1
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Cameron SR, Nandi S, Kahn TG, Barrasa JI, Stenberg P, Schwartz YB. PTE, a novel module to target Polycomb Repressive Complex 1 to the human cyclin D2 ( CCND2) oncogene. J Biol Chem 2018; 293:14342-14358. [PMID: 30068546 DOI: 10.1074/jbc.ra118.005010] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/24/2018] [Indexed: 11/06/2022] Open
Abstract
Polycomb group proteins are essential epigenetic repressors. They form multiple protein complexes of which two kinds, PRC1 and PRC2, are indispensable for repression. Although much is known about their biochemical properties, how mammalian PRC1 and PRC2 are targeted to specific genes is poorly understood. Here, we establish the cyclin D2 (CCND2) oncogene as a simple model to address this question. We provide the evidence that the targeting of PRC1 to CCND2 involves a dedicated PRC1-targeting element (PTE). The PTE appears to act in concert with an adjacent cytosine-phosphate-guanine (CpG) island to arrange for the robust binding of PRC1 and PRC2 to repressed CCND2 Our findings pave the way to identify sequence-specific DNA-binding proteins implicated in the targeting of mammalian PRC1 complexes and provide novel link between polycomb repression and cancer.
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Affiliation(s)
| | - Soumyadeep Nandi
- From the Department of Molecular Biology and.,the Computational Life Science Cluster (CLiC), Umeå University, 901 87 Umeå, Sweden and
| | | | | | - Per Stenberg
- From the Department of Molecular Biology and.,the Computational Life Science Cluster (CLiC), Umeå University, 901 87 Umeå, Sweden and.,the Division of Chemical, Biological, Radioactive and Nuclear (CBRN) Security and Defence, FOI-Swedish Defence Research Agency, 906 21 Umeå Sweden
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2
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Wei KHC, Lower SE, Caldas IV, Sless TJS, Barbash DA, Clark AG. Variable Rates of Simple Satellite Gains across the Drosophila Phylogeny. Mol Biol Evol 2018; 35:925-941. [PMID: 29361128 PMCID: PMC5888958 DOI: 10.1093/molbev/msy005] [Citation(s) in RCA: 41] [Impact Index Per Article: 6.8] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/21/2022] Open
Abstract
Simple satellites are tandemly repeating short DNA motifs that can span megabases in eukaryotic genomes. Because they can cause genomic instability through nonallelic homologous exchange, they are primarily found in the repressive heterochromatin near centromeres and telomeres where recombination is minimal, and on the Y chromosome, where they accumulate as the chromosome degenerates. Interestingly, the types and abundances of simple satellites often vary dramatically between closely related species, suggesting that they turn over rapidly. However, limited sampling has prevented detailed understanding of their evolutionary dynamics. Here, we characterize simple satellites from whole-genome sequences generated from males and females of nine Drosophila species, spanning 40 Ma of evolution. We show that PCR-free library preparation and postsequencing GC-correction better capture satellite quantities than conventional methods. We find that over half of the 207 simple satellites identified are species-specific, consistent with previous descriptions of their rapid evolution. Based on a maximum parsimony framework, we determined that most interspecific differences are due to lineage-specific gains. Simple satellites gained within a species are typically a single mutation away from abundant existing satellites, suggesting that they likely emerge from existing satellites, especially in the genomes of satellite-rich species. Interestingly, unlike most of the other lineages which experience various degrees of gains, the lineage leading up to the satellite-poor D. pseudoobscura and D. persimilis appears to be recalcitrant to gains, providing a counterpoint to the notion that simple satellites are universally rapidly evolving.
