Amyotrophic Lateral Sclerosis (ALS) is a fatal, late-onset, progressive motor neurodegenerative disorder. A key pathological feature of the disease is the presence of heavily ubiquitinated protein inclusions. Both the Unfolded Protein Response (UPR) and the Ubiquitin Proteasome System (UPS) appear significantly impaired in patients and animal models of ALS. We have studied cellular and molecular mechanisms involved in ALS using a vesicle-associated membrane protein-associated protein B (VAPB/ALS8) Drosophila model (Moustaqim-Barrette et al., 2014), which mimics many systemic aspects of the human disease. Here, we show that VAPB, located on the cytoplasmic face of the ER membrane, interacts with Caspar, an ortholog of human fas associated factor 1 (FAF1). Caspar, in turn, interacts with transitional endoplasmic reticulum ATPase (TER94), a fly ortholog of ALS14 (VCP/p97, Valosin-containing protein). Caspar overexpression in the glia extends lifespan and also slows the progression of motor dysfunction in the ALS8 disease model, a phenomenon that we ascribe to its ability to restrain age-dependant inflammation, which is modulated by Relish/NFκB signalling. Caspar binds to VAPB via an FFAT motif, and we find that Caspar’s ability to negatively regulate NFκB signalling is not dependant on the VAPB:Caspar interaction. We hypothesize that Caspar is a key molecule in the pathogenesis of ALS. The VAPB:Caspar:TER94 complex appears to be a candidate for regulating both protein homeostasis and NFκB signalling, with our study highlighting a role for Caspar in glial inflammation. We project human FAF1 as an important protein target to alleviate the progression of motor neuron disease.

Monensin-sensitive 1 (Mon1) is an endocytic regulator that participates in the conversion of Rab5-positive early endosomes to Rab7-positive late endosomes. In Drosophila, loss of mon1 leads to sterility as the mon1 mutant females have extremely small ovaries with complete absence of late stage egg chambersa phenotype reminiscent of mutations in the insulin pathway genes. Here, we show that expression of many Drosophila insulin-like peptides (ILPs) is reduced in mon1 mutants and feeding mon1 adults an insulin-rich diet can rescue the ovarian defects. Surprisingly, however, mon1 functions in the tyramine/ octopaminergic neurons (OPNs) and not in the ovaries or the insulinproducing cells (IPCs). Consistently, knockdown of mon1 in only the OPNs is sufficient to mimic the ovarian phenotype, while expression of the gene in the OPNs alone can 'rescue' the mutant defect. Last, we have identified ilp3 and ilp5 as critical targets of mon1. This study thus identifies mon1 as a novel molecular player in the brain-gonad axis and underscores the significance of inter-organ systemic communication during development.

Amyotrophic Lateral Sclerosis (ALS) is a fatal, late-onset, progressive motor neurodegenerative disorder. We have been studying cellular and molecular mechanisms involved in ALS using a vesicle-associated membrane protein-associated protein B (VAPB/ALS8) Drosophila model, which mimics many systemic aspects of the human disease. Here, we show that the ER-resident VAPB interacts with Caspar, an ortholog of human fas associated factor 1 (FAF1). Caspar, in turn, interacts with transitional endoplasmic reticulum ATPase (TER94), a fly ortholog of ALS14 (VCP/p97, Valosin-containing protein), via its UBX domain and poly-ubiquitinated proteins with its UBA domain. Caspar overexpression in the glia extends lifespan and also slows the progression of motor dysfunction in the ALS8 model, a phenomenon that we ascribe to its ability to restrain age-dependant inflammation, modulated by Relish/NFBκ signaling. We hypothesize that Caspar is a key molecule in the pathogenesis of ALS. Caspar connects the plasma membrane (PM) localized immune signalosome to the ER-based VAPB degradative machinery, presumably at PM:ER contact sites. The Caspar:TER94:VAPB complex appears to be a strong candidate for regulating both protein homeostasis and NFκ signaling. These, in turn, regulate glial inflammation and determine the progression of the disease. Our study projects human FAF1 as an important protein target to alleviate the progression of motor neuron disease.

Monensin Sensitive 1 (Mon1) is a component of the Mon1:Ccz1 complex that mediates Rab5 to Rab7 conversion in eukaryotic cells by serving as a guanine nucleotide exchange factor for Rab7 during vesicular trafficking. We find that Mon1 activity modulates the complexity of Class IV dendritic arborization (da) neurons during larval development. Loss of Mon1 function leads to an increase in arborization and complexity, while increased expression, leads to reduced arborization. The ability of Mon1 to influence dendritic development is possibly a function of its interactions with Rab family GTPases that are central players in vesicular trafficking. Earlier, these GTPases, specifically Rab1, Rab5, Rab10, and Rab11 have been shown to regulate dendritic arborization. We have conducted genetic epistasis experiments, by modulating the activity of Rab5, Rab7, and Rab11 in da neurons, in Mon1 mutants, and demonstrate that the ability of Mon1 to regulate arborization is possibly due to its effect on the recycling pathway. Dendritic branching is critical for proper connectivity and physiological function of the neuron. An understanding of regulatory elements, such as Mon1, as demonstrated in our study, is essential to understand neuronal function.