title: Orthologs, turn-over, and remolding of tRNAs in primates and fruit flies.
abstract: Transfer RNAs (tRNAs) are ubiquitous in all living organism. They implement the genetic code so that most genomes contain distinct tRNAs for almost all 61 codons. They behave similar to mobile elements and proliferate in genomes spawning both local and non-local copies. Most tRNA families are therefore typically present as multicopy genes. The members of the individual tRNA families evolve under concerted or rapid birth-death evolution, so that paralogous copies maintain almost identical sequences over long evolutionary time-scales. To a good approximation these are functionally equivalent. Individual tRNA copies thus are evolutionary unstable and easily turn into pseudogenes and disappear. This leads to a rapid turnover of tRNAs and often large differences in the tRNA complements of closely related species. Since tRNA paralogs are not distinguished by sequence, common methods cannot not be used to establish orthology between tRNA genes.
  
  
  
  In this contribution we introduce a general framework to distinguish orthologs and paralogs in gene families that are subject to concerted evolution. It is based on the use of uniquely aligned adjacent sequence elements as anchors to establish syntenic conservation of sequence intervals. In practice, anchors and intervals can be extracted from genome-wide multiple sequence alignments. Syntenic clusters of concertedly evolving genes of different families can then be subdivided by list alignments, leading to usually small clusters of candidate co-orthologs. On the basis of recent advances in phylogenetic combinatorics, these candidate clusters can be further processed by cograph editing to recover their duplication histories. We developed a workflow that can be conceptualized as stepwise refinement of a graph of homologous genes. We apply this analysis strategy with different types of synteny anchors to investigate the evolution of tRNAs in primates and fruit flies. We identified a large number of tRNA remolding events concentrated at the tips of the phylogeny. With one notable exception all phylogenetically old tRNA remoldings do not change the isoacceptor class.
  
  
  
  Gene families evolving under concerted evolution are not amenable to classical phylogenetic analyses since paralogs maintain identical, species-specific sequences, precluding the estimation of correct gene trees from sequence differences. This leaves conservation of syntenic arrangements with respect to "anchor elements" that are not subject to concerted evolution as the only viable source of phylogenetic information. We have demonstrated here that a purely synteny-based analysis of tRNA gene histories is indeed feasible. Although the choice of synteny anchors influences the resolution in particular when tight gene clusters are present, and the quality of sequence alignments, genome assemblies, and genome rearrangements limits the scope of the analysis, largely coherent results can be obtained for tRNAs. In particular, we conclude that a large fraction of the tRNAs are recent copies. This proliferation is compensated by rapid pseudogenization as exemplified by many very recent alloacceptor remoldings.
authors: Biology Department, Universidad Nacional de Colombia, Carrera 45 # 26-85, Edif. Uriel Gutiérrez, Bogotá, D.C, Colombia.
authors: Cristian A
authors: CA
authors: Velandia-Huerto
authors: Max Planck Institute for Mathematics in the Sciences, Inselstraße 22, Leipzig, D-04103, Germany.|Bioinformatics Group, Department of Computer Science, and Interdisciplinary Center for Bioinformatics, Universität Leipzig, Härtelstraße 16-18D-04107, Leipzig, Germany.
authors: Sarah J
authors: SJ
authors: Berkemer
authors: Bioinformatics Group, Department of Computer Science, and Interdisciplinary Center for Bioinformatics, Universität Leipzig, Härtelstraße 16-18D-04107, Leipzig, Germany.
authors: Anne
authors: A
authors: Hoffmann
authors: Max Planck Institute for Mathematics in the Sciences, Inselstraße 22, Leipzig, D-04103, Germany.|Bioinformatics Group, Department of Computer Science, and Interdisciplinary Center for Bioinformatics, Universität Leipzig, Härtelstraße 16-18D-04107, Leipzig, Germany.
authors: Nancy
authors: N
authors: Retzlaff
authors: Biology Department, Universidad Nacional de Colombia, Carrera 45 # 26-85, Edif. Uriel Gutiérrez, Bogotá, D.C, Colombia.
authors: Liliana C
authors: LC
authors: Romero Marroquín
authors: CONACYT - Instituto de Matemáticas, UNAM Juriquilla, Av. Juriquilla #3001, Santiago de Querétaro, MX-76230, QRO, México.
authors: Maribel
authors: M
authors: Hernández-Rosales
authors: Max Planck Institute for Mathematics in the Sciences, Inselstraße 22, Leipzig, D-04103, Germany. studla@bioinf.uni-leipzig.de.|Bioinformatics Group, Department of Computer Science, and Interdisciplinary Center for Bioinformatics, Universität Leipzig, Härtelstraße 16-18D-04107, Leipzig, Germany. studla@bioinf.uni-leipzig.de.|Fraunhofer Institut for Cell Therapy and Immunology, Perlickstraße 1, Leipzig, D-04103, Germany. studla@bioinf.uni-leipzig.de.|Department of Theoretical Chemistry, University of Vienna, Währinger Straße 17, Vienna, A-1090, Austria. studla@bioinf.uni-leipzig.de.|Center for non-coding RNA in Technology and Health, Grønegårdsvej 3, Frederiksberg C, DK-1870, Denmark. studla@bioinf.uni-leipzig.de.|Santa Fe Institute, 1399 Hyde Park Rd., Santa Fe, NM87501, USA. studla@bioinf.uni-leipzig.de.
authors: Peter F
authors: 0000-0002-5016-5191
authors: PF
authors: Stadler
authors: Biology Department, Universidad Nacional de Colombia, Carrera 45 # 26-85, Edif. Uriel Gutiérrez, Bogotá, D.C, Colombia.
authors: Clara I
authors: CI
authors: Bermúdez-Santana
mesh_terms: D000818:Animals; D001483:Base Sequence; D003062:Codon; D004330:Drosophila / Q000235:genetics*; D019143:Evolution, Molecular; D005815:Genetic Code; D016678:Genome; D005810:Multigene Family; D010802:Phylogeny; D011323:Primates / Q000235:genetics*; D011544:Pseudogenes; D012343:RNA, Transfer / Q000235:genetics*; D016415:Sequence Alignment; D012689:Sequence Homology, Nucleic Acid; D026801:Synteny
chemical_list: D003062:Codon; D012343:RNA, Transfer
keywords: Concerted evolution; Orthology; Synteny; tRNA remolding