RESUMO
X chromosome inactivation (XCI) is a female-specific process in which one X chromosome is silenced to balance X-linked gene expression between the sexes. XCI is initiated in early development by upregulation of the lncRNA Xist on the future inactive X (Xi). A subset of X-linked genes escape silencing and thus have higher expression in females, suggesting female-specific functions. One of these genes is the highly conserved gene Kdm6a , which encodes a histone demethylase that removes methyl groups at H3K27 to facilitate gene expression. Here, we investigate the role of KDM6A in the regulation of Xist . We observed impaired upregulation of Xist during early stages of differentiation in hybrid mouse ES cells following CRISPR/Cas9 knockout of Kdm6a . This is associated with reduced Xist RNA coating of the Xi, suggesting diminished XCI potency. Indeed, Kdm6a knockout results in aberrant overexpression of genes from the Xi after differentiation. KDM6A binds to the Xist promoter and knockout cells show an increase in H3K27me3 at Xist . These results indicate that KDM6A plays a role in the initiation of XCI through histone demethylase-dependent activation of Xist during early differentiation.
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Background: The number and escape levels of genes that escape X chromosome inactivation (XCI) in female somatic cells vary among tissues and cell types, potentially contributing to specific sex differences. Here we investigate the role of CTCF, a master chromatin conformation regulator, in regulating escape from XCI. CTCF binding profiles and epigenetic features were systematically examined at constitutive and facultative escape genes using mouse allelic systems to distinguish the inactive X (Xi) and active X (Xa) chromosomes. Results: We found that escape genes are located inside domains flanked by convergent arrays of CTCF binding sites, consistent with the formation of loops. In addition, strong and divergent CTCF binding sites often located at the boundaries between escape genes and adjacent neighbors subject to XCI would help insulate domains. Facultative escapees show clear differences in CTCF binding dependent on their XCI status in specific cell types/tissues. Concordantly, deletion but not inversion of a CTCF binding site at the boundary between the facultative escape gene Car5b and its silent neighbor Siah1b resulted in loss of Car5b escape. Reduced CTCF binding and enrichment of a repressive mark over Car5b in cells with a boundary deletion indicated loss of looping and insulation. In mutant lines in which either the Xi-specific compact structure or its H3K27me3 enrichment was disrupted, escape genes showed an increase in gene expression and associated active marks, supporting the roles of the 3D Xi structure and heterochromatic marks in constraining levels of escape. Conclusion: Our findings indicate that escape from XCI is modulated both by looping and insulation of chromatin via convergent arrays of CTCF binding sites and by compaction and epigenetic features of the surrounding heterochromatin.
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BACKGROUND: KDM6A is a demethylase encoded by a gene with female-biased expression due to escape from X inactivation. Its main role is to facilitate gene expression through removal of the repressive H3K27me3 mark, with evidence of some additional histone demethylase-independent functions. KDM6A mutations have been implicated in congenital disorders such as Kabuki Syndrome, as well as in sex differences in cancer. METHODS: Kdm6a was knocked out using CRISPR/Cas9 gene editing in F1 male and female mouse embryonic stem cells (ES) derived from reciprocal crosses between C57BL6 x Mus castaneus. Diploid and allelic RNA-seq analyses were done to compare gene expression between wild-type and Kdm6a knockout (KO) clones. The effects of Kdm6a KO on sex-biased gene expression were investigated by comparing gene expression between male and female ES cells. Changes in H3K27me3 enrichment and chromatin accessibility at promoter regions of genes with expression changes were characterized by ChIP-seq and ATAC-seq followed by diploid and allelic analyses. RESULTS: We report that Kdm6a KO in male and female embryonic stem (ES) cells derived from F1 hybrid mice cause extensive gene dysregulation, disruption of sex biases, and specific parental allele effects. Among the dysregulated genes are candidate genes that may explain abnormal developmental features of Kabuki syndrome caused by KDM6A mutations in human. Strikingly, Kdm6a knockouts result in a decrease in sex-biased expression and in preferential downregulation of the maternal alleles of a number of genes. Most promoters of dysregulated genes show concordant epigenetic changes including gain of H3K27me3 and loss of chromatin accessibility, but there was less concordance when considering allelic changes. CONCLUSIONS: Our study reveals new sex-related roles of KDM6A in the regulation of developmental genes, the maintenance of sex-biased gene expression, and the differential expression of parental alleles.
