The expression of cellular oncogenes c-myc and c-fos in rat skeletal muscle : changes during development and hypertrophy
A study has been made on the expression of cellular oncogenes c-myc and c-fos in rate skeletal muscle both in vitro in cell lines and primary culture and in vivo during development and after the induction of two models of hypertrophy. Using the technique of Northern hybridisation, results showed that the pattern of expression of c-myc and c-fos mRNA in primary myoblast cells and in established myoblast and fibroblast cells in culture were similar; stimulation of quiescent cells to proliferate induced expression from the c-fos gene within 30 minutes and the c-myc gene by 2 hours. The findings demonstrate that c-myc and c-fos mRNA levels are increased in terminally differentiated rat skeletal muscle both in vitro and in vivo. They confirm work which showed that c-myc is not exclusively connected with cell proliferation (Endo and Nadal-Ginard 1986) and extend previous work into the increased expression of c-myc and c-fos mRNA in cardiac muscle induced to hypertrophy (Mulvagh et al., 1987; Izumo et al., 1988; Komuro et al., 1988). The possible location of the elevated expression within the muscle after hypertrophy and the relative contributions from an inflammatory response, satellite cells and myofibres are discussed. Elevation of c-myc and c-fos mRNA in hypertrophy induced both surgically by tenotomy and pharmocologically with clenbuterol argue against a significant contribution from infiltrating fibroblasts, while from the literature, the activation of satellite cells appears to occur later. It is concluded that the elevated expression of c-myc in skeletal muscle is probably located within the myofibres and may be linked to mechanisms of cell enlargement. However further confirmation with in situ hybridisation and immunohistochemistry is required.