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Extensive, recent intron gains in Daphnia populations.

ABSTRACT: Rates and mechanisms of intron gain and loss have traditionally been inferred from alignments of highly conserved genes sampled from phylogenetically distant taxa. We report a population-genomic approach that detected 24 discordant intron/exon boundaries between the whole-genome sequences of two Daphnia pulex isolates. Sequencing of presence/absence loci across a collection of D. pulex isolates and outgroup Daphnia species shows that most polymorphisms are a consequence of recent gains, with parallel gains often occurring at the same locations in independent allelic lineages. More than half of the recent gains are associated with short sequence repeats, suggesting an origin via repair of staggered double-strand breaks. By comparing the allele-frequency spectrum of intron-gain alleles with that for derived single-base substitutions, we also provide evidence that newly arisen introns are intrinsically deleterious and tend to accumulate in population-genetic settings where random genetic drift is a relatively strong force.

SUBMITTER: Li W

PROVIDER: S-EPMC3878872 | biostudies-literature | 2009 Nov

REPOSITORIES: biostudies-literature

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Extensive, recent intron gains in Daphnia populations.

Li Wenli W Tucker Abraham E AE Sung Way W Thomas W Kelley WK Lynch Michael M

Science (New York, N.Y.) 20091101 5957

Rates and mechanisms of intron gain and loss have traditionally been inferred from alignments of highly conserved genes sampled from phylogenetically distant taxa. We report a population-genomic approach that detected 24 discordant intron/exon boundaries between the whole-genome sequences of two Daphnia pulex isolates. Sequencing of presence/absence loci across a collection of D. pulex isolates and outgroup Daphnia species shows that most polymorphisms are a consequence of recent gains, with par ...[more]

PMID: 19965475

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Project description:BackgroundGenome-wide studies of intron dynamics in mammalian orthologous genes have found convincing evidence for loss of introns but very little for intron turnover. Similarly, large-scale analysis of intron dynamics in a few vertebrate genomes has identified only intron losses and no gains, indicating that intron gain is an extremely rare event in vertebrate evolution. These studies suggest that the intron-rich genomes of vertebrates do not allow intron gain. The aim of this study was to search for evidence of de novo intron gain in domesticated genes from an analysis of their exon/intron structures.ResultsA phylogenomic approach has been used to analyse all domesticated genes in mammals and chordates that originated from the coding parts of transposable elements. Gain of introns in domesticated genes has been reconstructed on well established mammalian, vertebrate and chordate phylogenies, and examined as to where and when the gain events occurred. The locations, sizes and amounts of de novo introns gained in the domesticated genes during the evolution of mammals and chordates has been analyzed. A significant amount of intron gain was found only in domesticated genes of placental mammals, where more than 70 cases were identified. De novo gained introns show clear positional bias, since they are distributed mainly in 5' UTR and coding regions, while 3' UTR introns are very rare. In the coding regions of some domesticated genes up to 8 de novo gained introns have been found. Intron densities in Eutheria-specific domesticated genes and in older domesticated genes that originated early in vertebrates are lower than those for normal mammalian and vertebrate genes. Surprisingly, the majority of intron gains have occurred in the ancestor of placentals.ConclusionsThis study provides the first evidence for numerous intron gains in the ancestor of placental mammals and demonstrates that adequate taxon sampling is crucial for reconstructing intron evolution. The findings of this comprehensive study slightly challenge the current view on the evolutionary stasis in intron dynamics during the last 100 - 200 My. Domesticated genes could constitute an excellent system on which to analyse the mechanisms of intron gain in placental mammals.

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Extensive, recent intron gains in Daphnia populations.

Publications

Extensive, recent intron gains in Daphnia populations.

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