Fig. 4. The fate of CNCCs in Ltbp1L mutants. (A,B) Whole-mount in situ hybridizations of E9.5 wild-type (A) and knockout (KO; B) embryos, using a Crabp1 ribo-probe. Broken lines outline streams of cardiac neural crest cells (CNCCs) migrating into the outflow tract (OFT). (C,D) Fate mapping of CNCCs in Ltbp1L mutants. E11.5 wild-type (C) and Ltbp1L^-/- (D) transverse sections at the level at which the fourth pair of pharyngeal arch arteries (PAAs) branches out of the aortic sac. Green cells represent CNCCs. Arrowheads points to the aortico-pulmonary (AP) septum (C), or where it is missing (D). (E,F) Transverse sections of E11.5 heterozygous (E) and KO (F) embryos, stained with X-gal and Eosin. Blue cells express Ltbp1L. Black arrowheads indicate the AP septum (E) or its absence (F). Red arrowheads indicate Ltbp1L-expressing smooth muscle cells (SMCs) surrounding dorsal aortae. Ms, pharyngeal mesenchyme. (G) Quantification of mesenchymal cells and proliferating mesenchymal cells in E11.5 control and KO OFTs. Average of three sets of samples is shown. (H-K) Whole-mount in situ hybridization of E11.5 control (H,J) and KO (I,K) hearts using plexin A2 (H,I) and FoxC1 (J,K) ribo-probes. Plexin A2 and FoxC1 visualize post-migratory CNCCs in the control (arrows in H and J) but not Ltbp1L^-/- OFT.