small RNA from D. melanogaster female gonads

Telomeric Associated Sequences, TAS-R and TAS-L, form the major subtelomeric repeats families identified in Drosophila melanogaster. They are PIWI-interacting RNA (piRNA) clusters involved in repression of Transposable Elements. In this study, we have revisited their structural and functional dynamics in D. melanogaster and its related species. In silico analysis revealed that TAS-R family members, including X-TAS, are composed of domains organized in a telomere-specific order and that TAS-L repeats are composed of arrays of a region called TLL found in X-TAS. Our analyses strongly imply that TLL could represent an ancestral subtelomeric piRNA core-cluster conserved in the melanogaster subgroup. Furthermore, all D. melanogaster genomes tested possessed at least one of the TAS-R loci, whereas TAS-L can be absent. A screen of 110 D. melanogaster lines showed that X-TAS is always present in flies living in the wild, but often absent in long-term laboratory stocks and that natural populations frequently lose their X-TAS within the first two years upon lab conditioning. Finally, we discuss the unexpected temporal and structural dynamics of subtelomeric piRNA clusters whose stability within genomes could be subjected to environmental selection questioning how the genomes of domesticated flies have been shaped and varied from wild populations.