Academic literature on the topic 'Rett syndrome MeCP2'

Rett Syndrome was long considered to be simply a disorder of postnatal development, with phenotypes that manifest only late in development and into adulthood. A variety of recent evidence demonstrates that the phenotypes of Rett Syndrome are present at the earliest stages of brain development, including developmental stages that define neurogenesis, migration, and patterning in addition to stages of synaptic and circuit development and plasticity. These phenotypes arise from the pleotropic effects of MeCP2, which is expressed very early in neuronal progenitors and continues to be expressed into adulthood. The effects of MeCP2 are mediated by diverse signaling, transcriptional, and epigenetic mechanisms. Attempts to reverse the effects of Rett Syndrome need to take into account the developmental dynamics and temporal impact of MeCP2 loss.

Rett syndrome (RTT) is a rare X-linked syndrome that predominantly affects girls. It is characterized by a severe and progressive neurodevelopmental disorder with neurological regression and autism spectrum features. The Rett syndrome is associated with a broad phenotypic spectrum. It ranges from a classical Rett syndrome defined by well-established criteria to atypical cases with symptoms similar to other syndromes, such as Angelman syndrome. The first case of a Moroccan female child carrying a R306X mutation in the MECP2 (Methyl-CpG-Binding Protein 2) gene, with an unusual manifestation of Rett syndrome, is presented here. She showed autistic regression, behavioral stagnation, epilepsy, unmotivated laughter, and craniofacial dysmorphia. Whole exome sequencing revealed a nonsense mutation (R306X), resulting in a truncated, nonfunctional MECP2 protein. The overlapping phenotypic spectrums between Rett and Angelman syndromes have been described, and an interaction between the MECP2 gene and the UBE3A (Ubiquitin Protein Ligase E3A) gene pathways is possible but has not yet been proven. An extensive genetic analysis is highly recommended in atypical cases to ensure an accurate diagnosis and to improve patient management and genetic counseling.

Rett syndrome is a severe form of autism spectrum disorder, mainly caused by mutations of a single gene methyl CpG binding protein 2 (MeCP2) on the X chromosome. Patients with Rett syndrome exhibit a period of normal development followed by regression of brain function and the emergence of autistic behaviors. However, the mechanism behind the delayed onset of symptoms is largely unknown. Here we demonstrate that neuron-specific K+-Cl− cotransporter2 (KCC2) is a critical downstream gene target of MeCP2. We found that human neurons differentiated from induced pluripotent stem cells from patients with Rett syndrome showed a significant deficit in KCC2 expression and consequently a delayed GABA functional switch from excitation to inhibition. Interestingly, overexpression of KCC2 in MeCP2-deficient neurons rescued GABA functional deficits, suggesting an important role of KCC2 in Rett syndrome. We further identified that RE1-silencing transcriptional factor, REST, a neuronal gene repressor, mediates the MeCP2 regulation of KCC2. Because KCC2 is a slow onset molecule with expression level reaching maximum later in development, the functional deficit of KCC2 may offer an explanation for the delayed onset of Rett symptoms. Our studies suggest that restoring KCC2 function in Rett neurons may lead to a potential treatment for Rett syndrome.

Mutations in the MECP2 gene are found in a large proportion of girls with Rett Syndrome. Despite extensive research, the principal role of MeCP2 protein remains elusive. Is MeCP2 a regulator of genes, acting in concert with co-activators and co-repressors, predominantly as an activator of target genes or is it a methyl CpG binding protein acting globally to change the chromatin state and to supress transcription from repeat elements? If MeCP2 has no specific targets in the genome, what causes the differential expression of specific genes in the Mecp2 knockout mouse brain? We discuss the discrepancies in current data and propose a hypothesis to reconcile some differences in the two viewpoints. Since transcripts from repeat elements contribute to piRNA biogenesis, we propose that piRNA levels may be higher in the absence of MeCP2 and that increased piRNA levels may contribute to the mis-regulation of some genes seen in the Mecp2 knockout mouse brain. We provide preliminary data showing an increase in piRNAs in the Mecp2 knockout mouse cerebellum. Our investigation suggests that global piRNA levels may be elevated in the Mecp2 knockout mouse cerebellum and strongly supports further investigation of piRNAs in Rett syndrome.

