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

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Abstract
SUMMARY: Segregation-distortingt-sperm show a specific increase inN-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 +- andt-sperm suspensions. In this study, three additional points are analysed. First, galactosyltransferases are assayed on sperm homozygous for a semilethal haplotype (tW2/tW2), relative to heterozygous (+ /tw2) and wild-type (+/+) controls.tW2/tW2assays circumvent the +-sperm inhibition oft-sperm galactosyltransferases that occurs in heterozygous + /t-assays and show thatt-sperm are actually four times as active as wild-type. Second, sperm which are compound heterozygotes for two complementing lethalt-haplotypes (tlx/tly), have nearly twice the theoretical enzyme level oftlx/tlysperm. Thus, in either homozygous (tW2/tW2) or double heterozygous (tlx/tly) formt-haplotypes act synergistically on sperm galactosyltransferase activity.Third, and most interesting, sperm bearing either recombinant, viablet-haplotypes (+/tv,tvx/tvy), or one of three dominantT/t-complex mutations, were assayed to determine which portions of theT/t-complex are responsible for elevated galactosyltransferase activity. Results show that sperm bearing recombinant, non-segregation-distorting, viabletv-haplotypes no longer show elevated transferase activity. Therefore, the elevatedt1-sperm galactosyltransferase activity strictly correlates with the increased transmission frequency oft1-sperm. These studies strengthen further the hypothesis that sperm surface galactosyltransferases are involved in egg binding during fertilization, and thatt1-sperm segregation-distortion results, at least in part, from increased galactosyltransferase activity.