Which signaling pathway provides repulsion for commissural axons at the midline?

Which signaling pathway provides repulsion for commissural axons at the midline?

• A. Netrin-1
• B. BMP
• C. Slit–Robo signaling
• D. WNT

Answer: (C)

Axon guidance at the midline relies on a switch from attraction to repulsion, and the repulsive cue for commissural axons after crossing is Slit–Robo signaling. The floor plate and midline glia secrete Slit proteins, which bind to Robo receptors on the crossing axons and push them away from the midline, preventing re-crossing and guiding them to extend laterally. While netrin-1 acts as an attractant that brings axons toward the midline, Slit–Robo signaling provides the necessary repulsion once the axons have crossed. BMP and WNT have roles in other developmental patterning and guidance contexts, but they are not the primary midline repulsive pathway for commissural axons.

Axon guidance at the midline relies on a switch from attraction to repulsion, and the repulsive cue for commissural axons after crossing is Slit–Robo signaling. The floor plate and midline glia secrete Slit proteins, which bind to Robo receptors on the crossing axons and push them away from the midline, preventing re-crossing and guiding them to extend laterally. While netrin-1 acts as an attractant that brings axons toward the midline, Slit–Robo signaling provides the necessary repulsion once the axons have crossed. BMP and WNT have roles in other developmental patterning and guidance contexts, but they are not the primary midline repulsive pathway for commissural axons.