Rett Syndrome is a severe neurological disorder mainly due to de novo mutations in the methyl-CpG-binding protein 2 gene (MECP2). Mecp2 is known to play a role in chromatin organization and transcriptional regulation. In this review, we report the latest advances on the molecular function of Mecp2 and the new animal and cellular models developed to better study Rett syndrome. Finally, we present the latest innovative therapeutic approaches, ranging from classical pharmacology to correct symptoms to more innovative approaches intended to cure the pathology.

The Rett syndrome protein MeCP2 was described as a methyl-CpG-binding protein, but its exact function remains unknown. Here we show that mouse MeCP2 is a microsatellite binding protein that specifically recognizes hydroxymethylated CA repeats. Depletion of MeCP2 alters chromatin organization of CA repeats and lamina-associated domains and results in nucleosome accumulation on CA repeats and genome-wide transcriptional dysregulation. The structure of MeCP2 in complex with a hydroxymethylated CA repeat reveals a characteristic DNA shape, with considerably modified geometry at the 5-hydroxymethylcytosine, which is recognized specifically by Arg133, a key residue whose mutation causes Rett syndrome. Our work identifies MeCP2 as a microsatellite DNA binding protein that targets the 5hmC-modified CA-rich strand and maintains genome regions nucleosome-free, suggesting a role for MeCP2 dysfunction in Rett syndrome.

Rett syndrome (RTT) is a neurological disorder caused by mutations in the X-linked gene methyl-CpG-binding protein 2 ( MECP2 ), a ubiquitously expressed transcriptional regulator. Despite remarkable scientific progress since its discovery, the mechanism by which MECP2 mutations cause RTT symptoms is largely unknown. Consequently, treatment options for patients are currently limited and centred on symptom relief. Thought to be an entirely neurological disorder, RTT research has focused on the role of MECP2 in the central nervous system. However, the variety of phenotypes identified in Mecp2 mutant mouse models and RTT patients implicate important roles for MeCP2 in peripheral systems. Here, we review the history of RTT, highlighting breakthroughs in the field that have led us to present day. We explore the current evidence supporting metabolic dysfunction as a component of RTT, presenting recent studies that have revealed perturbed lipid metabolism in the brain and peripheral tissues of mouse models and patients. Such findings may have an impact on the quality of life of RTT patients as both dietary and drug intervention can alter lipid metabolism. Ultimately, we conclude that a thorough knowledge of MeCP2's varied functional targets in the brain and body will be required to treat this complex syndrome.

Rett syndrome (RTT) is a monogenic neurodevelopmental disorder primarily caused by mutations in X-linked MECP2 gene, encoding for methyl-CpG binding protein 2 (MeCP2), a multifaceted modulator of gene expression and chromatin organization. Based on the type of mutation, RTT patients exhibit a broad spectrum of clinical phenotypes with various degrees of severity. In addition, as a complex multisystem disease, RTT shows several clinical manifestations ranging from neurological to non-neurological symptoms. The most common non-neurological comorbidities include, among others, orthopedic complications, mainly scoliosis but also early osteopenia/osteoporosis and a high frequency of fractures. A characteristic low bone mineral density dependent on a slow rate of bone formation due to dysfunctional osteoblast activity rather than an increase in bone resorption is at the root of these complications. Evidence from human and animal studies supports the idea that MECP2 mutation could be associated with altered epigenetic regulation of bone-related factors and signaling pathways, including SFRP4/WNT/β-catenin axis and RANKL/RANK/OPG system. More research is needed to better understand the role of MeCP2 in bone homeostasis. Indeed, uncovering the molecular mechanisms underlying RTT bone problems could reveal new potential pharmacological targets for the treatment of these complications that adversely affect the quality of life of RTT patients for whom the only therapeutic approaches currently available include bisphosphonates, dietary supplements, and physical activity.