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Affiliation(s)
- Kevin H -C Wei
- Department of Molecular Biology and Genetics, Cornell University, Ithaca, NY
- Department of Integrative Biology, University of California, Berkeley, CA
| | - Sarah E Lower
- Department of Molecular Biology and Genetics, Cornell University, Ithaca, NY
| | - Ian V Caldas
- Department of Biological Statistics and Computational Biology, Cornell University, Ithaca, NY
| | - Trevor J S Sless
- Department of Ecology and Evolutionary Biology, Cornell University, Ithaca, NY
| | - Daniel A Barbash
- Department of Molecular Biology and Genetics, Cornell University, Ithaca, NY
| | - Andrew G Clark
- Department of Molecular Biology and Genetics, Cornell University, Ithaca, NY
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Faucillion ML, Larsson J. Increased expression of X-linked genes in mammals is associated with a higher stability of transcripts and an increased ribosome density. Genome Biol Evol 2015; 7:1039-52. [PMID: 25786432 PMCID: PMC4419800 DOI: 10.1093/gbe/evv054] [Citation(s) in RCA: 21] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/19/2022] Open
Abstract
Mammalian sex chromosomes evolved from the degeneration of one homolog of a pair of ancestral autosomes, the proto-Y. This resulted in a gene dose imbalance that is believed to be restored (partially or fully) through upregulation of gene expression from the single active X-chromosome in both sexes by a dosage compensatory mechanism. We analyzed multiple genome-wide RNA stability data sets and found significantly longer average half-lives for X-chromosome transcripts than for autosomal transcripts in various human cell lines, both male and female, and in mice. Analysis of ribosome profiling data shows that ribosome density is higher on X-chromosome transcripts than on autosomal transcripts in both humans and mice, suggesting that the higher stability is causally linked to a higher translation rate. Our results and observations are in accordance with a dosage compensatory upregulation of expressed X-linked genes. We therefore propose that differential mRNA stability and translation rates of the autosomes and sex chromosomes contribute to an evolutionarily conserved dosage compensation mechanism in mammals.
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Affiliation(s)
| | - Jan Larsson
- Department of Molecular Biology, Umeå University, Sweden
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4
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Coubard OA. A method for processing multivariate data in medical studies. Stat Med 2013; 32:3436-48. [PMID: 23553725 DOI: 10.1002/sim.5788] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/23/2011] [Revised: 01/12/2013] [Accepted: 01/30/2013] [Indexed: 11/09/2022]
Abstract
Traditional displays of principal component analyses lack readability to discriminate between putative clusters of variables or cases. Here, the author proposes a method that clusterizes and visualizes variables or cases through principal component analyses thus facilitating their analysis. The method displays pre-determined clusters of variables or cases as urchins that each has a soma (the average point) and spines (the individual variables or cases). Through three examples in the field of neuropsychology, the author illustrates how urchins help examine the modularity of cognitive tasks on the one hand and identify groups of healthy versus brain-damaged participants on the other hand. Some of the data used in this article were obtained from the Alzheimer's Disease Neuroimaging Initiative database. The urchin method was implemented in MATLAB, and the source code is available in the Supporting information. Urchins can be useful in biomedical studies to identify distinct phenomena at first glance, each having several measures (clusters of variables) or distinct groups of participants (clusters of cases).
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Affiliation(s)
- Olivier A Coubard
- The Neuropsychological Laboratory, CNS-Fed, 39 rue Meaux, 75019 Paris, France.
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5
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Figueiredo MLA, Philip P, Stenberg P, Larsson J. HP1a recruitment to promoters is independent of H3K9 methylation in Drosophila melanogaster. PLoS Genet 2012; 8:e1003061. [PMID: 23166515 PMCID: PMC3499360 DOI: 10.1371/journal.pgen.1003061] [Citation(s) in RCA: 42] [Impact Index Per Article: 3.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/05/2012] [Accepted: 09/19/2012] [Indexed: 11/19/2022] Open
Abstract
Heterochromatin protein 1 (HP1) proteins, recognized readers of the heterochromatin mark methylation of histone H3 lysine 9 (H3K9me), are important regulators of heterochromatin-mediated gene silencing and chromosome structure. In Drosophila melanogaster three histone lysine methyl transferases (HKMTs) are associated with the methylation of H3K9: Su(var)3-9, Setdb1, and G9a. To probe the dependence of HP1a binding on H3K9me, its dependence on these three HKMTs, and the division of labor between the HKMTs, we have examined correlations between HP1a binding and H3K9me patterns in wild type and null mutants of these HKMTs. We show here that Su(var)3-9 controls H3K9me-dependent binding of HP1a in pericentromeric regions, while Setdb1 controls it in cytological region 2L:31 and (together with POF) in chromosome 4. HP1a binds to the promoters and within bodies of active genes in these three regions. More importantly, however, HP1a binding at promoters of active genes is independent of H3K9me and POF. Rather, it is associated with heterochromatin protein 2 (HP2) and open chromatin. Our results support a hypothesis in which HP1a nucleates with high affinity independently of H3K9me in promoters of active genes and then spreads via H3K9 methylation and transient looping contacts with those H3K9me target sites. HP1 is a key protein in heterochromatin and epigenetic silencing, a phenomenon involving chromatin condensation. It is generally accepted that HP1 forms a dimer that links two adjacent nucleosomes through interactions with histone 3 methylated at lysine 9 (H3K9me). Since HP1 also interacts with the histone lysine methyltransferases (HKMTs) generating this modification, histone H3 becomes methylated and HP1 spreading is propagated. Here, we show that HP1a in Drosophila binds to promoters of active genes on chromosome 4 and pericentromeric regions. In contrast to current dogma, this binding is independent of H3K9me. In the presence of the HKMTs and H3K9me, HP1a is also enriched within the bodies of the bound genes. These findings shed new light on the role of HP1a and the epigenetic nature of this chromatin mark. We propose that HP1a interacts independently of H3K9me with the nucleosome with high affinity, probably via the H3 histone-fold. This interaction is followed by a more transient interaction between HP1a and H3K9me, which results in spreading of the HP1a enrichment into gene bodies. Overall, the presented results and hypothesized model provide an explanation for this epigenetic mark and possibly more general insights into the relationships between chromo-domain proteins and methylated histones.
