A Role for Myosin VI in the Localization of Axonal Proteins

Tommy L Lewis,Don B Arnold,Tianyi Mao,William Harris

doi:10.1371/journal.pbio.1001021

Tommy L Lewis, Don B Arnold + Show 2 more

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https://doi.org/10.1371/journal.pbio.1001021

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Abstract

In neurons polarized trafficking of vesicle-bound membrane proteins gives rise to the distinct molecular composition and functional properties of axons and dendrites. Despite their central role in shaping neuronal form and function, surprisingly little is known about the molecular processes that mediate polarized targeting of neuronal proteins. Recently, the plus-end-directed motor Myosin Va was shown to play a critical role in targeting of transmembrane proteins to dendrites; however, the role of myosin motors in axonal targeting is unknown. Here we show that Myosin VI, a minus-end-directed motor, plays a vital role in the enrichment of proteins on the surface of axons. Engineering non-neuronal proteins to interact with Myosin VI causes them to become highly concentrated at the axonal surface in dissociated rat cortical neurons. Furthermore, disruption of either Myosin VI function or expression leads to aberrant dendritic localization of axonal proteins. Myosin VI mediates the enrichment of proteins on the axonal surface at least in part by stimulating dendrite-specific endocytosis, a mechanism that has been shown to underlie the localization of many axonal proteins. In addition, a version of Channelrhodopsin 2 that was engineered to bind to Myosin VI is concentrated at the surface of the axon of cortical neurons in mice in vivo, suggesting that it could be a useful tool for probing circuit structure and function. Together, our results indicate that myosins help shape the polarized distributions of both axonal and dendritic proteins.

Highlights

Following synthesis in the secretory pathway, axonal and dendritic transmembrane proteins follow distinct transport pathways to the plasma membrane
Several studies have shown that many axonal proteins are targeted to both compartments initially, and are subsequently enriched on the axonal surface after they have been removed from the surface of the dendrites by endocytosis
We show here that this dendritespecific endocytosis is promoted by interaction with Myosin VI, whereas blocking Myosin VI function prevents axonal protein from being internalized from the surface of dendrites

Summary

Introduction

Following synthesis in the secretory pathway, axonal and dendritic transmembrane proteins follow distinct transport pathways to the plasma membrane. The net effect of these processes is that axonal transmembrane proteins are distributed roughly evenly to the intracellular regions of both the axon and dendrites, but are dramatically enriched on the axonal membrane The transport of both axonal and dendritic proteins is mediated by kinesin motors [6,7,8,9,10]. Recent work from our laboratory indicates that vesicles are targeted to dendrites through the actions of plus-end-directed myosin motors, which direct the vesicles away from the axon and towards the cell body [12] This result suggests that a minus-end-directed motor might participate in the localization of axonal proteins. It associates with both clathrin-coated vesicles and proteins that mediate endocytosis [15,16,17] and plays a prominent role in the endocytosis of at least two neuronal proteins [18,19]

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