Rett syndrome (RTT) is a severe neurological disorder that affects approximately 1:10000 girls. Classical RTT is defined by a developmental regression phase and subsequent stabilisation of diagnostic criteria, which include partial or complete loss of spoken language, dyspraxic gait and stereotypic hand movements such as hand mouthing. RTT is a monogenic disorder, with the majority of cases being due to loss-of-function mutations in MeCP2 (methyl-CpG binding protein 2). Due to this clear genotype-phenotype link multiple RTT mouse models have been used to elucidate the molecular details, and consequent neuropathogenesis, of this complex neurological disease, as well as for the development of potential therapeutics for RTT. However, as the molecular details become clearer, the need for a simpler model system becomes evident. Human induced pluripotent stem cells (hiPSCs) generated from RTT patient fibroblasts are an option; however the handling of these cells is laborious, time-consuming and expensive and they often differentiate into a heterogeneous population of cells. To explore an alternative human model system I have been genetically engineering and experimenting with the human dopaminergic LUHMES cell line. LUHMES cells are an immortalised pre-neuronal cell line derived from an 8-week old, female foetus and can readily be differentiated into a homogeneous population of mature, electrically active neurons in just one week. In this thesis I have assessed the phenotypic properties of the wild-type cell line, demonstrated the ease of genetic manipulation of LUHMES cells by CRISPR/Cas9 approaches, generated seven mutant MECP2 LUHMES cell lines and explored the potential of protein therapy as a therapeutic approach for RTT. The LUHMES cell line proves to be extremely easy to handle and robust and has yielded novel molecular insights into the function of MeCP2 in human neurons. In particular, MeCP2-null cells show a striking relationship between the level of gene body methylation and the extent of transcriptional upregulation when compared to wild-type neurons. In contrast neurons that express a form of MeCP2 that can bind to DNA but cannot recruit a transcriptional corepressor complex (the R306C mutant) do not exhibit substantial gene expression alterations, yet do display a consistent decrease in total RNA amount. This decrease in total RNA is recapitulated in MeCP2-null LUHMES-derived neurons and in brain regions from MeCP2-R306C mice. The requirement for functional DNA binding for normal gene-body methylation dependent gene repression is demonstrated by assessing LUHMES cells that overexpress MeCP2-R111G, a protein that cannot bind to DNA. Furthermore, overexpression of the MeCP2-R306C protein highlights the importance of NCoR binding for normal gene repression, but also demonstrates that MeCP2-R306C protein retains some gene repression activity. Thinking more broadly, this cell line also has applications as a model system for a variety of other neurological disorders; as a simplified model system to elucidate molecular and neurological phenotypes, and as a relevant human system that can be cultured in a high-throughput manner for testing therapeutic strategies.

It is now commonly agreed that Rett Syndrome is a monogenic neurological disease caused by mutations in MECP2 gene. Rett Syndrome mainly occurs in girls and it is characterised by a period of normal development until around 6­18 months, followed by a rapid regression. After the regression, symptoms persist as severe mental retardation, reduced head size, seizures, ataxia, hyperventilation and repetitive hand wringing movements. The phenotype of mice with a deleted Mecp2 gene mimics some Rett Syndrome symptoms. The Mecp2­null mouse develops normally until about 6 weeks of age after which tremors, irregular breathing, lack of mobility and hindlimb clasping develop. To understand how the lack of MeCP2 causes Rett Syndrome, the search for MeCP2 regulated genes was initiated in Mecp2-null mouse brain. Examination of candidate genes revealed that Bdnf is down-regulated and Hes1 is up-regulated in pre, early and late symptomatic Mecp2-null mice. Further, global analysis of gene expression was examined by ADDER differential display. Some mis-regulated genes were identified, two of which are involved in mitochondrial respiration. Oxygen electrode measurements revealed defects in brain mitochondrial respiration, which commenced coincident with symptom onset in Mecp2-null mice. This finding suggests mitochondrial involvement in the pathogenesis of Rett Syndrome symptoms. In the course of these studies, the structure of the Mecp2 gene was re-investigated, leading to the identification of a new MeCP2 isoform. Data in this thesis demonstrates that the new isoform is the major form of MeCP2 in both mouse and human brain.