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Affiliation(s)
| | - Philge Philip
- Department of Molecular Biology, Umeå University, Umeå, Sweden
- Computational Life Science Cluster (CLiC), Umeå University, Umeå, Sweden
| | - Per Stenberg
- Department of Molecular Biology, Umeå University, Umeå, Sweden
- Computational Life Science Cluster (CLiC), Umeå University, Umeå, Sweden
| | - Jan Larsson
- Department of Molecular Biology, Umeå University, Umeå, Sweden
- * E-mail:
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6
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POF regulates the expression of genes on the fourth chromosome in Drosophila melanogaster by binding to nascent RNA. Mol Cell Biol 2012; 32:2121-34. [PMID: 22473994 DOI: 10.1128/mcb.06622-11] [Citation(s) in RCA: 30] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/22/2022] Open
Abstract
In Drosophila, two chromosome-wide compensatory systems have been characterized: the dosage compensation system that acts on the male X chromosome and the chromosome-specific regulation of genes located on the heterochromatic fourth chromosome. Dosage compensation in Drosophila is accomplished by hypertranscription of the single male X chromosome mediated by the male-specific lethal (MSL) complex. The mechanism of this compensation is suggested to involve enhanced transcriptional elongation mediated by the MSL complex, while the mechanism of compensation mediated by the painting of fourth (POF) protein on the fourth chromosome has remained elusive. Here, we show that POF binds to nascent RNA, and this binding is associated with increased transcription output from chromosome 4. We also show that genes located in heterochromatic regions spend less time in transition from the site of transcription to the nuclear envelope. These results provide useful insights into the means by which genes in heterochromatic regions can overcome the repressive influence of their hostile environment.
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7
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Philip P, Pettersson F, Stenberg P. Sequence signatures involved in targeting the Male-Specific Lethal complex to X-chromosomal genes in Drosophila melanogaster. BMC Genomics 2012; 13:97. [PMID: 22424303 PMCID: PMC3355045 DOI: 10.1186/1471-2164-13-97] [Citation(s) in RCA: 12] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/04/2011] [Accepted: 03/19/2012] [Indexed: 11/18/2022] Open
Abstract
Background In Drosophila melanogaster, the dosage-compensation system that equalizes X-linked gene expression between males and females, thereby assuring that an appropriate balance is maintained between the expression of genes on the X chromosome(s) and the autosomes, is at least partially mediated by the Male-Specific Lethal (MSL) complex. This complex binds to genes with a preference for exons on the male X chromosome with a 3' bias, and it targets most expressed genes on the X chromosome. However, a number of genes are expressed but not targeted by the complex. High affinity sites seem to be responsible for initial recruitment of the complex to the X chromosome, but the targeting to and within individual genes is poorly understood. Results We have extensively examined X chromosome sequence variation within five types of gene features (promoters, 5' UTRs, coding sequences, introns, 3' UTRs) and intergenic sequences, and assessed its potential involvement in dosage compensation. Presented results show that: the X chromosome has a distinct sequence composition within its gene features; some of the detected variation correlates with genes targeted by the MSL-complex; the insulator protein BEAF-32 preferentially binds upstream of MSL-bound genes; BEAF-32 and MOF co-localizes in promoters; and that bound genes have a distinct sequence composition that shows a 3' bias within coding sequence. Conclusions Although, many strongly bound genes are close to a high affinity site neither our promoter motif nor our coding sequence signatures show any correlation to HAS. Based on the results presented here, we believe that there are sequences in the promoters and coding sequences of targeted genes that have the potential to direct the secondary spreading of the MSL-complex to nearby genes.