Assuntos
Histona Desmetilases , Histonas , Anormalidades Múltiplas , Alelos , Animais , Cromatina , Face/anormalidades , Feminino , Doenças Hematológicas , Histona Desmetilases/genética , Histona Desmetilases/metabolismo , Histonas/genética , Histonas/metabolismo , Humanos , Masculino , Camundongos , Doenças VestibularesRESUMO
X inactivation represents a complex multi-layer epigenetic mechanism that profoundly modifies chromatin composition and structure of one X chromosome in females. The heterochromatic inactive X chromosome adopts a unique 3D bipartite structure and a location close to the nuclear periphery or the nucleolus. X-linked lncRNA loci and their transcripts play important roles in the recruitment of proteins that catalyze chromatin and DNA modifications for silencing, as well as in the control of chromatin condensation and location of the inactive X chromosome. A subset of genes escapes X inactivation, raising questions about mechanisms that preserve their expression despite being embedded within heterochromatin. Escape gene expression differs between males and females, which can lead to physiological sex differences. We review recent studies that emphasize challenges in understanding the role of lncRNAs in the control of epigenetic modifications, structural features and nuclear positioning of the inactive X chromosome. Second, we highlight new findings about the distribution of genes that escape X inactivation based on single cell studies, and discuss the roles of escape genes in eliciting sex differences in health and disease.
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Conventional methods for single-cell genome sequencing are limited with respect to uniformity and throughput. Here, we describe sci-L3, a single-cell sequencing method that combines combinatorial indexing (sci-) and linear (L) amplification. The sci-L3 method adopts a 3-level (3) indexing scheme that minimizes amplification biases while enabling exponential gains in throughput. We demonstrate the generalizability of sci-L3 with proof-of-concept demonstrations of single-cell whole-genome sequencing (sci-L3-WGS), targeted sequencing (sci-L3-target-seq), and a co-assay of the genome and transcriptome (sci-L3-RNA/DNA). We apply sci-L3-WGS to profile the genomes of >10,000 sperm and sperm precursors from F1 hybrid mice, mapping 86,786 crossovers and characterizing rare chromosome mis-segregation events in meiosis, including instances of whole-genome equational chromosome segregation. We anticipate that sci-L3 assays can be applied to fully characterize recombination landscapes, to couple CRISPR perturbations and measurements of genome stability, and to other goals requiring high-throughput, high-coverage single-cell sequencing.
Assuntos
Perfilação da Expressão Gênica , Sequenciamento de Nucleotídeos em Larga Escala , Técnicas de Amplificação de Ácido Nucleico , Análise de Sequência de DNA , Análise de Sequência de RNA , Análise de Célula Única/métodos , Sequenciamento Completo do Genoma , Animais , Segregação de Cromossomos , Masculino , Meiose/genética , Camundongos , Estudo de Prova de Conceito , Espermatozoides/fisiologia , Transcriptoma , Fluxo de TrabalhoRESUMO
X chromosome inactivation silences one X chromosome in female mammals. However, this silencing is incomplete, and some genes escape X inactivation. We describe methods to determine the chromosome-wide X inactivation status of genes in tissues or cell lines derived from mice using a combination of skewing of X inactivation and allele-specific analyses of gene expression based on RNA-seq.
Assuntos
Alelos , Embrião de Mamíferos/metabolismo , Perfilação da Expressão Gênica/métodos , Inativação do Cromossomo X , Animais , Linhagem Celular , Epigenômica/métodos , Feminino , Regulação da Expressão Gênica no Desenvolvimento , Camundongos , Camundongos Endogâmicos C57BL , Polimorfismo de Nucleotídeo Único , Análise de Sequência de RNA/métodosRESUMO
We applied a combinatorial indexing assay, sci-ATAC-seq, to profile genome-wide chromatin accessibility in â¼100,000 single cells from 13 adult mouse tissues. We identify 85 distinct patterns of chromatin accessibility, most of which can be assigned to cell types, and â¼400,000 differentially accessible elements. We use these data to link regulatory elements to their target genes, to define the transcription factor grammar specifying each cell type, and to discover in vivo correlates of heterogeneity in accessibility within cell types. We develop a technique for mapping single cell gene expression data to single-cell chromatin accessibility data, facilitating the comparison of atlases. By intersecting mouse chromatin accessibility with human genome-wide association summary statistics, we identify cell-type-specific enrichments of the heritability signal for hundreds of complex traits. These data define the in vivo landscape of the regulatory genome for common mammalian cell types at single-cell resolution.
