Complete biallelic insulation at the H19/Igf2 imprinting control region position results in fetal growth retardation and perinatal lethality

Establishment of paternal methylation imprint at the H19/Igf2 imprinting control region

The insulator model explains the workings of the H19 and Igf2 imprinted domain in the soma, where insulation of the Igf2 promoter from its enhancers occurs by CTCF in the maternally inherited unmethylated chromosome but not the paternally inherited methylated allele. The molecular mechanism that targets paternal methylation imprint establishment to the imprinting control region (ICR) in the male germline is unknown. We tested the function of prospermatogonia-specific broad low-level transcription in this process using mouse genetics. Paternal imprint establishment was abnormal when transcription was stopped at the entry point to the ICR. The germline epimutation persisted into the paternal allele of the soma, resulting in reduced Igf2 in fetal organs and reduced fetal growth, consistent with the insulator model and insulin-like growth factor 2 (IGF2)'s role as fetal growth factor. These results collectively support the role of broad low-level transcription through the H19/Igf2 ICR in the establishment of its paternal methylation imprint in the male germ line, with implications for Silver-Russell syndrome.

Insulin-Like Growth Factor-II and Ischemic Stroke-A Prospective Observational Study

Insulin-like growth factor-II (IGF-II) regulates prenatal brain development, but the role in adult brain function and injury is unclear. Here, we determined whether serum levels of IGF-II (s-IGF-II) are associated with mortality and functional outcome after ischemic stroke (IS). The study population comprised ischemic stroke cases (n = 492) and controls (n = 514) from the Sahlgrenska Academy Study on Ischemic Stroke (SAHLSIS). Functional outcome was evaluated after 3 months and 2 years using the modified Rankin Scale (mRS), and additionally, survival was followed at a minimum of 7 years or until death. S-IGF-II levels were higher in IS cases both in the acute phase and at 3-month follow-up compared to controls (p < 0.05 and p < 0.01, respectively). The lowest quintile of acute s-IGF-II was, compared to the four higher quintiles, associated with an increased risk of post-stroke mortality (median follow-up 10.6 years, crude hazard ratio (HR) 2.34, 95% confidence interval (CI) 1.56–3.49, and fully adjusted HR 1.64, 95% CI 1.02–2.61). In contrast, crude associations with poor functional outcome (mRS 3–6) lost significance after full adjustment for covariates. In conclusion, s-IGF-II was higher in IS cases than in controls, and low acute s-IGF-II was an independent risk marker of increased mortality.

Prenatal correction of IGF2 to rescue the growth phenotypes in mouse models of Beckwith-Wiedemann and Silver-Russell syndromes

Beckwith-Wiedemann syndrome (BWS) and Silver-Russell syndrome (SRS) are imprinting disorders manifesting as aberrant fetal growth and severe postnatal-growth-related complications. Based on the insulator model, one-third of BWS cases and two-thirds of SRS cases are consistent with misexpression of insulin-like growth factor 2 (IGF2), an important facilitator of fetal growth. We propose that the IGF2-dependent BWS and SRS cases can be identified by prenatal diagnosis and can be prevented by prenatal intervention targeting IGF2. We test this hypothesis using our mouse models of IGF2-dependent BWS and SRS. We find that genetically normalizing IGF2 levels in a double rescue experiment corrects the fetal overgrowth phenotype in the BWS model and the growth retardation in the SRS model. In addition, we pharmacologically rescue the BWS growth phenotype by reducing IGF2 signaling during late gestation. This animal study encourages clinical investigations to target IGF2 for prenatal diagnosis and prenatal prevention in human BWS and SRS.

Liao et al. use mouse models to test a prenatal approach for correcting growth anomalies in two imprinting diseases, BWS and SRS. They find that cases where the fetal growth factor IGF2 is misregulated can be diagnosed, and growth can be corrected by prenatally adjusting IGF2 or its signaling output.

