Figure 6.

A model for the position of iro3 and the iro3-expressing dorsal endodermal domain in organizer patterning. In the dorsal YSL, the β-catenin signal is activated and sqt is expressed. The activation of iro3 in the overlying endoderm depends on the function of the YSL. In turn, iro3 has a role in inducing organizer genes in the overlying mesoderm, presumably through the mediation of an unknown secreted molecule. Each of the arrows implies multiple steps in molecular pathways. This model is similar to a model in Xenopus that distinguishes the Nieuwkoop center, late blastula organizer, and gastrula organizer. See text for additional details.