Pub Date : 2021-12-01DOI: 10.1080/19491034.2021.1889858
Weihua Qin, Andreas Stengl, Enes Ugur, Susanne Leidescher, Joel Ryan, M Cristina Cardoso, Heinrich Leonhardt
Liquid-liquid phase separation (LLPS) mediated formation of membraneless organelles has been proposed to coordinate biological processes in space and time. Previously, the formation of phase-separated droplets was described as a unique property of HP1α. Here, we demonstrate that the positive net charge of the intrinsically disordered hinge region (IDR-H) of HP1 proteins is critical for phase separation and that the exchange of four acidic amino acids is sufficient to confer LLPS properties to HP1β. Surprisingly, the addition of mono-nucleosomes promoted H3K9me3-dependent LLPS of HP1β which could be specifically disrupted with methylated but not acetylated H3K9 peptides. HP1β mutants defective in H3K9me3 binding were less efficient in phase separationin vitro and failed to accumulate at heterochromatin in vivo. We propose that multivalent interactions of HP1β with H3K9me3-modified nucleosomes via its chromodomain and dimerization via its chromoshadow domain enable phase separation and contribute to the formation of heterochromatin compartments in vivo.
{"title":"HP1β carries an acidic linker domain and requires H3K9me3 for phase separation.","authors":"Weihua Qin, Andreas Stengl, Enes Ugur, Susanne Leidescher, Joel Ryan, M Cristina Cardoso, Heinrich Leonhardt","doi":"10.1080/19491034.2021.1889858","DOIUrl":"https://doi.org/10.1080/19491034.2021.1889858","url":null,"abstract":"<p><p>Liquid-liquid phase separation (LLPS) mediated formation of membraneless organelles has been proposed to coordinate biological processes in space and time. Previously, the formation of phase-separated droplets was described as a unique property of HP1α. Here, we demonstrate that the positive net charge of the intrinsically disordered hinge region (IDR-H) of HP1 proteins is critical for phase separation and that the exchange of four acidic amino acids is sufficient to confer LLPS properties to HP1β. Surprisingly, the addition of mono-nucleosomes promoted H3K9me3-dependent LLPS of HP1β which could be specifically disrupted with methylated but not acetylated H3K9 peptides. HP1β mutants defective in H3K9me3 binding were less efficient in phase separation<i>in vitro </i>and failed to accumulate at heterochromatin <i>in vivo</i>. We propose that multivalent interactions of HP1β with H3K9me3-modified nucleosomes via its chromodomain and dimerization via its chromoshadow domain enable phase separation and contribute to the formation of heterochromatin compartments <i>in vivo</i>.</p>","PeriodicalId":74323,"journal":{"name":"Nucleus (Austin, Tex.)","volume":null,"pages":null},"PeriodicalIF":0.0,"publicationDate":"2021-12-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://sci-hub-pdf.com/10.1080/19491034.2021.1889858","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"25427755","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"OA","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2021-12-01DOI: 10.1080/19491034.2021.1930681
Kentaro Tamura, Haruko Ueda, Ikuko Hara-Nishimura
The coordinated regulation of the nucelar envelope (NE) reassembly during cell division is an essential event. However, there is little information on the molecular components involved in NE assembly in plant cells. Here we developed an in vitro assay of NE assembly using tobacco BY-2 cultured cells. To start the NE assembly reaction, the demembranated nuclei and the S12 fraction (cytosol and microsomes) were mixed in the presence of GTP and ATP nucleotides. Time-course analysis indicated that tubule structures were extended from the microsomal vesicles that accumulated on the demembranated nuclei, and finally sealed the NE. Immunofluorescence confirmed that the assembled membrane contains a component of nuclear pore complex. The efficiency of the NE assembly is significantly inhibited by GTPγS that suppresses membrane fusion. This in-vitro assay system may elucidate the role of specific proteins and provide important insights into the molecular machinery of NE assembly in plant cells.
