Biochemical events during progesteroneinduced maturation in vitro

Reports by Masui (1967) and others in the late 1960s on the ability to obtain complete oocyte maturation in vitro by addition of progesterone were a great stimulus to work in the field. Additional stimulation came in 1971 from the work of Masui & Markert (1971) and Smith & Ecker (1971) that described a cytoplasmic activity capable of inducing complete maturation when microinjected into resting oocytes in the absence of progesterone. This activity, known as maturation-promoting factor (MPF), could be detected in all types of M phase cells. It was ultimately purified in this laboratory from Xenopus eggs (Lohka et al 1988) and shown to consist of a cyclin B/Cdc2 complex (Gautier et al 1988, Dunphy et al 1988). Combined with genetic work in yeast showing that cdc2 is a universal mitotic control gene (Lee & Nurse 1987), the field of cell cycle control entered a new, more energetic phase that continues today. The system in which MPF was characterized and purified, the frog oocyte system, has continued as a leading model for cell cycle control from at least three perspectives: mechanism of MPF activation; mechanism of MPF inactivation, and the linkage of consecutive M phases in meiosis (Fig. 1).

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