title: Preferential association of glycoproteins to the euchromatin regions of cross-fractured nuclei is revealed by fracture-label.
abstract: We used fracture-label to establish ultrastructural localization of glycoproteins in cross-fractured nuclei of duodenal columnar and exocrine pancreatic cells. Mannose residues were detected in cell nuclei by labeling freeze-fractured tissues with concanavalin A-horseradish peroxidase X colloidal gold (Con A-HRP X CG) or direct concanavalin A X colloidal gold (Con A X CG); fucose residues were detected with Ulex Europaeus I X colloidal gold (UEA I X CG) markers. Areas of the three main intranuclear compartments (euchromatin, heterochromatin, and nucleolus) exposed by freeze-fracture were determined by automated image analysis. Colloidal gold particles bound to each nuclear subcompartment were counted and the results expressed in number of colloidal gold particles per square micrometer +/- SEM. Duodenal and pancreatic tissues fractured and labeled with Con A-HRP X CG complex or direct Con A X CG conjugates showed that the vast majority of Con A binding sites was confined to euchromatin regions with only sparse labeling of the heterochromatin and nucleolus. UEA I labeling of duodenal columnar cells showed that colloidal gold particles were almost exclusively confined to cross-fractured areas where euchromatin is exposed. Trypsinization of the fractured tissues before labeling with Con A and UEA I abolished 95-100% of the original label. Our results show that, within the nucleoplasm, mannose and fucose are residues of glycoproteins preferentially located within the regions of euchromatin.
mesh_terms: D000818:Animals; D002466:Cell Nucleolus / Q000378:metabolism; D002843:Chromatin / Q000378:metabolism*; D003208:Concanavalin A / Q000378:metabolism; D004386:Duodenum / Q000648:ultrastructure; D005614:Freeze Fracturing / Q000379:methods*; D006023:Glycoproteins / Q000378:metabolism*; D006046:Gold; D006570:Heterochromatin / Q000378:metabolism; D006801:Humans; D007223:Infant; D037102:Lectins / Q000378:metabolism; D008854:Microscopy, Electron; D009685:Nuclear Envelope / Q000648:ultrastructure*; D010179:Pancreas / Q000648:ultrastructure; D037121:Plant Lectins; D051381:Rats
chemical_list: D002843:Chromatin; D006023:Glycoproteins; D006570:Heterochromatin; D037102:Lectins; D037121:Plant Lectins; C036850:Ulex europaeus lectins; D003208:Concanavalin A; D006046:Gold