A specific defect in galactosyltransferase regulation on sperm bearing mutant alleles of the T/t locus

Abstract

The relationship between sperm surface glycosyltransferases and surface antigens coded for by the T/t locus of the mouse has been examined. Sperm expressing t antigens associated with six different complementation groups of recessive lethalt alleles produce more than two to five times theN-acetylglucosamine:galactosyltransferase activity of wild-type sperm. Eight other enzymes assayed show essentially equal activities in normal andt-sperm preparations. The following observations suggest that the increased galactosyltransferase activity ont sperm is due to a deficiency of galactosyltransferase inhibition relative to normal sperm. (1) The presence of a wild-type galactosyltransferase inhibitor is shown when wild-type andt sperm are mixed and assayed for transferase activity. The wild-type sperm inhibitt-sperm enzyme activity by 80%. (2) Sperm from mice which carry a T/t locus deletion (THp), which presumably interferes with inhibitor synthesis, show about three times the galactosyltransferase activity of normal littermates. (3) Pretreatment of wild-type ort sperm with antiserum directed against the appropriate T/t locus antigen stimulates galactosyltransferase activity 2- to 15-fold, apparently by inactivating the transferase inhibitor. These data suggest that the characteristic increases in galactosyltransferase activity shown byt sperm are due to reduced inhibition of the transferase activity. It is possible that the increased availability of galactosyltransferases ont sperm is at least partly responsible for their preferential fertilizing ability.