Galactosyltransferase activities on mouse sperm bearing multipletlethalandtviablehaplotypes of the T/t-complex

SUMMARY Segregation-distorting t -sperm show a specific increase in N -acetylglucosamine: galactosyltransferase activity over wild-type (+/+) due to a deficiency of a wild-type galactosyltransferase inhibitor (Shur & Bennett, 1979). Eight other enzymic activities are indistinguishable between +- and t -sperm suspensions. In this study, three additional points are analysed. First, galactosyltransferases are assayed on sperm homozygous for a semilethal haplotype ( t W2 / t W2 ), relative to heterozygous (+ / t w2 ) and wild-type (+/+) controls. t W2 / t W2 assays circumvent the +-sperm inhibition of t -sperm galactosyltransferases that occurs in heterozygous + / t -assays and show that t -sperm are actually four times as active as wild-type. Second, sperm which are compound heterozygotes for two complementing lethal t -haplotypes ( t lx / t ly ), have nearly twice the theoretical enzyme level of t lx / t ly sperm. Thus, in either homozygous ( t W2 / t W2 ) or double heterozygous ( t lx / t ly ) form t -haplotypes act synergistically on sperm galactosyltransferase activity. Third, and most interesting, sperm bearing either recombinant, viable t -haplotypes (+/ t v , t vx / t vy ), or one of three dominant T / t -complex mutations, were assayed to determine which portions of the T / t -complex are responsible for elevated galactosyltransferase activity. Results show that sperm bearing recombinant, non-segregation-distorting, viable t v -haplotypes no longer show elevated transferase activity. Therefore, the elevated t 1 -sperm galactosyltransferase activity strictly correlates with the increased transmission frequency of t 1 -sperm. These studies strengthen further the hypothesis that sperm surface galactosyltransferases are involved in egg binding during fertilization, and that t 1 -sperm segregation-distortion results, at least in part, from increased galactosyltransferase activity.