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Morphological differentiation of cumulus-oocyte complexes induced by the administration of gonadotropins in mice
I Kanayama1, E Sato, K Shimoda
1Department of Animal Science, Faculty of Agriculture, Kyoto University, Japan.
Abstract:
The morphological changes were examined in the present study in mouse cumulus-oocyte complexes and granulosa cells induced by the administration of pregnant mare serum gonadotropin (PMSG) and human chorionic gonadotropin (hCG). Dissolution of the germinal vesicle (GVBD) occurred in oocytes at 3 hr after hCG administration. Partial expansion of the cumulus cell investment was observed in the cumulus-oocyte complexes, especially those with the oocytes having undergone GVBD. Cumulus expansion due to the deposition of intercellular materials stained with colloidal iron proceeded up to 8 hr after hCG administration. The number of cells in the follicles containing matured oocytes is smaller than that in the follicles containing intact germinal vesicles in the granulosa cell layer, which indicates that the dispersion of cells occurs during meiotic maturation not only in the cumulus-oocyte complexes but also in the granulosa cell layer. Examination of the expansion of mouse cumulus-oocyte complexes by electron microscopy revealed the abundant deposition of intercellular materials and the retraction of the cytoplasmic processes joining the cumulus cells to the oocyte at 3 hr after hCG administration.
Insights
Administration of pregnant mare serum gonadotropin (PMSG) and human chorionic gonadotropin (hCG) induced morphological changes in mouse oocytes and cumulus cells. Key changes included germinal vesicle breakdown and cumulus expansion with intercellular material deposition.
Area of Science:
- Reproductive Biology
- Developmental Biology
- Cell Biology
Background:
- Cumulus-oocyte complexes (COCs) are crucial for female fertility, undergoing significant morphological changes during maturation.
- Hormonal stimulation, using pregnant mare serum gonadotropin (PMSG) and human chorionic gonadotropin (hCG), is a common method to induce ovulation and oocyte maturation in research settings.
- Understanding the cellular dynamics during COC expansion is vital for reproductive research and assisted reproductive technologies.
Purpose of the Study:
- To investigate the morphological alterations in mouse COCs and granulosa cells following PMSG and hCG administration.
- To characterize the timing and extent of germinal vesicle breakdown (GVBD) and cumulus expansion.
- To examine cellular dispersion within the granulosa cell layer during meiotic maturation.
Main Methods:
- Mice were administered PMSG followed by hCG to induce oocyte maturation.
- Cumulus-oocyte complexes and granulosa cells were collected at various time points post-hCG administration.
- Morphological changes, including GVBD and cumulus expansion, were assessed using light and electron microscopy.
- Colloidal iron staining was used to visualize intercellular material deposition during cumulus expansion.
Main Results:
- Germinal vesicle breakdown (GVBD) was observed in oocytes as early as 3 hours after hCG administration.
- Cumulus expansion, characterized by the deposition of intercellular matrix, initiated by 3 hours and progressed up to 8 hours post-hCG.
- Electron microscopy revealed abundant intercellular material and retraction of cytoplasmic processes between cumulus cells and the oocyte at 3 hours.
- A decrease in granulosa cell number within follicles containing mature oocytes indicated cell dispersion during meiotic maturation.
Conclusions:
- Hormonal induction with PMSG and hCG triggers rapid morphological changes in mouse COCs, including GVBD and extensive cumulus expansion.
- The observed cellular dispersion in the granulosa layer suggests a coordinated process during meiotic maturation.
- These findings provide a detailed timeline of COC morphological transformations essential for understanding oocyte maturation.