Illuminating Transfer RNA Variants as Genetic Modifiers in Models of Human Disease
Abstract
Transfer RNAs (tRNAs) physically link the genetic code to an amino acid sequence, by recruiting amino acids to three-nucleotide codons in messenger RNAs. To ensure that the genetic code is translated as intended, tRNAs must be accurately aminoacylated and faithfully recognize codons in the ribosome during protein synthesis. Given the critical function of tRNAs, it has often been assumed that mutations in human tRNA genes would be either lethal to cells or not significantly impair tRNA function. My goal was to rigorously test this assumption in mammalian cell models, prompted by the recent discovery of unprecedented variation in human tRNA gene sequences.
First, I review existing knowledge on links between human cytosolic tRNA biology and disease. Next, I demonstrate that synthetic tRNA mutants can elicit significant levels of amino acid misincorporation in human cells, which is surprisingly well tolerated. I then test the effects of mistranslation by synthetic and natural tRNA variants on cellular models of neurodegenerative disease, based on our hypothesis that mistranslation would exacerbate protein-folding stress-associated diseases. I find that a natural tRNA variant occurring in ~2% of the sequenced human population has significant potential to modify the progression and severity of Huntington’s disease, amyotrophic lateral sclerosis, and potentially other diseases. Lastly, I investigate methodological approaches which could aid in the characterization of other natural human tRNA variants, while demonstrating that even identical tRNA variants may differ in phenotypic severity and effected tissues depending on local sequence context of the tRNA gene.