Alterations to DNA structure as a cause of expression modifications of selected genes of known intrauterine-growth-restriction-association shared by chosen species - a review

The review aimed at searching for DNA structure markers of epigenetic modifications leading to intrauterine growth restriction (IUGR) in three livestock species, mouse and human. IUGR affects mammals by harming their wellbeing and the profitability of breeding enterprises. Of the livestock species, we chose cow, pig and sheep owing to there being many reports on the epigenetics of IUGR. IUGR investigations in human and mouse are particularly numerous, as we are interested in our own wellbeing and the mouse is a model species. We decided to focus on five genes (Igf2r, Igf2, H19, Peg3 and Mest) of known IUGR association, reported in all of those species. Despite the abundance of papers on IUGR, naturally occurring mutations responsible for epigenetic modifications have been described only in human and cow. The effect of induced DNA structural modifications upon epigenetics has been described in mouse and pig. One paper regarding mouse was chosen from among those describing DNA modifications performed to obtain parthenogenetic progeny. Papers regarding pig parthenogenetic progeny described the epigenetics of genes involved in foetal development, with no interference with the genome structure. No reports on DNA modifications altering IUGR epigenetics in sheep were found. Only environmental effects were studied and we could not conclude from the experiment designs whether the gene setup could affect the expression of involved genes, as different populations were not included or not specified within particular experiments. Apparently, DNA markers of IUGR epigenetics exist. It has been reported that the small number of them, occurring naturally, may result from neglecting existing evidence of such selection or health status forecasting markers.

Genome-wide methylation analysis in Silver-Russell syndrome patients

Silver-Russell syndrome (SRS) is a clinically heterogeneous disorder characterised by severe in utero growth restriction and poor postnatal growth, body asymmetry, irregular craniofacial features and several additional minor malformations. The aetiology of SRS is complex and current evidence strongly implicates imprinted genes. Approximately, half of all patients exhibit DNA hypomethylation at the H19/IGF2 imprinted domain, and around 10% have maternal uniparental disomy of chromosome 7. We measured DNA methylation in 18 SRS patients at >485,000 CpG sites using DNA methylation microarrays. Using a novel bioinformatics methodology specifically designed to identify subsets of patients with a shared epimutation, we analysed methylation changes genome-wide as well as at known imprinted regions to identify SRS-associated epimutations. Our analysis identifies epimutations at the previously characterised domains of H19/IGF2 and at imprinted regions on chromosome 7, providing proof of principle that our methodology can detect DNA methylation changes at imprinted loci. In addition, we discovered two novel epimutations associated with SRS and located at imprinted loci previously linked to relevant mouse and human phenotypes. We identify RB1 as an additional imprinted locus associated with SRS, with a region near the RB1 differentially methylated region hypermethylated in 13/18 (~70%) patients. We also report 6/18 (~33%) patients were hypermethylated at a CpG island near the ANKRD11 gene. We do not observe consistent co-occurrence of epimutations at multiple imprinted loci in single SRS individuals. SRS is clinically heterogeneous and the absence of multiple imprinted loci epimutations reflects the heterogeneity at the molecular level. Further stratification of SRS patients by molecular phenotypes might aid the identification of disease causes.

The role of CCCTC-binding factor (CTCF) in genomic imprinting, development, and reproduction

CCCTC-binding factor (CTCF) is the major protein involved in insulator activity in vertebrates, with widespread DNA binding sites in the genome. CTCF participates in many processes related to global chromatin organization and remodeling, contributing to the repression or activation of gene transcription. It is also involved in epigenetic reprogramming and is essential during gametogenesis and embryo development. Abnormal DNA methylation patterns at CTCF motifs may impair CTCF binding to DNA, and are related to fertility disorders in mammals. Therefore, CTCF and its binding sites are important candidate regions to be investigated as molecular markers for gamete and embryo quality. This article reviews the role of CTCF in genomic imprinting, gametogenesis, and early embryo development and, moreover, highlights potential opportunities for environmental influences associated with assisted reproductive techniques (ARTs) to affect CTCF-mediated processes. We discuss the potential use of CTCF as a molecular marker for assessing gamete and embryo quality in the context of improving the efficiency and safety of ARTs.

