Journal Article•
Gonadotropin action on gametogenesis and steroidogenesis in teleost gonads
About: This article is published in Zoological Science.The article was published on 1987-04-01 and is currently open access. It has received 202 citations till now. The article focuses on the topics: Gonadotropin & Gametogenesis.
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TL;DR: Findings on the identification of steroidal mediators involved in each process of gametogenesis, and the sites and mechanisms of action of the mediators are reviewed.
Abstract: The pituitary-gonadal axis plays an important role in regulating gametogenesis in vertebrates. In most cases, gonadotropins act through the biosynthesis of gonadal steroid hormones which in turn mediate various stages of gametogenesis. A series of studies in our laboratory using several species of teleost fishes as experimental animals has provided new information about the endocrine regulation of gametogenesis, including oocyte growth, oocyte maturation, spermatogenesis and sperm maturation. This article briefly reviews our findings on the identification of steroidal mediators involved in each process of gametogenesis, and the sites and mechanisms of action of the mediators. These observations collectively demonstrate the appropriateness of using teleost fishes as valid models for examining hormonal influences on gametogenesis. Such models could also have applications and validity for vertebrates in general.
733 citations
Cites background from "Gonadotropin action on gametogenesi..."
...This finding implies that there may be little species specificity ot each of these cell layers among salmonids (Nagahama, 1987b)....
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...In this model, the thecal cell layer, under the influence of gonadotropin, secretes the androgen substrate (probably testosterone) which diffuses into the granulosa cell layer where the aromatase is localized exclusively (Kagawa el al., 1985; Nagahama, 1987b; Adachi el al., 1990)....
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TL;DR: This article showed that oocyte maturation is a three-step induction process involving gonadotropin (LH), maturation-inducing hormone (MIH), and maturationpromoting factor (MPF).
Abstract: 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.
698 citations
TL;DR: The effects of temperature and pH on the motility of spermatozoa in three fish species: salmonids, cyprinids and sturgeons are reviewed and summarized.
351 citations
Cites background from "Gonadotropin action on gametogenesi..."
...Miura et al. (1991), Nagahama (1987, 1994) and Yaron (1995) studied the endocrinological mechanisms involved in sperm motility....
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TL;DR: Of considerable interest is the finding that MIH, unlike most steroid hormones, acts on its receptors at the surface of oocytes, and the mechanism of MIH-induced MPF activation in fish oocytes differs from that in Xenopus and starfish.
Abstract: Publisher Summary This chapter discusses the current status of the investigations on the hormonal regulation of oocyte growth and maturation in fish. Pituitary gonadotropins are of primary importance in triggering these processes in fish oocytes. In both cases, however, the actions of gonadotropins are not direct but are mediated by the follicular production of steroidal mediators, estradiol-17β (oocyte growth), and 17α,20β-dihydroxy-4-pregnene-3-one (DP) or 4-pregnen-17,20β,21-triol-3-one (20β-S) (oocyte maturation). It has been established that both estradiol- 17β and 17α,20β-DP are biosynthesized by salmonid ovarian follicles through an interaction of two cell layers—namely, the thecal and the granulosa cell layers (two-cell-type model). The granulosa cell layers are the sites of production of these two steroidal mediators, but their production depends on the provision of the precursor steroids by the thecal cell layers.
347 citations
TL;DR: It is demonstrated that BKME exposure affects reproduction by acting at multiple sites in the pituitary-gonadal axis by reducing responsiveness to the GtH analog human chorionic gonadotropin and to forskolin, a direct activator of adenylate cyclase.
276 citations