Transforming growth factor-α in a defined medium during in vitro maturation of porcine oocytes improves their developmental competence and intracellular ultrastructure

Abstract

We examined the effects of transforming growth factor-α (TGF-α) to develop a defined medium for in vitro maturation (IVM) of porcine (Sus scrofa domesticus) oocytes. Cumulus-oocyte complexes (COCs) were matured in porcine oocyte medium containing 3 mg/mL polyvinyl alcohol (POM) and TGF-α (0, 1, 10, or 100 ng/mL) in the presence or absence of the gonadotropins equine chorionic gonadotropin (eCG) and human chorionic gonadotropin (hCG). In the absence of gonadotropins, adding 10 ng/mL TGF-α increased (P < 0.05) the percentage of oocytes that reached metaphase II (24.2%) compared with that of the control (no TGF-α addition; 5.6%). In the presence of gonadotropins, although maturation rate did not differ among TGF-α treatments (75.4% to 84.8%), the rate of blastocyst formation (28.1%) was higher (P < 0.05) in the TGF-α group (28.1%) than that in the control group (15.9%) after in vitro fertilization and embryo culture. An electron microscope study revealed that TGF-α–treated oocytes contained more homogenous lipid droplets than did control oocytes. Moreover, mitochondria surrounded by the endoplasmic reticulum were observed only in the TGF-α–treated oocytes. In blastocysts derived from the latter oocytes, mitochondria with numerous cristae were frequently observed compared with that in blastocysts from control oocytes. When the Day-5 blastocysts obtained from oocytes matured with TGF-α were surgically transferred into four recipients, a total of 29 piglets were farrowed. We concluded that the addition of TGF-α to the defined IVM medium of porcine oocytes improved the subsequent blastocyst formation and that the blastocysts produced by the defined in vitro production system have developmental competence to full term after embryo transfer.