Assuntos
Cromatina/química , Análise de Célula Única/métodos , Animais , Análise por Conglomerados , Epigênese Genética , Epigenômica , Regulação da Expressão Gênica , Genoma Humano , Estudo de Associação Genômica Ampla , Humanos , Masculino , Mamíferos , Camundongos , Camundongos Endogâmicos C57BL , Fatores de TranscriçãoRESUMO
DNA methylation at gene promoters in a CG context is associated with transcriptional repression, including at genes silenced on the inactive X chromosome in females. Non-CG methylation (mCH) is a distinct feature of the neuronal epigenome that is differentially distributed between males and females on the X chromosome. However, little is known about differences in mCH on the active (Xa) and inactive (Xi) X chromosomes because stochastic X-chromosome inactivation (XCI) confounds allele-specific epigenomic profiling. We used whole-genome bisulfite sequencing in a mouse model with nonrandom XCI to examine allele-specific DNA methylation in frontal cortex. Xi was largely devoid of mCH, whereas Xa contained abundant mCH similar to the male X chromosome and the autosomes. In contrast to the repressive association of DNA methylation at CG dinucleotides (mCG), mCH accumulates on Xi in domains with transcriptional activity, including the bodies of most genes that escape XCI and at the X-inactivation center, validating this epigenetic mark as a signature of transcriptional activity. Escape genes showing CH hypermethylation were the only genes with CG-hypomethylated promoters on Xi, a well-known mark of active transcription. Finally, we found extensive allele-specific mCH and mCG at autosomal imprinted regions, some with a negative correlation between methylation in the two contexts, further supporting their distinct functions. Our findings show that neuronal mCH functions independently of mCG and is a highly dynamic epigenomic correlate of allele-specific gene regulation.
Assuntos
Encéfalo/fisiologia , Cromatina/metabolismo , Metilação de DNA , Alelos , Animais , Epigênese Genética , Feminino , Impressão Genômica , Masculino , Camundongos Endogâmicos C57BL , Camundongos Mutantes , Polimorfismo de Nucleotídeo Único , RNA Longo não Codificante/genética , Cromossomo X , Inativação do Cromossomo XRESUMO
X-chromosome inactivation, which was discovered by Mary Lyon in 1961 results in random silencing of one X chromosome in female mammals. This review is dedicated to Mary Lyon, who passed away last year. She predicted many of the features of X inactivation, for e.g., the existence of an X inactivation center, the role of L1 elements in spreading of silencing and the existence of genes that escape X inactivation. Starting from her published work here we summarize advances in the field.
Assuntos
Inativação Gênica/fisiologia , Inativação do Cromossomo X/genética , Cromossomo X/genética , Animais , HumanosRESUMO
X chromosome inactivation (XCI) is a female-specific mechanism that serves to balance gene dosage between the sexes whereby one X chromosome in females is inactivated during early development. Despite this silencing, a small portion of genes escape inactivation and remain expressed from the inactive X (Xi). Little is known about the distribution of escape from XCI in different tissues in vivo and about the mechanisms that control tissue-specific differences. Using a new binomial model in conjunction with a mouse model with identifiable alleles and skewed X inactivation we are able to survey genes that escape XCI in vivo. We show that escape from X inactivation can be a common feature of some genes, whereas others escape in a tissue specific manner. Furthermore, we characterize the chromatin environment of escape genes and show that expression from the Xi correlates with factors associated with open chromatin and that CTCF co-localizes with escape genes. Here, we provide a detailed description of the experimental design and data analysis pipeline we used to assay allele-specific expression and epigenetic characteristics of genes escaping X inactivation. The data is publicly available through the GEO database under ascension numbers GSM1014171, GSE44255, and GSE59779. Interpretation and discussion of these data are included in a previously published study (Berletch et al., 2015) [1].
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BACKGROUND: In mammals, one of the female X chromosomes and all imprinted genes are expressed exclusively from a single allele in somatic cells. To evaluate structural changes associated with allelic silencing, we have applied a recently developed Hi-C assay that uses DNase I for chromatin fragmentation to mouse F1 hybrid systems. RESULTS: We find radically different conformations for the two female mouse X chromosomes. The inactive X has two superdomains of frequent intrachromosomal contacts separated by a boundary region. Comparison with the recently reported two-superdomain structure of the human inactive X shows that the genomic content of the superdomains differs between species, but part of the boundary region is conserved and located near the Dxz4/DXZ4 locus. In mouse, the boundary region also contains a minisatellite, Ds-TR, and both Dxz4 and Ds-TR appear to be anchored to the nucleolus. Genes that escape X inactivation do not cluster but are located near the periphery of the 3D structure, as are regions enriched in CTCF or RNA polymerase. Fewer short-range intrachromosomal contacts are detected for the inactive alleles of genes subject to X inactivation compared with the active alleles and with genes that escape X inactivation. This pattern is also evident for imprinted genes, in which more chromatin contacts are detected for the expressed allele. CONCLUSIONS: By applying a novel Hi-C method to map allelic chromatin contacts, we discover a specific bipartite organization of the mouse inactive X chromosome that probably plays an important role in maintenance of gene silencing.
