Fig. 2. Skeletal defects in Six1^–/–Six4^–/– newborn mice as revealed by Alizarin Red (bones) and Alcian Blue (cartilage) staining. (A,D,F) Six1^+/–Six4^+/– fetuses, (B,C,E,G) Six1^–/–Six4^–/– fetuses. Lateral and ventral view (A-C) of the trunk skeleton, showing truncation of the ribs, fusion and branching (black arrow in B). The sternum is shortened (black arrow in C). (D,E) Lateral view at the head level showing a shortened mandible bone (^*), shortened squamosal bone devoid of retrotympanic process (arrow) and lack of Meckel's cartilage (arrowhead) in the dKO fetuses, and complete absence of ear structure (^**). (F,G) Dorsal view of hands of forelimbs at the left or hindlimbs at the right of Six1^+/–Six4^+/– (F) and Six1^–/–Six4^–/– fetuses (G) showing a clinodactily in the dKO. The fifth finger is curved (arrows in G). (H) Human DNA samples from one individual with a 14q22 deletion (1), and two control DNA samples (2,3). DNA was digested with BamHI and hybridized with SIX1 cDNA (a, left panel) or SIX5 cDNA (c, right panel), or digested with HindIII and hybridized with SIX4 cDNA (b, middle panel). M.W., standard molecular weights. The signal observed for SIX1 and SIX4 in the individual with the 14q22 deletion is half that one observed in the control DNA, while the signal for SIX5 is comparable in all samples.