Figure 1. Temporal and structural organization of oocyte meiotic maturation.

(A) State transitions during mitotic cycles (mi) and meiotic maturation (me). Haploid and diploid states are indicated by one or two asterisks, respectively. The four main stages of meiosis are (a) meiotic resumption following the progesterone pulse, (b) metaphase of the first meiosis, (c) meiotic transition and (d) metaphase arrest during the second meiosis. (B) The typical time course of MPF kinase activity during the maturation process of Xenopus oocytes where the four main stages (a–d) are indicated. Experimental data are from [54] (black circles), [7] (orange diamonds), [6] (blue triangles), [55] (magenta plus), [22] (green asterisks) and [13] (red squares). The zeroes of the time axis have been calibrated and the MPF axis have been normalized to have the first peak of MPF activy occur at the same time and with the same amplitude for each time course. (C) Detailed representation of the network of translational and post-translational interactions regulating metazoan oocyte maturation. This network involves a tight and precise coupling between the MPF and MAPK pathways at multiple levels. See text for details.