Exacting Requirements for Development of the Egg

The hallmark of successful human reproduction is the fusion between a haploid spermatozoon and a metaphase II oocyte. The generation of such an oocyte involves a series of steps whereby germinal-vesicle oocytes (in which the nuclei are intact) at prophase I are stimulated to resume meiosis and mature to metaphase II, a sequence of events that prepares the oocyte for fertilization. Meiosis in mammalian females entails two reductive divisions of DNA to produce ovulated oocytes that can be fertilized in the oviduct (Figure 1). In the first meiotic division, replicated chromosomes condense and attach to kinetochores through their centromeres to . . .