INTRODUCTION To answer many complex and fascinating biological phenomena, we must go over or above (epi-) genetics because the DNA blueprint is identical in each of the abovementioned somatic cells. The mechanisms by which epigenetics affects so deeply the cell physiology are mediated by a large number of actors, most of them represented by covalently modified nucleotides and amino acids, non-coding RNAs and proteins. MeCP2 is an epigenetic reader able to bind to methylated and 5- hydroxymethylated cytosines. Despite all the initial evidences proposing a chromatin-repression role for MeCP2, many other functions have been demonstrated, including transcriptional activation, mRNA splicing regulation and protein synthesis modulation. Importantly, MeCP2 impairments are the primary responsible for RTT syndrome and have also been shown to be involved in several other disorders, albeit in very few patients, as Prader-Willi syndrome, Angelman syndrome, nonsyndromic mental retardation, and autism. AIMS To date, no MeCP2-regulated gene has been successfully targeted in order to improve the severe symptoms of RTT. In the present Doctoral Thesis we sought to identify new MeCP2 targets through different approaches with the purpose of expanding the knowledge of the impaired biological pathways in RTT. * In the first study we focused on a class of transcriptional regulators called long non-coding RNAs (lncRNAs). * In the second study we took advantage of RNA sequencing, a powerful high-throughput technique with the ability to detect very low amounts of transcript. Then, we proposed to investigate also the consequence of MeCP2 over-expression in a well-known developmental model such as the chicken embryo. RESULTS STUDY I DYSREGULATION OF THE LONG NON-CODING RNA TRANSCRIPTOME IN A RETT SYNDROME MOUSE MODEL * We found 701 lncRNAs that had a different expression pattern in wild-type and Mecp2-null brain with a score of <0.05 in the false discovery rate (FDR) test and a >1.5-fold expression change. Among the altered lncRNAs, downregulation of transcripts was predominant (520 of 701, 74%), whereas upregulation occurred in the minority of differentially expressed genes (181 of 701, 26%). * Following a selection of lncRNAs with a fold-change >2 that were associated with an annotated protein-coding gene involved in neuronal or glial functions, we validated two up-regulated lncRNAs, AK081227 and AK087060, in the Mecp2-null brain using qRT-PCR on independent samples. * We showed that AK081227 and AK087060 promoters were occupied by the MeCP2 protein in wild-type mouse brains. * We reported that the up-regulation of AK081227 in Mecp2-null mice was associated with a down-regulation of its host gene Gabrr2 in four brain regions (frontal cortex, hypothalamus, thalamus and cerebellum) (Pearson's correlation test = 0.44, p = 0.06). * In the case of AK087060, we found that the up-regulation of this 1ncRNA was correlated with an increase in the expression of its host gene Arhgef26 in the four studied brain regions (Pearson's correlation test = 0.41, p = 0.08). STUDY II RNA-SEQUENCING OF A RETT SYNDROME MOUSE MODEL REVEALS GLOBAL IMPAIRMENT OF IMMEDIATE-EARLY GENES EXPRESSION * We sequenced the transcriptome of Mecp2-null and control mice and we detected 1049 and 1154 differentially expressed genes in HIP and PFC, respectively. The ratio of up- and down-regulated genes was different between the two regions. In the HIP the ratio was favorable to the less expressed genes, being 388 (37%) and 661 (63%) the up- and down-regulated genes, respectively. On the other hand, in the PFC there were slightly more up-regulated genes, 630 (55%), compared to the down-regulated ones, 523 (45%). In addition we reported that only a small fraction of genes, 76 and 109, were up- and down-regulated, respectively, in both brain areas. * Gene Ontology (GO) analysis of differentially expressed transcripts revealed that both HIP and PFC up-regulated genes were enriched in neuronal function terms and, to a lesser extent, signal transduction ones. The scenario was similar for the down-regulated genes but in this case we found many inflammatory, apoptosis, oxidative stress and immune system-related terms. * We found several members of the immediate-early genes (IEGs) family to be up-regulated both in the PFC and HIP of Mecp2-null mouse. Consistent with the findings from the RNA-sequencing analysis in the HIP, qRT-PCR showed significant alterations in the expression of Fos, Junb, Egr2, Nr4a1, Npas4, Fosb and Egr1. Furthermore, Fos, Junb, Npas4 and Fosb were validated also in the PFC. * We demonstrated the binding of MeCP2 upon the regulatory regions of IEGs. In both PFC and HIP wild-type brain, we observed a reduction of MeCP2 occupancy upon the regions associated with high CpG content of Fos, Junb, Nr4a1, Npas4, Fosb and Egr1 promoters. We also found that the HIP chromatin was more accessible to MNase digestion in the Mecp2-null brain. * Then, we showed that four IEGs (Fos, Junb, Egr2, Npas4) displayed altered expression in Mecp2-null cultured neurons treated with forskolin. Precisely, this four IEG exhibited an aberrant kinetic of recovery to the basal state. One hour after forskolin withdrawal, Fos, Junb, Egr2 and Npas4 expression levels in the Mecp2-null hippocampal neurons continue to increase, while in wild-type they did not change or even decrease. The situation is the opposite in cortical neurons, where Fos, Junb, Egr2 and Npas4 are less expressed after forskolin withdrawal in Mecp2-null samples. * Finally, we evaluated whether the IEGs response was impaired in vivo as well. Indeed, we observed a significant increase of Junb expression in the hippocampus of Mecp2-null animals treated with kainic