Elevated galactosyltransferase activity ont-bearing sperm segregates with T/t-complex distorter loci-2

Abstract

SummarySperm bearing completet-haplotypes are preferentially transmitted during fertilization from heterozygous +/tmales, often in excess of 95% relative to their +-bearing meiotic partner. Sperm fromt-bearing males have an approximate two- to fourfold increase in β1, 4-galactosyltransferase (GalTase) activity, a cell surface protein that mediates sperm binding to the egg zona pellucida. The elevated GalTase activity strictly correlates with the preferential transmission oft-sperm from +/tmales, since eight other enzymes show normal levels of activity ont-sperm. Furthermore, sperm bearing proximal partialt-haplotypes, which are no longer favoured during fertilization, have normal levels of GalTase activity. Nevertheless, it has been unclear whether the elevated sperm GalTase activity ont-sperm is due to specific loci in the distal segment of the T/t-complex, or rather, is an indirect consequence of the abnormal sperm function characteristic of +/tandtx/tymales. In this study, it is shown that the elevated sperm GalTase activity is due specifically to factors that reside within the distal segment of the T/t complex, which also containsTcd-2, the strongest of the distorter loci. Since the structural locus for GalTase is located on mouse chromosome 4, these results also show that T/t-complex alleles on chromosome 17 are regulatory in nature and affect the expression of sperm surface components critical for normal fertilization. Models are presented to explain how elevated GalTase activity could contribute to sperm transmission distortion.