Cells and Materials


Bone cells possess the ability to synthesize, secrete and direct the assembly and maintenance of extracellular matrix to form a functionally rigid and/or weight-bearing mineralized tissue complex, the skeleton. The skeleton not only supports and protects the organs and tissues of the body, but also acts as a mineral ion reservoir for maintaining systemic calcium balance (calcium homeostasis). The remarkable biological precision necessary for the formation, turnover and constant adaptation of bone to external mechanical forces is a dynamic process requiring a coordinated cellular effort relying on a variety of cell-cell and cell-matrix/mineral interactions. Indeed, cell-matrix interfaces found in a variety of locations in bone are sites potentially rich in signalling mechanisms related to bone modeling and remodeling. Detailed examination of the structure, composition and function of bone cells, and the extracellular matrix they produce and continuously remodel, is a complex task for such a mineralized tissue and requires integration and correlation of data from numerous sources. Various morphological approaches have added significantly to our understanding of bone form and function, and have allowed us to partly unravel some of the complex cellmatrix-mineral associations that occur during osteogenesis. In this context, the present article reviews some of our recent ultrastructural, cytochemical and immunocytochemical data on mammalian and avian intramembranous and endochondral bone formation (modeling) and turnover (remodeling).