Fertilization is initiated by the species-specific binding of sperm to the extracellular coat of the egg. One sperm receptor for the mouse egg is beta-1,4-galactosyltransferase (GalTase), which binds O-linked oligosaccharides on the egg coat glycoprotein ZP3. ZP3 binding induces acrosomal exocytosis through the activation of a pertussis toxin-sensitive heterotrimeric guanine nucleotide-binding protein (G protein). The cytoplasmic domain of sperm surface GalTase bound to and activated a heterotrimeric G protein complex that contained the Gi alpha subunit. Aggregation of GalTase by multivalent ligands elicited G protein activation. Sperm from transgenic mice that overexpressed GalTase had higher rates of G protein activation than did wild-type sperm, which rendered transgenic sperm hypersensitive to their ZP3 ligand. Thus, the cytoplasmic domain of cell surface GalTase appears to enable it to function as a signal-transducing receptor for extracellular oligosaccharide ligands.

The objectives of the present study were to develop an antibody probe to the porcine estrogen-dependent oviductal glycoproteins and to determine, by use of immunogold electron microscopy, whether these glycoproteins become associated with oviductal and uterine oocytes and early embryos. Polyclonal antibody, prepared using the M(r) 75,000-85,000 glycoprotein, separated from other proteins by two-dimensional SDS-PAGE, specifically recognized all three estrogen-dependent glycoproteins (acidic 75,000-85,000 M(r); acidic 100,000 M(r); basic 100,000 M(r)). In ampullary tissue collected from ovariectomized and estrogen-treated gilts and from gilts at Day 1 of estrus, gold particles were clustered over putative secretory granules restricted to the apical region of secretory epithelial cells. While follicular oocytes did not react with immunoreactive colloidal gold, oviductal and uterine unfertilized oocytes were found to be densely and uniformly labeled by colloidal gold throughout the zona pellucida, associated with flocculent material in the perivitelline space, and associated with microvilli and vitelline membrane. Similarly, in oviductal (1-4-cell) and unhatched uterine (4-cell/blastocyst) embryos, colloidal gold particles were distributed throughout the zona pellucida, heavily associated with flocculent material in the perivitelline space, and associated with the plasma membrane of the blastomeres. Immunoreactive colloidal gold remained detectable within Day 7 hatched uterine embryos, but not with embryos from later days. These results further support the proposal that porcine estrogen-dependent oviductal glycoproteins are released into the oviductal lumen, become associated with oviductal and uterine oocytes and early embryos, and are retained by oocytes and early embryos in the uterus.

ABSTRACT1&1,4-Galactosyltransferase (GalTase) is localized to two subcellular compartments, the Golgi complex, where it participates in cellular glycosylation, and the plasma membrane, where it functions as a receptor for oligosaccharide ligands on opposing cells or in the extracellular matrix. The gene for GalTase encodes two nearly identical proteins that differ only in their N-terminal cytoplasmic domains: both short and long GalTases share an 11-aa cytoplasmic tail, but long GalTase has an additional 13-aa sequence on its cytoplasmic domain. In this study, we investigated the subcellular distribution of endogenous long GalTase in untransfected F9 and 3T3 cells by using confocal microscopy and antibodies specific for the 13-aa sequence unique to long GalTase. Long GalTase was found in the Golgi complex as expected; long GalTase was also found on the plasma membrane in cell-type-specific distributions. In 3T3 cells, long GalTase was evident on the basal surface of cells possessing a migratory phenotype, being concentrated at the leading and trailing edges; nonmigratory cells had little detectable surface immunoreactivity. In F9 cells, long GalTase was localized on the plasma membrane, being concentrated at the apical aspect of intercellular junctions. These results demonstrate that in 3T3 and F9 cells, long GalTase is present on the cell surface in addition to the Golgi complex. The pattern of surface expression shows cell-type specificity that is consistent with GalTase function in cellular interactions.

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This study examined differences in selected components of uterine secretions from Large White and prolific Chinese Meishan gilts during the oestrous cycle or early pregnancy. Total recoverable protein, uteroferrin (measured as acid phosphatase activity), acyl aminopeptidase, calcium, sodium, potassium, immunoglobulins A and G, glucose, fructose, oestradiol-17 beta, and prostaglandins F2 alpha (PGF2 alpha) and E2 (PGE2) in uterine flushings were measured. During the oestrous cycle, breed effects were detected only for total protein (P = 0.07), which tended to be higher for Large White gilts. However, for pregnant gilts, total recoverable glucose (P less than 0.05), fructose (P less than 0.05) sodium (P less than 0.05), immunoglobulin A (P less than 0.01), PGF (P less than 0.01), PGE (P less than 0.01), and acyl aminopeptidase (P less than 0.05) were greater in uterine flushings from Meishan gilts. Only uteroferrin was higher (P = 0.06) in uterine flushings from Large White gilts. Concentrations of prolactin were higher (P less than 0.05) in plasma from cyclic or pregnant Meishan gilts, but concentrations of total oestrogens and progesterone were not affected by pregnancy status or breed. These results suggest that Meishan conceptuses, individually or collectively, are more stimulatory to endometrial secretion and/or transport of the components of histotroph into the uterine lumen, or that the endometrium of Meishan gilts is more sensitive to conceptus signals responsible for the accumulation of histotroph in the uterine lumen.