Fig. 1. Tbx1/TBX1 suppresses expression of neural bHLH genes in the otic placode. (A-F) Lateral surface views of whole mount hybridized embryos. Arrowheads mark the anterior and posterior poles of the invaginating otic placode. asterisk, facial ganglion progenitors; m, Tbx1-positive mesenchyme. ss, somite stage. (G,H,J-L) Transverse sections (7 µm) through the otic epithelium of whole-mount hybridized embryos. Arrowheads in G and H mark limits of detectable signal; Tg, transgenic. Scale bars in A for A-F and in G for G-L. (I) Quantification of otic epithelial Ngn1 hybridization signals (perinuclear rings) by serial section analyses for various genotypes at two stages near the onset of neurogenesis (16-17 somites, 19-21 somites; n=8-10 epithelia/genotype/stage. *P<0.01).