Patterns of gene expression associated with BMP-2-induced osteoblast and adipocyte differentiation of mesenchymal progenitor cell 3T3-F442A.

The pluripotent mesenchymal stem cells give rise to osteoblasts, adipocytes, chondrocytes, and myoblasts. The differentiation of these stem cells into each of the mature functional cells may be controlled by a distinctive master gene(s) and is associated with temporal and spatial expression of diverse genes. Identification of genes that are expressed during the differentiation of the mesenchymal cells to osteoblasts is, therefore, important to obtain insights into the molecular mechanisms of osteogenesis. The murine undifferentiated mesenchymal cell 3T3-F442A, when treated with the bone morphogenetic protein 2 (BMP-2), a well-characterized inducer of mesenchymal cell differentiation, exhibited both osteoblastic and adipocytic differentiation. Using the SAGE (serial analysis of gene expression) technique, which has been shown to enable quantitative analysis of large numbers of genes in a simple and quick manner, we obtained 1600 sequence tags representing 2107 individual nucleotide sequences from control and BMP-2-treated 3T3-F442A cells, respectively. By comparing the frequency of tag occurrence, we found profiles of up- or downregulated genes associated with osteoblast or adipocyte phenotype such as type I collagen, osteonectin and OSF-2, or C/EBPbeta, aP2, fatty acid synthase, and lipoprotein lipase, respectively, in BMP-2-treated 3T3-F442A cells. Our data show that BMP-2 induces not only osteoblastic but also adipocytic differentiation in the 3T3-F442A cells. They also show that the 3T3-F442A cells have bipotentials of differentiating toward osteoblasts and adipocytes. The results, therefore, might explain the inverse correlation between trabecular bone volume and fat volume in the bone marrow cavity. The results also suggest that the SAGE may be a useful technique that allows us a fast and efficient way to generate global and local views of gene expression associated with cellular differentiation of the mesenchymal stem cells.