Selective methylation of CpGs at regulatory binding sites controls NNAT expression in Wilms tumors

AIMER: A SNP-independent software for identifying imprinting-like allelic methylated regions from DNA methylome

Genomic imprinting is essential for mammalian growth and embryogenesis. High-throughput bisulfite sequencing accompanied with parental haplotype-specific information allows analysis of imprinted genes and imprinting control regions (ICRs) on a large scale. Currently, although several allelic methylated regions (AMRs) detection software were developed, methods for detecting imprinted AMRs is still limited. Here, we developed a SNP-independent statistical approach, AIMER, to detect imprinting-like AMRs. By using the mouse frontal cortex methylome as input, we demonstrated that AIMER performs very well in detecting known germline ICRs compared with other methods. Furthermore, we found the putative parental AMRs AIMER detected could be distinguished from sequence-dependent AMRs. Finally, we found a novel germline imprinting-like AMR using WGBS data from 17 distinct mouse tissue samples. The results indicate that AIMER is a good choice for detecting imprinting-like (parent-of-origin-dependent) AMRs. We hope this method will be helpful for future genomic imprinting studies. The Python source code for our project is now publicly available on both GitHub (https://github.com/ZhaoLab-TMU/AIMER) and Gitee (https://gitee.com/zhaolab_tmu/AIMER).

Spontaneous and ART-induced large offspring syndrome: similarities and differences in DNA methylome

Large/abnormal offspring syndrome (LOS/AOS) is a congenital overgrowth syndrome reported in ruminants produced by assisted reproduction (ART-LOS) which exhibit global disruption of the epigenome and transcriptome. LOS/AOS shares phenotypes and epigenotypes with the human congenital overgrowth condition Beckwith-Wiedemann syndrome. We have reported that LOS occurs spontaneously (SLOS); however, to date, no study has been conducted to determine if SLOS has the same methylome epimutations as ART-LOS. In this study, we performed whole-genome bisulphite sequencing to examine global DNA methylation in bovine SLOS and ART-LOS tissues. We observed unique patterns of global distribution of differentially methylated regions (DMRs) over different genomic contexts, such as promoters, CpG Islands, shores and shelves, as well as at repetitive sequences. In addition, we included data from two previous LOS studies to identify shared vulnerable genomic loci in LOS. Overall, we identified 320 genomic loci in LOS that have alterations in DNA methylation when compared to controls. Specifically, there are 25 highly vulnerable loci that could potentially serve as molecular markers for the diagnosis of LOS, including at the promoters of DMRT2 and TBX18, at the imprinted gene bodies of IGF2R, PRDM8, and BLCAP/NNAT, and at multiple CpG Islands. We also observed tissue-specific DNA methylation patterns between muscle and blood, and conservation of ART-induced DNA methylation changes between muscle and blood. We conclude that as ART-LOS, SLOS is an epigenetic condition. In addition, SLOS and ART-LOS share similarities in methylome epimutations.

Both Epimutations and Chromosome Aberrations Affect Multiple Imprinted Loci in Aggressive Wilms Tumors

The embryonal renal cancer Wilms tumor (WT) accounts for 7% of all children's malignancies. Its most frequent molecular defect is represented by DNA methylation abnormalities at the imprinted 11p15.5 region. Multiple imprinted methylation alterations dictated by chromosome copy-number variations have been recently demonstrated in adult cancers, raising the question of whether multiple imprinted loci were also affected in WT. To address this issue, we analyzed DNA methylation and chromosome profiles of 7 imprinted loci in 48 WT samples. The results demonstrated that methylation abnormalities of multiple imprinted loci occurred in 35% of the cases, but that they were associated with either chromosome aberrations or normal chromosome profiles. Multiple imprinted methylation changes were correlated with tumor stage and presence of metastasis, indicating that these epimutations were more frequent in highly aggressive tumors. When chromosome profiles were affected, these alterations were extended to flanking cancer driver genes. Overall, this study demonstrates the presence of multiple imprinted methylation defects in aggressive WTs and suggests that the mechanism by which they arise in embryonal and adult cancers is different.

