Aberrant axon-Schwann cell junctions in dystrophic mouse nerves

Area of Science:

• Neuroscience
• Cell Biology
• Peripheral Nervous System Research

Background:

• Dystrophic mouse nerves exhibit amyelinated axons lacking typical nodal and paranodal specializations.
• Schwann cells normally ensheath myelinated axons, forming specialized axoglial junctions.

Purpose of the Study:

• To investigate the membrane specializations of amyelinated axons in dystrophic mouse nerves.
• To determine if Schwann cells form specialized junctions with amyelinated axons.

Main Methods:

• Light microscopy and freeze-fracture electron microscopy were used to examine spinal roots of dystrophic mice.
• Axoglial junctions and Schwann cell-axon interactions were analyzed at the ultrastructural level.

Main Results:

• Amyelinated axons in dystrophic nerves lack typical nodal/paranodal structures.
• Aberrant junctions resembling transverse bands form between amyelinated axons and Schwann cells of neighboring myelinated axons.
• Schwann cells form finger-like projections resembling nodes of Ranvier on amyelinated axons with cytoplasmic undercoating.
• Freeze-fracture revealed paracrystalline membrane patches at aberrant junctions, but no typical nodal/paranodal specializations on amyelinated fibers.
• Schwann cells can form specialized junctions with multiple axons simultaneously.

Conclusions:

• Axon membrane specialization, including sodium channel distribution, depends on intimate contact with myelinating Schwann cells.
• Amyelinated axons do not develop independent regional differentiation in the absence of myelin.
• Schwann cells exhibit plasticity in forming specialized junctions with multiple axons.