# Mechanism of a Microtubule Polymerase Complex Critical for Axon Outgrowth

> **NIH NIH R03** · UNIV OF NORTH CAROLINA CHAPEL HILL · 2020 · $155,500

## Abstract

There is a fundamental gap in our knowledge to explain how microtubules polymerize in neurons. The
microtubule cytoskeleton is critical for neuronal structure, dynamics, and trafficking. How factors spatially
regulate the microtubule cytoskeleton to promote axon outgrowth is poorly understood. Microtubule
polymerases are key regulators that localize to microtubule plus ends and promote microtubule polymerization.
In neurons, microtubule polymerases associate with the factors Sentin and TACC. Knockdown of the
microtubule polymerase or its associated factors compromises microtubule dynamics, yielding aberrant
responses to guidance cues and defects in axon outgrowth. How the microtubule polymerase binds Sentin and
TACC and how this complex collectively regulates the microtubule cytoskeleton is poorly understood. We have
mapped Sentin and TACC binding to a conserved C-terminal domain of the microtubule polymerase Msps and
determined that this conserved domain has microtubule-binding activity. Drawn from our preliminary data, we
hypothesize that the components of the Sentin-Msps-TACC microtubule polymerase complex work
synergistically to bind the microtubule lattice and drive microtubule polymerization. The rationale for the
proposed research is to determine how the components of a microtubule polymerase complex potentiate
microtubule polymerization, a polymer required for neuronal structure, polarity, signaling and dynamics. Two
specific aims examine the structure and mechanism of the microtubule polymerase complex. The first aim is to
determine the molecular architecture of the microtubule polymerase complex using X-ray crystallography,
elucidate binding stoichiometry and affinity, and design and test mutations that prevent complex formation. The
second aim is to map residues in the microtubule polymerase complex involved in microtubule binding and
determine how the complex affects microtubule dynamics using an in vitro reconstituted microtubule dynamics
assay. These two independent aims work to develop a high-resolution model for Sentin-Msps-TACC
microtubule polymerase activity. The approach is innovative because it marshals a diverse set of biophysical,
biochemical, and cellular assays to provide a multi-resolution model of the microtubule polymerase
mechanism. The proposed research is significant because it tests a core molecular process required for
neuronal shape, dynamics, and signaling. The investigation's long-term objective is to determine how the
microtubule polymerase complex regulates cytoskeletal dynamics in neuronal growth cones in response to
guidance cues. The proposed research will impact public health by establishing a mechanistic framework from
which cytoskeletal-based defects in axon outgrowth can be investigated, providing molecular insight into
mutant microtubule polymerase, Sentin, and TACC phenotypes, including spontaneous axon retraction and
defects in the response to axon guidance cues.

## Key facts

- **NIH application ID:** 10043009
- **Project number:** 1R03NS118155-01
- **Recipient organization:** UNIV OF NORTH CAROLINA CHAPEL HILL
- **Principal Investigator:** Kevin C Slep
- **Activity code:** R03 (R01, R21, SBIR, etc.)
- **Funding institute:** NIH
- **Fiscal year:** 2020
- **Award amount:** $155,500
- **Award type:** 1
- **Project period:** 2020-06-01 → 2024-05-31

## Primary source

NIH RePORTER: https://reporter.nih.gov/project-details/10043009

## Citation

> US National Institutes of Health, RePORTER application 10043009, Mechanism of a Microtubule Polymerase Complex Critical for Axon Outgrowth (1R03NS118155-01). Retrieved via AI Analytics 2026-05-23 from https://api.ai-analytics.org/grant/nih/10043009. Licensed CC0.

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