Assuntos
Inativação do Cromossomo X , Cromossomo X/química , Animais , Fator de Ligação a CCCTC , Linhagem Celular , Nucléolo Celular/metabolismo , Células Cultivadas , Cromossomos Humanos X/química , Feminino , Impressão Genômica , Humanos , Masculino , Camundongos , RNA Polimerase II/química , RNA Polimerase II/metabolismo , Proteínas Repressoras/química , Proteínas Repressoras/metabolismo , Cromossomo X/metabolismoRESUMO
BACKGROUND: In mammals, X chromosome genes are present in one copy in males and two in females. To balance the dosage of X-linked gene expression between the sexes, one of the X chromosomes in females is silenced. X inactivation is initiated by upregulation of the lncRNA (long non-coding RNA) Xist and recruitment of specific chromatin modifiers. The inactivated X chromosome becomes heterochromatic and visits a specific nuclear compartment adjacent to the nucleolus. RESULTS: Here, we show a novel role for the lncRNA Firre in anchoring the inactive mouse X chromosome and preserving one of its main epigenetic features, H3K27me3. Similar to Dxz4, Firre is X-linked and expressed from a macrosatellite repeat locus associated with a cluster of CTCF and cohesin binding sites, and is preferentially located adjacent to the nucleolus. CTCF binding present initially in both male and female mouse embryonic stem cells is lost from the active X during development. Knockdown of Firre disrupts perinucleolar targeting and H3K27me3 levels in mouse fibroblasts, demonstrating a role in maintenance of an important epigenetic feature of the inactive X chromosome. No X-linked gene reactivation is seen after Firre knockdown; however, a compensatory increase in the expression of chromatin modifier genes implicated in X silencing is observed. Further experiments in female embryonic stem cells suggest that Firre does not play a role in X inactivation onset. CONCLUSIONS: The X-linked lncRNA Firre helps to position the inactive X chromosome near the nucleolus and to preserve one of its main epigenetic features.
Assuntos
Histona Desmetilases com o Domínio Jumonji/genética , RNA Longo não Codificante/genética , Proteínas Repressoras/genética , Inativação do Cromossomo X/genética , Animais , Sítios de Ligação , Fator de Ligação a CCCTC , Metilação de DNA/genética , Feminino , Masculino , Camundongos , Regiões Promotoras Genéticas , Proteínas Repressoras/metabolismo , Cromossomo X/genéticaRESUMO
X chromosome inactivation (XCI) silences most genes on one X chromosome in female mammals, but some genes escape XCI. To identify escape genes in vivo and to explore molecular mechanisms that regulate this process we analyzed the allele-specific expression and chromatin structure of X-linked genes in mouse tissues and cells with skewed XCI and distinguishable alleles based on single nucleotide polymorphisms. Using a binomial model to assess allelic expression, we demonstrate a continuum between complete silencing and expression from the inactive X (Xi). The validity of the RNA-seq approach was verified using RT-PCR with species-specific primers or Sanger sequencing. Both common escape genes and genes with significant differences in XCI status between tissues were identified. Such genes may be candidates for tissue-specific sex differences. Overall, few genes (3-7%) escape XCI in any of the mouse tissues examined, suggesting stringent silencing and escape controls. In contrast, an in vitro system represented by the embryonic-kidney-derived Patski cell line showed a higher density of escape genes (21%), representing both kidney-specific escape genes and cell-line specific escape genes. Allele-specific RNA polymerase II occupancy and DNase I hypersensitivity at the promoter of genes on the Xi correlated well with levels of escape, consistent with an open chromatin structure at escape genes. Allele-specific CTCF binding on the Xi clustered at escape genes and was denser in brain compared to the Patski cell line, possibly contributing to a more compartmentalized structure of the Xi and fewer escape genes in brain compared to the cell line where larger domains of escape were observed.
