The t haplotypes of mouse sperm are a valuable model system for understanding the genetic and biochemical basis of mammalian sperm dysfunction. Sperm from mice carrying two t haplotypes have extremely poor sperm quality, are deficient in the ability to bind to the zona pellucida, and are unable to penetrate zona-free oocytes. The ultimate objectives of this research are to determine the biochemical mechanisms by which loci in the t haplotypes cause dysfunction in fertilization and to identify and characterize these loci. Gene sequences can then be used as probes to identify human homologs. The sterility of t/t males is caused by the interaction of three genetic factors, S1-S3, each located in a different chromosomal inversion. When homozygous, S1 enhances defects in motility and egg penetration caused by heterozygosity of S2.
Aim I is to determine the type of mechanism underlying this enhancement and map the genes responsible to a region small enough for positional cloning. This can be done using Mus spretus-Mus domesticus chromosome 17 recombinant mice, since M. spretus contains noncomplementing alleles to the t haplotype loci affecting sperm, and M. spretus DNA is not inverted relative to M. domesticus. Biochemical defects associated with either S1 or S2 could be involved in zona-binding deficiency.
Aim II is to determine which possibility is correct by mapping this deficiency within the t complex. These experiments have the potential to identify the molecular basis for reduced sperm-zona binding. The t haplotype causes an abnormality in the tyrosine phosphorylation of a specific subset of sperm proteins. Since these phosphorylation events are coupled with capacitation in wildtype sperm, the t haplotype-specific defect(s) that affect this pathway could be involved in pathways leading to defective motility and/or egg penetration.
Aim III is to determine whether this is so by determining the requirements for the abnormal protein tyrosine phosphorylation, and by mapping the defect to a specific region of the t complex.
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