acid, when compared to treated wild type mice. STUDY III AN INCREASE IN MECP2 DOSAGE IMPAIRS NEURAL TUBE FORMATION * We detected the expression of both chicken MeCP2 (cMECP2) transcript and protein in a wide window of developmental stages. In addition, we showed that nuclear localization and the sequence of the region encompassing the methyl-CpG binding domain are conserved between human and chicken. * We found that the overexpression of MeCP2 in the neural tube of chicken embryos provokes an overall decrease in the number of proliferating BrdUpositive cells, with the most affected part being the ventricular zone. In addition, normal H3S1Op pattern along the lumen is disrupted upon MeCP2 overexpression. * Also, MeCP2 increase in dosage cause a clear decrease in the amounts of differentiated neuronal population located at the mantle zone, as it was demonstrated through immunostaining of neural tubes with TUJ1 and HUC/D, two neuronal-lineage restricted markers. Moreover, MeCP2 overexpression leads to a decrease of a neuroepithelial polarity marker such as N-cadherin. * Finally, we showed that one of the possible explanations of our phenotype is the increased cell death occurring upon MeCP2 increase in dosage. We reported an increment of apoptotic cells in MeCP2-overexpressing neural tubes immunostained with Caspase-3 and -8. Furthermore, we described also an increase of pyknotic cells number in MeCP2 electroporated neural tubes.
Introducción: El síndrome de Rett (RTT, OMIM#312750) fue por primera vez descrito en 1966 por el pediatra austriaco Andreas Rett. El síndrome de Rett causa retraso mental en 1 de cada 10000 niñas, lo que hace que sea la segunda causa de retraso mental en niñas. En 1999 en el laboratorio de Huda Zoghbi descubrieron las bases genéticas de la enfermedad. El 95% de los casos de Rett clásico se produce por mutaciones en MeCP2. Es interesante el hecho de que mutaciones que provocan el incremento de copias del gen MECP2 también llevan a enfermedades neurológicas, como es el caso del trastorno provocado por la duplicación de MeCP2. MeCP2 es una proteína nuclear, que se expresa en diferentes tejidos, pero es especialmente abundante en neuronas del sistema nervioso maduro. MeCP2 es una proteína con capacidad para unirse a dinucleótidos CpG. Entre las varias funciones biológicas propuesta para MeCP2 se encuentran: 1) Silenciamento transcripcional; 2) activador transcripcional; 3) regulador de splicing; 4) Regulador de la cromatina. Objetivos del estudio: El principal objetivo de esta tesis es evaluar el impacto del incremento o disminución de expresión de MeCP2 , tanto a nivel transcripcional como de desarrollo, al fin de caracterizar las vías moleculares desreguladas en las manifestaciones clínicas relacionadas con MeCP2. En los primeros dos estudios se buscarán nuevos targets de MeCP2 a través de dos diferentes tecnologías, secuenciación del ARN y microarray. En ambos estudios utilizaremos un modelo murino bien establecido (MeCP2-null), obtenido mediante supresión del gen MeCP2, que simula el síndrome de Rett. Las diferencias entre los primeros dos estudios es que mientras en el primero se buscarán solo "long non-coding RNA" relacionados con MeCP2, el segundo será enfocado en todos los ARN codificantes. En el tercer estudio evaluaremos el efecto de la sobreexpresión de MeCP2 en un bien establecido modelo de desarrollo embrionario como es el embrión de pollo. Resultados y conclusiones: Parte 1 * Se han encontrado 701 lncRNAs diferencialmente expresados entre el cerebro del ratón Mecp2-null y el control (salvaje). * MeCP2 está unido a los promotores de los lncRNAs AK081227 y AK087060. * El incremento de expresión de AK081227 en ratones Mecp2-null está asociado con la bajada de expresión de su gen huésped Gabrr2 en cuatro regiones del cerebro. * La sobre regulación de AK087060 se correlaciona con un aumento en la expresión de su gen huésped Arhgef26 en las cuatro regiones cerebrales estudiadas. Parte 2 * Hemos encontrados 1049 y 1154 transcritos diferencialmente expresado en el hipocampo (HIP) y la corteza pre-frontal (PFC), respectivamente, del ratón Mecp2- null. * Los genes "immediate early genes" (IEGs) Fos, JunB, EGR2, NR4A1, Npas4, FosB y Egrl están sobreexpresados en el HIP de Mecp2-null. Además, Fos, JunB, Npas4 y FosB están sobreexpresados también en el PFC. * En tanto la PFC como en el HIP del ratón wild-type, la unión de MeCP2 se reduce en las regiones asociadas con alto contenido de CpG de los genes Fos, JunB, NR4A1, Npas4, FosB y Egr1. Además, los promotores de Fos, JunB y Npas4 son más accesibles a la digestión con nucleasas micrococales (MNase) en el HIP de ratones Mecp2-null. * Cuatro IEGs (Fos, JunB, Egr2, Npas4) muestran un patrón de expresión alterado en neuronas derivadas de animales Mecp2-null y tratadas con forskolina. * La expresión de JunB es incrementada significativamente en el hipocampo de los animales Mecp2-null tratados con ácido kaínico, en comparación con ratones controles tratados. Parte 3 * El transcrito y la proteína de MeCP2 de pollo se expresan en varios estadio del desarrollo embrionario y especialmente en el tubo neural * La sobreexpresión de MeCP2 en el tubo neural de embriones de pollo provoca una disminución general en el número de células proliferantes. Además, el patrón de localización del marcador mitótico H3S1Op es aberrante en tubos neurales que sobreexpresan MeCP2. * Una dosis elevada de MeCP2 provoca una clara disminución de las neuronas diferenciadas localizadas en la zona del mantel. Por otra parte, la sobreexpresión de MeCP2 conduce a una disminución del marcador de polaridad neuroepitelia Ncadherin. * La sobreexpresión de MeCP2 en tubos neurales provoca un aumento de apoptosis.

