Mesoderm induction in amphibians is initiated by:
Mesoderm induction in amphibians follows Nieuwkoop model where vegetal endoderm signals to equatorial region rather than autonomous specification. Vegetal cells expressing maternal VegT transcribe Nodal-related TGF-beta ligands Xnr1, Xnr2, Xnr4, Xnr5, Xnr6. These ligands diffuse to marginal zone activating Smad2 phosphorylation via activin receptors and FoxH1. Gradient interpretation leads to dose-dependent fates, high Nodal plus beta-catenin dorsally inducing organizer mesoderm, moderate levels inducing ventral mesoderm forming blood. Animal cap cells alone lack Nodal and become ectoderm. Rem
Ref: Gilbert, Developmental Biology, 12th ed., Chapter 9: Mesoderm induction by vegetal Nodal signals in amphibians.
