The molecular basis of variable phenotypic severity among common missense mutations causing Rett syndrome

Brown, Kyla; Selfridge, Jim; Lagger, Sabine; Connelly, John C.; Sousa, Dina De; Kerr, Alastair; Webb, Shaun; Guy, Jacky; Merusi, Cara; Koerner, Martha V.; Bird, Adrian

doi:10.1093/hmg/ddv496

Cited by 86 publications

(149 citation statements)

References 34 publications

(83 reference statements)

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“…Instead, our data are consistent with the dysfunction associated with changes in MeCP2 levels in both MeCP2-null and -overexpressing mice [5,38–40]. Furthermore, Rett Syndrome associated mutations lead to much lower MeCP2 cellular concentrations as compared to wild type [41]. Perhaps aggregates of destabilized MeCP2 more readily signal for degradation and the remaining soluble protein cannot fully occupy high affinity sites, creating a dilution effect that is further amplified by the lower overall affinity of the mutant protein for both mCpA and mCpG sites.…”

Section: Discussionsupporting

confidence: 85%

Structural Basis of MeCP2 Distribution on Non-CpG Methylated and Hydroxymethylated DNA

Sperlazza

Bilinovich

Sinanan

et al. 2017

Journal of Molecular Biology

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The Rett syndrome-associated methyl-CpG binding protein 2 (MeCP2) selectively binds methylated DNA to regulate transcription during the development of mature neurons. Like other members of the methyl-CpG binding domain (MBD) family, MeCP2 functions through the recognition of symmetrical 5-methylcytosines in CpG (mCG) dinucleotides. Advances in base level resolution epigenetic mapping techniques have revealed, however, that MeCP2 can bind asymmetrically methylated and hydroxymethylated CpA (h/mCA) dinucleotides and this alternative binding selectivity modifies gene expression in the developing mammalian brain. The structural determinants of binding to mCA and hydroxymethylated DNA have not been previously investigated. Here, we employ ITC and NMR spectroscopy to characterize MeCP2 binding to methylated and hydroxymethylated mCG and mCA DNA; examine the effects of Rett syndrome-associated missense mutations; and make comparisons to the related and evolutionarily most ancient protein, MBD2. These analyses reveal that MeCP2 binds mCA with high affinity in a strand-specific and orientation-dependent manner. In contrast, MBD2 does not show high affinity or methyl-specific binding to mCA. The Rett-associated missense mutations (T158M, R106W, and P101S) destabilize the MeCP2 MBD and disrupt recognition of mCG and mCA equally. Finally, hydroxymethylation of a high-affinity mCA site does not alter the binding properties; whereas, hemi-hydroxylation of the equivalent cytosine in an mCG site decreases affinity and specificity. Based on these findings, we suggest MeCP2 recognition of methylated/hydroxymethylated CpA dinucleotides functions as an epigenetic switch redistributing MeCP2 among mCG and mCA loci.

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Section: Discussionsupporting

confidence: 85%

Structural Basis of MeCP2 Distribution on Non-CpG Methylated and Hydroxymethylated DNA

Sperlazza

Bilinovich

Sinanan

et al. 2017

Journal of Molecular Biology

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“…The p.T158M mutation affects the chromatin-binding capacity of MeCP2, leading to loss of the punctate element of MeCP2 labeling in the nucleus (Figure 4A) 9 . Immunolabeling of hippocampal neurons from treated Mecp2 T158M/y mice showed WT patterns of MeCP2 expression, with restored localization to DAPI bright spots, only in transduced (Myc-positive) cells (Figure 4B).…”

Section: Resultsmentioning

confidence: 99%

“…Animals were maintained on 12-hr:12-hr light/dark cycles with free access to normal mouse food. Mice were genotyped as described previously 9, 15…”

Section: Methodsmentioning

confidence: 99%

“…Typical RTT is almost exclusively caused by de novo germline mutations in the X-linked gene, MECP2 2 (as reviewed elsewhere3, 4). Several mouse models of RTT have been generated that harbor Mecp2 deletions5, 6, 7 or knocked-in mutations 8, 9, 10, 11. Many of these models recapitulate the principal features that characterize RTT in humans, although there are differences that reflect the phenotypic variability seen in patients 12, 13, 14.…”

Section: Introductionmentioning

confidence: 99%

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Development of a Novel AAV Gene Therapy Cassette with Improved Safety Features and Efficacy in a Mouse Model of Rett Syndrome