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Affiliation(s)
- Philge Philip
- Deptartment of Molecular Biology, Umeå University, 901 87 Umeå, Sweden
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8
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Stenberg P, Larsson J. Buffering and the evolution of chromosome-wide gene regulation. Chromosoma 2011; 120:213-25. [PMID: 21505791 PMCID: PMC3098985 DOI: 10.1007/s00412-011-0319-8] [Citation(s) in RCA: 46] [Impact Index Per Article: 3.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/07/2011] [Revised: 03/15/2011] [Accepted: 03/31/2011] [Indexed: 11/30/2022]
Abstract
Copy number variation (CNV) in terms of aneuploidies of both entire chromosomes and chromosomal segments is an important evolutionary driving force, but it is inevitably accompanied by potentially problematic variations in gene doses and genomic instability. Thus, a delicate balance must be maintained between mechanisms that compensate for variations in gene doses (and thus allow such genomic variability) and selection against destabilizing CNVs. In Drosophila, three known compensatory mechanisms have evolved: a general segmental aneuploidy-buffering system and two chromosome-specific systems. The two chromosome-specific systems are the male-specific lethal complex, which is important for dosage compensation of the male X chromosome, and Painting of fourth, which stimulates expression of the fourth chromosome. In this review, we discuss the origin and function of buffering and compensation using Drosophila as a model.
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Affiliation(s)
- Per Stenberg
- Department of Molecular Biology, Umeå University, Sweden
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9
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Georgiev P, Chlamydas S, Akhtar A. Drosophila dosage compensation: males are from Mars, females are from Venus. Fly (Austin) 2011; 5:147-54. [PMID: 21339706 DOI: 10.4161/fly.5.2.14934] [Citation(s) in RCA: 24] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/19/2022] Open
Abstract
Dosage compensation of X-linked genes is a phenomenon of concerted, chromosome-wide regulation of gene expression underpinned by sustained and tightly regulated histone modifications and chromatin remodeling, coupled with constrains of nuclear architecture. This elaborate process allows the accomplishment of regulated expression of genes on the single male X chromosome to levels comparable to those expressed from the two X chromosomes in females. The ribonucleoprotein Male Specific Lethal (MSL) complex is enriched on the male X chromosome and is intricately involved in this process in Drosophila melanogaster. In this review we discuss the recent advances that highlight the complexity lying behind regulation of gene expression by just two-fold.
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Affiliation(s)
- Plamen Georgiev
- Max Planck Institute of Immunobiology and Epigenetics, Freiburg, Germany
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10
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Jung CH, Makunin IV, Mattick JS. Identification of conserved Drosophila-specific euchromatin-restricted non-coding sequence motifs. Genomics 2010; 96:154-66. [PMID: 20595017 DOI: 10.1016/j.ygeno.2010.05.006] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/23/2010] [Revised: 05/25/2010] [Accepted: 05/26/2010] [Indexed: 01/19/2023]
Abstract
Non-protein-coding DNA comprises the majority of animal genomes but its functions are largely unknown. We identified over 17,000 different tetranucleotide pairs in the Drosophila melanogaster genome that are over-represented at distances up to 100nt in conserved non-exonic sequences. Those exhibiting the highest information content in surrounding nucleotides were classified into five groups: tRNAs, motifs associated with histone genes, Suppressor-of-Hairy-wing binding sites, and two sets of previously unrecognized motifs (DLM3 and DLM4). There are hundreds to thousands of copies of DLM3 and DLM4, respectively, in the genome, located almost exclusively in non-coding regions. They have similar copy numbers among drosophilids, but are largely absent in other insects. DLM3 is likely a cis-regulatory element, whereas DLM4 sequences are capable of forming a short hairpin structure and are expressed as approximately 80nt RNAs. This work reports the existence of Drosophila genus-specific sequence motifs, and suggests that many more novel functional elements may be discovered in genomes using the general approach outlined herein.
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Affiliation(s)
- Chol-Hee Jung
- Institute for Molecular Bioscience, The University of Queensland, St Lucia QLD, Australia
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11
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Vermaak D, Bayes JJ, Malik HS. A surrogate approach to study the evolution of noncoding DNA elements that organize eukaryotic genomes. J Hered 2009; 100:624-36. [PMID: 19635763 DOI: 10.1093/jhered/esp063] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/17/2022] Open
Abstract
Comparative genomics provides a facile way to address issues of evolutionary constraint acting on different elements of the genome. However, several important DNA elements have not reaped the benefits of this new approach. Some have proved intractable to current day sequencing technology. These include centromeric and heterochromatic DNA, which are essential for chromosome segregation as well as gene regulation, but the highly repetitive nature of the DNA sequences in these regions make them difficult to assemble into longer contigs. Other sequences, like dosage compensation X chromosomal sites, origins of DNA replication, or heterochromatic sequences that encode piwi-associated RNAs, have proved difficult to study because they do not have recognizable DNA features that allow them to be described functionally or computationally. We have employed an alternate approach to the direct study of these DNA elements. By using proteins that specifically bind these noncoding DNAs as surrogates, we can indirectly assay the evolutionary constraints acting on these important DNA elements. We review the impact that such "surrogate strategies" have had on our understanding of the evolutionary constraints shaping centromeres, origins of DNA replication, and dosage compensation X chromosomal sites. These have begun to reveal that in contrast to the view that such structural DNA elements are either highly constrained (under purifying selection) or free to drift (under neutral evolution), some of them may instead be shaped by adaptive evolution and genetic conflicts (these are not mutually exclusive). These insights also help to explain why the same elements (e.g., centromeres and replication origins), which are so complex in some eukaryotic genomes, can be simple and well defined in other where similar conflicts do not exist.
