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1.
Nucleic Acids Res ; 48(18): 10500-10517, 2020 10 09.
Artigo em Inglês | MEDLINE | ID: mdl-32986830

RESUMO

The Xist lncRNA requires Repeat A, a conserved RNA element located in its 5' end, to induce gene silencing during X-chromosome inactivation. Intriguingly, Repeat A is also required for production of Xist. While silencing by Repeat A requires the protein SPEN, how Repeat A promotes Xist production remains unclear. We report that in mouse embryonic stem cells, expression of a transgene comprising the first two kilobases of Xist (Xist-2kb) causes transcriptional readthrough of downstream polyadenylation sequences. Readthrough required Repeat A and the ∼750 nucleotides downstream, did not require SPEN, and was attenuated by splicing. Despite associating with SPEN and chromatin, Xist-2kb did not robustly silence transcription, whereas a 5.5-kb Xist transgene robustly silenced transcription and read through its polyadenylation sequence. Longer, spliced Xist transgenes also induced robust silencing yet terminated efficiently. Thus, in contexts examined here, Xist requires sequence elements beyond its first two kilobases to robustly silence transcription, and the 5' end of Xist harbors SPEN-independent transcriptional antiterminator activity that can repress proximal cleavage and polyadenylation. In endogenous contexts, this antiterminator activity may help produce full-length Xist RNA while rendering the Xist locus resistant to silencing by the same repressive complexes that the lncRNA recruits to other genes.


Assuntos
Proteínas de Ligação a DNA/genética , RNA Longo não Codificante/genética , Proteínas de Ligação a RNA/genética , Transcrição Genética , Inativação do Cromossomo X/genética , Animais , Cromatina/genética , Regulação da Expressão Gênica no Desenvolvimento/genética , Inativação Gênica , Camundongos , Células-Tronco Embrionárias Murinas/metabolismo , Poliadenilação/genética , Sequências Repetitivas de Ácido Nucleico/genética , Cromossomo X/genética
2.
Nat Cell Biol ; 22(9): 1116-1129, 2020 09.
Artigo em Inglês | MEDLINE | ID: mdl-32807903

RESUMO

How allelic asymmetry is generated remains a major unsolved problem in epigenetics. Here we model the problem using X-chromosome inactivation by developing "BioRBP", an enzymatic RNA-proteomic method that enables probing of low-abundance interactions and an allelic RNA-depletion and -tagging system. We identify messenger RNA-decapping enzyme 1A (DCP1A) as a key regulator of Tsix, a noncoding RNA implicated in allelic choice through X-chromosome pairing. DCP1A controls Tsix half-life and transcription elongation. Depleting DCP1A causes accumulation of X-X pairs and perturbs the transition to monoallelic Tsix expression required for Xist upregulation. While ablating DCP1A causes hyperpairing, forcing Tsix degradation resolves pairing and enables Xist upregulation. We link pairing to allelic partitioning of CCCTC-binding factor (CTCF) and show that tethering DCP1A to one Tsix allele is sufficient to drive monoallelic Xist expression. Thus, DCP1A flips a bistable switch for the mutually exclusive determination of active and inactive Xs.


Assuntos
Endorribonucleases/metabolismo , RNA/metabolismo , Transativadores/metabolismo , Cromossomo X/metabolismo , Alelos , Animais , Fator de Ligação a CCCTC/metabolismo , Linhagem Celular , Feminino , Regulação da Expressão Gênica no Desenvolvimento/fisiologia , Camundongos , Camundongos Endogâmicos C57BL , RNA Mensageiro/metabolismo , Transcrição Genética/fisiologia , Regulação para Cima/fisiologia , Inativação do Cromossomo X/fisiologia
3.
Nucleic Acids Res ; 48(16): 9320-9335, 2020 09 18.
Artigo em Inglês | MEDLINE | ID: mdl-32813011

