title: Nonsense-mediated decay enables intron gain in Drosophila.
abstract: Intron number varies considerably among genomes, but despite their fundamental importance, the mutational mechanisms and evolutionary processes underlying the expansion of intron number remain unknown. Here we show that Drosophila, in contrast to most eukaryotic lineages, is still undergoing a dramatic rate of intron gain. These novel introns carry significantly weaker splice sites that may impede their identification by the spliceosome. Novel introns are more likely to encode a premature termination codon (PTC), indicating that nonsense-mediated decay (NMD) functions as a backup for weak splicing of new introns. Our data suggest that new introns originate when genomic insertions with weak splice sites are hidden from selection by NMD. This mechanism reduces the sequence requirement imposed on novel introns and implies that the capacity of the spliceosome to recognize weak splice sites was a prerequisite for intron gain during eukaryotic evolution.
authors.affiliation: Institut für Populationsgenetik, Veterinärmedizinische Universität Wien, Wien, Austria.
authors.forename: Ashley
authors.initials: A
authors.lastname: Farlow
authors.forename: Eshwar
authors.initials: E
authors.lastname: Meduri
authors.forename: Marlies
authors.initials: M
authors.lastname: Dolezal
authors.forename: Liushuai
authors.initials: L
authors.lastname: Hua
authors.forename: Christian
authors.initials: C
authors.lastname: Schlötterer
mesh_terms: D000595:Amino Acid Sequence; D000818:Animals; D018389:Codon, Nonsense; D004330:Drosophila / Q000737:chemistry / Q000235:genetics* / Q000378:metabolism; D029721:Drosophila Proteins / Q000737:chemistry / Q000235:genetics / Q000378:metabolism; D007438:Introns; D008969:Molecular Sequence Data; D012326:RNA Splicing; D016415:Sequence Alignment; D017381:Spliceosomes / Q000737:chemistry / Q000235:genetics / Q000378:metabolism
chemical_list: D018389:Codon, Nonsense; D029721:Drosophila Proteins