Origins of DNA methylation defects in Wilms tumors

Wilms tumor is an embryonic renal cancer that typically presents in early childhood and accounts for 7% of all paediatric cancers. Different genetic alterations have been described in this malignancy, however, only a few of them are associated with a majority of Wilms tumors. Alterations in DNA methylation, in contrast, are frequent molecular defects observed in most cases of Wilms tumors. How these epimutations are established in this tumor is not yet completely clear. The recent identification of the molecular actors required for the epigenetic reprogramming during embryogenesis suggests novel possible mechanisms responsible for the DNA methylation defects in Wilms tumor. Here, we provide an overview of the DNA methylation alterations observed in this malignancy and discuss the distinct molecular mechanisms by which these epimutations can arise.

Activation of the Wnt/β-catenin pathway is common in wilms tumor, but rarely through β-catenin mutation and APC promoter methylation

PURPOSE

The Wnt/β-catenin pathway is known to be crucial for the regulation of embryogenesis and cell differentiation, and its constitutive activation is associated with a wide range of malignancies. There are two major principles for an activated Wnt/β-catenin pathway. The first is caused by the failure of the destruction complex, mainly due to the decreased expression of the tumor suppressor gene adenomatous polyposis coli (APC); the second is the mutation of the β-catenin (CTNNB1) protein itself. Wilms tumors (WTs) are also thought to be malignancies with a high rate of Wnt/β-catenin pathway activation. The aim of this study was to analyze a large cohort of WT for activated Wnt/β-catenin pathway.

METHODS

The transcription of axis inhibition protein 2 (AXIN2) and APC was analyzed by real-time PCR. Expression was compared with those in healthy renal tissues as a control. Methylation status of the APC promoter was measured by pyrosequencing and correlated with APC expression. Finally, the mutations of CTNNB1 itself were detected by Sanger sequencing.

RESULTS

The analysis was done in a cohort of 103 WTs, treated in our institution. There was a significant overexpression of AXIN2 in WTs (P < 0.0001), with 33 (32 %) tumors showing higher expression (median + 3× SD) than normal kidney tissue. In contrast, the expression of APC as well as its promoter methylation did not differ from control (P = 0.78; P = 0.82). Finally, there were only seven (6.8 %) mutations detectable in CTNNB1, and five out of seven were seen in WTs with AXIN2 overexpression.

CONCLUSION

The finding that AXIN2, one of the major Wnt target genes, is overexpressed in our cohort of WTs, is indicative for the activation of the Wnt/β-catenin pathway. However, neither the alteration of APC nor frequent CTNNB1 mutations were seen in our analyses. Therefore, other mechanisms might be responsible for the common activation of the Wnt/β-catenin pathway.

Identification of differentially methylated regions (DMRs) of neuronatin in mice

BACKGROUND

Neuronatin (NNAT) is a paternal-inherited imprinted gene, first discovered in the rat neonatal brain, where it plays vital roles for neuronal growth, brain development, and metabolic regulation. The maternal imprint of NNAT has been identified in mice; however, the differentially methylated regions (DMRs) involved in the monoallelic expression of NNAT have not yet been investigated.

RESULTS

In this study, we confirmed expression of two isoforms of the NNAT (α and β) in the mice brain via quantitative RT-PCR. Additionally, the methylation profile of the CpG island located in the NNAT gene locus was determined in the mice liver, brain, sperm, and the MII oocyte via bisulfite sequencing PCR.

CONCLUSION

In summary, we provide the first evidence for tissue- and gamete-specific methylation patterns of CpG3 that are located on exon 1, to be putative DMR of NNAT in mice.

