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Fig. 3. The endodermal regulatory network. VegT activates the transcription
of pro-endodermal transcription factors, including Xsox17, GATA5 and Mixer,
and of signaling molecules, including Xnr5, Wnt8 and the signaling antagonist
cerberus. Vg1 and activin B also activate signaling pathways that lead to the
transcription of the signaling antagonists chordin and cerberus, and the
signaling molecule Xnr2. Xnr2, Xnr5 and Wnt8 are important mesoderm-inducing
molecules, responsible for the transcriptional activation of pro-myogenic
genes Xbra and eomesodermin, and FGF genes, which can
regulate specific myogenic genes such as MyoD. Cerberus suppresses
Xnr, Wnt and BMP signals extracellularly, and is required for head
(prechordal) mesoderm formation, while BMP suppression by chordin is required
for notochord formation. Signaling molecules are shown in blue and signaling
antagonists in red.
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