Netrin1 establishes multiple boundaries for axon growth in the developing spinal cord

Area of Science:

• Neuroscience
• Developmental Biology
• Molecular Biology

Background:

• The canonical model proposed Netrin-1 as a long-range chemotropic guidance cue for axons.
• Netrin-1 from the floor plate was thought to attract commissural axons to the ventral midline.
• Recent studies challenge this long-range model, suggesting a local role for Netrin-1.

Purpose of the Study:

• To investigate the local function of Netrin-1 in spinal cord axon guidance.
• To determine if Netrin-1 acts as a haptotactic substrate or a boundary cue.
• To elucidate the complex roles of Netrin-1 in shaping axonal trajectories during development.

Main Methods:

• Analysis of Netrin-1 expression patterns in the developing spinal cord.
• Investigation of Netrin-1's role in guiding pioneering and commissural axons.
• Examination of Netrin-1's function in neural progenitor cells (NPCs) and specific spinal cord domains.

Main Results:

• Netrin-1 is produced by NPCs in the ventricular zone and deposited on the pial surface as a local haptotactic substrate.
• This Netrin-1 substrate guides Dcc+ axon growth and orients pioneering spinal axons ventrally.
• Netrin-1 expressing cells in the ventricular zone form a boundary that commissural axons navigate around, suggesting a role beyond adhesion.

Conclusions:

• Netrin-1 functions locally as a growth substrate and a boundary cue, termed 'hederal' boundaries.
• Netrin-1 promotes axon extension along specific paths while preventing innervation of Netrin-1 expressing domains.
• Additional Netrin-1 expression domains near the dorsal root entry zone are crucial for sculpting axonal growth.