Ectopic assembly of heterochromatin in Drosophila melanogaster triggered by transposable elements.
A persistent question in biology is how cis-acting sequence elements influence trans-acting factors and the local chromatin environment to modulate gene expression. We reported previously that the DNA transposon 1360 can enhance silencing of a reporter in a heterochromatic domain of Drosophila melanogaster. We have now generated a collection of variegating phiC31 landing-pad insertion lines containing 1360 and a heat-shock protein 70 (hsp70)-driven white reporter to explore the mechanism of 1360-sensitive silencing. Many 1360-sensitive sites were identified, some in apparently euchromatic domains, although all are close to heterochromatic masses. One such site (line 1198; insertion near the base of chromosome arm 2L) has been investigated in detail. ChIP analysis shows 1360-dependent Heterochromatin Protein 1a (HP1a) accumulation at this otherwise euchromatic site. The phiC31 landing pad system allows different 1360 constructs to be swapped with the full-length element at the same genomic site to identify the sequences that mediate 1360-sensitive silencing. Short deletions over sites with homology to PIWI-interacting RNAs (piRNAs) are sufficient to compromise 1360-sensitive silencing. Similar results were obtained on replacing 1360 with Invader4 (a retrotransposon), suggesting that this phenomenon likely applies to a broader set of transposable elements. Our results suggest a model in which piRNA sequence elements behave as cis-acting targets for heterochromatin assembly, likely in the early embryo, where piRNA pathway components are abundant, with the heterochromatic state subsequently propagated by chromatin modifiers present in somatic tissue.
Department of Biology, Washington University, St. Louis, MO 63130, USA.
Monica F
MF
Sentmanat
Sarah C R
SC
Elgin
D000818:Animals; D004251:DNA Transposable Elements / Q000235:genetics*; D004331:Drosophila melanogaster / Q000235:genetics*; D044127:Epigenesis, Genetic / Q000235:genetics*; D005260:Female; D020868:Gene Silencing; D017344:Genes, Insect / Q000235:genetics; D017930:Genes, Reporter; D005816:Genetic Complementation Test; D006570:Heterochromatin / Q000235:genetics*; D008297:Male; D020411:Oligonucleotide Array Sequence Analysis; D016372:RNA, Antisense / Q000235:genetics; D034741:RNA, Small Interfering / Q000235:genetics; D024363:Transcription Initiation Site
D004251:DNA Transposable Elements; D006570:Heterochromatin; D016372:RNA, Antisense; D034741:RNA, Small Interfering