Gadalla

Vudhironarit

Hector

et al. 2017

Molecular Therapy - Methods & Clinical Development

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Rett syndrome (RTT), caused by loss-of-function mutations in the MECP2 gene, is a neurological disorder characterized by severe impairment of motor and cognitive functions. The aim of this study was to investigate the impact of vector design, dosage, and delivery route on the efficacy and safety of gene augmentation therapy in mouse models of RTT. Our results show that AAV-mediated delivery of MECP2 to Mecp2 null mice by systemic administration, and utilizing a minimal endogenous promoter, was associated with a narrow therapeutic window and resulted in liver toxicity at higher doses. Lower doses of this vector significantly extended the survival of mice lacking MeCP2 or expressing a mutant T158M allele but had no impact on RTT-like neurological phenotypes. Modifying vector design by incorporating an extended Mecp2 promoter and additional regulatory 3′ UTR elements significantly reduced hepatic toxicity after systemic administration. Moreover, direct cerebroventricular injection of this vector into neonatal Mecp2-null mice resulted in high brain transduction efficiency, increased survival and body weight, and an amelioration of RTT-like phenotypes. Our results show that controlling levels of MeCP2 expression in the liver is achievable through modification of the expression cassette. However, it also highlights the importance of achieving high brain transduction to impact the RTT-like phenotypes.

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“…S1A). One NID mutation, R306C, causes a severe RTT-like phenotype in mice (13,15,16). Moreover, mouse models of MeCP2 duplication syndrome suggest that both the MBD and the NID must be intact for this adverse molecular pathology to develop (16,17).…”

mentioning

confidence: 99%

Structure of the MeCP2–TBLR1 complex reveals a molecular basis for Rett syndrome and related disorders

Kruusvee

Lyst

Taylor

et al. 2017

Proc. Natl. Acad. Sci. U.S.A.

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Rett syndrome (RTT) is an X-linked neurological disorder caused by mutations in the methyl-CpG-binding protein 2 (MeCP2) gene. The majority of RTT missense mutations disrupt the interaction of the MeCP2 with DNA or the nuclear receptor corepressor (NCoR)/silencing mediator of retinoic acid and thyroid receptors (SMRT) corepressor complex. Here, we show that the "NCoR/SMRT interaction domain" (NID) of MeCP2 directly contacts transducin beta-like 1 (TBL1) and TBL1 related (TBLR1), two paralogs that are core components of NCoR/SMRT. We determine the cocrystal structure of the MeCP2 NID in complex with the WD40 domain of TBLR1 and confirm by in vitro and ex vivo assays that mutation of interacting residues of TBLR1 and TBL1 disrupts binding to MeCP2. Strikingly, the four MeCP2-NID residues mutated in RTT are those residues that make the most extensive contacts with TBLR1. Moreover, missense mutations in the gene for TBLR1 that are associated with intellectual disability also prevent MeCP2 binding. Our study therefore reveals the molecular basis of an interaction that is crucial for optimal brain function.T he methyl-CpG-binding protein 2 (MeCP2) is a chromatinassociated factor that is highly expressed in the brain (1, 2). Loss-of-function mutations in MeCP2 lead to the severe pediatric neurological disorder, Rett syndrome (RTT) (3), which affects around one in 10,000 girls. In addition, extra copies of the gene cause MeCP2 duplication syndrome (4, 5), a distinct intellectual disability disorder that predominantly affects males (6). The importance of MeCP2 for brain function has prompted investigation of its molecular function. The protein was identified because of its ability to bind DNA via its methyl-CpG-binding domain (MBD) (1, 7) and many residues mutated in RTT disrupt this interaction (8-11). In addition to DNA, numerous protein partners of MeCP2 have been reported (11). Of these protein partners, only the interactions with the nuclear receptor corepressor (NCoR) and its close relative silencing mediator of retinoic acid and thyroid receptors (SMRT) (12-14) are known to be disrupted by RTT missense mutations (13). Accordingly, Rett missense mutations outside the MBD are found clustered within the so-called "NCoR/SMRT interaction domain" (NID) (13) (Fig. 1A and Fig. S1A). One NID mutation, R306C, causes a severe RTT-like phenotype in mice (13,15,16). Moreover, mouse models of MeCP2 duplication syndrome suggest that both the MBD and the NID must be intact for this adverse molecular pathology to develop (16,17).These findings indicate that the NID mediates an essential function of MeCP2. This function may be recruitment of the NCoR/ SMRT corepressor complexes to chromatin. Alternatively, the NID may perform other essential roles, such as DNA binding, whose loss leads to RTT (16). In an attempt to distinguish among these possibilities, we investigated the molecular basis of the interaction between MeCP2 and NCoR/SMRT. The latter are ∼1.2-MDa multisubunit complexes that include NCoR1 (and/or SMRT), HDAC3, GPS2, and...

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The molecular basis of variable phenotypic severity among common missense mutations causing Rett syndrome

Cited by 86 publications

References 34 publications

Structural Basis of MeCP2 Distribution on Non-CpG Methylated and Hydroxymethylated DNA

Structural Basis of MeCP2 Distribution on Non-CpG Methylated and Hydroxymethylated DNA

Development of a Novel AAV Gene Therapy Cassette with Improved Safety Features and Efficacy in a Mouse Model of Rett Syndrome

Structure of the MeCP2–TBLR1 complex reveals a molecular basis for Rett syndrome and related disorders

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