OTTR-seq of FXTAS brain reveals tRNA ligase dysfunction

Protein aggregates are a hallmark of neurodegenerative disease proposed to promote neurotoxicity through a diverse and growing set of mechanisms. Aggregation of polyglycine is specifically implicated in the pathogenesis of an emerging group of neurodegenerative GGC repeat expansion diseases. Here, we find that polyglycine aggregates incorporate endogenous proteins harboring glycine-rich sequences, including FAM98B, a conserved component of the vertebrate tRNA ligase complex. Through sequestration and accelerated proteosome-dependent turnover mediated by the FAM98B glycine-rich intrinsically disordered region (IDR), polyglycine depletes the ligase complex and disrupts tRNA processing. Accordingly, brains of affected patients reveal aggregate-associated sequestration and depletion of the tRNA-LC as well as accumulation of aberrant tRNA species. Total RNA from 4 control human cerebellum samples and 4 FXTAS individuals was isolated using TRIzol reagent. Total RNA from clonal FAM98B-knockout HEK293T cells lentivirally complemented with a doxycycline (DOX) suppressible full-length (FAM98B_FL) allele was isolated using TRIzol reagent. Libraries were generated for sequencing using ordered two-template relay (OTTR) sequencing.