Shox2 is expressed in mesenchymal progenitors of multiple cell types in the proximal limb. (A,B) Live imaging on Shox2HA/+ embryo reveals proximal expression of Shox2 (arrowhead) in embryonic forelimb (A) and hindlimb (B) at E12.5. (C) Immunofluorescence using anti-HA antibody on Shox2HA/+ embryo reveals strong perichondrial expression of Shox2 (arrowhead). (D-G) MF20 and GFP immunofluorescence on Shox2Cre/+;RosamTmG embryonic (D) and postnatal (E) mice reveals broad contribution of Shox2+ cells to connective tissue cell types such as chondrocyte (arrowheads in D), osteoblast/osteocyte (arrowheads in F) and dermal fibroblast (arrowhead in G). H, humerus; R, radius; U, ulna; F, femur.