Abnormal actomyosin assembly in proliferating and differentiating myoblasts upon expression of a cytosolic DMPK isoform

► Expression of DMPK in the cytosol induces formation of stellar actomyosin stress fibers. ► Stellar stress fiber formation is accompanied by augmented phosphorylation of MLC2. ► Myoblasts expressing active cytosolic DMPK display altered cell morphology and motility. ► Early steps in myogenesis are delayed upon DMPK activity expression in the cytosol. ► High cytosolic DMPK activity during myogenesis supports formation of myosacs.