Translation-dependent quality control pathways such as no-go decay (NGD), non-stop decay (NSD), and nonsense-mediated decay (NMD) govern protein synthesis and proteostasis by resolving non-translating ribosomes and preventing the production of potentially toxic peptides derived from faulty and aberrant mRNAs. However, how translation is altered and the in vivo defects that arise in the absence of these pathways are poorly understood. Here, we show that the NGD/NSD factors Pelo and Hbs1l are critical in mice for cerebellar neurogenesis but expendable for survival of these neurons after development. Analysis of mutant mouse embryonic fibroblasts revealed translational pauses, alteration of signaling pathways, and translational reprogramming. Similar effects on signaling pathways, including mTOR activation, the translatome and mouse cerebellar development were observed upon deletion of the NMD factor Upf2. Our data reveal that these quality control pathways that function to mitigate errors at distinct steps in translation can evoke similar cellular responses.

Ribosome-associated quality control pathways respond to defects in translational elongation to recycle arrested ribosomes and degrade aberrant polypeptides and mRNAs. Loss of a tRNA gene leads to ribosomal pausing that is resolved by the translational GTPase GTPBP2, and in its absence causes neuron death. Here, we show that loss of the homologous protein GTPBP1 during tRNA deficiency in the mouse brain also leads to codon-specific ribosome pausing and neurodegeneration, suggesting that these non-redundant GTPases function in the same pathway to mitigate ribosome pausing. As observed in Gtpbp2-/- mice (Ishimura et al., 2016), GCN2-mediated activation of the integrated stress response (ISR) was apparent in the Gtpbp1-/- brain. We observed decreased mTORC1 signaling which increased neuronal death, whereas ISR activation was neuroprotective. Our data demonstrate that GTPBP1 functions as an important quality control mechanism during translation elongation and suggest that translational signaling pathways intricately interact to regulate neuronal homeostasis during defective elongation.

Editing domains of aminoacyl tRNA synthetases correct tRNA charging errors to maintain translational fidelity. A mutation in the editing domain of alanyl tRNA synthetase (AlaRS) in Aars ^sti mutant mice results in an increase in the production of serine-mischarged tRNA^Ala and the degeneration of cerebellar Purkinje cells. Here, using positional cloning, we identified Ankrd16, a gene that acts epistatically with the Aars ^sti mutation to attenuate neurodegeneration. ANKRD16, a vertebrate-specific protein that contains ankyrin repeats, binds directly to the catalytic domain of AlaRS. Serine that is misactivated by AlaRS is captured by the lysine side chains of ANKRD16, which prevents the charging of serine adenylates to tRNA^Ala and precludes serine misincorporation in nascent peptides. The deletion of Ankrd16 in the brains of Aars^sti/sti mice causes widespread protein aggregation and neuron loss. These results identify an amino-acid-accepting co-regulator of tRNA synthetase editing as a new layer of the machinery that is essential to the prevention of severe pathologies that arise from defects in editing.