Structural effects in axoplasm of DNase I, an actin depolymerizer that blocks fast axonal transport

Area of Science:

• Neuroscience
• Cell Biology

Background:

• Fast axonal transport is crucial for neuronal function.
• The role of the actin cytoskeleton in fast axonal transport is debated.

Purpose of the Study:

• To investigate the effect of actin depolymerization on axonal transport and cytoskeleton organization.
• To determine if actin disruption leads to fast transport blockage by cytoskeletal disorganization.

Main Methods:

• Electron microscopy was used to examine microtubule and neurofilament organization in Aplysia neurons.
• DNase I (an actin depolymerizer) was microinjected into axons.
• The effect of the microtubule-stabilizing drug taxol was assessed.

Main Results:

• DNase I injection caused organelle clumping and reduced microtubules near the axoplasm perimeter.
• Microtubules and neurofilaments were intermingled, not segregated.
• Transmitter storage vesicles were often found near microtubules.
• Taxol partially rescued the transport inhibition caused by DNase I.

Conclusions:

• Actin disruption leads to localized microtubule loss, inhibiting fast axonal transport.
• Actin likely plays a structural role in maintaining axonal organization for transport.
• These findings suggest actin's role is structural rather than directly involved in force generation for fast transport.