Single-cell transcriptional mapping of Mustn1 exhibits consistent mural cell localization across musculoskeletal tissues.

The musculoskeletal temporally activated novel gene (Mustn1) is a 9.2-kDa microprotein that has been extensively studied within musculoskeletal tissues. Utilizing open-source, single-cell RNA sequencing datasets, we used a top-down, transcriptional approach that combines systems-wide and targeted-tissue mapping of Mustn1. In doing so, we observed robust mural cell-state colocalization of Mustn1 and Acta2 (encoding alpha smooth muscle actin [aSMA]) within bone, synovium, muscle, and tendon tissues. Mapping Mustn1 within recently documented, uncharacterized cell clusters of Sox9 lineage also revealed overlap with musculoskeletal fibroadipogenic progenitors (FAPs) and mural cells. Overall, these findings demonstrate that aSMA-expressing cells of the periosteum and tendon sheath provide a highly selective cell population to leverage the study of Mustn1 during musculoskeletal development and repair.