201
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Nagano T, Fraser P. Emerging similarities in epigenetic gene silencing by long noncoding RNAs. Mamm Genome 2009; 20:557-62. [PMID: 19727951 DOI: 10.1007/s00335-009-9218-1] [Citation(s) in RCA: 57] [Impact Index Per Article: 3.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/30/2009] [Accepted: 07/20/2009] [Indexed: 10/20/2022]
Abstract
Long noncoding RNAs (lncRNAs) such as Xist, Air, and Kcnq1ot1 are required for epigenetic silencing of multiple genes in cis within large chromosomal domains, including distant genes located hundreds of kilobase pairs away. Recent evidence suggests that all three of these lncRNAs are functional and that they silence gene expression, in part, through an intimate interaction with chromatin. Here we provide an overview of lncRNA-dependent gene silencing, focusing on recent findings for the Air and Kcnq1ot1 lncRNAs. We review molecular evidence indicating that these lncRNAs interact with chromatin and correlate their presence with specific histone modifications associated with gene silencing. A general model for a lncRNA-dependent gene-silencing mechanism is presented based on the apparent ability of lncRNAs to recruit histone-modifying activities to chromatin. However, alternate mechanisms may be required to explain the silencing of some lncRNA-dependent genes. Finally, we discuss unanswered questions and future perspectives associated with these enigmatic lncRNA molecules.
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Affiliation(s)
- Takashi Nagano
- Laboratory of Chromatin and Gene Expression, The Babraham Institute, Babraham Research Campus, Cambridge CB223AT, UK.
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202
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Burkhardt J, Petit-Teixeira E, Teixeira VH, Kirsten H, Garnier S, Ruehle S, Oeser C, Wolfram G, Scholz M, Migliorini P, Balsa A, Westhovens R, Barrera P, Alves H, Pascual-Salcedo D, Bombardieri S, Dequeker J, Radstake TR, Van Riel P, van de Putte L, Bardin T, Prum B, Buchegger-Podbielski U, Emmrich F, Melchers I, Cornelis F, Ahnert P. Association of the X-chromosomal genes TIMP1 and IL9R with rheumatoid arthritis. J Rheumatol 2009; 36:2149-57. [PMID: 19723899 DOI: 10.3899/jrheum.090059] [Citation(s) in RCA: 26] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
OBJECTIVE Rheumatoid arthritis (RA) is an inflammatory joint disease with features of an autoimmune disease with female predominance. Candidate genes located on the X-chromosome were selected for a family trio-based association study. METHODS A total of 1452 individuals belonging to 3 different sample sets were genotyped for 16 single-nucleotide polymorphisms (SNP) in 7 genes. The first 2 sets consisted of 100 family trios, each of French Caucasian origin, and the third of 284 additional family trios of European Caucasian origin. Subgroups were analyzed according to sex of patient and presence of anti-cyclic citrullinated peptide (anti-CCP) autoantibodies. RESULTS Four SNP were associated with RA in the first sample set and were genotyped in the second set. In combined analysis of sets 1 and 2, evidence remained for association of 3 SNP in the genes UBA1, TIMP1, and IL9R. These were again genotyped in the third sample set. Two SNP were associated with RA in the joint analysis of all samples: rs6520278 (TIMP1) was associated with RA in general (p = 0.035) and rs3093457 (IL9R) with anti-CCP-positive RA patients (p = 0.037) and male RA patients (p = 0.010). A comparison of the results with data from whole-genome association studies further supports an association of RA with TIMPL The sex-specific association of rs3093457 (IL9R) was supported by the observation that men homozygous for rs3093457-CC are at a significantly higher risk to develop RA than women (risk ratio male/female = 2.98; p = 0.048). CONCLUSION We provide evidence for an association of at least 2 X-chromosomal genes with RA: TIMP1 (rs6520278) and IL9R (rs3093457).
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Affiliation(s)
- Jana Burkhardt
- Institute of Clinical Immunology and Transfusion Medicine/Center for Biotechnology and Biomedicine (BBZ), Leipzig, Germany.
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203
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Rapicavoli NA, Blackshaw S. New meaning in the message: Noncoding RNAs and their role in retinal development. Dev Dyn 2009; 238:2103-14. [DOI: 10.1002/dvdy.21844] [Citation(s) in RCA: 54] [Impact Index Per Article: 3.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/01/2023] Open
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204
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Cantrell MA, Carstens BC, Wichman HA. X chromosome inactivation and Xist evolution in a rodent lacking LINE-1 activity. PLoS One 2009; 4:e6252. [PMID: 19603076 PMCID: PMC2705805 DOI: 10.1371/journal.pone.0006252] [Citation(s) in RCA: 21] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/19/2008] [Accepted: 05/28/2009] [Indexed: 02/05/2023] Open
Abstract
Dosage compensation in eutherian mammals occurs by inactivation of one X chromosome in females. Silencing of that X chromosome is initiated by Xist, a large non-coding RNA, whose coating of the chromosome extends in cis from the X inactivation center. LINE-1 (L1) retrotransposons have been implicated as possible players for propagation of the Xist signal, but it has remained unclear whether they are essential components. We previously identified a group of South American rodents in which L1 retrotransposition ceased over 8 million years ago and have now determined that at least one species of these rodents, Oryzomys palustris, still retains X inactivation. We have also isolated and analyzed the majority of the Xist RNA from O. palustris and a sister species retaining L1 activity, Sigmodon hispidus, to determine if evolution in these sequences has left signatures that might suggest a critical role for L1 elements in Xist function. Comparison of rates of Xist evolution in the two species fails to support L1 involvement, although other explanations are possible. Similarly, comparison of known repeats and potential RNA secondary structures reveals no major differences with the exception of a new repeat in O. palustris that has potential to form new secondary structures.
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Affiliation(s)
- Michael A. Cantrell
- Department of Biological Sciences, University of Idaho, Moscow, Idaho, United States of America
| | - Bryan C. Carstens
- Department of Biological Sciences, University of Idaho, Moscow, Idaho, United States of America
| | - Holly A. Wichman
- Department of Biological Sciences, University of Idaho, Moscow, Idaho, United States of America
- * E-mail:
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205
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Schneider DA, Tibary A, Raudsepp T, Das PJ, O'Rourke KI. Blood chimerism confounds genetic relative susceptibility testing for classical scrapie in sheep. J Vet Diagn Invest 2009; 21:295-305. [PMID: 19407081 DOI: 10.1177/104063870902100301] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/15/2022] Open
Abstract
Classical scrapie disease is a transmissible spongiform encephalopathy of sheep that is enzootic in the United States. Susceptibility of sheep to classical scrapie is linked to single nucleotide polymorphisms in the prion protein gene (PRNP), forming the basis for genetic testing strategies used by national efforts to eradicate scrapie. Such efforts are occasionally hampered by inconclusive results stemming from the detection of "complex" genotypes. Naturally occurring cases of ovine chimerism are thought to account for some of these instances. In the current report, 4 naturally occurring ovine chimeras are documented through cytogenetic and molecular analyses. All 4 of these sheep had chimeric cells circulating in their blood. Blood and alternate tissue samples of ear punch and hair bulbs from one of these chimeras was submitted in batch with similar samples from control sheep for routine scrapie genetic relative susceptibility testing. A complex PRNP genotype was detected in the blood of the chimeric female but not in the alternate tissue samples or in the control sheep samples. The results demonstrate that naturally occurring blood chimerism can confound current testing efforts. The potential impacts of undetected chimeras on current scrapie eradication efforts are discussed.
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Affiliation(s)
- David A Schneider
- Department of Agriculture, Agricultural Research Service, Animal Disease Research Unit, Pullman, WA 99164-6630, USA.
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206
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Kalantry S, Purushothaman S, Bowen RB, Starmer J, Magnuson T. Evidence of Xist RNA-independent initiation of mouse imprinted X-chromosome inactivation. Nature 2009; 460:647-51. [PMID: 19571810 PMCID: PMC2754729 DOI: 10.1038/nature08161] [Citation(s) in RCA: 105] [Impact Index Per Article: 6.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/10/2009] [Accepted: 05/19/2009] [Indexed: 11/09/2022]
Abstract
XX female mammals undergo transcriptional silencing of most genes on one of their two X-chromosomes to equalize X-linked gene dosage with XY males in a process referred to as X-chromosome inactivation (XCI). XCI is a paradigm of epigenetic regulation1. Once enacted in individual cells of the early female embryo, XCI is stably transmitted such that most descendant cells maintain silencing of that X-chromosome2. In eutherian mammals, XCI is thought to be triggered by the expression of the non-coding Xist RNA from the future inactive-X (Xi)3,4,5; Xist RNA in turn is proposed to recruit protein complexes that bring about heterochromatinization of the Xi6,7. Here we test whether imprinted XCI, which results in preferential inactivation of the paternal X-chromosome (Xp), occurs in mouse embryos inheriting an Xp lacking Xist. We find that silencing of Xp-linked genes can initiate in the absence of paternal Xist; Xist is, however, required to stabilize silencing of the Xp. Xp-linked gene silencing associated with mouse imprinted XCI, therefore, can initiate in the embryo independently of Xist RNA.
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Affiliation(s)
- Sundeep Kalantry
- Department of Genetics, and Carolina Center for Genome Sciences, University of North Carolina, Chapel Hill, North Carolina 27599-7264, USA
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207
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Munshi A, Duvvuri S. Genomic imprinting - the story of the other half and the conflicts of silencing. J Genet Genomics 2009; 34:93-103. [PMID: 17469781 DOI: 10.1016/s1673-8527(07)60010-1] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/04/2006] [Accepted: 09/26/2006] [Indexed: 11/20/2022]
Abstract
Genomic imprinting is an epigenetic mechanism that produces functional differences between the paternal and maternal genomes and plays an essential role in mammalian development and growth. There are a number of genes in our genomes that are subject to genomic imprinting where one parent's copy of the gene is expressed while the other is silent. Silencing of one allele predetermines that any function ascribed to that gene are now dependant on the single active copy. Possession of only a single active allele can lead to deleterious health consequences in humans. If imprinted genes are crucial in mammalian development, one would also expect mutations in these genes to cause diseases. Since imprinting is an epigenetic mechanism, mistakes in maintaining epigenetic mark also cause imprinting disorders. Here we in this review focus on the current understanding of this unique genetic mechanism more than two decades after the first description of the imprinting phenomenon was given by McGrath and Solter. Although the possible molecular mechanisms by which imprinting is imposed and maintained are being identified, we have a long way to go in understanding the molecular mechanisms that regulate the expression of these oddly behaving genes, the function of imprinting and the evolution. Post genomic technologies might ultimately lead to a better understanding of the 'imprinting effects'.
