A, B. Lineage tracing of the NC in control and FN-null embryos at E9.5. Wnt1-Cre transgenic (A, B), Pax3Cre/+ knock-in (C, D) and R26R reporter strains were used to detect the NCCs and their descendants. Brackets mark pharyngeal regions containing CNCCs; asterisks in A and D mark interruption in NCC distribution at sites of putative trigeminal ganglia in the mutants. Dotted lines mark approximate planes of section shown in A″–D″. Asterisk in D″ marks a blood vessel contiguous with the common cardinal vein in serial sections caudal to the one shown. A–D. Distributions of NCCs in the head and branchial arches are similar between control and mutant embryos. A′–D′. Magnified views of branchial arches show that NCCs fill the arches to their ventral-most extent. Arrows point to the ventral pharyngeal ectoderm, the furthest border of the arches and show that NCCs have reached this border in controls and mutants. A″–D″. CNCCs entered the cardiac outflow tract in control and mutant embryos (arrows). Scale bars are 100 μm.