Single-cell RNA sequencing of sclerotome-derived fibroblasts in zebrafish

Despite their importance in tissue maintenance and repair, fibroblast
diversity and plasticity remain poorly understood. Using single-cell RNA
sequencing, we uncover distinct sclerotome-derived fibroblast populations
in zebrafish, including progenitor-like perivascular/interstitial
fibroblasts, and specialized fibroblasts such as tenocytes. To determine
fibroblast plasticity in vivo, we develop a laser-induced tendon ablation
and regeneration model. Lineage tracing reveals that laser-ablated
tenocytes are quickly regenerated by preexisting fibroblasts. By combining
single-cell clonal analysis and live imaging, we demonstrate that
perivascular/interstitial fibroblasts actively migrate to the injury site,
where they proliferate and give rise to new tenocytes. By contrast,
perivascular fibroblast-derived pericytes or specialized fibroblasts,
including tenocytes, exhibit no regenerative plasticity. Interestingly,
active Hedgehog (Hh) signaling is required for the proliferation of
activated fibroblasts to ensure efficient tenocyte regeneration. Together,
our work highlights the functional diversity of fibroblasts and
establishes perivascular/interstitial fibroblasts as tenocyte progenitors
that promote tendon regeneration in a Hh signaling-dependent manner.