LAUSR

OBJECTIVE In chondrogenesis, BMP signaling was inferred to exhibit regional specificity during Meckel's cartilage morphogenesis. This study aimed to explore the differences in BMP signaling activity between different parts of Meckel's cartilage and the impacts of BMP4 or ALK3 deficiency on the development of Meckel's cartilage during embryogenesis. MATERIALS AND METHODS The BRE-gal reporter mouse line was utilized to gain an overall picture of canonical BMP signaling activity, as assessed by X-gal staining. Mouse models lacking either Bmp4 or Alk3 in neural crest cells (Wnt1-Cre;Bmp4fl/fl and Wnt1-Cre;Alk3fl/fl ) were generated to explore the morphogenesis of Meckel's cartilage and the mandibular symphysis, as assessed by skeletal staining, histology, and immunostaining. RESULTS Different parts of Meckel's cartilage exhibited activation of different combinations of BMP signaling pathways. In Wnt1-Cre;Bmp4fl/fl mutants, Sox9+ condensation of the chondrogenic rostral process failed to form, and the V-shaped Runx2+ tissue was split in the median mandibular symphysis. The Wnt1-Cre;Bmp4fl/fl and Wnt1-Cre;Alk3fl/fl mouse models both exhibited truncated Meckel's cartilage, aberrant mandibular intramembranous bone, and tongue muscle abnormalities. CONCLUSIONS The central hard-tissue loss of both mutant mouse models led to a mandibular symphysis cleft, mimicking the typical sign of the median mandible Tessier 30 cleft in humans.