SoxB1 factors acts as transcriptional repressors to inhibit the expression of <i>fgf3</i> and <i>fgf8.</i>

<p>At 4.5 hpf, the expression of <i>fgf3</i> and <i>fgf8</i> is restricted in the dorsal shield region of un-injected embryos (<b>A–B</b>). Injection of <i>sox3, sox19a</i> or <i>sox19b</i> RNA at the 1–2 cell stage caused complete loss of expression of both <i>fgf3</i> and <i>fgf8</i> at 4.5 hpf (<b>C–H</b>). A Sox3HMG-EnR (<b>I</b>,<b>J</b>) but not a Sox3HMG-VP16 (<b>K</b>,<b>L</b>) fusion mimicked the function of wild-type Sox3 to inhibit <i>fgf3</i> and <i>fgf8</i> expression. Ectopic expression of <i>fgf3</i> and <i>fgf8</i> was induced by the dnSox3 construct injected at the 1–2 cell stage and analysed at 4.5 hpf (<b>M</b>,<b>N</b>) or later at 30% epiboly (5.5 hpf) (<b>O</b>,<b>P</b>). All images are lateral views with dorsal to the right (where this can be determined). The proportion of embryos exhibiting these phenotypes is shown at the bottom right of each panel. Scale bar in panel <b>A</b> represents approximately 100 µm.