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      Rett syndrome is caused by mutations in X-linked MECP2, encoding methyl-CpG-binding protein 2

      , , , , ,

      Nature Genetics

      Springer Science and Business Media LLC

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          Abstract

          Rett syndrome (RTT, MIM 312750) is a progressive neurodevelopmental disorder and one of the most common causes of mental retardation in females, with an incidence of 1 in 10,000-15,000 (ref. 2). Patients with classic RTT appear to develop normally until 6-18 months of age, then gradually lose speech and purposeful hand use, and develop microcephaly, seizures, autism, ataxia, intermittent hyperventilation and stereotypic hand movements. After initial regression, the condition stabilizes and patients usually survive into adulthood. As RTT occurs almost exclusively in females, it has been proposed that RTT is caused by an X-linked dominant mutation with lethality in hemizygous males. Previous exclusion mapping studies using RTT families mapped the locus to Xq28 (refs 6,9,10,11). Using a systematic gene screening approach, we have identified mutations in the gene (MECP2 ) encoding X-linked methyl-CpG-binding protein 2 (MeCP2) as the cause of some cases of RTT. MeCP2 selectively binds CpG dinucleotides in the mammalian genome and mediates transcriptional repression through interaction with histone deacetylase and the corepressor SIN3A (refs 12,13). In 5 of 21 sporadic patients, we found 3 de novo missense mutations in the region encoding the highly conserved methyl-binding domain (MBD) as well as a de novo frameshift and a de novo nonsense mutation, both of which disrupt the transcription repression domain (TRD). In two affected half-sisters of a RTT family, we found segregation of an additional missense mutation not detected in their obligate carrier mother. This suggests that the mother is a germline mosaic for this mutation. Our study reports the first disease-causing mutations in RTT and points to abnormal epigenetic regulation as the mechanism underlying the pathogenesis of RTT.

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          Most cited references 20

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          Methylated DNA and MeCP2 recruit histone deacetylase to repress transcription.

          CpG methylation in vertebrates correlates with alterations in chromatin structure and gene silencing. Differences in DNA-methylation status are associated with imprinting phenomena and carcinogenesis. In Xenopus laevis oocytes, DNA methylation dominantly silences transcription through the assembly of a repressive nucleosomal array. Methylated DNA assembled into chromatin binds the transcriptional repressor MeCP2 which cofractionates with Sin3 and histone deacetylase. Silencing conferred by MeCP2 and methylated DNA can be relieved by inhibition of histone deacetylase, facilitating the remodelling of chromatin and transcriptional activation. These results establish a direct causal relationship between DNA methylation-dependent transcriptional silencing and the modification of chromatin.
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            Identification and characterization of a family of mammalian methyl-CpG binding proteins.

            Methylation at the DNA sequence 5'-CpG is required for mouse development. MeCP2 and MBD1 (formerly PCM1) are two known proteins that bind specifically to methylated DNA via a related amino acid motif and that can repress transcription. We describe here three novel human and mouse proteins (MBD2, MBD3, and MBD4) that contain the methyl-CpG binding domain. MBD2 and MBD4 bind specifically to methylated DNA in vitro. Expression of MBD2 and MBD4 tagged with green fluorescent protein in mouse cells shows that both proteins colocalize with foci of heavily methylated satellite DNA. Localization is disrupted in cells that have greatly reduced levels of CpG methylation. MBD3 does not bind methylated DNA in vivo or in vitro. MBD1, MBD2, MBD3, and MBD4 are expressed in somatic tissues, but MBD1 and MBD2 expression is reduced or absent in embryonic stem cells which are known to be deficient in MeCP1 activity. The data demonstrate that MBD2 and MBD4 bind specifically to methyl-CpG in vitro and in vivo and are therefore likely to be mediators of the biological consequences of the methylation signal.
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              MeCP2 is a transcriptional repressor with abundant binding sites in genomic chromatin.

               X Nan,  F Campoy,  Gregory Bird (1997)
              MeCP2 is an abundant mammalian protein that binds to methylated CpG. We have found that native and recombinant MeCP2 repress transcription in vitro from methylated promoters but do not repress nonmethylated promoters. Repression is nonlinearly dependent on the local density of methylation, becoming significant at the density found in bulk vertebrate genomic DNA. Transient transfection using fusions with the GAL4 DNA binding domain identified a region of MeCP2 that is capable of long-range repression in vivo. Moreover, MeCP2 is able to displace histone H1 from preassembled chromatin that contains methyl-CpG. These properties, together with the abundance of MeCP2 and the high frequency of its 2 bp binding site, suggest a role as a global transcriptional repressor in vertebrate genomes.
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                Author and article information

                Journal
                Nature Genetics
                Nat Genet
                Springer Science and Business Media LLC
                1061-4036
                1546-1718
                October 1999
                October 1999
                : 23
                : 2
                : 185-188
                Article
                10.1038/13810
                10508514
                © 1999

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