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Affiliation(s)
- Danielle Vermaak
- Division of Basic Sciences, Fred Hutchinson Cancer Research Center, Seattle, WA 98109, USA
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12
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Gelbart ME, Kuroda MI. Drosophila dosage compensation: a complex voyage to the X chromosome. Development 2009; 136:1399-410. [PMID: 19363150 DOI: 10.1242/dev.029645] [Citation(s) in RCA: 194] [Impact Index Per Article: 12.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/16/2022]
Abstract
Dosage compensation is the crucial process that equalizes gene expression from the X chromosome between males (XY) and females (XX). In Drosophila, the male-specific lethal (MSL) ribonucleoprotein complex mediates dosage compensation by upregulating transcription from the single male X chromosome approximately twofold. A key challenge is to understand how the MSL complex distinguishes the X chromosome from autosomes. Recent studies suggest that this occurs through a multi-step targeting mechanism that involves DNA sequence elements and epigenetic marks associated with transcription. This review will discuss the relative contributions of sequence elements and transcriptional marks to the complete pattern of MSL complex binding.
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Affiliation(s)
- Marnie E Gelbart
- Department of Medicine, Brigham and Women's Hospital, Boston, MA 02115, USA
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13
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A sequence motif within chromatin entry sites directs MSL establishment on the Drosophila X chromosome. Cell 2008; 134:599-609. [PMID: 18724933 DOI: 10.1016/j.cell.2008.06.033] [Citation(s) in RCA: 203] [Impact Index Per Article: 12.7] [Reference Citation Analysis] [Abstract] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/29/2008] [Revised: 05/22/2008] [Accepted: 06/13/2008] [Indexed: 01/13/2023]
Abstract
The Drosophila MSL complex associates with active genes specifically on the male X chromosome to acetylate histone H4 at lysine 16 and increase expression approximately 2-fold. To date, no DNA sequence has been discovered to explain the specificity of MSL binding. We hypothesized that sequence-specific targeting occurs at "chromatin entry sites," but the majority of sites are sequence independent. Here we characterize 150 potential entry sites by ChIP-chip and ChIP-seq and discover a GA-rich MSL recognition element (MRE). The motif is only slightly enriched on the X chromosome ( approximately 2-fold), but this is doubled when considering its preferential location within or 3' to active genes (>4-fold enrichment). When inserted on an autosome, a newly identified site can direct local MSL spreading to flanking active genes. These results provide strong evidence for both sequence-dependent and -independent steps in MSL targeting of dosage compensation to the male X chromosome.