RESUMO

Heterogeneous nuclear ribonuclear protein K (hnRNPK) is an abundant RNA-binding protein crucial for a wide variety of biological processes. While its binding preference for multi-cytosine-patch (C-patch) containing RNA is well documented, examination of binding to known cellular targets that contain C-patches reveals an unexpected breadth of binding affinities. Analysis of in-cell crosslinking data reinforces the notion that simple C-patch preference is not fully predictive of hnRNPK localization within transcripts. The individual RNA-binding domains of hnRNPK work together to interact with RNA tightly, with the KH3 domain being neither necessary nor sufficient for binding. Rather, the RG/RGG domain is implicated in providing essential contributions to RNA-binding, but not DNA-binding, affinity. hnRNPK is essential for X chromosome inactivation, where it interacts with Xist RNA specifically through the Xist B-repeat region. We use this interaction with an RNA motif derived from this B-repeat region to determine the RNA-structure dependence of C-patch recognition. While the location preferences of hnRNPK for C-patches are conformationally restricted within the hairpin, these structural constraints are relieved in the absence of RNA secondary structure. Together, these results illustrate how this multi-domain protein's ability to accommodate and yet discriminate between diverse cellular RNAs allows for its broad cellular functions.


Assuntos
Ribonucleoproteínas Nucleares Heterogêneas Grupo K/genética , Motivos de Nucleotídeos/genética , RNA Longo não Codificante/genética , Ribonucleoproteínas/genética , Animais , Pareamento de Bases/genética , Núcleo Celular/genética , Feminino , Humanos , Proteínas de Ligação a RNA/genética , Inativação do Cromossomo X/genética
4.
BMC Med Genet ; 21(1): 153, 2020 07 22.
Artigo em Inglês | MEDLINE | ID: mdl-32698785

RESUMO

BACKGROUND: NAA10 is the catalytic subunit of the major N-terminal acetyltransferase complex NatA which acetylates almost half the human proteome. Over the past decade, many NAA10 missense variants have been reported as causative of genetic disease in humans. Individuals harboring NAA10 variants often display variable degrees of intellectual disability (ID), developmental delay, and cardiac anomalies. Initially, carrier females appeared to be oligo- or asymptomatic with X-inactivation pattern skewed towards the wild type allele. However, recently it has been shown that NAA10 variants can cause syndromic or non-syndromic intellectual disability in females as well. The impact of specific NAA10 variants and the X-inactivation pattern on the individual phenotype in females remains to be elucidated. CASE PRESENTATION: Here we present a novel de novo NAA10 (NM_003491.3) c.[47A > C];[=] (p.[His16Pro];[=]) variant identified in a young female. The 10-year-old girl has severely delayed motor and language development, disturbed behavior with hyperactivity and restlessness, moderate dilatation of the ventricular system and extracerebral CSF spaces. Her blood leukocyte X-inactivation pattern was skewed (95/5) towards the maternally inherited X-chromosome. Our functional study indicates that NAA10 p.(H16P) impairs NatA complex formation and NatA catalytic activity, while monomeric NAA10 catalytic activity appears to be intact. Furthermore, cycloheximide experiments show that the NAA10 H16P variant does not affect the cellular stability of NAA10. DISCUSSION AND CONCLUSIONS: We demonstrate that NAA10 p.(His16Pro) causes a severe form of syndromic ID in a girl most likely through impaired NatA-mediated Nt-acetylation of cellular proteins. X-inactivation analyses showed a skewed X-inactivation pattern in DNA from blood of the patient with the maternally inherited allele being preferentially methylated/inactivated.


Assuntos
Deficiência Intelectual/genética , Mutação/genética , Acetiltransferase N-Terminal A/genética , Acetiltransferase N-Terminal E/genética , Inativação do Cromossomo X/genética , Sequência de Aminoácidos , Biocatálise , Criança , Cicloeximida/metabolismo , Feminino , Células HeLa , Heterozigoto , Humanos , Masculino , Acetiltransferase N-Terminal A/química , Acetiltransferase N-Terminal E/química , Linhagem , Síndrome
5.
Nat Rev Genet ; 21(9): 555-571, 2020 09.
Artigo em Inglês | MEDLINE | ID: mdl-32514155

RESUMO

Genomic imprinting and X-chromosome inactivation (XCI) are classic epigenetic phenomena that involve transcriptional silencing of one parental allele. Germline-derived differential DNA methylation is the best-studied epigenetic mark that initiates imprinting, but evidence indicates that other mechanisms exist. Recent studies have revealed that maternal trimethylation of H3 on lysine 27 (H3K27me3) mediates autosomal maternal allele-specific gene silencing and has an important role in imprinted XCI through repression of maternal Xist. Furthermore, loss of H3K27me3-mediated imprinting contributes to the developmental defects observed in cloned embryos. This novel maternal H3K27me3-mediated non-canonical imprinting mechanism further emphasizes the important role of parental chromatin in development and could provide the basis for improving the efficiency of embryo cloning.