细胞分裂过程中核包膜(NE)重新组装的协调调控是一个重要事件。然而,有关植物细胞中 NE 组装所涉及的分子成分的信息却很少。在这里,我们利用烟草 BY-2 培养细胞开发了一种 NE 组装的体外检测方法。为了启动 NE 组装反应,在 GTP 和 ATP 核苷酸存在的情况下,将去膜的细胞核和 S12 部分(细胞质和微粒体)混合。时程分析表明,小管结构从微粒体囊泡中延伸出来,积聚在去膜核上,最终密封了 NE。免疫荧光证实,组装的膜含有核孔复合体的一种成分。GTPγS可抑制膜融合,从而显著抑制NE的组装效率。这种体外检测系统可阐明特定蛋白的作用,并为了解植物细胞中 NE 组装的分子机制提供重要信息。
{"title":"<i>In vitro</i> assembly of nuclear envelope in tobacco cultured cells.","authors":"Kentaro Tamura, Haruko Ueda, Ikuko Hara-Nishimura","doi":"10.1080/19491034.2021.1930681","DOIUrl":"10.1080/19491034.2021.1930681","url":null,"abstract":"<p><p>The coordinated regulation of the nucelar envelope (NE) reassembly during cell division is an essential event. However, there is little information on the molecular components involved in NE assembly in plant cells. Here we developed an <i>in vitro</i> assay of NE assembly using tobacco BY-2 cultured cells. To start the NE assembly reaction, the demembranated nuclei and the S12 fraction (cytosol and microsomes) were mixed in the presence of GTP and ATP nucleotides. Time-course analysis indicated that tubule structures were extended from the microsomal vesicles that accumulated on the demembranated nuclei, and finally sealed the NE. Immunofluorescence confirmed that the assembled membrane contains a component of nuclear pore complex. The efficiency of the NE assembly is significantly inhibited by GTPγS that suppresses membrane fusion. This <i>in-vitro assay</i> system may elucidate the role of specific proteins and provide important insights into the molecular machinery of NE assembly in plant cells.</p>","PeriodicalId":74323,"journal":{"name":"Nucleus (Austin, Tex.)","volume":null,"pages":null},"PeriodicalIF":0.0,"publicationDate":"2021-12-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://sci-hub-pdf.com/10.1080/19491034.2021.1930681","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"39014852","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"OA","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2021-12-01DOI: 10.1080/19491034.2021.1962610
Matthew Goelzer, Julianna Goelzer, Matthew L Ferguson, Corey P Neu, Gunes Uzer
The nucleus, central to cellular activity, relies on both direct mechanical input as well as its molecular transducers to sense external stimuli and respond by regulating intra-nuclear chromatin organization that determines cell function and fate. In mesenchymal stem cells of musculoskeletal tissues, changes in nuclear structures are emerging as a key modulator of their differentiation and proliferation programs. In this review we will first introduce the structural elements of the nucleoskeleton and discuss the current literature on how nuclear structure and signaling are altered in relation to environmental and tissue level mechanical cues. We will focus on state-of-the-art techniques to apply mechanical force and methods to measure nuclear mechanics in conjunction with DNA, RNA, and protein visualization in living cells. Ultimately, combining real-time nuclear deformations and chromatin dynamics can be a powerful tool to study mechanisms of how forces affect the dynamics of genome function.
