the absence of EGF-family members and dibutyryl cAMP, the incidence of metaphase-II oocytes was significantly increased and was not different from that of oocytes cultured in a standard IVM system with gonadotropins. The developmental competence of the oocytes to the blastocyst stage following IVF was no different from that of control oocytes matured with gonadotropins. When these blastocysts were transferred into the uterine horn of three recipients, all of gilts became pregnant and delivered a total of 11 piglets. These observations indicate that supplementation of a chemically defined maturation medium with EGF-family members and dibutyryl cAMP during the first 20 h of IVM can support well the meiotic progress and developmental competence of porcine oocytes.