RESUMEN

The molecular mechanisms that promote excitatory synapse development have been extensively studied. However, the molecular events preventing precocious excitatory synapse development so that synapses form at the correct time and place are less well understood. Here, we report the functional characterization of ARHGAP12, a previously uncharacterized Rho GTPase-activating protein (RhoGAP) in the brain. ARHGAP12 is specifically expressed in the CA1 region of the hippocampus, where it localizes to the postsynaptic compartment of excitatory synapses. ARHGAP12 negatively controls spine size via its RhoGAP activity and promotes, by interacting with CIP4, postsynaptic AMPA receptor endocytosis. Arhgap12 knockdown results in precocious maturation of excitatory synapses, as indicated by a reduction in the proportion of silent synapses. Collectively, our data show that ARHGAP12 is a synaptic RhoGAP that regulates excitatory synaptic structure and function during development.

Asunto(s)

Proteínas Activadoras de GTPasa/genética , Regulación del Desarrollo de la Expresión Génica , Proteínas Asociadas a Microtúbulos/genética , Antígenos de Histocompatibilidad Menor/genética , Células Piramidales/metabolismo , Receptores AMPA/genética , Sinapsis/fisiología , Animales , Animales Recién Nacidos , Región CA1 Hipocampal/citología , Región CA1 Hipocampal/metabolismo , Espinas Dendríticas/fisiología , Espinas Dendríticas/ultraestructura , Embrión de Mamíferos , Endocitosis , Proteínas Activadoras de GTPasa/metabolismo , Proteínas Asociadas a Microtúbulos/metabolismo , Antígenos de Histocompatibilidad Menor/metabolismo , Técnicas de Placa-Clamp , Cultivo Primario de Células , Células Piramidales/citología , Ratas , Ratas Wistar , Receptores AMPA/metabolismo , Análisis de la Célula Individual , Sinapsis/ultraestructura , Transmisión Sináptica , Técnicas de Cultivo de Tejidos

Asunto(s)

Anomalías Múltiples/genética , Anomalías Múltiples/patología , Deleción Cromosómica , Cromosomas Humanos Par 1/genética , Genes Dominantes/genética , Anomalías Múltiples/diagnóstico , Anomalías Múltiples/diagnóstico por imagen , Niño , Preescolar , Rotura Cromosómica , Femenino , Humanos , Lactante , Masculino , Radiografía , Síndrome

RESUMEN

Several studies have shown that array based comparative genomic hybridisation (CGH) is a powerful tool for the detection of copy number changes in the genome of individuals with a congenital disorder. In this study, 40 patients with non-specific X linked mental retardation were analysed with full coverage, X chromosomal, bacterial artificial chromosome arrays. Copy number changes were validated by multiplex ligation dependent probe amplification as a fast method to detect duplications and deletions in patient and control DNA. This approach has the capacity to detect copy number changes as small as 100 kb. We identified three causative duplications: one family with a 7 Mb duplication in Xp22.2 and two families with a 500 kb duplication in Xq28 encompassing the MECP2 gene. In addition, we detected four regions with copy number changes that were frequently identified in our group of patients and therefore most likely represent genomic polymorphisms. These results confirm the power of array CGH as a diagnostic tool, but also emphasise the necessity to perform proper validation experiments by an independent technique.

Asunto(s)

Aberraciones Cromosómicas , Discapacidad Intelectual Ligada al Cromosoma X/diagnóstico , Análisis de Secuencia por Matrices de Oligonucleótidos/métodos , Femenino , Genoma Humano , Haplotipos , Humanos , Masculino , Discapacidad Intelectual Ligada al Cromosoma X/genética , Polimorfismo Genético , Sensibilidad y Especificidad

RESUMEN

BACKGROUND: A new syndrome has been recognised following thorough analysis of patients with a terminal submicroscopic subtelomeric deletion of chromosome 9q. These have in common severe mental retardation, hypotonia, brachycephaly, flat face with hypertelorism, synophrys, anteverted nares, thickened lower lip, carp mouth with macroglossia, and conotruncal heart defects. The minimum critical region responsible for this 9q subtelomeric deletion syndrome (9q-) is approximately 1.2 Mb and encompasses at least 14 genes. OBJECTIVE: To characterise the breakpoints of a de novo balanced translocation t(X;9)(p11.23;q34.3) in a mentally retarded female patient with clinical features similar to the 9q- syndrome. RESULTS: Sequence analysis of the break points showed that the translocation was fully balanced and only one gene on chromosome 9 was disrupted--Euchromatin Histone Methyl Transferase1 (Eu-HMTase1)--encoding a histone H3 lysine 9 methyltransferase (H3-K9 HMTase). This indicates that haploinsufficiency of Eu-HMTase1 is responsible for the 9q submicroscopic subtelomeric deletion syndrome. This observation was further supported by the spatio-temporal expression of the gene. Using tissue in situ hybridisation studies in mouse embryos and adult brain, Eu-HMTase1 was shown to be expressed in the developing nervous system and in specific peripheral tissues. While expression is selectively downregulated in adult brain, substantial expression is retained in the olfactory bulb, anterior/ventral lateral ventricular wall, and hippocampus and weakly in the piriform cortex. CONCLUSIONS: The expression pattern of this gene suggests a role in the CNS development and function, which is in line with the severe mental retardation and behaviour problems in patients who lack one copy of the gene.

Asunto(s)

Anomalías Múltiples/genética , Deleción Cromosómica , Cromosomas Humanos Par 9/genética , Metiltransferasas/genética , Telómero/genética , Animales , Etiquetas de Secuencia Expresada , Femenino , N-Metiltransferasa de Histona-Lisina , Humanos , Discapacidad Intelectual/genética , Discapacidad Intelectual/metabolismo , Ratones , Fenotipo , Síndrome , Translocación Genética

Asunto(s)

Proteínas de Unión al ADN/genética , Discapacidad Intelectual Ligada al Cromosoma X/genética , Mutación , Factores de Transcripción/genética , Línea Celular , Mapeo Cromosómico , Cromosomas Humanos X , Análisis Mutacional de ADN , Exones , Femenino , Predisposición Genética a la Enfermedad , Humanos , Recién Nacido , Intrones , Factores de Transcripción de Tipo Kruppel , Datos de Secuencia Molecular , ARN Mensajero/análisis , Translocación Genética

RESUMEN

Rett syndrome (RTT) is an X-linked neurodevelopmental disorder caused by mutations in the MECP2 gene, with apparent lethality in male embryos. However, recent studies indicate that mutations in the MECP2 gene can cause congenital encephalopathy, an Angelman-like phenotype and even nonspecific mental retardation in males. We report on a 10-year-old boy with moderate mental retardation, hypotonia, obesity and gynaecomastia and a de novo 2-bp deletion in the MECP2 gene that resulted in a frameshift and premature stop codon. As some of the clinical features were suggestive of the Prader-Willi syndrome, it might be worthwhile screening for MECP2 mutations in patients with an atypical Prader-Willi phenotype but without the characteristic abnormalities on chromosome 15q. This report contributes to the phenotypic knowledge of male patients with MECP2 mutations. Moreover, this is the first reported male case of a de novo MECP2 mutation.

Asunto(s)

Proteínas Cromosómicas no Histona , Proteínas de Unión al ADN/genética , Mutación del Sistema de Lectura , Ginecomastia/genética , Discapacidad Intelectual/genética , Obesidad/genética , Proteínas Represoras , Niño , Análisis Mutacional de ADN , Humanos , Masculino , Proteína 2 de Unión a Metil-CpG , Síndrome de Rett/genética