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14
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Johansson AM, Stenberg P, Pettersson F, Larsson J. POF and HP1 bind expressed exons, suggesting a balancing mechanism for gene regulation. PLoS Genet 2008; 3:e209. [PMID: 18020713 PMCID: PMC2077892 DOI: 10.1371/journal.pgen.0030209] [Citation(s) in RCA: 51] [Impact Index Per Article: 3.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/14/2007] [Accepted: 10/08/2007] [Indexed: 12/31/2022] Open
Abstract
Two specific chromosome-targeting and gene regulatory systems are present in Drosophila melanogaster. The male X chromosome is targeted by the male-specific lethal complex believed to mediate the 2-fold up-regulation of the X-linked genes, and the highly heterochromatic fourth chromosome is specifically targeted by the Painting of Fourth (POF) protein, which, together with heterochromatin protein 1 (HP1), modulates the expression level of genes on the fourth chromosome. Here we use chromatin immunoprecipitation and tiling microarray analysis to map POF and HP1 on the fourth chromosome in S2 cells and salivary glands at high resolution. The enrichment profiles were complemented by transcript profiles to examine the link between binding and transcripts. The results show that POF specifically binds to genes, with a strong preference for exons, and the HP1 binding profile is a mirror image of POF, although HP1 displays an additional “peak” in the promoter regions of bound genes. HP1 binding within genes is much higher than the basal HP1 enrichment on Chromosome 4. Our results suggest a balancing mechanism for the regulation of the fourth chromosome where POF and HP1 competitively bind at increasing levels with increased transcriptional activity. In addition, our results contradict transposable elements as a major nucleation site for HP1 on the fourth chromosome. Species where males and females have a different number of sex chromosomes have to equalize the transcriptional output from the genes located on the X chromosome. In Drosophila this mechanism is achieved by a 2-fold up-regulation of the single male X chromosome. Flies also possess an additional chromosome-wide regulatory system that regulates the transcriptional output from genes on the fourth chromosome. In this case the protein Painting of Fourth (POF), together with heterochromatin protein 1 (HP1) bind to the fourth chromosome and fine tune gene expression. By using a high resolution map of POF and HP1 binding, we can show that they bind to the same sequences on the fourth chromosome. We also demonstrate that POF and HP1 bind to active genes with preferences for exon sequences. In gene regulatory mechanisms, including chromosome-wide gene regulation, a simple on/off switch is often not enough. Our findings support the presence of a balancing mechanism in which the dual recruitment of a repressing and a stimulating factor makes the transcription efficiency more stable and less sensitive to fluctuations.
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Affiliation(s)
| | - Per Stenberg
- Umeå Center for Molecular Pathogens, Umeå University, Umeå, Sweden
| | | | - Jan Larsson
- Umeå Center for Molecular Pathogens, Umeå University, Umeå, Sweden
- * To whom correspondence should be addressed. E-mail:
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15
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Straub T, Becker PB. DNA sequence and the organization of chromosomal domains. Curr Opin Genet Dev 2008; 18:175-80. [DOI: 10.1016/j.gde.2008.01.001] [Citation(s) in RCA: 16] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/07/2008] [Revised: 01/10/2008] [Accepted: 01/11/2008] [Indexed: 10/22/2022]
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16
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Arnau V, Gallach M, Marín I. Fast comparison of DNA sequences by oligonucleotide profiling. BMC Res Notes 2008; 1:5. [PMID: 18710530 PMCID: PMC2518268 DOI: 10.1186/1756-0500-1-5] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/31/2008] [Accepted: 02/28/2008] [Indexed: 11/24/2022] Open
Abstract
Background The comparison of DNA sequences is a traditional problem in genomics and bioinformatics. Many new opportunities emerge due to the improvement of personal computers, allowing the implementation of novel strategies of analysis. Findings We describe a new program, called UVWORD, which determines the number of times that each DNA word present in a sequence (target) is found in a second sequence (source), a procedure that we have called oligonucleotide profiling. On a standard computer, the user may search for words of a size ranging from k = 1 to k = 14 nucleotides. Average counts for groups of contiguous words may also be established. The rate of analysis on standard computers is from 3.4 (k = 14) to 16 millions of words per second (1 ≤ k ≤ 8). This makes feasible the fast screening of even the longest known DNA molecules. Discussion We show that the combination of the ability of analyzing words of relatively long size, which occur very rarely by chance, and the fast speed of the program allows to perform novel types of screenings, complementary to those provided by standard programs such as BLAST. This method can be used to determine oligonucleotide content, to characterize the distribution of repetitive sequences in chromosomes, to determine the evolutionary conservation of sequences in different species, to establish regions of similar DNA among chromosomes or genomes, etc.
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Affiliation(s)
- Vicente Arnau
- Departmento de Informática. Universidad de Valencia, Spain. vicente@
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17
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Gallach M, Arnau V, Marín I. Global patterns of sequence evolution in Drosophila. BMC Genomics 2007; 8:408. [PMID: 17996078 PMCID: PMC2180185 DOI: 10.1186/1471-2164-8-408] [Citation(s) in RCA: 17] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/14/2007] [Accepted: 11/09/2007] [Indexed: 01/30/2023] Open
Abstract
Background Sequencing of the genomes of several Drosophila allows for the first precise analyses of how global sequence patterns change among multiple, closely related animal species. A basic question is whether there are characteristic features that differentiate chromosomes within a species or between different species. Results We explored the euchromatin of the chromosomes of seven Drosophila species to establish their global patterns of DNA sequence diversity. Between species, differences in the types and amounts of simple sequence repeats were found. Within each species, the autosomes have almost identical oligonucleotide profiles. However, X chromosomes and autosomes have, in all species, a qualitatively different composition. The X chromosomes are less complex than the autosomes, containing both a higher amount of simple DNA sequences and, in several cases, chromosome-specific repetitive sequences. Moreover, we show that the right arm of the X chromosome of Drosophila pseudoobscura, which evolved from an autosome 10 – 18 millions of years ago, has a composition which is identical to that of the original, left arm of the X chromosome. Conclusion The consistent differences among species, differences among X chromosomes and autosomes and the convergent evolution of X and neo-X chromosomes demonstrate that strong forces are acting on drosophilid genomes to generate peculiar chromosomal landscapes. We discuss the relationships of the patterns observed with differential recombination and mutation rates and with the process of dosage compensation.