The chicken HS4 insulator element does not protect the H19 ICR from differential DNA methylation in yeast artificial chromosome transgenic mouse

Mono-allelic expression at the mouse IGF2/H19 locus is controlled by differential allelic DNA methylation of the imprinting control region (ICR). Because a randomly integrated H19 ICR fragment, when incorporated into the genome of transgenic mice (TgM), was allele-specifically methylated in somatic, but not in germ cells, it was suggested that allele-discriminating epigenetic signature, set within or somewhere outside of the Tg H19 ICR fragment in germ cells, was later translated into a differential DNA methylation pattern. To test if the chicken β-globin HS4 (cHS4) chromatin insulator might interfere with methylation imprinting establishment at the H19 ICR, we inserted the H19 ICR fragment, flanked by a set of floxed cHS4 core sequences, into a human β-globin locus YAC and generated TgM (insulated ICR' TgM). As controls, the cHS4 sequences were removed from one side (5'HS4-deleted ICR') or both sides (pseudo-WT ICR') of the insulated ICR' by in vivo cre-loxP recombination. The data show that while maternally inherited transgenic H19 ICR was not methylated in insulated ICR' TgM, it was significantly methylated upon paternal transmission, though the level was lower than in the pseudo-WT ICR' control. Because this reduced level of methylation was also observed in the 5'HS4-deleted ICR' TgM, we speculate that the phenotype is due to VEZF1-dependent demethylation activity, rather than the insulator function, borne in cHS4. Collectively, although we cannot rule out the possibility that cHS4 is incapable of blocking an allele-discriminating signal from outside of the transgene, the epigenetic signature appears to be marked intrinsically within the H19 ICR.

miR-141 contributes to fetal growth restriction by regulating PLAG1 expression

BACKGROUND

Fetal growth restriction (FGR) is an important but poorly understood condition of pregnancy, which results in significant fetal, neonatal and long-term morbidity and mortality. Novel research has suggested that altered miRNA expression in the plasma and placenta is associated with adverse pregnancy. We hypothesized that aberrant expression of microRNA-141 (miR-141) in the placenta is associated with FGR. Additionally, expression levels of predicted target genes of miR-141 were also analyzed in placental tissues of FGR and normal controls.

METHODOLOGY/PRINCIPAL FINDINGS

Using quantitative real time PCR, we analyzed the expression level of miR-141 and its target genes in placentas of FGR pregnancies (n = 21) and normal controls (n = 34). Western blot was used to detect the protein expression level of the target genes of miR-141. MiR-141 showed significant up regulation in FGR and significant down regulation of its targets, i.e. E2F transcription factor 3 (E2F3) protein, pleiomorphic adenoma gene 1 (PLAG1) mRNA and protein. Moreover, a positive correlation was found between PLAG1 and insulin-like growth factor 2 (IGF2) expression levels (Spearman r = 0.56, p<0.0001). MiR-141 yields an AUC of 0.83 with 88.5% sensitivity and 71.7% specificity for separating FGR from normal controls. This study indicates that miR-141 may be diagnostically important in FGR.

CONCLUSIONS/SIGNIFICANCE

Our results indicate that aberrant high expression level of miR-141 might play important roles in the pathogenesis of FGR by suppressing E2F3 and PLAG1. We propose that miR-141 may participate in a miR-141-PLAG1-IGF2 network relating to FGR development. These findings may provide new targets via miR-141 in diagnosis and therapy of FGR in the future.

More than insulator: multiple roles of CTCF at the H19-Igf2 imprinted domain

CTCF (CCCTC-binding factor)-mediated insulation at the H19-Insulin-like growth factor 2 (Igf2) imprinted domain is a classic example for imprinted gene regulation. DNA methylation difference in the imprinting control region (ICR) is inherited from the gametes and subsequently determines parental allele-specific enhancer blocking and imprinted expression in the soma. Recent genetic studies showed that proper monoallelic enhancer blocking at the H19-Igf2 ICR is critical for development. Strict biallelic insulation at this locus causes perinatal lethality, whereas leaky biallelic insulation results in smaller size but no lethality. Apart from enhancer blocking, CTCF is also the master organizer of chromatin composition in the maternal allele along this imprinted domain, affecting not only histone tail covalent modifications but also those in the histone core. Additionally, CTCF binding in the soma protects the maternal allele from de novo DNA methylation. CTCF binding is not involved in the establishment of the gametic marks at the ICR, but it slightly delays de novo methylation in the maternally inherited ICR allele in prospermatogonia. This review focuses on the developmental and epigenetic consequences of CTCF binding at the H19-Igf2 ICR.

