Drosophila Exo70 Is Essential for Neurite Extension and Survival under Thermal Stress

Abstract

The octomeric exocyst complex governs the final step of exocytosis in both plants and animals. Its roles, however, extend beyond exocytosis and include organelle biogenesis, ciliogenesis, cell migration, and cell growth. Exo70 is a conserved component of the exocyst whose function in is unclear. In this study, we characterized two mutant alleles of mutants exhibit reduced synaptic growth, locomotor activity, glutamate receptor density, and mEPSP amplitude. We found that presynaptic Exo70 is necessary for normal synaptic growth at the neuromuscular junction (NMJ). At the neuromuscular junction, genetically interacts with the small GTPase to regulate synaptic growth. Loss of Exo70 leads to the blockage of JNK signaling-, activity-, and temperature-induced synaptic outgrowths. We showed that this phenotype is associated with an impairment of integral membrane protein transport to the cell surface at synaptic terminals. In octopaminergic motor neurons, Exo70 is detected in synaptic varicosities, as well as the regions of membrane extensions in response to activity stimulation. Strikingly, mild thermal stress causes severe neurite outgrowth defects and pharate adult lethality in mutants. mutants also display defective locomotor activity in response to starvation stress. These results demonstrated that Exo70 is an important regulator of induced synaptic growth and is crucial for an organism's adaptation to environmental changes. The exocyst complex is a conserved protein complex directing secretory vesicles to the site of membrane fusion during exocytosis, which is essential for transporting proteins and membranes to the cell surface. Exo70 is a subunit of the exocyst complex whose roles in neurons remain elusive, and its function in is unclear. In, Exo70 is expressed in both glutamatergic and octopaminergic neurons, and presynaptic Exo70 regulates synaptic outgrowth. Moreover, mutants have impaired integral membrane transport to the cell surface at synaptic terminals and block several kinds of induced synaptic growth. Remarkably, elevated temperature causes severe arborization defects and lethality in mutants, thus underpinning the importance of Exo70 functions in development and adaptation to the environment.

A fine balance between Prpf19 and Exoc7 in achieving degradation of aggregated protein and suppression of cell death in spinocerebellar ataxia type 3

“…4 ). When the Exoc7 ortholog, exocyst 70 ( exo70 ), was knocked down in Drosophila 37 , the soluble and aggregated ATXN3fl-Q84 protein levels were reduced (Supplementary Fig. 6a–d ), similar to what we observed when prp19 was overexpressed (Fig.…”

Exocyst-mediated membrane trafficking of the lissencephaly-associated ECM receptor dystroglycan is required for proper brain compartmentalization

“…All of these processes require robust protein trafficking within the neuron to result in the directional delivery of proteins to the axonal termini. Since the exocyst controls polarized secretion, and exocyst subunits have been implicated in neurite outgrowth and cell polarity ( Koon et al, 2018 ; Lira et al, 2019 ), one possibility is that exocyst-mediated regulation of Dg trafficking takes place at specific stages, ensuring a temporally dynamic Dg protein expression pattern necessary for proper neuronal differentiation.…”

“…However, a more interesting hypothesis is that the exocyst could be involved in Dg trafficking. During synaptogenesis, the exocyst has been shown to play a role in the localized delivery of several neurotransmitter receptors ( Gerges et al, 2006 ; Koon et al, 2018 ; Lee and Schwarz, 2016 ; Riefler et al, 2003 ; Sans et al, 2003 ). For example, previous data show that Dg is required for proper localization of glutamate receptor at the Drosophila neuromuscular junction ( Marrone et al, 2011b ).…”

Mutations in the exocyst component EXOC2 cause severe defects in human brain development

“…A Drosophila Sec15 ( EXOC6 ) knockout demonstrates that Sec15 is critical for a specific vesicle trafficking event that ensures the correct polarized, asymmetrical cell division of progenitor cells and proper cell fate specification ( Jafar-Nejad et al, 2005 ). Furthermore, Drosophila Exo70 mutants exhibited impaired integral membrane trafficking to the cell surface, severe neurite outgrowth defects, and reduced synaptic growth at the neuromuscular junction ( Koon et al, 2018 ). All other existing full knockouts of exocyst genes are lethal in mice at the blastocyst stage (reviewed in Martin-Urdiroz et al, 2016 ).…”

“…Exocyst is also needed for dendrite arbor formation and spine maturation in hippocampal neurons ( Lira et al, 2019 ; Vega and Hsu, 2001 ). Components of the exocyst complex are enriched in actin-containing growth cones, synaptic boutons, and filopodia ( Hazuka et al, 1999 ; Koon et al, 2018 ). When filopodia are suppressed, axons become disorientated ( Bentley and Toroian-Raymond, 1986 ; Chien et al, 1993 ), and consistent with a guidance role, filopodia are critical to the migration of neuronal growth cones ( Letourneau, 1981 ).…”