Methyl-CpG binding protein 2 (MeCP2) was discovered as a protein binding to methylated DNA more than 20 years ago. It is very abundant in the brain and was shown to be able to repress transcription. The mutations in MeCP2 cause Rett syndrome, an autism-spectrum neurological disorder affecting girls. Yet, the exact role of MeCP2 in Rett disease, its function and mechanism of action are not fully elucidated. In order to shed some light on its role in the disease the aim of this project was to identify proteins interacting with MeCP2. Affinity purification of MeCP2 from mouse brains and mass spectrometry analysis revealed new interactions between MeCP2 and protein complexes. Detailed analysis confirmed the findings and narrowed down the top interactions to distinct regions of MeCP2. One of the domains interacts with identified NCoR/SMRT co-repressor complex and is mutated in many patients with Rett syndrome. In vitro assays proved that these mutations abolish the putative transcriptional repressor function of MeCP2. We propose a model in which Rett syndrome is caused by two types of mutations: either disrupting the interaction with DNA or affecting the interaction with the identified complex, which has an effect on the global state of chromatin. The presented findings can help to develop new therapies for Rett syndrome in the future.

MeCP2 was initially identified as an abundant protein in the brain, with an affinity for methylated DNA in vitro. Interestingly, both deficiency and excess of the protein leads to severe neurological problems, such as Rett syndrome, which is the result of mutations in the MECP2 gene. Subsequent transfection experiments showed that MeCP2 can recruit corepressor complexes and inhibit gene expression in vivo. MeCP2 was therefore thought to repress specific gene targets and the aetiology of Rett syndrome was proposed to result from aberrant gene expression in the MeCP2-deficient brain. Although gene expression is perturbed in the Mecp2-null mouse brain, few specific targets have been verified and alternative hypotheses for MeCP2 function have been put forward. Previous binding studies have also failed to clearly identify MeCP2 targets. To shed light on these matters, a novel technique was generated to isolate neuronal and glial nuclei and established that the amount of MeCP2 is unexpectedly high in neurons, with an abundance approaching that of the histone octamer. Chromatin immunoprecipitation experiments on mature mouse brain showed widespread binding of MeCP2, consistent with its high abundance, tracking the methyl-CpG density of the genome. MeCP2 deficiency results in global changes in neuronal chromatin structure, including elevated histone acetylation and a doubling of histone H1. The mutant brain also shows elevated transcription of repetitive elements, which are distributed throughout the mouse genome. Based on this data, we propose that MeCP2 binds genome wide and suppresses spurious transcription through binding in a DNA methylation dependent manner.

