Hongjae Sunwoo

Howard Hughes Medical Institute, Ашбърн, Virginia, United States

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Publications (8)112.08 Total impact

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    ABSTRACT: The long noncoding X-inactivation-specific transcript (Xist gene) is responsible for mammalian X-chromosome dosage compensation between the sexes, the process by which one of the two X chromosomes is inactivated in the female soma. Xist is essential for both the random and imprinted forms of X-chromosome inactivation. In the imprinted form, Xist is paternally marked to be expressed in female embryos. To investigate the mechanism of Xist imprinting, we introduce Xist transgenes (Tg) into the male germ line. Although ectopic high-level Xist expression on autosomes can be compatible with viability, transgenic animals demonstrate reduced fitness, subfertility, defective meiotic pairing, and other germ-cell abnormalities. In the progeny, paternal-specific expression is recapitulated by the 200-kb Xist Tg. However, Xist imprinting occurs efficiently only when it is in an unpaired or unpartnered state during male meiosis. When transmitted from a hemizygous father (+/Tg), the Xist Tg demonstrates paternal-specific expression in the early embryo. When transmitted by a homozygous father (Tg/Tg), the Tg fails to show imprinted expression. Thus, Xist imprinting is directed by sequences within a 200-kb X-linked region, and the hemizygous (unpaired) state of the Xist region promotes its imprinting in the male germ line.
    Proceedings of the National Academy of Sciences 10/2015; DOI:10.1073/pnas.1519528112 · 9.67 Impact Factor
  • Hongjae Sunwoo · John Y Wu · Jeannie T Lee ·
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    ABSTRACT: X-chromosome inactivation (XCI) is initiated by the long noncoding RNA Xist, which coats the inactive X (Xi) and targets Polycomb repressive complex 2 (PRC2) in cis. Epigenomic analyses have provided significant insight into Xist binding patterns and chromatin organization of the Xi. However, such epigenomic analyses are limited by averaging of population-wide dynamics and do not inform behavior of single cells. Here we view Xist RNA and the Xi at 20-nm resolution using STochastic Optical Reconstruction Microscopy (STORM) in mouse cells. We observe dynamics at the single-cell level not predicted by epigenomic analysis. Only ∼50 hubs of Xist RNA occur on the Xi in the maintenance phase, corresponding to 50-100 Xist molecules per Xi and contrasting with the chromosome-wide "coat" observed by deep sequencing and conventional microscopy. Likewise, only ∼50 hubs PRC2 are observed. PRC2 and Xist foci are not randomly distributed but showed statistically significant spatial association. Knock-off experiments enable visualization of the dynamics of dissociation and relocalization onto the Xi and support a functional tethering of Xist and PRC2. Our analysis reveals that Xist-PRC2 complexes are less numerous than expected and suggests methylation of nucleosomes in a hit-and-run model.
    Proceedings of the National Academy of Sciences 07/2015; 112(31). DOI:10.1073/pnas.1503690112 · 9.67 Impact Factor
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    ABSTRACT: The inactive X chromosome (Xi) serves as a model to understand gene silencing on a global scale. Here, we perform "identification of direct RNA interacting proteins" (iDRiP) to isolate a comprehensive protein interactome for Xist, an RNA required for Xi silencing. We discover multiple classes of interactors, including cohesins, condensins, topoisomerases, RNA helicases, chromatin remodelers and modifiers, which synergistically repress Xi transcription. Inhibiting two or three interactors destabilizes silencing. While Xist attracts some interactors, it repels architectural factors. Xist evicts cohesins from the Xi and directs an Xi-specific chromosome conformation. Upon deleting Xist, the Xi acquires the cohesin-binding and chromosomal architecture of the active X. Our study unveils many layers of Xi repression and demonstrates a central role for RNA in the topological organization of mammalian chromosomes. Copyright © 2015, American Association for the Advancement of Science.
    Science 06/2015; 349(6245). DOI:10.1126/science.aab2276 · 33.61 Impact Factor