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Affiliation(s)
- Anjana Munshi
- Department of Genetics, Shadan PG Centre for Biosciences, Khairtabad Hyderabad 500016, India.
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208
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Goodrich JA, Kugel JF. From bacteria to humans, chromatin to elongation, and activation to repression: The expanding roles of noncoding RNAs in regulating transcription. Crit Rev Biochem Mol Biol 2009; 44:3-15. [PMID: 19107624 DOI: 10.1080/10409230802593995] [Citation(s) in RCA: 30] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/11/2022]
Abstract
Noncoding RNAs (ncRNAs) have emerged as key regulators of transcription, often functioning as trans-acting factors akin to prototypical protein transcriptional regulators. Inside cells, ncRNAs are now known to control transcription of single genes as well as entire transcriptional programs in response to developmental and environmental cues. In doing so, they target nearly all levels of the transcription process from regulating chromatin structure through controlling transcript elongation. Moreover, trans-acting ncRNA transcriptional regulators have been found in organisms as diverse as bacteria and humans. With the recent discovery that much of the DNA in genomes is transcribed into ncRNAs with yet unknown function, it is likely that future studies will reveal many more ncRNA regulators of transcription.
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Affiliation(s)
- James A Goodrich
- Department of Chemistry and Biochemistry, University of Colorado at Boulder, 80309-0215, USA.
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209
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Sirchia SM, Tabano S, Monti L, Recalcati MP, Gariboldi M, Grati FR, Porta G, Finelli P, Radice P, Miozzo M. Misbehaviour of XIST RNA in breast cancer cells. PLoS One 2009; 4:e5559. [PMID: 19440381 PMCID: PMC2679222 DOI: 10.1371/journal.pone.0005559] [Citation(s) in RCA: 58] [Impact Index Per Article: 3.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/02/2009] [Accepted: 04/14/2009] [Indexed: 11/18/2022] Open
Abstract
A role of X chromosome inactivation process in the development of breast cancer have been suggested. In particular, the relationship between the breast cancer predisposing gene BRCA1 and XIST, the main mediator of X chromosome inactivation, has been intensely investigated, but still remains controversial. We investigated this topic by assessing XIST behaviour in different groups of breast carcinomas and in a panel of breast cancer cell lines both BRCA1 mutant and wild type. In addition, we evaluated the occurrence of broader defects of heterochromatin in relation to BRCA1 status in breast cancer cells. We provide evidence that in breast cancer cells BRCA1 is involved in XIST regulation on the active X chromosome, but not in its localization as previously suggested, and that XIST can be unusually expressed by an active X and can decorate it. This indicates that the detection of XIST cloud in cancer cell is not synonymous of the presence of an inactive X chromosome. Moreover, we show that global heterochromatin defects observed in breast tumor cells are independent of BRCA1 status. Our observations sheds light on a possible previously uncharacterized mechanism of breast carcinogenesis mediated by XIST misbehaviour, particularly in BRCA1-related cancers. Moreover, the significant higher levels of XIST-RNA detected in BRCA1-associated respect to sporadic basal-like cancers, opens the possibility to use XIST expression as a marker to discriminate between the two groups of tumors.
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Affiliation(s)
- Silvia M Sirchia
- Department of Medicine, Surgery and Dentistry, Medical Genetics Unit, Università degli Studi di Milano, Milano, Italy.
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210
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Dimitri P, Caizzi R, Giordano E, Carmela Accardo M, Lattanzi G, Biamonti G. Constitutive heterochromatin: a surprising variety of expressed sequences. Chromosoma 2009; 118:419-35. [PMID: 19412619 DOI: 10.1007/s00412-009-0211-y] [Citation(s) in RCA: 39] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/09/2008] [Revised: 03/30/2009] [Accepted: 04/01/2009] [Indexed: 10/20/2022]
Abstract
The organization of chromosomes into euchromatin and heterochromatin is amongst the most important and enigmatic aspects of genome evolution. Constitutive heterochromatin is a basic yet still poorly understood component of eukaryotic chromosomes, and its molecular characterization by means of standard genomic approaches is intrinsically difficult. Although recent evidence indicates that the presence of transcribed genes in constitutive heterochromatin is a conserved trait that accompanies the evolution of eukaryotic genomes, the term heterochromatin is still considered by many as synonymous of gene silencing. In this paper, we comprehensively review data that provide a clearer picture of transcribed sequences within constitutive heterochromatin, with a special emphasis on Drosophila and humans.
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Affiliation(s)
- Patrizio Dimitri
- Laboratorio di Genomica Funzionale e Proteomica di Sistemi modello and Istituto Pasteur-Fondazione Bolognetti, Dipartimento di Genetica e Biologia Molecolare Charles Darwin, Università La Sapienza, 00185, Italy.
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211
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Charles C, Pantalacci S, Tafforeau P, Headon D, Laudet V, Viriot L. Distinct impacts of Eda and Edar loss of function on the mouse dentition. PLoS One 2009; 4:e4985. [PMID: 19340299 PMCID: PMC2659790 DOI: 10.1371/journal.pone.0004985] [Citation(s) in RCA: 33] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/11/2008] [Accepted: 02/25/2009] [Indexed: 01/21/2023] Open
Abstract
Background The Eda-A1-Edar signaling pathway is involved in the development of organs with an ectodermal origin, including teeth. In mouse, mutants are known for both the ligand, Eda-A1 (Tabby), and the receptor, Edar (Downless). The adult dentitions of these two mutants have classically been considered to be similar. However, previous studies mentioned differences in embryonic dental development between EdaTa and Edardl-J mutants. A detailed study of tooth morphology in mutants bearing losses of functions of these two genes thus appears necessary to test the pattern variability induced by the developmental modifications. Methodology/Principal Findings 3D-reconstructions of the cheek teeth have been performed at the ESRF (Grenoble, France) by X-ray synchrotron microtomography to assess dental morphology. The morphological variability observed in EdaTa and Edardl-J mutants have then been compared in detail. Despite patchy similarities, our detailed work on cheek teeth in EdaTa and Edardl-J mice show that all dental morphotypes defined in Edardl-J mice resolutely differ from those of EdaTa mice. This study reveals that losses of function of Eda and Edar have distinct impacts on the tooth size and morphology, contrary to what has previously been thought. Conclusion/Signifiance The results indicate that unknown mechanisms of the Eda pathway are implicated in tooth morphogenesis. Three hypotheses could explain our results; an unexpected role of the Xedar pathway (which is influenced by the Eda gene product but not that of Edar), a more complex connection than has been appreciated between Edar and another protein, or a ligand-independent activity for Edar. Further work is necessary to test these hypotheses and improve our understanding of the mechanisms of development.
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Affiliation(s)
- Cyril Charles
- Institut International de Paléoprimatologie Paléontologie Humaine: Evolution et Paléoenvironnements UMR CNRS 6046, Université de Poitiers, Poitiers, France
| | - Sophie Pantalacci
- Team 〈〈 Molecular Zoology 〉〉, Institut de Génomique Fonctionnelle de Lyon, Université de Lyon, UMR CNRS 5242, INRA, Université Claude Bernard Lyon 1, Ecole Normale Supérieure de Lyon, Lyon, France
| | - Paul Tafforeau
- European Synchrotron Radiation Facility, Grenoble, France
| | - Denis Headon
- The Roslin Institute and Royal (Dick) School of Veterinary Studies, University of Edinburgh, Edinburgh, United Kingdom
| | - Vincent Laudet
- Team 〈〈 Molecular Zoology 〉〉, Institut de Génomique Fonctionnelle de Lyon, Université de Lyon, UMR CNRS 5242, INRA, Université Claude Bernard Lyon 1, Ecole Normale Supérieure de Lyon, Lyon, France
| | - Laurent Viriot
- Team 〈〈 Evo-Devo of Vertebrate Dentition 〉〉, Institut de Génomique Fonctionnelle de Lyon, Université de Lyon, UMR CNRS 5242, INRA, Université Claude Bernard Lyon 1, Ecole Normale Supérieure de Lyon, Lyon, France
- * E-mail:
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212
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Abstract
The development of genetic sex determination and cytologically distinct sex chromosomes leads to the potential problem of gene dosage imbalances between autosomes and sex chromosomes and also between males and females. To circumvent these imbalances, mammals have developed an elaborate system of dosage compensation that includes both upregulation and repression of the X chromosome. Recent advances have provided insights into the evolutionary history of how both the imprinted and random forms of X chromosome inactivation have come about. Furthermore, our understanding of the epigenetic switch at the X-inactivation center and the molecular aspects of chromosome-wide silencing has greatly improved recently. Here, we review various facets of the ever-expanding field of mammalian dosage compensation and discuss its evolutionary, developmental, and mechanistic components.
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Affiliation(s)
- Bernhard Payer
- Howard Hughes Medical Institute, Department of Molecular Biology, Massachusetts General Hospital, Boston, Massachusetts 02114, USA.
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213
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Abstract
Dicer is central to the RNA interference (RNAi) pathway, because it is required for processing of double-stranded RNA (dsRNA) precursors into small RNA effector molecules. In principle, any long dsRNA could serve as a substrate for Dicer. The X inactive specific transcript (Xist) is an untranslated RNA that is required for dosage compensation in mammals. It coats and silences 1 of the 2 X chromosomes in female cells and initiates a chromosomewide change in chromatin structure that includes the recruitment of Polycomb proteins, but it is largely unknown how Xist RNA mediates these processes. To investigate a potential link between the RNAi pathway and X inactivation, we generated and analyzed Dicer-deficient embryonic stem (ES) cells. In the absence of Dicer, coating by Xist RNA, initiation of silencing, and recruitment of Polycomb proteins occur normally. Dicer ablation had modest effects on the steady-state levels of spliced Xist RNA. Together our data indicate that the RNAi machinery is not essential for the initiation of X inactivation.
