The human homologue (PEG3) of the mouse paternally expressed gene 3 (Peg3) is maternally imprinted but not mutated in women with familial recurrent hydatidiform molar pregnancies
We mapped a locus for autosomal recessive molar pregnancies with biparental genomic contribution to chromosome 19q13.4 between D19S924 and D19S890. This 5-Mb region is homologous to proximal mouse chromosome 7 and contains a cluster of Krüppel-type zinc finger genes, including the human homologue of the mouse imprinted genes: the paternally expressed gene 3 (PEG3) and the maternally expressed Zim1 genes. We analyzed the PEG3 gene for mutations in women with familial recurrent hydatidiform moles and to determine its imprinting status in humans.
We used database searches and screened cDNA libraries to find the complete genomic structure of PEG3. Polymerase chain reaction (PCR) amplification and direct sequencing of coding exons and flanking introns were performed on genomic DNA from the affected women. Allele-specific methylation and expression were studied by methylation-sensitive Southern analysis of a 5' located CpG island and by reverse-transcription PCR of total lymphoblast-derived RNA of normal individuals who were informative for two expressed polymorphisms.
We did not detect any mutations in the coding region of PEG3 in the affected women. We observed allele-specific methylation of the CpG island and expression from the paternal allele in two independent informative pedigrees.
Consistent with the findings in the mouse, the human PEG3 gene is expressed from the paternal allele. Our data support that PEG3 is not mutated in women with familial recurrent hydatidiform moles, although mutations in the regulatory regions that might affect imprinting or transcriptional level of the gene could not be evaluated.
Available from: Donagh P Berry
- "The paternally expressed PEG3 gene encodes a Krüppel-type zinc finger protein that may play a role in transcriptional regulation [72-74]. Also, the murine ortholog of this gene, Peg3, has been shown to be critical in cellular and behavioural functions including cellular proliferation, apoptosis and nurturing behaviour [40,75]. The role of the maternally expressed ZIM2 gene is less well understood, but it has been shown to share at least seven upstream exons and a transcriptional start site with PEG3 in humans, suggesting some similarities for the function of the PEG3 and ZIM2 gene products . "
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ABSTRACT: Studies in mice and humans have shown that imprinted genes, whereby expression from one of the two parentally inherited alleles is attenuated or completely silenced, have a major effect on mammalian growth, metabolism and physiology. More recently, investigations in livestock species indicate that genes subject to this type of epigenetic regulation contribute to, or are associated with, several performance traits, most notably muscle mass and fat deposition. In the present study, a candidate gene approach was adopted to assess 17 validated single nucleotide polymorphisms (SNPs) and their association with a range of performance traits in 848 progeny-tested Irish Holstein-Friesian artificial insemination sires. These SNPs are located proximal to, or within, the bovine orthologs of eight genes (CALCR, GRB10, PEG3, PHLDA2, RASGRF1, TSPAN32, ZIM2 and ZNF215) that have been shown to be imprinted in cattle or in at least one other mammalian species (i.e. human/mouse/pig/sheep).
Heterozygosities for all SNPs analysed ranged from 0.09 to 0.46 and significant deviations from Hardy-Weinberg proportions (P ≤ 0.01) were observed at four loci. Phenotypic associations (P ≤ 0.05) were observed between nine SNPs proximal to, or within, six of the eight analysed genes and a number of performance traits evaluated, including milk protein percentage, somatic cell count, culled cow and progeny carcass weight, angularity, body conditioning score, progeny carcass conformation, body depth, rump angle, rump width, animal stature, calving difficulty, gestation length and calf perinatal mortality. Notably, SNPs within the imprinted paternally expressed gene 3 (PEG3) gene cluster were associated (P ≤ 0.05) with calving, calf performance and fertility traits, while a single SNP in the zinc finger protein 215 gene (ZNF215) was associated with milk protein percentage (P ≤ 0.05), progeny carcass weight (P ≤ 0.05), culled cow carcass weight (P ≤ 0.01), angularity (P ≤ 0.01), body depth (P ≤ 0.01), rump width (P ≤ 0.01) and animal stature (P ≤ 0.01).
