Start and stop signals of oocyte meiotic maturation

Abstract

Oocytes are made in the fetal ovary and are only ever fertilized some ­considerable time later in the adult. During this time, they have to undergo two meiotic divisions (meiosis I and II), which must be executed faithfully and on time so as to produce a mature egg, with a haploid chromosome content, that is ovulated into the fallopian tube ready to be fertilized. The two meiotic divisions are controlled by both internal and external (hormonal) triggers, principally executed by changes in the activity of the kinase CDK1 in the oocyte. Here, we focus on how the oocyte controls CDK1 activity at three important time points: (1) the arrest at prophase I in the ovary and the hormone-driven release from this arrest, (2) the progression through meiosis I, and finally (3) the rearrest at metaphase II and subsequent completion of meiosis triggered by a sperm calcium signal.