eLife Assessment
This study offers valuable information on how titin derived from different nuclei within the syncytium is organized and integrated during skeletal muscle development and remodeling. The authors developed a novel mCherry titin knock-in mice with the fluorophore mCherry inserted into titin's Z-disk region to track the titin during cell fusion. The approach using mcherry adds to understanding of the role and localization of titin in controlling stiffness of striated muscles and fine tuning contraction. The results demonstrate that the integration of titin into the sarcomere is tightly regulated, with its unexpected mobility aiding in the uniform distribution of titin post-cell fusion. Although the experimental approach is convincing, the work is very qualitative in its approaches, and the data needs rigorous statistical analysis. There is a need for some clarification concerning numbers of animals and control groups. Future studies will need more rigorous data analysis and interpretation.