Efa6 protects axons and regulates their growth and branching by inhibiting microtubule polymerisation at the cortex
- University of Manchester, United Kingdom
- University of Nottingham, United Kingdom
- University of Liverpool, United Kingdom
Abstract
Cortical collapse factors affect microtubule (MT) dynamics at the plasma membrane. They play important roles in neurons, as suggested by inhibition of axon growth and regeneration through the Arf activator Efa6 in C. elegans, and by neurodevelopmental disorders linked to the mammalian kinesin Kif21A. How cortical collapse factors influence axon growth is little understood. Here we studied them, focussing on the function of Drosophila Efa6 in experimentally and genetically amenable fly neurons. First, we show that Drosophila Efa6 can inhibit MTs directly without interacting molecules via an N-terminal 18 amino acid motif (MT elimination domain/MTED) that binds tubulin and inhibits microtubule growth in vitro and cells. If N-terminal MTED-containing fragments are in the cytoplasm they abolish entire microtubule networks of mouse fibroblasts and whole axons of fly neurons. Full-length Efa6 is membrane-attached, hence primarily blocks MTs in the periphery of fibroblasts, and explorative MTs that have left axonal bundles in neurons. Accordingly, loss of Efa6 causes an increase of explorative MTs: in growth cones they enhance axon growth, in axon shafts they cause excessive branching, as well as atrophy through perturbations of MT bundles. Efa6 over-expression causes the opposite phenotypes. Taken together, our work conceptually links molecular and sub-cellular functions of cortical collapse factors to axon growth regulation and reveals new roles in axon branching and in the prevention of axonal atrophy. Furthermore, the MTED delivers a promising tool that can be used to inhibit MTs in a compartmentalised fashion when fusing it to specifically localising protein domains.
Data availability
All data generated or analysed during this study are included in the manuscript and supporting files. Source data files have been provided.
Article and author information
Author details
Pilar Okenve-Ramos
Funding
Biotechnology and Biological Sciences Research Council (BB/I002448/1)
- Andreas Prokop
Biotechnology and Biological Sciences Research Council (BB/P020151/1)
- Andreas Prokop
Biotechnology and Biological Sciences Research Council (BB/L000717/1)
- Andreas Prokop
Biotechnology and Biological Sciences Research Council (BB/M007553/1)
- Andreas Prokop
Biotechnology and Biological Sciences Research Council (BB/M007456/1)
- Natalia Sanchez-Soriano
Biotechnology and Biological Sciences Research Council (BB/J005983/1)
- Karel Dorey
Leverhulme Trust (ECF-2017-247)
- Ines Hahn
Deutsche Forschungsgemeinschaft (VO 2071/1-1)
- André Voelzmann
The funders had no role in study design, data collection and interpretation, or the decision to submit the work for publication.
Ethics
Animal experimentation: All experiments involving Xenopus laevis were approved by the Ethical Review Committe of the University of Manchester and a Home Office license (ref . PFDA14F2D).
Copyright
© 2019, Qu et al.
This article is distributed under the terms of the Creative Commons Attribution License permitting unrestricted use and redistribution provided that the original author and source are credited.
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