[Frontiers in Bioscience S5, 451-477, January 1, 2013]

Oocyte Maturation: A story of arrest and release

Aritro Sen1, Francesco Caiazza1

1Division of Endocrinology and Metabolism, Department of Medicine, University of Rochester School of Medicine and Dentistry, Rochester NY 14642


1. Abstract
2. Introduction
3. Regulation of meiotic arrest of oocytes at prophase I stage
3.1. High cAMP levels are essential for meiotic arrest: role of G-protein coupled receptors and gap junctions
3.2. Role of cell cycle proteins (Maturation Promoting Factors-MPF) in maintaining oocyte meiotic arrest
3.3. Role of cAMP-activated PKA in regulating MPF activity during oocyte arrest
4. Oocyte maturation
4.1. LH-induced resumption of meiosis in oocytes
4.1.1. Role of epidermal growth factor (EGF)-related proteins
4.1.2. Role of steroids in oocyte maturation
4.2. Underlying mechanisms of LH-induced signals involved in decrease of cAMP levels in the oocyte
4.2.1. Role of gap junctions in oocyte maturation
4.2.2. Role of G-proteins in decreasing cAMP levels in the oocyte for resumption of meiosis
4.2.3. Role of phosphodiesterase (PDE) in oocyte maturation
4.3. Signaling pathways involved in resumption of meiosis and GVBD
4.3.1. MAP Kinase pathway
4.3.2.Other signaling pathways
4.3.3. Regulation of MPF complex for resumption of meiosis and GVBD- Species difference
4.4. Meiosis I and transition from Meiosis I to Metaphase II stage
4.4.1. Meiosis I (MI) completion: Mechanism of MPF decline by proteosomal degradation
4.4.2. Meiosis I to metaphase II transition
5. Metaphase II stage arrest
6. Ca2+-induced completion of meiosis
7. Conclusion
8. References


The release of a mature healthy egg for fertilization is the center of the entire reproductive process. From the time of embryonic development till fertilization, the oocyte undergoes several stop-and-go periods. In most animals, oocytes are held in meiotic arrest in prophase I prior to ovulation. The ovulatory luteinizing hormone (LH) surge promotes the resumption of meiosis of the arrested oocytes and their progression through the second meiotic cycle, only to be arrested again at metaphase II until fertilization. This review addresses the underlying mechanisms involved in maintaining the oocyte in meiotic arrest as well as the signaling pathways responsible for releasing it from the arrested phase just prior to ovulation until the completion of meiosis at the time of fertilization.