HeT-A_pi1, a piRNA Target Sequence in the Drosophila Telomeric Retrotransposon HeT-A, Is Extremely Conserved across Copies and Species

Abstract

The maintenance of the telomeres in Drosophila species depends on the transposition of the non-LTR retrotransposons HeT-A, TAHRE and TART. HeT-A and TART elements have been found in all studied species of Drosophila suggesting that their function has been maintained for more than 60 million years. Of the three elements, HeT-A is by far the main component of D. melanogaster telomeres and, unexpectedly for an element with an essential role in telomere elongation, the conservation of the nucleotide sequence of HeT-A is very low. In order to better understand the function of this telomeric retrotransposon, we studied the degree of conservation along HeT-A copies. We identified a small sequence within the 3′ UTR of the element that is extremely conserved among copies of the element both, within D. melanogaster and related species from the melanogaster group. The sequence corresponds to a piRNA target in D. melanogaster that we named HeT-A_pi1. Comparison with piRNA target sequences from other Drosophila retrotransposons showed that HeT-A_pi1 is the piRNA target in the Drosophila genome with the highest degree of conservation among species from the melanogaster group. The high conservation of this piRNA target in contrast with the surrounding sequence, suggests an important function of the HeT-A_pi1 sequence in the co-evolution of the HeT-A retrotransposon and the Drosophila genome.

Transposable elements inDrosophila

“… 121-123 Observations of telomeric retrotransposon regulation in the germline indicate that regulation of these elements is significant to development as sequences targeted by piRNAs in the HeT-A 3′ UTR are highly conserved in D. melanogaster and closely related species. 122 …”

Regulatory RNAs in the light of Drosophila genomics

“…Interestingly, piRNAs are likely to regulate Drosophila telomeric chromatin, which is mostly composed of retrotransposons (reviewed in [72]). In agreement with these observations, specific piRNA targets in the Drosophila telomeric retrotransposon HeT-A have been identified [73]. These targets are conserved in other Drosophila species [73].…”

“…In agreement with these observations, specific piRNA targets in the Drosophila telomeric retrotransposon HeT-A have been identified [73]. These targets are conserved in other Drosophila species [73]. Other instances of piRNA-mediated chromatin regulation involving TEs are still unknown.…”

Specific Localization of the Drosophila Telomere Transposon Proteins and RNAs, Give Insight in Their Behavior, Control and Telomere Biology in This Organism

“…Nevertheless, we have been using the ovary to detect changes in HeT-A and TART expression through quantitative RT-PCR [21], [22]. …”

“…The telomere retrotransposons are expressed at low levels and previous studies have shown that HeT-A and TART sense RNAs are not detected by in situ hybridization in the germ line tissues of the Drosophila ovary in wild type conditions [ 19 ], [ 20 ]. Nevertheless, we have been using the ovary to detect changes in HeT-A and TART expression through quantitative RT-PCR [ 21 ], [ 22 ].…”