Medically Assisted Conception An Agenda for Research (1989) / Chapter Skim
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Mammalian Oocyte Maturation: Mechanisms for Regulation and Prospects for Practical Application of In Vitro Technology
Mammalian Oocyte Maturation: Mechanisms for Regulation and Prospects for Practical Application of In Vitro Technology
Pages 176-190
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From page 176... ...
The Ovarian Follicle as the Support System for Oocyte Development In Viva After a period of mitotic proliferation in the fetus, oogonia enter meiosis, but the germ cells now called oocytes progress only as far as the diplotene stage where they are arrested until shortly before ovulation. Diplotene oocytes develop a close association with somatic cells that are probably progenitors of granulosa cells and form a primordial follicle.
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From page 177... ...
Once meiotic competence is achieved , granulosa cel is , via gap junctional communication, help to maintain the oocyte in meiotic arrest (Eppig and Downs, 1987~. Because cumulus granulosa cells are coupled by gap junctions to the oocyte and to the mural granulosa cells which make up the follicle wall, the follicle may be a functional syncytium allowing the movement of low molecular weight molecules throughout the follicle by diffusion.
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From page 178... ...
In addition, murine follicular fluid was found to contain substantial amounts of adenosine. Although it is still possible that the concentration of hypaxanthine in mouse follicular fluid is not as high as reported because of rapid intrafollicular changes, it should be kept in mind that the ovarian follicle is not vascularized central to the thecal layers and a low oxygen concentration may be a natural condition in situ.
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From page 179... ...
Because of the evidence indicating the importance of cAMP in maintaininq meiotic arrest in mouse oocytes, the hypothesis that purines, particularly hypoxanthine and adenosine, may maintain meiotic arrest by promoting meiosis-blocking levels of cAMP in oocytes was tested. The maintenance of meiotic arrest was correlated with elevated cAMP levels in cumulus cell-enclosed oocytes cultured in medium containing hypoxanthine or hypoxanthine plus adenosine .
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From page 180... ...
It is possible that there are differences between the movement of the molecular markers used to measure gap junctional communication and the movement of meiosis-arresting substances, but if they are analogous, then it can be concluded that a disruption in the communication between cumulus cells and the oocyte is not the mechanism of LH-induced oocyte maturation. It has been suggested that LH induces a reduction in the communication between the mural granulosa cells and cumulus cells and tbereby reduces the movement of meiosis-arresting substances to the oocyte-cumulus cell complex (Larsen et al., 19873.
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From page 181... ...
Similarities Between Mechanisms that Govern Meiotic and Mitotic Cel 1 · · ~ Division ~ There are several lines of evidence suggesting that mechanisms that govern the induction of oocyte maturation are similar to the mechanisms involved in the induction of mitotic cell division. First, an autocatalytic maturation-promoting factor (MPF)
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From page 182... ...
Much remains to be done, however, to resolve the optimal conditions for oocyte maturation for each species that will promote maximal developmental potential. Murine oocytes indicate that oocytes sequentially develop competence for maturation, then fertilization and cleavage to the two-cel1 stage, and then development to blastocyst (Eppig and Schroeder, 1989~.
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From page 183... ...
This technology would be applicable to the expansion of populations of agriculturally important animals such as those that have been genetically engineered for desirable characteristics, of important genetically engineered experimental animals, or of endangered species. Our culture system for murine oocyte maturation in vitro rescues degenerating oocytes from deceased mice.
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From page 184... ...
Clinical realization of maturation in vitro as an antecedent to IVF will require basic studies to resolve likely differences in conditions for oocyte maturation that impart full developmental capacity between human and mouse oocytes. It would probably be advantageous and appropriate to carry out initial studies using non-human primate oocytes.
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From page 185... ...
Acknowledgments Research in my laboratory is supported by grants HD20575, HD21970 and ED23839 from the National Institutes of Health. The contents of this paper do not necessarily represent the official views of that agency.
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From page 186... ...
1982. Intercellular communication between granulosa cells and mouse oocytes: existence and possible nutritional role during oocyte growth.
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From page 187... ...
1988. Induction: of maturation in cumulus cell-enclosed mouse oocytes by follicle-stimulating hormone and epidemical growth factor: evidence for a positive stimulus of somatic cell origin.
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From page 188... ...
1984. Regulation of mouse oocyte growth: probable nutritional role for intercellular communication between follicle cells and oocytes in oocyte growth.
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From page 189... ...
1984. The developmental capacity of mouse oocytes that matured spontaneously in vitro is normal.
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From page 190... ...
1983. Regulation of mouse oocyte maturation: implication of a decrease in oocyte cAMP and protein dephosphorylation in commitment to resume meiosis.
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