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214
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Assessing the impact of tissue devitalization time on genome-wide gene expression analysis in ovarian tumor samples. ACTA ACUST UNITED AC 2008; 17:200-6. [PMID: 18382347 DOI: 10.1097/pdm.0b013e318169bfaf] [Citation(s) in RCA: 20] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/25/2022]
Abstract
The utilization of genome-wide gene expression microarray technology in tumor stratification has proven a powerful tool to identify gene expression signatures associated with cancer prognosis and is currently under evaluation in clinical laboratories. Standardized protocols, including tumor tissue postoperatively handling guidelines are yet to be defined. We aimed at assessing a systematic effect of devitalization in ovarian tumors' gene expression profiling, using high-density oligonucleotide microarrays, under a standardized protocol following strict quality control criteria. Residual tissue from the surgical pathology specimen was divided into 5 samples. Half of each was immediately snap frozen in liquid nitrogen. The remaining halves were kept at room temperature for 0, 15, 30, 60, and 120 minutes, at which time the tissue was snap frozen in liquid nitrogen, and stored at -80 degrees C until RNA extraction. The entire process from RNA extraction through feature intensity distribution was rigorously monitored for quality. Identification of altered gene expression among each pair of snap frozen and devitalized samples per ovarian tumor specimen was assessed by using the Significance score (S-score) method. We identified only 4 probe sets that seemed to correlate with devitalization time in one of the ovarian tumor specimens, suggesting that they are not likely to have an impact on gene expression profiling tumor stratification. Our study suggests that with proper sample handling and rigorous quality control procedures for RNA extraction and microarray analysis, tumor classification based on global gene expression data will not be adversely affected if devitalization times are kept within a 120-minute window.
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215
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MEN epsilon/beta nuclear-retained non-coding RNAs are up-regulated upon muscle differentiation and are essential components of paraspeckles. Genome Res 2008; 19:347-59. [PMID: 19106332 DOI: 10.1101/gr.087775.108] [Citation(s) in RCA: 533] [Impact Index Per Article: 31.4] [Reference Citation Analysis] [Abstract] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/25/2022]
Abstract
Studies of the transcriptional output of the human and mouse genomes have revealed that there are many more transcripts produced than can be accounted for by predicted protein-coding genes. Using a custom microarray, we have identified 184 non-coding RNAs that exhibit more than twofold up- or down-regulation upon differentiation of C2C12 myoblasts into myotubes. Here, we focus on the Men epsilon/beta locus, which is up-regulated 3.3-fold during differentiation. Two non-coding RNA isoforms are produced from a single RNA polymerase II promoter, differing in the location of their 3' ends. Men epsilon is a 3.2-kb polyadenylated RNA, whereas Men beta is an approximately 20-kb transcript containing a genomically encoded poly(A)-rich tract at its 3'-end. The 3'-end of Men beta is generated by RNase P cleavage. The Men epsilon/beta transcripts are localized to nuclear paraspeckles and directly interact with NONO. Knockdown of MEN epsilon/beta expression results in the disruption of nuclear paraspeckles. Furthermore, the formation of paraspeckles, after release from transcriptional inhibition by DRB treatment, was suppressed in MEN epsilon/beta-depleted cells. Our findings indicate that the MEN epsilon/beta non-coding RNAs are essential structural/organizational components of paraspeckles.
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216
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Non-coding RNAs revealed during identification of genes involved in chicken immune responses. Immunogenetics 2008; 61:55-70. [PMID: 19009289 DOI: 10.1007/s00251-008-0337-8] [Citation(s) in RCA: 15] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/05/2008] [Accepted: 10/13/2008] [Indexed: 12/12/2022]
Abstract
Recent large-scale cDNA cloning studies have shown that a significant proportion of the transcripts expressed from vertebrate genomes do not appear to encode protein. Moreover, it was reported in mammals (human and mice) that these non-coding transcripts are expressed and regulated by mechanisms similar to those involved in the control of protein-coding genes. We have produced a collection of cDNA sequences from immunologically active tissues with the aim of discovering chicken genes involved in immune mechanisms, and we decided to explore the non-coding component of these immune-related libraries. After finding known non-coding RNAs (miRNA, snRNA, snoRNA), we identified new putative mRNA-like non-coding RNAs. We characterised their expression profiles in immune-related samples. Some of them showed changes in expression following viral infections. As they exhibit patterns of expression that parallel the behaviour of protein-coding RNAs in immune tissues, our study suggests that they could play an active role in the immune response.
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217
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Khil PP, Camerini-Otero RD. Molecular Features and Functional Constraints in the Evolution of the Mammalian X Chromosome. Crit Rev Biochem Mol Biol 2008; 40:313-30. [PMID: 16338684 DOI: 10.1080/10409230500356703] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/25/2022]
Abstract
Recent advances in genomic sequencing of multiple organisms have fostered significant advances in our understanding of the evolution of the sex chromosomes. The integration of this newly available sequence information with functional data has facilitated a considerable refinement of our conceptual framework of the forces driving this evolution. Here we address multiple functional constraints that were encountered in the evolution of the X chromosome and the impact that this evolutionary history has had on its modern behavior.
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Affiliation(s)
- Pavel P Khil
- Genetics and Biochemistry Branch, National Institutes of Health, Bethesda, MD 20892, USA
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218
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Mittal T, Saralaya KM, Kuruvilla A, Achary C. Sex determination from buccal mucosa scrapes. Int J Legal Med 2008; 123:437-40. [PMID: 18813940 DOI: 10.1007/s00414-008-0285-8] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/13/2007] [Accepted: 09/08/2008] [Indexed: 11/28/2022]
Abstract
Establishing individuality is an imperative aspect in any investigation procedure. At times, it becomes necessary to determine the sex of the individual to establish identity, and saliva stains found at the scene of crime are of major help in such cases. In the present study, we have determined the sex of the individual from buccal mucosal scrapings. Buccal smears prepared from 100 men and 100 women were stained by the Papanicolaou staining method. Cells were observed for Barr bodies under oil immersion with a compound microscope, and the percentage of Barr-body-positive cells was determined. It was observed that 1.14% of buccal mucosal cells in men (range = 0-4%) and 39.29% of buccal mucosal cells in women (range = 20-78%) showed Barr bodies. Inferences from the study show that the presence of Barr body in buccal mucosal cells can be demonstrated with a fair degree of accuracy using Papanicolaou staining. The sex of the individual can be determined accurately, as two non-overlapping ranges for the percentage of Barr-body-positive cells has been obtained for men and women. This method not only proves to be accurate but is also simple and economic.
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Affiliation(s)
- Tushar Mittal
- Kasturba Medical College, Mangalore, Karnataka, India.
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219
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Jonkers I, Monkhorst K, Rentmeester E, Grootegoed JA, Grosveld F, Gribnau J. Xist RNA is confined to the nuclear territory of the silenced X chromosome throughout the cell cycle. Mol Cell Biol 2008; 28:5583-94. [PMID: 18625719 PMCID: PMC2546918 DOI: 10.1128/mcb.02269-07] [Citation(s) in RCA: 59] [Impact Index Per Article: 3.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/21/2007] [Revised: 02/04/2008] [Accepted: 07/04/2008] [Indexed: 11/20/2022] Open
Abstract
In mammalian female cells, one X chromosome is inactivated to prevent a dose difference in the expression of X-encoded proteins between males and females. Xist RNA, required for X chromosome inactivation, is transcribed from the future inactivated X chromosome (Xi), where it spreads in cis, to initiate silencing. We have analyzed Xist RNA transcription and localization throughout the cell cycle. It was found that Xist transcription is constant and that the mature RNA remains attached to the Xi throughout mitosis. Diploid and tetraploid cell lines with an MS2-tagged Xist gene were used to investigate spreading of Xist. Most XXXX(MS2) tetraploid mouse embryonic stem (ES) cells inactivate the X(MS2) chromosome and one other X chromosome. Analysis of cells with two Xi's indicates that Xist RNA is retained by the Xi of its origin and does not spread in trans. Also, in XX(MS2) diploid mouse ES cells with an autosomal Xist transgene, there is no trans exchange of Xist RNA from the Xi to the autosome. We propose that Xist RNA does not dissociate from the Xi of its origin, which precludes a model of diffusion-mediated trans spreading of Xist RNA.
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Affiliation(s)
- Iris Jonkers
- Department of Cell Biology, Erasmus MC-University Medical Center, Rotterdam, The Netherlands
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220
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Epigenetic processes in a tetraploid mammal. Mamm Genome 2008; 19:439-47. [PMID: 18758856 DOI: 10.1007/s00335-008-9131-z] [Citation(s) in RCA: 10] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/17/2008] [Accepted: 07/01/2008] [Indexed: 10/21/2022]
Abstract
Polyploidy has played a most important role in speciation and evolution of plants and animals. It is thought that low frequency of polyploidy in mammals is due to a dosage imbalance that would interfere with proper development in mammalian polyploids. The first tetraploid mammal, Tympanoctomys barrerae (Octodontidae), appears to be an exception to this rule. In this study we investigated X chromosome inactivation (XCI) and genomic imprinting in T. barrerae, two epigenetic processes usually involved in dosage control in mammalian genomes. The imprinting status of the Peg1 gene was determined by Peg1 allelic expression studies. The inactive X chromosome was identified on interphase nuclei by immunofluorescence using specific antisera raised against Met3H3K27 and macroH2A1. Quantitative PCR was used to compare the Peg1/Dmd ratio in T. barrerae and in its most closely related diploid species, Octomys mimax. Our data demonstrate that parental-specific silencing of at least one gene and normal X chromosomal dosage mechanism are conserved in the tetraploid genome. We hypothesize a concerted action of genetic and epigenetic mechanisms during the process of functional diploidization of this tetraploid genome.
