Abstract
In Drosophila, the non-LTR retrotransposons HeT-A, TART and TAHRE build a head-to-tail array of repetitions that constitute the telomere domain by targeted transposition at the end of the chromosome whenever needed. As a consequence, Drosophila telomeres have the peculiarity to harbor the genes in charge of telomere elongation. Understanding telomere expression is important in Drosophila since telomere homeostasis depends in part on the expression of this genomic compartment. We have recently shown that the essential kinase JIL-1 is the first positive regulator of the telomere retrotransposons. JIL-1 mediates chromatin changes at the promoter of the HeT-A retrotransposon that are necessary to obtain wild type levels of expression of these telomere transposons. With the present study, we show how JIL-1 is also needed for the expression of a reporter gene embedded in the telomere domain. Our analysis, using different reporter lines from the telomere and subtelomere domains of different chromosomes, indicates that JIL-1 likely acts protecting the telomere domain from the spreading of repressive chromatin from the adjacent subtelomere domain. Moreover, the analysis of the 4R telomere suggests a slightly different chromatin structure at this telomere. In summary, our results strongly suggest that the action of JIL-1 depends on which telomere domain, which chromosome and which promoter is embedded in the telomere chromatin.
Highlights
Drosophila telomeres are the best-studied telomerase exception to date
We report that JIL-1 protects the telomere domain from the spreading of repressive chromatin from the flanking subtelomere domain and that JIL-1 action depends on which telomere domain, which chromosome and which promoter is embedded in the telomere chromatin
In order to assess the possible role of JIL-1 regulating gene expression at the HTT array, we chose several lines that contain a mini-white reporter gene at the telomere domain (HTT array), or at the subtelomere domain (TAS sequences) from different chromosomes [6,17,18]
Summary
The transposition of three special non-LTR retrotransposons; HeT-A, TART and TAHRE (HTT), buffers the receding chromosome ends when needed [1,2]. In Drosophila the genes responsible for telomere elongation are embedded in the telomere chromatin and to understand telomere regulation in this organism it is necessary to understand gene expression from this genomic compartment. Drosophila telomeres are organized in two different domains; the cap domain protecting the very end of the chromosome, and the telomere domain composed of the HTT array. Immediately adjacent to the HTT array exists the subtelomere domain, composed of the Telomere Associated Sequences (TAS) [3,4,5]. The subtelomere domain is not strictly part of the telomere, its closeness to the HTT array influences some of its functions
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