Transcription profiling of mouse G9a-/- knockouts vs controls reveals G9a histone methyltransferase maintains genomic imprinting IN THE mouse placenta.
ABSTRACT: Whereas DNA methylation is essential for genomic imprinting, the importance of histone methylation in the allelic repression of imprinted genes is unclear. ‘Imprinting control regions’ (ICRs), however, are consistently marked by histone H3 K9 methylation on their DNA-methylated allele. In the placenta, the paternal silencing along the Kcnq1 domain on distal chromosome 7 also correlates with the presence of H3-K9 methylation, but imprinted repression at these genes is maintained independently of DNA methylation. To explore which histone methyltransferase (HMT) could mediate the allelic H3-K9 methylation on distal chromosome 7, and at ICRs, we generated mouse conceptuses deficient for the SET-domain protein G9a. We find that in the embryo and placenta, the differential DNA methylation at ICRs and imprinted genes is maintained in the absence of G9a. Accordingly, in embryos, imprinted gene expression is unchanged at the domains analysed, in spite of a global loss of H3-K9 di-methylation (H3K9me2). In contrast, the placenta-specific imprinting of genes on distal chromosome 7 is lost in the absence of G9, and this correlates with a loss of H3K9me2 and H3K9me3. These findings provide the first in vivo evidence for the involvement of a SET domain protein in imprinting and highlight the importance of histone lysine methylation rather than DNA methylation in the maintenance of imprinting in the trophoblast lineage. Experiment Overall Design: Number of samples: four (two biologically replicate G9a-/- pooled placentae samples, and two biologically replicate wildtype pooled placentae samples). The first G9a-/- and wildtype replicates were used to hybridize Affymetrix MOE430A and MOE430B arrays (four arrays total). The second replicates were used to hybridize Affymetrix Mouse430_2 arrays (two arrays total).
Project description:The maternal and paternal copies of the genome are both required for mammalian development and this is primarily due to imprinted genes, those that are mono-allelically expressed based on parent-of-origin. Typically, this pattern of expression is regulated by differentially methylated regions (DMRs) that are established in the germline and maintained after fertilisation. There are a large number of germline DMRs that have not yet been associated with imprinting and their function in development is unknown. In this study, we developed a genome-wide approach to identify novel imprinted DMRs, specifically in the human placenta, and investigated the dynamics of imprinted DMRs during development in somatic and extra-embryonic tissues. DNA methylation was evaluated using the Illumina HumanMethylation450 array in 116 human tissue samples, publically available reduced representation bisulfite sequencing in the human embryo and germ cells, and targeted bisulfite sequencing in term placentas. 43 known and 101 novel imprinted DMRs were identified in the human placenta, by comparing methylation between diandric and digynic triploids and female and male gametes. 72 novel DMRs showed a pattern consistent with placental-specific imprinting and this monoallelic methylation was entirely maternal in origin. Strikingly, these DMRs exhibited polymorphic imprinted methylation specifically in placenta. These data suggest that imprinting in human development is far more extensive and dynamic than previously reported and that the placenta preferentially maintains maternal germline-derived DNA methylation. Overall design: Multiplexed targeted bisulfite seequencing of 151 assays for imprinted differentially methylated regions in human placental villous, trophoblast and whole blood samples
Project description:Genomic imprinting is an allelic gene expression phenomenon primarily controlled by allele-specific DNA methylation at the imprinting control region (ICR), of which the underlying mechanism remains largely unclear. Mammalian N-α-acetyltransferase 10 protein (Naa10p) catalyzes N-α-acetylation of nascent proteins. Mutation of human Naa10p is linked to severe developmental delays. Here we report that Naa10-null mice display partial embryonic lethality, growth retardation, brain disorder and maternaleffect lethality, phenotypes commonly observed in defective genomic imprinting. Genome-wide analyses further revealed global DNA hypomethylation and enriched dysregulation of imprinted genes in Naa10p-knockout embryos and ES cells. Mechanistically, Naa10p facilitates the binding of DNA methyltransferase 1 (Dnmt1) to DNA substrates and recruits Dnmt1 to ICRs of the imprinted allele during S phase. Moreover, the clinical lethal Ogden syndrome-associated mutation of Naa10p disrupts its binding to H19-ICR and Dnmt1 recruitment. Our study thus links Naa10p mutationassociated human disease to defective DNA methylation and genomic imprinting. Overall design: Examination of Naa10p binding sites in WT mouse embryonic stem (ES) cells using Naa10-KO ES cells as control
Project description:ZFP57 is necessary for maintaining repressive epigenetic modifications at Imprinting control regions (ICRs). In mouse embryonic stem cells (ESCs), ZFP57 binds ICRs (ICRBS) and many other loci (non-ICRBS). To address the role of ZFP57 on all its target sites, we performed high-throughput and multi-locus analyses of inbred and hybrid mouse ESC lines carrying different gene knockouts. By using an allele-specific RNA-seq approach, we demonstrate that ZFP57 loss results in derepression of the imprinted allele of multiple genes in the imprinted clusters. We also find marked epigenetic differences between ICRBS and non-ICRBS suggesting that different cis-acting regulatory functions are repressed by ZFP57 at these two classes of target loci. Overall, these data demonstrate that ZFP57 is pivotal to maintain the allele-specific epigenetic modifications of ICRs that in turn are necessary for maintaining the imprinted expression over long distances. At non-ICRBS, ZFP57 inactivation results in acquisition of epigenetic features that are characteristic of poised enhancers, suggesting that another function of ZFP57 in early embryogenesis is to repress cis-acting regulatory elements whose activity is not yet required. Overall design: Examination of methylation levels in Zfp57-/- mouse ESCs compared to the wild-type.