Assuntos
Cromossomos Humanos X , Metilação de DNA , Impressão Genômica , Histonas/metabolismo , Inativação do Cromossomo X , Animais , Gametogênese/genética , Regulação da Expressão Gênica no Desenvolvimento , Humanos , Lisina/metabolismo
6.
Cytogenet Genome Res ; 160(5): 245-254, 2020.
Artigo em Inglês | MEDLINE | ID: mdl-32485717

RESUMO

Chromosomal microdeletion syndromes present with a wide spectrum of clinical phenotypes that depend on the size and gene content of the affected region. In a healthy carrier, epigenetic mechanisms may compensate for the same microdeletion, which may segregate through several generations without any clinical symptoms until the epigenetic modifications no longer function. We report 2 novel cases of Xq24 microdeletions inherited from mothers with extremely skewed X-chromosome inactivation (sXCI). The first case is a boy presenting with X-linked mental retardation, Nascimento type, due to a 168-kb Xq24 microdeletion involving 5 genes (CXorf56, UBE2A, NKRF, SEPT6, and MIR766) inherited from a healthy mother and grandmother with sXCI. In the second family, the presence of a 239-kb Xq24 microdeletion involving 3 additional genes (SLC25A43, SLC25A5-AS1, and SLC25A5) was detected in a woman with sXCI and a history of recurrent pregnancy loss with a maternal family history without reproductive wastages or products of conception. These cases provide evidence that women with an Xq24 microdeletion and sXCI may be at risk for having a child with intellectual disability or for experiencing a pregnancy loss due to the ontogenetic pleiotropy of a chromosomal microdeletion and its incomplete penetrance modified by sXCI.


Assuntos
Aborto Habitual/genética , Deleção Cromossômica , Cromossomos Humanos X/genética , Mães , Enzimas de Conjugação de Ubiquitina/deficiência , Enzimas de Conjugação de Ubiquitina/genética , Inativação do Cromossomo X/genética , Adulto , Pré-Escolar , Epigênese Genética , Feminino , Humanos , Lactente , Recém-Nascido , Deficiência Intelectual/genética , Masculino , Fenótipo , Síndrome , Adulto Jovem
7.
J Genet ; 992020.
Artigo em Inglês | MEDLINE | ID: mdl-32529990

RESUMO

IQSEC2 is an X-linked gene highly expressed at the excitatory synapses where it plays a crucial role in α-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid receptor trafficking and synaptic plasticity. To date, several males and females with severe to profound intellectual disability have been reported harbouring frameshift and nonsense variants in this gene, whereas a milder phenotype has been recognized in females carrying missense pathogenic variants. Here, we report two novel IQSEC2 variants in four females with psychiatric features and otherwise variable cognitive impairment. A female (case 1) with severe verbal language learning disorder and a psychotic episode (precipitated by exposure to anti-contraceptive pill) harboured a de novo pathogenic frameshift variant (c.1170dupG,p.Gln391Alafs*5), whereas the female proband of family 2, displaying severe psychomotor regression and complex psychiatric features carried a missense variant of uncertain significance (c.770G[A,p.Ser257Asn) that was maternally inherited. Skewed X-inactivation was noted in the carrier mother. The maternal aunt, affected by schizophrenia, was found to bear the same IQSEC2 variant. We discuss the variable clinical presentation of IQSEC2 spectrum disorders and the challenging genotype-phenotype correlation, including the possible role of environmental factors as triggers for decompensation. Our report highlights how psychiatric features may be the main clinical presentation in subtle IQSEC2 phenotype, suggesting that the prevalence of IQSEC2 mutations in patients with psychiatric disorders may be underestimated.


