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Sperm from mice carrying one or two t haplotypes are deficient in investment and oocyte penetration
L R Johnson1, S H Pilder, J L Bailey
1Department of Anatomy and Cell Biology, Temple University School of Medicine, Philadelphia, Pennsylvania 19140.
Abstract:
The t haplotypes, mutant forms of the proximal third of mouse chromosome 17 (the t complex), contain factors that contribute to defective sperm function in fertilization. Males carrying two t haplotypes (tx/ty mice) are sterile; their sperm have very poor motility and are unable to penetrate zona-free eggs. Although males carrying one t haplotype (t/+) are fertile, genetic evidence suggests that the sperm carrying the normal form of chromosome 17 (+t) are dysfunctional in fertilization, and some or all sperm have abnormal motility. Some of the same genetic factors that cause sterility in tx/ty males probably contribute to the dysfunction of +t sperm from t/+ males; however, it is unclear which steps in gamete interaction are defective in sperm from t/+ males, or whether the defects are similar to those observed in sperm from tx/ty males. We have developed a unique low sperm:egg ratio IVF assay for sperm function in fertilization. Using this assay, we have shown that tw5/+ sperm are less able than congenic +/+ sperm to penetrate the zona (probably due to their abnormal motility) and to penetrate the zona-free oocyte. Since tw5/tw32 sperm are unable to complete these same two steps in sperm-egg interaction, these specific deficits could be involved in both transmission ratio distortion and sterility. We have also shown that tw5/tw32 sperm are deficient in their ability to bind to the zona and to the oolemma. These results suggest that t haplotypes contain loci which affect a number of sperm functions and thus could be a rich source of genes important for sperm-egg interaction.
Insights
Mouse t haplotypes cause defective sperm function, impacting fertilization. These genetic factors in t-complex mutations affect sperm motility and binding, potentially explaining sterility and transmission ratio distortion.
Area of Science:
- Reproductive Biology
- Genetics
- Developmental Biology
Background:
- Mouse t haplotypes, located on chromosome 17, are known to influence male fertility.
- Males with two t haplotypes (tx/ty) are sterile with severely impaired sperm motility and egg penetration.
- Even in fertile males with one t haplotype (t/+), sperm carrying the normal chromosome 17 (+t) exhibit fertilization defects.
Purpose of the Study:
- To investigate the specific defects in sperm function caused by t haplotypes during fertilization.
- To compare the fertilization defects in sperm from t/+ males with those from tx/ty males.
- To identify the roles of t haplotypes in sperm-egg interactions.
Main Methods:
- Development of a unique low sperm:egg ratio in vitro fertilization (IVF) assay.
- Assessment of sperm ability to penetrate the zona pellucida and zona-free oocytes.
- Evaluation of sperm binding to the zona and oolemma.
Main Results:
- Sperm from tw5/+ mice showed reduced ability to penetrate the zona and zona-free oocytes compared to controls.
- Sperm from tw5/tw32 mice exhibited defects in zona penetration, oocyte penetration, zona binding, and oolemma binding.
- These deficits in sperm function mirror those seen in tx/ty males, suggesting a common genetic basis.
Conclusions:
- t haplotypes significantly impair multiple sperm functions essential for fertilization, including motility, zona penetration, and binding.
- The identified sperm function deficits are linked to both transmission ratio distortion and male sterility.
- The t complex represents a valuable resource for discovering genes critical for successful sperm-egg interaction.