Single-cell analysis of homeostatic and regenerative adult skeletal muscle stem cells

Skeletal muscle stem cells (MuSCs) ensure the formation and homeostasis of skeletal muscle and are responsible for its growth and repair processes. For repair to occur, MuSCs must exit from quiescence, abandon their niche and asymmetrically and symmetrically divide to reconstitute the stem cell pool and give rise to muscle progenitors, respectively. The transcriptomes of pooled MuSCs have provided a rich source of information for describing the genetic programs underlying distinct static cell states; however, bulk microarray and RNA-seq afford only averaged gene expression profiles, which blur the heterogeneity and developmental dynamics of asynchronous MuSC populations. The granularity required to identify distinct cell types, states, and their dynamics can be provided by single-cell analysis. We were able to compare the transcriptomes of thousands of MuSCs and primary myoblasts isolated from homeostatic or regenerating muscles by single-cell RNA- sequencing. Using computational approaches, we could reconstruct dynamic trajectories and place, in a pseudotemporal manner, the transcriptomes of individual MuSC within these trajectories. This approach allowed for the identification of distinct clusters of MuSCs and primary myoblasts with partially overlapping but distinct transcriptional signatures, as well as the description of metabolic pathways associated with defined MuSC states.