Assuntos
Fatores de Troca do Nucleotídeo Guanina/genética , Deficiência Intelectual/genética , Mutação/genética , Feminino , Genes Ligados ao Cromossomo X , Estudos de Associação Genética , Humanos , Sequenciamento Completo do Exoma , Inativação do Cromossomo X
8.
Cytogenet Genome Res ; 160(6): 283-294, 2020.
Artigo em Inglês | MEDLINE | ID: mdl-32575101

RESUMO

X dosage compensation between XX female and XY male mammalian cells is achieved by a process known as X-chromosome inactivation (XCI). XCI initiates early during preimplantation development in female cells, and it is subsequently stably maintained in somatic cells. However, XCI is a reversible process that occurs in vivo in the inner cell mass of the blastocyst, in primordial germ cells or in spermatids during reprogramming. Erasure of transcriptional gene silencing can occur though a mechanism named X-chromosome reactivation (XCR). XCI and XCR have been substantially deciphered in the mouse, whereas they still remain debated in the human. In this review, we summarized the recent advances in the knowledge of X-linked gene dosage compensation during mouse and human preimplantation development and in pluripotent stem cells.


Assuntos
Desenvolvimento Embrionário/genética , Células-Tronco Pluripotentes/metabolismo , Inativação do Cromossomo X , Animais , Humanos , Camundongos
9.
Genes Dev ; 34(11-12): 733-744, 2020 06 01.
Artigo em Inglês | MEDLINE | ID: mdl-32482714

RESUMO

The X inactive-specific transcript (Xist) gene is the master regulator of X chromosome inactivation in mammals. Xist produces a long noncoding (lnc)RNA that accumulates over the entire length of the chromosome from which it is transcribed, recruiting factors to modify underlying chromatin and silence X-linked genes in cis Recent years have seen significant progress in identifying important functional elements in Xist RNA, their associated RNA-binding proteins (RBPs), and the downstream pathways for chromatin modification and gene silencing. In this review, we summarize progress in understanding both how these pathways function in Xist-mediated silencing and the complex interplay between them.


Assuntos
Proteínas/metabolismo , RNA Longo não Codificante/metabolismo , Inativação do Cromossomo X/genética , Proteínas de Ligação a DNA/metabolismo , Inativação Gênica/fisiologia , Metiltransferases/metabolismo , RNA Longo não Codificante/genética , Proteínas de Ligação a RNA/metabolismo , Receptores Citoplasmáticos e Nucleares/metabolismo
12.
Nature ; 580(7801): 142-146, 2020 04.
Artigo em Inglês | MEDLINE | ID: mdl-32238933

RESUMO

Paternal and maternal epigenomes undergo marked changes after fertilization1. Recent epigenomic studies have revealed the unusual chromatin landscapes that are present in oocytes, sperm and early preimplantation embryos, including atypical patterns of histone modifications2-4 and differences in chromosome organization and accessibility, both in gametes5-8 and after fertilization5,8-10. However, these studies have led to very different conclusions: the global absence of local topological-associated domains (TADs) in gametes and their appearance in the embryo8,9 versus the pre-existence of TADs and loops in the zygote5,11. The questions of whether parental structures can be inherited in the newly formed embryo and how these structures might relate to allele-specific gene regulation remain open. Here we map genomic interactions for each parental genome (including the X chromosome), using an optimized single-cell high-throughput chromosome conformation capture (HiC) protocol12,13, during preimplantation in the mouse. We integrate chromosome organization with allelic expression states and chromatin marks, and reveal that higher-order chromatin structure after fertilization coincides with an allele-specific enrichment of methylation of histone H3 at lysine 27. These early parental-specific domains correlate with gene repression and participate in parentally biased gene expression-including in recently described, transiently imprinted loci14. We also find TADs that arise in a non-parental-specific manner during a second wave of genome assembly. These de novo domains are associated with active chromatin. Finally, we obtain insights into the relationship between TADs and gene expression by investigating structural changes to the paternal X chromosome before and during X chromosome inactivation in preimplantation female embryos15. We find that TADs are lost as genes become silenced on the paternal X chromosome but linger in regions that escape X chromosome inactivation. These findings demonstrate the complex dynamics of three-dimensional genome organization and gene expression during early development.


