Vps54 regulates Drosophila neuromuscular junction development and interacts genetically with Rab7 to control composition of the postsynaptic density.

Prajal H Patel,Malea R Mcgimsey,Scott A Barbee,Emily C Wilkinson,Emily L Starke,J Todd Blankenship

doi:10.1242/bio.053421

Prajal H Patel, Malea R Mcgimsey + Show 4 more

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https://doi.org/10.1242/bio.053421

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Journal: Biology open	Publication Date: Jan 1, 2020
Citations: 7	License type: CC BY 4.0

Affiliation: University of Denver

Abstract

ABSTRACTVps54 is a subunit of the Golgi-associated retrograde protein (GARP) complex, which is involved in tethering endosome-derived vesicles to the trans-Golgi network (TGN). In the wobbler mouse, a model for human motor neuron (MN) disease, reduction in the levels of Vps54 causes neurodegeneration. However, it is unclear how disruption of the GARP complex leads to MN dysfunction. To better understand the role of Vps54 in MNs, we have disrupted expression of the Vps54 ortholog in Drosophila and examined the impact on the larval neuromuscular junction (NMJ). Surprisingly, we show that both null mutants and MN-specific knockdown of Vps54 leads to NMJ overgrowth. Reduction of Vps54 partially disrupts localization of the t-SNARE, Syntaxin-16, to the TGN but has no visible impact on endosomal pools. MN-specific knockdown of Vps54 in MNs combined with overexpression of the small GTPases Rab5, Rab7, or Rab11 suppresses the Vps54 NMJ phenotype. Conversely, knockdown of Vps54 combined with overexpression of dominant negative Rab7 causes NMJ and behavioral abnormalities including a decrease in postsynaptic Dlg and GluRIIB levels without any effect on GluRIIA. Taken together, these data suggest that Vps54 controls larval MN axon development and postsynaptic density composition through a mechanism that requires Rab7.

Highlights

Endocytic trafficking is critical for many specialized processes in neurons including axon growth, guidance, plasticity, and for the maintenance of cellular homeostasis (Wojnacki and Galli, 2016)
vacuolar protein sorting-associated protein 54 (Vps54) is a core subunit of the evolutionarily conserved Golgi-associated retrograde protein (GARP) complex, which localizes to the trans-Golgi network (TGN) and is involved in tethering retrograde transport carriers derived from endosomes (Bonifacino and Hierro, 2011)
In order to better understand the function of Vps54 in motor neuron (MN), we have examined the development of the neuromuscular junction (NMJ) following depletion of the single Drosophila ortholog of Vps54

Summary

INTRODUCTION

Endocytic trafficking is critical for many specialized processes in neurons including axon growth, guidance, plasticity, and for the maintenance of cellular homeostasis (Wojnacki and Galli, 2016). Unlike what is seen in yeast and mammalian cells, depletion of scat has no impact on the size, number, or localization of either early or late endosomes (EEs and LEs) (Palmisano et al, 2011; Quenneville et al, 2006) Both phenotypes are distinctly different from those reported in Vps reduction-of-function (wobbler) and loss-of-function mouse models (Palmisano et al, 2011; Schmitt-John et al, 2005). Presynaptic knockdown of scat combined with disruption of Rab function significantly decreases NMJ complexity and alters the composition of the postsynaptic density (PSD) This suggest that Vps54-mediated endosomal trafficking is required to control NMJ development and synaptic morphology in Drosophila

MATERIALS AND METHODS

Findings

DISCUSSION