Dataset Information

Oocyte Maturation in Starfish.

ABSTRACT: Oocyte maturation is a process that occurs in the ovaries, where an immature oocyte resumes meiosis to attain competence for normal fertilization after ovulation/spawning. In starfish, the hormone 1-methyladenine binds to an unidentified receptor on the plasma membrane of oocytes, inducing a conformational change in the heterotrimeric GTP-binding protein ?-subunit (G?), so that the ?-subunit binds GTP in exchange of GDP on the plasma membrane. The GTP-binding protein ??-subunit (G??) is released from G?, and the released G?? activates phosphatidylinositol-3 kinase (PI3K), followed by the target of rapamycin kinase complex2 (TORC2) and 3-phosphoinositide-dependent protein kinase 1 (PDK1)-dependent phosphorylation of serum- and glucocorticoid-regulated kinase (SGK) of ovarian oocytes. Thereafter, SGK activates Na+/H+ exchanger (NHE) to increase the intracellular pH (pHi) from ~6.7 to ~6.9. Moreover, SGK phosphorylates Cdc25 and Myt1, thereby inducing the de-phosphorylation and activation of cyclin B-Cdk1, causing germinal vesicle breakdown (GVBD). Both pHi increase and GVBD are required for spindle assembly at metaphase I, followed by MI arrest at pHi 6.9 until spawning. Due to MI arrest or SGK-dependent pHi control, spawned oocytes can be fertilized normally.

SUBMITTER: Chiba K

PROVIDER: S-EPMC7072822 | biostudies-literature | 2020 Feb

REPOSITORIES: biostudies-literature

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Oocyte Maturation in Starfish.

Chiba Kazuyoshi K

Cells 20200219 2

Oocyte maturation is a process that occurs in the ovaries, where an immature oocyte resumes meiosis to attain competence for normal fertilization after ovulation/spawning. In starfish, the hormone 1-methyladenine binds to an unidentified receptor on the plasma membrane of oocytes, inducing a conformational change in the heterotrimeric GTP-binding protein α-subunit (Gα), so that the α-subunit binds GTP in exchange of GDP on the plasma membrane. The GTP-binding protein βγ-subunit (Gβγ) is released ...[more]

PMID: 32092921

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Project description:Study questionDoes exposure to bisphenol-A (BPA) affect the maturation of human oocytes in vitro?Summary answerThere was a dose-response association of BPA exposure with altered human oocyte maturation in vitro.What is known alreadyThere is widespread exposure of the general population to BPA. BPA has been detected in the human follicular fluid. Animal studies have shown that BPA exposure is associated with maturation arrest and spindle abnormalities in maturing oocytes.Study design, size, durationA randomized trial, using 352 clinically discarded oocytes from 121 patients.Participants/materials, setting, methodsThe study population was drawn from patients undergoing IVF/ICSI cycles in our program at Brigham and Women's Hospital from March 2011 to April 2012. Oocytes from only one cycle for each patient were included in the study. Cycles with at least two germinal vesicle stage oocytes were included with random allocation of one oocyte to culture for 30 h without BPA and remaining sibling oocytes to medium-containing BPA (20, 200 ng/ml or 20 µg/ml). Oocytes were fixed and labeled for tubulin, actin and chromatin and examined with immunofluorescence and confocal microscopy. Oocytes were assessed for meiotic stage (n = 292), and those at metaphase II (MII, n = 175) were further classified according to their spindle configurations and patterns of chromosome alignment. McNemar's test was used to compare dichotomized maturation status. Generalized estimating equations were used to account for the correlation between oocytes from the same woman and for the spindle analysis.Main results and the role of chanceAs the BPA dose increased, there was a decrease in the percentage of oocytes that progressed to MII (P = 0.002) and increases in the percentage of oocytes that were degenerated (P = 0.01) or that had undergone spontaneous activation (P = 0.007). Among MII oocytes, as the BPA dose increased, there was a significant trend (by test for trend) for a decreased incidence of bipolar spindles (P < 0.0001) and aligned chromosomes (P = 0.02).Limitations, reasons for cautionAlthough we used sibling oocytes to overcome potential confounders, such as infertility diagnosis and maternal age, additional studies with a larger number of oocytes are required to confirm the present results. Having access only to clinically discarded oocytes, we were limited to evaluating only those oocytes that failed to mature in vivo despite having been exposed to gonadotrophin stimulation and the ovulatory trigger of HCG.Wider implications of the findingsTo our knowledge, this is the first study investigating the effect of BPA on oocyte meiotic maturation, spindle morphology and chromosome alignment in human oocytes. Together with prior animal studies, the data support the negative influences of BPA on cell cycle progression, spindle architecture and chromosome organization during oocyte maturation. Furthermore, the increased rates of abnormal maturation in oocytes exposed to BPA may be relevant to our understanding of the decrease in fertility reported in the last decades.Study funding/competing interest(s)This study was funded by the NIEHS Center Grant Pilot Project (P30-ES000002). R.M. was sponsored by a fellowship from the Environmental Health Fund, Israel and by the Frederick L. Hisaw Endowment, Harvard School of Public Health. There are no conflicts of interest.Trial registration numbern/a.

Dataset Information

Oocyte Maturation in Starfish.

Publications

Oocyte Maturation in Starfish.

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