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Fig. 1 Sox3 inhibits gastrulation and represses markers of the zebrafish organizer and mesoderm. (Aa-c′) Injection of sox3 mRNA at the 1- to 2-cell stage (Aa′) caused disruption of the blastoderm/yolk cell border at 6.5 hpf (asterisk). At 9 hpf, sox3-injected embryos (Ab′) showed delayed gastrulation and a thickening on one side (asterisk) with a pronounced ventralised phenotype in those that survived to 24 hpf (Ac′). (Ba-e′) Injected sox3 caused a dramatic reduction in the expression of sqt, gsc, chd and nog1 and a substantial gap in the ring of ntl expression, which was coincident with the region of injected sox3, as shown by staining for HA (brown) (Bd′, inset). (C) Compared with wild-type (WT) (a-e), injection of the dominant-negative forms of Sox3, Sox3N40I (f-j) and Sox3dNLS (k-o), did not repress the endogenous domains of expression of sqt, gsc, chd, ntl or nog1, but caused ectopic expression in the majority of embryos (arrowheads). The numbers of embryos showing ectopic expression/number injected are shown bottom right. The period of development is shown below each panel. Gene expression was analysed by whole-mount in situ hybridisation (blue). Animal pole views, except for A which was viewed laterally. Dorsal is to the right, except for Aa, Aa′, Bd, Bd′, for which orientation cannot be certain. Scale bars: ∼200 μm.