Of the eight candidate bovine imprinted genes assessed, DNA sequence polymorphisms in six of these genes (CALCR, GRB10, PEG3, RASGRF1, ZIM2 and ZNF215) displayed associations with several of the phenotypes included for analyses. The genotype-phenotype associations detected here are further supported by the biological function of these six genes, each of which plays important roles in mammalian growth, development and physiology. The associations between SNPs within the imprinted PEG3 gene cluster and traits related to calving, calf performance and gestation length suggest that this domain on chromosome 18 may play a role regulating pre-natal growth and development and fertility. SNPs within the bovine ZNF215 gene were associated with bovine growth and body conformation traits and studies in humans have revealed that the human ZNF215 ortholog belongs to the imprinted gene cluster associated with Beckwith-Wiedemann syndrome--a genetic disorder characterised by growth abnormalities. Similarly, the data presented here suggest that the ZNF215 gene may have an important role in regulating bovine growth. Collectively, our results support previous work showing that (candidate) imprinted genes/loci contribute to heritable variation in bovine performance traits and suggest that DNA sequence polymorphisms within these genes/loci represents an important reservoir of genomic markers for future genetic improvement of dairy and beef cattle populations.
Available from: ncbi.nlm.nih.gov
- "Once we obtain the imprinting status of human and cow ZIM3, it is possible that the relationship between this genomic deletion and the imprinting status of the surrounding genes will be clarified. PEG3 expression is silenced in various tumor types, including gliomas, choriocarcinomas, and ovarian tumors (Maegawa et al., 2001; Van den Veyver et al., 2001). This silencing of human PEG3 was found to be a result of DNA methylation (Murphy et al., 2001). "
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ABSTRACT: In this study, we performed the first systematic survey of DNA methylation status of the CpG islands of the PEG3 (Paternally expressed gene 3) imprinted domain in the mouse, cow, and human genomes. Previous studies have shown that the region surrounding the first exon of PEG3 contains a differentially methylated CpG island. In addition, we have discovered two previously unreported differentially methylated regions (DMR): one in the promoter region of mouse Zim3 and another in the promoter region of human USP29. In the cow, the Peg3-CpG island was the only area that showed DMR status. We have also examined the methylation status of several CpG islands in this region using human tumor-derived DNA. The CpG islands near PEG3 and USP29 both showed hypermethylation in DNA derived from breast and ovarian tumors. Overall, this study shows that the PEG3 imprinted domain of humans, cows, and mice contains differing numbers of DMRs, but the PEG3-CpG island is the only DMR that is conserved among these three species.
Available from: humupd.oxfordjournals.org
- "The original 15.2 cM critical interval encompassed the imprinted PEG3/ZIM2 locus (paternally expressed gene 3/zinc- finger gene 2 from imprinted domain) (Kim et al., 2000; Van den Veyver et al., 2001). PEG3 is the human homologue of the imprinted mouse Peg3 gene, is highly expressed in placenta and is silenced from the maternal allele in both human and mouse (Kuroiwa et al., 1996; Hiby et al., 2001). "
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ABSTRACT: Highly recurrent hydatidiform moles (HMs) studied to date are not androgenetic but have biparental genomic contribution (BiHM). Affected women have an autosomal recessive mutation that causes their pregnancies to develop into HM. Although there is genetic heterogeneity, a major locus maps to chromosome 19q13.42, but a mutated gene has not yet been identified. Molecular studies have shown that maternal imprinting marks are deregulated in the BiHM trophoblast. The mutations that cause this condition are, therefore, hypothesized to occur in genes that encode transacting factors required for the establishment of imprinting marks in the maternal germline or for their maintenance in the embryo. Although only DNA methylation marks at imprinted loci have been studied in the BiHM, the mutation may affect genes that are essential for other forms of chromatin remodelling at imprinted loci and necessary for correct maternal allele-specific DNA methylation and imprinted gene expression. Normal pregnancies interspersed with BiHM have been reported in some of the pedigrees, but affected women repeatedly attempting pregnancy should be counselled about the risk for invasive trophoblastic disease with each subsequent BiHM.
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