Ordered assembly of roX RNAs into MSL complexes on the dosage-compensated X chromosome in Drosophila

Meller, Victoria H.; Gordadze, Polina R.; Park, Y.; Chu, Xiaowen; Stuckenholz, Carsten; Kelley, R. L.; Kuroda, Mitzi I.

doi:10.1016/s0960-9822(00)00311-0

Cited by 160 publications

(196 citation statements)

References 32 publications

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“…These MSL proteins assemble into complexes that bind to hundreds of sites along the polytene male X in a reproducible XIST RNA Association with Inactive X 36493 pattern (24). It has been proposed that localization of the MSL complex is mediated by the noncoding RNAs (roX1 and roX2) expressed from the male X that provide nucleation sites for assembly of the MSL complexes and their subsequent spreading in cis along the male X (25). By analogy to the mechanism of dosage compensation employed by Drosophila, it is possible that expression of XIST RNA from the Xi nucleates the assembly of ribonucleoprotein complexes that possess chromatin modifying activity, as well as the spread of these complexes along the Xi in cis.…”

Section: Discussionmentioning

confidence: 99%

XIST RNA Associates with Specific Regions of the Inactive X Chromatin

Gilbert¹,

Pehrson²,

Sharp³

2000

Journal of Biological Chemistry

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Microscopy studies have shown that XIST RNA colocalizes with the inactive X chromosome (Xi). However, the molecular basis for this colocalization is unknown. Here we provide two lines of evidence from chromatin immunoprecipitation experiments that XIST RNA physically associates with the Xi chromatin. First, XIST RNA can be co-precipitated by antiserum against macroH2A, a histone H2A variant enriched in the Xi. Second, XIST RNA can be co-precipitated by antisera that recognize unacetylated, but not acetylated, isoforms of histones H3 and H4. The specificity of XIST RNA association with hypoacetylated chromatin, together with the previous finding that hypoacetylated histone H4 is enriched at promoters of X-inactivated genes, raises the possibility that XIST RNA may contribute to the hypoacetylation of specific regions of the Xi so as to alter the expression of X-linked genes.X-chromosome inactivation in mammals is controlled by the cis-acting XIST locus, which in humans encodes a 17-kilobase untranslated RNA that is expressed only from the inactive X (Xi) 1 (1). Mouse X chromosomes with targeted deletions of the Xist gene lose the ability to undergo X inactivation (2, 3). In addition, ectopic expression of Xist RNA from multicopy transgenes during embryonic stem cell differentiation causes autosomes to exhibit features typically associated with X inactivation, such as late replication, histone H4 hypoacetylation, and transcriptional down-regulation (4, 5). These studies indicate that the Xist locus is required for X inactivation, but they do not distinguish between several possible modes of Xist action; one model is that the Xist genomic locus serves as a chromatin organizing region that, when transcribed, initiates changes in chromatin structure that are propagated in cis along the length of the Xi chromosome (6). An alternative model is that the noncoding RNA expressed from the Xist gene is functional and directly participates in the silencing process (1). One observation suggesting that the XIST transcript may directly participate in silencing comes from fluorescence in situ hybridization experiments that show that XIST RNA colocalizes with the inactive X chromosome (1, 7). However, the limited resolution of microscopy analysis does not provide any information on the molecular basis or the consequences of this colocalization.To examine the nature of the colocalization between XIST RNA and the Xi chromatin, the chromatin IP assay was used to precipitate chromatin from human female cells and then RT-PCR was performed to determine whether XIST RNA was co-precipitated. The results indicate that XIST RNA is indeed co-precipitated with chromatin by antibodies directed against several histone species. Significantly, XIST RNA was co-precipitated with antibodies against unacetylated, but not acetylated, histones H3 and H4. Given the previous finding that histone H4 is hypoacetylated at promoters of X-inactivated genes (8), these results raise the possibility that XIST RNA may be associated with promoters of silenced gen...

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Section: Discussionmentioning

confidence: 99%

XIST RNA Associates with Specific Regions of the Inactive X Chromatin

Gilbert¹,

Pehrson²,

Sharp³

2000

Journal of Biological Chemistry

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“…Intriguingly, the fly dosage compensation system also involves multiple ncRNAs: roX1 and roX2 (RNA on the X). These RNAs are members of the dosage compensation complex (DCC), a huge RNA-protein complex that binds to hundreds of sites along the male X chromosome in a highly reproducible, banded pattern (Meller 2000;Meller et al 2000). In addition to roX1 and roX2 RNAs, the DCC also contains a specific set of proteins that include MLE (maleless); MSL1, MSL2, and MSL3 (male-specific lethal 1, 2, and 3, respectively); and MOF (males absent on the first).…”

Section: X-chromosome Hyperactivation In Drosophilamentioning

confidence: 99%

Eukaryotic regulatory RNAs: an answer to the ‘genome complexity’ conundrum

Prasanth¹,

Spector²

2007

Genes Dev.

