Poster abstracts

Poster number 120 submitted by Yi-Ju Tseng

Identifying regulators of C9orf72 ALS/FTD associated RAN translation

Yi-Ju Tseng (Molecular, Cellular, and Developmental Biology Graduate Program, University of Michigan, Ann Arbor, MI), Alexander E. Linsalata (Cellular and Molecular Biology Graduate Program, University of Michigan, Ann Arbor, MI), Katelyn M. Green (Cellular and Molecular Biology Graduate Program, University of Michigan, Ann Arbor, MI), Nicholas Santoro (Center for Chemical Genomics, Life Sciences Institute, University of Michigan, Ann Arbor, MI), Martha J. Larson (Center for Chemical Genomics, Life Sciences Institute, University of Michigan, Ann Arbor, MI), Peter K. Todd (Department of Neurology, University of Michigan, Ann Arbor, MI; VA medical Center, Ann Arbor, MI)

Abstract:
A GGGGCC repeat expansion in C9orf72 is the most common known cause of amyotrophic lateral sclerosis (ALS) and frontotemporal dementia (FTD). Recently this locus was shown to support Repeat-Associated Non-AUG (RAN) translation, a non-canonical initiation process that generates toxic dipeptide repeat proteins from C9orf72 repeat-containing mRNAs. To better understand the mechanism underlying RAN translation, we performed a genome-wide siRNA screen using luciferase-based reporters for G4C2-expanded C9orf72 RAN translation (C9RAN). We identified 642 of genes that exhibited selective inhibition of RAN translation while sparing translation of an AUG initiated control. One candidate gene, the RNA and DNA helicase DHX36, was validated using overexpression and knock-down studies at both the DNA and RNA level. Overexpression of DHX36 strongly suppressed global translation while sparing C9RAN translation across reading frames. In contrast, knockdown of DHX36 caused a greater impact on RAN translation than AUG initiated translation. Identifying factors that selectively modulate RAN translation should lay the groundwork for rational therapeutic design in these currently untreatable neurologic disorders.

Keywords: C9orf72, DHX36, RAN translation