SPERM FROM MICE CARRYING ONE OR 2 T-HAPLOTYPES ARE DEFICIENT IN INVESTMENT AND OOCYTE PENETRATION

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 (t(x)/t(y) 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 t(x)/t(y) 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 t(x)/t(y) males. We have developed a unique low sperm:egg ratio IVF assay for sperm function in fertilization. Using this assay, we have shown that t(w5)/+ 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 t(w5)/t(w32) 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 t(w5)/t(w32) 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. (C) 1995 Academic Press, Inc.