Secondary

2017
McElroy KA, Jung YL, Zee BM, Wang CI, Park PJ, Kuroda MI. upSET, the Drosophila homologue of SET3, Is Required for Viability and the Proper Balance of Active and Repressive Chromatin Marks. G3 (Bethesda) 2017;7(2):625-635.Abstract

Chromatin plays a critical role in faithful implementation of gene expression programs. Different post-translational modifications (PTMs) of histone proteins reflect the underlying state of gene activity, and many chromatin proteins write, erase, bind, or are repelled by, these histone marks. One such protein is UpSET, the Drosophila homolog of yeast Set3 and mammalian KMT2E (MLL5). Here, we show that UpSET is necessary for the proper balance between active and repressed states. Using CRISPR/Cas-9 editing, we generated S2 cells that are mutant for upSET We found that loss of UpSET is tolerated in S2 cells, but that heterochromatin is misregulated, as evidenced by a strong decrease in H3K9me2 levels assessed by bulk histone PTM quantification. To test whether this finding was consistent in the whole organism, we deleted the upSET coding sequence using CRISPR/Cas-9, which we found to be lethal in both sexes in flies. We were able to rescue this lethality using a tagged upSET transgene, and found that UpSET protein localizes to transcriptional start sites (TSS) of active genes throughout the genome. Misregulated heterochromatin is apparent by suppressed position effect variegation of the w(m4) allele in heterozygous upSET-deleted flies. Using nascent-RNA sequencing in the upSET-mutant S2 lines, we show that this result applies to heterochromatin genes generally. Our findings support a critical role for UpSET in maintaining heterochromatin, perhaps by delimiting the active chromatin environment.

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2016
Saini N, Roberts SA, Klimczak LJ, Chan K, Grimm SA, Dai S, Fargo DC, Boyer JC, Kaufmann WK, Taylor JA, Lee E, Cortes-Ciriano I, Park PJ, Schurman SH, Malc EP, Mieczkowski PA, Gordenin DA. The impact of environmental and endogenous damage on somatic mutation load in human skin fibroblasts. PLoS genetics 2016;12(10):e1006385. pdf
Mieczkowski J, Cook A, Bowman SK, Mueller B, Alver BH, Kundu S, Deaton AM, Urban JA, Larschan E, Park PJ, Kingston RE, Tolstorukov MY. MNase titration reveals differences between nucleosome occupancy and chromatin accessibility. Nat Commun 2016;7:11485.Abstract

Chromatin accessibility plays a fundamental role in gene regulation. Nucleosome placement, usually measured by quantifying protection of DNA from enzymatic digestion, can regulate accessibility. We introduce a metric that uses micrococcal nuclease (MNase) digestion in a novel manner to measure chromatin accessibility by combining information from several digests of increasing depths. This metric, MACC (MNase accessibility), quantifies the inherent heterogeneity of nucleosome accessibility in which some nucleosomes are seen preferentially at high MNase and some at low MNase. MACC interrogates each genomic locus, measuring both nucleosome location and accessibility in the same assay. MACC can be performed either with or without a histone immunoprecipitation step, and thereby compares histone and non-histone protection. We find that changes in accessibility at enhancers, promoters and other regulatory regions do not correlate with changes in nucleosome occupancy. Moreover, high nucleosome occupancy does not necessarily preclude high accessibility, which reveals novel principles of chromatin regulation.