Association of FOXM1 expression with tumor histology and prognosis in Wilms tumor: Potential for a new prognostic marker

Wilms tumor (WT) is the most common pediatric renal malignancy. A recent ontogenic model suggests that undifferentiated tumor state, and hence poor prognosis, in WT is determined by stabilization of β-catenin in the nucleus. Forkhead box M1 (FOXM1) is a downstream component of the Wnt pathway and promotes nuclear localization of β-catenin. As elevation of FOXM1 gene expression is prognostic in various types of malignancy, we hypothesized that high FOXM1 expression in WT is associated with undifferentiated histology and thus poor prognosis. In the current study, the expression of FOXM1 mRNA was determined in 46 WT specimens and 11 renal tissue controls from patients undergoing tumor nephrectomy, and these data were assessed with regard to clinicopathological parameters. The results demonstrated an upregulation of FOXM1 in WT by 10-fold compared to normal tissue. Expression differed significantly between controls and tumors of intermediate- and high-risk histopathology (P<0.001, Kruskal-Wallis), and distinguished normal tissue from tumors of good and adverse clinical outcome (P<0.001, Kruskal-Wallis). Notably, FOXM1 expression was significantly lower (P=0.009) in patients that received preoperative doxorubicin. These results suggest that FOXM1 may serve as a companion diagnostic factor for doxorubicin-based therapies in WT.

Characterization of global loss of imprinting in fetal overgrowth syndrome induced by assisted reproduction

Embryos generated with the use of assisted reproductive technologies (ART) can develop overgrowth syndromes. In ruminants, the condition is referred to as large offspring syndrome (LOS) and exhibits variable phenotypic abnormalities including overgrowth, enlarged tongue, and abdominal wall defects. These characteristics recapitulate those observed in the human loss-of-imprinting (LOI) overgrowth syndrome Beckwith-Wiedemann (BWS). We have recently shown LOI at the KCNQ1 locus in LOS, the most common epimutation in BWS. Although the first case of ART-induced LOS was reported in 1995, studies have not yet determined the extent of LOI in this condition. Here, we determined allele-specific expression of imprinted genes previously identified in human and/or mouse in day ∼105 Bos taurus indicus × Bos taurus taurus F1 hybrid control and LOS fetuses using RNAseq. Our analysis allowed us to determine the monoallelic expression of 20 genes in tissues of control fetuses. LOS fetuses displayed variable LOI compared with controls. Biallelic expression of imprinted genes in LOS was associated with tissue-specific hypomethylation of the normally methylated parental allele. In addition, a positive correlation was observed between body weight and the number of biallelically expressed imprinted genes in LOS fetuses. Furthermore, not only was there loss of allele-specific expression of imprinted genes in LOS, but also differential transcript amounts of these genes between control and overgrown fetuses. In summary, we characterized previously unidentified imprinted genes in bovines and identified misregulation of imprinting at multiple loci in LOS. We concluded that LOS is a multilocus LOI syndrome, as is BWS.

The yin and yang of kidney development and Wilms' tumors

Wilms' tumor, or nephroblastoma, is the most common pediatric renal cancer. The tumors morphologically resemble embryonic kidneys with a disrupted architecture and are associated with undifferentiated metanephric precursors. Here, we discuss genetic and epigenetic findings in Wilms' tumor in the context of renal development. Many of the genes implicated in Wilms' tumorigenesis are involved in the control of nephron progenitors or the microRNA (miRNA) processing pathway. Whereas the first group of genes has been extensively studied in normal development, the second finding suggests important roles for miRNAs in general-and specific miRNAs in particular-in normal kidney development that still await further analysis. The recent identification of Wilms' tumor cancer stem cells could provide a framework to integrate these pathways and translate them into new or improved therapeutic interventions.

Comparative methylome analysis identifies new tumour subtypes and biomarkers for transformation of nephrogenic rests into Wilms tumour

BACKGROUND

Wilms tumours (WTs) are characterised by several hallmarks that suggest epimutations such as aberrant DNA methylation are involved in tumour progression: loss of imprinting at 11p15, lack of recurrent mutations and formation of nephrogenic rests (NRs), which are lesions of retained undifferentiated embryonic tissue that can give rise to WTs.

