Compact chromatin packaging of inactive X Chromosome involves the actively transcribed Xist gene

1999 ◽  
Vol 10 (6) ◽  
pp. 606-610 ◽  
Author(s):  
Yoshio Endo ◽  
Takuya Watanabe ◽  
Yukio Mishima ◽  
Akira Yoshimura ◽  
Nobuo Takagi ◽  
...  
Keyword(s):  
X Chromosome ◽  
Xist Gene ◽  
Inactive X Chromosome

scholarly journals Regulation of X-Chromosome Inactivation in Development in Mice and Humans

1998 ◽  
Vol 62 (2) ◽  
pp. 362-378 ◽  
Author(s):  
Tetsuya Goto ◽  
Marilyn Monk
Keyword(s):  
Dna Methylation ◽  
X Chromosome ◽  
Regulatory Gene ◽  
X Chromosome Inactivation ◽  
Xist Gene ◽  
Chromosome Inactivation ◽  
Preimplantation Embryos ◽  
Paternal Allele ◽  
Inactive X Chromosome ◽  
Extraembryonic Tissues

SUMMARY Dosage compensation for X-linked genes in mammals is accomplished by inactivating one of the two X chromosomes in females. X-chromosome inactivation (XCI) occurs during development, coupled with cell differentiation. In somatic cells, XCI is random, whereas in extraembryonic tissues, XCI is imprinted in that the paternally inherited X chromosome is preferentially inactivated. Inactivation is initiated from an X-linked locus, the X-inactivation center (Xic), and inactivity spreads along the chromosome toward both ends. XCI is established by complex mechanisms, including DNA methylation, heterochromatinization, and late replication. Once established, inactivity is stably maintained in subsequent cell generations. The function of an X-linked regulatory gene, Xist, is critically involved in XCI. The Xist gene maps to the Xic, it is transcribed only from the inactive X chromosome, and the Xist RNA associates with the inactive X chromosome in the nucleus. Investigations with Xist-containing transgenes and with deletions of the Xist gene have shown that the Xist gene is required in cis for XCI. Regulation of XCI is therefore accomplished through regulation of Xist. Transcription of the Xist gene is itself regulated by DNA methylation. Hence, the differential methylation of the Xist gene observed in sperm and eggs and its recognition by protein binding constitute the most likely mechanism regulating imprinted preferential expression of the paternal allele in preimplantation embryos and imprinted paternal XCI in extraembryonic tissues. This article reviews the mechanisms underlying XCI and recent advances elucidating the functions of the Xist gene in mice and humans.

scholarly journals XIST RNA paints the inactive X chromosome at interphase: evidence for a novel RNA involved in nuclear/chromosome structure.

1996 ◽  
Vol 132 (3) ◽  
pp. 259-275 ◽  
Author(s):  
C M Clemson ◽  
J A McNeil ◽  
H F Willard ◽  
J B Lawrence
Keyword(s):  
Nuclear Structure ◽  
X Chromosome ◽  
Chromosome Territory ◽  
Xist Gene ◽  
Chromosomal Dna ◽  
Interphase Chromosome ◽  
Reading Frame ◽  
Inactive X Chromosome ◽  
Xist Rna ◽  
Rna Accumulation

The XIST gene is implicated in X chromosome inactivation, yet the RNA contains no apparent open reading frame. An accumulation of XIST RNA is observed near its site of transcription, the inactive X chromosome (Xi). A series of molecular cytogenetic studies comparing properties of XIST RNA to other protein coding RNAs, support a critical distinction for XIST RNA; XIST does not concentrate at Xi simply because it is transcribed and processed there. Most notably, morphometric and 3-D analysis reveals that XIST RNA and Xi are coincident in 2- and 3-D space; hence, the XIST RNA essentially paints Xi. Several results indicate that the XIST RNA accumulation has two components, a minor one associated with transcription and processing, and a spliced major component, which stably associates with Xi. Upon transcriptional inhibition the major spliced component remains in the nucleus and often encircles the extra-prominent heterochromatic Barr body. The continually transcribed XIST gene and its polyadenylated RNA consistently localize to a nuclear region devoid of splicing factor/poly A RNA rich domains. XIST RNA remains with the nuclear matrix fraction after removal of chromosomal DNA. XIST RNA is released from its association with Xi during mitosis, but shows a unique highly particulate distribution. Collective results indicate that XIST RNA may be an architectural element of the interphase chromosome territory, possibly a component of nonchromatin nuclear structure that specifically associates with Xi. XIST RNA is a novel nuclear RNA which potentially provides a specific precedent for RNA involvement in nuclear structure and cis-limited gene regulation via higher-order chromatin packaging.

