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Fig. 7 T-box sites are required for activity of the tbx6 mesodermal regulatory region. (A) The 1.7kb region upstream of tbx6 is shown with gray rectangles representing predicted Spt- and/or Ntl-binding site motifs. (B) A detailed view of 300 bp upstream of the tbx6 transcription start site [gray rectangles indicate putative T-box sites (a-d) and diamonds indicate Tcf/Lef-binding sites important for regulatory element function (Szeto and Kimelman, 2004)]. (C,D) mCherry expression driven by the full-length construct is robust at mid-gastrulation (8 hpf) (C) and mid-segmentation (14 somites) (D). (E-P) During gastrulation, mCherry expression driven by constructs in which one T-box site has been mutated (E,H,K,N) is reduced (F,I,L,O), but is normal during segmentation (G,J,M,P). (Q-S) When all four sites are mutated (Q) expression is abolished at both stages (R,S). The percentages of embryos with robust, faint or no mCherry expression are given in Table 1.