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Query: UNIPROT:P06889 (Mol)
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Rett syndrome (RS) is a severe and progressive neurodevelopmental disorder caused by heterozygous mutations in the X-linked methyl CpG binding protein 2 (MeCP2) gene. MeCP2 is a nuclear protein that binds specifically to methylated DNA and functions as a general transcription repressor in the context of chromatin remodeling complexes. RS shares clinical features with those of Angelman syndrome (AS), an imprinting neurodevelopmental disorder. In AS patients, the maternally expressed copy of UBE3A that codes for the ubiquitin protein ligase 3A (E6-AP) is repressed. The similar phenotype of these two syndromes led us to hypothesize that part of the RS phenotype is due to MeCP2-associated silencing of UBE3A. Indeed, UBE3A mRNA and protein are shown here to be significantly reduced in human and mouse MECP2 deficient brains. This reduced UBE3A level was associated with biallelic production of the UBE3A antisense RNA. In addition, MeCP2 deficiency resulted in elevated histone H3 acetylation and H3(K4) methylation and reduced H3(K9) methylation at the PWS/AS imprinting center, with no effect on DNA methylation or SNRPN expression. We conclude, therefore, that MeCP2 deficiency causes epigenetic aberrations at the PWS imprinting center. These changes in histone modifications result in loss of imprinting of the UBE3A antisense gene in the brain, increase in UBE3A antisense RNA level and, consequently reduction in UBE3A production.
Hum Mol Genet 2005 Apr 15
PMID:MeCP2 deficiency in Rett syndrome causes epigenetic aberrations at the PWS/AS imprinting center that affects UBE3A expression. 1575 75

In the past 25 years, the frequency of assisted reproductive technology (ART) births has increased rapidly to account for 1-2% of all births in many developed countries. ART procedures such as in vitro fertilization and intracytoplasmic sperm injection are generally considered to be safe, but recent studies suggest a small excess of birth defects and low-birth weight in ART children. In addition, several clinical studies have reported an increased frequency of ART conceptions among children with Beckwith-Wiedemann syndrome or Angelman syndrome caused by an imprinting defect. Although these studies require further confirmation, they are consistent with animal studies reporting disordered expression and epigenetic changes in imprinted genes following in vitro embryo culture. The absolute risk of an imprinting disorder after ART appears to be very small, but further data are required to determine whether the association between ART and human imprinting disorders reflects the effect of embryo culture (or some other aspect of ART) and/or a common mechanism for infertility and imprinting disorders. Retinoblastoma and neurodevelopmental defects have been only tentatively linked to ART, but in view of the role of epigenetic processes in the regulation of gene expression in development and cancer, further research is required into long-term health outcomes for ART children and the epigenetic consequences of ART protocols.
Hum Mol Genet 2005 Apr 15
PMID:Imprinting and assisted reproductive technology. 1580 65

Recent studies suggest that IVF and assisted reproduction technologies (ART) may result in abnormal genomic imprinting, leading to an increased frequency of Angelman syndrome (AS) and Beckwith-Weidemann syndrome (BWS) in IVF children. To learn how ART might alter the epigenome, we examined morulas and blastocysts derived from C57BL/6J X M. spretus F1 mice conceived in vivo and in vitro and determined the allelic expression of four imprinted genes: Igf2, H19, Cdkn1c and Slc221L. IVF-derived mouse embryos that were cultured in human tubal fluid (HTF) (Quinn's advantage) media displayed a high frequency of aberrant H19 imprinting, whereas in vivo and IVF embryos showed normal maternal expression of Cdkn1c and normal biallelic expression of Igf2 and Slc221L. Embryonic stem (ES) cells derived from IVF blastocysts also showed abnormal Igf2/H19 imprinting. Allele-specific bisulphite PCR reveals abnormal DNA methylation at a CCCTC-binding factor (CTCF) site in the imprinting control region (ICR), as the normally unmethylated maternal allele acquired a paternal methylation pattern. Chromatin immunoprecipitation (ChIP) assays indicate an increase of lysine 4 methylation (dimethyl Lys4-H3) on the paternal chromatin and a gain in lysine 9 methylation (trimethyl Lys9-H3) on the maternal chromatin at the same CTCF-binding site. Our results indicate that de novo DNA methylation on the maternal allele and allele-specific acquisition of histone methylation lead to aberrant Igf2/H19 imprinting in IVF-derived ES cells. We suggest that ART, which includes IVF and various culture media, might cause imprinting errors that involve both aberrant DNA methylation and histone methylation at an epigenetic switch of the Igf2-H19 gene region.
Mol Hum Reprod 2005 Sep
PMID:IVF results in de novo DNA methylation and histone methylation at an Igf2-H19 imprinting epigenetic switch. 1621 28

