FGF8 induces bone and joint regeneration at middle phalanx amputation wounds in neonate mice

Mice and humans have limited regenerative capacity following limb amputation, with regenerative responses restricted to amputations transecting the distal digit tip, (P3). Unlike P3, amputations of the adjacent skeletal segment, the middle phalanx, P2, are non-regenerative. Here, we report that FGF8 drives synovial joint regeneration at P2 amputation wounds in neonate mice. This response is characterized by the regeneration of a synovial cavity, a skeletal nodule lined with articular-like cartilage, tendon and ligament regeneration, and partial P2 stump regeneration. FGF8-induced joint regeneration is associated with the upregulation of several, but not all, genes that characterize joint development, and is morphologically distinct from digit joint development. Lineage tracing studies demonstrate that cells at the amputation wound contribute to the regenerated joint structures. These studies provide evidence that the otherwise non-regenerative P2 amputation wound possesses tremendous regenerative capacity that is not activated under normal circumstances. Overall design: scRNA-seq analysis of middle phalanx amputations in neonate mice (8 days postnatal, PN8).