TRIM46 Organizes Microtubule Fasciculation in the Axon Initial Segment

Area of Science:

• Neuroscience
• Cell Biology
• Molecular Biology

Background:

• Selective cargo transport via microtubules is vital for neuron polarization.
• The axon initial segment (AIS) regulates microtubule-dependent transport and has unique microtubule fascicle organization.
• TRIM46, a microtubule-binding protein, localizes to the AIS and can induce fascicle-like structures.

Purpose of the Study:

• To investigate the precise role of TRIM46 in microtubule fasciculation within the AIS of neurons.
• To elucidate the developmental timing of TRIM46 localization and microtubule organization in the AIS.

Main Methods:

• Developed a novel correlative light and electron microscopy approach.
• Studied cultured rat hippocampal neurons of both sexes.
• Assessed TRIM46 levels, microtubule spacing, and cross-bridge formation during neuronal differentiation.

Main Results:

• TRIM46 levels increase at the AIS during early neuronal differentiation, coinciding with initial microtubule spacing.
• TRIM46 localizes to electron-dense cross-bridges within AIS microtubule fascicles.
• TRIM46 depletion leads to loss of cross-bridges and increased microtubule spacing in the AIS.

Conclusions:

• TRIM46 plays an essential role in organizing microtubule fascicles at the AIS.
• TRIM46 is critical for establishing the specialized microtubule organization required for neuron polarity and axonal transport.