Long Noncoding RNA Isoform Specificity and Chemical Modification on tRNA-Derived Fragments Leading to Divergent...

Noncoding RNAs (ncRNAs) are important regulators of gene expression in development, immunity, and disease. Among them, long noncoding RNAs (lncRNAs) and tRNA-derived fragments (tRFs) represent two major types of ncRNA that differ in size, structure, and function. As regulators, lncRNAs display remarkable structural complexity and extensive isoform diversity. Discrete motifs (such as hairpins, triple helices, G-quadruplexes, and scaffold domains) harbored by a given isoform govern interactions with DNA, RNA, and proteins, yet isoform-specific structures are rarely addressed, leading to contradictory findings across studies. In contrast, tRFs (14 to 35 nucleotides) arise from precise cleavage of precursor or mature tRNAs and regulate translation, stress responses, and epigenetic inheritance. Their limited length constrains large-scale structural isoform diversity, but their functions are strongly shaped by chemical modifications, which affect stability, localization, and association with RNA-binding proteins. Here, two underappreciated principles are highlighted: isoform- and structure-resolved mechanisms are essential for truly understanding lncRNA biology; and modification-driven rules diversify tRF functions. An integrated framework that combines sequence, structure, isoform, and modification to refine mechanisms of action of ncRNAs and accelerate ncRNA-based diagnostics and therapeutics is proposed.