Aminoacyl-tRNA synthetases are ubiquitously expressed proteins that charge tRNAs with their cognate amino acids. By ensuring the fidelity of protein synthesis, these enzymes are essential for viability of every cell. Yet, mutations in six tRNA synthetases specifically affect the peripheral nerves and cause Charcot-Marie-Tooth disease (CMT). The CMT-causing mutations in tyrosyl- and glycyl-tRNA synthetases (YARS and GARS, respectively) alter the activity of the proteins in a range of ways (some mutations do not impact charging function, while others abrogate it), making a loss of function in tRNA charging unlikely to be the cause of disease pathology. It is currently unknown which cellular mechanisms are triggered by the mutant enzymes and how this leads to neurodegeneration. Here, by expressing two pathogenic mutations (G240R, P234KY) in Drosophila, we generated a model for GARS-associated neuropathy. We observed compromised viability, and behavioral, electrophysiological and morphological impairment in flies expressing the cytoplasmic isoform of mutant GARS. Their features recapitulated several hallmarks of CMT pathophysiology and were similar to the phenotypes identified in our previously described Drosophila model of YARS-associated neuropathy. Furthermore, CG8316 and CG15599 – genes identified in a retinal degeneration screen to modify mutant YARS, also modified the mutant GARS phenotypes. Our study presents genetic evidence for common mutant-specific interactions between two CMT-associated aminoacyl-tRNA synthetases, lending support for a shared mechanism responsible for the synthetase-induced peripheral neuropathies.

Charcot-Marie-Tooth disease (CMT) is a length-dependent peripheral neuropathy. The aminoacyl-tRNA synthetases constitute the largest protein family implicated in CMT. Aminoacyl-tRNA synthetases are predominantly cytoplasmic, but are also present in the nucleus. Here we show that a nuclear function of tyrosyl-tRNA synthetase (TyrRS) is implicated in a Drosophila model of CMT. CMT-causing mutations in TyrRS induce unique conformational changes, which confer capacity for aberrant interactions with transcriptional regulators in the nucleus, leading to transcription factor E2F1 hyperactivation. Using neuronal tissues, we reveal a broad transcriptional regulation network associated with wild-type TyrRS expression, which is disturbed when a CMT-mutant is expressed. Pharmacological inhibition of TyrRS nuclear entry with embelin reduces, whereas genetic nuclear exclusion of mutant TyrRS prevents hallmark phenotypes of CMT in the Drosophila model. These data highlight that this translation factor may contribute to transcriptional regulation in neurons, and suggest a therapeutic strategy for CMT.