Fig. 1. Cranial and appendicular skeletons are derived from a different embryonic origin. (A,B) In an adult Wnt1Cre::Z/EG mouse, mandibular osteocytes and periosteal cells are GFP-positive (neural crest-derived) (A), whereas the adjacent muscle and endothelium (arrowhead) is β-galactosidase-positive (mesoderm-derived) (B). (C,D) Secondary cartilage underlying the skull bone is GFP-positive (C), whereas the hematopoietic system residing in the bone marrow cavity is β-galactosidase-positive (D). (E) The Schwann cells surrounding a peripheral nerve in the hind limb are GFP-positive (arrowheads). (F) Osteocytes and periosteal cells in the tibia stain positive for β-galactosidase. bm, bone marrow; ca, cartilage; cb, cortical bone; mn, mandible; mu, muscle; po, periosteum; tib, tibia. Scale bar: 200 µm in A-C,E; 100 µm in D,F.