Synchronization of in vitro maturation in porcine oocytes.

When removed from the follicles, during the 44 h process of in vitro maturation (IVM) fully grown porcine oocytes resume meiosis spontaneously from the late diplotene stage of the first meiotic prophase and proceed to the metaphase-II (MII) stage at which they remain arrested until fertilization. However, the resumption may start at various times causing heterogeneity in the nuclear stage and also in cytoplasmic characteristics (i.e., the activity of certain protein kinases) within a population. Those oocytes that reach the MII stage earlier than others undergo an ageing process which is detrimental for further embryo development. The synchronization of nuclear progression is possible by a transient inhibition of meiotic resumption during the first 20-22 h of IVM either by (1) the elevation of intracellular levels of cyclic adenosine monophosphate (cAMP) or (2) suppressing the activity of the metaphase promoting factor (MPF). A protocol for each approach is described.