Dataset Information

The evolutionary dynamics of the Helena retrotransposon revealed by sequenced Drosophila genomes.

ABSTRACT: BACKGROUND: Several studies have shown that genomes contain a mixture of transposable elements, some of which are still active and others ancient relics that have degenerated. This is true for the non-LTR retrotransposon Helena, of which only degenerate sequences have been shown to be present in some species (Drosophila melanogaster), whereas putatively active sequences are present in others (D. simulans). Combining experimental and population analyses with the sequence analysis of the 12 Drosophila genomes, we have investigated the evolution of Helena, and propose a possible scenario for the evolution of this element. RESULTS: We show that six species of Drosophila have the Helena transposable element at different stages of its evolution. The copy number is highly variable among these species, but most of them are truncated at the 5' ends and also harbor several internal deletions and insertions suggesting that they are inactive in all species, except in D. mojavensis in which quantitative RT-PCR experiments have identified a putative active copy. CONCLUSION: Our data suggest that Helena was present in the common ancestor of the Drosophila genus, which has been vertically transmitted to the derived lineages, but that it has been lost in some of them. The wide variation in copy number and sequence degeneration in the different species suggest that the evolutionary dynamics of Helena depends on the genomic environment of the host species.

SUBMITTER: Granzotto A

PROVIDER: S-EPMC3087515 | biostudies-literature | 2009

REPOSITORIES: biostudies-literature

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The evolutionary dynamics of the Helena retrotransposon revealed by sequenced Drosophila genomes.

Granzotto Adriana A Lopes Fabrício R FR Lerat Emmanuelle E Vieira Cristina C Carareto Claudia M A CM

BMC evolutionary biology 20090722

<h4>Background</h4>Several studies have shown that genomes contain a mixture of transposable elements, some of which are still active and others ancient relics that have degenerated. This is true for the non-LTR retrotransposon Helena, of which only degenerate sequences have been shown to be present in some species (Drosophila melanogaster), whereas putatively active sequences are present in others (D. simulans). Combining experimental and population analyses with the sequence analysis of the 12 ...[more]

PMID: 19624823

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Project description:BackgroundHarnessing vast amounts of genomic data in phylogenetic context stemming from massive sequencing of multiple closely related genomes requires new tools and approaches. We present a tool for the genome-wide analysis of frequencies and patterns of amino acid substitutions in multiple alignments of genes' coding regions, and a database of amino acid substitutions in the phylogeny of 12 Drosophila genomes. We illustrate the use of these resources to address three types of evolutionary genomics questions: about fluxes in amino acid composition in proteins, about asymmetries in amino acid substitutions and about patterns of molecular evolution in duplicated genes.ResultsWe demonstrate that amino acid composition of Drosophila proteins underwent a significant shift over the last 70 million years encompassed by the studied phylogeny, with less common amino acids (Cys, Met, His) increasing in frequency and more common ones (Ala, Leu, Glu) becoming less frequent. These fluxes are strongly correlated with polarity of source and destination amino acids, resulting in overall systematic decrease of mean polarity of amino acids found in Drosophila proteins. Frequency and radicality of amino acid substitutions are higher in paralogs than in orthologous single-copy genes and are higher in gene families with paralogs than in gene families without surviving duplications. Rate and radicality of substitutions, as expected, are negatively correlated with overall level and uniformity of gene expression. However, these correlations are not observed for substitutions occurring in duplicated genes, indicating a different selective constraint on the evolution of paralogous sequences. Clades resulting from duplications show a marked asymmetry in rate and radicality of amino acid substitutions, possibly a signal of widespread neofunctionalization. These patterns differ among protein families of different functionality, with genes coding for RNA-binding proteins differing from most other functional groups in terms of amino acid substitution patterns in duplicated and single-copy genes.ConclusionsWe demonstrate that deep phylogenetic analysis of amino acid substitutions can reveal interesting genome-wide patterns. Amino acid composition of drosophilid proteins is shaped by fluxes similar to those previously observed in prokaryotic, yeast and mammalian genomes, indicating globally present patterns. Increased frequency and radicality of amino acid substitutions in duplicated genes and the presence of asymmetry of these parameters between paralogous clades indicate widespread neofunctionalization among paralogs as the mechanism of duplication retention.

Project description:BACKGROUND AND AIMS: The genus Fritillaria (Liliaceae) comprises species with extremely large genomes (1C = 30 000-127 000 Mb) and a bicontinental distribution. Most North American species (subgenus Liliorhiza) differ from Eurasian Fritillaria species by their distinct phylogenetic position and increased amounts of heterochromatin. This study examined the contribution of major repetitive elements to the genome obesity found in Fritillaria and identified repeats contributing to the heterochromatin arrays in Liliorhiza species. METHODS: Two Fritillaria species of similar genome size were selected for detailed analysis, one from each phylogeographical clade: F. affinis (1C = 45·6 pg, North America) and F. imperialis (1C = 43·0 pg, Eurasia). Fosmid libraries were constructed from their genomic DNAs and used for identification, sequence characterization, quantification and chromosome localization of clones containing highly repeated sequences. KEY RESULTS AND CONCLUSIONS: Repeats corresponding to 6·7 and 4·7 % of the F. affinis and F. imperialis genome, respectively, were identified. Chromoviruses and the Tat lineage of Ty3/gypsy group long terminal repeat retrotransposons were identified as the predominant components of the highly repeated fractions in the F. affinis and F. imperialis genomes, respectively. In addition, a heterogeneous, extremely AT-rich satellite repeat was isolated from F. affinis. The FriSAT1 repeat localized in heterochromatic bands makes up approx. 26 % of the F. affinis genome and substantial genomic fractions in several other Liliorhiza species. However, no evidence of a relationship between heterochromatin content and genome size variation was observed. Also, this study was unable to reveal any predominant repeats which tracked the increasing/decreasing trends of genome size evolution in Fritillaria. Instead, the giant Fritillaria genomes seem to be composed of many diversified families of transposable elements. We hypothesize that the genome obesity may be partly determined by the failure of removal mechanisms to counterbalance effectively the retrotransposon amplification.

Dataset Information

The evolutionary dynamics of the Helena retrotransposon revealed by sequenced Drosophila genomes.

Publications

The evolutionary dynamics of the Helena retrotransposon revealed by sequenced Drosophila genomes.

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