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Suh A, Churakov G, Ramakodi MP, Platt RN, Jurka J, Kojima KK, Caballero J, Smit AF, Vliet KA, Hoffmann FG, Brosius J, Green RE, Braun EL, Ray DA, Schmitz J. Multiple lineages of ancient CR1 retroposons shaped the early genome evolution of amniotes. Genome Biol Evol 2014; 7:205-17. [PMID: 25503085 PMCID: PMC4316615 DOI: 10.1093/gbe/evu256] [Citation(s) in RCA: 46] [Impact Index Per Article: 4.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/14/2022] Open
Abstract
Chicken repeat 1 (CR1) retroposons are long interspersed elements (LINEs) that are ubiquitous within amniote genomes and constitute the most abundant family of transposed elements in birds, crocodilians, turtles, and snakes. They are also present in mammalian genomes, where they reside as numerous relics of ancient retroposition events. Yet, despite their relevance for understanding amniote genome evolution, the diversity and evolution of CR1 elements has never been studied on an amniote-wide level. We reconstruct the temporal and quantitative activity of CR1 subfamilies via presence/absence analyses across crocodilian phylogeny and comparative analyses of 12 crocodilian genomes, revealing relative genomic stasis of retroposition during genome evolution of extant Crocodylia. Our large-scale phylogenetic analysis of amniote CR1 subfamilies suggests the presence of at least seven ancient CR1 lineages in the amniote ancestor; and amniote-wide analyses of CR1 successions and quantities reveal differential retention (presence of ancient relics or recent activity) of these CR1 lineages across amniote genome evolution. Interestingly, birds and lepidosaurs retained the fewest ancient CR1 lineages among amniotes and also exhibit smaller genome sizes. Our study is the first to analyze CR1 evolution in a genome-wide and amniote-wide context and the data strongly suggest that the ancestral amniote genome contained myriad CR1 elements from multiple ancient lineages, and remnants of these are still detectable in the relatively stable genomes of crocodilians and turtles. Early mammalian genome evolution was thus characterized by a drastic shift from CR1 prevalence to dominance and hyperactivity of L2 LINEs in monotremes and L1 LINEs in therians.
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Affiliation(s)
- Alexander Suh
- Institute of Experimental Pathology (ZMBE), University of Münster, Germany Department of Evolutionary Biology (EBC), Uppsala University, Sweden
| | - Gennady Churakov
- Institute of Experimental Pathology (ZMBE), University of Münster, Germany
| | - Meganathan P Ramakodi
- Department of Biochemistry, Molecular Biology, Entomology and Plant Pathology, Mississippi State University Institute for Genomics, Biocomputing and Biotechnology, Mississippi State University Present address: Cancer Prevention and Control Program, Fox Chase Cancer Center, Philadelphia, PA Present address: Department of Biology, Temple University, Philadelphia, PA
| | - Roy N Platt
- Department of Biochemistry, Molecular Biology, Entomology and Plant Pathology, Mississippi State University Institute for Genomics, Biocomputing and Biotechnology, Mississippi State University Department of Biological Sciences, Texas Tech University
| | - Jerzy Jurka
- Genetic Information Research Institute, Mountain View, California
| | - Kenji K Kojima
- Genetic Information Research Institute, Mountain View, California
| | | | - Arian F Smit
- Institute for Systems Biology, Seattle, Washington
| | | | - Federico G Hoffmann
- Department of Biochemistry, Molecular Biology, Entomology and Plant Pathology, Mississippi State University Institute for Genomics, Biocomputing and Biotechnology, Mississippi State University
| | - Jürgen Brosius
- Institute of Experimental Pathology (ZMBE), University of Münster, Germany
| | - Richard E Green
- Department of Biomolecular Engineering, University of California
| | - Edward L Braun
- Department of Biology and Genetics Institute, University of Florida
| | - David A Ray
- Department of Biochemistry, Molecular Biology, Entomology and Plant Pathology, Mississippi State University Institute for Genomics, Biocomputing and Biotechnology, Mississippi State University Department of Biological Sciences, Texas Tech University
| | - Jürgen Schmitz
- Institute of Experimental Pathology (ZMBE), University of Münster, Germany
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Nam K, Ellegren H. Recombination drives vertebrate genome contraction. PLoS Genet 2012; 8:e1002680. [PMID: 22570634 PMCID: PMC3342960 DOI: 10.1371/journal.pgen.1002680] [Citation(s) in RCA: 54] [Impact Index Per Article: 4.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/21/2011] [Accepted: 03/15/2012] [Indexed: 11/19/2022] Open
Abstract