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Affiliation(s)
- Miguel Gallach
- Instituto de Biomedicina de Valencia, Consejo Superior de Investigaciones Científicas (IBV-CSIC), Valencia, Spain.
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Rodriguez MA, Vermaak D, Bayes JJ, Malik HS. Species-specific positive selection of the male-specific lethal complex that participates in dosage compensation in Drosophila. Proc Natl Acad Sci U S A 2007; 104:15412-7. [PMID: 17878295 PMCID: PMC2000485 DOI: 10.1073/pnas.0707445104] [Citation(s) in RCA: 45] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/24/2023] Open
Abstract
In many taxa, males and females have unequal ratios of sex chromosomes to autosomes, which has resulted in the invention of diverse mechanisms to equilibrate gene expression between the sexes (dosage compensation). Failure to compensate for sex chromosome dosage results in male lethality in Drosophila. In Drosophila, a male-specific lethal (MSL) complex of proteins and noncoding RNAs binds to hundreds of sites on the single male X chromosome and up-regulates gene expression. Here we use population genetics of two closely related Drosophila species to show that adaptive evolution has occurred in all five protein-coding genes of the MSL complex. This positive selection is asymmetric between closely related species, with a very strong signature apparent in Drosophila melanogaster but not in Drosophila simulans. In particular, the MSL1 and MSL2 proteins have undergone dramatic positive selection in D. melanogaster, in domains previously shown to be responsible for their specific targeting to the X chromosome. This signature of positive selection at an essential protein-DNA interface of the complex is unexpected and suggests that X chromosomal MSL-binding DNA segments may themselves be changing rapidly. This highly asymmetric, rapid evolution of the MSL genes further suggests that misregulated dosage compensation may represent one of the underlying causes of male hybrid inviability in Drosophila, wherein the fate of hybrid males depends on which species' X chromosome is inherited.
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Affiliation(s)
- Monica A. Rodriguez
- Division of Basic Sciences, Fred Hutchinson Cancer Research Center, Seattle, WA 98109; and
| | - Danielle Vermaak
- Division of Basic Sciences, Fred Hutchinson Cancer Research Center, Seattle, WA 98109; and
| | - Joshua J. Bayes
- Division of Basic Sciences, Fred Hutchinson Cancer Research Center, Seattle, WA 98109; and
- Molecular and Cellular Biology Program, University of Washington, Seattle, WA 98195
| | - Harmit S. Malik
- Division of Basic Sciences, Fred Hutchinson Cancer Research Center, Seattle, WA 98109; and
- To whom correspondence should be addressed. E-mail:
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Johansson AM, Stenberg P, Bernhardsson C, Larsson J. Painting of fourth and chromosome-wide regulation of the 4th chromosome in Drosophila melanogaster. EMBO J 2007; 26:2307-16. [PMID: 17318176 PMCID: PMC1864965 DOI: 10.1038/sj.emboj.7601604] [Citation(s) in RCA: 54] [Impact Index Per Article: 3.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/10/2006] [Accepted: 01/24/2007] [Indexed: 12/16/2022] Open
Abstract
Drosophila melanogaster exhibits two expression-regulating systems that target whole, specific chromosomes: the dosage compensation system whereby the male-specific lethal complex doubles transcription of genes on the male X-chromosome and the chromosome 4-specific protein Painting of fourth, POF. POF is the first example of an autosome-specific protein and its presence raises the question of the universality of chromosome-specific regulation. Here we show that POF and heterochromatin protein 1 (HP1) are involved in the global regulation of the 4th chromosome. Contrary to previous conclusions, Pof is not essential for survival of diplo-4th karyotype flies. However, Pof is essential for survival of haplo-4th individuals and expression of chromosome 4 genes in diplo-4th individuals is decreased in the absence of Pof. Mapping of POF using chromatin immunoprecipitation suggested that it binds within genes. Furthermore, we show that POF binding is dependent on heterochromatin and that POF and HP1 bind interdependently to the 4th chromosome. We propose a balancing mechanism involving POF and HP1 that provides a feedback system for fine-tuning expression status of genes on the 4th chromosome.
