Fig. 1

Two-stage therapeutic utility of ectopically formed bone tissue induced by AAV-BMP4 in skeletal muscle. a Experimental design of two-stage therapeutic utility of ectopically formed bone tissue induced by AAV-BMP4 in skeletal muscle. b–d H&E staining of sample sections showing that the process of endochondral bone formation was triggered by the AAV-BMP4 with Gelfoam implantation in the muscle pocket. Cartilage (c) and bone (d) tissues were observed at weeks 2 and 4 after the implantation, respectively. e–g μCT assessments showed ectopic bone tissues appeared at weeks 2 (e), 12 (f), and 24 (g) after implantation. The density of ectopic bone tissues increased with time