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#neural tube

3 public questions tagged with this topic.

Morphogen Induction-l

Which morphogen is required for neural tube ventralization?

Ventral identities in neural tube are induced by Sonic hedgehog derived from notochord then floor plate reinforcing gradient ventrally. Ventral progenitors experience highest Shh leading to Gli activator induction of Nkx2.2 floor plate, Olig2 motor neuron progenitors and Nkx6.1 V3 interneurons, while dorsal BMP counter-gradient promotes Pax6. Adding Shh to dorsal explants ventralizes them generating motor neurons, while Shh blockade dorsalizes. BMP4 promotes dorsal fates, retinoic acid posteriorizes, Wnt3a dorsalizes. Thus Shh functions as ventralizing morphogen interpreting concentration into distinct neuronal progenitor domains essential for spinal cord.

Ref: Briscoe et al., Nature 2000, Shh Gradient Specifies Ventral Neural Tube Fates.

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Specification Determination-ll

Which of the following morphogens is required for neural tube ventralization?

Dorsoventral patterning of vertebrate neural tube requires opposing gradients from roof plate and floor plate. Ventralizing signal is Sonic hedgehog, cholesterol-modified protein secreted by notochord and later by floor plate cells, diffusing dorsally to create ventral high, dorsal low gradient. High Shh induces floor plate via FoxA2, slightly lower induces p3 progenitors expressing Nkx2.2 generating V3 interneurons, intermediate levels induce motor neuron progenitors expressing Olig2, lower levels trigger distinct interneuron classes. Ectopic Shh ventralizes dorsal tube, while loss dorsalizes ventral tube, confirming dose-dependent morphogen action via Gli activators.

Ref: Gilbert, Developmental Biology, 12th ed., Chapter 13: Sonic Hedgehog and Neural Tube Ventralization.

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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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