# Mechanisms that control neuronal microtubule polarity

> **NIH NIH R01** · PENNSYLVANIA STATE UNIVERSITY, THE · 2020 · $331,247

## Abstract

Project Summary
Neuronal microtubules are intimately interconnected with neuronal health, yet many basic principles that
control neuronal microtubule organization remain mysterious. For example, microtubules can be nucleated
throughout axons and dendrites, but regulators that position nucleation sites far from the cell body have not
been identified. Nucleation is upregulated throughout the neuron by axon injury and stress so it is particularly
important to understand how it is controlled. If basic mechanisms that control neuronal microtubule
organization are not elucidated, it will be very difficult to understand the relationships between the microtubule
regulatory proteins and neurodegeneration. Hereditary spastic paraplegia is genetically one of the simplest
forms of neurodegenerative disease, and mutations in the gene that encodes the microtubule severing protein
spastin cause 40% of cases. However, how and where spastin functions in mature neurons has not been
pinned down, and why its reduction sensitizes neurons to degeneration is also not clear. In this proposal
Drosophila is used as a model system in which to efficiently identify basic mechanisms that regulate neuronal
microtubules to provide a framework for future work on regeneration and degeneration.
Aim 1. An unexpected pathway controls microtubule nucleation in dendrites. Using a screening
approach, Wnt signaling proteins emerged as key regulators that position microtubule nucleation sites in
dendrites. Preliminary data in this aim indicates Wnt signaling proteins likely activate nucleation on
endosomes. These preliminary findings will be strengthened by pairing a new nucleation assay with
localization of Wnt signaling proteins and endosomes.
Aim 2. The role of severing proteins in converting minus end nucleation to minus end growth. It was
recently shown that minus ends grow in dendrites and this is important for polarity control and dendrite
regeneration. Preliminary data indicates spastin plays a role in generating growing minus ends. Using new
assays to visualize nucleation and severing in combination with genetic tools, how and where microtubules are
severed in dendrites will be investigated.
Aim 3. Control of disruptive nucleation by a checkpoint system. Microtubule nucleation has the potential
to disrupt polarity by generating microtubules in random orientations. Detailed live imaging of growing
microtubule plus ends determined that a checkpoint system depolymerizes microtubules nucleated in the
“wrong” orientation. Two players required for promoting growth of “right” orientation microtubules have been
identified. Their function, localization and interactions with one another will be investigated.
Conclusion: We will elucidate fundamental but poorly understood mechanisms that control dendrite
microtubule organization to fill in key gaps in our understanding of the neuronal cytoskeleton that are essential
context for understanding neuronal regeneration and degeneration.

## Key facts

- **NIH application ID:** 9971136
- **Project number:** 2R01GM085115-10
- **Recipient organization:** PENNSYLVANIA STATE UNIVERSITY, THE
- **Principal Investigator:** Melissa Rolls
- **Activity code:** R01 (R01, R21, SBIR, etc.)
- **Funding institute:** NIH
- **Fiscal year:** 2020
- **Award amount:** $331,247
- **Award type:** 2
- **Project period:** 2010-05-01 → 2024-04-30

## Primary source

NIH RePORTER: https://reporter.nih.gov/project-details/9971136

## Citation

> US National Institutes of Health, RePORTER application 9971136, Mechanisms that control neuronal microtubule polarity (2R01GM085115-10). Retrieved via AI Analytics 2026-05-24 from https://api.ai-analytics.org/grant/nih/9971136. Licensed CC0.

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