Nutritional control of protein translation

• Applicant: Dr. Francesca Tuorto
• Subject Area: Molecular Biology and Physiology of Neurons and Glial Cells ; Cell Biology
• Term: since 2016
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 332766670

Post-transcriptional modifications in the anticodon loop of tRNAs are important regulators of the decoding process during protein synthesis. We recently showed that nutritional determined levels of queuosine (Q), a bacteria-derived nucleoside found in eukaryotic tRNA, influence the levels of 5-methylcytosine (5mC) of C38-tRNAAsp in human cell culture and in germ-free mice. Using proteomic and Ribo-Seq approaches, we discovered a direct connection between these anticodon loop tRNA modifications and the speed of codon-biased translation, whereby Q-dependent translation at the level of single codons, especially at Q-decoded and near cognate-codons, promotes protein folding and prevents the accumulation of misfolded proteins. Q-modifications of tRNA are conducted by tRNA-guaninetransglycosylase (TGT) composed of the QTRT1-QTRT2 enzyme complex. Using a Qtrt1 knockout mouse model, we observed that the loss of Q-tRNA modifications causes learning and memory deficits, which is accompanied by a reduction of neuronal populations. Ribo-Seq analysis in the hippocampus of Qtrt1-deficient mice revealed not only stalling of ribosomes on Q-decoded codons, but also a global imbalance of translation elongation speed. The aim of this new project is to study how altered translation decoding causes the onset of neuro-pathological phenotypes in the mammalian brain. Using classical immunohistochemical methods to study brain defects in vivo we will first analyze if lack of Q modifications alters neurogenesis or alternatively induces neurodegeneration. Using primary culture of mouse hippocampal neurons, reporters of stalled ribosomes and inhibitors of protein translation regulators, we will investigate if Q-tRNA affects processes like ribosome quality control (RQC), No-Go Decay (NGD) and eIF2 signaling. Finally, using C. elegans as model system, we will determine if lack of Q-tRNA alters co-translational protein folding by screening the chaperones involved in the process. Taken together, our data will provide a direct link between the altered decoding of the neuronal transcriptome by a bacterial micronutrient and the onset of neuronal phenotypes.

• DFG Programme: Research Grants