Molecular mechanisms orchestrating the lifecycle of human tRNAs

By delivering amino acids to translating ribosomes, transfer RNAs (tRNAs) are central to protein synthesis. These small (~76 nucleotide-long) molecules have very similar three-dimensional structures, which must withstand substantial conformational changes throughout the tRNA lifecycle. To meet these demands, tRNAs are decorated by diverse chemical modifications at multiple nucleotides by highly conserved enzymes. Defects in the genes encoding these enzymes are linked to neurodevelopmental disorders. Yet, our understanding of how chemical modifications promote the biogenesis, function, and stability of individual tRNAs is limited due to technical challenges in quantifying tRNAs and the impact of their modifications on mRNA translation in human cells. We recently developed workflows to meet these challenges, enabling dissection of the tRNA lifecycle in physiologically relevant human induced pluripotent stem cell (hiPSC)-based models. Building on these advances, this proposal aims to uncover the key mechanisms orchestrating the birth, life, and destruction of human tRNAs by answering three questions: which chemical modification steps are essential for the function of individual tRNAs; how do cells sense and respond to defects in translation due to tRNA dysfunction, and how do cells dispose of excess or aberrant tRNAs. To achieve this, we will combine functional genomics with quantitative high-throughput approaches and biochemical assays in hiPSC-derived cells and brain organoid models. This project will significantly advance our understanding of the fundamental mechanisms governing the lifecycle of tRNAs to ensure accurate and efficient protein synthesis in pluripotent and differentiated human cells, and identify molecular triggers for neurodevelopmental disorders linked to tRNA dysfunction. Our discoveries will have implications for predicting the functional consequences of pathological mutations in tRNA-modifying genes and for designing effective RNA therapeutics.