a, The periosteum of mouse femur 6 (left), 9 (middle) and 15 (right) days after fracture. b, Haematoxylin and eosin staining of callus tissue 6 (top), 9 (middle) and 15 (bottom) days after fracture. c, CD200 (magenta) immunostaining of femurs collected 6 (top and middle) and 9 (bottom) days after fracture. d, Immunostaining for type 2 collagen (magenta) 9 days after fracture. e, TRAP staining (magenta), identifying osteoclasts in the bone callus (top) and bone marrow (middle) of fractured femurs. Few to no TRAP-positive cells were present in the periosteal region (bottom). Images in a–e are representative of 3 independent experiments. f, PSCs isolated from fracture callus were transplanted into kidney capsule secondary hosts. µCT images of bone formation at 3 (left), 4 (middle) and 5 weeks (right) after PSC transplantation to the kidney capsule (i). Safranin O staining (red), and Von-Kossa staining (black) were performed on sectioned kidney samples to detect cartilage and bone at 3 (ii), 4 (iii) and 5 (iv) weeks after PSC transplantation. Scale bar, 10 µm. Haematoxylin and eosin staining indicates that PSCs isolated from fracture callus are competent to recruit host-derived haematopoietic elements at the site of transplantation (yellow arrows, v). g, Immunostaining reveals co-localization of CTSK–mGFP+ cells (green) with cartilage-specific markers such as COMP (magenta, top and middle) and aggrecan (magenta, bottom) 4 weeks after PSC transplantation. Scale bar, 20 µm. Images in f and g are representative of 3 independent experiments.