Project description:Genomic imprinting is regulated by parental-specific epigenetic marks that differentiate between maternal and paternal chromosomes. Despite identical DNA sequence, the presence or absence of DNA methylation leads to the establishment of two distinct epigenetic states at Imprinting Control Regions (ICR). Here we combine targeted epigenome engineering to generate ectopic loci in the mouse embryonic stem cell genome that recapitulate the epigenetic properties of ICRs. We describe these ectopic ICRs as strong cis-regulatory sequences that can adopt and memorise one of two opposing epigenetic states, dependent of pre-imposed DNA methylation. This bistability is unique to ICRs and enabled us to systematically study the genetic and epigenetic determinants required for creating and maintaining the observed states. Through sequence manipulation we show that the ICR DNA sequence confers autonomy of ICRs and is required for creating epigenetic bistability. Genetic screens using DNA-methylation-sensitive reporters identify key components involved in regulating maintenance of epigenetic states. Besides DNMT1, UHRF1 and ZFP57, we identify novel factors that prevent switching between methylated and unmethylated states and validate two of these candidates, ATF7IP and ZMYM2, to be important for epigenetic memory at ICRs. In summary we show that the DNA sequence of ICRs provides the prerequisite for establishment of two distinct epigenetic states, while DNA and histone modifications ensure their stable propagation.
Project description:Genomic imprinting is regulated by parental-specific epigenetic marks that differentiate between maternal and paternal chromosomes. Despite identical DNA sequence, the presence or absence of DNA methylation leads to the establishment of two distinct epigenetic states at Imprinting Control Regions (ICR). Here we combine targeted epigenome engineering to generate ectopic loci in the mouse embryonic stem cell genome that recapitulate the epigenetic properties of ICRs. We describe these ectopic ICRs as strong cis-regulatory sequences that can adopt and memorise one of two opposing epigenetic states, dependent of pre-imposed DNA methylation. This bistability is unique to ICRs and enabled us to systematically study the genetic and epigenetic determinants required for creating and maintaining the observed states. Through sequence manipulation we show that the ICR DNA sequence confers autonomy of ICRs and is required for creating epigenetic bistability. Genetic screens using DNA-methylation-sensitive reporters identify key components involved in regulating maintenance of epigenetic states. Besides DNMT1, UHRF1 and ZFP57, we identify novel factors that prevent switching between methylated and unmethylated states and validate two of these candidates, ATF7IP and ZMYM2, to be important for epigenetic memory at ICRs. In summary we show that the DNA sequence of ICRs provides the prerequisite for establishment of two distinct epigenetic states, while DNA and histone modifications ensure their stable propagation.
Project description:Genomic imprinting is regulated by parental-specific epigenetic marks that differentiate between maternal and paternal chromosomes. Despite identical DNA sequence, the presence or absence of DNA methylation leads to the establishment of two distinct epigenetic states at Imprinting Control Regions (ICR). Here we combine targeted epigenome engineering to generate ectopic loci in the mouse embryonic stem cell genome that recapitulate the epigenetic properties of ICRs. We describe these ectopic ICRs as strong cis-regulatory sequences that can adopt and memorise one of two opposing epigenetic states, dependent of pre-imposed DNA methylation. This bistability is unique to ICRs and enabled us to systematically study the genetic and epigenetic determinants required for creating and maintaining the observed states. Through sequence manipulation we show that the ICR DNA sequence confers autonomy of ICRs and is required for creating epigenetic bistability. Genetic screens using DNA-methylation-sensitive reporters identify key components involved in regulating maintenance of epigenetic states. Besides DNMT1, UHRF1 and ZFP57, we identify novel factors that prevent switching between methylated and unmethylated states and validate two of these candidates, ATF7IP and ZMYM2, to be important for epigenetic memory at ICRs. In summary we show that the DNA sequence of ICRs provides the prerequisite for establishment of two distinct epigenetic states, while DNA and histone modifications ensure their stable propagation.
Project description:DNA methylation is essential for embryonic development and implicated in the regulation of genomic imprinting. Genomic imprinting is established in the germline through parent-specific methylation of distinct cis-regulatory DNA sequences, called imprinting control regions (ICRs). Which factors bind to the opposing chromatin states at ICRs within the same nuclear environment was not systematically addressed. By using a proximity labelling approach with the methylation sensitive transcription factor ZFP57, we identified ATF7IP and other major components of the epigenetic maintenance machinery at ICRs.
Project description: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.
Project description:Background: Imprinted genes are defined by their preferential expression from one of the two parental alleles. This unique mode of gene expression is dependent on allele-specific DNA methylation profiles established at regulatory sequences called imprinting control regions. These loci are frequently used as biosensors to study how environmental exposures affect methylation and transcription. However, a critical unanswered question is whether they are more, less or equally sensitive to environmental stressors as the rest of the genome. Objectives: Using cadmium exposure in humans as a model, we determined the relative sensitivity of imprinting control regions to perturbation of methylation compared to similar, non-imprinted loci in the genome. Methods: We assayed DNA methylation genome-wide using bisulfite sequencing of newborn cord blood and maternal blood samples selected on the basis of maternal blood cadmium levels. Differentially methylated regions associated with cadmium exposure were identified. Results: In newborn cord blood and maternal blood, 641 and 1945 cadmium-associated differentially methylated regions were identified, respectively. These were strongly enriched at maternally-methylated imprinting control regions when compared to similar loci in newborn cord blood (P = 5.64E-8) and maternal blood (P = 6.22E-14), suggesting an increased sensitivity for imprinting control regions to cadmium. Genome-wide, methylation changes were enriched in maternal blood at genes implicated in body mass index (P = 2.0E-5), blood pressure (P = 3.8E-5) and body weight (P = 1.4E-3), with similar trends for metabolic and cardiovascular functions in cord blood, suggesting that epigenetic changes may contribute to the etiology of cadmium-associated diseases. Conclusions: We present the first global nucleotide-resolution DNA methylation profile associated with cadmium exposure in humans. We identify imprinting control regions as hotspots for perturbation by cadmium, possibly due to their unique modes of regulation, motivating further study of these loci to provide insight into the mechanisms of cadmium action.