Journal Article

Pervasive Horizontal Transfer of Rolling-Circle Transposons among Animals

Jainy Thomas, Sarah Schaack and Ellen J. Pritham

in Genome Biology and Evolution

Published on behalf of Society for Molecular Biology and Evolution

Volume 2, issue , pages 656-664
Published in print January 2010 |
Published online August 2010 | e-ISSN: 1759-6653 | DOI:

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  • Bioinformatics and Computational Biology
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Horizontal transfer (HT) of genes is known to be an important mechanism of genetic innovation, especially in prokaryotes. The impact of HT of transposable elements (TEs), however, has only recently begun to receive widespread attention and may be significant due to their mutagenic potential, inherent mobility, and abundance. Helitrons, also known as rolling-circle transposons, are a distinctive subclass of TE with a unique transposition mechanism. Here, we describe the first evidence for the repeated HT of four different families of Helitrons in an unprecedented array of organisms, including mammals, reptiles, fish, invertebrates, and insect viruses. The Helitrons present in these species have a patchy distribution and are closely related (80–98% sequence identity), despite the deep divergence times among hosts. Multiple lines of evidence indicate the extreme conservation of sequence identity is not due to selection, including the highly fragmented nature of the Helitrons identified and the lack of any signatures of selection at the nucleotide level. The presence of horizontally transferred Helitrons in insect viruses, in particular, suggests that this may represent a potential mechanism of transfer in some taxa. Unlike genes, Helitrons that have horizontally transferred into new host genomes can amplify, in some cases reaching up to several hundred copies and representing a substantial fraction of the genome. Because Helitrons are known to frequently capture and amplify gene fragments, HT of this unique group of DNA transposons could lead to horizontal gene transfer and incur dramatic shifts in the trajectory of genome evolution.

Keywords: Helitrons; insect viruses; transposable elements; lateral transfer

Journal Article.  5260 words.  Illustrated.

Subjects: Bioinformatics and Computational Biology ; Evolutionary Biology ; Genetics and Genomics

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