<em>Bari1</em> Transposon Arrays in <em>Drosophila melanogaster</em> Display High Stability over Time and Limited Impact on Ectopic Heterochromatin Assembly

Transposable elements (TEs) impact genes and genomes in different ways. In Drosophila, TEs play a critical role in establishing heterochromatic loci, such as centromeric and pericentromeric regions, and contribute to ectopic heterochromatin formation especially when found in a tandem repeat configuration. The Bari transposon family belongs to the Tc1/mariner superfamily. Bari1 is featured by a unique tandem repeat arrangement in the heterochromatin of D. melanogaster. Despite its conservation could suggest a structural role in both natural and laboratory populations, little is known about the role of the Bari1 repeat in the heterochromatin. In this paper, we have studied the impact of the Bari1 transposon clusters on chromatin. We obtained transgenic strains of D. melanogaster carrying arrays of either three or seven copies of the Bari1 transposon in a typical heterochromatic tandem repeat configuration. We performed qualitative and quantitative phenotypic assays to evaluate the impact of these arrays on the chromatin status. Besides, we performed Southern Blot Hybridization analyses to evaluate the stability of Bari1 repeats over multiple generations. Our results suggest that Bari1 arrays are very stable over time and can poorly act as heterochromatin seeding sites. Our findings expand the knowledge on the structural and functional impact of TEs, whose potentially neutral, beneficial, or detrimental effect cannot be envisioned without experimental validation.