Sonic Hedgehog (SHH) signalling from the notochord is required for floor plate induction and ventral neural tube patterning. Inactivation of SHH in the notochord leads to absence of which spinal cord neuron population?

• A Dorsal interneurons (dI1-dI6) of the dorsal horn
• B Dorsal root ganglion neurons derived from neural crest
• C V3 interneurons and motor neurons of the ventral horn ✓
• D Oligodendrocyte precursor cells in the dorsal spinal cord

Explanation

SHH released from the notochord and floor plate forms a ventral-to-dorsal gradient in the neural tube. High SHH concentrations specify the most ventral progenitor domains (p3, pMN) that give rise to V3 interneurons and somatic motor neurons respectively. Loss of SHH eliminates these ventral identities while dorsal progenitor domains (specified by BMP and Wnt from the dorsal ectoderm) are relatively preserved. Dorsal root ganglia arise from neural crest cells outside the neural tube and are not primarily dependent on notochordal SHH for their specification.

Reference: BD Chaurasia's Human Anatomy, 8th ed.

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