Regulation of oocyte maturation in fish
Article first published online: 14 MAY 2008
© 2008 The Authors. Journal compilation © 2008 Japanese Society of Developmental Biologists
Development, Growth & Differentiation
Special Issue: Special ISSUE for the 50th Volume: History and Current Highlights of Developmental Biology
Volume 50, Issue Supplement s1, pages S195–S219, June 2008
How to Cite
Nagahama, Y. and Yamashita, M. (2008), Regulation of oocyte maturation in fish. Development, Growth & Differentiation, 50: S195–S219. doi: 10.1111/j.1440-169X.2008.01019.x
- Issue published online: 14 MAY 2008
- Article first published online: 14 MAY 2008
- Received 22 February 2008; accepted 24 February 2008.
- oocyte maturation;
- maturation-inducing hormone;
- maturation-promoting factor
A period of oocyte growth is followed by a process called oocyte maturation (the resumption of meiosis) which occurs prior to ovulation and is a prerequisite for successful fertilization. Our studies using fish models have revealed that oocyte maturation is a three-step induction process involving gonadotropin (LH), maturation-inducing hormone (MIH), and maturation-promoting factor (MPF). LH acts on the ovarian follicle layer to produce MIH (17α, 20β-dihydroxy-4-pregnen-3-one, 17α, 20β-DP, in most fishes). The interaction of ovarian thecal and granulosa cell layers (two-cell type model), is required for the synthesis of 17α,20β-DP. The dramatic increase in the capacity of postvitellogenic follicles to produce 17α,20β-DP in response to LH is correlated with decreases in P450c17 (P450c17-I) and P450 aromatase (oP450arom) mRNA and increases in the novel form of P450c17 (P450c17-II) and 20β-hydroxysteroid dehydrogenase (20β-HSD) mRNA. Transcription factors such as Ad4BP/SF-1, Foxl2, and CREB may be involved in the regulation of expression of these steroidogenic enzymes. A distinct family of G-protein-coupled membrane-bound MIH receptors has been shown to mediate non-genomic actions of 17α, 20β-DP. The MIH signal induces the de novo synthesis of cyclin B from the stored mRNA, which activates a preexisting 35 kDa cdc2 kinase via phosphorylation of its threonine 161 by cyclin-dependent kinase activating kinase, thus producing the 34 kDa active cdc2 (active MPF). Upon egg activation, MPF is inactivated by degradation of cyclin B. This process is initiated by the 26S proteasome through the first cut in its NH2 terminus at lysine 57.