Observations on ovarian follicle ultrastructure in the marine teleost, Pagrus major, during vitellogenesis and oocyte maturation

Activin is a dimeric protein consisting of two similar but distinct β-subunits, βA and βB. In our previous studies, both activin A (βAβA) and activin B (βBβB) have been demonstrated to stimulate oocyte maturation and promote oocyte maturational competence in the zebrafish. Follistatin, a specific activin-binding protein, can block both activin- and gonadotropin-induced final oocyte maturation in vitro, suggesting that activin is likely a downstream mediator of gonadotropin actions in the zebrafish ovary. In the present study, a full-length cDNA encoding zebrafish ovarian activin βA was cloned and sequenced. The precursor of zebrafish activin βA consists of 395 amino acids and its mature region exhibits about 78% homology with that of mammals. Using an in vitro primary culture of the ovarian follicle cells and semiquantitative RT-PCR assays, we examined the regulation of activin βA and βB expression by human chorionic gonadotropin (hCG) and its intracellular signal transduction mechanisms. hCG (15 IU/ml) increased the mRNA level of activin βA-subunit; however, it significantly down-regulated the steady-state expression level of activin βB in a time- and dose-dependent manner. The differential regulation of the two β-subunits by hCG could be mimicked by 3-isobutyl-1-methylxanthine, forskolin, and dibutyryl-cAMP, suggesting involvement of the intracellular cAMP pathway. Interestingly, H89 (a specific inhibitor of protein kinase A, PKA) could effectively block hCG- and forskolin-stimulated activin βA expression at 10 μm, but it was unable to reverse the inhibitory effects of hCG and forskolin on βB expression. This suggests that the hCG-stimulated activin βA expression is dependent on the activation of the cAMP-PKA pathway, whereas the inhibitory effect of hCG on activin βB expression is likely mediated by PKA-independent pathway(s).

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Membrane estrogen receptor (GPER) and follicle-stimulating hormone receptor heteromeric complexes promote human ovarian follicle survival

10.1101/2020.04.21.053348 ◽

2020 ◽

Author(s):

Livio Casarini ◽

Clara Lazzaretti ◽

Elia Paradiso ◽

Silvia Limoncella ◽

Laura Riccetti ◽

...

Keyword(s):

Estrogen Receptor ◽

Cell Viability ◽

Oocyte Maturation ◽

Granulosa Cells ◽

Hormone Receptor ◽

Ovarian Follicle ◽

Follicle Stimulating Hormone ◽

Oocyte Growth ◽

Expression Levels ◽

Stimulating Hormone

AbstractClassically, follicle stimulating hormone receptor (FSHR) driven cAMP-mediated signaling boosts human ovarian follicle growth and would be essential for oocyte maturation. However, contradicting in vitro suggest a different view on physiological and clinical significance of FSHR-mediated cAMP signaling. We found that the G protein coupled estrogen receptor (GPER) heteromerizes with FSHR, reprogramming cAMP/death signals into proliferative stimuli fundamental for sustaining oocyte survival. In human granulosa cells, survival signals are effectively delivered upon equal expression levels of both receptors, while they are missing at high FSHR:GPER ratio, which negatively impacts follicle maturation and strongly correlates with FSH responsiveness of patients undergoing controlled ovarian stimulation. Consistent with high FSHR expression levels during follicular selection, cell viability is dramatically reduced in FSHR overexpressing cells due to preferential coupling to the Gαs protein/cAMP pathway. In contrast, FSHR/GPER heteromer formation resulted in FSH-triggered anti-apoptotic/proliferative signaling delivered via the Gβγ dimer while heteromer impairment or GPER-associated Gαs inhibitory protein complexes resulted in cell death. GPER-depleted granulosa cells have an amplified FSH-dependent decrease in cell viability and steroidogenesis, consistent with the requirement of estrogen signaling for successful oocyte growth. Therefore, our findings indicate how oocyte maturation depends on the capability of GPER to shape FSHR selective signals, indicating hormone receptor heteromers may be a marker of cell proliferation.One Sentence SummaryFSHR/GPER heteromers block cAMP-dependent selection of ovarian follicles and target tumor growth and poor FSH-response in women.

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1-Methyladenine: a starfish oocyte maturation-inducing substance

Zygote ◽

10.1017/s0967199400130047 ◽

1999 ◽

Vol 8 (S1) ◽

pp. S9-S11 ◽

Cited By ~ 4

Author(s):

Masatoshi Mita

Keyword(s):

Oocyte Maturation ◽

Hormone Receptor ◽

Ovarian Follicle ◽

Germinal Vesicle ◽

Follicle Cells ◽

Glycoprotein Hormone ◽

Late Prophase ◽

Immature Oocytes ◽

Extracellular Region ◽

Glycoprotein Hormone Receptor

1-Methyladenine (1-MeAde) in starfish was the first compound to be identified as an oocyte maturation-inducing substance (MIS) among invertebrates in 1969 by Kanatani and co-workers. In starfish, the ripe ovary contains a huge number of fully grown oocytes of almost equal size. Each oocyte possesses a large nucleus (germinal vesicle, GV), which is arrested in late prophase of the first maturation division. The oocyte is surrounded by a single follicle layer. Such immature oocytes are not fertilisable. Resumption of meiosis in immature oocytes can be induced by 1-MeAde, and the mature oocytes thus become fertilisable (Kanatani et al., 1969; Kanatani, 1985). 1-MeAde is produced by ovarian follicle cells upon stimulation with a gonad-stimulating substance (GSS) released from the radial nerves (Fig. 1).It has been demonstrated that GSS is a peptide hormone (Kanatani et al., 1971). The action of GSS on 1-MeAde production in follicle cells appears to be mediated by its receptor, G-proteins and adenylyl cyclase (Mita & Nagahama, 1991). These findings suggest that a G-protein coupled (seven transmembrane type) receptor is involved in GSS signal transduction, similarly to the pituitary-gonadal axis in vertebrates.Thus, using degenerate probes derived from consensus sequences of the mammalian glycoprotein hormone (GTH and TSH) receptors, cDNA was cloned from mRNA of ovaries of Asterina pectinifera. The cDNA showed striking structural homology with members of the glycoprotein hormone receptor family in the transmembrane region, and contained a very large extracellular region. Expression was observed in isolated ovarian follicle cells. Thus, it seems likely that the glycoprotein hormone receptor (GTHR) family gene is related to GSS receptor in ovarian follicle cells. The phylogenic relatedness of the starfish GTHR was also assessed in relation to other vertebrate GTHRs. The analysis showed that the starfish gene diverged before differentiation of the gonadotropin (LH and FSH) and TSH receptors in vertebrates.

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