cMolecules involved in WNT/-catenin signaling show specific spatiotemporal expression and play vital roles in myogenesis; however, it is still largely unknown how WNT/-catenin signaling regulates each step of myogenesis. Here, we show that WNT/ -catenin signaling can control diverse biological processes of myogenesis by regulating step-specific molecules. In order to identify the temporally specific roles of WNT/-catenin signaling molecules in muscle development and homeostasis, we used in vitro culture systems for both primary mouse myoblasts and C2C12 cells, which can differentiate into myofibers. We found that a blockade of WNT/-catenin signaling in the proliferating cells decreases proliferation activity, but does not induce cell death, through the regulation of genes cyclin A2 (Ccna2) and cell division cycle 25C (Cdc25c). During muscle differentiation, the inhibition of WNT/-catenin signaling blocks myoblast fusion through the inhibition of the Fermitin family homolog 2 (Fermt2) gene. Blocking WNT/-catenin signaling in the well-differentiated myofibers results in the failure of maintenance of their structure by disruption of cadherin/-catenin/actin complex formation, which plays a crucial role in connecting a myofiber's cytoskeleton to the surrounding extracellular matrix. Thus, our results indicate that WNT/-catenin signaling can regulate multiple steps of myogenesis, including cell proliferation, myoblast fusion, and homeostasis, by targeting step-specific molecules.S keletal muscle plays highly specialized roles in the generation of force and is capable of extensive metabolic and functional plasticity. Skeletal muscle also exhibits robust regenerative capacity, and its formation is composed of complex and highly regulated processes among embryonic development and regeneration in mature skeletal musculature (1). Muscle precursor cells (also known as satellite cells in the adult) lie under, or are embedded in, the basal lamina of the myofiber in skeletal muscles and are the major source of regeneration and growth of skeletal muscles (2). During development and regeneration in response to injury or recovery from atrophy, muscle precursor cells start to proliferate, at which stage they are referred to as myoblasts, and subsequently differentiate to form new myofibers or fuse with existing myofibers (2). These processes require fine-tuned regulations of proliferation and differentiation that are likely regulated by signal transduction pathways.The WNT family (wingless-type mouse mammary tumor virus [MMTV] integration site family) of signaling molecules consists of 21 secreted glycoprotein ligands. WNT ligands are essential to activate downstream pathways (canonical -catenin-dependent and/or noncanonical -catenin-independent pathways) in physiological and pathological conditions. WNT/-catenin signaling can regulate a variety of genes in a specific spatiotemporal manner (3). In the absence of WNT ligands, -catenin is incorporated into a protein complex containing axin, adenomatous polyposis coli (A...