Widespread evidence for horizontal transfer of transposable elements across Drosophila genomes

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We have extracted and compared the nucleotide sequences of all potentially functional autonomous TEs present in the genomes of Drosophila melanogaster, D. simulans and D. yakuba - 1,436 insertions classified into 141 distinct families - and show that a large fraction of the families found in two or more species display levels of genetic divergence and within-species diversity that are significantly lower than expected by assuming copy-number equilibrium and vertical transmission, and consistent with a recent origin by HT. Long terminal repeat (LTR) retrotransposons form nearly 90% of the HT cases detected. HT footprints are also frequent among DNA transposons (40% of families compared) but rare among non-LTR retroelements (6%). Our results suggest a genomic rate of 0.04 HT events per family per million years between the three species studied, as well as significant variation between major classes of elements.The genome-wide patterns of sequence diversity of the active autonomous TEs in the genomes of D. melanogaster, D. simulans and D. yakuba suggest that one-third of the TE families originated by recent HT between these species. This result emphasizes the important role of horizontal transmission in the natural history of Drosophila TEs.Transposable elements (TEs) are short DNA sequences (usually <15 kb) that behave as intragenomic parasites, vertically transmitted through generations [1]. According to their molecular structure and life cycle, they are classified into DNA transposons (type 1) and retrotransposons (RTs; type 2), reflecting the absence or presence, respectively, of an RNA intermediate in the transposition process. The latter are further divided into two major classes according to whether or not they are flanked by long terminal repeats (LTRs): LTR RTs and non-LTR RTs [2-4]. TEs have been linked to fundamental genomic features [5] such as size [6-8], chromosome structure [9,10] and chromatin organization [11], and their abundance is determined by an e

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Animals Drosophila DNA Transposable Elements Base Sequence Terminal Repeat Sequences Genes, Insect Gene Transfer, Horizontal Genome Genetic Variation