Vps54 regulatesDrosophilaneuromuscular junction development and controls postsynaptic density composition via a Rab7-dependent mechanism

Abstract

ABSTRACTVps54 is a subunit of the Golgi-associated retrograde protein (GARP) complex, which is involved in tethering endosome-derived vesicles to thetrans-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 GARP-mediated vesicle transport leads to MN dysfunction and ultimately neurodegeneration. To better understand the role of Vps54 in MNs, we have disrupted expression of theVps54ortholog inDrosophilaand examined the impact on the larval neuromuscular junction (NMJ). Here, we show that both null mutants and MN-specific knockdown ofVps54leads to NMJ overgrowth. Reduction ofVps54partially disrupts localization of the t-SNARE, Syntaxin-16, to the TGN but has no impact on endosomal pools. Presynaptic knockdown ofVps54in MNs combined with overexpression of the small GTPases Rab5, Rab7, or Rab11 suppresses theVps54NMJ phenotype. Conversely, knockdown ofVps54combined with overexpression of dominant negative Rab7 causes axonal and behavioral abnormalities including a decrease in postysynaptic Dlg and GluRIIB levels without any effect on GluRIIA. Taken together, these data suggest thatVps54controls larval MN axon development and postsynaptic density composition by modulating Rab7-mediated endosomal trafficking.