The Gene Encoding Murine α1,3-Galactosyltransferase Is Expressed in Female Germ Cells but Not in Male Germ Cells

An essential step in murine fertilization is the binding of acrosome-intact sperm to specific O-linked glycans on zona pellucida glycoprotein 3 (ZP3). While there is agreement on the primary role of O-linked glycans in sperm-ZP3 binding, there is a striking lack of consensus on both the terminal monosaccharide(s) required for a functional binding site and the cognate protein on the sperm cell surface that recognizes this glycan. Much current debate centers on the essential role of nonreducing terminal N -acetyl-glucosaminyl or alternatively, α-galactosyl residues, to form a functional sperm binding ligand. Relevant to this debate, we demonstrated that α1,3-galactosyltransferase (α3-GT), which adds nonreducing terminal α-galactosyl residues to glycans, is not expressed in murine spermatocytes or spermatids. The objectives of this study were to determine whether α3-GT is expressed in female germ cells and to compare the pattern of expression of two other terminal glycosyltransferases, β1,4-galactosyltransferase (β4-GT) and α2,6-sialyltransferase (α6-ST), between male and female germ cells. Total RNA was isolated from growing oocytes obtained from 15-day-old animals, fully grown oocytes, and eggs as wall as spermatogonia, spermatocytes, and spermatids. The presence of α3-GT, β4-GT, and α6-ST mRNAs was analyzed by an RT-PCR-based assay. Our data demonstrate that the α3-GT gene is expressed in female germ cells, but not in male germ cells. In contrast, both β4-GT and α6-ST are expressed during oogenesis and spermatogenesis. This differential expression of α3-GT in female germ cells is consistent with the model of sperm-egg binding in which a nonreducing terminal α-galactosyl residue is required for a functional determinant on ZP3 and with our hypothesis that the biological significance for the suppression of α3-GT expression in male germ cells is to prevent sperm-sperm aggregation.