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221
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Analysis of transposon interruptions suggests selection for L1 elements on the X chromosome. PLoS Genet 2008; 4:e1000172. [PMID: 18769724 PMCID: PMC2517846 DOI: 10.1371/journal.pgen.1000172] [Citation(s) in RCA: 24] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/26/2008] [Accepted: 07/17/2008] [Indexed: 01/02/2023] Open
Abstract
It has been hypothesised that the massive accumulation of L1 transposable elements on the X chromosome is due to their function in X inactivation, and that the accumulation of Alu elements near genes is adaptive. We tested the possible selective advantage of these two transposable element (TE) families with a novel method, interruption analysis. In mammalian genomes, a large number of TEs interrupt other TEs due to the high overall abundance and age of repeats, and these interruptions can be used to test whether TEs are selectively neutral. Interruptions of TEs, which are beneficial for the host, are expected to be deleterious and underrepresented compared with neutral ones. We found that L1 elements in the regions of the X chromosome that contain the majority of the inactivated genes are significantly less frequently interrupted than on the autosomes, while L1s near genes that escape inactivation are interrupted with higher frequency, supporting the hypothesis that L1s on the X chromosome play a role in its inactivation. In addition, we show that TEs are less frequently interrupted in introns than in intergenic regions, probably due to selection against the expansion of introns, but the insertion pattern of Alus is comparable to other repeats. Recent experimental findings (for example the ENCODE project) show that many functional non-coding regions of genomes are not conserved across species, making the in-silico discovery of such regions challenging. Transposable elements (TEs), which represent 45 percent of the human genome and typically show no sequence conservation, are particularly intriguing from this point of view, because the highly nonrandom genomic distribution of many TE families in genomes has led to hypotheses that their presence is adaptive and have an epigenetic (regulatory) function. We use a novel approach based on the analysis of interrupted TEs to investigate if repeats are under selection that does not rely on sequence conservation. L1 elements, the most active transposable elements of the human genome, are highly overrepresented on the X-chromosome and were suggested to enhance its inactivation in mammals. We find that the interruption pattern of L1 repeats indicates a function for L1 elements in the inactivation of the mammalian X chromosome. Additionally, we show that a considerable fraction of TEs in introns are under selection for integrity, possibly due to selection on intron size or on TEs themselves.
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222
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Ideraabdullah FY, Vigneau S, Bartolomei MS. Genomic imprinting mechanisms in mammals. Mutat Res 2008; 647:77-85. [PMID: 18778719 DOI: 10.1016/j.mrfmmm.2008.08.008] [Citation(s) in RCA: 173] [Impact Index Per Article: 10.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/05/2008] [Revised: 07/31/2008] [Accepted: 08/07/2008] [Indexed: 11/25/2022]
Abstract
Genomic imprinting is a form of epigenetic gene regulation that results in expression from a single allele in a parent-of-origin-dependent manner. This form of monoallelic expression affects a small but growing number of genes and is essential to normal mammalian development. Despite extensive studies and some major breakthroughs regarding this intriguing phenomenon, we have not yet fully characterized the underlying molecular mechanisms of genomic imprinting. This is in part due to the complexity of the system in that the epigenetic markings required for proper imprinting must be established in the germline, maintained throughout development, and then erased before being re-established in the next generation's germline. Furthermore, imprinted gene expression is often tissue or stage-specific. It has also become clear that while imprinted loci across the genome seem to rely consistently on epigenetic markings of DNA methylation and/or histone modifications to discern parental alleles, the regulatory activities underlying these markings vary among loci. Here, we discuss different modes of imprinting regulation in mammals and how perturbations of these systems result in human disease. We focus on the mechanism of genomic imprinting mediated by insulators as is present at the H19/Igf2 locus, and by non-coding RNA present at the Igf2r and Kcnq1 loci. In addition to imprinting mechanisms at autosomal loci, what is known about imprinted X-chromosome inactivation and how it compares to autosomal imprinting is also discussed. Overall, this review summarizes many years of imprinting research, while pointing out exciting new discoveries that further elucidate the mechanism of genomic imprinting, and speculating on areas that require further investigation.
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Affiliation(s)
- Folami Y Ideraabdullah
- Department of Cell and Developmental Biology, University of Pennsylvania School of Medicine, Philadelphia, PA 19104, USA
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223
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Zhou Q, Wang J, Huang L, Nie W, Wang J, Liu Y, Zhao X, Yang F, Wang W. Neo-sex chromosomes in the black muntjac recapitulate incipient evolution of mammalian sex chromosomes. Genome Biol 2008; 9:R98. [PMID: 18554412 PMCID: PMC2481430 DOI: 10.1186/gb-2008-9-6-r98] [Citation(s) in RCA: 33] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/09/2007] [Revised: 03/04/2008] [Accepted: 06/14/2008] [Indexed: 11/17/2022] Open
Abstract
BACKGROUND The regular mammalian X and Y chromosomes diverged from each other at least 166 to 148 million years ago, leaving few traces of their early evolution, including degeneration of the Y chromosome and evolution of dosage compensation. RESULTS We studied the intriguing case of black muntjac, in which a recent X-autosome fusion and a subsequent large autosomal inversion within just the past 0.5 million years have led to inheritance patterns identical to the traditional X-Y (neo-sex chromosomes). We compared patterns of genome evolution in 35-kilobase noncoding regions and 23 gene pairs on the homologous neo-sex chromosomes. We found that neo-Y alleles have accumulated more mutations, comprising a wide variety of mutation types, which indicates cessation of recombination and is consistent with an ongoing neo-Y degeneration process. Putative deleterious mutations were observed in coding regions of eight investigated genes as well as cis-regulatory regions of two housekeeping genes. In vivo assays characterized a neo-Y insertion in the promoter of the CLTC gene that causes a significant reduction in allelic expression. A neo-Y-linked deletion in the 3'-untranslated region of gene SNX22 abolished a microRNA target site. Finally, expression analyses revealed complex patterns of expression divergence between neo-Y and neo-X alleles. CONCLUSION The nascent neo-sex chromosome system of black muntjacs is a valuable model in which to study the evolution of sex chromosomes in mammals. Our results illustrate the degeneration scenarios in various genomic regions. Of particular importance, we report--for the first time--that regulatory mutations were probably able to accelerate the degeneration process of Y and contribute to further evolution of dosage compensation.
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Affiliation(s)
- Qi Zhou
- CAS-Max Planck Junior Research Group, State Key Laboratory of Genetic Resources and Evolution, Kunming Institute of Zoology, Chinese Academy of Sciences (CAS), 32# Jiao-chang Road, Kunming, Yunnan 650223, People's Republic of China
- Graduate School of Chinese Academy Sciences, 19# Yu-quan Road, Beijing 100039, People's Republic of China
| | - Jun Wang
- The Institute of Human Genetics, University of Aarhus, Nordre Ringgade 1, DK-8000 Aarhus C, Denmark
- Department of Biochemistry and Molecular Biology, University of Southern Denmark, Campusvej 55, DK-5230, Odense M, Denmark
- Beijing Genomics Institute, Bei-shan Road, Shenzhen 518083, People's Republic of China
| | - Ling Huang
- Graduate School of Chinese Academy Sciences, 19# Yu-quan Road, Beijing 100039, People's Republic of China
- Kunming Cell Bank, State Key Laboratory of Genetic Resources and Evolution, Kunming Institute of Zoology, Chinese Academy of Sciences, 32# Jiao-chang Road, Kunming, Yunnan 650223, People's Republic of China
| | - Wenhui Nie
- Kunming Cell Bank, State Key Laboratory of Genetic Resources and Evolution, Kunming Institute of Zoology, Chinese Academy of Sciences, 32# Jiao-chang Road, Kunming, Yunnan 650223, People's Republic of China
| | - Jinhuan Wang
- Kunming Cell Bank, State Key Laboratory of Genetic Resources and Evolution, Kunming Institute of Zoology, Chinese Academy of Sciences, 32# Jiao-chang Road, Kunming, Yunnan 650223, People's Republic of China
| | - Yan Liu
- Graduate School of Chinese Academy Sciences, 19# Yu-quan Road, Beijing 100039, People's Republic of China
- Kunming Cell Bank, State Key Laboratory of Genetic Resources and Evolution, Kunming Institute of Zoology, Chinese Academy of Sciences, 32# Jiao-chang Road, Kunming, Yunnan 650223, People's Republic of China
| | - Xiangyi Zhao
- CAS-Max Planck Junior Research Group, State Key Laboratory of Genetic Resources and Evolution, Kunming Institute of Zoology, Chinese Academy of Sciences (CAS), 32# Jiao-chang Road, Kunming, Yunnan 650223, People's Republic of China
| | - Fengtang Yang
- Wellcome Trust Sanger Institute, Wellcome Trust Genome Campus, Ickleton Road, Hinxton, Cambridge, CB10 1SA, UK
| | - Wen Wang
- CAS-Max Planck Junior Research Group, State Key Laboratory of Genetic Resources and Evolution, Kunming Institute of Zoology, Chinese Academy of Sciences (CAS), 32# Jiao-chang Road, Kunming, Yunnan 650223, People's Republic of China
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224
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Brace MD, Peters O, Menzies P, King WA, Nino-Soto MI. Sex chromosome chimerism and the freemartin syndrome in Rideau Arcott sheep. Cytogenet Genome Res 2008; 120:132-9. [PMID: 18467837 DOI: 10.1159/000118752] [Citation(s) in RCA: 15] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Accepted: 10/19/2007] [Indexed: 11/19/2022] Open
Abstract
In cattle, nearly all heifers born co-twin to a male are freemartins, XX/XY chimeras that exhibit a characteristic masculinized phenotype. However, in sheep, while litters containing males and females are common, freemartins are relatively rare. The primary aim of this study was to determine the frequency and features of XX/XY chimerism in female Rideau Arcott sheep. Also, breeding records were used to investigate the effect of litter size and sex ratios, as well as the genetic basis of the condition. Finally, the migration and transcriptional competence of cells of the opposite sex in the XX/XY female and male chimeras was explored. Genomic DNA (gDNA) from peripheral blood cells of ewes was screened by PCR for the male-specific SRY gene. Of 230 lambs screened, 10 were identified as chimeras. Litter size and sex ratio showed no statistically significant effect on the frequency of chimerism. PCR and FISH analysis confirmed the presence of opposite sex cells in female and male chimeras, and in the case of ewes, their migration to tissues other than blood. Transcriptional activity of SRY and AMH was detected in gonads of ewes, whereas XIST expression was detected in white blood cells of chimeric rams. It was concluded that the frequency of sex chromosome chimerism in Rideau Arcott sheep is estimated at 4.35%, with no significant effect of litter size and sex ratio. Moreover, as it was shown that opposite sex cells can migrate to tissues other than blood and be transcriptionally active in chimeric sheep, we speculate on the role they can play in these animals.
