Trim9 and Klp61F promote polymerization of new dendritic microtubules along parallel microtubules

Area of Science:

• Cell Biology
• Neuroscience
• Molecular Biology

Background:

• Microtubule polarity is crucial for distinguishing neuronal axons and dendrites.
• Dendrites typically exhibit minus-end-out microtubule orientation, while axons show plus-end-out orientation.
• Local microtubule nucleation in dendrites can generate microtubules in both orientations, posing a challenge to maintaining polarity.

Purpose of the Study:

• To investigate the mechanisms that prevent disruption of dendritic microtubule polarity despite local nucleation of oppositely oriented microtubules.
• To understand how newly nucleated microtubules navigate dendritic branch points and contribute to overall polarity.

Main Methods:

• Live imaging of microtubule dynamics in Drosophila neurons.
• Analysis of microtubule exit rates from branch points based on orientation.
• Candidate screening to identify proteins involved in microtubule growth and orientation.
• In vitro and in vivo assays to assess the function of identified proteins (Trim9, kinesin-5/Klp61F) and their interactions (Eb1 recruitment).

Main Results:

• Microtubules with the correct minus-end-out orientation were twice as successful at exiting dendritic branch points compared to incorrectly oriented ones.
• The success of microtubule exit was dependent on the presence of parallel microtubules.
• Trim9 and kinesin-5 (Klp61F) were identified as key factors promoting microtubule growth.
• Kinesin-5 (Klp61F) was shown to promote microtubule growth in vitro and in vivo and recruit Trim9, which is recruited to microtubules by Eb1.

Conclusions:

• The findings suggest that Trim9 and kinesin-5 (Klp61F) collaborate at microtubule plus ends.
• This collaboration facilitates the growth of new microtubules that are parallel to existing ones.
• This mechanism helps polymerizing microtubules resist catastrophe, thereby maintaining correct dendritic polarity.