Immunolocalization of blood group A gene specified alpha 1,3N-acetylgalactosaminyltransferase and blood group A substance in the trans-tubular network of the Golgi apparatus and mucus of intestinal goblet cells.
The subcellular distribution of blood group A gene specified alpha 1,3N-acetylgalactosaminyltransferase and its product was studied in human intestinal goblet cells by immunoelectron microscopy. The O-glycosylation step yielding blood group A-active glycoconjugates occurred in the trans region of the Golgi apparatus as indicated by the presence of immunolabel for both antigens. In the Golgi apparatus, immunoreactive alpha 1,3N-acetylgalactosaminyltransferase was detectable in trans cisternae and in the trans-tubular network which was found to be continuous with the cisternal stack and exhibited acid phosphatase activity. This demonstrates that in intestinal goblet cells (i) the trans-tubular network does not constitute a compartment distinct from trans cisternae, and (ii) structures corresponding to GERL are structurally and functionally part of the Golgi apparatus. In addition to immunolabel for transferase at the inner surface of the cisternal membranes, luminally located immunolabel indicating the presence of free, not membrane-associated transferase became first detectable in the trans-tubular network and early forming mucus droplets contained therein. Further, the content of mature mucus droplets as well as the extracellular mucus layer were labeled. Absence of immunolabel in blood group 0 subjects lacking the blood group A gene specified transferase and the apparent non-reactivity of the antibodies with carbohydrate epitopes indicates that free alpha 1,3N-acetylgalactosaminyltransferase is present in mucus droplets and becomes secreted by intestinal goblet cells.
D000017:ABO Blood-Group System / Q000235:genetics*; D000936:Antigen-Antibody Complex / Q000032:analysis; D004386:Duodenum / Q000166:cytology / Q000201:enzymology* / Q000648:ultrastructure; D005700:Galactosyltransferases / Q000235:genetics* / Q000378:metabolism; D005796:Genes; D006056:Golgi Apparatus / Q000201:enzymology; D006801:Humans; D007082:Ileum / Q000166:cytology / Q000201:enzymology* / Q000648:ultrastructure; D007150:Immunohistochemistry; D017350:N-Acetylgalactosaminyltransferases
D000017:ABO Blood-Group System; D000936:Antigen-Antibody Complex; D005700:Galactosyltransferases; D017350:N-Acetylgalactosaminyltransferases; C003742:UDPgalactosamine-galactose acetylgalactosaminyltransferase