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Affiliation(s)
- M D Brace
- Department of Biomedical Science, Ontario Veterinary College, University of Guelph, Guelph, ON, Canada
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225
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Tsai CL, Rowntree RK, Cohen DE, Lee JT. Higher order chromatin structure at the X-inactivation center via looping DNA. Dev Biol 2008; 319:416-25. [PMID: 18501343 DOI: 10.1016/j.ydbio.2008.04.010] [Citation(s) in RCA: 65] [Impact Index Per Article: 3.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/17/2008] [Revised: 03/24/2008] [Accepted: 04/08/2008] [Indexed: 01/30/2023]
Abstract
In mammals, the silencing step of the X-chromosome inactivation (XCI) process is initiated by the non-coding Xist RNA. Xist is known to be controlled by the non-coding Xite and Tsix loci, but the mechanisms by which Tsix and Xite regulate Xist are yet to be fully elucidated. Here, we examine the role of higher order chromatin structure across the 100-kb region of the mouse X-inactivation center (Xic) and map domains of specialized chromatin in vivo. By hypersensitive site mapping and chromosome conformation capture (3C), we identify two domains of higher order chromatin structure. Xite makes looping interactions with Tsix, while Xist makes contacts with Jpx/Enox, another non-coding gene not previously implicated in XCI. These regions interact in a developmentally-specific and sex-specific manner that is consistent with a regulatory role in XCI. We propose that dynamic changes in three-dimensional architecture leads to formation of separate chromatin hubs in Tsix and Xist that together regulate the initiation of X-chromosome inactivation.
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Affiliation(s)
- Chia-Lun Tsai
- Department of Molecular Biology, Howard Hughes Medical Institute, Massachusetts General Hospital, Boston, MA 02114-2790, USA
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226
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Jöchl C, Rederstorff M, Hertel J, Stadler PF, Hofacker IL, Schrettl M, Haas H, Hüttenhofer A. Small ncRNA transcriptome analysis from Aspergillus fumigatus suggests a novel mechanism for regulation of protein synthesis. Nucleic Acids Res 2008; 36:2677-89. [PMID: 18346967 PMCID: PMC2377427 DOI: 10.1093/nar/gkn123] [Citation(s) in RCA: 135] [Impact Index Per Article: 7.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/28/2023] Open
Abstract
Small non-protein-coding RNAs (ncRNAs) have systematically been studied in various model organisms from Escherichia coli to Homo sapiens. Here, we analyse the small ncRNA transcriptome from the pathogenic filamentous fungus Aspergillus fumigatus. To that aim, we experimentally screened for ncRNAs, expressed under various growth conditions or during specific developmental stages, by generating a specialized cDNA library from size-selected small RNA species. Our screen revealed 30 novel ncRNA candidates from known ncRNA classes such as small nuclear RNAs (snRNAs) and C/D box-type small nucleolar RNAs (C/D box snoRNAs). Additionally, several candidates for H/ACA box snoRNAs could be predicted by a bioinformatical screen. We also identified 15 candidates for ncRNAs, which could not be assigned to any known ncRNA class. Some of these ncRNA species are developmentally regulated implying a possible novel function in A. fumigatus development. Surprisingly, in addition to full-length tRNAs, we also identified 5′- or 3′-halves of tRNAs, only, which are likely generated by tRNA cleavage within the anti-codon loop. We show that conidiation induces tRNA cleavage resulting in tRNA depletion within conidia. Since conidia represent the resting state of A. fumigatus we propose that conidial tRNA depletion might be a novel mechanism to down-regulate protein synthesis in a filamentous fungus.
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Affiliation(s)
- Christoph Jöchl
- Innsbruck Biocenter, Division of Genomics and RNomics - Innsbruck Medical University, Fritz-Pregl-Strasse 3, 6020 Innsbruck, Austria
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227
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Differential allelic expression in the human genome: a robust approach to identify genetic and epigenetic cis-acting mechanisms regulating gene expression. PLoS Genet 2008; 4:e1000006. [PMID: 18454203 PMCID: PMC2265535 DOI: 10.1371/journal.pgen.1000006] [Citation(s) in RCA: 192] [Impact Index Per Article: 11.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/10/2007] [Accepted: 01/15/2008] [Indexed: 11/19/2022] Open
Abstract
The recent development of whole genome association studies has lead to the robust identification of several loci involved in different common human diseases. Interestingly, some of the strongest signals of association observed in these studies arise from non-coding regions located in very large introns or far away from any annotated genes, raising the possibility that these regions are involved in the etiology of the disease through some unidentified regulatory mechanisms. These findings highlight the importance of better understanding the mechanisms leading to inter-individual differences in gene expression in humans. Most of the existing approaches developed to identify common regulatory polymorphisms are based on linkage/association mapping of gene expression to genotypes. However, these methods have some limitations, notably their cost and the requirement of extensive genotyping information from all the individuals studied which limits their applications to a specific cohort or tissue. Here we describe a robust and high-throughput method to directly measure differences in allelic expression for a large number of genes using the Illumina Allele-Specific Expression BeadArray platform and quantitative sequencing of RT-PCR products. We show that this approach allows reliable identification of differences in the relative expression of the two alleles larger than 1.5-fold (i.e., deviations of the allelic ratio larger than 60∶40) and offers several advantages over the mapping of total gene expression, particularly for studying humans or outbred populations. Our analysis of more than 80 individuals for 2,968 SNPs located in 1,380 genes confirms that differential allelic expression is a widespread phenomenon affecting the expression of 20% of human genes and shows that our method successfully captures expression differences resulting from both genetic and epigenetic cis-acting mechanisms. We describe a new methodology to identify individual differences in the expression of the two copies of one gene. This is achieved by comparing the mRNA level of the two alleles using a heterozygous polymorphism in the transcript as marker. We show that this approach allows an exhaustive survey of cis-acting regulation in the genome; we can identify allelic expression differences due to epigenetic mechanisms of gene regulation (e.g. imprinting or X-inactivation) as well as differences due to the presence of polymorphisms in regulatory elements. The direct comparison of the expression of both alleles nullifies possible trans-acting regulatory effects (that influence equally both alleles) and thus complements the findings from gene expression association studies. Our approach can be easily applied to any cohort of interest for a wide range of studies. It notably allows following up association signals and testing whether a gene sitting on a particular haplotype is over- or under-expressed, or can be used for screening cancer tissues for aberrant gene expression due to newly arisen mutations or alteration of the methylation patterns.
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228
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Erickson JW, Quintero JJ. Indirect effects of ploidy suggest X chromosome dose, not the X:A ratio, signals sex in Drosophila. PLoS Biol 2008; 5:e332. [PMID: 18162044 PMCID: PMC2222971 DOI: 10.1371/journal.pbio.0050332] [Citation(s) in RCA: 145] [Impact Index Per Article: 8.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/02/2007] [Accepted: 11/09/2007] [Indexed: 11/18/2022] Open
Abstract
In the textbook view, the ratio of X chromosomes to autosome sets, X:A, is the primary signal specifying sexual fate in Drosophila. An alternative idea is that X chromosome number signals sex through the direct actions of several X-encoded signal element (XSE) proteins. In this alternative, the influence of autosome dose on X chromosome counting is largely indirect. Haploids (1X;1A), which possess the male number of X chromosomes but the female X:A of 1.0, and triploid intersexes (XX;AAA), which possess a female dose of two X chromosomes and the ambiguous X:A ratio of 0.67, represent critical tests of these hypotheses. To directly address the effects of ploidy in primary sex determination, we compared the responses of the signal target, the female-specific SxlPe promoter of the switch gene Sex-lethal, in haploid, diploid, and triploid embryos. We found that haploids activate SxlPe because an extra precellular nuclear division elevates total X chromosome numbers and XSE levels beyond those in diploid males. Conversely, triploid embryos cellularize one cycle earlier than diploids, causing premature cessation of SxlPe expression. This prevents XX;AAA embryos from fully engaging the autoregulatory mechanism that maintains subsequent Sxl expression, causing them to develop as sexual mosaics. We conclude that the X:A ratio predicts sexual fate, but does not actively specify it. Instead, the instructive X chromosome signal is more appropriately seen as collective XSE dose in the early embryo. Our findings reiterate that correlations between X:A ratios and cell fates in other organisms need not implicate the value of the ratio as an active signal.
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Affiliation(s)
- James W Erickson
- Department of Biology, Texas A&M University, College Station, Texas, United States of America.
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229
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Clark SJ. Action at a distance: epigenetic silencing of large chromosomal regions in carcinogenesis. Hum Mol Genet 2007; 16 Spec No 1:R88-95. [PMID: 17613553 DOI: 10.1093/hmg/ddm051] [Citation(s) in RCA: 81] [Impact Index Per Article: 4.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/31/2022] Open
Abstract
Despite the completion of the Human Genome Project, we are still far from understanding the molecular events underlying epigenetic change in cancer. Cancer is a disease of the DNA with both genetic and epigenetic changes contributing to changes in gene expression. Epigenetics involves the interplay between DNA methylation, histone modifications and expression of non-coding RNAs in the regulation of gene transcription. We now know that tumour suppressor genes, with CpG island-associated promoters, are commonly hypermethylated and silenced in cancer, but we do not understood what triggers this process or when it occurs during carcinogenesis. Epigenetic gene silencing has always been envisaged as a local event silencing discrete genes, but recent data now indicates that large regions of chromosomes can be co-coordinately suppressed; a process termed long range epigenetic silencing (LRES). LRES can span megabases of DNA and involves broad heterochromatin formation accompanied by hypermethylation of clusters of contiguous CpG islands within the region. It is not clear if LRES is initiated by one critical gene target that spreads and conscripts innocent bystanders, analogous to large genetic deletions or if coordinate silencing of multiple genes is important in carcinogenesis? Over the next decade with the exciting new genomic approaches to epigenome analysis and the initiation of a Human Epigenome Project, we will understand more about the interplay between DNA methylation and chromatin modifications and the expression of non-coding RNAs, promising a new range of molecular diagnostic cancer markers and molecular targets for cancer epigenetic therapy.
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Affiliation(s)
- Susan J Clark
- Cancer Program, Garvan Institute of Medical Research, Darlinghurst Sydney, 2010 NSW, Australia.
