FIG. 4.

Sia/Twn are required for blastula expression of Foxd4 and Sox11. Paired bright field (top row) and fluorescence (bottom row) images of blastula stage embryos in which Sia+Twn MOs were injected into a 16-cell blastomere that gives rise to the dorsal-equatorial blastula precursors of the Organizer mesoderm and neural ectoderm (marked by a bracket in the top row). The location of the MOs is visualized by red (lissamine) fluorescence on the left side of the embryo (above the white arrows in the bottom row). Normal Foxd4 and Sox11 expression is more restricted to these dorsal-equatorial cells (brackets), whereas Zic2 and Gmnn normally are expressed throughout the animal hemisphere including the dorsal-equatorial cells (shown in right side of each embryo; below the black arrows). Foxd4 and Sox11 expression is greatly reduced in the region containing Sia/Twn MOs (above the black arrows in the top row). In contrast, Gmnn and Zic2 expression appears unaffected. The numbers refer to the number of embryos in which gene expression was repressed by Sia/Twn knock down. Dorsal views of embryos are oriented with animal pole to the right.