{"title":"Nuclear envelope mechanobiology: linking the nuclear structure and function.","authors":"Matthew Goelzer, Julianna Goelzer, Matthew L Ferguson, Corey P Neu, Gunes Uzer","doi":"10.1080/19491034.2021.1962610","DOIUrl":"10.1080/19491034.2021.1962610","url":null,"abstract":"<p><p>The nucleus, central to cellular activity, relies on both direct mechanical input as well as its molecular transducers to sense external stimuli and respond by regulating intra-nuclear chromatin organization that determines cell function and fate. In mesenchymal stem cells of musculoskeletal tissues, changes in nuclear structures are emerging as a key modulator of their differentiation and proliferation programs. In this review we will first introduce the structural elements of the nucleoskeleton and discuss the current literature on how nuclear structure and signaling are altered in relation to environmental and tissue level mechanical cues. We will focus on state-of-the-art techniques to apply mechanical force and methods to measure nuclear mechanics in conjunction with DNA, RNA, and protein visualization in living cells. Ultimately, combining real-time nuclear deformations and chromatin dynamics can be a powerful tool to study mechanisms of how forces affect the dynamics of genome function.</p>","PeriodicalId":74323,"journal":{"name":"Nucleus (Austin, Tex.)","volume":null,"pages":null},"PeriodicalIF":0.0,"publicationDate":"2021-12-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://www.ncbi.nlm.nih.gov/pmc/articles/PMC8432354/pdf/","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"10732493","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"OA","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2021-12-01DOI: 10.1080/19491034.2021.1910437
Stephen Lindsly, Can Chen, Sijia Liu, Scott Ronquist, Samuel Dilworth, Michael Perlman, Indika Rajapakse
Data on genome organization and output over time, or the 4D Nucleome (4DN), require synthesis for meaningful interpretation. Development of tools for the efficient integration of these data is needed, especially for the time dimension. We present the '4DNvestigator', a user-friendly network-based toolbox for the analysis of time series genome-wide genome structure (Hi-C) and gene expression (RNA-seq) data. Additionally, we provide methods to quantify network entropy, tensor entropy, and statistically significant changes in time series Hi-C data at different genomic scales.
{"title":"4DNvestigator: time series genomic data analysis toolbox.","authors":"Stephen Lindsly, Can Chen, Sijia Liu, Scott Ronquist, Samuel Dilworth, Michael Perlman, Indika Rajapakse","doi":"10.1080/19491034.2021.1910437","DOIUrl":"https://doi.org/10.1080/19491034.2021.1910437","url":null,"abstract":"<p><p>Data on genome organization and output over time, or the 4D Nucleome (4DN), require synthesis for meaningful interpretation. Development of tools for the efficient integration of these data is needed, especially for the time dimension. We present the '4DNvestigator', a user-friendly network-based toolbox for the analysis of time series genome-wide genome structure (Hi-C) and gene expression (RNA-seq) data. Additionally, we provide methods to quantify network entropy, tensor entropy, and statistically significant changes in time series Hi-C data at different genomic scales.</p>","PeriodicalId":74323,"journal":{"name":"Nucleus (Austin, Tex.)","volume":null,"pages":null},"PeriodicalIF":0.0,"publicationDate":"2021-12-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://sci-hub-pdf.com/10.1080/19491034.2021.1910437","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"10641278","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"OA","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2020-12-01DOI: 10.1080/19491034.2020.1845012
Tristan Dubos, Axel Poulet, Céline Gonthier-Gueret, Guillaume Mougeot, Emmanuel Vanrobays, Yanru Li, Sylvie Tutois, Emilie Pery, Frédéric Chausse, Aline V Probst, Christophe Tatout, Sophie Desset
NucleusJ 1.0, an ImageJ plugin, is a useful tool to analyze nuclear morphology and chromatin organization in plant and animal cells. NucleusJ 2.0 is a new release of NucleusJ, in which image processing is achieved more quickly using a command-lineuser interface. Starting with large collection of 3D nuclei, segmentation can be performed by the previously developed Otsu-modified method or by a new 3D gift-wrapping method, taking better account of nuclear indentations and unstained nucleoli. These two complementary methods are compared for their accuracy by using three types of datasets available to the community at https://www.brookes.ac.uk/indepth/images/ . Finally, NucleusJ 2.0 was evaluated using original plant genetic material by assessing its efficiency on nuclei stained with DNA dyes or after 3D-DNA Fluorescence in situ hybridization. With these improvements, NucleusJ 2.0 permits the generation of large user-curated datasets that will be useful for software benchmarking or to train convolution neural networks.