The Human Xist Gene Promoter Prevents Silencing of an Integrated Reporter Gene.

Blood ◽  
2004 ◽  
Vol 104 (11) ◽  
pp. 2114-2114
Author(s):  
Michael R. Greene ◽  
Christopher H. Lowrey
Keyword(s):  
Cell Line ◽  
Reporter Gene ◽  
X Chromosome ◽  
Cpg Island ◽  
Gene Promoter ◽  
Epigenetic Silencing ◽  
Xist Gene ◽  
Proximal Promoter ◽  
Inactive X Chromosome ◽  
Xist Promoter

Abstract Epigenetic silencing and position dependent expression are long-standing problems which continue to limit the development of gene replacement therapy. As a strategy to overcome this problem we have tested the ability of the human XIST (X inactivation-specific transcript) gene promoter to overcome epigenetic silencing. The XIST gene is one of a relatively small number of genes which are expressed from the inactive X chromosome. The product of this gene is an untranslated structural RNA which coats the X chromosome destined for inactivation prior to H3 Lys 9 hypoacetylation, H3 Lys 9 methylation, CpG island methylation and the subsequent silencing of most of the genes on the chromosome. Continued expression of the XIST gene in this highly repressive environment is required to maintain the chromosome in an inactive state. The region of the proximal promoter of the XIST gene on the inactive X chromosome has been shown to retain an active chromatin structure. Based on these findings we hypothesized that the XIST gene promoter would be able to resist the epigenetic changes which lead to transgene silencing. To test this idea, we subcloned a minimal XIST promoter upstream of an enhanced GFP reporter gene in a pUC-based plasmid which also contained a neomycin resistance gene. The same plasmid, with a CMV promoter, served as a control vector. The plasmids were electroporated into mouse erythroleukemia (MEL) cells and then grown in media containing G418. The MEL cell line was chosen because genes transferred into these cells are frequently silenced and because it is often used as a first screen for vectors with potential for use in therapeutic gene transfer to erythroid cells. Individual colonies were selected and G418 removed. After expansion of the clones, flow cytometry was used to determine the percentage of cells in each clonal population which were expressing GFP as determined by comparison to the untransduced MEL cell line. Silencing typically involves a gradual decrease in the proportion of cells expressing the integrated transgene. Statistical analyses of results were performed using the t-test. 16 XIST and 13 CMV clones were available for analysis at the start of the experiment (time 0). 11/13 CMV clones and 12/16 XIST clones initially expressed GFP. Of the clones which were expressing GFP, the average percentages of positive cells were higher for those with the XIST promoter (63% vs. 41%, p= 0.015). Expression was reanalyzed after 6 weeks of culture in the absence of G418 selection. At this time point, the average percentage of GFP expressing cells was much higher for the XIST clones (57% vs. 19%, p=0.00008) and when analyzed for silencing, XIST clones were expressing at an average of 90% of their time 0 levels vs. 46% for the CMV clones (p=.0008). These results indicate that the XIST promoter is resistant to silencing in our model system and is a candidate for further development and mechanistic studies.

scholarly journals Differential activation of the hprt gene on the inactive X chromosome in primary and transformed Chinese hamster cells.

1989 ◽  
Vol 9 (4) ◽  
pp. 1635-1641 ◽  
Author(s):  
S G Grant ◽  
R G Worton
Keyword(s):  
Cell Lines ◽  
X Chromosome ◽  
Gene Activation ◽  
Chinese Hamster ◽  
Fibroblast Cell ◽  
Dna Demethylation ◽  
Hprt Gene ◽  
Primary Fibroblast ◽  
Chinese Hamster Cells ◽  
Inactive X Chromosome

