Endoribonuclease L (RNase L) regulates the myogenic and adipogenic potential of myogenic cells.

Skeletal muscle maintenance and repair involve several finely coordinated steps in which pluripotent stem cells are activated, proliferate, exit the cell cycle and differentiate. This process is accompanied by activation of hundreds of muscle-specific genes and repression of genes associated with cell proliferation or pluripotency. Mechanisms controlling myogenesis are precisely coordinated and regulated in time to allow the sequence of activation/inactivation of genes expression. Muscular differentiation is the result of the interplay between several processes such as transcriptional induction, transcriptional repression and mRNA stability. mRNA stability is now recognized as an essential mechanism of control of gene expression. For instance, we previously showed that the endoribonuclease L (RNase L) and its inhibitor (RLI) regulates MyoD mRNA stability and consequently muscle differentiation.We now performed global gene expression analysis by SAGE to identify genes that were down-regulated upon activation of RNase L in C2C12 myogenic cells, a model of satellite cells. We found that RNase L regulates mRNA stability of factors implicated in the control of pluripotency and cell differentiation. Moreover, inappropriate RNase L expression in C2C12 cells led to inhibition of myogenesis and differentiation into adipocytes even when cells were grown in conditions permissive for muscle differentiation. Conversely, over-expression of RLI allowed muscle differentiation of myogenic C2C12 cells even in non permissive conditions.These findings reveal the central role of RNase L and RLI in controlling gene expression and cell fate during myogenesis. Our data should provide valuable insights into the mechanisms that control muscle stem cell differentiation and into the mechanism of metaplasia observed in aging or muscular dystrophy where adipose infiltration of muscle occurs.