Germinal vesicle materials are not required for the activation of MAP kinase in porcine oocyte maturation

The requirement of the germinal vesicle (GV) for the normal kinetics of mit ogen-activated protein (MAP) kinase activity during porcine oocyte maturati on was investigated. Porcine follicular oocytes were enucleated, and the lo cations of their extracellular signal-regulated kinases 1 and 2 (ERK1/2), m ajor MAP kinases in maturating porcine oocytes, were detected by indirect i mmunofluorescent microscopy. The MAP kinase activity was assayed as myelin basic protein (MBP) kinase activity, and the phosphorylation states of ERK1 /2 were detected by immunoblotting analyses. Translocation of MAP kinase in to the GV and association with the spindle were observed in intact oocytes, while MAP kinase in enucleated oocytes was distributed almost uniformly in cytoplasm throughout the culturing period. The phosphorylation and the act ivation of MAP kinase were induced, and the activity was comparable with th at of control denuded oocytes. The high level of activity was maintained th rough maturation, even in the absence of spindle formation. These results i ndicate that the presence of nuclear material and translocation into the GV are dispensable for the activation of MAP kinase and that associating with the spindle is not required for maintenance of its activity though porcine oocyte maturation. Mol. Reprod. Dev. 59:215-220, 2001. (C) 2001 Wiley-Liss , Inc.