Patricia Olds-Clarke

Fertility of sperm from t/+ mice: evidence that +-bearing sperm are dysfunctional.

Male mice carrying one complete t haplotype transmit it to virtually all offspring. This implies that either the sperm carrying the t haplotype have an advantage in fertilization, or that the sperm not carrying a t haplotype are dysfunctional. To distinguish between these possibilities, epididymal sperm from t w 32 / + and congenic + / + males were artificially inseminated into the uterus of T / + females, and the transmission ratio determined from the phenotype of the offspring. After artificial insemination (AI) of sperm from t w 32 / + males, the mean ratio was 0·95 (3 experiments, 5 litters), demonstrating that the transmission ratio remains high after AI into the uterus. After AI of a mixture of equal numbers of motile sperm from t w 32 / + and congenic + / + males, the mean ratio was 0·22 (6 experiments, 8 litters). These results suggest that sperm carrying a t haplotype from t / + males are not superior to sperm from + / + males, and therefore imply that sperm not carrying a t haplotype from t / + males are dysfunctional.

Unresolved issues in mammalian fertilization

This review considers the role of the sperm in fertilization, addressing areas of misunderstanding and unfounded assumptions and taking particular advantage of the large body of data resulting from work with rodent species in vitro. Considerable attention is given to the appropriate use and interpretation of assays for capacitation, acrosomal exocytosis, hyperactivation, and sperm protein phosphorylation, as well as tests for sperm-zona and sperm-oocyte membrane interactions. The lack of general agreement on the means of sperm adhesion to and penetration of the zona pellucida is addressed, and the need for new approaches to this problem is pointed out. Some molecular advances in our understanding of specific steps in the process of fertilization are discussed in the context of intact cell-matrix and cell-cell interaction. This review should provide practical information for researchers just beginning the study of fertilization and interesting but not widely known observations to stimulate new ideas in experienced scientists.

Transmission ratio distortion of mouse t haplotypes is not a consequence of wild-type sperm degeneration

A mouse t-complex-specific DNA probe was used to determine the ratio of t-carrying and (+)-carrying sperm in epididymal, vas deferens, and postejaculatory sperm cell populations from heterozygous (+/t) mice with transmission ratios of greater than 95%. No detectable degeneration of (+)-carrying sperm was observed. In this respect, mouse t haplotypes differ from Drosophila melanogaster SD chromosomes. High transmission of t haplotypes must be a consequence of differential transport and/or differential sperm function during the fertilization process itself.

Nonprogressive sperm motility is characteristic of most complete t haplotypes in the mouse.

Epididymal sperm from male mice carrying t w32 ( t 12 complementation group) exhibit a peculiar nonprogressive type of motility called ‘dancing’; sperm from congenie wild-type mice do not. To determine whether this effect was unique to t w32 or common to all t haplotypes, sperm from mice carrying other t haplotypes were examined. A male was considered to have nonprogressive sperm if more than 20% of the motile sperm had nonprogressive trajectories. The mean percentage of nonprogressive but motile sperm for 33 wild-type and Brachyury males of various genetic backgrounds was 4. All males carrying t w12 ( t w1 complementation group), t w5 or t w73 , and 56% of males carrying t 0 or t Lub1 had nonprogressive motile sperm. Five per cent of males carrying t chromatin or a deletion in the proximal (to the centromere) half of the t complex had nonprogressive motile sperm, but all males carrying t chromatin in the distal half of the t complex had nonprogressive motile sperm. These observations suggest that the factor or factors causing nonprogressive sperm motility may be common to all complete t haplotypes, and located in the distal region of the t complex.

The cellular basis for interaction of sterility factors in the mouse t haplotype.

The t haplotypes are variant forms of the proximal one-third of chromosome 17 in the mouse. They contain four inversions (relative to the wildtype DNA) extending over most of this region and house a number of male sterility factors. Males carrying two complete t haplotypes (t/t) are sterile, as are males homozygous for S2, the sterility factor located in the most distal (relative to the centromere) inversion. Males homozygous for the sterility factor S1, located in the most proximal inversion, are not sterile; however, if such a male also is heterozygous for other sterility factors, then sterility results. It has been suggested therefore that homozygosity for S1 enhances the detrimental action of other sterility factors. Sperm from t/t males have severe motility defects and are unable to penetrate investment-free eggs, while sperm from fertile t/+ mice have less serious motility defects and exhibit a delay in penetration of investment-free eggs. To determine whether homozygosity for S1 enhances the cellular defects exhibited by sperm from mice heterozygous for other sterility factors, we compared the motility and egg-penetrating ability of sperm from fertile mice homozygous for S1 to that of sperm from mice carrying one complete t haplotype and one proximal or distal partial t haplotype. The data suggest that sperm from males carrying a proximal partial t haplotype and a complete t haplotype have serious defects in motility and penetration of the investment-free egg, and support the hypothesis that S1 enhances the detrimental effects of other sterility factors within the t haplotype.

Genetic analysis of mammalian spermatogenesis: use of the t complex in the mouse in studies of spermatogenesis and sperm function.

Our observations suggest that sperm populations from the caudae epididymides of tw32/+ mice undergo hyperactivation in vitro sooner and to a much greater extent than do sperm populations from congenic +/+ mice: (1) epididymal tw32/+ sperm populations become significantly less progressive in vitro than do +/+ sperm populations; (2) low (0.1 mM) levels of Ca2+ prevent this loss of progressiveness; (3) epididymal tw32/+ sperm populations have trajectories and progressiveness values similar to both +/+ and tw32/+ oviductal sperm populations; (4) an inhibitor of capacitation inhibits the loss of progressiveness. This divergence from normal motility may be the result of expression of one of the factors involved in transmission distortion of the t complex.