Differential differences in methylation status of putative imprinted genes among cloned swine genomes

DNA methylation is a major epigenetic modification in the mammalian genome that regulates crucial aspects of gene function. Mammalian cloning by somatic cell nuclear transfer (SCNT) often results in gestational or neonatal failure with only a small proportion of manipulated embryos producing live births. Many of the embryos that survive to term later succumb to a variety of abnormalities that are likely due to inappropriate epigenetic reprogramming. Aberrant methylation patterns of imprinted genes in cloned cattle and mice have been elucidated, but few reports have analyzed the cloned pig genome. Four surviving cloned sows that were created by ear fibroblast nuclear transfer, each with a different life span and multiple organ defects, such as heart defects and bone growth delay, were used as epigenetic study materials. First, we identified four putative differential methylation regions (DMR) of imprinted genes in the wild-type pig genome, including two maternally imprinted loci (INS and IGF2) and two paternally imprinted loci (H19 and IGF2R). Aberrant DNA methylation, either hypermethylation or hypomethylation, commonly appeared in H19 (45% of imprinted loci hypermethylated vs. 30% hypomethylated), IGF2 (40% vs. 0%), INS (50% vs. 5%), and IGF2R (15% vs. 45%) in multiple tissues from these four cloned sows compared with wild-type pigs. Our data suggest that aberrant epigenetic modifications occur frequently in the genome of cloned swine. Even with successful production of cloned swine that avoid prenatal or postnatal death, the perturbation of methylation in imprinted genes still exists, which may be one of reason for their adult pathologies and short life. Understanding the aberrant pattern of gene imprinting would permit improvements in future cloning techniques.

Enhancer-blocking activity is associated with hypersensitive site V sequences in the human growth hormone locus control region

Activation of the human growth hormone gene (hGH-N) is linked to a locus control region (LCR) containing four (I-III, V) hypersensitive sites (HS). Pit-1 binding to HS I/II is required for efficient pituitary expression. However, inclusion of HS III and V, located about 28 and 32 kb upstream of the hGH-N gene, respectively, is also required for consistent hGH-N expression levels in vivo. HS V is referred to as a boundary for the hGH LCR, but no specific enhancer blocking or barrier function is reported. We examined a 547 bp fragment containing HS V sequences (nucleotides -32,718/-32,172 relative to hGH-N) for enhancer-blocking activity using a well-established transient gene transfer system and assessed these sequences for CCCTC binding factor (CTCF), which is linked to enhancer-blocking activity. The 547 bp HS V fragment decreased enhancer activity with a reverse-orientation preference when inserted between HS III enhancer sequences and a minimal thymidine kinase promoter (TKp). These sequences are associated with CTCF in human pituitary and nonpituitary chromatin. Enhancer-blocking activity with an orientation preference was further localized to a 45 bp sub-fragment, with evidence of CTCF and upstream binding factor 1 (USF1) binding; USF1 is linked more closely with barrier function. The presence of yin and yang 1 (Yy1) that cooperates with CTCF in the regulation of X-chromosome inactivation was also seen. A decrease in CTCF and Yy1 RNA levels was associated with a significant reduction in enhancer-blocking activity. Assessment of CpG-dinucleotides in the TKp indicates that the presence of HS V sequences are associated with an increased incidence of CpG-dinucleotide methylation of the GC box region. These data support association of CTCF and enhancer-blocking activity with HS V that is consistent with a role as a (LCR) boundary element and also implicates Yy1 in this process.