Acquisition of a unique mesenchymal precursor-like blastema state underlies successful adult mammalian digit tip regeneration

Here, we investigate the origin and nature of blastema cells that regenerate the adult murine digit tip. We show that Pdgfra-expressing mesenchymal cells in uninjured digits establish the regenerative blastema and are essential for regeneration. Single cell profiling shows that the mesenchymal blastema cells are distinct from both uninjured digit and embryonic limb/digit Pdgfra-positive cells. This unique blastema state is environmentally determined; dermal fibroblasts transplanted into the regenerative, but not non-regenerative, digit express blastema markers and contribute to bone regeneration. Moreover, lineage tracing with single cell profiling indicates that endogenous osteoblasts/osteocytes acquire a blastema mesenchymal transcriptional state and contribute to both dermis and bone regeneration. Thus, mammalian digit tip regeneration occurs via a distinct adult mechanism where the regenerative environment promotes acquisition of a unique blastema state that allows cells from tissues like bone to contribute to regeneration of other mesenchymal tissues such as the dermis. High-throughput single cell transcriptomic profiles of uninjured (dataset1 and duplicate dataset), regenerating (7, 10, 14, duplicate 14 dataset, 28, 56 days post amputation) and non-regenerative (10, duplicate 10 dataset, 14 days post amputation) digit tips of C57BL/6 and transgenic Dmp1CreERT2;TdTomato (Uninjured and 14 day post amputation) adult mice, together with embryonic limbs (E11)/digit tips (E14) or neonatal (P3) digit tips of C57BL/6 mice were generated by single cell RNA sequencing, using the 10X Genomics platform. Processed data for 16 datasets are included as indicated.