[Change of beta-actin gene expression during culture on osteoblast-like cell line, MC3T3-E1].

Multiple forms of actin (alpha, beta, and gamma-actin) have been found in a variety of mammalian cell lines and tissues by the use of high resolution, two-dimensional gel electrophoresis. alpha-Actin is found only in differentiated muscle cells, and its synthesis is induced during myogenesis in culture, beta- and gamma-actin isotypes are the principal components of microfilaments, structures believed to be involved in cellular morphogenesis, motility, and mitosis. Recent studies have shown that mammalian actin mRNA levels are modulated in response to changes in cell shape and during cell differentiation in vitro. On the other hand, Kodama et al. isolated clone MC3T3-E1 cells from newborn mouse calvaria, which have retained the ability to produce and mineralize a bone-like ground substance after many serial passages. Thus clone is useful for studying osteoblast differentiation as well as the mechanism of calcification. It is demonstrated that bone cells assume a stellate morphology after some hormone treatment and these changes were clearly associated with altered reorganization of the microfillaments which resulted in an enhanced osteoblast phenotype. We have now examined the effect of culture day on expression of beta-actin gene in MC3T3-E1 cells and found that expression of beta-actin gene reduced with culture days. These alternative on the expression of actin gene suggest that beta-actin may be involved in bone remodeling in vivo.