Some of the important players in mesoderm induction and early patterning in Xenopus

1) The Dishevelled protein is a maternal factor localized to the vegetal pole. Cortical rotation moves some Dishevelled protein into the future dorsal region (the area of the Nieuwkoop center and activates it. Dishevelled binds to GSK-3 and blocks it from degrading b-catenin transcription factor (a coregulator) which can activate transcription of genes like in the figure below.

2) Veg-T is a transcription factor that is a maternal factor found initially as mRNA in the vegetal pole. Veg-T activates transcription in vegetal pole cells of genes related to nodal (Xnr) that are secreted signaling factors. These cells also secrete Vg-1 and these signaling factors activate other transcription factors not shown in the above figure.

3) Vg-1 is a TGF-b family member of signaling factors that is loaded as an inactive preprotein in the vegetal pole. It signals cells through receptors.

4) Goosecoid protein (and others ) are transcription factors made in the dorsal lip of the blastopore (the Spemann center). Goosecoid activates transcription of genes like noggin, chordin, and frisbe. Noggin protein gets secreted and binds to BMP-4 (and other TGF-b family members) blocking them from binding to their receptors (in the same way, Frizbe binds to Xwnt-8 and blocks it). BMPs are maternal factors found throughout most of the embryo and induce ventral mesoderm programs. When the BMPs are blocked, dorsal mesoderm such as notochord and somites are induced. Hooray!