Osr2-IresCre;Smoc/c mutant mice exhibit cleft palate and open eyelids at birth. (A, B) Neonatal control (A) and Osr2-IresCre;Smoc/c mutant (B) mice showing open eyelids (arrow) at birth in the mutant. (C, D) Frontal sections of E17.5 control (C) and Osr2-IresCre;Smoc/c mutant (D) embryos showing cleft palate in the mutant. (E, F) Skeletal preparations of control (E) and Osr2-IresCre;Smoc/c mutant (F) neonatal mice showing widely separate palatine bones (arrows) in the mutant. The insets show high magnification views of the tympanic rings (arrowheads) in the Osr2-IresCre;Smo+/c (E) and Osr2-IresCre;Smoc/c mutant (F) skeletons. Bones are stained red and cartilage blue. Asterisk in F marks the presphenoid bone of the cranial base, which is hidden under the palatine bones from the oral view of the skeleton in the control mouse in E but fully exposed in the Osr2-IresCre;Smoc/c mutant skeleton due to cleft palate. n, nasal septum; p, palatal shelf; t, tongue.