ABSTRACT
Genomic imprinting is regulated by parental-specific DNA methylation of imprinting control regions (ICRs). Despite an identical DNA sequence, ICRs can exist in two distinct epigenetic states that are memorized throughout unlimited cell divisions and reset during germline formation. Here, we systematically study the genetic and epigenetic determinants of this epigenetic bistability. By iterative integration of ICRs and related DNA sequences to an ectopic location in the mouse genome, we first identify the DNA sequence features required for maintenance of epigenetic states in embryonic stem cells. The autonomous regulatory properties of ICRs further enabled us to create DNA-methylation-sensitive reporters and to screen for key components involved in regulating their epigenetic memory. Besides DNMT1, UHRF1 and ZFP57, we identify factors that prevent switching from methylated to unmethylated states and show that two of these candidates, ATF7IP and ZMYM2, are important for the stability of DNA and H3K9 methylation at ICRs in embryonic stem cells.
Subject(s)
DNA Methylation , Genomic Imprinting , Mice , Animals , Base Sequence , DNA Methylation/genetics , Epigenomics , Chromatin/genetics , Repressor Proteins/geneticsABSTRACT
Nucleosome-depleted regions (NDRs) at gene promoters support initiation of RNA polymerase II transcription. Interestingly, transcription often initiates in both directions, resulting in an mRNA and a divergent non-coding (DNC) transcript of unclear purpose. Here, we characterized the genetic architecture and molecular mechanism of DNC transcription in budding yeast. Using high-throughput reverse genetic screens based on quantitative single-cell fluorescence measurements, we identified the Hda1 histone deacetylase complex (Hda1C) as a repressor of DNC transcription. Nascent transcription profiling showed a genome-wide role of Hda1C in repression of DNC transcription. Live-cell imaging of transcription revealed that mutations in the Hda3 subunit increased the frequency of DNC transcription. Hda1C contributed to decreased acetylation of histone H3 in DNC transcription regions, supporting DNC transcription repression by histone deacetylation. Our data support the interpretation that DNC transcription results as a consequence of the NDR-based architecture of eukaryotic promoters, but that it is governed by locus-specific repression to maintain genome fidelity.
Subject(s)
Histone Deacetylases/metabolism , Histones/metabolism , RNA Polymerase II/metabolism , RNA, Untranslated/metabolism , Saccharomyces cerevisiae Proteins/metabolism , Saccharomyces cerevisiae/metabolism , Transcription, Genetic , Acetylation , Gene Expression Regulation, Fungal , Histone Deacetylases/genetics , Histones/genetics , Nucleosomes , Promoter Regions, Genetic , RNA Polymerase II/genetics , RNA, Untranslated/genetics , Saccharomyces cerevisiae/genetics , Saccharomyces cerevisiae Proteins/geneticsABSTRACT
RNA polymerase (RNAP)II frequently transcribes non-protein-coding DNA sequences in eukaryotic genomes into long noncoding RNA (lncRNA). Distinct molecular mechanisms linked to the position of lncRNA relative to the coding gene illustrate how noncoding transcription controls gene expression. Here, we focus on the impact of the act of lncRNA transcription on nearby functional DNA units. We review the biological significance of the act of lncRNA transcription on DNA processing, highlighting common themes, such as mediating cellular responses to environmental changes. This review combines the background of chromatin signaling with examples in several organisms to clarify when functions of ncDNA can be interpreted through the act of RNAPII transcription.
