In Vitro Maturation and Fertilization of Pig Oocytes

In pigs, as in many other species, immature oocytes liberated from ovarian follicles can resume meiosis and complete maturation in culture. Although the matured oocytes can be penetrated in vitro by spermatozoa under appropriate conditions, low rates of pronuclear formation and a high incidence of polyspermy have been reported by many workers. Recently, pigs have become increasingly important in the field of biomedical research and there is increasing interest in using transgenic pigs as potential xenograf donors in the future. Because most studies that attempt to produce transgenic pigs by nuclear transfer/cloning techniques or pronuclear microinjection use matured oocytes and early embryos, respectively, it is becoming more important to produce a large number of developmentally competent oocytes and embryos for research. Furthermore, accumulating information suggests that rodents may be atypical with regard to regulating mechanisms of oocyte maturation and fertilization. The mechanisms for fertilization in domestic animals such as pig and cattle may be more similar to low vertebrates and human than the mouse (1). Therefore, porcine oocytes have now become an important model for studying the molecular control of the meiotic cell cycle and signal transduction during fertilization.