Retinoic acid promotes tissue regeneration by resolving stem cell lineage plasticity

Stem cells upended from their niche upon injury display lineage plasticity, a transient multi-lineage state essential for tissue repair. Employing high-throughput approaches and three-dimensional cultures of hair follicle stem cells (HFSCs), we investigate the signals that govern the transition between homeostatic regeneration and lineage plasticity. We identify retinoic acid (RA) as a master orchestrator of HFSC behavior during these two processes. In the hair follicle, RA signals within defined niches and interacts with WNT and BMP cues to drive hair regeneration. In wounded skin, reduced RA signaling prompts HFSCs to prioritize epidermal re-epithelialization and must be restored to promote hair regrowth. Substantiated in vivo, our findings have profound therapeutic implications for hair growth and for chronic wounds and cancers, where lineage plasticity is unresolved.