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Motor neuron diseases (MNDs) are progressive neurodegenerative disorders characterized by selective death of motor neurons leading to spasticity, muscle wasting and paralysis. Human VAMP-associated protein B (hVAPB) is the causative gene of a clinically diverse group of MNDs including amyotrophic lateral sclerosis (ALS), atypical ALS and late-onset spinal muscular atrophy. The pathogenic mutation is inherited in a dominant manner. Drosophila VAMP-associated protein of 33 kDa A (DVAP-33A) is the structural homologue of hVAPB and regulates synaptic remodeling by affecting the size and number of boutons at neuromuscular junctions. Associated with these structural alterations are compensatory changes in the physiology and ultrastructure of synapses, which maintain evoked responses within normal boundaries. DVAP-33A and hVAPB are functionally interchangeable and transgenic expression of mutant DVAP-33A in neurons recapitulates major hallmarks of the human diseases including locomotion defects, neuronal death and aggregate formation. Aggregate accumulation is accompanied by a depletion of the endogenous protein from its normal localization. These findings pinpoint to a possible role of hVAPB in synaptic homeostasis and emphasize the relevance of our fly model in elucidating the patho-physiology underlying motor neuron degeneration in humans.

Disrupted dopamine (DA) signaling is believed to contribute to the core features of multiple neuropsychiatric and neurodegenerative disorders. Essential features of DA neurotransmission are conserved in the nematode Caenorhabditis elegans, providing us with an opportunity to implement forward genetic approaches that may reveal novel, in vivo regulators of DA signaling. Previously, we identified a robust phenotype, termed Swimming-induced paralysis (Swip), that emerges in animals deficient in the plasma membrane DA transporter. Here, we report the use and quantitative analysis of Swip in the identification of mutant genes that control DA signaling. Two lines captured in our screen (vt21 and vt22) bear novel dat-1 alleles that disrupt expression and surface trafficking of transporter proteins in vitro and in vivo. Two additional lines, vt25 and vt29, lack transporter mutations but exhibit genetic, biochemical, and behavioral phenotypes consistent with distinct perturbations of DA signaling. Our studies validate the utility of the Swip screen, demonstrate the functional relevance of DA transporter structural elements, and reveal novel genomic loci that encode regulators of DA signaling.

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