Epigenetic mark sequence of the H19 gene in human sperm

DNA methylation patterns at the IGF2-H19 locus in sperm of Swiss Landrace and Swiss Large White boars

DNA methylation patterns at the IGF2-H19 locus were investigated in sperm DNA from Swiss Landrace (SL) and Swiss Large White (LW) boars. The putative IGF2 differentially methylated regions (DMR) 0, 1 and 2, a quantitative trait nucleotide (QTN) region in the intron 3 and a CpG island in the intron 4 of the IGF2 gene as well as three regions around porcine CTCF binding sites within the H19 differentially methylated domain (DMD) were selected for the DNA methylation analysis. In both breeds putative IGF2 DMR0, 1, 2 and H19 DMD were hypermethylated. Significant differences in DNA methylation content were found between the two breeds in the two DMD regions proximal to the H19 gene. The IGF2 QTN region and the CpG island in the IGF2 intron 4 were hypomethylated in sperm DNA of both breeds. The methylation analysis revealed significantly more methylated CpG sites in the intron 4 of sperm from the LW breed than in that from SL. No difference was found in global DNA methylation between the two breeds. These results indicate differences in DNA methylation patterns between breeds and it remains to be established whether variation in DNA methylation patterns impacts on phenotypic traits.

Methylation status of differentially methylated regions at Igf2/H19 locus in porcine gametes and preimplantation embryos

The aim of this study was to demonstrate how differential methylation imprints are established during porcine preimplantation embryo development. For the methylation analysis, the primers for the three Igf2/H19 DMRs were designed and based upon previously published sequences. The methylation marks of Igf2/H19 DMRs were analysed in sperm and MII oocytes with our results showing that these regions are fully methylated in sperm but remain unmethylated in MII oocytes. In order to identify the methylation pattern at the pronuclear stage, we indirectly compared the methylation profile of Igf2/H19 DMR3 in each zygote derived by in vitro fertilization, parthenogenesis, and androgenesis. Interestingly, this region was found to be differently methylated according to parental origins; DMR3 was hemimethylated in in vitro fertilized zygotes, fully methylated in parthenogenetic zygotes, and demethylated in androgenetic zygotes. These results indicate that the methylation mark of the paternal allele is erased by active demethylation, and that of the maternal one is de novo methylated. We further examined the methylation imprints of Igf2/H19 DMR3 during early embryonic development. The hemimethylated pattern as seen in zygotes fertilized in vitro was observed up to the 4-cell embryo stage. However, this mark was exclusively demethylated at the 8-cell stage and then restored at the morula stage. These results suggest that methylation imprints are established via dynamic changes during early embryonic development in porcine embryos.

IGF2/H19 hypomethylation in Silver-Russell syndrome and isolated hemihypoplasia

Silver-Russell syndrome (SRS) is a clinically and genetically heterogeneous syndrome characterized by severe pre and postnatal growth retardation, body asymmetry and a typical facial phenotype with a triangular face and relative macrocephaly. In 30% of patients, the differentially methylated IGF2/H19 imprinting center region (ICR1) on chromosome 11p15 was found to be hypomethylated, as determined by Southern blot analysis of an HpaII restriction site close to the third CTCF-binding site (CTS3) within ICR1. Using bisulfite treatment and a real-time PCR-based methylation assay (QAMA), we analyzed the third and sixth CTCF-binding sites (CTS3, CTS6) in 5 patients with CTS3 hypomethylation, in 14 patients who were suspected to have SRS but were normal by Southern blot analysis, and in 1 patient with body asymmetry without any other features of SRS or Beckwith-Wiedemann syndrome (BWS). In all 5 patients with CTS3 hypomethylation, in 5 of 14 patients who were judged to be normal at CTS3 by Southern blot analysis and in the patient with isolated body asymmetry, we found CTS3 and CTS6 hypomethylation by QAMA. Using methylation-specific multiplex ligation-dependent probe amplification (MS-MLPA), we obtained similar results at four additional ICR1 sites in the CTS6 region. These results show that ICR1 hypomethylation occurs more often in SRS patients than as previously thought as well as in isolated hemihypoplasia. Furthermore, we show that methylation analysis by QAMA and MLPA is more sensitive in detecting ICR1 hypomethylation than Southern blot analysis of CTS3.

