During neural tube closure, PAX3 and PAX7 are expressed in the dorsal neural tube while NKX2.2 and OLIG2 are expressed ventrally. Which signalling molecule establishes this dorsoventral pattern by inducing ventral progenitor identities?
- A Sonic Hedgehog (SHH) secreted from the notochord and floor plate ✓
- B BMP4 secreted from the roof plate
- C Wnt1 expressed in dorsal neural tube
- D Noggin secreted from the organizer to inhibit BMP signalling
Correct answer: A. Sonic Hedgehog (SHH) secreted from the notochord and floor plate
Explanation
SHH secreted from the notochord and then the floor plate creates a ventral-to-dorsal gradient that induces the expression of ventral transcription factors (NKX2.2, OLIG2, NKX6.1) specifying motor neuron and interneuron progenitor domains. BMP4 from the roof plate establishes dorsal identity (PAX3, PAX7) via the opposing gradient. Wnt1 maintains dorsal identity and induces neural crest specification. Noggin from the node inhibits BMP during gastrulation, not neural tube DV patterning.
Reference: BD Chaurasia's Human Anatomy, 8th ed.
High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP
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