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Suppression of chromosome condensation during meiotic maturation induces parthenogenetic development of mouse oocytes
H J Clarke1, J Rossant, Y Masui
1Department of Zoology, University of Toronto, Canada.
Abstract:
Mouse oocytes at metaphase I were treated with puromycin, which caused the chromosomes to become decondensed within an interphase nucleus. When the oocytes were allowed to resume protein synthesis, they returned to metaphase within 8-10 h and neither synthesized DNA nor cleaved, indicating that they had not been parthenogenetically activated by the puromycin treatment. However, when dibutyryl cyclic AMP was added to the medium after protein synthesis resumed, the oocytes remained in interphase. These oocytes maintained in interphase began DNA synthesis beginning 20 h after puromycin withdrawal, even though no activation stimulus had been given to them. After transfer to the oviducts of foster mothers, the oocytes could develop to the blastocyst stage. These results indicate that oocytes whose chromosomes were decondensed by puromycin treatment at metaphase I could begin parthenogenetic development in the absence of an activating stimulus, provided that they were prevented from returning to metaphase. In contrast, when the puromycin-treated oocytes were allowed to return to metaphase, they became developmentally arrested at the end of maturation. This suggests that the mechanism responsible for the developmental arrest of mature oocytes at metaphase II depends on cytoplasmic conditions that cause chromosome condensation to the metaphase state.
Insights
Puromycin treatment decondensed mouse oocyte chromosomes, enabling parthenogenetic development if oocytes stayed in interphase. Allowing return to metaphase caused developmental arrest, suggesting metaphase II arrest depends on cytoplasmic conditions.
Area of Science:
- Reproductive Biology
- Developmental Biology
- Cell Cycle Regulation
Background:
- Mouse oocytes arrest at metaphase II, a crucial stage for fertilization.
- Understanding the factors regulating oocyte maturation and developmental arrest is vital for reproductive research.
Purpose of the Study:
- To investigate the role of chromosome decondensation and cytoplasmic state in initiating parthenogenetic development in mouse oocytes.
- To explore the mechanism underlying developmental arrest at metaphase II.
Main Methods:
- Treatment of mouse oocytes at metaphase I with puromycin to induce chromosome decondensation.
- Manipulation of protein synthesis and cyclic AMP levels to control oocyte progression.
- Assessment of DNA synthesis, cleavage, and subsequent development to the blastocyst stage after in vitro culture and transfer to foster mothers.
Main Results:
- Puromycin treatment decondensed metaphase I chromosomes, leading to an interphase state.
- Oocytes prevented from returning to metaphase initiated DNA synthesis and parthenogenetic development, reaching the blastocyst stage.
- Oocytes allowed to resume metaphase after puromycin treatment exhibited developmental arrest.
Conclusions:
- Chromosome decondensation at metaphase I can initiate parthenogenetic development if oocytes are maintained in interphase.
- The transition to metaphase, influenced by cytoplasmic conditions, is critical for developmental arrest at the end of maturation.
- This study provides insights into the regulatory mechanisms of oocyte maturation and developmental potential.