ANTAGONISTIC ROLES FOR ATAXIN-2 STRUCTURED AND DISORDERED DOMAINS IN RNP CONDENSATION

ABSTRACT Ataxin-2 is a conserved translational control protein associated with spinocerebellar ataxia type II (SCA2) and amyotrophic lateral sclerosis (ALS) as well as an important target for ALS therapeutics under development. Despite its clinical and biological significance, Ataxin-2’s activities, mechanisms and functions are not well understood. While Drosophila Ataxin-2 (Atx2) mediates mRNP condensation via a C-terminal intrinsically disordered domain (cIDR), how Ataxin-2 IDRs work with structured (Lsm, Lsm-AD and PAM2) domains to enable positive and negative regulation of target mRNAs remains unclear. Using TRIBE (Targets of RNA-Binding Proteins Identified by Editing) technology, we identified and analysed Atx-2 target mRNAs in the Drosophila brain. We show that Atx2 preferentially interacts with AU-rich elements (AREs) in 3’UTRs and plays a broad role in stabilization of identified target mRNAs. Strikingly, Atx2 interaction with its targets is dependent on the cIDR domain required for neuronal-granule formation. In contrast, Atx2 lacking its Lsm domain not only interacts more efficiently with the target mRNA identified, but also forms larger RNP granules. Providing an extensive dataset of Atx2-interacting brain mRNAs, our results demonstrate that Atx2: (a) interacts with target mRNAs within RNP granules; (b) modulates the turnover of these target mRNAs; (c) has an additional essential role outside of mRNP granules; and (d) contains distinct protein domains that drive or oppose RNP-granule assembly. These findings increase understanding of neuronal translational control mechanisms and inform Ataxin-2-based interventions in development for SCA2 and ALS.