Ectopic and excessive cell death in E9.5 <i>RockDN;Wnt1-cre</i> embryos.

<p>A–D are sections through the neural tube (line i in M), E–H through the pharyngeal arch 1 (line i in M) and I–L through the frontonasal processes (line ii in M). A,C,E,G,I,K show caspase 3-expressing cells (red) and Wnt1-cre+ve NCCs (green). B,D,F,H,J,L are the same sections but only showing the caspase 3-expressing cells. <b>A–D</b>) Whereas only very occasional activated caspase 3-expressing, dying, cells (red) are seen in the neural epithelium in control embryos, there are many dying cells observed in the dorsal part of the neural tube, from which the NCC emerge, in <i>RockDN;Wnt1-cre</i> mutant embryos (arrows in C and D). <b>E–L</b>) Very few activated caspase3-expressing cells are observed in the NCC-derived ectomesenchyme of pharyngeal arch 1 (E,F) and the frontonasal region (I,J) in control embryos. In contrast, many dying cells are seen in corresponding regions from <i>RockDN;Wnt1-cre</i> mutants (G,H,K,L). The surface ectoderm in the mutant is more irregular, compared to controls (arrowheads in E,G,I,K) and the inner NCC-derived ectomesenchyme is loosely arranged with gaps between the cells (arrows in G,K). <b>N,O</b>) The mean apoptotic and mitotic indexes were calculated for NCC within E9.5 pharyngeal arches. There is a significant increase in cell death in the mutant samples compared to controls (P = 0.019; * in N). There is no significant difference in cell proliferation between the two samples (P = 0.433; O). Scale bar = 50 µm.