LINE-1 amplification accompanies explosive genome repatterning in rodents.

Transposable elements (TEs) sometimes induce karyotypic changes following recombination, breakage and rearrangement. We used FISH and Southern blot analyses to investigate the amount and distribution of LINE-1 retrotransposons in rodents (genus Taterillus, Muridae, Gerbillinae) that have recently undergone an important genome repatterning. Our results were interpreted in a known phylogenetic framework and clearly showed that LINE-1 elements were greatly amplified and non-randomly distributed in the most rearranged karyotypes. A comparison between FISH and conventional banding patterns provided evidence that LINE-1 insertion sites and chromosome breakpoints were not strongly correlated, thus suggesting that LINE-1 amplification subsequently accompanied Taterillus chromosome evolution. Similar patterns are observed in some cases of genomic stresses (hybrid genomes, cancer and DNA-damaged cells) and usually associated with DNA hypomethylation. We propose that intensively repatterned genomes face transient stress phases during which some epigenetic features, such as DNA methylation, are relaxed, thus allowing TE amplification.