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Tica J*, Lee E*, Untergasser A, Meiers S, Garfield DA, Gokcumen O, Furlong EEM, Park PJ, Stütz AM**, Korbel JO**. Next-generation sequencing-based detection of germline L1-mediated transductions. BMC Genomics 2016;17(1):342.Abstract

BACKGROUND: While active LINE-1 (L1) elements possess the ability to mobilize flanking sequences to different genomic loci through a process termed transduction influencing genomic content and structure, an approach for detecting polymorphic germline non-reference transductions in massively-parallel sequencing data has been lacking. RESULTS: Here we present the computational approach TIGER (Transduction Inference in GERmline genomes), enabling the discovery of non-reference L1-mediated transductions by combining L1 discovery with detection of unique insertion sequences and detailed characterization of insertion sites. We employed TIGER to characterize polymorphic transductions in fifteen genomes from non-human primate species (chimpanzee, orangutan and rhesus macaque), as well as in a human genome. We achieved high accuracy as confirmed by PCR and two single molecule DNA sequencing techniques, and uncovered differences in relative rates of transduction between primate species. CONCLUSIONS: By enabling detection of polymorphic transductions, TIGER makes this form of relevant structural variation amenable for population and personal genome analysis.

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Ordulu Z, Nucci MR, Dal Cin P, Hollowell ML, Otis CN, Hornick JL, Park PJ, Kim T-M, Quade BJ, Morton CC. Intravenous leiomyomatosis: an unusual intermediate between benign and malignant uterine smooth muscle tumors. Mod Pathol 2016;Abstract

Intravenous leiomyomatosis is an unusual smooth muscle neoplasm with quasi-malignant intravascular growth but a histologically banal appearance. Herein, we report expression and molecular cytogenetic analyses of a series of 12 intravenous leiomyomatosis cases to better understand the pathogenesis of intravenous leiomyomatosis. All cases were analyzed for the expression of HMGA2, MDM2, and CDK4 proteins by immunohistochemistry based on our previous finding of der(14)t(12;14)(q14.3;q24) in intravenous leiomyomatosis. Seven of 12 (58%) intravenous leiomyomatosis cases expressed HMGA2, and none expressed MDM2 or CDK4. Colocalization of hybridization signals for probes from the HMGA2 locus (12q14.3) and from 14q24 by interphase fluorescence in situ hybridization (FISH) was detected in a mean of 89.2% of nuclei in HMGA2-positive cases by immunohistochemistry, but in only 12.4% of nuclei in negative cases, indicating an association of HMGA2 expression and this chromosomal rearrangement (P=8.24 × 10(-10)). Four HMGA2-positive cases had greater than two HMGA2 hybridization signals per cell. No cases showed loss of a hybridization signal by interphase FISH for the frequently deleted region of 7q22 in uterine leiomyomata. One intravenous leiomyomatosis case analyzed by array comparative genomic hybridization revealed complex copy number variations. Finally, expression profiling was performed on three intravenous leiomyomatosis cases. Interestingly, hierarchical cluster analysis of the expression profiles revealed segregation of the intravenous leiomyomatosis cases with leiomyosarcoma rather than with myometrium, uterine leiomyoma of the usual histological type, or plexiform leiomyoma. These findings suggest that intravenous leiomyomatosis cases share some molecular cytogenetic characteristics with uterine leiomyoma, and expression profiles similar to that of leiomyosarcoma cases, further supporting their intermediate, quasi-malignant behavior.Modern Pathology advance online publication, 19 February 2016; doi:10.1038/modpathol.2016.36.

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2015
Cheloufi S, Elling U, Hopfgartner B, Jung YL, Murn J, Ninova M, Hubmann M, Badeaux AI, Euong Ang C, Tenen D, Wesche DJ, Abazova N, Hogue M, Tasdemir N, Brumbaugh J, Rathert P, Jude J, Ferrari F, Blanco A, Fellner M, Wenzel D, Zinner M, Vidal SE, Bell O, Stadtfeld M, Chang HY, Almouzni G, Lowe SW, Rinn J, Wernig M, Aravin A, Shi Y, Park PJ, Penninger JM, Zuber J, Hochedlinger K. The histone chaperone CAF-1 safeguards somatic cell identity. Nature 2015;528(7581):218-24.Abstract

