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Fusion of mammalian oocytes: SEM observations of surface changes
J Fulka1, B Fléchon, J E Fléchon
1Research Institute of Animal Production, Prague, Czechoslovakia.
Abstract:
Mouse oocytes at the germinal vesicle (GV) stage were fused with maturing oocytes in which GVs were no longer visible. The fused cells were fixed at different time-intervals after the initiation of fusion and prepared for scanning electron microscope (SEM) observation. Concomitantly, some fused cells were prepared for light microscope evaluation. Our SEM observations showed no significant differences in surface morphology between immature and maturing oocytes. However, immediately after fusion was initiated, dramatic changes occurred on the surface of the maturing oocytes. The microvilli were shortened or disappeared locally and the plasma membrane was deeply ruffled. One hour after fusion, when the giant cells were nearly spherical, the microvilli reappeared and the ruffling gradually disappeared. In some areas, the microvilli were extremely long. Three hours after fusion, the fused cells were perfectly round and their surfaces were generally covered with microvilli of equal length. No further ruffling was observed. It is suggested that cytoplasmic mechanisms regulate the surface morphology of the oocytes during fusion.
Insights
Cell fusion in mouse oocytes triggers rapid surface changes. Microvilli shorten and ruffling occurs, followed by recovery and uniform microvilli, suggesting cytoplasmic regulation of oocyte surface morphology.
Area of Science:
- Cell Biology
- Developmental Biology
- Reproductive Biology
Background:
- Oocyte maturation involves significant cellular changes.
- Surface morphology plays a crucial role in oocyte function and fertilization.
Purpose of the Study:
- To investigate the dynamic surface morphological changes in mouse oocytes during cell fusion.
- To understand the role of cytoplasmic factors in regulating oocyte surface dynamics.
Main Methods:
- Fusion of germinal vesicle (GV) stage mouse oocytes with maturing oocytes.
- Scanning electron microscopy (SEM) for surface morphology observation.
- Light microscopy for cellular evaluation at various time points post-fusion.
Main Results:
- No significant surface differences between immature and maturing oocytes before fusion.
- Immediate post-fusion: microvilli shortening/disappearance and plasma membrane ruffling.
- 1 hour post-fusion: microvilli reappearance, reduced ruffling, and some elongated microvilli.
- 3 hours post-fusion: spherical cells with uniformly distributed microvilli, absence of ruffling.
Conclusions:
- Cytoplasmic mechanisms are implicated in regulating oocyte surface morphology during fusion.
- Dynamic surface remodeling occurs rapidly following oocyte fusion.
- The observed changes suggest active cellular processes controlling plasma membrane organization.