Assuntos
Blastocisto/citologia , Blastocisto/metabolismo , Cromatina/metabolismo , Desenvolvimento Embrionário/genética , Fertilização/genética , Células Germinativas/citologia , Pais , Alelos , Animais , Cromatina/química , Cromatina/genética , Posicionamento Cromossômico , Cromossomos de Mamíferos/química , Cromossomos de Mamíferos/genética , Cromossomos de Mamíferos/metabolismo , Feminino , Regulação da Expressão Gênica no Desenvolvimento , Genoma/genética , Impressão Genômica , Células Germinativas/metabolismo , Histonas/química , Histonas/metabolismo , Masculino , Metilação , Camundongos , Proteínas do Grupo Polycomb/metabolismo , Análise de Célula Única , Inativação do Cromossomo X/genética
13.
Cytogenet Genome Res ; 160(3): 124-133, 2020.
Artigo em Inglês | MEDLINE | ID: mdl-32187602

RESUMO

Trisomy 14 is incompatible with live, but there are several patients reported with mosaic trisomy 14. We aimed to study the pattern of X inactivation and its effect on a translocated autosome and to find out an explanation of the involvement of chromosome 14 in 2 different structural chromosomal abnormalities. We report on a girl with frontal bossing, hypertelorism, low-set ears, micrognathia, cleft palate, congenital heart disease, and abnormal skin pigmentations. The patient displayed iris, choroidal, and retinal coloboma and agenesis of the corpus callosum and cerebellar vermis hypoplasia. Cytogenetic analysis revealed a karyotype 45,X,der(X)t(X;14)(q24;q11)[85]/46,XX,rob(14;14)(q10;q10),+14[35]. Array-CGH for blood and buccal mucosa showed high mosaic trisomy 14 and an Xq deletion. MLPA detected trisomy 14 in blood and buccal mucosa and also showed normal methylation of the imprinting center. FISH analysis confirmed the cell line with trisomy 14 (30%) and demonstrated the mosaic deletion of the Xq subtelomere in both tissues. There was 100% skewed X inactivation for the t(X;14). SNP analysis of the patient showed no region of loss of heterozygosity on chromosome 14. Also, genotype call analysis of the patient and her parents showed heterozygous alleles of chromosome 14 with no evidence of uniparental disomy. Our patient had a severe form of mosaic trisomy 14. We suggest that this cytogenetic unique finding that involved 2 cell lines with structural abnormalities of chromosome 14 occurred in an early postzygotic division. These 2 events may have happened separately or maybe there is a kind of trisomy or monosomy rescue due to dynamic cytogenetic interaction between different cell lines to compensate for gene dosage.


Assuntos
Anormalidades Múltiplas/genética , Trissomia/genética , Inativação do Cromossomo X/genética , Anormalidades Múltiplas/fisiopatologia , Pré-Escolar , Cromossomos Humanos Par 14/genética , Feminino , Humanos , Hibridização in Situ Fluorescente , Cariótipo , Cariotipagem , Mosaicismo , Fenótipo , Translocação Genética/genética , Trissomia/fisiopatologia
14.
Nature ; 578(7795): 365-366, 2020 02.
Artigo em Inglês | MEDLINE | ID: mdl-32066915
15.
Cytogenet Genome Res ; 160(2): 80-84, 2020.
Artigo em Inglês | MEDLINE | ID: mdl-32018271

RESUMO

Unbalanced X;autosome translocations are a rare occurrence with a wide variability in clinical presentation in which the X chromosome unbalance is usually mitigated by a favorable X inactivation pattern. In most cases, this compensation mechanism is incomplete, and the patients show a syndromic clinical presentation. We report the case of a family with 4 women, of 3 different generations, carrying an unbalanced X;7 translocation with a derivative X;7 chromosome and showing a skewed X inactivation pattern with a preferential activation of the normal X. None of the carriers show intellectual disability, and all of them have a very mild clinical presentation mainly characterized by gynecological/hormonal issues and autoimmune disorders. We underline the necessity of family testing for a correct genetic consultation, especially in the field of prenatal diagnosis. We indeed discuss the fact that X;autosome translocations may lead to self-immunization, as skewed X chromosome inactivation has already been proved to be related to autoimmune disorders.


Assuntos
Doenças Autoimunes/genética , Transtornos Cromossômicos/genética , Cromossomos Humanos X/genética , Translocação Genética , Adulto , Feminino , Humanos , Pessoa de Meia-Idade , Linhagem , Fenótipo , Gravidez , Inativação do Cromossomo X
16.
F1000Res ; 92020.
Artigo em Inglês | MEDLINE | ID: mdl-32047616

RESUMO

Female mammals express the long noncoding X inactivation-specific transcript ( Xist) RNA to initiate X chromosome inactivation (XCI) that eventually results in the formation of the Barr body. Xist encompasses half a dozen repeated sequence stretches containing motifs for RNA-binding proteins that recruit effector complexes with functions for silencing genes and establishing a repressive chromatin configuration. Functional characterization of these effector proteins unveils the cooperation of a number of pathways to repress genes on the inactive X chromosome. Mechanistic insights can be extended to other noncoding RNAs with similar structure and open avenues for the design of new therapies to switch off gene expression. Here we review recent advances in the understanding of Xist and on this basis try to synthesize a model for the initiation of XCI.


