GNAS/PKA pathway promotes aberrant osteochondral differentiation of Gli1+ tendon  sheath progenitors
We have employed a single cell sequencing approach using 10x Genomics scRNAseq to study the identity and fate determination of Gli1+ tendon sheath progenitors in heterotopic ossification(HO) formation following tenotomy. Gli1 is a signature gene for several tissue-specific Mesenchymal stem cells (MSCs). Aberrant osteochondral differentiation of MSCs in soft tissues leads to incorrect tissue regeneration into HO. This study demonstrated a subpopulation of Gli1+ tendon sheath cells that function as tendon stem/progenitors and can initially differentiate into normal or osteochondral tendon-lineage progenitors, with the latter subsequently giving rise to chondrocytes and osteocytes in development of tendon HO. Overall design: Gli1+ cells from uninjured and injured tendon(7-, and 21-days post-injury) of Gli1-CreERT2; Ai9 reporter mice with tamoxifen induction (n=24, equal sex distribution) were isolated by Fluorescence-activated cell sorting (FACS) and analyzed using scRNA-seq.