The mesenchymal architecture of the cranial mesoderm of mouse embryos is disrupted by the loss of Twist1 function

► Loss or malformation of skull vault and base in mesoderm-specific Twist1 mutants. ► CKO cranial mesoderm loses mesenchymal properties and gains epithelial properties. ► Extraocular muscles, eyelids and hypochiasmatic cartilage are lost or reduced. ► Abnormal ingression of mesoderm into neural crest and ectoderm-derived tissues.