1
|
Rajshekar S, Adame-Arana O, Bajpai G, Lin K, Colmenares S, Safran S, Karpen GH. Affinity hierarchies and amphiphilic proteins underlie the co-assembly of nucleolar and heterochromatin condensates. Res Sq 2023:rs.3.rs-3385692. [PMID: 37841837 PMCID: PMC10571612 DOI: 10.21203/rs.3.rs-3385692/v1] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 10/17/2023]
Abstract
Nucleoli are surrounded by Pericentromeric Heterochromatin (PCH), reflecting a close spatial association between the two largest biomolecular condensates in eukaryotic nuclei. This nuclear organizational feature is highly conserved and is disrupted in diseased states like senescence, however, the mechanisms driving PCH-nucleolar association are unclear. High-resolution live imaging during early Drosophila development revealed a highly dynamic process in which PCH and nucleolar formation is coordinated and interdependent. When nucleolus assembly was eliminated by deleting the ribosomal RNA genes (rDNA), PCH showed increased compaction and subsequent reorganization to a shell-like structure. In addition, in embryos lacking rDNA, some nucleolar proteins were redistributed into new bodies or 'neocondensates,' including enrichment in the core of the PCH shell. These observations, combined with physical modeling and simulations, suggested that nucleolar-PCH associations are mediated by a hierarchy of affinities between PCH, nucleoli, and 'amphiphilic' protein(s) that interact with both nucleolar and PCH components. This result was validated by demonstrating that the depletion of one candidate amphiphile, the nucleolar protein Pitchoune, significantly reduced PCH-nucleolar associations. Together, these results unveil a dynamic program for establishing nucleolar-PCH associations during animal development, demonstrate that nucleoli are required for normal PCH organization, and identify Pitchoune as an amphiphilic molecular link that promotes PCH-nucleolar associations. Finally, we propose that disrupting affinity hierarchies between interacting condensates can liberate molecules to form neocondensates or other aberrant structures that could contribute to cellular disease phenotypes.
Collapse
Affiliation(s)
- Srivarsha Rajshekar
- Department of Molecular and Cell Biology, University of California Berkeley, Berkeley, USA
| | - Omar Adame-Arana
- Department of Chemical and Biological Physics, Weizmann Institute of Science, Rehovot, Israel
- Max Planck Institute for the Physics of Complex Systems, Dresden, Germany
| | - Gaurav Bajpai
- Department of Chemical and Biological Physics, Weizmann Institute of Science, Rehovot, Israel
| | - Kyle Lin
- Department of Molecular and Cell Biology, University of California Berkeley, Berkeley, USA
| | - Serafin Colmenares
- Department of Molecular and Cell Biology, University of California Berkeley, Berkeley, USA
| | - Samuel Safran
- Department of Chemical and Biological Physics, Weizmann Institute of Science, Rehovot, Israel
| | - Gary H Karpen
- Department of Molecular and Cell Biology, University of California Berkeley, Berkeley, USA
- Division of Biological Sciences and the Environment, Lawrence Berkeley National Laboratory, Berkeley, USA
| |
Collapse
|
2
|
Rajshekar S, Adame-Arana O, Bajpai G, Lin K, Colmenares S, Safran S, Karpen GH. Affinity hierarchies and amphiphilic proteins underlie the co-assembly of nucleolar and heterochromatin condensates. bioRxiv 2023:2023.07.06.547894. [PMID: 37808710 PMCID: PMC10557603 DOI: 10.1101/2023.07.06.547894] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 10/10/2023]
Abstract
Nucleoli are surrounded by Pericentromeric Heterochromatin (PCH), reflecting a close spatial association between the two largest biomolecular condensates in eukaryotic nuclei. This nuclear organizational feature is highly conserved and is disrupted in diseased states like senescence, however, the mechanisms driving PCH-nucleolar association are unclear. High-resolution live imaging during early Drosophila development revealed a highly dynamic process in which PCH and nucleolar formation is coordinated and interdependent. When nucleolus assembly was eliminated by deleting the ribosomal RNA genes (rDNA), PCH showed increased compaction and subsequent reorganization to a shell-like structure. In addition, in embryos lacking rDNA, some nucleolar proteins were redistributed into new bodies or 'neocondensates,' including enrichment in the core of the PCH shell. These observations, combined with physical modeling and simulations, suggested that nucleolar-PCH associations are mediated by a hierarchy of affinities between PCH, nucleoli, and 'amphiphilic' protein(s) that interact with both nucleolar and PCH components. This result was validated by demonstrating that the depletion of one candidate amphiphile, the nucleolar protein Pitchoune, significantly reduced PCH-nucleolar associations. Together, these results unveil a dynamic program for establishing nucleolar-PCH associations during animal development, demonstrate that nucleoli are required for normal PCH organization, and identify Pitchoune as an amphiphilic molecular link that promotes PCH-nucleolar associations. Finally, we propose that disrupting affinity hierarchies between interacting condensates can liberate molecules to form neocondensates or other aberrant structures that could contribute to cellular disease phenotypes.
