RESUMO
Most cases of Angelman syndrome (AS) result from loss or inactivation of ubiquitin protein ligase 3A (UBE3A), a gene displaying maternal-specific expression in brain. Epigenetic silencing of the paternal UBE3A allele in brain appears to be mediated by a non-coding UBE3A antisense (UBE3A-ATS). In human, UBE3A-ATS extends approximately 450 kb to UBE3A from the small nuclear ribonucleoprotein N (SNURF/SNRPN) promoter region that contains a cis-acting imprinting center (IC). The concept of a single large antisense transcript is difficult to reconcile with the observation that SNURF/SNRPN shows a ubiquitous pattern of expression while the more distal part of UBE3A-ATS, which overlaps UBE3A, is brain specific. To address this problem, we examined murine transcripts initiating from several alternative exons dispersed within a 500 kb region upstream of Snurf/Snrpn. Similar to Ube3a-ATS, these upstream (U) exon-containing transcripts are expressed at neuronal stages of differentiation in a cell culture model of neurogenesis. These findings suggest the novel hypothesis that brain-specific transcription of Ube3a-ATS is regulated by the U exons rather than Snurf/Snrpn exon 1 as previously suggested from human studies. In support of this hypothesis, we describe U-Ube3a-ATS transcripts where U exons are spliced to Ube3a-ATS with the exclusion of Snurf-Snrpn. We also show that the murine U exons have arisen by genomic duplication of segments that include elements of the IC, suggesting that the brain specific silencing of Ube3a is due to multiple alternatively spliced IC-Ube3a-ATS transcripts.
Assuntos
Processamento Alternativo , Encéfalo/metabolismo , Éxons , Impressão Genômica , Camundongos/genética , RNA Antissenso/genética , Ubiquitina-Proteína Ligases/genética , Alelos , Animais , Autoantígenos , Sequência de Bases , Diferenciação Celular , Linhagem Celular Tumoral , Inativação Gênica , Íntrons , Camundongos Endogâmicos C57BL , Dados de Sequência Molecular , Neurônios/citologia , Neurônios/metabolismo , Proteínas Nucleares/genética , RNA Antissenso/metabolismo , RNA Nucleolar Pequeno/metabolismo , Ratos , Ribonucleoproteínas Nucleares Pequenas/genética , Alinhamento de Sequência , Proteínas Centrais de snRNPAssuntos
Cromossomos Humanos Par 15 , RNA Nucleolar Pequeno/metabolismo , Receptores 5-HT2 de Serotonina/genética , Adulto , Encéfalo/metabolismo , Estudos de Casos e Controles , Pré-Escolar , Lobo Frontal/patologia , Regulação da Expressão Gênica , Humanos , Modelos Genéticos , Fenótipo , Síndrome de Prader-Willi/genética , Edição de RNARESUMO
Mammalian neural progenitor cells divide asymmetrically to self-renew and produce a neuron by segregating cytosolic Numb proteins primarily to one daughter cell. Numb signaling specifies progenitor over neuronal fates but, paradoxically, also promotes neuronal differentiation. Here we report that ACBD3 is a Numb partner in cell-fate specification. ACBD3 and Numb proteins interact through an essential Numb domain, and the respective loss- and gain-of-function mutant mice share phenotypic similarities. Interestingly, ACBD3 associates with the Golgi apparatus in neurons and interphase progenitor cells but becomes cytosolic after Golgi fragmentation during mitosis, when Numb activity is needed to distinguish the two daughter cells. Accordingly, cytosolic ACBD3 can act synergistically with Numb to specify cell fates, and its continuing presence during the progenitor cell cycle inhibits neuron production. We propose that Golgi fragmentation and reconstitution during cell cycle differentially regulate Numb signaling through changes in ACBD3 subcellular distribution and represent a mechanism for coupling cell-fate specification and cell-cycle progression.
Assuntos
Divisão Celular , Complexo de Golgi/metabolismo , Proteínas de Membrana/metabolismo , Proteínas do Tecido Nervoso/metabolismo , Receptores de GABA-A/metabolismo , Transdução de Sinais , Proteínas Adaptadoras de Transdução de Sinal , Animais , Animais Geneticamente Modificados , Linhagem da Célula , Citosol/química , Drosophila , Embrião de Mamíferos/metabolismo , Embrião não Mamífero , Desenvolvimento Embrionário/genética , Camundongos , Mitose , Neurônios/citologia , Fenótipo , Estrutura Terciária de Proteína , Receptores de GABA-A/genética , Células-Tronco/citologiaRESUMO
The epigenetic states of key regulatory genes must be altered to drive cell fate decisions in differentiating cells. This process must be coupled, at least transiently, to the DNA replication machinery. Only a few genes, however, have been shown to require DNA replication for their activation or repression upon induction of differentiation. We have developed a methodology for examining how gene expression is coupled to cell division during the early stages of differentiation of embryonal carcinoma (EC) cells. Using this approach, we find that the expression of the 5-hydroxytryptamine (serotonin) receptor 2C (Htr2c) is strongly increased in the second division after all-trans retinoic acid addition. We propose that the epigenetic activation of Htr2c in EC cells results from a chromatin remodeling process that requires at least two passages through S phase.