Assuntos
Inativação do Cromossomo X , Cromossomo X , Animais , Cromatina , Feminino , Inativação Gênica , RNA Longo não Codificante/genética
17.
Proc Natl Acad Sci U S A ; 117(8): 4262-4272, 2020 02 25.
Artigo em Inglês | MEDLINE | ID: mdl-32041873

RESUMO

Long thought to be dispensable after establishing X chromosome inactivation (XCI), Xist RNA is now known to also maintain the inactive X (Xi). To what extent somatic X reactivation causes physiological abnormalities is an active area of inquiry. Here, we use multiple mouse models to investigate in vivo consequences. First, when Xist is deleted systemically in post-XCI embryonic cells using the Meox2-Cre driver, female pups exhibit no morbidity or mortality despite partial X reactivation. Second, when Xist is conditionally deleted in epithelial cells using Keratin14-Cre or in B cells using CD19-Cre, female mice have a normal life span without obvious illness. Third, when Xist is deleted in gut using Villin-Cre, female mice remain healthy despite significant X-autosome dosage imbalance. Finally, when the gut is acutely stressed by azoxymethane/dextran sulfate (AOM/DSS) exposure, both Xist-deleted and wild-type mice develop gastrointestinal tumors. Intriguingly, however, under prolonged stress, mutant mice develop larger tumors and have a higher tumor burden. The effect is female specific. Altogether, these observations reveal a surprising systemic tolerance to Xist loss but importantly reveal that Xist and XCI are protective to females during chronic stress.


Assuntos
Neoplasias Gastrointestinais/fisiopatologia , Doenças Genéticas Ligadas ao Cromossomo X/genética , Doenças Genéticas Ligadas ao Cromossomo X/microbiologia , RNA Longo não Codificante/genética , Cromossomo X/genética , Animais , Feminino , Neoplasias Gastrointestinais/etiologia , Neoplasias Gastrointestinais/genética , Neoplasias Gastrointestinais/metabolismo , Trato Gastrointestinal/metabolismo , Doenças Genéticas Ligadas ao Cromossomo X/complicações , Doenças Genéticas Ligadas ao Cromossomo X/metabolismo , Humanos , Masculino , Camundongos , RNA Longo não Codificante/metabolismo , Estresse Fisiológico , Carga Tumoral , Inativação do Cromossomo X
18.
Cell Mol Life Sci ; 77(15): 2949-2958, 2020 Aug.
Artigo em Inglês | MEDLINE | ID: mdl-32040694

RESUMO

During embryonic development, one of the two X chromosomes of a mammalian female cell is randomly inactivated by the X chromosome inactivation mechanism, which is mainly dependent on the regulation of the non-coding RNA X-inactive specific transcript at the X chromosome inactivation center. There are three proteins that are essential for X-inactive specific transcript to function properly: scaffold attachment factor-A, lamin B receptor, and SMRT- and HDAC-associated repressor protein. In addition, the absence of X-inactive specific transcript expression promotes tumor development. During the process of chromosome inactivation, some tumor suppressor genes escape inactivation of the X chromosome and thereby continue to play a role in tumor suppression. A well-functioning tumor suppressor gene on the idle X chromosome in women is one of the reasons they have a lower propensity to develop cancer than men, women thereby benefit from this enhanced tumor suppression. This review will explore the mechanism of X chromosome inactivation, discuss the relationship between X chromosome inactivation and tumorigenesis, and consider the consequent sex differences in cancer.


