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


CONCLUSIONS
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.
Granzotto
Adriana
A
UNESP - São Paulo State University, Laboratory of Molecular Evolution, Department of Biology, 15054-000 São José do Rio Preto, São Paulo, Brazil. adrianag@ibilce.unesp.br
Lopes
Fabrício R
FR
Lerat
Emmanuelle
E
Vieira
Cristina
C
Carareto
Claudia M A
CM
D000818:Animals; D004330:Drosophila / Q000235:genetics*; D019143:Evolution, Molecular; D005828:Genetics, Population; D049750:Genome, Insect; D010802:Phylogeny; D018626:Retroelements; D017422:Sequence Analysis, DNA
D018626:Retroelements