Barx1 positively influences cellular proliferation within the pharyngeal arches. (A, B) Sagittal serial sections (10 μm) of the pharyngeal arch region stained with Phosphohistone-H3 antibody. (A) Control embryo at 48 hpf. (B) barx1 morphant. The neural crest derived mesenchyme is overlaid in green; arrows indicate stained nuclei; e, eye; m, mandibular arch; h, hyoid arch; gill arches are numbered. Anterior is to the left. Scale bar: 50 μm. (C) Averaged cell proliferation in control uninjected embryos (black bars) and barx1 morphants (see Fig. 4; white bars) was determined within the mesenchyme as shown in (A,B) at the indicated four time points. Approximately fifty serial sections per embryo were examined. Number of embryos examined is indicated above each bar. Scale bar: (A, B) 50 μm.