Assuntos
Inativação do Cromossomo X , Animais , Fator de Ligação a CCCTC , Desoxirribonuclease I/metabolismo , Feminino , Camundongos , Especificidade de Órgãos , Polimorfismo de Nucleotídeo Único , RNA Polimerase II/metabolismo , Proteínas Repressoras/metabolismo , Análise de Sequência de RNARESUMO
Genes on the mammalian X chromosome are present in one copy in males and two copies in females. The complex mechanisms that regulate the X chromosome lead to evolutionary and physiological variability in gene expression between species, the sexes, individuals, developmental stages, tissues and cell types. In early development, delayed and incomplete X chromosome inactivation (XCI) in some species causes variability in gene expression. Additional diversity stems from escape from XCI and from mosaicism or XCI skewing in females. This causes sex-specific differences that manifest as differential gene expression and associated phenotypes. Furthermore, the complexity and diversity of X dosage regulation affect the severity of diseases caused by X-linked mutations.
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Transtornos Cromossômicos , Cromossomos Humanos X , Regulação da Expressão Gênica , Doenças Genéticas Ligadas ao Cromossomo X , Caracteres Sexuais , Inativação do Cromossomo X , Animais , Transtornos Cromossômicos/genética , Transtornos Cromossômicos/metabolismo , Cromossomos Humanos X/genética , Cromossomos Humanos X/metabolismo , Feminino , Doenças Genéticas Ligadas ao Cromossomo X/genética , Doenças Genéticas Ligadas ao Cromossomo X/metabolismo , Humanos , Masculino , MosaicismoRESUMO
The Rhox cluster on the mouse X chromosome contains reproduction-related homeobox genes expressed in a sexually dimorphic manner. We report that two members of the Rhox cluster, Rhox6 and 9, are regulated by de-methylation of histone H3 at lysine 27 by KDM6A, a histone demethylase with female-biased expression. Consistent with other homeobox genes, Rhox6 and 9 are in bivalent domains prior to embryonic stem cell differentiation and thus poised for activation. In female mouse ES cells, KDM6A is specifically recruited to Rhox6 and 9 for gene activation, a process inhibited by Kdm6a knockdown in a dose-dependent manner. In contrast, KDM6A occupancy at Rhox6 and 9 is low in male ES cells and knockdown has no effect on expression. In mouse ovary where Rhox6 and 9 remain highly expressed, KDM6A occupancy strongly correlates with expression. Our study implicates Kdm6a, a gene that escapes X inactivation, in the regulation of genes important in reproduction, suggesting that KDM6A may play a role in the etiology of developmental and reproduction-related effects of X chromosome anomalies.
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Células-Tronco Embrionárias/metabolismo , Histona Desmetilases/genética , Proteínas de Homeodomínio/genética , Reprodução/genética , Animais , Metilação de DNA , Células-Tronco Embrionárias/citologia , Feminino , Regulação da Expressão Gênica no Desenvolvimento , Histona Desmetilases/metabolismo , Proteínas de Homeodomínio/metabolismo , Histona Desmetilases com o Domínio Jumonji/genética , Camundongos , Reprodução/fisiologia , Caracteres Sexuais , Inativação do Cromossomo X/genéticaRESUMO
X upregulation in mammals increases levels of expressed X-linked transcripts to compensate for autosomal biallelic expression. Here, we present molecular mechanisms that enhance X expression at transcriptional and posttranscriptional levels. Active mouse X-linked promoters are enriched in the initiation form of RNA polymerase II (PolII-S5p) and in specific histone marks, including histone H4 acetylated at lysine 16 (H4K16ac) and histone variant H2AZ. The H4K16 acetyltransferase males absent on the first (MOF), known to mediate the Drosophila X upregulation, is also enriched on the mammalian X. Depletion of MOF or male-specific lethal 1 (MSL1) in mouse ES cells causes a specific decrease in PolII-S5p and in expression of a subset of X-linked genes. Analyses of RNA half-life data sets show increased stability of mammalian X-linked transcripts. Both ancestral X-linked genes, defined as those conserved on chicken autosomes, and newly acquired X-linked genes are upregulated by similar mechanisms but to a different extent, suggesting that subsets of genes are distinctly regulated depending on their evolutionary history.
