Bone stem cells

Osteoblasts are the skeletal cells responsible for synthesis, deposition, a nd mineralization of the extracellular matrix of bone. By mechanisms that a re only beginning to be understood, stem and primitive osteoprogenitors and related mesenchymal precursors arise in the embryo and at least some appea r to persist in the adult organism, where they contribute to replacement of osteoblasts in bone turnover and in fracture healing. In this paper, the n ature of these cells, whether they constitute a stem cell pool or a committ ed progenitor pool, and aspects of their apparent plasticity are discussed. Current understanding of differential expression of osteoblast-associated genes during osteoprogenitor proliferation and differentiation to mature ma trix synthesizing osteoblasts is summarized. Finally evidence is discussed that supports the hypothesis that the mature osteoblast phenotype is hetero geneous with subpopulations of osteoblasts expressing only subsets of the k nown osteoblast markers, raising also the possibility of multiple parallel differentiation pathways and perhaps even different progenitor pools. I. Ce ll. Biochem. Suppls. 30/31 :73-82, 1998. (C) 1998 Wiley-Liss, Inc.