Non-functional genes repaired at the RNA level

Abstract

Genomes and genes continuously evolve. Gene sequences undergo substitutions, deletions or nucleotide insertions; mobile genetic elements invade genomes and interleave in genes; chromosomes break, even within genes, and pieces reseal in reshuffled order. To maintain functional gene products and assure an organism's survival, two principal strategies are used - either repair of the gene itself or of its product. I will introduce common types of gene aberrations and how gene function is restored secondarily, and then focus on systematically fragmented genes found in a poorly studied protist group, the diplonemids. Expression of their broken genes involves restitching of pieces at the RNA-level, and substantial RNA editing, to compensate for point mutations. I will conclude with thoughts on how such a grotesquely unorthodox system may have evolved, and why this group of organisms persists and thrives since tens of millions of years.

Keywords: Diplonemids; Diplonémides; Evolution of complexity; Gene fragmentation; Gènes fragmentés; Insertion and substitution RNA editing; Protistes; Protists; Trans-splicing; Édition de l’ARN par insertion et substitution; Épissage en trans; Évolution de la complexité.