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Updated: Jun 16, 2026
Analysis of Epididymal Protein Synthesis and Secretion
Published on: August 25, 2018
Endoplasmic reticulum protein 29 (ERp29), a protein related to sperm maturation is involved in sperm-oocyte fusion in
Xiaoqian Ying1, Yue Liu, Qiangsu Guo
1Shanghai Key Laboratory for Reproductive Medicine, Department of Histology and Embryology, School of Medicine, Shanghai Jiao Tong University, Shanghai 200025, China.
Background:
Sperm-oocyte fusion is a critical step in fertilization, which requires a series of proteins from both spermatozoa and oocyte to mediate membrane adhesion and subsequent fusion. A rat spermatozoa membrane protein is endoplasmic reticulum protein 29 (ERp29), which significantly increases on the sperm surface as well as in the cytoplasm of epididymal epithelia from caput to cauda as the sperm undergo epididymal maturation. Moreover, ERp29 facilitates viral infection via mediating membrane penetration. We determined if in addition to promoting sperm maturation ERp29 may also play a role in facilitating gamete fusion during the fertilization process.
Methods:
Laser scanning confocal microscopy (LSCM) and Western blot analysis were employed to probe for ERp29 protein in BALB/c mouse epididymal and acrosome-reacted spermatozoa. We prepared rabbit polyclonal antibodies against mouse recombinant ERp29 (rERp29) to characterize: 1) fertilization rate (FR); 2) fertilization index (FI); 3) sperm motility and 4) acrosome reaction (AR).
Results:
Confocal microscopy indicated that ERp29 was partially localized at the sperm head of the epididymal caput as well as over the whole head and part of the principal piece of the tail region from the epididymal cauda. However, when the acrosome reacted, ERp29 remained in the equatorial and post-acrosomal regions of the sperm head, which is the initial site of sperm-oocyte membrane fusion. Such localization changes were confirmed based on the results of Western blot analysis. Furthermore, the antibodies against mouse rERp29 inhibited the spermatozoa from penetrating into the zona pellucida (ZP)-free oocytes. The functional blocking antibodies reduced both mouse sperm-oocyte FR and FI at concentrations of 100 and 200 micro g/ml compared with pre-immunized rabbit IgG or with anti-mouse recombinant bactericidal/permeability-increasing protein (BPI, a sperm surface protein unrelated to sperm-oocyte fusion) antibodies (100 micro g/ml), but they had no effect on sperm motility and AR.
Conclusion:
This study demonstrates that ERp29 on mouse spermatozoa membrane changes during epididymal transit and AR. Accordingly, in mice this protein may be one of the important factors involved in sperm fertilization by facilitating sperm-oocyte membrane fusion.
Insights
Endoplasmic reticulum protein 29 (ERp29) on sperm surfaces changes during maturation and acrosome reaction. This protein facilitates sperm-oocyte fusion, a key step in fertilization.
Area of Science:
- Reproductive Biology
- Cell Biology
- Molecular Biology
Background:
- Sperm-oocyte fusion is essential for fertilization, involving proteins mediating membrane adhesion and fusion.
- Endoplasmic reticulum protein 29 (ERp29) is a sperm membrane protein that increases during epididymal maturation.
- ERp29's role in viral membrane penetration suggests a potential role in gamete fusion.
Purpose of the Study:
- To investigate the role of ERp29 in sperm maturation and its potential involvement in sperm-oocyte fusion.
- To determine the localization and function of ERp29 during the fertilization process in mice.
Main Methods:
- Laser scanning confocal microscopy (LSCM) and Western blot analysis were used to detect ERp29 in mouse sperm.
- Rabbit polyclonal antibodies against mouse recombinant ERp29 (rERp29) were generated.
- Fertilization rate (FR), fertilization index (FI), sperm motility, and acrosome reaction (AR) were assessed.
Main Results:
- ERp29 localization varied in sperm during epididymal transit and changed upon acrosome reaction, concentrating in fusion-relevant regions.
- Antibodies against rERp29 inhibited sperm penetration into zona pellucida-free oocytes.
- These antibodies reduced sperm-oocyte FR and FI but did not affect sperm motility or AR.
Conclusions:
- ERp29 undergoes dynamic changes on the sperm membrane during epididymal transit and acrosome reaction.
- ERp29 plays a significant role in facilitating sperm-oocyte membrane fusion in mice.
- ERp29 is identified as a key factor in successful fertilization.
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