Fig. 7. Model for Mixer function in the early Xenopus embryo. This and previous work suggest the following model for formation of boundaries of expression of several VegT target genes. After MBT, VegT activates the expression of Xnr genes, Xsox17, Gata4, Gata5 and Gata6, and Fgf genes in vegetal cells. The secreted mesoderm inducing molecules induce adjacent marginal cells, which do not express VegT, to express more of themselves as well as the presumptive mesodermal genes including eomesodermin and Xbra. At the early gastrula stage, Mixer is cell autonomously induced by VegT-expressing cells. It reduces, directly or indirectly, the expression of Xnr1 and Xnr5, Fgf3 and Fgf8 and eomesodermin by vegetal cells and therefore prevents further mesoderm inducing signals being released by the vegetal mass. Mixer also activates a second round of Xsox17 and Gata5 expression, consolidating endodermal fates for vegetal cells. Together with maternal XTcf3/ß-catenin, Mixer initiates cerberus expression and cerberus protein blocks further Xnr, Wnt and BMP signaling in the anterior endoderm.