THE GENE ENCODING MURINE ALPHA-1,3-GALACTOSYLTRANSFERASE IS EXPRESSEDIN FEMALE GERM-CELLS BUT NOT IN MALE GERM-CELLS

An essential step in murine fertilization is the binding of acrosome-i ntact sperm to specific O-linked glycans on zona pellucida glycoprotei n 3 (ZP3). While there is agreement on the primary role of O-linked gl ycans in sperm-ZP3 binding, there is a striking lack of consensus on b oth the terminal monosaccharide(s) required for a functional binding s ite and the cognate protein on the sperm cell surface that recognizes this glycan. Much current debate centers on the essential role of nonr educing terminal N-acetyl-glucosaminyl or alternatively, alpha-galacto syl residues, to form a functional sperm binding ligand. Relevant to t his debate, we demonstrated that alpha 1,3-galactosyltransferase (alph a 3-GT), which adds nonreducing terminal alpha-galactosyl residues to glycans, is not expressed in murine spermatocytes or spermatids. The o bjectives of this study were to determine whether alpha 3-GT is expres sed in female germ cells and to compare the pattern of expression of t wo other terminal glycosyltransferases, beta 1,4-galactosyltransferase (beta 4-GT) and alpha 2,6-sialyltransferase (alpha 6-ST), between mal e and female germ cells. Total RNA was isolated from growing oocytes o btained from 15-day-old animals, fully grown oocytes, and eggs as well as spermatogonia, spermatocytes, and spermatids. The presence of alph a 3-GT, beta 4-GT, and alpha 6-ST mRNAs was analyzed by an RT-PCR-base d assay. Our data demonstrate that the alpha 3-GT gene is expressed in female germ cells, but not in male germ cells. In contrast, both beta 4-GT and alpha 6-ST are expressed during oogenesis and spermatogenesi s. This differential expression of alpha 3-GT in female germ cells is consistent with the model of sperm-egg binding in which a nonreducing terminal alpha-galactosyl residue is required for a functional determi nant on ZP3 and with our hypothesis that the biological significance f or the suppression of alpha 3-GT expression in male germ cells is to p revent sperm-sperm aggregation. (C) 1995 Academic Press, Inc.