RESUMEN
Strong evidence indicates that regulated mRNA translation in neuronal dendrites underlies synaptic plasticity and brain development. The fragile X mental retardation protein (FMRP) is involved in this process; here, we show that it acts by inhibiting translation initiation. A binding partner of FMRP, CYFIP1/Sra1, directly binds the translation initiation factor eIF4E through a domain that is structurally related to those present in 4E-BP translational inhibitors. Brain cytoplasmic RNA 1 (BC1), another FMRP binding partner, increases the affinity of FMRP for the CYFIP1-eIF4E complex in the brain. Levels of proteins encoded by known FMRP target mRNAs are increased upon reduction of CYFIP1 in neurons. Translational repression is regulated in an activity-dependent manner because BDNF or DHPG stimulation of neurons causes CYFIP1 to dissociate from eIF4E at synapses, thereby resulting in protein synthesis. Thus, the translational repression activity of FMRP in the brain is mediated, at least in part, by CYFIP1.
Asunto(s)
Encéfalo/metabolismo , Proteína de la Discapacidad Intelectual del Síndrome del Cromosoma X Frágil/metabolismo , Proteínas del Tejido Nervioso/metabolismo , Biosíntesis de Proteínas , Proteínas Adaptadoras Transductoras de Señales , Secuencia de Aminoácidos , Animales , Encéfalo/embriología , Células Cultivadas , Factor 4E Eucariótico de Iniciación/genética , Factor 4E Eucariótico de Iniciación/metabolismo , Proteína de la Discapacidad Intelectual del Síndrome del Cromosoma X Frágil/química , Proteína de la Discapacidad Intelectual del Síndrome del Cromosoma X Frágil/genética , Ratones , Ratones Endogámicos C57BL , Ratones Noqueados , Modelos Moleculares , Datos de Secuencia Molecular , Proteínas del Tejido Nervioso/genética , Neuronas/metabolismo , Alineación de Secuencia , SinapsisRESUMEN
Adult neural stem cell proliferation is dynamic and has the potential for massive self-renewal yet undergoes limited cell division in vivo. Here, we report an epigenetic mechanism regulating proliferation and self-renewal. The recruitment of the PI3K-related kinase signaling pathway and histone H2AX phosphorylation following GABA(A) receptor activation limits subventricular zone proliferation. As a result, NSC self-renewal and niche size is dynamic and can be directly modulated in both directions pharmacologically or by genetically targeting H2AX activation. Surprisingly, changes in proliferation have long-lasting consequences on stem cell numbers, niche size, and neuronal output. These results establish a mechanism that continuously limits proliferation and demonstrates its impact on adult neurogenesis. Such homeostatic suppression of NSC proliferation may contribute to the limited self-repair capacity of the damaged brain.
Asunto(s)
Células Madre Adultas/fisiología , Ciclo Celular/fisiología , Proliferación Celular , Reparación del ADN/fisiología , Epigénesis Genética/fisiología , Histonas/metabolismo , Células-Madre Neurales/fisiología , Transducción de Señal/fisiología , Animales , Inmunohistoquímica , Masculino , Ratones , Ratones Endogámicos C57BL , Fosfatidilinositol 3-Quinasas/metabolismo , Fosforilación , Estadísticas no ParamétricasRESUMEN
Fragile X syndrome (FXS) results from the loss of the fragile X mental retardation protein (FMRP), an RNA-binding protein that regulates a variety of cytoplasmic mRNAs. FMRP regulates mRNA translation and may be important in mRNA localization to dendrites. We report a third cytoplasmic regulatory function for FMRP: control of mRNA stability. In mice, we found that FMRP binds, in vivo, the mRNA encoding PSD-95, a key molecule that regulates neuronal synaptic signaling and learning. This interaction occurs through the 3' untranslated region of the PSD-95 (also known as Dlg4) mRNA, increasing message stability. Moreover, stabilization is further increased by mGluR activation. Although we also found that the PSD-95 mRNA is synaptically localized in vivo, localization occurs independently of FMRP. Through our functional analysis of this FMRP target we provide evidence that dysregulation of mRNA stability may contribute to the cognitive impairments in individuals with FXS.
Asunto(s)
Proteína de la Discapacidad Intelectual del Síndrome del Cromosoma X Frágil/fisiología , Péptidos y Proteínas de Señalización Intracelular/genética , Proteínas de la Membrana/genética , Estabilidad del ARN/fisiología , ARN Mensajero/metabolismo , Animales , Encéfalo/citología , Supervivencia Celular/fisiología , Células Cultivadas , Homólogo 4 de la Proteína Discs Large , Ensayo de Cambio de Movilidad Electroforética/métodos , Embrión de Mamíferos , Proteína de la Discapacidad Intelectual del Síndrome del Cromosoma X Frágil/genética , Guanilato-Quinasas , Inmunoprecipitación/métodos , Hibridación in Situ/métodos , Péptidos y Proteínas de Señalización Intracelular/metabolismo , Masculino , Proteínas de la Membrana/metabolismo , Ratones , Ratones Endogámicos C57BL , Ratones Noqueados , Neuronas/metabolismo , Biosíntesis de Proteínas , Reacción en Cadena de la Polimerasa de Transcriptasa Inversa/métodos , Transfección , Tubulina (Proteína)/metabolismoRESUMEN
Embryonic stem cells (ESCs) display an abbreviated cell cycle, resulting in a short doubling time and rapid proliferation. The histone variant H2A.X is critical for proliferation of stem cells, although mechanistic insights have remained obscure. Here, we show that H2A.X defines the rate of mouse ESC proliferation independently of the DNA damage response pathway, and it associates with three major chromatin-modifying complexes. Our functional and biochemical analyses demonstrate that H2A.X-associated factors mediate the H2A.X-dependent effect on ESC proliferation and involve the nucleolar remodeling complex (NoRC). A specific H2A.X deposition at rDNA promoters determines the chromatin recruitment of the NoRC, histone modifications, the rRNA transcription, and the rate of proliferation. Collectively, our results suggest that NoRC assembly by H2A.X deposition at rRNA promoters silences transcription, and this represents an important regulatory component for ESC proliferation.