{"title":"Automated 3D bio-imaging analysis of nuclear organization by NucleusJ 2.0.","authors":"Tristan Dubos, Axel Poulet, Céline Gonthier-Gueret, Guillaume Mougeot, Emmanuel Vanrobays, Yanru Li, Sylvie Tutois, Emilie Pery, Frédéric Chausse, Aline V Probst, Christophe Tatout, Sophie Desset","doi":"10.1080/19491034.2020.1845012","DOIUrl":"https://doi.org/10.1080/19491034.2020.1845012","url":null,"abstract":"<p><p>NucleusJ 1.0, an ImageJ plugin, is a useful tool to analyze nuclear morphology and chromatin organization in plant and animal cells. NucleusJ 2.0 is a new release of NucleusJ, in which image processing is achieved more quickly using a command-lineuser interface. Starting with large collection of 3D nuclei, segmentation can be performed by the previously developed Otsu-modified method or by a new 3D gift-wrapping method, taking better account of nuclear indentations and unstained nucleoli. These two complementary methods are compared for their accuracy by using three types of datasets available to the community at <u>https://www.brookes.ac.uk/indepth/images/</u> . Finally, NucleusJ 2.0 was evaluated using original plant genetic material by assessing its efficiency on nuclei stained with DNA dyes or after 3D-DNA Fluorescence <i>in situ</i> hybridization. With these improvements, NucleusJ 2.0 permits the generation of large user-curated datasets that will be useful for software benchmarking or to train convolution neural networks.</p>","PeriodicalId":74323,"journal":{"name":"Nucleus (Austin, Tex.)","volume":null,"pages":null},"PeriodicalIF":0.0,"publicationDate":"2020-12-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://sci-hub-pdf.com/10.1080/19491034.2020.1845012","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"38570296","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"OA","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2020-12-01DOI: 10.1080/19491034.2020.1744415
Stefania Mamberti, M Cristina Cardoso
Decades of investigation on genomic DNA have brought us deeper insights into its organization within the nucleus and its metabolic mechanisms. This was fueled by the parallel development of experimental techniques and has stimulated model building to simulate genome conformation in agreement with the experimental data. Here, we will discuss our recent discoveries on the chromatin units of DNA replication and DNA damage response. We will highlight their remarkable structural similarities and how both revealed themselves as clusters of nanofocal structures each on the hundred thousand base pair size range corresponding well with chromatin loop sizes. We propose that the function of these two global genomic processes is determined by the loop level organization of chromatin structure with structure dictating function.Abbreviations: 3D-SIM: 3D-structured illumination microscopy; 3C: chromosome conformation capture; DDR: DNA damage response; FISH: fluorescent in situ hybridization; Hi-C: high conformation capture; HiP-HoP: highly predictive heteromorphic polymer model; IOD: inter-origin distance; LAD: lamina associated domain; STED: stimulated emission depletion microscopy; STORM: stochastic optical reconstruction microscopy; SBS: strings and binders switch model; TAD: topologically associated domain.
{"title":"Are the processes of DNA replication and DNA repair reading a common structural chromatin unit?","authors":"Stefania Mamberti, M Cristina Cardoso","doi":"10.1080/19491034.2020.1744415","DOIUrl":"https://doi.org/10.1080/19491034.2020.1744415","url":null,"abstract":"<p><p>Decades of investigation on genomic DNA have brought us deeper insights into its organization within the nucleus and its metabolic mechanisms. This was fueled by the parallel development of experimental techniques and has stimulated model building to simulate genome conformation in agreement with the experimental data. Here, we will discuss our recent discoveries on the chromatin units of DNA replication and DNA damage response. We will highlight their remarkable structural similarities and how both revealed themselves as clusters of nanofocal structures each on the hundred thousand base pair size range corresponding well with chromatin loop sizes. We propose that the function of these two global genomic processes is determined by the loop level organization of chromatin structure with structure dictating function.<b>Abbreviations:</b> 3D-SIM: 3D-structured illumination microscopy; 3C: chromosome conformation capture; DDR: DNA damage response; FISH: fluorescent in situ hybridization; Hi-C: high conformation capture; HiP-HoP: highly predictive heteromorphic polymer model; IOD: inter-origin distance; LAD: lamina associated domain; STED: stimulated emission depletion microscopy; STORM: stochastic optical reconstruction microscopy; SBS: strings and binders switch model; TAD: topologically associated domain.</p>","PeriodicalId":74323,"journal":{"name":"Nucleus (Austin, Tex.)","volume":null,"pages":null},"PeriodicalIF":0.0,"publicationDate":"2020-12-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://sci-hub-pdf.com/10.1080/19491034.2020.1744415","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"37821767","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"OA","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2020-12-01DOI: 10.1080/19491034.2020.1783783
