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Updated: Aug 9, 2026
Mouse Oocyte Microinjection, Maturation and Ploidy Assessment
Published on: July 23, 2011
Characterization and localization of a mouse egg cortical granule antigen prior to and following fertilization or egg
K E Pierce1, M C Siebert, G S Kopf
1Department of Biology, University of Pennsylvania, Philadelphia 19104.
Insights
Researchers identified a 75,000 molecular weight protein (p75) within mouse oocyte cortical granules. This protein is released upon fertilization or activation, indicating its role in early embryonic development.
Area of Science:
- Reproductive Biology
- Cell Biology
- Immunology
Background:
- Cortical granules in mouse oocytes store proteins essential for fertilization.
- The molecular composition and release mechanisms of these proteins are not fully understood.
Purpose of the Study:
- To characterize an antigen localized to mouse oocyte cortical granules.
- To determine the identity and release dynamics of this antigen during fertilization and activation.
Main Methods:
- Immunoelectron microscopy for antigen localization.
- Western blotting and immunoprecipitation to identify the protein (p75).
- Analysis of protein release from activated eggs using radio-iodination and 2D gel electrophoresis.
Main Results:
- The antigen was identified as a 75,000 molecular weight protein (p75).
- p75 is localized to cortical granules and released into the perivitelline space post-fertilization.
- Multiple forms of p75, with intramolecular disulfide bonds, are released from activated eggs.
Conclusions:
- p75 is synthesized in oocytes, processed in cortical granules, and secreted upon fertilization or activation.
- This protein likely plays a role in the block to polyspermy or other post-fertilization events.
- The characterization of p75 provides insights into mammalian egg fertilization mechanisms.
Abstract:
Immunological approaches were used to characterize an antigen that is present within the cortical granules of mouse oocytes and eggs. Immunoelectron microscopy shows a specific localization of the antigen to the cortical granules in the cortex of mouse oocytes and eggs. Following in vitro fertilization, the antigen is present in the perivitelline space and is associated with the zona pellucida. No cortical granules and very little antigen are detected in the two-cell embryo. This antiserum detects a protein of Mr = 75,000 (p75) following immunostaining of egg proteins on Western blots, or immunoprecipitation of metabolically labeled oocyte proteins or radio-iodinated egg proteins. p75 is also present in exudates obtained from A23187-treated eggs, as detected by either radio-iodination of the released egg proteins, or maturation and ionophore activation of metabolically labeled oocytes. Two-dimensional gel electrophoresis of radio-iodinated egg proteins reveals four species of p75 with pIs between 4.9 and 5.3, whereas only the most basic form of p75 is detected in metabolically labeled oocytes. Multiple forms of the radio-iodinated p75 are present in the exudate of ionophore-treated eggs. p75 displays a greater electrophoretic mobility under nonreducing conditions, indicating the presence of intramolecular disulfide bonds, a common characteristic of secreted proteins. We conclude that p75 is synthesized in oocytes, modified and packaged into cortical granules, and released from eggs following fertilization or activation.
