[Development of RNA Hydrogels as a Potential System for Intracellular Biomimicry: A Method for the In Vitro Synthesis of ALS/FTD-related (G4C2)n RNA with over 100 Repeats].

In the motor neurons of amyotrophic lateral sclerosis (ALS) patients, excessive (G4C2)n repeats in the intronic region of the C9orf72 gene are transcribed to RNA, forming G-quadruplexes that sequester RNA-binding proteins, leading to gelation within the cytoplasm as one of the many mechanisms leading to pathogenesis. While ALS patients frequently harbor over 700 repeats, this kind of 100% GC-rich region is very difficult to clone, and past studies report the necessity to add additional sequences in the middle to clone more than a few dozen repeats. The goal of this study was the in vitro production of the longest repetitive RNA to date consisting solely of (G4C2)n repeats. T4 DNA ligase was used to connect (G4C2)10 stretches of DNA with 3nt overhangs. Then, using a heat-resistant T7 RNA polymerase, the RNA obtained contained transcripts over 100 repeats. Artificial biomimetic RNA gels generated by scaling up this synthesis method are expected to contribute to elucidating the molecular mechanisms of repetitive sequence-related pathogenesis, as well as screening for drugs that can disrupt the gel structure.