Semaphorin-6D and Plexin-A1 Act in a Non-Cell-Autonomous Manner to Position and Target Retinal Ganglion Cell Axons

Area of Science:

• Neuroscience
• Developmental Biology
• Molecular Biology

Background:

• Semaphorins and Plexins are essential ligand/receptor pairs in developmental processes, including cell proliferation and axon guidance.
• Semaphorins exhibit dual roles as signaling receptors and ligands, leading to diverse cellular responses.
• Proper organization of retinogeniculate axons is critical for visual system development.

Purpose of the Study:

• To investigate the role of Semaphorin-6D (Sema6D) and Plexin-A1 in the positioning and targeting of retinogeniculate axons.
• To elucidate the mechanism of action, including dose-dependency and cell autonomy, of Sema6D and Plexin-A1 in axon guidance.

Main Methods:

• Analysis of optic tract and retinogeniculate projections in Semaphorin-6D (Sema6D) or Plexin-A1 mutant mice.
• In utero electroporation of Sema6D or Plexin-A1 shRNA in retinal ganglion cells.
• Assessment of axon positioning, targeting, fasciculation, and arborization patterns.

Main Results:

• Mutations in Plexin-A1 or Sema6D lead to optic tract disorganization and ectopic retinal axon arborization within the dorsal lateral geniculate nucleus (dLGN).
• Sema6D and Plexin-A1 function in a dose-dependent manner, with altered projection phenotypes correlating with expression levels.
• Both Sema6D and Plexin-A1 are required in retinal ganglion cells for proper axon guidance, but can also act non-cell-autonomously, suggesting axon-axon interactions.

Conclusions:

• Semaphorin-6D and Plexin-A1 play a critical, dose-dependent, and non-cell-autonomous role in the organization of retinogeniculate axons.
• These guidance molecules are essential for maintaining optic tract cohesion and ensuring appropriate defasciculation and arborization within target regions.
• The findings reveal an underappreciated function of axon guidance molecules in regulating tract integrity and target innervation.