Research Notes: Genes - MeCP2 (Methyl-CpG-binding Protein 2)

Hum Mol Genet. 2007 Mar 15.
FXYD1 is an MeCP2 target gene overexpressed in the brains of Rett syndrome patients and Mecp2-null mice.
Deng V, Matagne V, Banine F, Frerking M, Ohliger P, Budden S, Pevsner J, Dissen GA, Sherman LS, Ojeda SR.
Division of Neuroscience, Oregon National Primate Research Center, Beaverton, OR, USA.

Rett syndrome (RTT) is an X-linked neurodevelopmental disorder linked to heterozygous de novo mutations in the MECP2 gene. MECP2 encodes methyl-CpG-binding protein 2 (MeCP2), which represses gene transcription by binding to 5-methylcytosine residues in symmetrically positioned CpG dinucleotides. Direct MeCP2 targets underlying RTT pathogenesis remain largely unknown. Here, we report that FXYD1, which encodes a transmembrane modulator of Na(+), K(+) -ATPase activity, is elevated in frontal cortex (FC) neurons of RTT patients and Mecp2-null mice. Increasing neuronal FXDY1 expression is sufficient to reduce dendritic arborization and spine formation, hallmarks of RTT neuropathology. Mecp2-null mouse cortical neurons have diminished Na(+),K(+)-ATPase activity, suggesting that aberrant FXYD1 expression contributes to abnormal neuronal activity in RTT. MeCP2 represses Fxyd1 transcription through direct interactions with sequences in the Fxyd1 promoter that are methylated in FC neurons. FXYD1 is therefore a MeCP2 target gene whose de-repression may directly contribute to RTT neuronal pathogenesis.

Hum Mol Genet. 2007 Mar 15.
15q11-13 GABAA receptor genes are normally biallelically expressed in brain yet are subject to epigenetic dysregulation in autism-spectrum disorders.
Hogart A, Nagarajan RP, Patzel KA, Yasui DH, Lasalle JM.
Medical Microbiology and Immunology, Rowe Program in Human Genetics, School of Medicine, University of California, Davis, CA, USA.

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 genes, 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.

Epigenetics. 2006 Oct.
Reduced MeCP2 expression is frequent in autism frontal cortex and correlates with aberrant MECP2 promoter methylation.
Nagarajan RP, Hogart AR, Gwye Y, Martin MR, Lasalle JM.
Medical Microbiology and Immunology, Rowe Program in Human Genetics, School of Medicine, One Shields Ave, University of California, Davis, CA, USA.
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Mutations in MECP2, encoding methyl CpG binding protein 2 (MeCP2), cause most cases of Rett syndrome (RTT), an X-linked neurodevelopmental disorder. Both RTT and autism are "pervasive developmental disorders" and share a loss of social, cognitive and language skills and a gain in repetitive stereotyped behavior, following apparently normal perinatal development. Although MECP2 coding mutations are a rare cause of autism, MeCP2 expression defects were previously found in autism brain. To further study the role of MeCP2 in autism spectrum disorders (ASDs), we determined the frequency of MeCP2 expression defects in brain samples from autism and other ASDs. We also tested the hypotheses that MECP2 promoter mutations or aberrant promoter methylation correlate with reduced expression in cases of idiopathic autism. MeCP2 immunofluorescence in autism and other neurodevelopmental disorders was quantified by laser scanning cytometry and compared with control postmortem cerebral cortex samples on a large tissue microarray. A significant reduction in MeCP2 expression compared to age-matched controls was found in 11/14 autism (79%), 9/9 RTT (100%), 4/4 Angelman syndrome (100%), 3/4 Prader-Willi syndrome (75%), 3/5 Down syndrome (60%), and 2/2 attention deficit hyperactivity disorder (100%) frontal cortex samples. One autism female was heterozygous for a rare MECP2 promoter variant that correlated with reduced MeCP2 expression. A more frequent occurrence was significantly increased MECP2 promoter methylation in autism male frontal cortex compared to controls. Furthermore, percent promoter methylation of MECP2 significantly correlated with reduced MeCP2 protein expression. These results suggest that both genetic and epigenetic defects lead to reduced MeCP2 expression and may be important in the complex etiology of autism.

