Fig. 3. `Exclusion' phenotype can be rescued by tbx2b mRNA. Compared with control (A), a 1/16 injection of tbx2b MO led to `exclusion' phenotype (B) at 10 hpf. Neural plate highlighted with sox19 in blue; fluorescein labelled cells in brown. By contrast, 1/16 injection of tbx2b mRNA (1.0 ng) led to (C) labelled cells with normal morphology in the midline (arrow) at 10 hpf and, (D) the notochord (arrows) at 24 hpf, consistent with the role of Tbx2b in axial mesodermal specification. (E) Exclusion phenotype at 10 hpf from tbx2b MO (0.05 pmol) was rescued with tbx2b mRNA lacking the target site in a dose-dependent manner. In the presence of tbx2b MO, 1.0 ng mRNA led to appearance of labelled cells in the midline similar to C and D, while significantly reducing the number of embryos with `exclusion' phenotype. 0.5 ng mRNA was less effective in reducing the `exclusion' phenotype but did not cause appearance of labelled cells in the midline.