title: Endogenous mechanisms for the origins of spliceosomal introns.
abstract: Over 30 years since their discovery, the origin of spliceosomal introns remains uncertain. One nearly universally accepted hypothesis maintains that spliceosomal introns originated from self-splicing group-II introns that invaded the uninterrupted genes of the last eukaryotic common ancestor (LECA) and proliferated by "insertion" events. Although this is a possible explanation for the original presence of introns and splicing machinery, the emphasis on a high number of insertion events in the genome of the LECA neglects a considerable body of empirical evidence showing that spliceosomal introns can simply arise from coding or, more generally, nonintronic sequences within genes. After presenting a concise overview of some of the most common hypotheses and mechanisms for intron origin, we propose two further hypotheses that are broadly based on central cellular processes: 1) internal gene duplication and 2) the response to aberrant and fortuitously spliced transcripts. These two nonmutually exclusive hypotheses provide a powerful way to explain the establishment of spliceosomal introns in eukaryotes without invoking an exogenous source.
authors.affiliation: Department of Biology, Indiana University, Bloomington, IN 47405, USA. fcatania@indiana.edu
authors.forename: Francesco
authors.initials: F
authors.lastname: Catania
authors.forename: Xiang
authors.initials: X
authors.lastname: Gao
authors.forename: Douglas G
authors.initials: DG
authors.lastname: Scofield
mesh_terms: D017398:Alternative Splicing / Q000235:genetics; D005057:Eukaryotic Cells; D019143:Evolution, Molecular; D020440:Gene Duplication; D007438:Introns / Q000235:genetics*; D008957:Models, Genetic; D012326:RNA Splicing; D017381:Spliceosomes / Q000235:genetics*