Development Of The Central Nervous System Practice Test

Which molecule acts as an attractant for commissural axons at the midline?

Slit–Robo WNT Netrin-1 SHH

Correct Answer:

Netrin-1

Explanation:

Guidance of commissural axons at the midline relies on a signal that lures growing tips toward the floor plate. Netrin-1 is secreted by the midline structure and creates a gradient that axons expressing DCC receptors interpret as an attractive cue, drawing them toward and across the midline. After crossing, they encounter Slit proteins that bind Robo receptors, producing repulsion to prevent re-crossing. SHH mainly patterns ventral neural tube identity rather than acting as a midline attractant, and WNT signaling has other guidance roles but is not the classic attractant for this crossing event. So netrin-1 best fits as the midline attractant guiding commissural axons.

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