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#VegT

3 public questions tagged with this topic.

amphibian Development-l

Which signaling molecule accumulates due to VegT and specifies mesoderm?

As downstream effector of VegT, Nodal-related TGF-beta signaling links endoderm specification to mesoderm induction critically. VegT induces transcription of Xnrs in vegetal cells, secreted ligands that bind activin type I and II receptors, phosphorylate Smad2, complex with Smad4, and activate mesodermal genes like eomesodermin, Xbra, and goosecoid in overlying marginal zone. Nodal dose determines mesoderm subtype, while BMP specifies ventral fates and FGF maintains competence. Wnt and Sonic hedgehog are not primary Nodal targets here. Thus VegT-dependent Nodal accumulation creates equatorial mesoderm ring essential for gastrulation and axis formation during embryogenesis.

Ref: Gilbert, Developmental Biology, 12th ed., Chapter 9: VegT induces Nodal ligands for mesoderm specification.

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amphibian Development-l

Which transcription factor is activated by VegT to specify endoderm?

In Xenopus, maternal VegT binds promoters of endodermal transcription factors. Chief among them is Sox17, a SoxF family member. VegT induces Sox17a and Sox17b expression in vegetal cells, driving endodermal differentiation through activation of FoxA2, HNF1beta, and other gut markers, while repressing mesoderm at high dosage. Sox17 then cooperates with beta-catenin to maintain endoderm identity. Knockdown of Sox17 reduces gut markers, while overexpression expands endoderm at expense of mesoderm, showing direct hierarchical relationship essential for endoderm formation in all vertebrate embryos and gut patterning.

Ref: Gilbert, Developmental Biology, 12th ed., Chapter 8: VegT activates Sox17 for endoderm specification Xenopus.

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amphibian Development-l

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. Removing vegetal hemisphere eliminates mesoderm, confirming vegetal Nodal initiation essential.

Ref: Gilbert, Developmental Biology, 12th ed., Chapter 9: Mesoderm induction by vegetal Nodal signals in amphibians.

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