Figure 1.

Tbx1 expression is controlled by separable pharyngeal endoderm and mesoderm regulatory regions in transgenic mice. (a) Genomic organization of the 5′ mouse Tbx1 locus and flanking region. Boxes indicate exons, and translation start site (ATG) is designated as nucleotide number zero. Construct number is indicated on the left, and the corresponding expression pattern of lacZ at E9.5 is summarized on the right. The far-right column indicates the fraction of F₀ transgenic embryos with Tbx1-like lacZ expression/lacZ gene positive embryos. (b,c) Endogenous expression of Tbx1 transcripts is shown by whole-mount RNA in situ hybridization in E9.5 mouse embryos. (d–k) Right lateral views of representative embryos obtained with each construct (indicated in upper-right corner of each panel). (c,e,g,i,k) Higher magnification of the pharyngeal arch of embryos in upper panels. Expression of lacZ in embryos with construct 1 (d,e) recapitulated endogenous Tbx1 expression (b,c). LacZ expression in the head mesenchyme (hm) and pharyngeal endoderm (white arrowheads) was detectable in each embryo with construct 1 (e), 3 (g), 4 (i), and 6 (k), whereas that in the pharyngeal mesoderm (black arrowheads) and cardiac outflow tract (ot) was only in embryos with construct 1 (e) or 3 (g). lacZ expression in limb buds (lb) in panel h represents ectopic expression. h, head; ht, heart.