Molecular characterization of two natural hotspots in the Drosophila buzzatii genome induced by transposon insertions

Transposable elements (TEs) have been implicated in the generation of genet ic rearrangements, but their potential to mediate changes in the organizati on and architecture of host genomes could be even greater than previously t hought. Here, we describe the naturally occurring Structural and nucleotide variation around two TE insertions in the genome of Drosophila buzzatii. T he Studied regions correspond to the breakpoints of a widespread chromosoma l inversion generated by ectopic recombination between oppositely oriented copies of a TE named Galileo. A detailed molecular analysis by Southern hyb ridization, PCR amplification, and DNA sequencing of 7.1 kb surrounding the inversion breakpoints in 39 A buzzatii lines revealed an unprecedented deg ree of restructuring, consisting of 22 insertions of ten previously undescr ibed TEs, 13 deletions, I duplication, and I small inversion. All of these alterations Occurred exclusively in inverted chromosomes and appear to have accumulated after the insertion of the Galileo elements, within or close t o them. The nucleotide variation at the studied regions is six times lower in inverted than in noninverted chromosomes, suggesting that most of the ob served changes originated in only 84,000 years. Galileo elements thus seeme d to promote the transformation of these, otherwise normal, chromosomal reg ions in genetically unstable hotspots and highly efficient traps for transp oson insertions. The particular features of two new Galileo copies found in dicate that this TE belongs to the Foldback family. Together, our results s trengthen the importance of TEs, and especially DNA transposons, as inducer s of genome plasticity in evolution.