Fig. 5. Increased apoptosis in Six1^–/–Six4^–/– embryos. Sections (10 µm) of heterozygous (A,C) and dKO (B,D) embryos at E10.5 at the hindlimb level, hybridized with antibodies revealing ß-gal protein (A,B) and activated caspase 3 (C,D), showing activated caspase 3-positive cells only in dKO embryos (white arrow in D). Sections (10 µm) of heterozygous (E) or dKO (F) embryos at E12.5 at the hindlimb level revealed with antibodies against ß-gal protein (in red) and activated caspase 3 (in green), and showing apoptosis of ß-gal-positive cells in dKO embryos that are rerouted ventrally (white arrow in F). Sections (10 µm) of heterozygous (G) and dKO (H) embryos at E10.5 at the first branchial arch level hybridized with antibodies revealing ß-gal protein (in red) and activated caspase 3 (in green), and showing apoptosis of ß-gal-positive cells in dKO embryos.