Abstract
Abstract Vertebrate oocytes arrested at meiotic prophase I are still immature even when they reach their fully grown stage. For the acquisition of fertilizability, the fully grown oocytes must undergo oocyte maturation, during which the meiosis is released from prophase I arrest and stops again at metaphase II until inseminated. The resumption of meiosis from prophase I to metaphase II is induced by the action of maturation-promoting factor (MPF). The molecular structure of MPF is common to all eukaryotes, but the mechanisms of its formation and activation vary in cell types and in species. In this review, I summarize the mechanisms of MPF formation during oocyte maturation in two amphibian species, Xenopus laevis and Rana japonica. In Xenopus, immature oocytes are equipped with inactive MPF (pre-MPF) sufficient for completing oocyte maturation, and therefore only its activation is required after hormonal stimulation. In contrast, immature Rana oocytes contain no pre-MPF. Therefore, MPF must be newly form...
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