The Journal of Cell Biology, Vol 91, 11-16, Copyright © 1981 by The Rockefeller University Press
Synthesis of rat myosin light chains in heterokaryons formed between undifferentiated rat myoblasts and chick skeletal myocytes
WE Wright
The control of gene expression during terminal myogenesis was explored in
heterokaryons between differentiated and undifferentiated myogenic cells by
analyzing the formation of species specific myosin light chains of chick
and rat skeletal muscle. Dividing L6 rat myoblasts served as the
biochemically undifferentiated parent. The differentiated parental cells
were mononucleated muscle cells (myocytes) that were obtained from primary
cultures of embryonic chick thigh muscle by blocking myotube formation with
EGTA and later incubating the postimitotic cells in cytochalasin B.
Heterokaryons were isolated by the selective rescue of fusion products
between cells previously treated with lethal doses of different cell
poisons. 95-99% pure populations of heterokaryons formed between
undifferentiated rat myoblasts and differentiated chick myocytes were
obtained. The cells were labeled with [35S]methionine, and whole cell
extracts were analyzed on two-dimensional polyacrylamide gels. These
heterokaryons synthesize the light chain of chick myosin and both embryonic
and adult light chains of rat skeletal myosin. Control homokaryons formed
by fusing undifferentiated cells to themselves did not synthesize skeletal
myosin light chains. Control heterokaryons formed between undifferentiated
rat myoblasts and chick fibroblasts also failed to synthesize myosin light
chains. These results indicate that differentiated chick muscle cells
provide some factor that induces L6 myoblasts to synthesize rat myosin
light chains. This system provides a model for investigating the processes
by which differentiated cell functions are induced.
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