Cellular differentiation involves profound remodelling of chromatic landscapes, yet the mechanisms by which somatic cell identity is subsequently maintained remain incompletely understood. To further elucidate regulatory pathways that safeguard the somatic state, we performed two comprehensive RNA interference (RNAi) screens targeting chromatin factors during transcription-factor-mediated reprogramming of mouse fibroblasts to induced pluripotent stem cells (iPS cells). Subunits of the chromatin assembly factor-1 (CAF-1) complex, including Chaf1a and Chaf1b, emerged as the most prominent hits from both screens, followed by modulators of lysine sumoylation and heterochromatin maintenance. Optimal modulation of both CAF-1 and transcription factor levels increased reprogramming efficiency by several orders of magnitude and facilitated iPS cell formation in as little as 4 days. Mechanistically, CAF-1 suppression led to a more accessible chromatin structure at enhancer elements early during reprogramming. These changes were accompanied by a decrease in somatic heterochromatin domains, increased binding of Sox2 to pluripotency-specific targets and activation of associated genes. Notably, suppression of CAF-1 also enhanced the direct conversion of B cells into macrophages and fibroblasts into neurons. Together, our findings reveal the histone chaperone CAF-1 to be a novel regulator of somatic cell identity during transcription-factor-induced cell-fate transitions and provide a potential strategy to modulate cellular plasticity in a regenerative setting.

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Bersani F, Lee E, Kharchenko PV, Xu AW, Liu M, Xega K, MacKenzie OC, Brannigan BW, Wittner BS, Jung H, Ramaswamy S, Park PJ, Maheswaran S, Ting DT, Haber DA. Pericentromeric satellite repeat expansions through RNA-derived DNA intermediates in cancer. Proc Natl Acad Sci U S A 2015;112(49):15148-53.Abstract

Aberrant transcription of the pericentromeric human satellite II (HSATII) repeat is present in a wide variety of epithelial cancers. In deriving experimental systems to study its deregulation, we observed that HSATII expression is induced in colon cancer cells cultured as xenografts or under nonadherent conditions in vitro, but it is rapidly lost in standard 2D cultures. Unexpectedly, physiological induction of endogenous HSATII RNA, as well as introduction of synthetic HSATII transcripts, generated cDNA intermediates in the form of DNA/RNA hybrids. Single molecule sequencing of tumor xenografts showed that HSATII RNA-derived DNA (rdDNA) molecules are stably incorporated within pericentromeric loci. Suppression of RT activity using small molecule inhibitors reduced HSATII copy gain. Analysis of whole-genome sequencing data revealed that HSATII copy number gain is a common feature in primary human colon tumors and is associated with a lower overall survival. Together, our observations suggest that cancer-associated derepression of specific repetitive sequences can promote their RNA-driven genomic expansion, with potential implications on pericentromeric architecture.

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De Los Angeles A, Ferrari F, Xi R, Fujiwara Y, Benvenisty N, Deng H, Hochedlinger K, Jaenisch R, Lee S, Leitch HG, Lensch WM, Lujan E, Pei D, Rossant J, Wernig M, Park PJ, Daley GQ. Hallmarks of pluripotency. Nature 2015;525(7570):469-78.Abstract

Stem cells self-renew and generate specialized progeny through differentiation, but vary in the range of cells and tissues they generate, a property called developmental potency. Pluripotent stem cells produce all cells of an organism, while multipotent or unipotent stem cells regenerate only specific lineages or tissues. Defining stem-cell potency relies upon functional assays and diagnostic transcriptional, epigenetic and metabolic states. Here we describe functional and molecular hallmarks of pluripotent stem cells, propose a checklist for their evaluation, and illustrate how forensic genomics can validate their provenance.