Project description:Genomic imprinting is a critical developmental process characteristic of parent-of-origin- specific gene expression. Here, we have identified the AFF family protein, Aff3, as a factor that functionally interacts with imprinted loci. Indeed, our genome-wide studies demonstrate that Aff3 specifically binds both imprinting control regions (ICRs) and enhancers within imprinted loci in an allele-specific manner. We have identified the molecular regulators involved in the recruitment of Aff3 to ICRs to impede transcription through the ICR, and provide a mechanism requiring Aff3 within the Super Elongation Complex-like 3 (SEC-L3) in the expression of an imprinted polycistronic transcript spanning the Dlk1-Dio3 locus. Our study also shows that DNA methylation at the ICR reinforces silencing of its related enhancers by controlling the binding and activity of Aff3 in an allele-specific manner. This study provides molecular details about the regulation of dosage-critical imprinted gene expression through Aff3’s function in transcriptional elongation control. ChIP-seq of Aff3 in different mES cells. ChIP-seq of Aff3, PolII, H3K9me3 in uniparental MEF cell lines. ChIP-seq of H3K27ac and PolII in mES cells after Aff3 shRNA and non-targeting shRNA. ChIP-seq of H3K27ac in wild type and Zfp57 knockout ES cells. Total RNA-seq and nascent RNA-seq of mES cells after Aff3 shRNA and non-targeting shRNA. Total RNA-seq of uniparental MEF cells after Aff3 shRNA and non-targeting shRNA.
Project description:Many questions about the regulation, functional specialization, computational prediction, and evolution of genomic imprinting would be better addressed by having an exhaustive genome-wide catalog of genes that display parent-of-origin differential expression. As a first-pass scan for novel imprinted genes, we performed mRNA-seq experiments on E17.5 mouse placenta cDNA samples from reciprocal cross F1 progeny of AKR and PWD mouse strains, and quantified the allele-specific expression and the degree of parent-of-origin effect transcriptome-wide. We confirmed the imprinting status of 23 known imprinted genes in the placenta, and found that 12 genes reported previously to be imprinted in other tissues are also imprinted in mouse placenta. Through a well-replicated design using an orthogonal technology, we verified five novel imprinted genes that are not known to be imprinted in mouse. It appears that most of the strongly imprinted genes have already been identified, at least in the placenta, and that evidence supports perhaps 100 additional weakly imprinted genes. Despite previous appearance that the placenta tends to display an excess of maternally-expressed imprinted genes, when the full set of genes is uniformly scored as in this study, this maternal bias disappeared. Examine allelic expression in E17.5 placenta tissues from two individual samples, one from each of the two reciprocal crosses.
Project description:The maternal and paternal copies of the genome are both required for mammalian development and this is primarily due to imprinted genes, those that are mono-allelically expressed based on parent-of-origin. Typically, this pattern of expression is regulated by differentially methylated regions (DMRs) that are established in the germline and maintained after fertilisation. There are a large number of germline DMRs that have not yet been associated with imprinting and their function in development is unknown. In this study, we developed a genome-wide approach to identify novel imprinted DMRs, specifically in the human placenta, and investigated the dynamics of imprinted DMRs during development in somatic and extra-embryonic tissues. DNA methylation was evaluated using the Illumina HumanMethylation450 array in 116 human tissue samples, publically available reduced representation bisulfite sequencing in the human embryo and germ cells, and targeted bisulfite sequencing in term placentas. 43 known and 101 novel imprinted DMRs were identified in the human placenta, by comparing methylation between diandric and digynic triploids and female and male gametes. 72 novel DMRs showed a pattern consistent with placental-specific imprinting and this mono-allelic methylation was entirely maternal in origin. Strikingly, these DMRs exhibited polymorphic imprinted methylation specifically in placenta. These data suggest that imprinting in human development is far more extensive and dynamic than previously reported and that the placenta preferentially maintains maternal germline-derived DNA methylation For the identification of imprinted DMRs in the placenta, chorionic villous samples from 5 diandric and 5 digynic triploids pregnancies were assayed, along with a pooled sample of complete hydatiform moles (CHM). Placental chorionic villous samples (n=63) included 29 control pregnancies delivered at term, while the remaining 34 were delivered preterm or miscarried, or had abnormal MSS results, IUGR or LOPET. The preterm births were associated with one or more of: preterm labour, premature rupture of membranes (PROM), chorioamnionitis, placental abruption, and incompetent cervix. All samples were determined to be chromosomally normal using standard karyotyping or comparative genome hybridization, as previously described (Robinson et al. 2010). Two to four independent sites were taken from each placenta and after DNA extraction from chorionic villous, the DNA was pooled before being utilized in this study. Thirty-three fetal tissues, including brain (n=8), spinal cord (n=7), muscle (n=9), and kidney (n=9) were collected from second trimester foetuses, as previously described (Price et al. 2012). Adult female whole blood samples (n=10) were collected from control women. Extra-embryonic cell types (n=19), including cord blood (embryonic), cord, amniotic membrane, chorionic membrane, 1st, 2nd and 3rd trimester trophoblast and mesenchyme, and decidua (maternal), were isolated from control placental samples.
