title: Refinement of collagen-mineral interaction: a possible role for osteocalcin in apatite crystal nucleation, growth and development.
abstract: Mineralization of vertebrate tissues such as bone, dentin, cementum, and calcifying tendon involves type I collagen, which has been proposed as a template for calcium and phosphate ion binding and subsequent nucleation of apatite crystals. Type I collagen thereby has been suggested to be responsible for the deposition of apatite mineral without the need for non-collagenous proteins or other extracellular matrix molecules. Based on studies in vitro, non-collagenous proteins, including osteocalcin and bone sialoprotein, are thought to mediate vertebrate mineralization associated with type I collagen. These proteins, as possibly related to mineral deposition, have not been definitively localized in vivo. The present study has reexamined their localization in the leg tendons of avian turkeys, a representative model of vertebrate mineralization. Immunocytochemistry of osteocalcin demonstrates its presence at the surface of, outside and within type I collagen while that of bone sialoprotein appears to be localized at the surface of or outside type I collagen. The association between osteocalcin and type I collagen structure is revealed optimally when calcium ions are added to the antibody solution in the methodology. In this manner, osteocalcin is found specifically located along the a4-1, b1, c2 and d bands defining in part the hole and overlap zones within type I collagen. From these data, while type I collagen itself may be considered a stereochemical guide for intrafibrillar mineral nucleation and subsequent deposition, osteocalcin bound to type I collagen may also possibly mediate nucleation, growth and development of platelet-shaped apatite crystals. Bone sialoprotein and osteocalcin as well, each immunolocalized at the surface of or outside type I collagen, may affect mineral deposition in these portions of the avian tendon.
authors.affiliation: Department of Polymer Science, University of Akron, Akron, OH, USA.
authors.forename: Ling
authors.initials: L
authors.lastname: Chen
authors.affiliation: Department of Polymer Science, University of Akron, Akron, OH, USA.
authors.forename: Robin
authors.initials: R
authors.lastname: Jacquet
authors.affiliation: Department of Polymer Science, University of Akron, Akron, OH, USA.
authors.forename: Elizabeth
authors.initials: E
authors.lastname: Lowder
authors.affiliation: Department of Polymer Science, University of Akron, Akron, OH, USA. Electronic address: wlandis@uakron.edu.
authors.forename: William J
authors.initials: WJ
authors.lastname: Landis
mesh_terms: D000818:Animals; D001031:Apatites / Q000737:chemistry*; D002113:Calcification, Physiologic; D003094:Collagen / Q000378:metabolism*; D003460:Crystallization; D058574:Integrin-Binding Sialoprotein / Q000378:metabolism; D008297:Male; D008903:Minerals / Q000378:metabolism*; D009942:Organometallic Compounds / Q000378:metabolism; D015675:Osteocalcin / Q000378:metabolism*; D011859:Radiography; D013710:Tendons / Q000000981:diagnostic imaging / Q000648:ultrastructure; D014422:Turkeys
chemical_list: D001031:Apatites; D058574:Integrin-Binding Sialoprotein; D008903:Minerals; D009942:Organometallic Compounds; D015675:Osteocalcin; C005460:uranyl acetate; D003094:Collagen
keywords: Bone sialoprotein; Collagen; Immunocytochemistry; Mineralization; Osteocalcin; Turkey leg tendon