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Cell cycle dynamics of maturation-promoting factor during mouse oocyte maturation
1Laboratory of Reproductive Biology, National Institute for Basic Biology, Okazaki, Japan.
Abstract:
The changes in activity of a cytoplasmic maturation-promoting factor (MPF), capable of inducing resumption of meiosis when injected into starfish oocytes, were examined during mouse oocyte maturation. MPF appeared first at the time of germinal vesicle breakdown (GVBD), and its activity fluctuated along with the meiotic cycle: it reached a peak at the first metaphase and disappeared at the first polar body emission. Then MPF reappeared and reached a peak again at the second metaphase. Thus, a good correlation was found between MPF activity and meiotic metaphase. When mouse oocytes were treated with cytochalasin D, metaphase chromosomes and meiotic spindles were maintained after the first metaphase. In such a case, MPF activity remained at an elevated level after the first peak. Addition of cycloheximide to these cytochalasin-treated oocytes caused diminution of MPF activity, followed by chromosome movement, decondensation and formation of nucleus-like structures. Thus, it is likely that disappearance of MPF activity induces transition from metaphase to the subsequent processes. Further, detailed observation of chromosomes revealed that only the monovalent chromosomes were competent to decondense in response to the disappearance of MPF. Therefore, it was suggested that dissociation of synapsis is necessary for the decondensation of chromosomes.
Insights
Maturation-promoting factor (MPF) activity correlates with meiotic metaphase in mouse oocytes. Its disappearance triggers chromosome decondensation and progression, suggesting synapsis dissociation is key for this process.
Area of Science:
- Cell Biology
- Developmental Biology
- Reproductive Biology
Background:
- Cytoplasmic maturation-promoting factor (MPF) regulates meiosis resumption.
- Understanding MPF dynamics is crucial for comprehending oocyte maturation.
- Mouse oocyte maturation involves complex cell cycle events.
Purpose of the Study:
- To investigate the changes in MPF activity during mouse oocyte maturation.
- To determine the correlation between MPF activity and meiotic progression.
- To elucidate the role of MPF in the transition from metaphase to subsequent meiotic events.
Main Methods:
- Injection of starfish oocyte MPF into mouse oocytes.
- Observation of MPF activity during the meiotic cycle.
- Treatment of oocytes with cytochalasin D and cycloheximide.
- Microscopic analysis of chromosomes and meiotic spindles.
Main Results:
- MPF activity appeared at germinal vesicle breakdown (GVBD), peaked at metaphase I and II, and decreased at polar body emission.
- A strong correlation was observed between MPF activity and meiotic metaphase.
- Cytochalasin D treatment maintained metaphase and elevated MPF activity.
- Cycloheximide addition reduced MPF activity, leading to chromosome decondensation and nuclear structure formation.
- Only monovalent chromosomes decondensed in response to MPF activity decrease.
Conclusions:
- MPF activity is tightly regulated throughout mouse oocyte meiosis.
- The disappearance of MPF activity is a critical trigger for metaphase-to-anaphase transition and subsequent meiotic events.
- Chromosome decondensation requires both MPF downregulation and dissociation of synapsis.