Rett syndrome (RTT) is an X-linked neurological disorder primarily caused by mutations in the MECP2 gene. The majority of RTT mutations disrupt the interaction of MeCP2 with DNA or TBL1X/TBL1XR1, which forms the scaffold of NCoR/SMRT co-repressor complex. Patients with RTT show no signs of neuronal death, although they have abnormal neuronal morphology, indicating that it is a neurodevelopmental rather than a neurodegenerative disease. It has been shown that reactivation of silenced MeCP2 in mice rescues the RTT phenotype, which implies that the disease is treatable. The RTT mutations in MeCP2 cluster to two regions - the methyl-CpG-binding domain (MBD) and NCoR/SMRT Interaction Domain (NID). While the interaction between MBD and DNA has been biochemically and structurally characterised, there are no structural data about the interaction between MeCP2 NID and TBL1XR1. The aim of this work was to understand how mutations in the NID cause RTT by characterising the interaction between MeCP2 and TBL1XR1. I have solved the structure of MeCP2 NID bound to TBL1XR1 WD40 domain. I show that a small region of the MeCP2 NID makes extensive contacts with TBL1XR1, and that these contacts are mediated primarily by MeCP2 residues known to be mutated in RTT. I also measured the affinities between TBL1XR1 and MeCP2-derived peptides using fluorescence anisotropy and surface plasmon resonance assays. I determined the affinity between MeCP2 NID peptide and TBL1XR1 to be around 10- 20 μM, and show that mutations in either MeCP2 or TBL1XR1 can abolish this interaction. Taken together, these data strongly suggest that the abolition of the interaction between MeCP2 NID and TBL1XR1 WD40 domain is sufficient to cause RTT. This knowledge can help with the rational design of small drug-like molecules that might be able to mediate the interaction between mutated MeCP2 and TBL1XR1, potentially helping to treat the disease.