Morgan Moser, Andrew Kirkpatrick, Norman Reid Groves, Iris Meier
Nuclear movement and positioning play a role in developmental processes throughout life. Nuclear movement and positioning are mediated primarily by linker of nucleoskeleton and cytoskeleton (LINC) complexes. LINC complexes are comprised of the inner nuclear membrane SUN proteins and the outer nuclear membrane (ONM) KASH proteins. In Arabidopsis pollen tubes, the vegetative nucleus (VN) maintains a fixed distance from the pollen tube tip during growth, and the VN precedes the sperm cells (SCs). In pollen tubes of wit12 and wifi, mutants deficient in the ONM component of a plant LINC complex, the SCs precede the VN during pollen tube growth and the fixed VN distance from the tip is lost. Subsequently, pollen tubes frequently fail to burst upon reception. In this study, we sought to determine if the pollen tube reception defect observed in wit12 and wifi is due to decreased sensitivity to reactive oxygen species (ROS). Here, we show that wit12 and wifi are hyposensitive to exogenous H2O2, and that this hyposensitivity is correlated with decreased proximity of the VN to the pollen tube tip. Additionally, we report the first instance of nuclear Ca2+ peaks in growing pollen tubes, which are disrupted in the wit12 mutant. In the wit12 mutant, nuclear Ca2+ peaks are reduced in response to exogenous ROS, but these peaks are not correlated with pollen tube burst. This study finds that VN proximity to the pollen tube tip is required for both response to exogenous ROS, as well as internal nuclear Ca2+ fluctuations.
{"title":"LINC-complex mediated positioning of the vegetative nucleus is involved in calcium and ROS signaling in Arabidopsis pollen tubes.","authors":"Morgan Moser, Andrew Kirkpatrick, Norman Reid Groves, Iris Meier","doi":"10.1080/19491034.2020.1783783","DOIUrl":"https://doi.org/10.1080/19491034.2020.1783783","url":null,"abstract":"<p><p>Nuclear movement and positioning play a role in developmental processes throughout life. Nuclear movement and positioning are mediated primarily by linker of nucleoskeleton and cytoskeleton (LINC) complexes. LINC complexes are comprised of the inner nuclear membrane SUN proteins and the outer nuclear membrane (ONM) KASH proteins. In Arabidopsis pollen tubes, the vegetative nucleus (VN) maintains a fixed distance from the pollen tube tip during growth, and the VN precedes the sperm cells (SCs). In pollen tubes of <i>wit12</i> and <i>wifi</i>, mutants deficient in the ONM component of a plant LINC complex, the SCs precede the VN during pollen tube growth and the fixed VN distance from the tip is lost. Subsequently, pollen tubes frequently fail to burst upon reception. In this study, we sought to determine if the pollen tube reception defect observed in <i>wit12</i> and <i>wifi</i> is due to decreased sensitivity to reactive oxygen species (ROS). Here, we show that <i>wit12</i> and <i>wifi</i> are hyposensitive to exogenous H<sub>2</sub>O<sub>2</sub>, and that this hyposensitivity is correlated with decreased proximity of the VN to the pollen tube tip. Additionally, we report the first instance of nuclear Ca<sup>2+</sup> peaks in growing pollen tubes, which are disrupted in the <i>wit12</i> mutant. In the <i>wit12</i> mutant, nuclear Ca<sup>2+</sup> peaks are reduced in response to exogenous ROS, but these peaks are not correlated with pollen tube burst. This study finds that VN proximity to the pollen tube tip is required for both response to exogenous ROS, as well as internal nuclear Ca<sup>2+</sup> fluctuations.</p>","PeriodicalId":74323,"journal":{"name":"Nucleus (Austin, Tex.)","volume":null,"pages":null},"PeriodicalIF":0.0,"publicationDate":"2020-12-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://sci-hub-pdf.com/10.1080/19491034.2020.1783783","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"38125161","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"OA","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2020-12-01DOI: 10.1080/19491034.2020.1782024
Anders S Hansen
Mammalian genome structure is closely linked to function. At the scale of kilobases to megabases, CTCF and cohesin organize the genome into chromatin loops. Mechanistically, cohesin is proposed to extrude chromatin loops bidirectionally until it encounters occupied CTCF DNA-binding sites. Curiously, loops form predominantly between CTCF binding sites in a convergent orientation. How CTCF interacts with and blocks cohesin extrusion in an orientation-specific manner has remained a mechanistic mystery. Here, we review recent papers that have shed light on these processes and suggest a multi-step interaction between CTCF and cohesin. This interaction may first involve a pausing step, where CTCF halts cohesin extrusion, followed by a stabilization step of the CTCF-cohesin complex, resulting in a chromatin loop. Finally, we discuss our own recent studies on an internal RNA-Binding Region (RBRi) in CTCF to elucidate its role in regulating CTCF clustering, target search mechanisms and chromatin loop formation and future challenges.