Selective and/or neutral processes may govern variation in DNA content and, ultimately, genome size. The observation in several organisms of a negative correlation between recombination rate and intron size could be compatible with a neutral model in which recombination is mutagenic for length changes. We used whole-genome data on small insertions and deletions within transposable elements from chicken and zebra finch to demonstrate clear links between recombination rate and a number of attributes of reduced DNA content. Recombination rate was negatively correlated with the length of introns, transposable elements, and intergenic spacer and with the rate of short insertions. Importantly, it was positively correlated with gene density, the rate of short deletions, the deletion bias, and the net change in sequence length. All these observations point at a pattern of more condensed genome structure in regions of high recombination. Based on the observed rates of small insertions and deletions and assuming that these rates are representative for the whole genome, we estimate that the genome of the most recent common ancestor of birds and lizards has lost nearly 20% of its DNA content up until the present. Expansion of transposable elements can counteract the effect of deletions in an equilibrium mutation model; however, since the activity of transposable elements has been low in the avian lineage, the deletion bias is likely to have had a significant effect on genome size evolution in dinosaurs and birds, contributing to the maintenance of a small genome. We also demonstrate that most of the observed correlations between recombination rate and genome contraction parameters are seen in the human genome, including for segregating indel polymorphisms. Our data are compatible with a neutral model in which recombination drives vertebrate genome size evolution and gives no direct support for a role of natural selection in this process. One major implication from genetic work done several decades ago is that the genome contains a lot of sequences that do not constitute genes or other functional elements. The total amount of DNA—the genome size—is thus not necessarily an indicator of DNA complexity or organismal complexity, an observation often referred to as the C-value paradox (C-value being a measure of DNA content). What then is it that determines genome size? One model posits that the evolution of genome size is not a consequence of natural selection but is instead governed by the incidence and character of naturally occurring mutations that affect the length of DNA, a process that is not affected by selection. Here we present the results of an analysis of how recombination affects the size of avian and human genomes. We find strong evidence that the rate of recombination is a driving force of genome size evolution. In regions of the genome where recombination occurs frequently, the loss of DNA caused by small deletions is particularly pronounced. Our simulations show that the effect of such recombination-driven genome contraction can be profound over evolutionary time scales. These observations lead to a model in which recombination is mutagenic for length changes and that the incidence of deletions increases with increasing recombination rate. Although we cannot formally exclude that natural selection contributes to the observed relationship between recombination and genome contraction, we find no evidence to support such a scenario.
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Affiliation(s)
| | - Hans Ellegren
- Department of Evolutionary Biology, Evolutionary Biology Centre, Uppsala University, Uppsala, Sweden
- * E-mail:
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Fabrick JA, Mathew LG, Tabashnik BE, Li X. Insertion of an intact CR1 retrotransposon in a cadherin gene linked with Bt resistance in the pink bollworm, Pectinophora gossypiella. INSECT MOLECULAR BIOLOGY 2011; 20:651-665. [PMID: 21815956 DOI: 10.1111/j.1365-2583.2011.01095.x] [Citation(s) in RCA: 19] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/29/2023]
Abstract
Three mutations in the Pectinophora gossypiella cadherin gene PgCad1 are linked with resistance to Bacillus thuringiensis (Bt) toxin Cry1Ac. Here we show that the r3 mutation entails recent insertion into PgCad1 of an active chicken repeat (CR1) retrotransposon, designated CR1-1_Pg. Unlike most other CR1 elements, CR1-1_Pg is intact, transcribed by a flanking promoter, contains target site duplications and has a relatively low number of copies. Examination of transcripts from the PgCad1 locus revealed that CR1-1_Pg disrupts both the cadherin protein and a long noncoding RNA of unknown function. Together with previously reported data, these findings show that transposable elements disrupt eight of 12 cadherin alleles linked with resistance to Cry1Ac in three lepidopteran species, indicating that the cadherin locus is a common target for disruption by transposable elements.
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Affiliation(s)
- Jeffrey A Fabrick
- USDA, ARS, US Arid Land Agricultural Research Center, Maricopa, AZ 85138, USA.
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