METHODS

To identify such epimutations, we performed a comprehensive methylome analysis on 20 matched trios of micro-dissected WTs, NRs and surrounding normal kidneys (NKs) using Illumina Infinium HumanMethylation450 Bead Chips and functionally validated findings using RNA sequencing.

RESULTS

Comparison of NRs with NK revealed prominent tissue biomarkers: 629 differentially methylated regions, of which 55% were hypermethylated and enriched for domains that are bivalent in embryonic stem cells and for genes expressed during development (P = 2.49 × 10(-5)). Comparison of WTs with NRs revealed two WT subgroups; group-2 WTs and NRs were epigenetically indistinguishable whereas group-1 WTs showed an increase in methylation variability, hypomethylation of renal development genes, hypermethylation and relative loss of expression of cell adhesion genes and known and potential new WT tumour suppressor genes (CASP8, H19, MIR195, RB1 and TSPAN32) and was strongly associated with bilateral disease (P = 0.032). Comparison of WTs and NRs to embryonic kidney highlighted the significance of polycomb target methylation in Wilms tumourigenesis.

CONCLUSIONS

Methylation levels vary during cancer evolution. We have described biomarkers related to WT evolution from its precursor NRs which may be useful to differentiate between these tissues for patients with bilateral disease.

DNA methylation-mediated silencing of neuronatin (NNAT) in pig parthenogenetic fetuses

It is generally believed that aberrant expression of imprinted genes participates in growth retardation of mammalian parthenogenesis. Neuronatin (NNAT), a paternally expressed gene, plays important roles in neuronal growth and metabolic regulation. Here we have compared the gene expression and promoter methylation pattern of NNAT between pig normally fertilized (Con) and parthenogenetic (PA) embryos. The results showed loss of NNAT expression (p<0.001) and hypermethylation of NNAT promoter in PA samples. Additionally, partial methylation was observed in Con fetuses, while almost full methylation and unmethylation of NNAT promoter were apparent in Metaphase II (MII) oocytes and mature sperms, respectively, which identified the CpG promoter region as a putative differentially methylated region (DMR) of NNAT. The data demonstrate that promoter hypermethylation is associated with the silencing of NNAT in pig PA fetuses, which may be related to developmental failure of pig parthenogenesis at early stages.

Methylome analysis identifies a Wilms tumor epigenetic biomarker detectable in blood

BACKGROUND

Wilms tumor is the most common pediatric renal malignancy and there is a clinical need for a molecular biomarker to assess treatment response and predict relapse. The known mutated genes in this tumor type show low mutation frequencies, whereas aberrant methylation at 11p15 is by far the most common aberration. We therefore analyzed the epigenome, rather than the genome, to identify ubiquitous tumor-specific biomarkers.

RESULTS

Methylome analysis of matched normal kidney and Wilms tumor identifies 309 preliminary methylation variable positions which we translate into three differentially methylated regions (DMR) for use as tumor-specific biomarkers. Using two novel algorithms we show that these three DMRs are not confounded by cell type composition. We further show that these DMRs are not methylated in embryonic blastema but are intermediately methylated in Wilms tumor precursor lesions. We validate the biomarker DMRs using two independent sample sets of normal kidney and Wilms tumor and seven Wilms tumor histological subtypes, achieving 100% and 98% correct classification, respectively. As proof-of-principle for clinical utility, we successfully use biomarker DMR-2 in a pilot analysis of cell-free circulating DNA to monitor tumor response during treatment in ten patients.

CONCLUSIONS

These findings define the most common methylated regions in Wilms tumor known to date which are not associated with their embryonic origin or precursor stage. We show that this tumor-specific methylated DNA is released into the blood circulation where it can be detected non-invasively showing potential for clinical utility.