Collapse
Affiliation(s)
- Srivarsha Rajshekar
- Department of Molecular and Cell Biology, University of California Berkeley, Berkeley, USA
| | - Omar Adame-Arana
- Department of Chemical and Biological Physics, Weizmann Institute of Science, Rehovot, Israel
- Max Planck Institute for the Physics of Complex Systems, Dresden, Germany
| | - Gaurav Bajpai
- Department of Chemical and Biological Physics, Weizmann Institute of Science, Rehovot, Israel
| | - Kyle Lin
- Department of Molecular and Cell Biology, University of California Berkeley, Berkeley, USA
| | - Serafin Colmenares
- Department of Molecular and Cell Biology, University of California Berkeley, Berkeley, USA
| | - Samuel Safran
- Department of Chemical and Biological Physics, Weizmann Institute of Science, Rehovot, Israel
| | - Gary H Karpen
- Department of Molecular and Cell Biology, University of California Berkeley, Berkeley, USA
- Division of Biological Sciences and the Environment, Lawrence Berkeley National Laboratory, Berkeley, USA
| |
Collapse
|
3
|
Adame-Arana O, Bajpai G, Lorber D, Volk T, Safran S. Regulation of chromatin microphase separation by binding of protein complexes. eLife 2023; 12:e82983. [PMID: 37436818 DOI: 10.7554/elife.82983] [Citation(s) in RCA: 1] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Grants] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/25/2022] [Accepted: 06/22/2023] [Indexed: 07/13/2023] Open
Abstract
We show evidence of the association of RNA polymerase II (RNAP) with chromatin in a core-shell organization, reminiscent of microphase separation where the cores comprise dense chromatin and the shell, RNAP and chromatin with low density. These observations motivate our physical model for the regulation of core-shell chromatin organization. Here, we model chromatin as a multiblock copolymer, comprising active and inactive regions (blocks) that are both in poor solvent and tend to be condensed in the absence of binding proteins. However, we show that the solvent quality for the active regions of chromatin can be regulated by the binding of protein complexes (e.g., RNAP and transcription factors). Using the theory of polymer brushes, we find that such binding leads to swelling of the active chromatin regions which in turn modifies the spatial organization of the inactive regions. In addition, we use simulations to study spherical chromatin micelles, whose cores comprise inactive regions and shells comprise active regions and bound protein complexes. In spherical micelles the swelling increases the number of inactive cores and controls their size. Thus, genetic modifications affecting the binding strength of chromatin-binding protein complexes may modulate the solvent quality experienced by chromatin and regulate the physical organization of the genome.