Assuntos
Cromossomos Humanos X/metabolismo , Neoplasias/patologia , Humanos , Mutação , Neoplasias/metabolismo , RNA Longo não Codificante/metabolismo , Caracteres Sexuais , Proteínas Supressoras de Tumor/genética , Proteínas Supressoras de Tumor/metabolismo , Inativação do Cromossomo X
19.
Nature ; 578(7795): 455-460, 2020 02.
Artigo em Inglês | MEDLINE | ID: mdl-32025035

RESUMO

Xist represents a paradigm for the function of long non-coding RNA in epigenetic regulation, although how it mediates X-chromosome inactivation (XCI) remains largely unexplained. Several proteins that bind to Xist RNA have recently been identified, including the transcriptional repressor SPEN1-3, the loss of which has been associated with deficient XCI at multiple loci2-6. Here we show in mice that SPEN is a key orchestrator of XCI in vivo and we elucidate its mechanism of action. We show that SPEN is essential for initiating gene silencing on the X chromosome in preimplantation mouse embryos and in embryonic stem cells. SPEN is dispensable for maintenance of XCI in neural progenitors, although it significantly decreases the expression of genes that escape XCI. We show that SPEN is immediately recruited to the X chromosome upon the upregulation of Xist, and is targeted to enhancers and promoters of active genes. SPEN rapidly disengages from chromatin upon gene silencing, suggesting that active transcription is required to tether SPEN to chromatin. We define the SPOC domain as a major effector of the gene-silencing function of SPEN, and show that tethering SPOC to Xist RNA is sufficient to mediate gene silencing. We identify the protein partners of SPOC, including NCoR/SMRT, the m6A RNA methylation machinery, the NuRD complex, RNA polymerase II and factors involved in the regulation of transcription initiation and elongation. We propose that SPEN acts as a molecular integrator for the initiation of XCI, bridging Xist RNA with the transcription machinery-as well as with nucleosome remodellers and histone deacetylases-at active enhancers and promoters.


Assuntos
Proteínas de Ligação a DNA/metabolismo , Epigênese Genética , Inativação Gênica , Proteínas de Ligação a RNA/metabolismo , Transcrição Genética , Inativação do Cromossomo X/genética , Cromossomo X/genética , Animais , Blastocisto/citologia , Blastocisto/metabolismo , Cromatina/genética , Cromatina/metabolismo , Proteínas de Ligação a DNA/química , Embrião de Mamíferos/citologia , Embrião de Mamíferos/metabolismo , Células-Tronco Embrionárias/metabolismo , Elementos Facilitadores Genéticos/genética , Feminino , Histona Desacetilases/metabolismo , Masculino , Metilação , Camundongos , Regiões Promotoras Genéticas/genética , Domínios Proteicos , RNA Longo não Codificante/genética , Proteínas de Ligação a RNA/química
20.
Exp Hematol ; 83: 2-11, 2020 03.
Artigo em Inglês | MEDLINE | ID: mdl-32001340

RESUMO

The history of clonal hematopoiesis (CH) research is punctuated by several seminal discoveries that have forged our understanding of cancer development. The clever application of the principle of random X-chromosome inactivation (XCI) in females led to the development of the first test to identify clonal derivation of cells. Initially limited by a low level of informativeness, the applicability of these assays expanded with differential methylation-based assays at highly polymorphic genes such as the human androgen receptor (HUMARA). Twenty years ago, the observation that skewing of XCI ratios increases as women age was the first clue that led to the identification of mutations in the TET2 gene in hematologically normal aging individuals. In 2014, large-scale genomic approaches of three cohorts allowed definition of CH, which was reported to increase the risk of developing hematologic cancers and cardiovascular diseases. These observations created a fertile field of investigation aimed at investigating the etiology and consequences of CH. The most frequently mutated genes in CH are DNMT3A, TET2, and ASXL1, which have a role in hematopoietic stem cell (HSC) development and self-renewal. These mutations confer a competitive advantage to the CH clones. However, the penetrance of CH is age dependent but incomplete, suggesting the influence of extrinsic factors. Recent data attribute a modest role to genetic predisposition, but several observations point to the impact of a pro-inflammatory milieu that advantages the mutated clones. CH may be a barometer of nonhealthy aging, and interventions devised at curbing its initiation or progression should be a research priority.


Assuntos
Envelhecimento/genética , Pesquisa Biomédica/história , Cromossomos Humanos X/genética , Hematopoese/genética , Mutação , Inativação do Cromossomo X , Adulto , Proteínas de Ligação a DNA/genética , Feminino , Células-Tronco Hematopoéticas , História do Século XX , História do Século XXI , Humanos , Masculino , Proteínas Proto-Oncogênicas/genética , Receptores Androgênicos/genética , Proteínas Repressoras/genética
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