European guidance for the molecular diagnosis of pseudohypoparathyroidism not caused by point genetic variants at GNAS: an EQA study

Pseudohypoparathyroidism is a rare endocrine disorder that can be caused by genetic (mainly maternally inherited inactivating point mutations, although intragenic and gross deletions have rarely been reported) or epigenetic alterations at GNAS locus. Clinical and molecular characterization of this disease is not that easy because of phenotypic, biochemical and molecular overlapping features between both subtypes of the disease. The European Consortium for the study of PHP (EuroPHP) designed the present work with the intention of generating the standards of diagnostic clinical molecular (epi)genetic testing in PHP patients. With this aim, DNA samples of eight independent PHP patients carrying GNAS genetic and/or epigenetic defects (three patients with GNAS deletions, two with 20q uniparental disomy and three with a methylation defect of unknown origin) without GNAS point mutations were anonymized and sent to the five participant laboratories for their routine genetic analysis (methylation-specific (MS)-MLPA, pyrosequencing and EpiTYPER) and interpretations. All laboratories were able to detect methylation defects and, after the data analysis, the Consortium compared the results to define technical advantages and disadvantages of different techniques. To conclude, we propose as first-level investigation in PHP patients copy number and methylation analysis by MS-MLPA. Then, in patients with partial methylation defect, the result should be confirmed by single CpG bisulphite-based methods (ie pyrosequencing), whereas in case of a complete methylation defect without detectable deletion, microsatellites or SNP genotyping should be performed to exclude uniparental disomy 20.

Imprinting genes associated with endometriosis

PURPOSE

Much work has been carried out to investigate the genetic and epigenetic basis of endometriosis and proposed that endometriosis has been described as an epigenetic disease. The purpose of this study was to extract the imprinting genes that are associated with endometriosis development.

METHODS

The information on the imprinting genes can be accessed publicly from a web-based interface at http://www.geneimprint.com/site/genes-by-species.

RESULTS

In the current version, the database contains 150 human imprinted genes derived from the literature. We searched gene functions and their roles in particular biological processes or events, such as development and pathogenesis of endometriosis. From the genomic imprinting database, we picked 10 genes that were highly associated with female reproduction; prominent among them were paternally expressed genes (DIRAS3, BMP8B, CYP1B1, ZFAT, IGF2, MIMT1, or MIR296) and maternally expressed genes (DVL1, FGFRL1, or CDKN1C). These imprinted genes may be associated with reproductive biology such as endometriosis, pregnancy loss, decidualization process and preeclampsia.

DISCUSSION

This study supports the possibility that aberrant epigenetic dysregulation of specific imprinting genes may contribute to endometriosis predisposition.

Neuronatin gene: Imprinted and misfolded: Studies in Lafora disease, diabetes and cancer may implicate NNAT-aggregates as a common downstream participant in neuronal loss

Neuronatin (NNAT) is a ubiquitous and highly conserved mammalian gene involved in brain development. Its mRNA isoforms, chromosomal location, genomic DNA structure and regulation have been characterized. More recently there has been rapid progress in the understanding of its function in physiology and human disease. In particular there is fairly direct evidence implicating neuronatin in the causation of Lafora disease and diabetes. Neuronatin protein has a strong predisposition to misfold and form cellular aggregates that cause cell death by apoptosis. Aggregation of Neuronatin within cortical neurons and resulting cell death is the hallmark of Lafora disease, a progressive and fatal neurodegenerative disease. Under high glucose conditions simulating diabetes, neuronatin protein also accumulates and destroys pancreatic beta cells. The neuronatin gene is imprinted and only the paternal allele is normally expressed in the adult. However, changes in DNA methylation may cause the maternal allele to lose imprinting and trigger cell proliferation and metastasis. Neuronatin has also been shown to be translated peripherally within the dendrites of neurons, a finding of relevance in synaptic plasticity. The current understanding of the function of neuronatin raises the possibility that this gene may participate in the common downstream mechanisms associated with aberrant neuronal growth and death. A better understanding of these mechanisms may open new therapeutic targets to help modify the progression of devastating neurodegenerative conditions such as Alzheimer's and anterior horn cell disease.