Figure 4. Sox3 represses expression of chd and gsc independently of repressing fgf expression.

(A) Model of the signalling network that controls organizer formation. Sox3 plays a central role in this model to repress Fgf signalling in addition to independently repressing other genes needed for organizer formation. Injection of fgf3 RNA at the 1–2 cell stage dramatically expanded both chd and gsc expression in the animal hemisphere (Ba,b,e,f). Injection of wild-type sox3 RNA not only inhibited the endogenous expression of chd and gsc (Bc,g), but was also able to partially inhibit the expansion of chd and gsc expression that was induced by injection of fgf3 (Bd,h). (C,D) Graphical representation of the numbers of embryos affected in these experiments. Lateral view and dorsal is to the right in upper panels, viewed from animal pole in lower panels. The proportion of embryos exhibiting these phenotypes is shown at the bottom right of each panel.