{"title":"CTCF as a boundary factor for cohesin-mediated loop extrusion: evidence for a multi-step mechanism.","authors":"Anders S Hansen","doi":"10.1080/19491034.2020.1782024","DOIUrl":"10.1080/19491034.2020.1782024","url":null,"abstract":"<p><p>Mammalian genome structure is closely linked to function. At the scale of kilobases to megabases, CTCF and cohesin organize the genome into chromatin loops. Mechanistically, cohesin is proposed to extrude chromatin loops bidirectionally until it encounters occupied CTCF DNA-binding sites. Curiously, loops form predominantly between CTCF binding sites in a convergent orientation. How CTCF interacts with and blocks cohesin extrusion in an orientation-specific manner has remained a mechanistic mystery. Here, we review recent papers that have shed light on these processes and suggest a multi-step interaction between CTCF and cohesin. This interaction may first involve a pausing step, where CTCF halts cohesin extrusion, followed by a stabilization step of the CTCF-cohesin complex, resulting in a chromatin loop. Finally, we discuss our own recent studies on an internal RNA-Binding Region (RBRi) in CTCF to elucidate its role in regulating CTCF clustering, target search mechanisms and chromatin loop formation and future challenges.</p>","PeriodicalId":74323,"journal":{"name":"Nucleus (Austin, Tex.)","volume":null,"pages":null},"PeriodicalIF":0.0,"publicationDate":"2020-12-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://sci-hub-pdf.com/10.1080/19491034.2020.1782024","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"38130485","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"OA","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2020-12-01DOI: 10.1080/19491034.2020.1802906
Brooke E Danielsson, Katie V Tieu, Kranthidhar Bathula, Travis J Armiger, Pragna S Vellala, Rebecca E Taylor, Kris Noel Dahl, Daniel E Conway
The nuclear lamina is a meshwork of intermediate filament proteins, and lamin A is the primary mechanical protein. An altered splicing of lamin A, known as progerin, causes the disease Hutchinson-Gilford progeria syndrome. Progerin-expressing cells have altered nuclear shapes and stiffened nuclear lamina with microaggregates of progerin. Here, progerin microaggregate inclusions in the lamina are shown to lead to cellular and multicellular dysfunction. We show with Comsol simulations that stiffened inclusions causes redistribution of normally homogeneous forces, and this redistribution is dependent on the stiffness difference and relatively independent of inclusion size. We also show mechanotransmission changes associated with progerin expression in cells under confinement and cells under external forces. Endothelial cells expressing progerin do not align properly with patterning. Fibroblasts expressing progerin do not align properly to applied cyclic force. Combined, these studies show that altered nuclear lamina mechanics and microstructure impacts cytoskeletal force transmission through the cell.
