PT  - JOURNAL ARTICLE
AU  - Michael S. Haney
AU  - Nicholas J. Kramer
AU  - David W. Morgens
AU  - Ana Jovičić
AU  - Julien Couthouis
AU  - Amy Li
AU  - James Ousey
AU  - Rosanna Ma
AU  - Gregor Bieri
AU  - Michael C. Bassik
AU  - Aaron D. Gitler
TI  - CRISPR-Cas9 screens in human cells and primary neurons identify modifiers of <em>C9orf72</em> dipeptide repeat protein toxicity
AID  - 10.1101/129254
DP  - 2017 Jan 01
TA  - bioRxiv
PG  - 129254
4099  - http://biorxiv.org/content/early/2017/04/21/129254.short
4100  - http://biorxiv.org/content/early/2017/04/21/129254.full
AB  - Hexanucleotide repeat expansions in the C9orf72 gene are the most common cause of amyotrophic lateral sclerosis and frontotemporal dementia (c9FTD/ALS). The nucleotide repeat expansions are translated into dipeptide repeat (DPR) proteins, which are aggregation-prone and may contribute to neurodegeneration. Studies in model organisms, including yeast and flies have converged upon nucleocytoplasmic transport as one underlying pathogenic mechanism, but a comprehensive understanding of the molecular and cellular underpinnings of DPR toxicity in human cells is still lacking. We used the bacteria-derived clustered regularly interspaced short palindromic repeats (CRISPR)-Cas9 system to perform genome-wide gene knockout screens for suppressors and enhancers of C9orf72 DPR toxicity in human cells. We validated hits by performing secondary CRISPR-Cas9 screens in primary mouse neurons. Our screens revealed genes involved in nucleocytoplasmic transport, reinforcing the previous findings from model systems. We also uncovered new potent modifiers of DPR toxicity whose gene products function in the endoplasmic reticulum (ER), proteasome, RNA processing pathways, and in chromatin modification. Since regulators of ER stress emerged prominently from the screens, we further investigated one such modifier, TMX2, which we identified as a modulator of the ER-stress signature elicited by C9orf72 DPRs in neurons. Together, this work identifies novel suppressors of DPR toxicity that represent potential therapeutic targets and demonstrates the promise of CRISPR-Cas9 screens to define mechanisms of neurodegenerative diseases.One Sentence Summary Genome-wide CRISPR-Cas9 screens in human cells reveal mechanisms and targets for ALS-associated C9orf72 dipeptide repeat protein toxicity.