摘要：

The osteoblast is the bone-forming cell. The molecular basis of osteoblast-specific gene expression and differentiation is beginning to be understood. Osf2/Cbfa1, the protein that binds to OSE2, an osteoblast- specific cis-acting element present in the Osteocalcin promoter, recently has been identified as a transcriptional activator of osteoblast differentiation. Osf2/Cbfa1 is a member of the runt family of transcription factors expressed in the mesenchymal condensations of the developing skeleton and in cells of the osteoblast lineage. Osf2/Cbfa1 binds to and regulates the expression of multiple genes expressed in osteoblasts, and forced expression of Osf2/Cbfa1 in nonosteoblastic cells induces the expression of the principal osteoblast- specific genes. Osf2/Cbfa1 gene inactivation in mice leads to failure of mesenchymal progenitor cells to differentiate into osteoblasts. Lastly, heterozygous mutations in the Osf2/Cbfa1 gene cause Cleidocranial dysplasia in humans and mice, a condition marked by generalized bone defects. These results demonstrate that Osf2/Cbfa1 controls osteoblast differentiation and that its function is nonredundant with the function of other gene products during development.

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