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230
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Liu G, Bissler JJ, Sinden RR, Leffak M. Unstable spinocerebellar ataxia type 10 (ATTCT*(AGAAT) repeats are associated with aberrant replication at the ATX10 locus and replication origin-dependent expansion at an ectopic site in human cells. Mol Cell Biol 2007; 27:7828-38. [PMID: 17846122 PMCID: PMC2169150 DOI: 10.1128/mcb.01276-07] [Citation(s) in RCA: 47] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
Spinocerebellar ataxia type 10 (SCA10) is associated with expansion of (ATTCT)n repeats (where n is the number of repeats) within the ataxin 10 (ATX10/E46L) gene. The demonstration that (ATTCT)n tracts can act as DNA unwinding elements (DUEs) in vitro has suggested that aberrant replication origin activity occurs at expanded (ATTCT)n tracts and may lead to their instability. Here, we confirm these predictions. The wild-type ATX10 locus displays inefficient origin activity, but origin activity is elevated at the expanded ATX10 loci in patient-derived cells. To test whether (ATTCT)n tracts can potentiate origin activity, cell lines were constructed that contain ectopic copies of the c-myc replicator in which the essential DUE was replaced by ATX10 DUEs with (ATTCT)n. ATX10 DUEs containing (ATTCT)27 or (ATTCT)48, but not (ATTCT)8 or (ATTCT)13, could substitute functionally for the c-myc DUE, but (ATTCT)48 could not act as an autonomous replicator. Significantly, chimeric c-myc replicators containing ATX10 DUEs displayed length-dependent (ATTCT)n instability. By 250 population doublings, dramatic two- and fourfold length expansions were observed for (ATTCT)27 and (ATTCT)48 but not for (ATTCT)8 or (ATTCT)13. These results implicate replication origin activity as one molecular mechanism associated with the instability of (ATTCT)n tracts that are longer than normal length.
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Affiliation(s)
- Guoqi Liu
- Department of Biochemistry and Molecular Biology, Boonshoft School of Medicine, Wright State University, Dayton, Ohio 45435, USA
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231
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Salstrom JL. X-inactivation and the dynamic maintenance of gene silencing. Mol Genet Metab 2007; 92:56-62. [PMID: 17604203 DOI: 10.1016/j.ymgme.2007.05.015] [Citation(s) in RCA: 13] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 04/10/2007] [Revised: 05/23/2007] [Accepted: 05/23/2007] [Indexed: 01/25/2023]
Abstract
X-inactivation has long been a topic of fascination for educators, researchers, and clinicians alike. From complex patterns of inheritance to phenotypic variation among females with X-linked traits, a myriad of hypothesis and interpretations exist. Once thought to be random yet complete, X-inactivation has proven itself the poster child of the exception rather than the rule. Indeed, patterns of X-inactivation are all too often non-random, and many X-linked genes are capable of escaping X-inactivation. Similarly, X-inactivation is well-known for being stably maintained for life, but some previously inactivated X-linked genes reactivate with increasing age. Moreover, recent papers illustrate that X-inactivation can be challenged in other ways, thereby rendering the stability of X-inactivation compromised. This review describes factors involved in the maintenance of X-inactivation as we know it and discusses these emerging data that suggest a more dynamic model of the maintenance of X-inactivation may be in order.
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Affiliation(s)
- Jennifer L Salstrom
- Department of Human Genetics, David Geffen School of Medicine at UCLA, 6505 Gonda Center-Mail Code 708822, 695 Charles E Young Drive South, Los Angeles, CA 90095-708822, USA.
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232
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Gierman HJ, Indemans MH, Koster J, Goetze S, Seppen J, Geerts D, van Driel R, Versteeg R. Domain-wide regulation of gene expression in the human genome. Genome Res 2007; 17:1286-95. [PMID: 17693573 PMCID: PMC1950897 DOI: 10.1101/gr.6276007] [Citation(s) in RCA: 108] [Impact Index Per Article: 6.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/26/2022]
Abstract
Transcription factor complexes bind to regulatory sequences of genes, providing a system of individual expression regulation. Targets of distinct transcription factors usually map throughout the genome, without clustering. Nevertheless, highly and weakly expressed genes do cluster in separate chromosomal domains with an average size of 80-90 genes. We therefore asked whether, besides transcription factors, an additional level of gene expression regulation exists that acts on chromosomal domains. Here we show that identical green fluorescent protein (GFP) reporter constructs integrated at 90 different chromosomal positions obtain expression levels that correspond to the activity of the domains of integration. These domains are up to 80 genes long and can exert an eightfold effect on the expression levels of integrated genes. 3D-FISH shows that active domains of integration have a more open chromatin structure than integration domains with weak activity. These results reveal a novel domain-wide regulatory mechanism that, together with transcription factors, exerts a dual control over gene transcription.
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Affiliation(s)
- Hinco J. Gierman
- Department of Human Genetics, Academic Medical Centre, University of Amsterdam, 1100 DE Amsterdam, The Netherlands
| | - Mireille H.G. Indemans
- Department of Human Genetics, Academic Medical Centre, University of Amsterdam, 1100 DE Amsterdam, The Netherlands
| | - Jan Koster
- Department of Human Genetics, Academic Medical Centre, University of Amsterdam, 1100 DE Amsterdam, The Netherlands
| | - Sandra Goetze
- Swammerdam Institute for Life Sciences, University of Amsterdam, 1100 DE Amsterdam, The Netherlands
| | - Jurgen Seppen
- AMC Liver Centre, 1105 BK Amsterdam, The Netherlands
| | - Dirk Geerts
- Department of Human Genetics, Academic Medical Centre, University of Amsterdam, 1100 DE Amsterdam, The Netherlands
| | - Roel van Driel
- Swammerdam Institute for Life Sciences, University of Amsterdam, 1100 DE Amsterdam, The Netherlands
| | - Rogier Versteeg
- Department of Human Genetics, Academic Medical Centre, University of Amsterdam, 1100 DE Amsterdam, The Netherlands
- Corresponding author.E-mail ; fax 31-20-6918626
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233
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Hinas A, Söderbom F. Treasure hunt in an amoeba: non-coding RNAs in Dictyostelium discoideum. Curr Genet 2007; 51:141-59. [PMID: 17171561 DOI: 10.1007/s00294-006-0112-z] [Citation(s) in RCA: 10] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/16/2006] [Revised: 11/22/2006] [Accepted: 11/23/2006] [Indexed: 12/20/2022]
Abstract
The traditional view of RNA being merely an intermediate in the transfer of genetic information, as mRNA, spliceosomal RNA, tRNA, and rRNA, has become outdated. The recent discovery of numerous regulatory RNAs with a plethora of functions in biological processes has truly revolutionized our understanding of gene regulation. Tiny RNAs such as microRNAs and small interfering RNAs play vital roles at different levels of gene control. Small nucleolar RNAs are much more abundant than previously recognized, and new functions beyond processing and modification of rRNA have recently emerged. Longer non-coding RNAs (ncRNAs) can also have important regulatory roles in the cell, e.g., antisense RNAs that control their target mRNAs. The majority of these important findings arose from analyses in various model organisms. In this review, we focus on ncRNAs in the social amoeba Dictyostelium discoideum. This important genetically tractable model organism has recently received renewed attention in terms of discovery, regulation and functional studies of ncRNAs. Old and recent findings are discussed and put in context of what we today know about ncRNAs in other organisms.
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Affiliation(s)
- Andrea Hinas
- Department of Molecular Biology, Biomedical Center, Swedish University of Agricultural Sciences, Box 590, 75124 Uppsala, Sweden
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234
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Song MA, Park JH, Jeong KS, Park DS, Kang MS, Lee S. Quantification of CpG methylation at the 5′-region of XIST by pyrosequencing from human serum. Electrophoresis 2007; 28:2379-84. [PMID: 17578842 DOI: 10.1002/elps.200600852] [Citation(s) in RCA: 21] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/07/2022]
Abstract
Aberrant methylation of X (inactive)-specific transcript (XIST) is common in serum derived from human prostate and testicular germ cell tumors. The direct quantification of XIST methylation is urgently required for clinical application because human serum contains both normal and cancer-originated XIST DNA. We directly quantitated the methylation percentage of three CpG sites (+947, +956, +971) from the 5'-region of XIST by pyrosequencing. The average methylation percentages at three CpG sites were 88% (+/-5.8) at CpG1, 98% (+/-3.4) at CpG2, and 92% (+/-5.6) at CpG3 from normal male (N = 19). From prostate cancer-derived sera, the average methylation percentage of XIST was 65% (+/-8.3) at CpG1, 82% (+/-10.9) at CpG2, and 74% (+/-4.4) at CpG3, which is lower than the normal XY serum DNA, but greater than normal XX serums. The methylation status of XIST also correlated with its gene expression in B-lymphoblastoid and prostate cancer cell lines. This method is sensitive for quantifying the small percentage change in the methylation status of XIST, and may be used for early diagnosis and monitoring of cancer in men using serum.
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Affiliation(s)
- Min-Ae Song
- Functional Genomics Laboratory, CHA Research Institute, College of Medicine, Seongnam-si, Gyeongii-do, South Korea
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235
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Mehler MF, Mattick JS. Noncoding RNAs and RNA Editing in Brain Development, Functional Diversification, and Neurological Disease. Physiol Rev 2007; 87:799-823. [PMID: 17615389 DOI: 10.1152/physrev.00036.2006] [Citation(s) in RCA: 226] [Impact Index Per Article: 12.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/27/2022] Open
Abstract
The progressive maturation and functional plasticity of the nervous system in health and disease involve a dynamic interplay between the transcriptome and the environment. There is a growing awareness that the previously unexplored molecular and functional interface mediating these complex gene-environmental interactions, particularly in brain, may encompass a sophisticated RNA regulatory network involving the twin processes of RNA editing and multifaceted actions of numerous subclasses of non-protein-coding RNAs. The mature nervous system encompasses a wide range of cell types and interconnections. Long-term changes in the strength of synaptic connections are thought to underlie memory retrieval, formation, stabilization, and effector functions. The evolving nervous system involves numerous developmental transitions, such as neurulation, neural tube patterning, neural stem cell expansion and maintenance, lineage elaboration, differentiation, axonal path finding, and synaptogenesis. Although the molecular bases for these processes are largely unknown, RNA-based epigenetic mechanisms appear to be essential for orchestrating these precise and versatile biological phenomena and in defining the etiology of a spectrum of neurological diseases. The concerted modulation of RNA editing and the selective expression of non-protein-coding RNAs during seminal as well as continuous state transitions may comprise the plastic molecular code needed to couple the intrinsic malleability of neural network connections to evolving environmental influences to establish diverse forms of short- and long-term memory, context-specific behavioral responses, and sophisticated cognitive capacities.
