Roles of gene transcription and PKA subtype activation in maturation of murine oocytes

Department of Animal Science, North Carolina State University, 231B Polk Hall, Raleigh, NC 27695-7621, USA.
Reproduction (Cambridge, England) (Impact Factor: 3.17). 07/2002; 123(6):799-806. DOI: 10.1530/rep.0.1230799
Source: PubMed


The aims of this study were to examine the role of transcription and the coincident involvement of type I and type II protein kinase A (PKA) in the resumption of meiosis in murine cumulus-oocyte complexes (COCs) using the transcriptional inhibitors 5,6-dichloro-1-beta-D-ribofuranosylbenzimidazole (DRB) and alpha-amanitin. The first series of experiments was designed to: (i) characterize the role of transcription in gonadotrophin-mediated and spontaneous maturation of murine oocytes; (ii) examine the roles of specific gonadotrophins (FSH versus hCG) and cumulus cells in transcriptionally mediated oocyte maturation; and (iii) determine the reversibility of the transcriptional arrest of meiosis. In the presence of FSH, transcriptional inhibitors arrested germinal vesicle breakdown (GVBD) (DRB: 2 +/- 2% and control: 76 +/- 2%; alpha-amanitin: 4 +/- 4% and control: 70 +/- 4%). Furthermore, cumulus cells were required for transcriptional inhibitors to arrest GVBD (DRB with cumulus cells: 0 +/- 15%; DRB without cumulus cells: 94 +/- 13%; alpha-amanitin with cumulus cells: 15 +/- 2%; alpha-amanitin without cumulus cells: 99 +/- 2%). Thus, in mice, FSH-mediated GVBD uses a transcriptional mechanism, which probably occurs within the cumulus cell compartment. In a second series of experiments, the role of transcription in mediating the resumption of meiosis after activation of either type I or type II PKA was examined. Activation of type I PKA in murine COCs resulted in an arrest of GVBD that was independent of a transcriptional event (with DRB: 7 +/- 9% GVBD; without DRB: 11 +/- 9% GVBD). In contrast, activation of type II PKA resulted in a resumption of meiosis, which required the occurrence of gene transcription (with DRB: 12 +/- 9% GVBD; without DRB: 80 +/- 9% GVBD). As FSH binding to cumulus cells activates the PKA second messenger system, our results indicate that, in cultured murine COCs, FSH binding to cumulus cells results in the activation of type II PKA, which, in turn, mediates a downstream transcriptional event required for the initiation of GVBD.

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Available from: Robert M Petters
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    • "FSHR is a GPCR (G-protein-coupled receptor) with a specific seven-transmembrane domain that was shown to activate the classical FSHR/AC/cAMP/PKA pathway. Among the two activated isoforms of PKA, only PKAII was shown to be involved in the transcriptional events in CCs required for meiosis resumption (GVBD) [74,75]. This de novo gene expression is indispensable for gonadotropin-induced oocyte maturation in murine and feline species [75,76] and was shown to involve the MAPK downstream of the cAMP-dependent PKA pathway in most mammals including mouse [77,78], rat [79] and cow [80]. "
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    ABSTRACT: The use of gonadotropins to trigger oocyte maturation both in vivo and in vitro has provided precious and powerful knowledge that has significantly increased our understanding of the ovarian function. Moreover, the efficacy of most assisted reproductive technologies (ART) used in both humans and livestock species relies on gonadotropin input, mainly FSH and LH. Despite the significant progress achieved and the huge impact of gonadotropins, the exact molecular pathways of the two pituitary hormones, FSH and LH, still remain poorly understood. Moreover, these pathways may not be the same when moving from the in vivo to the in vitro context. This misunderstanding of the intricate synergy between these two hormones leads to a lack of consensus about their use mainly in vitro or in ovulation induction schedules in vivo. In order to optimize their use, additional work is thus required with a special focus on comparing the in vitro versus the in vivo effects. In this context, this overview will briefly summarize the downstream gene expression pathways induced by both FSH in vitro and LH in vivo in the cumulus compartment. Based on micro array recent comparative analysis, we are reporting that in vitro FSH stimulation on cumulus cells appears to achieve at least part of the gene expression activity after in vivo LH stimulation. We are then proposing that the in vitro FSH-response of cumulus cells have similitudes with the in vivo LH-response.
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    • "It was concluded that type I PKA in the oocyte mediates meiotic arrest, while type II PKA in the granulosa cells mediates maturation of the oocyte–cumulus cell complex. Similar conclusions were drawn from studies by Rodriguez et al. (2002). However, more recent reports have demonstrated the presence of both type I and II regulatory PKA isoforms in mouse oocytes (Brown et al., 2002; Newhall et al., 2006), and in one of these studies (Newhall et al., 2006) a combination of site-selective cAMP analogs that preferentially stimulate type II PKA isoforms were presented as more potent in maintaining meiotic arrest when compared with a combination that selectively activated type I PKA, with the conclusion that type II PKA is the more relevant isoform performing this function. "
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    ABSTRACT: Regulation of maturation in meiotically competent mammalian oocytes is a complex process involving the carefully coordinated exchange of signals between the somatic and germ cell compartments of the ovarian follicle via paracrine and cell-cell coupling pathways. This review highlights recent advances in our understanding of how such signaling controls both meiotic arrest and gonadotropin-triggered meiotic resumption in competent oocytes and relates them to the historical context. Emphasis will be on rodent systems, where many of these new findings have taken place. A regulatory scheme is then proposed that integrates this information into an overall framework for meiotic regulation that demonstrates the complex interplay between different follicular compartments.
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    • "The pathway used by FSH to stimulate GVBD appears to involve cAMP-mediated activation of PKA that, in turn, leads to activation of MAPK (Su et al., 2002). Because activation of both Type II PKA and MAPK can each stimulate transcription as a downstream effect (Rodriguez et al., 2002; Conti et al., 2006), it would be likely that these activation events precede the transcriptional step required in the mechanism used by FSH to mediate meiotic resumption. "
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