Kang H, McElroy KA, Jung YL, Alekseyenko AA, Zee BM, Park PJ, Kuroda MI. Sex comb on midleg (Scm) is a functional link between PcG-repressive complexes in Drosophila. Genes Dev 2015;29(11):1136-50.Abstract

The Polycomb group (PcG) proteins are key regulators of development in Drosophila and are strongly implicated in human health and disease. How PcG complexes form repressive chromatin domains remains unclear. Using cross-linked affinity purifications of BioTAP-Polycomb (Pc) or BioTAP-Enhancer of zeste [E(z)], we captured all PcG-repressive complex 1 (PRC1) or PRC2 core components and Sex comb on midleg (Scm) as the only protein strongly enriched with both complexes. Although previously not linked to PRC2, we confirmed direct binding of Scm and PRC2 using recombinant protein expression and colocalization of Scm with PRC1, PRC2, and H3K27me3 in embryos and cultured cells using ChIP-seq (chromatin immunoprecipitation [ChIP] combined with deep sequencing). Furthermore, we found that RNAi knockdown of Scm and overexpression of the dominant-negative Scm-SAM (sterile α motif) domain both affected the binding pattern of E(z) on polytene chromosomes. Aberrant localization of the Scm-SAM domain in long contiguous regions on polytene chromosomes revealed its independent ability to spread on chromatin, consistent with its previously described ability to oligomerize in vitro. Pull-downs of BioTAP-Scm captured PRC1 and PRC2 and additional repressive complexes, including PhoRC, LINT, and CtBP. We propose that Scm is a key mediator connecting PRC1, PRC2, and transcriptional silencing. Combined with previous structural and genetic analyses, our results strongly suggest that Scm coordinates PcG complexes and polymerizes to produce broad domains of PcG silencing.

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Spatiotemporal Evolution of the Primary Glioblastoma Genome.
Kim J, Lee I-H, Cho HJ, Park C-K, Jung Y-S, Kim Y, Nam SH, Kim BS, Johnson MD, Kong D-S, Seol HJ, Lee J-I, Joo KM, Yoon Y, Park W-Y, Lee J, Park PJ**, Nam D-H**. Spatiotemporal Evolution of the Primary Glioblastoma Genome. Cancer Cell 2015;28(3):318-28.Abstract

Tumor recurrence following treatment is the major cause of mortality for glioblastoma multiforme (GBM) patients. Thus, insights on the evolutionary process at recurrence are critical for improved patient care. Here, we describe our genomic analyses of the initial and recurrent tumor specimens from each of 38 GBM patients. A substantial divergence in the landscape of driver alterations was associated with distant appearance of a recurrent tumor from the initial tumor, suggesting that the genomic profile of the initial tumor can mislead targeted therapies for the distally recurred tumor. In addition, in contrast to IDH1-mutated gliomas, IDH1-wild-type primary GBMs rarely developed hypermutation following temozolomide (TMZ) treatment, indicating low risk for TMZ-induced hypermutation for these tumors under the standard regimen.

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Kann M, Ettou S*, Jung YL*, Lenz MO, Taglienti ME, Park PJ, Schermer B, Benzing T, Kreidberg JA. Genome-Wide Analysis of Wilms' Tumor 1-Controlled Gene Expression in Podocytes Reveals Key Regulatory Mechanisms. J Am Soc Nephrol 2015;26(9):2097-104.Abstract

The transcription factor Wilms' tumor suppressor 1 (WT1) is key to podocyte development and viability; however, WT1 transcriptional networks in podocytes remain elusive. We provide a comprehensive analysis of the genome-wide WT1 transcriptional network in podocytes in vivo using chromatin immunoprecipitation followed by sequencing (ChIPseq) and RNA sequencing techniques. Our data show a specific role for WT1 in regulating the podocyte-specific transcriptome through binding to both promoters and enhancers of target genes. Furthermore, we inferred a podocyte transcription factor network consisting of WT1, LMX1B, TCF21, Fox-class and TEAD family transcription factors, and MAFB that uses tissue-specific enhancers to control podocyte gene expression. In addition to previously described WT1-dependent target genes, ChIPseq identified novel WT1-dependent signaling systems. These targets included components of the Hippo signaling system, underscoring the power of genome-wide transcriptional-network analyses. Together, our data elucidate a comprehensive gene regulatory network in podocytes suggesting that WT1 gene regulatory function and podocyte cell-type specification can best be understood in the context of transcription factor-regulatory element network interplay.

