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#dorsalization

2 public questions tagged with this topic.

Paracrine Factor

Which morphogen gradient is essential for neural tube dorsalization?

Neural tube dorsoventral axis opposite ventral Hedgehog is BMP dorsalization from roof plate and surface ectoderm. Roof plate secretes BMP2, BMP4, BMP6, BMP7 and Wnt1, Wnt3a establishing high dorsal BMP concentration activating Smad1/5/8 to induce transcription factors Atoh1, Olig3, Pax3, Pax7 specifying dorsal interneurons dl1-dl6 and neural crest progenitors via Id inhibition and Msx. Shh from floor plate induces ventral Nkx2.2, Olig2 motor neurons. Genetic ablation of BMP receptors causes loss of dorsal cell types with ventral expansion; opposite of Shh mutants. Therefore BMP gradient essential dorsal patterning complement to ventral Shh system.

Ref: Lee & Jessell, Annual Review Neuroscience 1999: BMP roof plate gradient dorsalizes neural tube and neural crest.

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frog development

UV-irradiated Xenopus embryos primarily form:

Blocking cortical rotation with UV crosslinks vegetal cortex microtubules preventing dorsal transport of beta-catenin determinants. Without Nieuwkoop center, Spemann organizer never forms, BMP antagonists absent, embryo retains only ventralizing BMP signaling globally. Embryos develop as cylindrical ventralized structures lacking notochord, somites, neural plate and head, termed Bauchstück. Histology shows expanded blood islands, coelom and atypical epidermis expressing ventral markers Vent1/2, Sizzled and Wnt8. Neural and dorsal markers like Sox2, MyoD absent, demonstrating formation of only ventral structures and requirement of rotation for dorsal axis. This illustrates conserved developmental logic of morphogen gradients patterning embryonic axes through Wnt and BMP antagonism.

Ref: Gilbert, Developmental Biology 11th ed., Chapter 9: UV ventralization and Bauchstück phenotype in Xenopus.

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