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Fig. 1 SoxB1 factors acts as transcriptional repressors to inhibit the expression of fgf3 and fgf8.
At 4.5 hpf, the expression of fgf3 and fgf8 is restricted in the dorsal shield region of un-injected embryos (A–B). Injection of sox3, sox19a or sox19b RNA at the 1–2 cell stage caused complete loss of expression of both fgf3 and fgf8 at 4.5 hpf (C–H). A Sox3HMG-EnR (I,J) but not a Sox3HMG-VP16 (K,L) fusion mimicked the function of wild-type Sox3 to inhibit fgf3 and fgf8 expression. Ectopic expression of fgf3 and fgf8 was induced by the dnSox3 construct injected at the 1–2 cell stage and analysed at 4.5 hpf (M,N) or later at 30% epiboly (5.5 hpf) (O,P). 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 A represents approximately 100 μm.