Project description:Genomic imprinting is a form of epigenetic regulation that results in expression of either the maternally or paternally inherited allele of a subset of genes. Imprinted loci contain differentially methylated regions (DMRs) where cytosine methylation marks one of the parental alleles, providing cis-acting regulatory elements that influence the allelic expression of surrounding genes, however to date the total number of imprinted loci within the human genome is unknown. To characterize known imprinted DMRS and identify novel imprinted loci we have performed whole-genome bisulphite sequencing and high-resolution DNA methylation array analysis of healthy tissues. Sequencing of bisulfite converted DNA analysis of normal brain (white matter), liver and term placenta tissue
Project description:G9a is the major mammalian H3-K9 methyltransferase that targets euchromatic regionsand is essential for murine embryogenesis . We demonstrate that G9a is endowed with methyltransferase activity to concomitantly repress the downstream effector Ep-CAM, thereby promoting the invasion step of the invasion-metastasis cascade. We used microarrays to detail the G9a regulated gene expression underlying invasion-metastasis cascade and identified distinct classes of up-regulated genes during this process. Lung adenocarcinoma cells with G9a knockdown or overexpression were selected for RNA extraction and hybridization on Affymetrix microarrays.
Project description:The discovery of genomic imprinting through studies of manipulated mouse embryos indicated that the paternal genome has a major influence on placental development. However, previous research has not demonstrated paternal bias in imprinted genes. We applied RNA sequencing to trophoblast tissue from reciprocal hybrids of horse and donkey, where genotypic differences allowed parent-of-origin identification of most expressed genes. Using this approach, we identified a core group of 15 ancient imprinted genes of which 10 were paternally expressed. An additional 78 candidate novel imprinted genes identified by RNA-seq also showed paternal bias. Pyrosequencing was used to confirm the imprinting status of six of the novel genes, including the insulin receptor (INSR), which may play a role in growth regulation with its reciprocally imprinted ligand, histone acetyltransferase (HAT1), the first example of an imprinted gene involved in chromatin modification, and LY6G6C, the first imprinted gene to be identified in the major histocompatibility complex. The 78 novel candidate imprinted genes displayed parent-of-origin expression bias in placenta but not fetus, and most showed less than 100% silencing of the imprinted allele. Some displayed variability in imprinting status among individuals. This results in a unique epigenetic signature for each placenta that contributes to variation in the intrauterine environment and thus presents the opportunity for natural selection to operate on parent-of-origin differential regulation. Taken together, these features highlight the plasticity of imprinting in mammals and the central importance of the placenta as a target tissue for genomic imprinting. Examine allelic expression from four individual samples of invasive trophoblast tissue of the chorionic girdle from gestation day 33 conceptuses of horse, donkey, mule and hinny.
Project description:5-hydroxymethylcytosine (5hmC), converted from 5-methylcytosine (5mC) by Tet enzymes, has recently drawn attention as the ‘sixth base’ of DNA since it is considered to be an intermediate of the demethylation pathway. Nonetheless, it remains to be addressed how 5hmC is linked to the development of human imprinting disorders. In this regard, conventional bisulfite (BS) treatment is unable to differentiate 5hmC from 5mC. It is thus hypothesized that BS conversion-derived ‘hypermethylation’ at imprinting control regions (ICRs), which may cause human imprinting disorders, would in fact be attributable to excessively increased levels of 5hmC as well as 5mC. To test this hypothesis, we applied the newly developed oxidative BS (oxBS) treatment to detect 5hmC in blood samples from Kagami-Ogata syndrome (KOS14) patients caused by perturbed expression of clustered imprinted genes on 14q32.2 resulting from the hypermethylation of ICRs at this locus, IG-DMR and MEG3-DMR. oxBS with pyrosequencing and cloning-based sequencing revealed that there were few amounts of 5hmC at the hypermethylated IG-DMR in blood samples from KOS14 patients. oxBS with genome-wide methylation array analysis demonstrated that global levels of 5hmC were very low with similar distribution patterns in blood samples from KOS14 patients and normal controls. We also confirmed the presence of a large amount of 5hmC in the brain sample from a normal control. 5hmC is not a major component in abnormally hypermethylated ICRs or at a global level, at least in blood from KOS14 patients. As the brain sample contained a large amount of 5hmC, the neural tissues of KOS14 patients are promising candidates for analysis in elucidating the role of 5hmC in the neurodevelopmental context. We generated illumina 450k DNA methylation data for BS or oxBS converted samples of three KOS14 blood samples, one control pooled blood sample and one control brain sample with two technical replicates for each sample.