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    ABSTRACT: Mechanistic roles for many lncRNAs are poorly understood, in part because their direct interactions with genomic loci and proteins are difficult to assess. Using a method to purify endogenous RNAs and their associated factors, we mapped the genomic binding sites for two highly expressed human lncRNAs, NEAT1 and MALAT1. We show that NEAT1 and MALAT1 localize to hundreds of genomic sites in human cells, primarily over active genes. NEAT1 and MALAT1 exhibit colocalization to many of these loci, but display distinct gene body binding patterns at these sites, suggesting independent but complementary functions for these RNAs. We also identified numerous proteins enriched by both lncRNAs, supporting complementary binding and function, in addition to unique associated proteins. Transcriptional inhibition or stimulation alters localization of NEAT1 on active chromatin sites, implying that underlying DNA sequence does not target NEAT1 to chromatin, and that localization responds to cues involved in the transcription process.
    Molecular Cell 08/2014; DOI:10.1016/j.molcel.2014.07.012 · 14.02 Impact Factor
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    Yuntao S Mao · Hongjae Sunwoo · Bin Zhang · David L Spector ·
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    ABSTRACT: The cell nucleus is a highly compartmentalized organelle harbouring a variety of dynamic membraneless nuclear bodies. How these subnuclear domains are established and maintained is not well understood. Here, we investigate the molecular mechanism of how one nuclear body, the paraspeckle, is assembled and organized. Paraspeckles are discrete ribonucleoprotein bodies found in mammalian cells and implicated in nuclear retention of hyperedited mRNAs. We developed a live-cell imaging system that allows for the inducible transcription of Men ɛ/β (also known as Neat1; ref. 12) noncoding RNAs (ncRNAs) and the direct visualization of the recruitment of paraspeckle proteins. Using this system, we demonstrate that Men ɛ/β ncRNAs are essential to initiate the de novo assembly of paraspeckles. These newly formed structures effectively harbour nuclear-retained mRNAs confirming that they are bona fide functional paraspeckles. By three independent approaches, we show that it is the act of Men ɛ/β transcription, but not ncRNAs alone, that regulates paraspeckle maintenance. Finally, fluorescence recovery after photobleaching (FRAP) analyses supported a critical structural role for Men ɛ/β ncRNAs in paraspeckle organization. This study establishes a model in which Men ɛ/β ncRNAs serve as a platform to recruit proteins to assemble paraspeckles.
    Nature Cell Biology 01/2011; 13(1):95-101. DOI:10.1038/ncb2140 · 19.68 Impact Factor
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    Jeremy E Wilusz · Hongjae Sunwoo · David L Spector ·
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    ABSTRACT: Most of the eukaryotic genome is transcribed, yielding a complex network of transcripts that includes tens of thousands of long noncoding RNAs with little or no protein-coding capacity. Although the vast majority of long noncoding RNAs have yet to be characterized thoroughly, many of these transcripts are unlikely to represent transcriptional "noise" as a significant number have been shown to exhibit cell type-specific expression, localization to subcellular compartments, and association with human diseases. Here, we highlight recent efforts that have identified a myriad of molecular functions for long noncoding RNAs. In some cases, it appears that simply the act of noncoding RNA transcription is sufficient to positively or negatively affect the expression of nearby genes. However, in many cases, the long noncoding RNAs themselves serve key regulatory roles that were assumed previously to be reserved for proteins, such as regulating the activity or localization of proteins and serving as organizational frameworks of subcellular structures. In addition, many long noncoding RNAs are processed to yield small RNAs or, conversely, modulate how other RNAs are processed. It is thus becoming increasingly clear that long noncoding RNAs can function via numerous paradigms and are key regulatory molecules in the cell.
    Genes & development 08/2009; 23(13):1494-504. DOI:10.1101/gad.1800909 · 10.80 Impact Factor
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    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.
    Genome Research 03/2009; 19(3):347-59. DOI:10.1101/gr.087775.108 · 14.63 Impact Factor

Publication Stats

897 Citations
112.08 Total Impact Points


  • 2015
    • Howard Hughes Medical Institute
      Ашбърн, Virginia, United States
  • 2014
    • Harvard University
      Cambridge, Massachusetts, United States
  • 2009
    • Stony Brook University
      스토니브룩, New York, United States