365

305

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A large portion of the eukaryotic genome is transcribed as noncoding RNAs (ncRNAs). While once thought of primarily as "junk," recent studies indicate that a large number of these RNAs play central roles in regulating gene expression at multiple levels. The increasing diversity of ncRNAs identified in the eukaryotic genome suggests a critical nexus between the regulatory potential of ncRNAs and the complexity of genome organization. We provide an overview of recent advances in the identification and function of eukaryotic ncRNAs and the roles played by these RNAs in chromatin organization, gene expression, and disease etiology.

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“…to a chromosomal entry site. Among the 30 -40 entry sites that have been identified by cytoimmunofluorescence, two are known to contain the roX genes (14,16). The MSL complex is found at either of the two roX genes when these are moved to ectopic autosomal sites and spreads in cis from the transgenes to new sequences.…”

Section: Lysine 16 Acetylation Is Enriched Along the Length Of Dosagementioning

confidence: 99%

“…The MSL complex is found at either of the two roX genes when these are moved to ectopic autosomal sites and spreads in cis from the transgenes to new sequences. The association of the complex with the roX transgenes occurs even when the latter are not transcribing, suggesting that the roX genes are not only sites of assembly for the complex but are also entry sites (14,16,23).…”

Section: Lysine 16 Acetylation Is Enriched Along the Length Of Dosagementioning

confidence: 99%

“…This histone acetyltransferase-containing complex is responsible for the dosage compensation of many X-linked genes by increasing their transcription in males to achieve a level of gene product equivalent to that generated by the two X chromosomes in females. In addition to its protein subunits, the MSL complex contains one of two nontranslated RNAs, roX1 and roX2 (11)(12)(13)(14)(15). Current models suggest that functional complexes form at the sites of transcription of these RNAs, then access the X chromosome at a small number of additional entry sites and subsequently spread to the hundreds of other locations along the X chromosome where they are normally found (16).…”

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confidence: 99%

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Linking Global Histone Acetylation to the Transcription Enhancement of X-chromosomal Genes in Drosophila Males

Smith¹,

Allis²,

Lucchesi³

2001

Journal of Biological Chemistry

148

150

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It has become well established for several genes that targeting of histone acetylation to promoters is required for the activation of transcription. In contrast, global patterns of acetylation have not been ascribed to any particular regulatory function. In Drosophila, a specific modification of H4, acetylation at lysine 16, is enriched at hundreds of sites on the male X chromosome due to the activity of the male-specific lethal (MSL) dosage compensation complex. Utilizing chromatin immunoprecipitation, we have determined that H4Ac16 is present along the entire length of X-linked genes targeted by the MSL complex with relatively modest levels of acetylation at the promoter regions and high levels in the middle and/or 3 end of the transcription units. We propose that global acetylation by the MSL complex increases the expression of X-linked genes by facilitating transcription elongation rather than by enhancing promoter accessibility. We have also determined that H4Ac16 is absent from a region of the X chromosome that includes a gene known to be dosage-compensated by a MSL-independent mechanism. This study represents the first biochemical interpretation of the very large body of cytological observations on the chromosomal distribution of the MSL complex.Many post-translational modifications of the highly conserved histone N-terminal tails are linked to transcriptional regulation (1), with the most widely studied modification being acetylation of histones H3 and H4. Genetic and biochemical data have demonstrated that histone acetyltransferases such as yGcn5p and yEsa1p are recruited to the promoters of specific genes for the activation of transcription (2-6). Loss of function mutations of the genes encoding these enzymes, however, reveal that they are also responsible for a broad pattern of acetylation with relatively modest effects on the level of transcription (2, 4, 6).In Drosophila, evidence for special roles for particular histone modifications was revealed with antisera to specific isoforms of H4. While H4 isoforms acetylated at lysine 5 or 8 are associated with numerous sites throughout the genome, H4 acetylated at lysine 12 is enriched in chromocentric heterochromatin, and H4 acetylated at lysine 16 (H4Ac16) is exclusively associated with the male X chromosome (7, 8). Male-specific acetylation of H4 at lysine 16 is mediated by males absent on the first (MOF), 1 a MYST-family histone acetyltransferase present in the male-specific lethal (MSL) complex (9 -11). This histone acetyltransferase-containing complex is responsible for the dosage compensation of many X-linked genes by increasing their transcription in males to achieve a level of gene product equivalent to that generated by the two X chromosomes in females. In addition to its protein subunits, the MSL complex contains one of two nontranslated RNAs, roX1 and roX2 (11-15). Current models suggest that functional complexes form at the sites of transcription of these RNAs, then access the X chromosome at a small number of additional entry sites and subseq...

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Ordered assembly of roX RNAs into MSL complexes on the dosage-compensated X chromosome in Drosophila

Abstract: Our results support a model in which MSL proteins assemble at specific chromatin entry sites (including the roX1 and roX2 genes); the roX RNAs join the complex at their sites of synthesis; and complete complexes spread in cis to dosage compensate most genes on the X chromosome.

Cited by 160 publications

References 32 publications

XIST RNA Associates with Specific Regions of the Inactive X Chromatin

XIST RNA Associates with Specific Regions of the Inactive X Chromatin

Eukaryotic regulatory RNAs: an answer to the ‘genome complexity’ conundrum

Linking Global Histone Acetylation to the Transcription Enhancement of X-chromosomal Genes in Drosophila Males

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