Osteonectin and Gla-protein in calf bone: ultrastructural immunohistochemical localization using the Protein A-gold method.

Osteonectin and bone Gla-protein have been localized at the ultrastructural level in calf scapula bone tissue. Post-embedding-decalcified thin sections of paraformaldehyde-fixed and Araldite-embedded specimens of calf scapula were incubated with rabbit antisera to bovine osteonectin and bone Gla-protein, and the sites of antigen-antibody reaction were demonstrated using the Protein A-gold technique. Specific labelling of the bone matrix was obtained with both antisera. The collagen fibers were labelled particularly intensely. Filamentous structures visible at the sites of early mineralization were labelled by rows of gold particles after incubation with anti-osteonectin antiserum. These findings are consistent with biochemical data available on the localization and properties of these non- collagenous proteins. 'Crystal ghost'-like structures are immunoreactive to anti-osteonectin antiserum.