The ins and outs of meiosis.

Abstract

During oogenesis the oocyte is arrested in meiosis twice. First at prophase I, then a second time at metaphase I in many invertebrates and in metaphase II in the vast majority of vertebrates. Meiosis resumption is triggered by the sperm. This article examines mechanisms that cause oocytes' arrest in meiosis and how spermatozoa help the oocyte to get out of this cellular predicament. J. Exp. Zool. (Mol. Dev. Evol.) 285:226-236, 1999.