Prader-Willi syndrome (PWS) and Angelman syndrome (AS) are caused by the loss of imprinted gene expression from chromosome 15q11-q13. Imprinted gene expression in the region is regulated by a bipartite imprinting centre (IC), comprising the PWS-IC and the AS-IC. The PWS-IC is a positive regulatory element required for bidirectional activation of a number of paternally expressed genes. The function of the AS-IC appears to be to suppress PWS-IC function on the maternal chromosome through a methylation imprint acquired during female gametogenesis. Here we have placed the entire mouse locus under the control of a human PWS-IC by targeted replacement of the mouse PWS-IC with the equivalent human region. Paternal inheritance of the human PWS-IC demonstrates for the first time that a positive regulatory element in the PWS-IC has diverged. These mice show postnatal lethality and growth deficiency, phenotypes not previously attributed directly to the affected genes. Following maternal inheritance, the human PWS-IC is able to acquire a methylation imprint in mouse oocytes, suggesting that acquisition of the methylation imprint is conserved. However, the imprint is lost in somatic cells, showing that maintenance has diverged. This maternal imprinting defect results in expression of maternal Ube3a-as and repression of Ube3a in cis, providing evidence that Ube3a is regulated by its antisense and creating the first reported mouse model for AS imprinting defects.
Hum Mol Genet 2006 Feb 01
PMID:A human imprinting centre demonstrates conserved acquisition but diverged maintenance of imprinting in a mouse model for Angelman syndrome imprinting defects. 1636 7

Rett syndrome (RTT) is a neurodevelopmental disorder characterized by cognitive regression, loss of purposeful hand movements and speech, stereotypies, ataxia, seizures, mental retardation and acquired microcephaly. Mutations in MECP2, encoding methyl-CpG-binding protein 2, are responsible for approximately 90% of classic RTT cases. RTT displays phenotypic overlap with Angelman syndrome, a disorder caused by loss of expression of the imprinted gene UBE3A. MeCP2 binds to methylated DNA and may alter the expression of imprinted genes, thereby suggesting a mechanistic link between the two disorders. Here, we tested the hypothesis that MeCP2 deficiency affects expression of Ube3a in mouse models of RTT. As Ube3a is only imprinted in brain, we evaluated Ube3a expression in brains of 15 different litters of neonatal or 8-week-old male Mecp2 mutant mice by real-time quantitative RT-PCR and western blot analysis. We found no significant differences between Mecp2(tm1.1Bird/Y) or Mecp2(tm1.1Jae/Y) mutants and their wild-type male siblings that served as negative controls. In positive control mice carrying a maternally inherited Ube3a deletion, Ube3a sense transcript and protein levels were drastically reduced. Our data contrast with two recent reports of substantially decreased Ube3a expression in brain tissues of MeCP2-deficient mice. We, therefore, challenge the conclusion that decreased UBE3A/Ube3a expression contributes to the pathophysiology of RTT.
Hum Mol Genet 2006 Jul 15
PMID:Ube3a expression is not altered in Mecp2 mutant mice. 1675 45

We applied genetic tools available in Drosophila to identify candidate substrates of the UBE3A ubiquitin ligase, the gene responsible for Angelman syndrome (AS). Human UBE3A was expressed in Drosophila heads to identify proteins differentially regulated in UBE3A-expressing versus wild-type extracts. Using two-dimensional gel and MALDI-TOF analysis, we detected 20 proteins that were differentially regulated by over-expression of human UBE3A in Drosophila heads. One protein responsive to UBE3A was the Rho-GEF pebble (pbl). Here, we present three lines of evidence suggesting that UBE3A regulates Pbl. First, we show genetic evidence that UBE3A and the Drosophila de-ubiquitinase fat facets (faf) exert opposing effects on Pbl function. Secondly, we find that both Pbl and ECT2, the mammalian orthologue of Pbl called epithelial cell transforming sequence 2 oncogene, physically interact with their respective ubiquitin E3 ligases. Finally, we show that Ect2 expression is regulated by Ube3a in mouse neurons as the pattern of Ect2 expression is dramatically altered in the hippocampus and cerebellum of Ube3a null mice. These results suggest that an orthologous UBE3A post-translational regulatory pathway regulates neuronal outgrowth in the mammalian brain and that dysregulation of this pathway may result in neurological phenotypes including AS and possibly other autism spectrum disorders.
Hum Mol Genet 2006 Sep 15
PMID:Expression of the Rho-GEF Pbl/ECT2 is regulated by the UBE3A E3 ubiquitin ligase. 1690 59

