Single-cell transcriptional mapping of <i>Mustn1</i> exhibits consistent mural cell localization across musculoskeletal tissues

The musculoskeletal temporally activated novel gene (<i>Mustn1</i>) 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 <i>Mustn1</i>. 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 <i>Mustn1</i> 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.