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Updated: Jun 29, 2026
Mouse Oocyte Microinjection, Maturation and Ploidy Assessment
Published on: July 23, 2011
Ultrastructural observations on gamete interactions using micromanipulated mouse oocytes
J M Cummins1, W R Edirisinghe, Y Odawara
1PIVET Medical Centre, Perth, Australia.
Abstract:
Cumulus-free mouse oocytes were subjected to zona opening by cracking with microhooks (ZC) or acid drilling (ZD) and fixed 30-90 min after insemination (10(5) pre-capacitated motile sperms/ml). Ultrastructural observations were made on serially thin-sectioned oocytes: 15 ZC and 12 ZD. The zona lesion in ZC oocytes was a clean cut, whereas in ZD oocytes it formed a patchy area of partial zona loss, with reduced microvillar height on the underlying oocyte surface. Spermatozoa were observed within the perivitelline space and partially fusing with the oocyte after 30 min in both situations. Only acrosome-reacted sperm heads were observed to fuse: acrosome intact forms were generally in contact with the zona pellucida, either with the inner or outer surface. Acrosome-intact spermatozoa were also observed deeply embedded in the zona matrix, possibly indicating surface enzyme activity preceding the membrane fusion events of the acrosome reaction proper. The observations are consistent with the need for spermatozoa to make contact preferentially with the zona pellucida during the course of the acrosome reaction.
Insights
Zona opening via microhooks or acid treatment allows sperm penetration. Sperm must undergo the acrosome reaction, involving contact with the zona pellucida, before fusing with the oocyte.
Area of Science:
- Reproductive Biology
- Cell Biology
- Developmental Biology
Background:
- Oocyte fertilization involves complex sperm-egg interactions.
- The zona pellucida is a key barrier that sperm must penetrate.
- The acrosome reaction is crucial for successful fertilization.
Purpose of the Study:
- To investigate the ultrastructural effects of different zona opening methods on sperm-zona pellucida and sperm-oocyte interactions.
- To observe the timing and nature of sperm penetration and fusion following zona opening.
Main Methods:
- Cumulus-free mouse oocytes were mechanically (zona cracking) or chemically (acid drilling) treated to open the zona pellucida.
- Oocytes were inseminated with capacitated sperm and fixed at 30-90 minutes post-insemination.
- Ultrastructural analysis was performed on serially thin-sectioned oocytes using transmission electron microscopy.
Main Results:
- Zona cracking created a clean cut, while acid drilling resulted in partial zona loss and reduced oocyte microvillar height.
- Sperm were observed in the perivitelline space and fusing with oocytes 30 minutes after insemination in both groups.
- Only acrosome-reacted sperm heads fused with the oocyte; acrosome-intact sperm interacted with the zona pellucida, sometimes embedding within it.
Conclusions:
- Both zona cracking and acid drilling facilitate sperm penetration, but acid treatment alters the oocyte surface.
- Sperm-zona pellucida interaction, including embedding and potential enzymatic activity, precedes the acrosome reaction and subsequent oocyte fusion.
- Preferential contact with the zona pellucida is essential for initiating the acrosome reaction and fertilization.