Assuntos
Histona Acetiltransferases/metabolismo , Histonas/metabolismo , Mamíferos/genética , Estabilidade de RNA , Transcrição Gênica , Acetilação , Animais , Células-Tronco Embrionárias/citologia , Células-Tronco Embrionárias/metabolismo , Evolução Molecular , Feminino , Regulação da Expressão Gênica , Técnicas de Silenciamento de Genes , Genes Ligados ao Cromossomo X , Meia-Vida , Histona Acetiltransferases/genética , Histonas/genética , Masculino , Camundongos , Camundongos Endogâmicos C57BL , Regiões Promotoras Genéticas , RNA Polimerase II/genética , RNA Polimerase II/metabolismo , Processamento Pós-Transcricional do RNA , RNA Mensageiro/genética , RNA Mensageiro/metabolismo , Cromossomo X/genética , Cromossomo X/metabolismoRESUMO
To achieve a balanced gene expression dosage between males (XY) and females (XX), mammals have evolved a compensatory mechanism to randomly inactivate one of the female X chromosomes. Despite this chromosome-wide silencing, a number of genes escape X inactivation: in women about 15% of X-linked genes are bi-allelically expressed and in mice, about 3%. Expression from the inactive X allele varies from a few percent of that from the active allele to near equal expression. While most genes have a stable inactivation pattern, a subset of genes exhibit tissue-specific differences in escape from X inactivation. Escape genes appear to be protected from the repressive chromatin modifications associated with X inactivation. Differences in the identity and distribution of escape genes between species and tissues suggest a role for these genes in the evolution of sex differences in specific phenotypes. The higher expression of escape genes in females than in males implies that they may have female-specific roles and may be responsible for some of the phenotypes observed in X aneuploidy.
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Aneuploidia , Evolução Biológica , Dosagem de Genes/genética , Genes Ligados ao Cromossomo X/genética , Fenótipo , Inativação do Cromossomo X/genética , Animais , Feminino , Humanos , Masculino , Camundongos , Fatores Sexuais , Especificidade da Espécie , Inativação do Cromossomo X/fisiologiaRESUMO
Studies of macroH2A histone variants indicate that they have a role in regulating gene expression. To identify direct targets of the macroH2A1 variants, we produced a genome-wide map of the distribution of macroH2A1 nucleosomes in mouse liver chromatin using high-throughput DNA sequencing. Although macroH2A1 nucleosomes are widely distributed across the genome, their local concentration varies over a range of 100-fold or more. The transcribed regions of most active genes are depleted of macroH2A1, often in sharply localized domains that show depletion of 4-fold or more relative to bulk mouse liver chromatin. We used macroH2A1 enrichment to help identify genes that appear to be directly regulated by macroH2A1 in mouse liver. These genes functionally cluster in the area of lipid metabolism. All but one of these genes has increased expression in macroH2A1 knockout mice, indicating that macroH2A1 functions primarily as a repressor in adult liver. This repressor activity is further supported by the substantial and relatively uniform macroH2A1 enrichment along the inactive X chromosome, which averages 4-fold. Genes that escape X inactivation stand out as domains of macroH2A1 depletion. The rarity of such genes indicates that few genes escape X inactivation in mouse liver, in contrast to what has been observed in human cells.
Assuntos
Cromatina/genética , Variação Genética , Histonas/genética , Fígado/metabolismo , Processamento Alternativo , Animais , Sequência de Bases , Mapeamento Cromossômico , DNA/genética , Feminino , Estudo de Associação Genômica Ampla , Humanos , Camundongos , Camundongos Endogâmicos C57BL , Nucleossomos/genética , Ativação Transcricional , Inativação do Cromossomo XRESUMO
A subset of X-linked genes escapes silencing by X inactivation and is expressed from both X chromosomes in mammalian females. Species-specific differences in the identity of these genes have recently been discovered, suggesting a role in the evolution of sex differences. Chromatin analyses have aimed to discover how genes remain expressed within a repressive environment.
Assuntos
Inativação do Cromossomo X/genética , Animais , Montagem e Desmontagem da Cromatina/genética , Doença/genética , Impressão Genômica/genética , Humanos , Meiose/genética , Camundongos , Cromossomos Sexuais/genéticaRESUMO
Telomerase, a ribonucleoprotein important to neoplastic immortality, is up-regulated in approximately 85% of cancers, including leukemias. In this study, 9cUAB30, a novel retinoic acid, resulted in differentiation of HL60 leukemia cells as indicated by morphologic changes characteristic of granulocytes. It also caused a down-regulation of hTERT gene expression and a decrease in telomerase activity. Telomerase inhibition was followed by loss of proliferative capacity, induction of apoptosis, and partial differentiation. These findings demonstrate the effectiveness of 9cUAB30 at inhibiting telomerase activity by down-regulating hTERT gene expression in human leukemic cells.