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Affiliation(s)
| | | | | | - Jan Larsson
- UCMP, Umeå University, Umeå, Sweden
- UCMP, Umeå University, SE-901 87 Umeå, Sweden. Tel.: +46 090 7856 785; Fax: +46 090 7780 07; E-mail:
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Abstract
Over the past 100 years Drosophila has been developed into an outstanding model system for the study of evolutionary processes. A fascinating aspect of evolution is the differentiation of sex chromosomes. Organisms with highly differentiated sex chromosomes, such as the mammalian X and Y, must compensate for the imbalance in gene dosage that this creates. The need to adjust the expression of sex-linked genes is a potent force driving the rise of regulatory mechanisms that act on an entire chromosome. This review will contrast the process of dosage compensation in Drosophila with the divergent strategies adopted by other model organisms. While the machinery of sex chromosome compensation is different in each instance, all share the ability to direct chromatin modifications to an entire chromosome. This review will also explore the idea that chromosome-targeting systems are sometimes adapted for other purposes. This appears the likely source of a chromosome-wide targeting system displayed by the Drosophila fourth chromosome.
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Affiliation(s)
- Jan Larsson
- Umeå Center for Molecular Pathogenesis, Umeå University, SE-901 87, Umeå, Sweden.
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Riddle NC, Elgin SCR. The dot chromosome of Drosophila: insights into chromatin states and their change over evolutionary time. Chromosome Res 2006; 14:405-16. [PMID: 16821136 DOI: 10.1007/s10577-006-1061-6] [Citation(s) in RCA: 44] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/14/2023]
Abstract
Historically, chromatin has been subdivided into heterochromatin, transcriptionally inactive regions that remain densely packaged throughout the cell cycle, and euchromatin, transcriptionally active regions that take on a diffuse appearance as the cell enters interphase. The banded portion of the small fourth chromosome (dot chromosome) of Drosophila melanogaster is unusual in exhibiting many characteristics of heterochromatic domains, and at the same time maintaining a gene density typical of euchromatin. Similar to genes embedded in pericentric heterochromatin, many of the dot chromosome genes have adapted to a heterochromatic environment. Little is known about the regulation of these genes and less about their evolution in a chromatin context. Interestingly, most of the genes from the D. melanogaster fourth chromosome remain clustered on a small chromosome throughout the genus Drosophila; yet the dot chromosome appears euchromatic in some species, such as D. virilis. Existing genomic sequence data allow an exploration of the underlying differences in DNA sequence organization between species. Here we review the available data describing the dot chromosome, which derives primarily from D. melanogaster. With its unusual and changing nature, the dot chromosome in the genus Drosophila provides a unique opportunity for the examination of transitions between chromatin states during evolution.
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Affiliation(s)
- Nicole C Riddle
- Department of Biology, Washington University, One Brookings Dr, St. Louis, MO 63130, USA
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Gilfillan GD, Straub T, de Wit E, Greil F, Lamm R, van Steensel B, Becker PB. Chromosome-wide gene-specific targeting of the Drosophila dosage compensation complex. Genes Dev 2006; 20:858-70. [PMID: 16547172 PMCID: PMC1475731 DOI: 10.1101/gad.1399406] [Citation(s) in RCA: 140] [Impact Index Per Article: 7.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/08/2023]
Abstract
The dosage compensation complex (DCC) of Drosophila melanogaster is capable of distinguishing the single male X from the other chromosomes in the nucleus. It selectively interacts in a discontinuous pattern with much of the X chromosome. How the DCC identifies and binds the X, including binding to the many genes that require dosage compensation, is currently unknown. To identify bound genes and attempt to isolate the targeting cues, we visualized male-specific lethal 1 (MSL1) protein binding along the X chromosome by combining chromatin immunoprecipitation with high-resolution microarrays. More than 700 binding regions for the DCC were observed, encompassing more than half the genes found on the X chromosome. In addition, several rare autosomal binding sites were identified. Essential genes are preferred targets, and genes binding high levels of DCC appear to experience the most compensation (i.e., greatest increase in expression). DCC binding clearly favors genes over intergenic regions, and binds most strongly to the 3' end of transcription units. Within the targeted genes, the DCC exhibits a strong preference for exons and coding sequences. Our results demonstrate gene-specific binding of the DCC, and identify several sequence elements that may partly direct its targeting.
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Affiliation(s)
- Gregor D Gilfillan
- Adolf-Butenandt-Institut, Molekularbiologie, Ludwig-Maximilians-Universität München, 80336 München, Germany
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