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Control of inducible gene expression by signal-dependent transcriptional elongation.

ABSTRACT: Most inducible transcriptional programs consist of primary and secondary response genes (PRGs and SRGs) that differ in their kinetics of expression and in their requirements for new protein synthesis and chromatin remodeling. Here we show that many PRGs, in contrast to SRGs, have preassembled RNA polymerase II (Pol II) and positive histone modifications at their promoters in the basal state. Pol II at PRGs generates low levels of full-length unspliced transcripts but fails to make mature, protein-coding transcripts in the absence of stimulation. Induction of PRGs is controlled at the level of transcriptional elongation and mRNA processing, through the signal-dependent recruitment of P-TEFb. P-TEFb is in turn recruited by the bromodomain-containing protein Brd4, which detects H4K5/8/12Ac inducibly acquired at PRG promoters. Our findings suggest that the permissive structure of PRGs both stipulates their unique regulation in the basal state by corepressor complexes and enables their rapid induction in multiple cell types.

SUBMITTER: Hargreaves DC

PROVIDER: S-EPMC2828818 | biostudies-literature |

REPOSITORIES: biostudies-literature

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Project description:BACKGROUND: Random monoallelic expression contributes to phenotypic variation of cells and organisms. However, the epigenetic mechanisms by which individual alleles are randomly selected for expression are not known. Taking cues from chromatin signatures at imprinted gene loci such as the insulin-like growth factor 2 gene 2 (IGF2), we evaluated the contribution of CTCF, a zinc finger protein required for parent-of-origin-specific expression of the IGF2 gene, as well as a role for allele-specific association with DNA methylation, histone modification and RNA polymerase II. RESULTS: Using array-based chromatin immunoprecipitation, we identified 293 genomic loci that are associated with both CTCF and histone H3 trimethylated at lysine 9 (H3K9me3). A comparison of their genomic positions with those of previously published monoallelically expressed genes revealed no significant overlap between allele-specifically expressed genes and colocalized CTCF/H3K9me3. To analyze the contributions of CTCF and H3K9me3 to gene regulation in more detail, we focused on the monoallelically expressed IGF2BP1 gene. In vitro binding assays using the CTCF target motif at the IGF2BP1 gene, as well as allele-specific analysis of cytosine methylation and CTCF binding, revealed that CTCF does not regulate mono- or biallelic IGF2BP1 expression. Surprisingly, we found that RNA polymerase II is detected on both the maternal and paternal alleles in B lymphoblasts that express IGF2BP1 primarily from one allele. Thus, allele-specific control of RNA polymerase II elongation regulates the allelic bias of IGF2BP1 gene expression. CONCLUSIONS: Colocalization of CTCF and H3K9me3 does not represent a reliable chromatin signature indicative of monoallelic expression. Moreover, association of individual alleles with both active (H3K4me3) and silent (H3K27me3) chromatin modifications (allelic bivalent chromatin) or with RNA polymerase II also fails to identify monoallelically expressed gene loci. The selection of individual alleles for expression occurs in part during transcription elongation.

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Control of inducible gene expression by signal-dependent transcriptional elongation.

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