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Affiliation(s)
- Mark F Mehler
- Institute for Brain Disorders and Neural Regeneration, Department of Neurology, Einstein Cancer Center, Albert Einstein College of Medicine, Bronx, New York 10461, USA.
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236
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Anguera MC, Sun BK, Xu N, Lee JT. X-chromosome kiss and tell: how the Xs go their separate ways. COLD SPRING HARBOR SYMPOSIA ON QUANTITATIVE BIOLOGY 2007; 71:429-37. [PMID: 17381325 DOI: 10.1101/sqb.2006.71.012] [Citation(s) in RCA: 22] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/25/2022]
Abstract
Loci associated with noncoding RNAs have important roles in X-chromosome inactivation (XCI), the dosage compensation mechanism by which one of two X chromosomes in female cells becomes transcriptionally silenced. The Xs start out as epigenetically equivalent chromosomes, but XCI requires a cell to treat two identical X chromosomes in completely different ways: One X chromosome must remain transcriptionally active while the other becomes repressed. In the embryo of eutherian mammals, the choice to inactivate the maternal or paternal X chromosome is random. The fact that the Xs always adopt opposite fates hints at the existence of a trans-sensing mechanism to ensure the mutually exclusive silencing of one of the two Xs. This paper highlights recent evidence supporting a model for mutually exclusive choice that involves homologous chromosome pairing and the placement of asymmetric chromatin marks on the two Xs.
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Affiliation(s)
- M C Anguera
- Howard Hughes Medical Institute, Department of Molecular Biology, Massachusetts General Hospital, Department of Genetics, Harvard Medical School, Boston, Massachusetts 02114, USA
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237
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Affiliation(s)
- David Haig
- Department of Organismic and Evolutionary Biology, Harvard University, Cambridge, Massachusetts 02138 E‐mail:
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238
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Liu J, Xie Y, Cooper R, Ducharme DMK, Tennant R, Diwan BA, Waalkes MP. Transplacental exposure to inorganic arsenic at a hepatocarcinogenic dose induces fetal gene expression changes in mice indicative of aberrant estrogen signaling and disrupted steroid metabolism. Toxicol Appl Pharmacol 2007; 220:284-91. [PMID: 17350061 PMCID: PMC2680420 DOI: 10.1016/j.taap.2007.01.018] [Citation(s) in RCA: 35] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/25/2006] [Revised: 01/16/2007] [Accepted: 01/26/2007] [Indexed: 10/23/2022]
Abstract
Exposure to inorganic arsenic in utero in C3H mice produces hepatocellular carcinoma in male offspring when they reach adulthood. To help define the molecular events associated with the fetal onset of arsenic hepatocarcinogenesis, pregnant C3H mice were given drinking water containing 0 (control) or 85 ppm arsenic from day 8 to 18 of gestation. At the end of the arsenic exposure period, male fetal livers were removed and RNA isolated for microarray analysis using 22K oligo chips. Arsenic exposure in utero produced significant (p<0.001) alterations in expression of 187 genes, with approximately 25% of aberrantly expressed genes related to either estrogen signaling or steroid metabolism. Real-time RT-PCR on selected genes confirmed these changes. Various genes controlled by estrogen, including X-inactive-specific transcript, anterior gradient-2, trefoil factor-1, CRP-ductin, ghrelin, and small proline-rich protein-2A, were dramatically over-expressed. Estrogen-regulated genes including cytokeratin 1-19 and Cyp2a4 were over-expressed, although Cyp3a25 was suppressed. Several genes involved with steroid metabolism also showed remarkable expression changes, including increased expression of 17beta-hydroxysteroid dehydrogenase-7 (HSD17beta7; involved in estradiol production) and decreased expression of HSD17beta5 (involved in testosterone production). The expression of key genes important in methionine metabolism, such as methionine adenosyltransferase-1a, betaine-homocysteine methyltransferase and thioether S-methyltransferase, were suppressed. Thus, exposure of mouse fetus to inorganic arsenic during a critical period in development significantly alters the expression of various genes encoding estrogen signaling and steroid or methionine metabolism. These alterations could disrupt genetic programming at the very early life stage, which could impact tumor formation much later in adulthood.
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Affiliation(s)
- Jie Liu
- Inorganic Carcinogenesis Section, Laboratory of Comparative Carcinogenesis, National Cancer Institute at NIEHS, Mail Drop F0-09, Research Triangle Park, NC 27709, USA.
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239
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Abstract
Mammalian X inactivation, imprinting, and allelic exclusion are classic examples of monoallelic gene expression. Two emerging themes are thought to be critical for monoallelic expression: (1) noncoding, often antisense, transcription linked to differential chromatin marks on otherwise homologous alleles and (2) physical segregation of alleles to separate domains within the nucleus. Here, we highlight recent progress in identifying these phenomena as possible key regulatory mechanisms of monoallelic expression.
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Affiliation(s)
- Pok Kwan Yang
- Howard Hughes Medical Institute, Boston, Massachusetts 02115, USA
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240
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Davidow LS, Breen M, Duke SE, Samollow PB, McCarrey JR, Lee JT. The search for a marsupial XIC reveals a break with vertebrate synteny. Chromosome Res 2007; 15:137-46. [PMID: 17333538 DOI: 10.1007/s10577-007-1121-6] [Citation(s) in RCA: 49] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/15/2006] [Revised: 01/19/2007] [Accepted: 01/19/2007] [Indexed: 01/09/2023]
Abstract
X-chromosome inactivation (XCI) evolved in mammals to deal with X-chromosome dosage imbalance between the XX female and the XY male. In eutherian mammals, random XCI of the soma requires a master regulatory locus known as the 'X-inactivation center' (XIC/Xic), wherein lies the noncoding XIST/Xist silencer RNA and its regulatory antisense Tsix gene. By contrast, marsupial XCI is imprinted to occur on the paternal X chromosome. To determine whether marsupials and eutherians share the XIC-driven mechanism, we search for the sequence equivalents in the genome of the South American opossum, Monodelphis domestica. Positional cloning and bioinformatic analysis reveal several interesting findings. First, protein-coding genes that flank the eutherian XIC are well-conserved in M. domestica, as well as in chicken, frog, and pufferfish. However, in M. domestica we fail to identify any recognizable XIST or TSIX equivalents. Moreover, cytogenetic mapping shows a surprising break in synteny with eutherian mammals and other vertebrates. Therefore, during the evolution of the marsupial X chromosome, one or more rearrangements broke up an otherwise evolutionarily conserved block of vertebrate genes. The failure to find XIST/TSIX in M. domestica may suggest that the ancestral XIC is too divergent to allow for detection by current methods. Alternatively, the XIC may have arisen relatively late in mammalian evolution, possibly in eutherians with the emergence of random XCI. The latter argues that marsupial XCI does not require XIST and opens the search for alternative mechanisms of dosage compensation.
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Affiliation(s)
- Lance S Davidow
- Department of Molecular Biology, Massachusetts General Hospital, Boston, MA 02114, USA
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241
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Cohen HR, Panning B. XIST RNA exhibits nuclear retention and exhibits reduced association with the export factor TAP/NXF1. Chromosoma 2007; 116:373-83. [PMID: 17333237 DOI: 10.1007/s00412-007-0100-1] [Citation(s) in RCA: 30] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/19/2006] [Revised: 12/18/2006] [Accepted: 01/18/2007] [Indexed: 10/23/2022]
Abstract
During splicing and polyadenylation, factors that stimulate export from the nucleus are recruited to nascent mRNAs. X-inactive specific transcript (XIST) RNA is unusual among capped, spliced, polyadenylated transcripts in that it accumulates exclusively in the nucleus. It is well established that, at steady state levels, XIST RNA is primarily nuclear. However, it was unknown whether XIST RNA spends its entire lifetime in the nucleus (nuclear retention) or passes briefly through the cytoplasm during maturation, like many other functional RNAs. In this study, we present the first evidence that XIST RNA exhibits nuclear retention. We report that a green fluorescent protein (GFP)-XIST fusion RNA is detected in the nucleus and not the cytoplasm, and GFP is not translated. XIST RNA does not shuttle in a heterokaryon assay or move between chromosomes in the same nucleus when expressed at wild-type levels. These results indicate that XIST RNA's nuclear localization is mediated by nuclear retention rather than export followed by import. We present evidence that the export factor TAP/NXF1 binds poorly to XIST RNA in comparison to exported mRNAs, suggesting that reduced TAP/NFX1 binding may contribute to nuclear retention of XIST RNA.
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Affiliation(s)
- Hannah R Cohen
- Department of Biochemistry and Biophysics, University of California San Francisco, Genentech Hall, Room S372B, 600 16th Street, San Francisco, CA 94143-2200, USA
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242
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Horvath JE, Willard HF. Primate comparative genomics: lemur biology and evolution. Trends Genet 2007; 23:173-82. [PMID: 17331617 DOI: 10.1016/j.tig.2007.02.007] [Citation(s) in RCA: 32] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/19/2006] [Revised: 01/08/2007] [Accepted: 02/12/2007] [Indexed: 12/23/2022]
Abstract
Comparative genome sequencing projects are providing insight into aspects of genome biology that raise new questions and challenge existing paradigms. Placement in the phylogenetic tree can often be a major determinant of which organism to choose for study. Lemurs hold a key position at the base of the primate evolutionary tree and will be highly informative for the genomics community by offering comparisons of primate-specific characteristics and processes. Combining research in chromosome evolution, genome evolution and behavior with lemur comparative genomic sequencing will offer insights into many levels of primate evolution. We discuss the current state of lemur cytogenetic and phylogenetic analyses, and suggest how focusing more genomic efforts on lemurs will be beneficial to understanding human and primate evolution, as well as disease, and will contribute to conservation efforts.
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Affiliation(s)
- Julie E Horvath
- Duke Institute for Genome Sciences & Policy, Duke University, Durham, NC 27708, USA.
