Extracellular bone acidic glycoprotein-75 defines condensed mesenchyme regions to be mineralized and localizes with bone sialoprotein during intramembranous bone formation.
Bone acidic glycoprotein-75 is expressed very early during in vivo models of intramembranous bone formation, highly enriched in condensing osteogenic mesenchyme after marrow ablation and the osteoprogenitor layer of tibial periosteum. Bone sialoprotein accumulates within bone acidic glycoprotein-75-enriched matrix areas at a later stage in both models. Decalcification of initial sites of mineralization consistently revealed focal immunostaining for bone acidic glycoprotein-75 underneath these sites suggesting that mineralization occurs within bone acidic glycoprotein-75-enriched matrix areas. Ultrastructural immunolocalization of bone acidic glycoprotein-75 does not support a direct association with banded collagen fibrils, but rather suggests it is a component of a separate, amorphous scaffold occupying interfibrillar spaces. Double immunogold labeling demonstrated that a sizeable proportion of bone sialoprotein particles were located within a 50-nm radius of bone acidic glycoprotein-75. These results define bone acidic glycoprotein-75 as the earliest bone-restricted, extracellular marker of osteogenic mesenchyme. Based on this early bone-restricted expression pattern and a previously documented propensity of bone acidic glycoprotein-75 to form supramolecular complexes through self-association, bone acidic glycoprotein-75 may serve a key structural role in setting boundary limits of condensing osteogenic mesenchyme.
Division of Biochemistry and Molecular Biology, School of Biological Sciences, School of Dentistry, University of Missouri-Kansas City, Kansas City, Missouri 64108, USA. Gorskij@umkc.edu
Jeff P
JP
Gorski
Aimin
A
Wang
Dinah
D
Lovitch
Douglas
D
Law
Kimerly
K
Powell
Ronald J
RJ
Midura
D000818:Animals; D001842:Bone and Bones / Q000737:chemistry*; D002113:Calcification, Physiologic; D002356:Cartilage / Q000196:embryology; D003094:Collagen / Q000032:analysis; D005109:Extracellular Matrix / Q000737:chemistry*; D006023:Glycoproteins / Q000032:analysis* / Q000502:physiology; D007150:Immunohistochemistry; D058574:Integrin-Binding Sialoprotein; D008297:Male; D008648:Mesoderm / Q000737:chemistry*; D010012:Osteogenesis; D051381:Rats; D017207:Rats, Sprague-Dawley; D012795:Sialoglycoproteins / Q000032:analysis* / Q000502:physiology
D006023:Glycoproteins; C546873:Ibsp protein, rat; D058574:Integrin-Binding Sialoprotein; D012795:Sialoglycoproteins; C512787:bone acidic glycoprotein-75, rat; D003094:Collagen