<i>Wnt5a</i> is expressed in the second heart field (SHF) and is downregulated in <i>Tbx1^−/−</i> embryos.

<p>(A–D′) The expression of <i>Wnt5a</i> was downregulated in the SHF, but not in the outflow tract (OFT) or the pharyngeal arch (PA) core mesoderm of <i>Tbx1^−/−</i> embryos at E8.0–11.5 (A′–D′), compared with the littermate controls (A–D), shown by whole-mount <i>in situ</i> hybridization (n = 3). Right view; arrowheads indicate the SHF. (E–J′) Transverse or sagittal sections cut from whole-mount <i>in situ</i> hybridized E8.0–9.0 <i>Tbx1^−/−</i> embryos (F, H, J) showed the downregulation of <i>Wnt5a</i> expression, compared with the littermate control (E, G, I, n = 3); squared regions are magnified on the adjacent panels; arrows indicate the SHF/splanchnic mesoderm domain. Arrowheads on panel E′ indicate a mesodermal expression domain strongly affected by the loss of <i>Tbx1</i>. (K–P) 3D reconstructions of E8.0 WT and <i>Tbx1^−/−</i> embryos provide a schematic, overall view of the expression domains regulated by <i>Tbx1</i>. Reconstructions were built using sections from embryos shown in E and F. Arrows indicate the SHF. PA: pharyngeal arch; OFT: outflow tract; SHF: second heart field; RV: right ventricle; ST: somite; NT, notochord; RA, right atrium; V: common ventricle; LV, left ventricle. Scale bars: 100 µm.