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243
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Ercan S, Giresi PG, Whittle CM, Zhang X, Green RD, Lieb JD. X chromosome repression by localization of the C. elegans dosage compensation machinery to sites of transcription initiation. Nat Genet 2007; 39:403-8. [PMID: 17293863 PMCID: PMC2753834 DOI: 10.1038/ng1983] [Citation(s) in RCA: 106] [Impact Index Per Article: 5.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/04/2006] [Accepted: 01/18/2007] [Indexed: 11/08/2022]
Abstract
Among organisms with chromosome-based mechanisms of sex determination, failure to equalize expression of X-linked genes between the sexes is typically lethal. In C. elegans, XX hermaphrodites halve transcription from each X chromosome to match the output of XO males. Here, we mapped the binding location of the condensin homolog DPY-27 and the zinc finger protein SDC-3, two components of the C. elegans dosage compensation complex (DCC). We observed strong foci of DCC binding on X, surrounded by broader regions of localization. Binding foci, but not adjacent regions of localization, were distinguished by clusters of a 10-bp DNA motif, suggesting a recruitment-and-spreading mechanism for X recognition. The DCC was preferentially bound upstream of genes, suggesting modulation of transcriptional initiation and polymerase-coupled spreading. Stronger DCC binding upstream of genes with high transcriptional activity indicated a mechanism for tuning DCC activity at specific loci. These data aid in understanding how proteins involved in higher-order chromosome dynamics can regulate transcription at individual loci.
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Affiliation(s)
- Sevinc Ercan
- Department of Biology and Carolina Center for the Genome Sciences CB #3280, 202 Fordham Hall University of North Carolina at Chapel Hill Chapel Hill, NC 27599-3280
| | - Paul G. Giresi
- Department of Biology and Carolina Center for the Genome Sciences CB #3280, 202 Fordham Hall University of North Carolina at Chapel Hill Chapel Hill, NC 27599-3280
| | - Christina M. Whittle
- Department of Biology and Carolina Center for the Genome Sciences CB #3280, 202 Fordham Hall University of North Carolina at Chapel Hill Chapel Hill, NC 27599-3280
| | - Xinmin Zhang
- Nimblegen Systems, Inc. 1 Science Court Madison, WI 53711
| | | | - Jason D. Lieb
- Department of Biology and Carolina Center for the Genome Sciences CB #3280, 202 Fordham Hall University of North Carolina at Chapel Hill Chapel Hill, NC 27599-3280
- Correspondence should be addressed to: Jason D. Lieb (919) 843-3228
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244
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Prasanth KV, Spector DL. Eukaryotic regulatory RNAs: an answer to the 'genome complexity' conundrum. Genes Dev 2007; 21:11-42. [PMID: 17210785 DOI: 10.1101/gad.1484207] [Citation(s) in RCA: 301] [Impact Index Per Article: 16.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/24/2022]
Abstract
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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245
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Breiling A, Sessa L, Orlando V. Biology of Polycomb and Trithorax Group Proteins. INTERNATIONAL REVIEW OF CYTOLOGY 2007; 258:83-136. [PMID: 17338920 DOI: 10.1016/s0074-7696(07)58002-2] [Citation(s) in RCA: 39] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 12/13/2022]
Abstract
Cellular phenotypes can be ascribed to different patterns of gene expression. Epigenetic mechanisms control the generation of different phenotypes from the same genotype. Thus differentiation is basically a process driven by changes in gene activity during development, often in response to transient factors or environmental stimuli. To keep the specific characteristics of cell types, tissue-specific gene expression patterns must be transmitted stably from one cell to the daughter cells, also in the absence of the early-acting determination factors. This heritability of patterns of active and inactive genes is enabled by epigenetic mechanisms that create a layer of information on top of the DNA sequence that ensures mitotic and sometimes also meiotic transmission of expression patterns. The proteins of the Polycomb and Trithorax group comprise such a cellular memory mechanism that preserves gene expression patterns through many rounds of cell division. This review provides an overview of the genetics and molecular biology of these maintenance proteins, concentrating mainly on mechanisms of Polycomb group-mediated repression.
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Affiliation(s)
- Achim Breiling
- Dulbecco Telethon Institute, Institute of Genetics and Biophysics, CNR, 80131 Naples, Italy
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246
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Calabrese JM, Sharp PA. Characterization of the short RNAs bound by the P19 suppressor of RNA silencing in mouse embryonic stem cells. RNA (NEW YORK, N.Y.) 2006; 12:2092-102. [PMID: 17135486 PMCID: PMC1664724 DOI: 10.1261/rna.224606] [Citation(s) in RCA: 30] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/12/2023]
Abstract
Studies of mammalian RNA interference (RNAi) have focused largely on the actions of microRNAs; however, in other organisms, endogenous short-interfering RNAs (siRNAs) are involved in silencing processes. To date, similar molecules have been difficult to characterize in mammalian cells. P19 is a plant suppressor of RNA silencing that binds with high affinity to siRNAs. Here, the short RNAs bound by P19 in mouse embryonic stem (ES) cells have been characterized. We show that P19 selectively immunoprecipitates endogenous short RNAs from ES cells. Cloning of immunoprecipitated RNA reveals a strong selection for short RNAs that are exact matches to ribosomal RNA (rRNA), with particular short rRNA species highly enriched in P19 immunoprecipitates. Complementary strands to the enriched rRNAs were not cloned, which was surprising because P19 was previously thought to bind only siRNAs. We show that P19 binds tightly to a noncanonical dsRNA substrate comprised of a short RNA annealed to a much longer partner, such that the double-stranded region between the two is 19 base pairs long. Binding to similar endogenous species might explain the association of P19 with short rRNAs in ES cells. Finally, we show that the P19-enriched rRNAs are not involved in canonical RNAi, as they exist in the absence of Dicer and do not function as post-transcriptional gene silencers. Our results support the previous observation that endogenous siRNAs are not abundant molecules in mouse ES cells.
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Affiliation(s)
- J Mauro Calabrese
- Department of Biology, Massachusetts Institute of Technology, Cambridge, Massachusetts 02144, USA
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247
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Corradini N, Rossi F, Giordano E, Caizzi R, Verní F, Dimitri P. Drosophila melanogaster as a model for studying protein-encoding genes that are resident in constitutive heterochromatin. Heredity (Edinb) 2006; 98:3-12. [PMID: 17080025 DOI: 10.1038/sj.hdy.6800877] [Citation(s) in RCA: 17] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/09/2022] Open
Abstract
The organization of chromosomes into euchromatin and heterochromatin is one of the most enigmatic aspects of genome evolution. For a long time, heterochromatin was considered to be a genomic wasteland, incompatible with gene expression. However, recent studies--primarily conducted in Drosophila melanogaster--have shown that this peculiar genomic component performs important cellular functions and carries essential genes. New research on the molecular organization, function and evolution of heterochromatin has been facilitated by the sequencing and annotation of heterochromatic DNA. About 450 predicted genes have been identified in the heterochromatin of D. melanogaster, indicating that the number of active genes is higher than had been suggested by genetic analysis. Most of the essential genes are still unknown at the molecular level, and a detailed functional analysis of the predicted genes is difficult owing to the lack of mutant alleles. Far from being a peculiarity of Drosophila, heterochromatic genes have also been found in Saccharomyces cerevisiae, Schizosaccharomyces pombe, Oryza sativa and Arabidopsis thaliana, as well as in humans. The presence of expressed genes in heterochromatin seems paradoxical because they appear to function in an environment that has been considered incompatible with gene expression. In the future, genetic, functional genomic and proteomic analyses will offer powerful approaches with which to explore the functions of heterochromatic genes and to elucidate the mechanisms driving their expression.
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Affiliation(s)
- N Corradini
- Laboratorio di Genomica Funzionale e Proteomica di Sistemi modello and Dipartimento di Genetica e Biologia Molecolare 'Charles Darwin', Università 'La Sapienza', Piazzale Aldo Moro 5, 00185 Roma, Italy
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248
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Abstract
PURPOSE OF REVIEW Similar to the majority of autoimmune rheumatic diseases, systemic sclerosis is characterized by a striking female predominance superimposed on a predisposing genetic background. At least two genetic mechanisms have been proposed that play a role in susceptibility to systemic sclerosis; firstly the maintenance of immune tolerance via genes on the X chromosomes and, secondly, fetal microchimerism. Based on these lines of evidence, experimental efforts have been most recently dedicated to investigating the role of X chromosome abnormalities (i.e. monosomy rates and inactivation patterns) in autoimmunity. We will review herein the most recent data on the role of the X chromosome in systemic sclerosis onset and discuss the potential implications. RECENT FINDINGS Women with systemic sclerosis manifest an enhanced rate of X monosomic cells in peripheral blood compared with healthy age-matched women. Furthermore, a severely skewed X chromosome inactivation pattern is found in women with systemic sclerosis. SUMMARY These observations, reproduced in other female-predominant autoimmune diseases, strongly support the role of the X chromosome in conferring susceptibility to tolerance breakdown and open novel scenarios to emphasize the unknown etiopathogenesis of systemic sclerosis. The implications of these findings will be discussed.
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Affiliation(s)
- Carlo Selmi
- Division of Rheumatology, Allergy, and Clinical Immunology, University of California, Davis, California 95616, USA
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249
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Santos-Rebouças CB, Pimentel MMG. Implication of abnormal epigenetic patterns for human diseases. Eur J Hum Genet 2006; 15:10-7. [PMID: 17047674 DOI: 10.1038/sj.ejhg.5201727] [Citation(s) in RCA: 65] [Impact Index Per Article: 3.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/25/2023] Open
Abstract
Significant evidences have brought new insights on the mechanisms by which epigenetic machinery proteins regulate gene expression, leading to a redefinition of chromatin regulation in terms of modification of core histones, DNA methylation, RNA-mediated silencing pathways, action of methylation-dependent sensitive insulators and Polycomb/Trithorax group proteins. Consistent with these fundamental aspects, an increasing number of human pathologies have been found to be associated with aberrant epigenetics regulation, including cancer, mental retardation, neurodegenerative symptoms, imprinting disorders, syndromes involving chromosomal instabilities and a great number of human life-threatening diseases. The possibility of reversing epigenetic marks, in contrast to genetic code, may provide new pharmacological targets for emerging therapeutic intervention.
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Affiliation(s)
- C B Santos-Rebouças
- Department of Cell Biology and Genetics, State University of Rio de Janeiro, Rio de Janeiro, Brazil.
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250
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Cheng MK, Nguyen DK, Disteche CM. Dosage compensation of the X chromosome and Turner syndrome. ACTA ACUST UNITED AC 2006. [DOI: 10.1016/j.ics.2006.06.012] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/17/2022]
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