Regulatory mechanisms of oocyte maturation and ovulation

Abstract

Oocytes are produced in the ovaries by the entry of mitotically proliferating oogonia into meiosis. In vertebrates, including fishes, oocytes stop their meiotic cell cycle at prophase I, during which they grow by the accumulation of substances, such as yolk and mRNAs, necessary for early embryonic development (see Chapters 1-3). These prophase I-Arrested oocytes are still immature and unable to be fertilized even when they reach their fully grown stage. Hormonal stimulation allows the oocytes to resume meiosis and proceed to metaphase II, where meiosis stops again. These metaphase II-Arrested oocytes are now mature (called ova or eggs) and can undergo embryonic development when fertilized. The process from prophase I arrest to metaphase II arrest is termed oocyte maturation in the field of biological sciences or final oocyte maturation in the field of fisheries sciences (Figure 1). © 2007 Springer Netherlands.