The cytoskeleton in myelinated axons: a freeze-etch replica study

Area of Science:

• Neuroscience
• Cell Biology
• Biochemistry

Background:

• The axonal cytoskeleton is crucial for neuronal structure and function.
• Understanding its organization is key to comprehending axonal transport mechanisms.

Purpose of the Study:

• To investigate the ultrastructural organization of the axonal cytoskeleton in rat myelinated axons.
• To identify components and interactions within the axonal cytoskeleton without chemical fixation.

Main Methods:

• Rapid freezing and deep-etching of rat trigeminal nerve samples.
• Freeze-etch replica electron microscopy.
• Triton X-100 extraction to identify stable cytoskeletal components.

Main Results:

• Visualized a cytoskeleton composed of longitudinally oriented microtubules and neurofilaments interconnected by slender strands.
• Demonstrated that these interconnecting filaments persist after Triton extraction, indicating they are stable structures.
• Observed granular structures associated with the cytoskeleton in non-extracted axons, which disappeared after extraction, suggesting they represent soluble proteins.

Conclusions:

• The study provides ultrastructural evidence for the reality of the axonal cytoskeleton and its role in axonal transport.
• Identified stable cross-linking filaments connecting microtubules and neurofilaments.
• Suggested that granular structures associated with the cytoskeleton may be slowly transported soluble proteins within the axoplasm.