Acquisition of meiotic competence in mouse oocytes: absolute amounts

M-Phase promoting factor (MPF) is a complex of p34cdc2 and cyclin B. Results of previous studies in which relative mass amounts of these cell cycle regulators were determined sug-gested that the accumulation of p34cdc2, rather than cyclin B, could be a limiting factor in the acquisition of meiotic compe-tence in mouse oocytes. Nevertheless, in the absence of mea-surements of the absolute amount of these components of MPF, it is possible that the molar amount of p34cdc2 is in excess to that of cyclin B, i.e., the accumulation of p34cdc2 is not a limiting factor. We report measurements of the absolute mass of p34cdc2 and cyclin B1, as well as the two proximal regulators of MPF, namely cdc25C and wee1, in meiotically incompetent and com-petent mouse oocytes. We find that the numbers of molecules of p34cdc2, cyclin B1, cdc25C, and wee1 in meiotically incom