Journal
JOURNAL OF MOLECULAR BIOLOGY
Volume 429, Issue 21, Pages 3280-3289Publisher
ACADEMIC PRESS LTD- ELSEVIER SCIENCE LTD
DOI: 10.1016/j.jmb.2016.12.002
Keywords
telomere; divergent transcription; piRNA cluster; chromatin; Rhino
Categories
Funding
- Russian Science Foundation [16-14-10167]
- Russian Foundation for Basic Researches [16-54-150003, 16-34-60176 mol_a_dk]
- Russian Science Foundation [16-14-10167] Funding Source: Russian Science Foundation
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PIWI-interacting RNAs (piRNAs) provide the silencing of transposable elements in the germline. Drosophila telomeres are maintained by transpositions of specialized telomeric retroelements. piRNAs generated from sense and antisense transcripts of telomeric elements provide telomere length control in the germline. Previously, we have found that antisense transcription of the major telomeric retroelement HeT-A is initiated upstream of the HeT-A sense transcription start site. Here, we performed a deletion analysis of the HeT-A promoter and show that common regulatory elements are shared by sense and antisense promoters of HeT-A. Therefore, the HeT-A promoter is a bidirectional promoter capable of processive sense and antisense transcription. Ovarian small RNA data show that a solo HeT-A promoter within an euchromatic transgene initiates the divergent transcription of transgenic reporter genes and subsequent processing of these transcripts into piRNAs. These events lead to the formation of a divergent unistrand piRNA cluster at solo HeT-A promoters, in contrast to endogenous telomeres that represent strong dual-strand piRNA clusters. Solo HeT-A promoters are not immunoprecipitated with heterochromatin protein 1 (HP1) homolog Rhino, a marker of the dual-strand piRNA clusters, but are associated with HP1 itself, which provides piRNA-mediated transcriptional repression of the reporter genes. Unlike endogenous dual-strand piRNA clusters, the solo HeT-A promoter does not produce overlapping transcripts. In a telomeric context, however, bidirectional promoters of tandem HeT-A repeats provide a read-through transcription of both genomic strands, followed by Rhi binding. These data indicate that Drosophila telomeres share properties of unistrand and dual-strand piRNA clusters. (C) 2016 Elsevier Ltd. All rights reserved.
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