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Sperm penetration into immature mouse oocytes and nuclear changes during maturation: an EM study
D Szöllösi1, M S Szöllösi, R Czolowska
1Institut National de Recherche Agronomique, Département de Physiologie Animale, Jouy-en-Josas, France.
Biology of the Cell
|January 1, 1990
Summary
In mouse oocytes, sperm nuclei and nuclear envelopes remain intact after penetration. However, after 3 hours of maturation, both sperm and oocyte nuclear envelopes fragment, with sperm centrioles unable to organize microtubules.
Area of Science:
- Reproductive Biology
- Cell Biology
- Developmental Biology
Background:
- Understanding early events in fertilization is crucial for reproductive science.
- The behavior of sperm and oocyte nuclei during initial fusion stages requires detailed ultrastructural analysis.
Purpose of the Study:
- To investigate the ultrastructural changes in mouse oocyte and sperm nuclei following in vitro insemination.
- To examine the role of the sperm centriole in early oocyte development and microtubule organization.
Main Methods:
- In vitro insemination of mouse ovarian oocytes.
- Culture of oocytes in media with or without maturation inhibitors (dbcAMP).
- Transmission electron microscopy (TEM) to study nuclear and centriolar ultrastructure at 1.5 and 3 hours post-maturation induction.
Main Results:
- Sperm nuclei and nuclear envelopes remain intact upon entering ovarian oocytes.
- After 3 hours of maturation, both oocyte (germinal vesicle) and sperm nuclear envelopes fragment.
- Sperm chromatin decondenses, while oocyte chromatin condenses into chromosomes; sperm centrioles do not form asters.
Conclusions:
- The sperm centriole does not function as a centrosome in early mouse oocyte development.
- Nuclear envelope dynamics differ between the oocyte and penetrating sperm during early maturation.
- These findings provide insights into the structural transformations during mammalian fertilization and early embryonic development.