Aging is associated with functional deterioration and reduced regenerative capacity of tissues and organ systems. Underlying molecular mechanisms are numerous and include accumulation of somatic mutations. Our project aims to functionally evaluate whether high number of random somatic mutations in skeletal muscle progenitor cells (satellite cells) could cause loss of muscle mass and strength and compromise muscle tissue regeneration, a phenotype observed in an aged organism. To this end we have generated a conditional knockout mouse model by deletion of DNA mismatch repair gene Msh2 in Pax7-positive satellite cells. Combining this with three cycles of chemically-induced muscle injury and regeneration established a mutator phenotype in muscle tissue of these mice producing a high number of random single- and di-nucleotide mutations. Using grip strength in vivo test and comparing the weight of the regenerated muscle we have observed a significantly reduced regeneration capacity in mice with the conditional knockout of Msh2. In this project we will WGS sequencing at 60x depth to confirm the expected accumulation of somatic mutations in muscle tissue of these mice and to acquire the induced mutational signatures. We have two types of samples for this, DNA isolated from PFA-fixed and paraffin-embedded (FFPE) mouse muscle tissue (experimental samples) and DNA isolated from frozen mouse spleen (reference samples). Since skeletal muscle tissue of these mice was exposed to repeated injury and regeneration cycles we expect a certain level of clonality for the accumulated somatic mutations in experimental samples. Reference samples will be used to distinguish between somatic and germline mutations.