[Frontiers in Bioscience 16, 1898-1914, January 1, 2011]

Recent advances in meiotic maturation and ovulation: comparing mammals and pisces

Balasubramanian Senthilkumaran

Department of Animal Sciences, School of Life Sciences-Centre for Advanced Studies, University of Hyderabad, P. O. Central University, Hyderabad - 500 046, Andhra Pradesh, India


1. Abstract
2. Introduction
3. Meiotic maturation and ovulation in mammals
3.1. Are follicular steroids indispensable for meiotic maturation?
3.2. Role of novel oocyte-specific A kinase anchoring protein and modulation of cAMP levels
3.3. MPF regulates meiosis reinitiation
3.4. Inactivation and reactivation of MPF is a feature of mammalian oocytes and role of Mos
3.5. Ovulation
4. Meiotic maturation and ovulation in pisces
4.1. Follicular steroids are indeed indispensable for meiotic maturation
4.2. Shift in steroidogenesis
4.3. Steroidogenic acute regulatory protein
4.4. Cytochrome P45017alpha-hydroxylase/c17-20 lyase
4.5. 3beta-hydroxysteroid dehydrogenase
4.6. 20beta-hydroxysteroid dehydrogenase-like carobonyl reductase
4.7. Transcription factors shift
4.8. Maturation Promoting Factor
4.9. Ovulation
5. Sexual difference in meiosis execution
6. Acknowledgements
7. References


Meiotic maturation is a complex process that involves resumption of meiosis in response to preovulatory luteinizing hormone (LH) surge just before ovulation. High levels of cAMP in oocytes maintain meiotic arrest at diplotene of prophase I in mammals and pisces. In mammals, the process by which LH induces recommencement of meiosis involves breakdown of oocyte-somatic cells communication, which is followed by a drop in intracellular cAMP levels that in turn causes exit from meiotic arrest. Maturation promoting factor (MPF) then accomplishes progression of oocytes to reach first metaphase followed by second metaphase after reinitiating meiosis. Pisces require precise completion of oocyte growth involving vitellogenesis before the entry of meiotic maturation. Then, both mammalian and fish oocytes enters resumption of meiosis involving germinal vesicle breakdown, chromosome condensation, assembly of meiotic spindle, and formation of first polar body. However, this process in pisces is regulated by three major mediators, LH, 17alpha,20beta-dihydroxy progesterone and MPF which are unique. The molecular mechanisms of meiotic maturation and ovulation by comparing mammalian and piscine research have been dealt in this review.