Fig. 5. Abnormal remodeling of PAAs in Ltbp1L mutants and normal differentiation of CNCCs into SMCs. (A,B) Visualization of pharyngeal arch arteries (PAAs) by India ink injection in E10.5 control (A) and knockout (KO; B) hearts. The third, fourth and sixth PAAs are properly formed in Ltbp1L^-/- embryos. (C,D) Semi-transverse sections of E11.5 control and mutant embryos, stained with SMA antibody and Hematoxylin. A ring of smooth muscle cells (SMCs; brown) surrounds all three pairs of PAAs both in control (C) and in KO (D) embryos. (E,F) Normal differentiation of CNCCs within the OFT of control and Ltbp1L^-/- into SMCs. SMCs are visualized by staining with an antibody to SMA. (G-J) Left fourth PAA is shown. Transverse sections of E12.5 control (G,I) and Ltbp1L^-/- (H,J) embryos stained with active caspase 3 (G,H) or SMA (I,J) antibody. Notice the clusters of apoptotic cells in the mutant left fourth PAA (arrowheads in H).