Appearance, fate and utilization of abnormal porcine embryos produced by in vitro maturation and fertilization.

In vitro production (IVP) including in vitro maturation (IVM) and fertilization (IVF) is now an important technology for obtaining live piglets. However, there are still two significant obstacles to the efficient production of viable porcine embryos: (1) polyspermy and (2) fertilization of oocytes arrested at the immature stage. These phenomena relate to production of embryos with abnormal ploidy (polyploidy). To avoid these problems, careful selection of mature oocytes for IVF, and regular monitoring of normal and abnormal fertilization (polyspermy and/or lack of male pronucleus formation) are very important. In our recent studies, however, we have confirmed that some oocytes with abnormal ploidy after polyspermy can develop into diploid embryos with potentially normal developmental ability. The mechanism by which such fertilized polyploid oocytes develop to a normal state during embryo development is still not well understood. Attempts to clarify this mechanism would hopefully reveal data that are very useful for not only IVP but also other technologies such as the production of transgenic or cloned animals using IVM oocytes, including other species, also for human reproductive manipulation. In this review, we focus on studies of normality of IVM oocytes and ploidy of IVP embryos, and try to suggest practical ways of solving the problems mentioned above in pigs.