Relationship between the morphological changes of somatic compartment and the kinetics of nuclear and cytoplasmic maturation of oocytes during in vitro maturation of porcine follicular oocytes

Based on the morphology and expansion of the cumulus cells, several different classes of porcine cumulus-oocyte complexes (COCs) can be distinguished, during their maturation in vitro. The goal of the present study was to find out the rate of each morphologic category in case of COCs and granulosacumulus-oocyte complexes (GCOCs), the characteristics of their nuclear progression, cytoplasmic maturation, and the frequency of monospermy after IVF. It was found that the frequency of cumulus expansion is higher in case of GCOCs than that of COCs. Nuclear progression of COCs was more accelerated than that of GCOCs. Oocytes attached to the bottom of culture dish with dark, compact cumulus underwent nuclear and acquired their ability to be activated earlier than that of oocytes showing normal cumulus expansion. The rate of monospermic fertilization after IVF of normal COCs showing normal cumulus expansion was higher than that of COCs attached to the dish. These results suggest that diverse behavior of cumulus cells during in vitro culture affects nuclear and cytoplasmic maturation of porcine oocytes, which also affects IVF results. It can be concluded that granulosa cells promote normal cumulus expansion thus decrease heterogeneity in nuclear and cytoplasmic maturation amongst oocytes. (C) 2004 Wiley-Liss, Inc.