Chez l’homme, des mutations dans le gène MECP2 sont à l’origine de maladies neurologiques dont la principale est le Syndrome de Rett (RTT). Le décours de la pathologie est caractérisé par un arrêt du développement entre 6 et 18 mois après la naissance, suivi par un ensemble de signes cliniques, dont une phase de régression importante avec des troubles moteurs, autonomes et cognitifs. Parmi les facteurs qui participent au développement de la pathologie, le BDNF joue un rôle clé. En effet l'expression du Bdnf est diminuée de moitié dans le système nerveux central en l’absence de celui-ci. C'est un acteur prépondérant dans l’apparition et dans la progression du phénotype anormal des neurones dans cette pathologie et donc une excellente cible thérapeutique. L’utilisation directe du Bdnf n’est actuellement pas envisageable car cette protéine ne traverse pas la BHE et que son temps de demi-vie est très court. Nous avons donc élaboré des stratégies alternatives afin d’agir indirectement sur le Bdnf, de façon à stimuler son transport vésiculaire et compenser les déficits en contenus, par une augmentation de sa biodisponibilité et de sa libération à la synapse. Dans cette optique j’ai utilisé deux approches visant à stimuler le transport axonal du Bdnf par la phosphorylation d'Htt afin d’augmenter la vitesse de transport antérograde de vésicules de Bdnf dans les neurones. Mes conclusions sont que la phosphorylation d'Htt corrige le déficit de transport axonal du Bdnf in vitro. Elle permet d'améliorer la survie et certains symptômes de la souris modèle de RTT. Cette phosphorylation apparait ainsi comme une piste thérapeutique intéressante
Rett syndrome (RTT) is a severe neurological disorder caused by mutations in the MECP2 gene, located on the X chromosome. After a period of apparent normal development, females with MECP2 mutations undergo a regression of early developmental milestones, resulting in the deterioration of motor skills, eye contact, speech, and hand movements and ultimately resulting in severe breathing disturbances, as the disease progresses, and severe handicap. Bdnf, a neuronal modulator that plays a key role in neuronal survival, development, and plasticity has been found to be one of the main factors altered in the absence of Mecp2. The Bdnf pathway is one of the most appealing pathways to target in RTT. Bdnf itself is unable to cross the blood-brain barrier (BBB) and needs to be indirectly activated. Thus, we developed an indirect strategy to enhance Bdnf trafficking in neurons. Huntingtin (Htt) phosphorylation of Serine 421 enhances Bdnf transport and promoting Htt phosphorylation may restore Bdnf homeostasis in Mecp2 KO brain. We tested this possibility using two approaches to promote Htt phosphorylation of S421 in Mecp2-deficient neurons and Mecp2 KO mice. We evaluated the consequences of Htt S421 phosphorylation on BDNF axonal trafficking in projecting corticostriatal neurons in vitro, and in vivo on the behavior of Mecp2 KO mice. Our findings demonstrate that pharmacological and genetic stimulation approaches correct Bdnf trafficking in vitro and improve longevity and behavioural features in Mecp2 KO mice. Htt S421 phosphorylation appears to be a possible target for the development of treatments in RTT

Rett Syndrome (RTT) is a neurodevelopmental disorder that predominantly affects females but males with RTT have been identified. RTT was first described by an Austrian pediatrician, Andreas Rett. Rett syndrome was mapped to chromosome Xq28 in 1998 and a year later it was determined to be due to mutations in the MeCP2 gene at this locus. Identification of the gene led to the broadening of the clinical phenotype and further characterization into classic and atypical forms of the disease that overlap with Autism spectrum disorders during the period of regression. More than 95% of individuals with classic RTT have mutations in the MeCP2 gene.

Chapter 6 reviews the phenotypes of the constitutive Mecp2 KO mutant mice, those generated by expressing RTT -causing mutations, and conditional Mecp2 KO mice in comparison to clinical phenotypes presented in patients with RTT. It also covers therapeutic approaches currently reported using these RTT -model mice.

Rett syndrome (RTT) is a genetic disorder resulting from an X-linked dominant mutation in MECP2 gene. It primarily affects females and is found in a variety of racial and ethnic groups worldwide with a versatile clinical phenotype. This chapter describes the authors musical and personal encounters with individuals with RTT and their families over many years with the aim of helping the reader to understand what lies behind those deep and penetrating eyes and behind the “screaming silence”. Through short vignettes, I will shed light on these girls’ inner capacity and demonstrate how music can help to bring them to life as well as motivate their families. Interactions in music therapy provide an opportunity to discover hidden resources that may not be readily accessed because of the disability. With each positive shift in musical interactions, the person can become empowered and experience new challenges that enhance growth.

Chapter 5 reviews the features of Rett syndrome (RTT) and its genetic bases, as well as the role of MECP2 in neurodevelopment at the clinical as well as molecular and cellular levels, exploring potential neurobiological mechanisms shared with other autism spectrum disorders.