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A comparative immunocytochemical study on the subcellular distributions of 44 kDa bone phosphoprotein and bone γ‐carboxyglutamic acid (Gla)‐containing protein in osteoblasts
Author(s) -
Mark Manuel P.,
Prince Charles W.,
Gay Steffen,
Austin Ronald L.,
Bhown Merra,
Finkelman Richard D.,
Butler William T.
Publication year - 1987
Publication title -
journal of bone and mineral research
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.882
H-Index - 241
eISSN - 1523-4681
pISSN - 0884-0431
DOI - 10.1002/jbmr.5650020411
Subject(s) - bone sialoprotein , phosphoprotein , osteocalcin , antigenicity , chemistry , antigen , golgi apparatus , immunocytochemistry , microbiology and biotechnology , endoplasmic reticulum , osteonectin , antibody , immunostaining , primary and secondary antibodies , osteopontin , alkaline phosphatase , biochemistry , immunohistochemistry , biology , immunology , endocrinology , enzyme , phosphorylation
Bone γ‐carboxyglutamic acid (Gla)‐containing protein (BGP or osteocalcin) and 44 kDa bone phosphoprotein (44K BPP, also called Sialoprotein I or osteopontin) have been localized at the ultrastructural level in osteoblasts from woven bones of newborn rats. Frozen, undecalcified sections of periodate‐lysine‐paraformal‐dehyde fixed specimens were incubated with affinity purified, monospecific antibodies against BGP or 44K BPP. The sites of the antigen‐antibody reaction were demonstrated by the avidin‐biotin‐peroxidase complex method using the Hanker‐Yates reagent as a peroxidase substrate. In some cases immunostaining could only be achieved after detergent treatment. The immunostained sections were then flat‐embedded in Epon 812 and processed for electron microscopy. Strong specific intracellular labeling was obtained with both antibodies, but the patterns of staining differed significantly: BGP antigenicity was mainly located in the endoplasmic reticulum (ER), whereas 44K BPP behaved as a Golgi‐specific antigen. In both cases, however, we found no evidence for immunostained secretory vesicles. There was no correlation between the expression of BGP by osteoblasts and the morphological aspect of these cells, their apparent degree of polarization with respect to the bone matrix, or their relation with the mineralized phase.