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Yang HW, Kim T-M, Song SS, Menon L, Jiang X, Huang W, Black PM, Park PJ, Carroll RS, Johnson MD. A small subunit processome protein promotes cancer by altering translation. Oncogene 2015;34(34):4471-81.Abstract

Dysregulation of ribosome biogenesis or translation can promote cancer, but the underlying mechanisms remain unclear. UTP18 is a component of the small subunit processome, a nucleolar multi-protein complex whose only known function is to cleave pre-ribosomal RNA to yield the 18S ribosomal RNA component of 40S ribosomal subunits. Here, we show that UTP18 also alters translation to promote stress resistance and growth, and that UTP18 is frequently gained and overexpressed in cancer. We observed that UTP18 localizes to the cytoplasm in a subset of cells, and that serum withdrawal increases cytoplasmic UTP18 localization. Cytoplasmic UTP18 associates with the translation complex and Hsp90 to upregulate the translation of IRES-containing transcripts such as HIF1a, Myc and VEGF, thereby inducing stress resistance. Hsp90 inhibition decreases cytoplasmic UTP18 and UTP18-induced increases in translation. Importantly, elevated UTP18 expression correlates with increased aggressiveness and decreased survival in numerous cancers. Enforced UTP18 overexpression promotes transformation and tumorigenesis, whereas UTP18 knockdown inhibits these processes. This stress adaptation mechanism is thus co-opted for growth by cancers, and its inhibition may represent a promising new therapeutic target.

2014
Ajay AK, Kim T-M, Ramirez-Gonzalez V, Park PJ, Frank DA, Vaidya VS. A bioinformatics approach identifies signal transducer and activator of transcription-3 and checkpoint kinase 1 as upstream regulators of kidney injury molecule-1 after kidney injury. J Am Soc Nephrol 2014;25(1):105-18.Abstract

Kidney injury molecule-1 (KIM-1)/T cell Ig and mucin domain-containing protein-1 (TIM-1) is upregulated more than other proteins after AKI, and it is highly expressed in renal damage of various etiologies. In this capacity, KIM-1/TIM-1 acts as a phosphatidylserine receptor on the surface of injured proximal tubular epithelial cells, mediating phagocytosis of apoptotic cells, and it may also act as a costimulatory molecule for immune cells. Despite recognition of KIM-1 as an important therapeutic target for kidney disease, the regulators of KIM-1 transcription in the kidney remain unknown. Using a bioinformatics approach, we identified upstream regulators of KIM-1 after AKI. In response to tubular injury in rat and human kidneys or oxidant stress in human proximal tubular epithelial cells (HPTECs), KIM-1 expression increased significantly in a manner that corresponded temporally and regionally with increased phosphorylation of checkpoint kinase 1 (Chk1) and STAT3. Both ischemic and oxidant stress resulted in a dramatic increase in reactive oxygen species that phosphorylated and activated Chk1, which subsequently bound to STAT3, phosphorylating it at S727. Furthermore, STAT3 bound to the KIM-1 promoter after ischemic and oxidant stress, and pharmacological or genetic induction of STAT3 in HPTECs increased KIM-1 mRNA and protein levels. Conversely, inhibition of STAT3 using siRNAs or dominant negative mutants reduced KIM-1 expression in a kidney cancer cell line (769-P) that expresses high basal levels of KIM-1. These observations highlight Chk1 and STAT3 as critical upstream regulators of KIM-1 expression after AKI and may suggest novel approaches for therapeutic intervention.

