The mouse egg's receptor for sperm: what is it and how does it work?
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Acrosome↗
Biomedical subjects
R J Roller
Publications and source records attributed to R J Roller.
Role of asparagine-linked oligosaccharides in secretion of glycoproteins of the mouse egg's extracellular coat.
Tunicamycin, an inhibitor of asparagine-linked glycosylation of glycoprotein, has been used here to examine the role of N-linked oligosaccharides in secretion of ZP2 and ZP3, two of the three glycoproteins that constitute the mouse egg's extracellular coat (zona pellucida). In the absence of tunicamycin, growing mouse oocytes cultured in vitro synthesize a 91,000-Mr ZP2 precursor and 53,000 and 56,000 Mr ZP3 precursors. All of these precursors contain high mannose-type oligosaccharides that are processed to complex-type prior to secretion of mature ZP2 (120,000 Mr) and ZP3 (80,000 Mr) (Greve, J. M., Salzmann, G. S., Roller, R. J., and Wassarman, P. M. (1982) Cell 31, 749-759; Salzmann, G. S., Greve, J. M., Roller, R. J., and Wassarman, P. M. (1983) Eur. Mol. Biol. Org. J. 2, 1451-1456). In the presence of 5 micrograms/ml of tunicamycin, growing oocytes cultured in vitro are unable to carry out "core" glycosylation of nascent ZP2 and ZP3. Consequently, under these conditions, ZP2 and ZP3 appear as 81,000 and 44,000 Mr polypeptide chains, respectively. The apparent rates of synthesis of core-glycosylated ZP2 and ZP3 precursors synthesized in the absence of tunicamycin and of precursors synthesized in the presence of the drug are virtually identical. On the other hand, in the presence of tunicamycin, nascent ZP3 is incorporated into the zona pellucida as an extremely heterogeneous species (approximately equal to 51,000 Mr) at about three times the rate observed for mature ZP3 in the absence of tunicamycin. In the presence of tunicamycin, ZP2 is incorporated into the zona pellucida as 81,000 and 76,000 Mr species at about one-sixth the rate observed for mature ZP2 in the absence of the drug. Results of pulse-chase experiments indicate that the low degree of incorporation of ZP2 lacking N-linked oligosaccharides into the zona pellucida is due to a greatly decreased rate of secretion as compared to the core-glycosylated precursor. ZP2 synthesized in the presence of tunicamycin is relatively stable and accumulates intracellularly. These results suggest that N-linked oligosaccharides are necessary for normal secretion of ZP2, but are probably not necessary for ZP3 secretion.
Animals↗
Biosynthesis of the sperm receptor during oogenesis in the mouse.
During their growth phase, mouse oocytes synthesize and secrete three different glycoproteins, called ZP1, 2 and 3, that constitute the extracellular coat, or zona pellucida, of the oocyte. One of these glycoproteins, ZP3, exhibits properties expected for a sperm receptor. We have now used rabbit antisera that recognize ZP3 to immunoprecipitate [35S]methionine-labeled, intracellular precursors of this glycoprotein from growing oocytes cultured in vitro in the presence or absence of tunicamycin, a drug that prevents addition of N-linked oligosaccharides to nascent polypeptide chains. Electrophoretic analyses of these immunoprecipitates, as well as of immunoprecipitates digested with endo-beta-N-acetylglucosaminidase H (Endo H), indicate that ZP3 is synthesized as a 44,000 mol. wt. polypeptide chain to which either three or four high-mannose-type oligosaccharides are added, resulting in 53,000 and 56,000 mol. wt. ZP3 precursors, respectively. The latter species are converted to mature ZP3 (mol. wt. approximately 80,000) by processing of the high-mannose-type oligosaccharides (Endo H-sensitive) to complex-type oligosaccharides (Endo H-insensitive) prior to ZP3 secretion. The evidence presented reveals that the extreme heterogeneity of mature ZP3, with respect to both mol. wt. and isoelectric point, is partly a consequence of the N-linked oligosaccharides and not the polypeptide chain itself.
Animals↗
Biosynthesis of the major zona pellucida glycoprotein secreted by oocytes during mammalian oogenesis.
An antiserum directed specifically against ZP2, the major glycoprotein of the mouse egg's extracellular coat (zona pellucida), has been used to immunoprecipitate intracellular precursors of ZP2 that were synthesized by growing mouse oocytes cultured in vitro. Pulse-chase experiments revealed that the immediate precursor of mature, 120 kilodalton (kd) ZP2 is a 91 kd species that unlike mature ZP2, is sensitive to digestion by endo-beta-N-acetylglucosaminidase H (Endo H) and is converted by the endoglycosidase into an 81 kd species. An 81 kd species is only found intracellularly when growing oocytes are cultured in the presence of tunicamycin. These results suggest that ZP2 is synthesized as an 81 kd polypeptide chain that is first "core"-glycosylated at asparagine residues with high-mannose-type oligosaccharides, giving rise to a 91 kd intermediate (Endo-H-sensitive), and then processed to complex-type oligosaccharides prior to secretion as mature, 120 kd ZP2 (Endo H-insensitive). Furthermore, electrophoretic analyses of mature ZP2, ZP2 precursor (91 kd) and Endo H-treated ZP2 precursor (81 kd) suggest that there are six N-linked oligosaccharides per molecule and that the extreme heterogeneity of mature ZP2 is a consequence of the oligosaccharides and not the polypeptide chain itself.
Acetylglucosaminidase↗
Minimal bile acid malabsorption and normal bile acid breath tests in cystic fibrosis and acquired pancreatic insufficiency.
This study was undertaken because of reports of a marked increase in fecal bile acid excretion by children with cystic fibrosis. We attempted to confirm this finding by performing [1-14C]cholylglycine breath tests and by measuring fecal bile acid and fat excretion in patients with cystic fibrosis and acquired pancreatic insufficiency. Studies were done when patients were taking pancreatic enzymes (Cotazym) and also without medication. 14CO2 excretion in breath was normal in patients with acquired pancreatic insufficiency and even lower in cystic fibrosis, both with and without Cotazym therapy. Fecal bile acid excretion was slightly elevated in both groups without Cotazym and became normal with Cotazym in patients with acquired pancreatic insufficiency. Steatorrhea was present in both patient groups and improved during Cotazym therapy. Bile acid malabsorption in cystic fibrosis and acquired pancreatic insufficiency is minimal and probably not clinically important.
Adult↗
Oral cholecystography after alcoholic pancreatitis.
Retrospective and prospective studies were done to evaluate the efficacy of oral cholecystography (OCG) performed before hospital discharge on alcoholic patients with acute pancreatitis. In the retrospective study, OCG adequately opacified the gallbladder in 21 of 26 patients (81%). Of the 5 patients with inadequate opacification, 1 was jaundiced at the time of OCG; the other 4 had OCG before resumption of solid food. In the prospective study, OCG done in nonjaundiced patients shortly after resumption of food yielded adequate opacification in 19 of 21 patients (90%) without gallstones. We conclude that in nonjaundiced alcoholic patients with acute pancreatitis not caused by gallstones, OCG performed after resumption of a solid diet and before hospital discharge is usually successful in opacifying the gallbladder.
Alcoholism↗