Which signaling molecule from the notochord and floor plate patterns ventral neural tube identities?

Which signaling molecule from the notochord and floor plate patterns ventral neural tube identities?

• A. Sonic hedgehog (SHH)
• B. BMP
• C. WNT
• D. FGF8

Answer: (A)

Sonic hedgehog signals from the notochord and floor plate set up the ventral patterning of the neural tube. It forms a graded cue that cells read to decide their fate along the ventral-dorsal axis. High SHH exposure near the floor plate induces ventral progenitors, including motor neuron lineages, while slightly lower levels specify other ventral interneurons; the gradient is interpreted through Gli transcription factors to activate or repress key downstream genes. This SHH-driven patterning explains why ventral identities form where SHH is strongest. In contrast, BMP and WNT come from dorsal sources (the roof plate and overlying ectoderm) and promote dorsal identities, opposing SHH to shape the dorsal neural tube. FGF8 has roles in other patterning contexts, such as anterior-posterior organization, rather than establishing ventral neural tube identities.

Sonic hedgehog signals from the notochord and floor plate set up the ventral patterning of the neural tube. It forms a graded cue that cells read to decide their fate along the ventral-dorsal axis. High SHH exposure near the floor plate induces ventral progenitors, including motor neuron lineages, while slightly lower levels specify other ventral interneurons; the gradient is interpreted through Gli transcription factors to activate or repress key downstream genes. This SHH-driven patterning explains why ventral identities form where SHH is strongest.

In contrast, BMP and WNT come from dorsal sources (the roof plate and overlying ectoderm) and promote dorsal identities, opposing SHH to shape the dorsal neural tube. FGF8 has roles in other patterning contexts, such as anterior-posterior organization, rather than establishing ventral neural tube identities.