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Cancer Genome Atlas Research Network TCGA. Integrated genomic characterization of papillary thyroid carcinoma. Cell 2014;159(3):676-90.Abstract

Papillary thyroid carcinoma (PTC) is the most common type of thyroid cancer. Here, we describe the genomic landscape of 496 PTCs. We observed a low frequency of somatic alterations (relative to other carcinomas) and extended the set of known PTC driver alterations to include EIF1AX, PPM1D, and CHEK2 and diverse gene fusions. These discoveries reduced the fraction of PTC cases with unknown oncogenic driver from 25% to 3.5%. Combined analyses of genomic variants, gene expression, and methylation demonstrated that different driver groups lead to different pathologies with distinct signaling and differentiation characteristics. Similarly, we identified distinct molecular subgroups of BRAF-mutant tumors, and multidimensional analyses highlighted a potential involvement of oncomiRs in less-differentiated subgroups. Our results propose a reclassification of thyroid cancers into molecular subtypes that better reflect their underlying signaling and differentiation properties, which has the potential to improve their pathological classification and better inform the management of the disease.

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Marinov GK, Kundaje A, Park PJ, Wold BJ. Large-scale quality analysis of published ChIP-seq data. G3 2014;4(2):209-23.Abstract

ChIP-seq has become the primary method for identifying in vivo protein-DNA interactions on a genome-wide scale, with nearly 800 publications involving the technique appearing in PubMed as of December 2012. Individually and in aggregate, these data are an important and information-rich resource. However, uncertainties about data quality confound their use by the wider research community. Recently, the Encyclopedia of DNA Elements (ENCODE) project developed and applied metrics to objectively measure ChIP-seq data quality. The ENCODE quality analysis was useful for flagging datasets for closer inspection, eliminating or replacing poor data, and for driving changes in experimental pipelines. There had been no similarly systematic quality analysis of the large and disparate body of published ChIP-seq profiles. Here, we report a uniform analysis of vertebrate transcription factor ChIP-seq datasets in the Gene Expression Omnibus (GEO) repository as of April 1, 2012. The majority (55%) of datasets scored as being highly successful, but a substantial minority (20%) were of apparently poor quality, and another ∼25% were of intermediate quality. We discuss how different uses of ChIP-seq data are affected by specific aspects of data quality, and we highlight exceptional instances for which the metric values should not be taken at face value. Unexpectedly, we discovered that a significant subset of control datasets (i.e., no immunoprecipitation and mock immunoprecipitation samples) display an enrichment structure similar to successful ChIP-seq data. This can, in turn, affect peak calling and data interpretation. Published datasets identified here as high-quality comprise a large group that users can draw on for large-scale integrated analysis. In the future, ChIP-seq quality assessment similar to that used here could guide experimentalists at early stages in a study, provide useful input in the publication process, and be used to stratify ChIP-seq data for different community-wide uses.

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Hoadley KA, Yau C, Wolf DM, Cherniack AD, Tamborero D, Ng S, Leiserson MDM, Niu B, McLellan MD, Uzunangelov V, Zhang J, Kandoth C, Akbani R, Shen H, Omberg L, Chu A, Margolin AA, Van't Veer LJ, Lopez-Bigas N, Laird PW, Raphael BJ, Ding L, Robertson GA, Byers LA, Mills GB, Weinstein JN, Van Waes C, Chen Z, Collisson EA, Cancer Genome Atlas Research Network TCGA, Benz CC, Perou CM, Stuart JM. Multiplatform analysis of 12 cancer types reveals molecular classification within and across tissues of origin. Cell 2014;158(4):929-44.Abstract

Recent genomic analyses of pathologically defined tumor types identify "within-a-tissue" disease subtypes. However, the extent to which genomic signatures are shared across tissues is still unclear. We performed an integrative analysis using five genome-wide platforms and one proteomic platform on 3,527 specimens from 12 cancer types, revealing a unified classification into 11 major subtypes. Five subtypes were nearly identical to their tissue-of-origin counterparts, but several distinct cancer types were found to converge into common subtypes. Lung squamous, head and neck, and a subset of bladder cancers coalesced into one subtype typified by TP53 alterations, TP63 amplifications, and high expression of immune and proliferation pathway genes. Of note, bladder cancers split into three pan-cancer subtypes. The multiplatform classification, while correlated with tissue-of-origin, provides independent information for predicting clinical outcomes. All data sets are available for data-mining from a unified resource to support further biological discoveries and insights into novel therapeutic strategies.