Standard methods used for genomic methylation analysis allow the detection of complete absence of either methylated or non-methylated alleles but are usually unable to detect changes in the proportion of methylated and unmethylated alleles. We compare two methods for quantitative methylation analysis, using the chromosome 15q11-q13 imprinted region as model. Absence of the non-methylated paternal allele in this region leads to Prader-Willi syndrome (PWS) whilst absence of the methylated maternal allele results in Angelman syndrome (AS). A proportion of AS is caused by mosaic imprinting defects which may be missed with standard methods and require quantitative analysis for their detection. Sequence-based quantitative methylation analysis (SeQMA) involves quantitative comparison of peaks generated through sequencing reactions after bisulfite treatment. It is simple, cost-effective and can be easily established for a large number of genes. However, our results support previous suggestions that methods based on bisulfite treatment may be problematic for exact quantification of methylation status. Methylation-specific multiplex ligation-dependent probe amplification (MS-MLPA) avoids bisulfite treatment. It detects changes in both CpG methylation as well as copy number of up to 40 chromosomal sequences in one simple reaction. Once established in a laboratory setting, the method is more accurate, reliable and less time consuming.
Mol Cell Probes 2007 Jun
PMID:Quantification of the methylation status of the PWS/AS imprinted region: comparison of two approaches based on bisulfite sequencing and methylation-sensitive MLPA. 1730 79

Human chromosome 15q11-13 is a complex locus containing imprinted genes as well as a cluster of three GABA(A) receptor subunit (GABR) genes-GABRB3, GABRA5 and GABRG3. Deletion or duplication of 15q11-13 GABR genes occurs in multiple human neurodevelopmental disorders including Prader-Willi syndrome (PWS), Angelman syndrome (AS) and autism. GABRB3 protein expression is also reduced in Rett syndrome (RTT), caused by mutations in MECP2 on Xq28. Although Gabrb3 is biallelically expressed in mouse brain, conflicting data exist regarding the imprinting status of the 15q11-13 GABR genes in humans. Using coding single nucleotide polymorphisms we show that all three GABR genes are biallelically expressed in 21 control brain samples, demonstrating that these genes are not imprinted in normal human cortex. Interestingly, four of eight autism and one of five RTT brain samples showed monoallelic or highly skewed allelic expression of one or more GABR gene, suggesting that epigenetic dysregulation of these genes is common to both disorders. Quantitative real-time RT-PCR analysis of PWS and AS samples with paternal and maternal 15q11-13 deletions revealed a paternal expression bias of GABRB3, while RTT brain samples showed a significant reduction in GABRB3 and UBE3A. Chromatin immunoprecipitation and bisulfite sequencing in SH-SY5Y neuroblastoma cells demonstrated that MeCP2 binds to methylated CpG sites within GABRB3. Our previous studies demonstrated that homologous 15q11-13 pairing in neurons was dependent on MeCP2 and was disrupted in RTT and autism cortex. Combined, these results suggest that MeCP2 acts as a chromatin organizer for optimal expression of both alleles of GABRB3 in neurons.
Hum Mol Genet 2007 Mar 15
PMID:15q11-13 GABAA receptor genes are normally biallelically expressed in brain yet are subject to epigenetic dysregulation in autism-spectrum disorders. 1733 70

Angelman syndrome (AS) is a neurogenetic disorder characterized by severe mental retardation, ataxia, seizures, EEG abnormalities and bouts of inappropriate laughter. AS individuals fail to inherit a normal active maternal copy of ubiquitin protein ligase E3A (UBE3A). UBE3A is subject to genomic imprinting, with predominant transcription of the maternal allele in brain. The known genetic causes of AS are maternal deletion of chromosome 15q11-q13, paternal chromosome 15 uniparental disomy, UBE3A mutation and an abnormality of the imprinting process, termed imprinting defect. There remain major questions concerning the molecular pathogenesis of AS, including: 1) the mechanisms underlying the imprinting defect class of AS, 2) the identity of proteins targeted by UBE3A, 3) the role of a noncoding antisense transcript in regulating UBE3A imprinting and 4) the contribution of other genes such as methyl-binding CpG-binding protein 2 and gamma-aminobutyric acid A receptor, subunit beta3 to the AS phenotype.
Cell Mol Life Sci 2007 Apr
PMID:Molecular epigenetics of Angelman syndrome. 1734 96

We analyzed the distribution of long interspersed nuclear elements (LINE)-1 (L1) along mouse autosomes at a 1-Mb scale, and found a unique combination of high density and strand asymmetry of L1 elements at the imprinted Prader-Willi syndrome/Angelman syndrome (PWS/AS) locus on mouse chromosome 7. This L1 signature overlaps the paternally expressed domain of the locus, excluding the maternally expressed Ube3a gene, and is conserved in rat and human. Unlike the PWS/AS locus, other instances of high L1 density and strand asymmetry in the mouse are not associated with imprinted regions and are not evolutionarily conserved in human. The evolutionary conservation of the L1 signature at the PWS/AS locus despite differences in composition of L1 elements between rodent and human, requires a mechanism for active perpetuation of L1 asymmetry during bursts of L1 activity, and indicates a possible functional role for L1 elements at this locus. Aside from the PWS/AS locus, rodents have a far greater correlation of L1 densities between DNA strands than do humans; we provide evidence that this difference in interstrand correlation between the two taxa is due largely to the difference in average age of the dominant L1 families.
J Mol Evol 2007 Oct
PMID:Unique retrotransposon LINE-1 distribution at the Prader-Willi Angelman syndrome locus. 1793 19


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