The Role of Ring1 and Rnf2 in Skeletal Muscle Regeneration

Abstract

The skeletal muscle environment is highly complex, with inputs from multiple cell types and environmental challenges in homeostatic and regenerative conditions. Satellite cells, a population of quiescent adult stem cells, maintain the regenerative potential of muscle well into adulthood, but the ability of the cells to maintain this is gradually lost as organisms age. In response to cues following injuries, or other insults to muscle integrity, satellite cells become activated. The activated satellite cells proliferate to provide nuclei to regenerate the damaged muscle, while also providing nuclei to return to the quiescent state for subsequent injuries. The changes between these states are tightly regulated and enabled through the flexible epigenetic modifications to the satellite cells. The Polycomb proteins have been shown to make significant contributions to cells' "memories of self", and in the regulation of stem cell fate transitions. How the Polycomb repressive complex 1 affects the regulation of the satellite cells has been poorly defined to date, but studies have shown that it is important for the regulation of myogenesis. In this study, we analyzed how the Polycomb repressive complex 1 affects the epigenetic regulation of satellite cells. To do this, we used shRNA's to Ring1 and Rnf2 to deplete the levels of the E3 ubiquitin ligases of the Polycomb repressive complex 1, and Prt4165 to determine the contribution of the enzymatic activity of the Polycomb repressive complex 1 complex without disrupting the non-enzymatic contributions of Ring1 and Rnf2. In our study, we have found in vitro that the Polycomb repressive complex 1 regulates the proliferation rate and differentiative capacity of C2C12 cells. We have also found that the enzymatic activity of the complex specifically regulates the ability of primary myocytes to fuse in vitro, potentially through regulating the motility of the cells. These results broaden our knowledge of the role of the Polycomb repressive complex 1 in skeletal muscle myogenesis, and the distinct contributions of the Prc1 complexes subunits to its regulatory functions.