Proc Natl Acad Sci USA. 2005 Dec 6.
Regulation of RNA splicing by the methylation-dependent transcriptional repressor methyl-CpG binding protein 2.
Young JI, Hong EP, Castle JC, Crespo-Barreto J, Bowman AB, Rose MF, Kang D, Richman R, Johnson JM, Berget S, Zoghbi HY.
Department of Molecular and Human Genetics, Baylor College of Medicine, Houston, TX, USA.
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Rett syndrome (RTT) is a postnatal neurodevelopmental disorder characterized by the loss of acquired motor and language skills, autistic features, and unusual stereotyped movements. RTT is caused by mutations in the X-linked gene encoding methyl-CpG binding protein 2 (MeCP2). Mutations in MECP2 cause a variety of neurodevelopmental disorders including X-linked mental retardation, psychiatric disorders, and some cases of autism. Although MeCP2 was identified as a methylation-dependent transcriptional repressor, transcriptional profiling of RNAs from mice lacking MeCP2 did not reveal significant gene expression changes, suggesting that MeCP2 does not simply function as a global repressor. Changes in expression of a few genes have been observed, but these alterations do not explain the full spectrum of Rett-like phenotypes, raising the possibility that additional MeCP2 functions play a role in pathogenesis. In this study, we show that MeCP2 interacts with the RNA-binding protein Y box-binding protein 1 and regulates splicing of reporter minigenes. Importantly, we found aberrant alternative splicing patterns in a mouse model of RTT. Thus, we uncovered a previously uncharacterized function of MeCP2 that involves regulation of splicing, in addition to its role as a transcriptional repressor.

Hum Mol Genet. 2004 Mar 15.
Multiple pathways regulate MeCP2 expression in normal brain development and exhibit defects in autism-spectrum disorders.
Samaco RC, Nagarajan RP, Braunschweig D, LaSalle JM.
Medical Microbiology and Immunology, Rowe Program in Human Genetics, School of Medicine, University of California, Davis, USA.
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Rett syndrome (RTT) is a neurodevelopmental disorder caused by mutations in MECP2, encoding methyl-CpG-binding protein 2 (MeCP2). Although MECP2 is ubiquitously transcribed, MeCP2 expression is developmentally regulated and heterogeneous in neuronal subpopulations, defined as MeCP2(lo) and MeCP2(hi). To test the hypothesis that pathways affecting MeCP2 expression changes may be defective in RTT, autism and other neurodevelopmental disorders without MECP2 mutations, a high-throughput quantitation of MeCP2 expression was performed on a tissue microarray containing frontal cortex samples from 28 different patients with neurodevelopmental disorders and age-matched controls. Combined quantitative analyses of MeCP2 protein and alternatively polyadenylated transcript levels were performed by laser scanning cytometry and tested for significant differences from age-matched controls. Normal cerebral samples showed an increase in total MeCP2 expression and the percentage of MeCP2(hi) cells with age that could be explained by increased MECP2 transcription within the MeCP2(hi) population. A significant decrease in the relative usage of the long transcript in the MeCP2(lo) population was observed in postnatal compared to fetal brain, but alternate polyadenylation did not correlate with MeCP2 expression changes at the single cell level. Brain samples from several related neurodevelopmental disorders, including autism, pervasive developmental disorder, Prader-Willi and Angelman syndromes showed significant differences in MeCP2 expression from age-matched controls by apparently different transcriptional and post-transcriptional mechanisms. These results suggest that multiple pathways regulate the complex developmental expression of MeCP2 and are defective in autism-spectrum disorders in addition to RTT.

My abstract :-)

Rett syndrome is a neurodevelopmental disorder that presents with cognitive impairment and autistic behavior and is caused by mutations in the MECP2 gene (on chromosome X) which carries the instructions for making methyl-CpG-binding protein 2 (MeCP2). The MeCP2 protein, which is found throughout both fetal and adult brains, has two different forms - a short form which contains a 1.9 kb transcript from the MECP2 grene and a long form which contains a 10 kb-long transcript that includes the 1.9 kb coding region of MECP2 as well as an exceptionally long untranslated region. To make things more complicated, some brain neurons have relatively high levels of the MeCP2 protein and are called MeCP2(hi) neurons, while other neurons have relatively low levels of MeCP2 and are called MeCP2(lo) neurons.

MeCP2 expression is developmentally regulated, that is, there are changes in the total amount of MeCP2 protein in the brain according to age, as well as changes in the amounts of short and long transcript forms of MeCP2 and changes in the number of MeCP2(lo) and MeCP2(hi) neurons. During normal brain development, the total amount of MeCP2 increases and there is a progressive increase in the number of MeCP2(hi) neurons from infancy to adulthood. At the same time, the amount of long-transcript MeCP2 falls relative to the amount of short-transcript MeCP2, even though juvenile and adult MeCP2(hi) neurons have more long-transcript MeCP2 than juvenile and adult MeCP2(lo) neurons.

In PWS, there are significantly higher MeCP2 levels in the MeCP2(hi) neurons compared to control subjects, even though total MECP2 levels are significantly lower. In addition, there are higher levels of both short and long-transcript MECP2 proteins in PWS. In other words, PWS brains do not shift to more MeCP2(hi) neurons during growth, nor does the normal fall in the amount of long-transcript MeCP2 occur. That means that the loss of expression of the genetic information on the paternal chromosome 15 gene that occurs in PWS somehow affects the expression of the MECP2 gene on chromosome X.