MBE Advance Access published online on November 13, 2007
Molecular Biology and Evolution, doi:10.1093/molbev/msm250
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Research Article |
Rapid R2 retrotransposition leads to the loss of previously inserted copies via large deletions of the rDNA locus
Department of Biology, University of Rochester, Rochester, New York 14627
Corresponding author: Thomas H. Eickbush, Department of Biology, University of Rochester, Rochester, NY 14627-0211. Email: eick{at}mail.rochester.edu
Received for publication September 19, 2007. Revision received November 7, 2007. Accepted for publication November 8, 2007.
R2 non-LTR retrotransposable elements insert specifically into the 28S rRNA genes of a wide range of animals. These elements maintain long-term stable relationships with the host genome. By scoring the variation present at the 5' ends of individual R2 copies, lines of Drosophila simulans have been identified with high rates of R2 retrotransposition. Comparing the R2 elements present in the parents with that of their progeny after one or 30 generations in this report revealed that retrotransposition rates were higher through the female germ line compared to the male germ line. In addition, most events in females occurring late in germ line development. Surprisingly, the gain of new R2 insertions by retrotranspositions was counter-balanced by deletions of pre-existing R2 insertions. These deletions occurred by the loss of large segments of the rDNA units that contained on average an estimated 15 R2 elements. When monitored over single generations the rate of loss of pre-existing elements was higher than the rate of new insertions. However, the chromosomes with the largest deletions appear to be eliminated from the population because the rates of R2 insertions and deletions after 30 generations were approximately equal. These findings suggest high rates of R2 retrotransposition does not necessarily lead to dramatic increases in the level of R2 insertions in the rDNA locus, but can lead to a more rapid turnover of rDNA units.
Key Words: Retrotransposable element • rates of retrotransposition • D. simulans • the rDNA locus
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