Characterization of heterokaryons between skeletal myoblasts and preadipocytes: myogenic potential of 3T3-L1 preadipocytes

It has been shown previously that heterokaryons between myoblasts and non-myogenic cells disturb myogenic differentiation (Hirayama et al. (2001); Cell Struct. Funct. 26, 37-47), suggesting that some myogenesis inhibitory factors exist in non-myogenic cells. Skeletal myoblasts and adipose cells are derived from a common mesodermal stem cell, indicating that both cells have a closer relationship in the developmental lineage than the other somatic cells. To investigate the functional relationship between myoblasts and adipose cells, heterokaryons between quail myoblasts and 3T3-L1 cells, a mouse preadipocyte cell line, were prepared and examined for characteristics of myogenic differentiation. Myogenic differentiation was inhibited in the heterokaryons between quail myoblasts and well-differentiated (adipocytes) 3T3-L1 cells. On the contrary, normal myogenic differentiation proceeded in the heterokaryons between quail myoblasts and undifferentiated (preadipocytes) 3T3-L1 cells. Further investigation showed that the mouse myogenin gene from 3T3-L1 cells was transactivated in the heterokaryons between quail myoblasts and undifferentiated 3T3-L1 cells. The results demonstrated that undifferentiated 3T3-L1 cells have no myogenesis inhibitory factors but acquire these during terminal differentiation into adipocytes.