{"title":"Lamin microaggregates lead to altered mechanotransmission in progerin-expressing cells.","authors":"Brooke E Danielsson, Katie V Tieu, Kranthidhar Bathula, Travis J Armiger, Pragna S Vellala, Rebecca E Taylor, Kris Noel Dahl, Daniel E Conway","doi":"10.1080/19491034.2020.1802906","DOIUrl":"https://doi.org/10.1080/19491034.2020.1802906","url":null,"abstract":"<p><p>The nuclear lamina is a meshwork of intermediate filament proteins, and lamin A is the primary mechanical protein. An altered splicing of lamin A, known as progerin, causes the disease Hutchinson-Gilford progeria syndrome. Progerin-expressing cells have altered nuclear shapes and stiffened nuclear lamina with microaggregates of progerin. Here, progerin microaggregate inclusions in the lamina are shown to lead to cellular and multicellular dysfunction. We show with Comsol simulations that stiffened inclusions causes redistribution of normally homogeneous forces, and this redistribution is dependent on the stiffness difference and relatively independent of inclusion size. We also show mechanotransmission changes associated with progerin expression in cells under confinement and cells under external forces. Endothelial cells expressing progerin do not align properly with patterning. Fibroblasts expressing progerin do not align properly to applied cyclic force. Combined, these studies show that altered nuclear lamina mechanics and microstructure impacts cytoskeletal force transmission through the cell.</p>","PeriodicalId":74323,"journal":{"name":"Nucleus (Austin, Tex.)","volume":null,"pages":null},"PeriodicalIF":0.0,"publicationDate":"2020-12-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://sci-hub-pdf.com/10.1080/19491034.2020.1802906","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"38290727","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"OA","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2020-12-01DOI: 10.1080/19491034.2020.1816053
Tatini Rakshit, Daniël P Melters, Emilios K Dimitriadis, Yamini Dalal
The interplay between transcription factors, chromatin remodelers, 3-D organization, and mechanical properties of the chromatin fiber controls genome function in eukaryotes. Besides the canonical histones which fold the bulk of the chromatin into nucleosomes, histone variants create distinctive chromatin domains that are thought to regulate transcription, replication, DNA damage repair, and faithful chromosome segregation. Whether histone variants translate distinctive biochemical or biophysical properties to their associated chromatin structures, and whether these properties impact chromatin dynamics as the genome undergoes a multitude of transactions, is an important question in biology. Here, we describe single-molecule nanoindentation tools that we developed specifically to determine the mechanical properties of histone variant nucleosomes and their complexes. These methods join an array of cutting-edge new methods that further our quantitative understanding of the response of chromatin to intrinsic and extrinsic forces which act upon it during biological transactions in the nucleus.
{"title":"Mechanical properties of nucleoprotein complexes determined by nanoindentation spectroscopy.","authors":"Tatini Rakshit, Daniël P Melters, Emilios K Dimitriadis, Yamini Dalal","doi":"10.1080/19491034.2020.1816053","DOIUrl":"https://doi.org/10.1080/19491034.2020.1816053","url":null,"abstract":"<p><p>The interplay between transcription factors, chromatin remodelers, 3-D organization, and mechanical properties of the chromatin fiber controls genome function in eukaryotes. Besides the canonical histones which fold the bulk of the chromatin into nucleosomes, histone variants create distinctive chromatin domains that are thought to regulate transcription, replication, DNA damage repair, and faithful chromosome segregation. Whether histone variants translate distinctive biochemical or biophysical properties to their associated chromatin structures, and whether these properties impact chromatin dynamics as the genome undergoes a multitude of transactions, is an important question in biology. Here, we describe single-molecule nanoindentation tools that we developed specifically to determine the mechanical properties of histone variant nucleosomes and their complexes. These methods join an array of cutting-edge new methods that further our quantitative understanding of the response of chromatin to intrinsic and extrinsic forces which act upon it during biological transactions in the nucleus.</p>","PeriodicalId":74323,"journal":{"name":"Nucleus (Austin, Tex.)","volume":null,"pages":null},"PeriodicalIF":0.0,"publicationDate":"2020-12-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://sci-hub-pdf.com/10.1080/19491034.2020.1816053","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"38401300","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"OA","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}