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Merlo P, Frost B, Peng S, Yang YJ, Park PJ, Feany M. p53 prevents neurodegeneration by regulating synaptic genes. Proc Natl Acad Sci U S A 2014;111(50):18055-60.Abstract

DNA damage has been implicated in neurodegenerative disorders, including Alzheimer's disease and other tauopathies, but the consequences of genotoxic stress to postmitotic neurons are poorly understood. Here we demonstrate that p53, a key mediator of the DNA damage response, plays a neuroprotective role in a Drosophila model of tauopathy. Further, through a whole-genome ChIP-chip analysis, we identify genes controlled by p53 in postmitotic neurons. We genetically validate a specific pathway, synaptic function, in p53-mediated neuroprotection. We then demonstrate that the control of synaptic genes by p53 is conserved in mammals. Collectively, our results implicate synaptic function as a central target in p53-dependent protection from neurodegeneration.

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Ferrari F, Alekseyenko AA, Park PJ, Kuroda MI. Transcriptional control of a whole chromosome: emerging models for dosage compensation. Nat Struct Mol Biol 2014;21(2):118-25.Abstract

Males and females of many animal species differ in their sex-chromosome karyotype, and this creates imbalances between X-chromosome and autosomal gene products that require compensation. Although distinct molecular mechanisms have evolved in three highly studied systems, they all achieve coordinate regulation of an entire chromosome by differential RNA-polymerase occupancy at X-linked genes. High-throughput genome-wide methods have been pivotal in driving the latest progress in the field. Here we review the emerging models for dosage compensation in mammals, flies and nematodes, with a focus on mechanisms affecting RNA polymerase II activity on the X chromosome.

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2013
Soruco MML*, Chery J*, Bishop EP*, Siggers T, Tolstorukov MY, Leydon AR, Sugden AU, Goebel K, Feng J, Xia P, Vedenko A, Bulyk ML, Park PJ, Larschan E. The CLAMP protein links the MSL complex to the X chromosome during Drosophila dosage compensation. Genes Dev 2013;27(14):1551-6.Abstract

The Drosophila male-specific lethal (MSL) dosage compensation complex increases transcript levels on the single male X chromosome to equal the transcript levels in XX females. However, it is not known how the MSL complex is linked to its DNA recognition elements, the critical first step in dosage compensation. Here, we demonstrate that a previously uncharacterized zinc finger protein, CLAMP (chromatin-linked adaptor for MSL proteins), functions as the first link between the MSL complex and the X chromosome. CLAMP directly binds to the MSL complex DNA recognition elements and is required for the recruitment of the MSL complex. The discovery of CLAMP identifies a key factor required for the chromosome-specific targeting of dosage compensation, providing new insights into how subnuclear domains of coordinate gene regulation are formed within metazoan genomes.

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Alekseyenko AA, Ellison CE, Gorchakov AA, Zhou Q, Kaiser VB, Toda N, Walton Z, Peng S, Park PJ, Bachtrog D, Kuroda MI. Conservation and de novo acquisition of dosage compensation on newly evolved sex chromosomes in Drosophila. Genes Dev 2013;27(8):853-8.Abstract

Dosage compensation has arisen in response to the evolution of distinct male (XY) and female (XX) karyotypes. In Drosophila melanogaster, the MSL complex increases male X transcription approximately twofold. X-specific targeting is thought to occur through sequence-dependent binding to chromatin entry sites (CESs), followed by spreading in cis to active genes. We tested this model by asking how newly evolving sex chromosome arms in Drosophila miranda acquired dosage compensation. We found evidence for the creation of new CESs, with the analogous sequence and spacing as in D. melanogaster, providing strong support for the spreading model in the establishment of dosage compensation.

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