An insulator blocks access to enhancers by an illegitimate promoter, preventing repression by transcriptional interference

Autoři: Miki Fujioka aff001;  Anastasiya Nezdyur aff001;  James B. Jaynes aff001
Působiště autorů: Thomas Jefferson University, Philadelphia, Pennsylvania, United States of America aff001
Vyšlo v časopise: An insulator blocks access to enhancers by an illegitimate promoter, preventing repression by transcriptional interference. PLoS Genet 17(4): e1009536. doi:10.1371/journal.pgen.1009536
Kategorie: Research Article


Several distinct activities and functions have been described for chromatin insulators, which separate genes along chromosomes into functional units. Here, we describe a novel mechanism of functional separation whereby an insulator prevents gene repression. When the homie insulator is deleted from the end of a Drosophila even skipped (eve) locus, a flanking P-element promoter is activated in a partial eve pattern, causing expression driven by enhancers in the 3’ region to be repressed. The mechanism involves transcriptional read-through from the flanking promoter. This conclusion is based on the following. Read-through driven by a heterologous enhancer is sufficient to repress, even when homie is in place. Furthermore, when the flanking promoter is turned around, repression is minimal. Transcriptional read-through that does not produce anti-sense RNA can still repress expression, ruling out RNAi as the mechanism in this case. Thus, transcriptional interference, caused by enhancer capture and read-through when the insulator is removed, represses eve promoter-driven expression. We also show that enhancer-promoter specificity and processivity of transcription can have decisive effects on the consequences of insulator removal. First, a core heat shock 70 promoter that is not activated well by eve enhancers did not cause read-through sufficient to repress the eve promoter. Second, these transcripts are less processive than those initiated at the P-promoter, measured by how far they extend through the eve locus, and so are less disruptive. These results highlight the importance of considering transcriptional read-through when assessing the effects of insulators on gene expression.

Klíčová slova:

DNA transcription – Gene expression – Genetic interference – Genetic loci – In situ hybridization – Insulators – Non-coding RNA – Embryonic pattern formation


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