Medically Assisted Conception An Agenda for Research (1989) / Chapter Skim
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Molecular Events Pre- and Post-Fertilization of Mouse Eggs: Oocyte Maturation, Egg Activation, and Polyspermy Block
Molecular Events Pre- and Post-Fertilization of Mouse Eggs: Oocyte Maturation, Egg Activation, and Polyspermy Block
Pages 262-281
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From page 262... ...
ACQUISITION OF MEIOTIC COMPETENCE During the period of oocyte growth, which takes about 14 days, mouse oocytes that are arrested in the first meiotic prophase grow from about 15 Am to 80 Am in diameter. Acquisition of meiotic competence is correlated with a specific stage of oocyte growth.
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From page 263... ...
Results from a series of similar experiments indicated that a constant amount of combined time that totals 15 days of in Vito growth or in vitro culture is necessary for acquisition of meiotic con etence. To provide a tighter correlation between the changes in the proteins synthesized during oocyte growth and the acquisition of meiotic competence, it should be demonstrated that the changes in protein synthesis that occur during oocyte growth also occur under the conditions of in vi tro culture that do not sustain oocyte growth but do foster meiotic competence.
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From page 264... ...
Thus, the mode of action of there compounds may be distal to that of cAMP. These changes in protein phosphorylation do not occur in meiotically incompetent oocytes, but do occur in the lO% of oocytes 60 Am in diameter that can undergo GVBD.
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From page 265... ...
2. .~.ti ~ ~ - Li ILL -ear An activity central to oocyte maturation and subsequent cell cycles is that of Maturation Promoting Factor (MPF)
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From page 266... ...
Meiotically incompetent mouse oocytes also possess an "anti-MPF" activity. Fusion of a meiotically competent oocyte with an intact GV with a meiotically incompetent oocyte preserves the integrity of each nucleus, which resides in the common cytoplasm (Fulka et al., 1985)
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From page 267... ...
All species apparently have mechanisms to block polyspermy. For example, sea urchins possess a fast electrical block that operates at the level of the plasma membrane (Jaffe and Gould, 1983 and references therein)
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From page 268... ...
. Cortical granules subjacent to the plasma membrane are thought to fuse with the plasma membrane and release into the perivitelline space enzymes that convert ZP2 to ZP2f and modify ZP3 such that it no longer possesses either sperm receptor activity or the ability to induce an acrosome reaction.
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From page 269... ...
In turn, this has prevented generation of molecular markers for mammalian cortical granules. Moreover, until recently, the only way to assess accurately the status and distribution of cortical granules was by electron microscopy, which is a tome consuming process and difficult to quantify easily.
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From page 270... ...
The half-maximal concentration of IP3 necessary to elicit the change in ZP3 is about 5 no, and this corresponds well to that necessary to induce the cortical granule-snediated elevation of the fertilization envelope in sea urchin eggs, as well as calcium release f ram intracellular stores in other systems (Whitaker and Irvine, 1984; Swann and Whitaker, 198 6)
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From page 271... ...
The lower level of sperm binding to IP3-injected eggs is therefore likely to be due to a reduced level of ZP3 sperm receptor activity. Fertilization is associated with a characteristic set of changes in the pattern of protein synthesis.
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From page 272... ...
In addition, the development of cortical granule probes may be used to study cortical granule biogenesis and to reveal if there is a heterogeneity in the cortical granule population. Electron microscopy studies reveal the existence of light and dark staining populations of cortical granules in mouse eggs (Nicosia et al., 1977)
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From page 273... ...
. Future studies addressing functional aspects of these gene products, coupled with the recent purification and identification of maturation promoting factor as a homolog of the fission yeast cell cycle control protein encoded by the cdc2+ gene will undoubtedly shed light on the process of meiotic maturation at the molecular level and define more clearly the role of protein phosphorylation in regulating this process.
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From page 274... ...
and R.M.S. would like to thank Philip Hugo for assistance with some of the experiments described above and Jeff Bleil for stimulating discussions about the role of ZP2 in sperm binding.
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From page 275... ...
. Immunocytochemical evidence suggesting heterogeneity in the population of sea urchin egg cortical granules.
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From page 276... ...
. Protein phosphorylation in meiotically competent and incompetent mouse oocytes.
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From page 277... ...
. Effects of a phorbol ester on mouse eggs: Dissociation of sperm receptor activity from acrosome reaction-inducing activity of the mouse zone pellucida protein, ZP3.
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From page 278... ...
. Cortical granule distribution and cell surface characteristic~ in mouse eggs.
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From page 279... ...
. Meiotic maturation of mouse oocytes in vitro: Protein synthesis In nucleate and anucleate oocyte fragments.
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(1986) The cell cycle control gene cdc2+ of fission yeast encoder a protein kinase potentially regulated by phosphorylation.
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From page 281... ...
. Induction of zonal and oolemmal blocks to sperm penetration in mouse eggs with cortical granule exudate.
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