We have investigated the genetic activation of the hprt (hypoxanthine-guanine phosphoribosyltransferase) gene located on the inactive X chromosome in primary and transformed female diploid Chinese hamster cells after treatment with the DNA methylation inhibitor 5-azacytidine (5azaCR). Mutants deficient in HPRT were first selected by growth in 6-thioguanine from two primary fibroblast cell lines and from transformed lines derived from them. These HPRT- mutants were then treated with 5azaCR and plated in HAT (hypoxanthine-methotrexate-thymidine) medium to select for cells that had reexpressed the hprt gene on the inactive X chromosome. Contrary to previous results with primary human cells, 5azaCR was effective in activating the hprt gene in primary Chinese hamster fibroblasts at a low but reproducible frequency of 2 x 10(-6) to 7 x 10(-6). In comparison, the frequency in independently derived transformed lines varied from 1 x 10(-5) to 5 x 10(-3), consistently higher than in the nontransformed cells. This increase remained significant when the difference in growth rates between the primary and transformed lines was taken into account. Treatment with 5azaCR was also found to induce transformation in the primary cell lines but at a low frequency of 4 x 10(-7) to 8 x 10(-7), inconsistent with a two-step model of transformation followed by gene activation to explain the derepression of hprt in primary cells. Thus, these results indicate that upon transformation, the hprt gene on the inactive Chinese hamster X chromosome is rendered more susceptible to action by 5azaCR, consistent with a generalized DNA demethylation associated with the transformation event or with an increase in the instability of an underlying primary mechanism of X inactivation.

scholarly journals Escape from X Chromosome Inactivation and the Female Predominance in Autoimmune Diseases

2021 ◽  
Vol 22 (3) ◽  
pp. 1114
Author(s):  
Ali Youness ◽  
Charles-Henry Miquel ◽  
Jean-Charles Guéry
Keyword(s):  
Autoimmune Diseases ◽  
X Chromosome ◽  
Gene Dosage ◽  
X Chromosome Inactivation ◽  
Chromosome Inactivation ◽  
X Chromosomes ◽  
Female Sex Hormones ◽  
Inactive X Chromosome ◽  
Immune Related Genes ◽  
Female Specific

Women represent 80% of people affected by autoimmune diseases. Although, many studies have demonstrated a role for sex hormone receptor signaling, particularly estrogens, in the direct regulation of innate and adaptive components of the immune system, recent data suggest that female sex hormones are not the only cause of the female predisposition to autoimmunity. Besides sex steroid hormones, growing evidence points towards the role of X-linked genetic factors. In female mammals, one of the two X chromosomes is randomly inactivated during embryonic development, resulting in a cellular mosaicism, where about one-half of the cells in a given tissue express either the maternal X chromosome or the paternal one. X chromosome inactivation (XCI) is however not complete and 15 to 23% of genes from the inactive X chromosome (Xi) escape XCI, thereby contributing to the emergence of a female-specific heterogeneous population of cells with bi-allelic expression of some X-linked genes. Although the direct contribution of this genetic mechanism in the female susceptibility to autoimmunity still remains to be established, the cellular mosaicism resulting from XCI escape is likely to create a unique functional plasticity within female immune cells. Here, we review recent findings identifying key immune related genes that escape XCI and the relationship between gene dosage imbalance and functional responsiveness in female cells.

scholarly journals Cell cycle–dependent localization of macroH2A in chromatin of the inactive X chromosome

2002 ◽  
Vol 157 (7) ◽  
pp. 1113-1123 ◽  
Author(s):  
Brian P. Chadwick ◽  
Huntington F. Willard
Keyword(s):  
Cell Cycle ◽  
X Chromosome ◽  
Degradation Pathway ◽  
S Phase ◽  
Histone H2a ◽  
The Core ◽  
Inactive X Chromosome ◽  
Inactivation Center ◽  
Chromatin Proteins ◽  
Cycle Dependent

One of several features acquired by chromatin of the inactive X chromosome (Xi) is enrichment for the core histone H2A variant macroH2A within a distinct nuclear structure referred to as a macrochromatin body (MCB). In addition to localizing to the MCB, macroH2A accumulates at a perinuclear structure centered at the centrosome. To better understand the association of macroH2A1 with the centrosome and the formation of an MCB, we investigated the distribution of macroH2A1 throughout the somatic cell cycle. Unlike Xi-specific RNA, which associates with the Xi throughout interphase, the appearance of an MCB is predominantly a feature of S phase. Although the MCB dissipates during late S phase and G2 before reforming in late G1, macroH2A1 remains associated during mitosis with specific regions of the Xi, including at the X inactivation center. This association yields a distinct macroH2A banding pattern that overlaps with the site of histone H3 lysine-4 methylation centered at the DXZ4 locus in Xq24. The centrosomal pool of macroH2A1 accumulates in the presence of an inhibitor of the 20S proteasome. Therefore, targeting of macroH2A1 to the centrosome is likely part of a degradation pathway, a mechanism common to a variety of other chromatin proteins.

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