The epigenetic imprinting defect of patients with Beckwith-Wiedemann syndrome born after assisted reproductive technology is not restricted to the 11p15 region

BACKGROUND

Genomic imprinting refers to an epigenetic marking resulting in monoallelic gene expression and has a critical role in fetal development. Various imprinting diseases have recently been reported in humans and animals born after the use of assisted reproductive technology (ART). All the epimutations implicated involve a loss of methylation of the maternal allele (demethylation of KvDMR1/KCNQ1OT1 in Beckwith-Wiedemann syndrome (BWS), demethylation of SNRPN in Angelman syndrome and demethylation of DMR2/IGF2R in large offspring syndrome), suggesting that ART impairs the acquisition or maintenance of methylation marks on maternal imprinted genes. However, it is unknown whether this epigenetic imprinting error is random or restricted to a specific imprinted domain.

AIM

To analyse the methylation status of various imprinted genes (IGF2R gene at 6q26, PEG1/MEST at 7q32, KCNQ1OT1 and H19 at 11p15.5, and SNRPN at 15q11-13) in 40 patients with BWS showing a loss of methylation at KCNQ1OT1 (11 patients with BWS born after the use of ART and 29 patients with BWS conceived naturally).

RESULTS

3 of the 11 (27%) patients conceived using ART and 7 of the 29 (24%) patients conceived normally displayed an abnormal methylation at a locus other than KCNQ1OT1.

CONCLUSIONS

Some patients with BWS show abnormal methylation at loci other than the 11p15 region, and the involvement of other loci is not restricted to patients with BWS born after ART was used. Moreover, the mosaic distribution of epimutations suggests that imprinting is lost after fertilisation owing to a failure to maintain methylation marks during pre-implantation development.

Applicability of the parentally imprinted allele (PIA) typing of a VNTR upstream the H19 gene to forensic samples of different tissues

The parentally imprinted allele (PIA) typing that we have recently developed determines parental alleles at a VNTR locus in the differentially methylated region upstream of the human H19 gene. The usefulness of this typing was demonstrated by its application to blood samples in paternity cases. However, its applicability to other tissue DNA remains to be tested. DNA samples from fifteen different postmortem tissues such as cerebrum, skeletal muscle and skin were examined, all of which were obtained from three autopsy cases 2-11h after death. DNA was digested with a methylation-sensitive HhaI enzyme and diluted solutions of the digests were subjected to the first PCR amplification, providing amplification of only the paternal H19 methylated allele. Subsequent VNTR typing was carried out for the amplified products to determine which allele was of paternal origin. No tissue-dependent difference was observed and all the samples examined, though degraded, were successfully used for determining the paternal allele. These results substantiate the usefulness of PIA typing in forensic examinations. Its application to two identity cases, a burned male body and a male body with adipocere formation, was also shown.

Reproductive epigenetics

Epigenetics refers to covalent modifications of DNA and core histones that regulate gene activity without altering DNA sequence. To date, the best-characterized DNA modification associated with the modulation of gene activity is methylation of cytosine residues within CpG dinucleotides. Human disorders associated with epigenetic abnormalities include rare imprinting diseases, molar pregnancies, and childhood cancers. Germ cell development and early embryo development are critical times when epigenetic patterns are initiated or maintained. This review focuses on the epigenetic modification DNA methylation and discusses recent progress that has been made in understanding when and how epigenetic patterns are differentially established in the male and female germlines, the mouse, and human disorders associated with abnormalities in epigenetic programming in germ cells and early embryos, as well as genetic and other modulators (e.g. nutrition and drugs) of reproductive epigenetic events.

Transcriptional derepression as a cause of genetic diseases

Transcription of DNA into mRNA is a highly regulated process directed by a complex molecular machine comprising more than 100 proteins. Regulation of transcription occurs by both positive (transcriptional activation) and negative (transcriptional repression) mechanisms. Recently, inappropriate transcriptional derepression has been found as the underlying basis of several human genetic diseases. The putative target genes, whose inappropriate expression is thought to cause disease, have remained elusive but are being searched for intensively.