Regulation of oocyte maturation in fish.
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.
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TL;DR: Recent advances on teleost fish oocyte differentiation, maturation and ovulation are highlighted, including those involved in the degeneration and reabsorption of ovarian follicles (atresia).
910 citations
TL;DR: Control of reproductive function in captivity is essential for the sustainability of commercial aquaculture production, and in many fishes it can be achieved by manipulating photoperiod, water temperature or spawning substrate, but a common question in regards to hormonal therapies is their effect on gamete quality.
531 citations
TL;DR: Recombinant fish GtHs were produced for carp, seabream, channel and African catfish, goldfish, eel, tilapia, zebrafish, Manchurian trout and Orange-spotted grouper, where FSHR expression in Leydig cells explains the strong steroidogenic activity of FSH in certain fish species.
468 citations
TL;DR: Many aspects of progestin signaling through these two families of novel membrane proteins remain unresolved, but evidence has been obtained that PGMRC1 mediates the antiapoptotic affects of progesterone in rat granulosa cells.
350 citations
TL;DR: Findings suggest that 17 alpha,20 beta-DP initiates translation of cyclin B mRNA through cytoplasmic 3' poly(A) elongation.
330 citations
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TL;DR: The lability of sex-determination systems in fish makes some species sensitive to environmental pollutants capable of mimicking or disrupting sex hormone actions, and such observations provide important insight into potential impacts from endocrine disruptors, and can provide useful monitoring tools for impacts on aquatic environments.
2,283 citations
TL;DR: Results provide direct support for progesterone's role as a pleiotropic coordinator of diverse reproductive events that together ensure species survival.
Abstract: Although progesterone has been recognized as essential for the establishment and maintenance of pregnancy, this steroid hormone has been recently implicated to have a functional role in a number of other reproductive events. The physiological effects of progesterone are mediated by the progesterone receptor (PR), a member of the nuclear receptor superfamily of transcription factors. In most cases the PR is induced by estrogen, implying that many of the in vivo effects attributed to progesterone could also be the result of concomitantly administered estrogen. Therefore, to clearly define those physiological events that are specifically attributable to progesterone in vivo, we have generated a mouse model carrying a null mutation of the PR gene using embryonic stem cell/gene targeting techniques. Male and female embryos homozygous for the PR mutation developed normally to adulthood. However, the adult female PR mutant displayed significant defects in all reproductive tissues. These included an inability to ovulate, uterine hyperplasia and inflammation, severely limited mammary gland development, and an inability to exhibit sexual behavior. Collectively, these results provide direct support for progesterone's role as a pleiotropic coordinator of diverse reproductive events that together ensure species survival.
1,785 citations
TL;DR: Fully grown oocytes of the frog (Rana pipiens) undergo cytoplasmic and nuclear maturation when treated with progesterone after the follicular envelopes have been removed, and the arrest of mitosis and cleavage can be attributed to a specific “cytostatic factor” in the cy toplasm of the secondary oocyte.
Abstract: Fully grown oocytes of the frog (Rana pipiens) undergo cytoplasmic and nuclear maturation when treated with progesterone after the follicular envelopes have been removed. The mechanism of this maturation was investigated by injection of cytoplasm from progesterone-treated oocytes at various stages of maturation into fully grown but immature oocytes. The injected cytoplasm becomes effective in inducing maturation by 12 hours after progesterone administration, reaches a maximum effectiveness around 20 hours, and then declines after the donor oocytes complete maturation. However, even cytoplasm from early embryos retains some capacity to induce oocyte maturation. The frequency with which maturation is induced is proportional to the volume of the injected cytoplasm. Progesterone itself is not directly responsible for the maturation-producing effect of injected cytoplasm since injected progesterone does not promote maturation. However, externally applied progesterone does induce the completion of the first meiotic division, presumably by releasing a cytoplasmic “maturation promoting factor.” The production of this cytoplasmic factor was not affected by removal of the nucleus.
After completion of the first meiotic division, oocytes cease further development at the metaphase of the second meiotic division, where they remain until fertilized or activated to develop. Cytoplasm from such secondary oocytes when injected into one of the blastomeres at the two-cell stage of development suppresses mitosis as well as cleavage. Mitosis is usually arrested at metaphase. No such inhibition was brought about by injection of cytoplasm from cleaving blastomeres. Thus, the arrest of mitosis and cleavage can be attributed to a specific “cytostatic factor” in the cytoplasm of the secondary oocyte. Activation of donor secondary oocytes by insemination or pricking with a glass needle soon destroys the cytostatic factor. Likewise, addition of cortical cytoplasm to endoplasm from the secondary oocyte rapidly destroys the cytostatic capacity. This result implies that cortical material is involved in the process of removing the cytostatic factor at the time of normal activation or fertilization. Enucleation of oocytes demonstrated that production and removal of the cytostatic factor is independent of the nucleus.
1,508 citations
TL;DR: Eggs of the sea urchin Lytechinus pictus and oocytes of the surf clam Spisula solidissima also contain proteins that only start to be made after fertilization and are destroyed at certain points in the cell division cycle, and it is proposed to call these proteins the cyclins.
1,488 citations
TL;DR: Teleosts offer examples of virtually every conceivable type of ovarian physiology and provide a wealth of experimental material for exploring the cellular and hormonal mechanisms which regulate oocyte recruitment and growth throughout ovarian recrudescence.
Abstract: SYNOPSIS. Four principal stages of oocyte growth are recognized among teleosts. During gonadotropin-independent primary growth, multiple nucleoli form as well as a Balbiani body which eventually disperses throughout the ooplasm. The first gonadotropin-dependent stage involves the formation of yolk vesicles, the precursors to the cortical alveoli. True vitellogenesis follows during which vitellogenin is sequestered from the maternal blood and packaged into yolk granules or spheres. The latter generally fuse centripetally at some time during oocyte growth to give a continuous fluid phase surrounded by a peripheral layer of cytoplasm containing the cortical alveoli. Maturation represents the final stage and is accompanied in many teleosts by water uptake; among marine teleosts with pelagic eggs, most of the final egg volume may be achieved by this process. Ovaries may be synchronous, asynchronous, or group-synchronous. Among the latter, a clutch of oocytes may be recruited from an asynchronous population of earlier stages into any of the subsequent stages. In teleosts which spawn repeatedly, recruitment of new clutches can usually be associated with the transition of a previously recruited clutch from one stage to the next. Teleosts thus offer examples of virtually every conceivable type of ovarian physiology and provide a wealth of experimental material for exploring the cellular and hormonal mechanisms which regulate oocyte recruitment and growth throughout ovarian recrudescence.
1,270 citations