Characterization of muscle growth and sarcomere branching in the striated musculature of .

Striated muscles are essential for locomotion and survival. Their function and structure are highly conserved across taxa. Muscles are highly plastic. Muscle growth can occur through several distinct processes including developmental, allometric, and hypertrophic growth. Additionally, pathological conditions like Duchenne Muscular Dystrophy (DMD) can lead to abnormal muscle growth. While human muscle studies have revealed complex structural adaptations such as sarcomere branching, these processes remain less explored in model organisms like . In this study, we present an anatomical characterization of muscle growth in under various conditions that parallel those in mammalian systems. We examined developmental, allometric, and hypertrophic growth, as well as muscle atrophy in a DMD model, . We find that muscles undergo growth patterns similar to those observed in mammals, with region-specific increases in myocyte size, sarcomere number, and band widths under different conditions. Moreover, we report for the first time the presence of sarcomere branching and splitting in muscles, phenomena previously described only in vertebrates and Drosophila. We further report that sarcomere branching is modulated by environmental conditions and pathological states, with increased branching in worms raised swimming and reduced branching in dystrophic muscles. These findings provide new insights into the mechanisms of muscle adaptation and highlight the potential of as a model for studying muscle pathologies like DMD, particularly during periods of rapid growth.