Study on the mechanism of bipotential cell differentiation

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TBR 31-2 cells, established from the bone marrow of temperature-sensitive T-antigen gene transgenic mice, showed bipotential differentiation into adipocytes and osteoblasts on addition of a differentiation inducer. Comparison of the period of induction in alkaline phosphatase and calcification, as differentiation markers of osteoblasts showed that 9-passage cells needed longer periods than 15-passage cells.To study the differentiation capacity of TBR 31-2 cells in the presence of differentiation inducer, the m-RNA expression of the differentiation factor and differentiation phenotypes were examined by reverse transcription-polymerase chain reaction. In the presence of BMP-2, expression of the differentiation factor osteoblast core binding factor 1 and differentiation phenotypes such as alkaline phosphatase, type I collagen, osteopontin, PTH receptor and vitamin D receptor were increased in the stage of cell differentiation. In addition, a decrease of the m-RNA expression level of adipocyte differentiation markers, such as lipoprotein lipase and adipsin, was also observed, although the expression level of the adipocyte differentiation factor, peroxisome proliferator-activated receptor y> was not changed. Troglitazone, a typical differentiation inducer of adipocytes, caused the opposite phenomenon.Cell phenotype-specific analysis was performed by histochemical study to detect differentiated bipotential cells. In the presence of BMP-2, some crystallized condensations were observed showing calcium mineral deposits. On the other hand, adipocytes with cytoplasmic lipid droplets with oil red O staining appeared on addition of troglitazone.These observations suggest that TBR 31-2 cells show bipotential characteristics, differentiating into adipocytes and osteoblasts.