Osteoblast precursors at different anatomic sites

Skeletal morphology depends on the local regulation of bone formation, both in a quantitative and qualitative sense. The formative cells, osteoblasts, adjust their synthetic activity in response to signals that influence cell differentiation and matrix production. Here, we review data concerning the morphological patterning during bone ontogenesis and its direct cause: osteoblasts at specific anatomic sites. An overview of the possible origins of osteogenic cells is presented, considering bone growth and homeostasis, and discussing the repair process. A testable model is proposed, in which functional differences between osteoblast populations are explained by homeobox-gene regulation. Newly developed markers for osteoblast recruitment and differentiation provide an experimental system to test the impact of homeobox-gene expression on osteoblast differentiation and bone matrix production.