title: A genetic screen identifies Tor as an interactor of VAPB in a Drosophila model of amyotrophic lateral sclerosis.
abstract: Amyotrophic Lateral Sclerosis (ALS) is a progressive neurodegenerative disorder characterized by selective death of motor neurons. In 5-10% of the familial cases, the disease is inherited because of mutations. One such mutation, P56S, was identified in human VAPB that behaves in a dominant negative manner, sequestering wild type protein into cytoplasmic inclusions. We have conducted a reverse genetic screen to identify interactors of Drosophila VAPB. We screened 2635 genes and identified 103 interactors, of which 45 were enhancers and 58 were suppressors of VAPB function. Interestingly, the screen identified known ALS loci - TBPH, alsin2 and SOD1. Also identified were genes involved in cellular energetics and homeostasis which were used to build a gene regulatory network of VAPB modifiers. One key modifier identified was Tor, whose knockdown reversed the large bouton phenotype associated with VAP(P58S) expression in neurons. A similar reversal was seen by over-expressing Tuberous Sclerosis Complex (Tsc1,2) that negatively regulates TOR signaling as also by reduction of S6K activity. In comparison, the small bouton phenotype associated with VAP(wt) expression was reversed with Tsc1 knock down as well as S6K-CA expression. Tor therefore interacts with both VAP(wt) and VAP(P58S), but in a contrasting manner. Reversal of VAP(P58S) bouton phenotypes in larvae fed with the TOR inhibitor Rapamycin suggests upregulation of TOR signaling in response to VAP(P58S) expression. The VAPB network and further mechanistic understanding of interactions with key pathways, such as the TOR cassette, will pave the way for a better understanding of the mechanisms of onset and progression of motor neuron disease.
authors.affiliation: Indian Institute of Science Education and Research, Pune 411021, India.
authors.forename: Senthilkumar
authors.initials: S
authors.lastname: Deivasigamani
authors.affiliation: Indian Institute of Science Education and Research, Pune 411021, India.
authors.forename: Hemant Kumar
authors.initials: HK
authors.lastname: Verma
authors.affiliation: National Institute of Genetics, Mishima, Shizuoka 411-8540, Japan.
authors.forename: Ryu
authors.initials: R
authors.lastname: Ueda
authors.affiliation: Agharkar Research Institute, Pune 411004, India girish@iiserpune.ac.in girish.iiserpune@gmail.com anu.aripune@gmail.com.
authors.forename: Anuradha
authors.initials: A
authors.lastname: Ratnaparkhi
authors.affiliation: Indian Institute of Science Education and Research, Pune 411021, India girish@iiserpune.ac.in girish.iiserpune@gmail.com anu.aripune@gmail.com.
authors.forename: Girish S
authors.initials: GS
authors.lastname: Ratnaparkhi
keywords: ALS; Drosophila RNAi screen; Neurodegeneration; TOR; VAP