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Analysis of transposon interruptions suggests selection for L1 elements on the X chromosome.

ABSTRACT: It has been hypothesised that the massive accumulation of L1 transposable elements on the X chromosome is due to their function in X inactivation, and that the accumulation of Alu elements near genes is adaptive. We tested the possible selective advantage of these two transposable element (TE) families with a novel method, interruption analysis. In mammalian genomes, a large number of TEs interrupt other TEs due to the high overall abundance and age of repeats, and these interruptions can be used to test whether TEs are selectively neutral. Interruptions of TEs, which are beneficial for the host, are expected to be deleterious and underrepresented compared with neutral ones. We found that L1 elements in the regions of the X chromosome that contain the majority of the inactivated genes are significantly less frequently interrupted than on the autosomes, while L1s near genes that escape inactivation are interrupted with higher frequency, supporting the hypothesis that L1s on the X chromosome play a role in its inactivation. In addition, we show that TEs are less frequently interrupted in introns than in intergenic regions, probably due to selection against the expansion of introns, but the insertion pattern of Alus is comparable to other repeats.

SUBMITTER: Abrusan G

PROVIDER: S-EPMC2517846 | biostudies-literature | 2008 Aug

REPOSITORIES: biostudies-literature

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Analysis of transposon interruptions suggests selection for L1 elements on the X chromosome.

Abrusán György G Giordano Joti J Warburton Peter E PE

PLoS genetics 20080829 8

It has been hypothesised that the massive accumulation of L1 transposable elements on the X chromosome is due to their function in X inactivation, and that the accumulation of Alu elements near genes is adaptive. We tested the possible selective advantage of these two transposable element (TE) families with a novel method, interruption analysis. In mammalian genomes, a large number of TEs interrupt other TEs due to the high overall abundance and age of repeats, and these interruptions can be use ...[more]

PMID: 18769724

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Project description:BACKGROUND: Sclerotinia sclerotiorum is a necrotrophic fungus that is pathogenic to many plants. Genomic analysis of its revealed transposable element expansion that has strongly influenced the evolutionary trajectory of several species. Transposons from the Tc1-Mariner superfamily are thought to be ubiquitous components of fungal genomes and are generally found in low copy numbers with large numbers of deleterious mutations in their transposase coding sequence. RESULTS: This study shows that the genome of S. sclerotiorum has a large number of copies of Tc1-Mariner transposons, and in silico analysis shows evidence that they were recently active. This finding was confirmed by expressed sequence tag (EST) analysis. Fourteen new Tc1-Mariner transposon families that were distributed throughout the genome were identified, and in some cases, due to the excision/retention of introns, different transcripts were observed for the same family, which might be the result of an efficient strategy to circumvent mutations that generate premature stop codons in the RNA sequence. In addition, the presence of these introns shows that the transposase protein has a flexible coding sequence and, consequently, conformation. No evidence for RIP-like gene silencing mechanisms, which are commonly found in fungi, was found in the identified Tc1-Mariner elements, and analysis of the genomic insertion sites of these elements showed that they were widely distributed throughout the genome with some copies located near the 3' regions of genes. In particular, EST analysis demonstrated that one of these copies was co-expressed with a gene, which showed the potential for these elements to undergo exaptation. CONCLUSIONS: Fourteen novel Tc1-Mariner families were characterized. Some families had evidence of introns, which might or might not be excised depending on the family or element in question, and this finding demonstrates a possible strategy for overcoming possible mutations that generate premature stop codons in a RNA sequence. Tc1-Mariner elements likely play an important role in the structure and evolution of the S. sclerotiorum genome.

Dataset Information

Analysis of transposon interruptions suggests selection for L1 elements on the X chromosome.

Publications

Analysis of transposon interruptions suggests selection for L1 elements on the X chromosome.

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