# Microtubule Dynamics and Axon Growth

> **NIH NIH R01** · DREXEL UNIVERSITY · 2020 · $340,161

## Abstract

Project Summary/Abstract
Neurons are terminally post-mitotic cells that use their microtubule arrays not for cell division but rather as
architectural elements required for the elaboration of elongated axons and dendrites. In addition to acting as
compression-bearing struts that provide for the shape of the neuron, microtubules also act as directional
railways for organelle transport. Microtubules in the axon are nearly uniformly oriented, with the plus ends of
the microtubules directed away from the cell body (“plus-ends-out”). Preservation of this microtubule pattern is
crucial for the normal functioning of an axon throughout the life of the neuron. This microtubule polarity pattern
is also important for distinguishing features of the axon from the dendrite, as dendrites of vertebrate neurons
have a mixed pattern of microtubule polarity orientation. Long-standing questions in cellular neuroscience are
how the plus-end-out polarity pattern of microtubules arises in the axon, how axons maintain this pattern during
the life of the neuron and how flaws arising from plastic events in the life of the neuron are repaired. This
competing renewal builds on a mechanism called “polarity sorting,” in which microtubules are organized
according to their polarity orientation via their transport by molecular motor proteins. Specifically, the
investigators hypothesize that in the case of the healthy axon, microtubules are transported with plus-ends
leading, so that plus-end-out microtubules move forward down the axon while minus-end-out microtubules are
transported back to the cell body to clear them from the axon. If not for this clearing mechanism, minus-end-
out microtubules would accumulate in the axon and corrupt its polarity pattern. The proposed experiments will
first test the polarity-sorting hypothesis. Experiments will then be conducted to test the hypothesis that two
minus-end-directed molecular motor proteins, namely cytoplasmic dynein and KIFC1, share the responsibility
of polarity sorting microtubules in the axon. Finally, studies will be conducted to identify the structures against
which the molecular motors generate forces to transport microtubules in the axon. Mobile microtubules are
generally quite short, and are hypothesized to move against either long microtubules or actin bundles,
depending on the particular motor protein. Computational modeling will add additional rigor to the project,
especially in terms of explaining why the axon’s microtubule polarity pattern is corrupted when various
molecular players are manipulated. The experiments will utilize contemporary live-cell imaging techniques with
unprecedented documentation of the polarity orientation of mobile microtubules in the axon, together with
methods for acutely inhibiting molecular motor proteins. The work has relevance to potential treatments for
diseases of the nervous system that may corrupt the microtubule polarity pattern of the axon.

## Key facts

- **NIH application ID:** 9990871
- **Project number:** 5R01NS028785-32
- **Recipient organization:** DREXEL UNIVERSITY
- **Principal Investigator:** PETER W. BAAS
- **Activity code:** R01 (R01, R21, SBIR, etc.)
- **Funding institute:** NIH
- **Fiscal year:** 2020
- **Award amount:** $340,161
- **Award type:** 5
- **Project period:** 1990-09-01 → 2022-07-31

## Primary source

NIH RePORTER: https://reporter.nih.gov/project-details/9990871

## Citation

> US National Institutes of Health, RePORTER application 9990871, Microtubule Dynamics and Axon Growth (5R01NS028785-32). Retrieved via AI Analytics 2026-05-23 from https://api.ai-analytics.org/grant/nih/9990871. Licensed CC0.

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