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Transcription reactivation steps stimulated by oocyte maturation in C. elegans.

ABSTRACT: Developing oocytes produce materials that will support early embryonic development then cease transcription before fertilization. Later, a distinct transcription program is established in the embryo. Little is understood about how these global gene regulation transitions are effected. We have investigated in C. elegans how oocyte transcription is influenced by maturation, a process that releases meiotic arrest and prepares for fertilization. By monitoring transcription-associated phosphorylation of the RNA polymerase II (Pol II) C-terminal domain (CTD), we find that oocyte transcription shuts down independently of maturation. Surprisingly, maturation signals then induce CTD phosphorylation that is associated specifically with transcription initiation steps and accumulates to high levels when expression of the CTD phosphatase FCP-1 is inhibited. This CTD phosphorylation is also uncovered when a ubiquitylation pathway is blocked, or when maturation is stimulated precociously. CTD phosphorylation is similarly detected during embryonic mitosis, when transcription is also largely silenced. We conclude that oocyte maturation signals induce abortive transcription events in which FCP-1 may recycle phosphorylated Pol II and that analogous processes may occur during mitosis. Our findings suggest that maturation signals may initiate preparations for embryonic transcription, possibly as part of a broader program that begins the transition from maternal to zygotic gene expression.

SUBMITTER: Walker AK

PROVIDER: S-EPMC1913287 | biostudies-literature | 2007 Apr

REPOSITORIES: biostudies-literature

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Transcription reactivation steps stimulated by oocyte maturation in C. elegans.

Walker Amy K AK Boag Peter R PR Blackwell T Keith TK

Developmental biology 20061223 1

Developing oocytes produce materials that will support early embryonic development then cease transcription before fertilization. Later, a distinct transcription program is established in the embryo. Little is understood about how these global gene regulation transitions are effected. We have investigated in C. elegans how oocyte transcription is influenced by maturation, a process that releases meiotic arrest and prepares for fertilization. By monitoring transcription-associated phosphorylation ...[more]

PMID: 17291483

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Project description:Objective: To evaluate intraday serum progesterone levels on the day of final oocyte maturation in women undergoing ovarian stimulation in a GnRH-antagonist protocol. Study design, size, and duration: The study was done as a prospective observational study at a Private IVF centre in Muscat, Oman. 30 patients were recruited from May 2018 to March 2019. Patients: Thirty patients with primary/secondary infertility and an indication for ovarian stimulation for IVF/ICSI treatment. The study was registered at the clinicaltrials.gov under the number: NCT03519776. Main outcome measures: Progesterone levels at 4 time points (8 a.m., 11 a.m., 2 p.m. and 5 p.m.) on the day of final oocyte maturation. Results: A total of 120 samples from 30 patients were included in this prospective study. Progesterone levels on the day of final oocyte maturation showed a significant decline over the day with the mean values at 8 a.m.:1.0 ng/ml, at 11 a.m.:0.8 ng/ml, at 2 a.m.: 0.7 ng/ml and at 5 p.m.:0.6 ng/ml. The difference between the first and the last progesterone level was 0.4 ng/ml, reflecting a 37.8% decline of the progesterone level within 9 h and there was a highly significant decrease in the progesterone levels recorded between 8 a.m. and 11 a.m., between 8 a.m. and 2 p.m., between 8 a.m. and 5 p.m. and 11 a.m. and 5 p.m. (p < 0.001). Conclusion: The study findings have two clinically important conclusions: Firstly, progesterone levels on the day of final oocyte maturation decline significantly from the morning to the afternoon in patients, questioning the reliability of one arbitrarily taken progesterone level regarding the decision to perform a fresh embryo transfer or to cryopreserve the embryos. Secondly, declining progesterone levels 12 h after the last administration of gonadotropins support the theory that enhanced ovarian stimulation at the end of the follicular phase leads to an overload of the capacity of the enzymes metabolizing progesterone further on, therefore resulting in elevated progesterone levels in circulation.

Project description:BackgroundThe LH surge promotes ovulation via activation of multiple signaling networks in the ovarian follicle. Studies in animal models have shown the importance of LH-induced activation of the epidermal growth factor (EGF)signaling network in critical peri-ovulatory events. We investigated the biological significance of regulatory mechanisms mediated by EGF-like growth factors during LH stimulation in humans.MethodsWe characterized the EGF signaling network in mature human ovarian follicles using in vivo and in vitro approaches. Amphiregulin (AREG) levels were measured in 119 follicular fluid (FF) samples from IVF/ICSI patients. Biological activity of human FF was assessed using in vitro oocyte maturation, cumulus expansion and cell mitogenic assays.ResultsAREG is the most abundant EGF-like growth factor accumulating in the FF of mature follicles of hCG-stimulated patients. No AREG was detected before the LH surge or before hCG stimulation of granulosa cells in vitro, demonstrating that the accumulation of AREG requires gonadotrophin stimulation. Epiregulin and betacellulin mRNA were detected in both human mural and cumulus granulosa cells, although at significantly lower levels than AREG. FF from stimulated follicles causes cumulus expansion and oocyte maturation in a reconstitution assay. Immunodepletion of AREG abolishes the ability of FF to stimulate expansion (P < 0.0001) and oocyte maturation (P < 0.05), confirming the biological activity of AREG. Conversely, mitogenic activity of FF remained after depletion of AREG, indicating that other mitogens accumulate in FF. FF from follicles yielding an immature germinal vesicle oocyte or from an oocyte that develops into an aberrant embryo contains lower AREG levels than that from follicles yielding a healthy oocyte (P = 0.008).ConclusionsEGF-like growth factors play a role in critical peri-ovulatory events in humans, and AREG accumulation is a useful marker of gonadotrophin stimulation and oocyte competence.

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Transcription reactivation steps stimulated by oocyte maturation in C. elegans.

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Transcription reactivation steps stimulated by oocyte maturation in C. elegans.

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