Collapse
Affiliation(s)
- Omar Adame-Arana
- Department of Chemical and Biological Physics, Weizmann Institute of Science, Rehovot, Israel
| | - Gaurav Bajpai
- Department of Chemical and Biological Physics, Weizmann Institute of Science, Rehovot, Israel
| | - Dana Lorber
- Department of Molecular Genetics, Weizmann Institute of Science, Rehovot, Israel
| | - Talila Volk
- Department of Molecular Genetics, Weizmann Institute of Science, Rehovot, Israel
| | - Samuel Safran
- Department of Chemical and Biological Physics, Weizmann Institute of Science, Rehovot, Israel
| |
Collapse
|
4
|
Bajpai G, Safran S. Mesoscale, long-time mixing of chromosomes and its connection to polymer dynamics. PLoS Comput Biol 2023; 19:e1011142. [PMID: 37228178 DOI: 10.1371/journal.pcbi.1011142] [Citation(s) in RCA: 1] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/06/2022] [Accepted: 05/01/2023] [Indexed: 05/27/2023] Open
Abstract
Chromosomes are arranged in distinct territories within the nucleus of animal cells. Recent experiments have shown that these territories overlap at their edges, suggesting partial mixing during interphase. Experiments that knock-down of condensin II proteins during interphase indicate increased chromosome mixing, which demonstrates control of the mixing. In this study, we use a generic polymer simulation to quantify the dynamics of chromosome mixing over time. We introduce the chromosome mixing index, which quantifies the mixing of distinct chromosomes in the nucleus. We find that the chromosome mixing index in a small confinement volume (as a model of the nucleus), increases as a power-law of the time, with the scaling exponent varying non-monotonically with self-interaction and volume fraction. By comparing the chromosome mixing index with both monomer subdiffusion due to (non-topological) intermingling of chromosomes as well as even slower reptation, we show that for relatively large volume fractions, the scaling exponent of the chromosome mixing index is related to Rouse dynamics for relatively weak chromosome attractions and to reptation for strong attractions. In addition, we extend our model to more realistically account for the situation of the Drosophila chromosome by including the heterogeneity of the polymers and their lengths to account for microphase separation of euchromatin and heterochromatin and their interactions with the nuclear lamina. We find that the interaction with the lamina further impedes chromosome mixing.
Collapse
Affiliation(s)
- Gaurav Bajpai
- Department of Chemical and Biological Physics, Weizmann Institute of Science, Rehovot, Israel
| | - Samuel Safran
- Department of Chemical and Biological Physics, Weizmann Institute of Science, Rehovot, Israel
| |
Collapse
|
5
|
Amiad Pavlov D, Unnikannan CP, Lorber D, Bajpai G, Olender T, Stoops E, Reuveny A, Safran S, Volk T. The LINC Complex Inhibits Excessive Chromatin Repression. Cells 2023; 12:cells12060932. [PMID: 36980273 PMCID: PMC10047284 DOI: 10.3390/cells12060932] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/16/2023] [Revised: 03/15/2023] [Accepted: 03/16/2023] [Indexed: 03/30/2023] Open
Abstract
The Linker of Nucleoskeleton and Cytoskeleton (LINC) complex transduces nuclear mechanical inputs suggested to control chromatin organization and gene expression; however, the underlying mechanism is currently unclear. We show here that the LINC complex is needed to minimize chromatin repression in muscle tissue, where the nuclei are exposed to significant mechanical inputs during muscle contraction. To this end, the genomic binding profiles of Polycomb, Heterochromatin Protein1 (HP1a) repressors, and of RNA-Pol II were studied in Drosophila larval muscles lacking functional LINC complex. A significant increase in the binding of Polycomb and parallel reduction of RNA-Pol-II binding to a set of muscle genes was observed. Consistently, enhanced tri-methylated H3K9 and H3K27 repressive modifications and reduced chromatin activation by H3K9 acetylation were found. Furthermore, larger tri-methylated H3K27me3 repressive clusters, and chromatin redistribution from the nuclear periphery towards nuclear center, were detected in live LINC mutant larval muscles. Computer simulation indicated that the observed dissociation of the chromatin from the nuclear envelope promotes growth of tri-methylated H3K27 repressive clusters. Thus, we suggest that by promoting chromatin-nuclear envelope binding, the LINC complex restricts the size of repressive H3K27 tri-methylated clusters, thereby limiting the binding of Polycomb transcription repressor, directing robust transcription in muscle fibers.
Collapse
Affiliation(s)
- Daria Amiad Pavlov
- Department of Molecular Genetics, Weizmann Institute of Science, Rehovot 7610001, Israel
| | | | - Dana Lorber
- Department of Molecular Genetics, Weizmann Institute of Science, Rehovot 7610001, Israel
| | - Gaurav Bajpai
- Department of Chemical and Biological Physics, Weizmann Institute of Science, Rehovot 7610001, Israel
| | - Tsviya Olender
- Department of Molecular Genetics, Weizmann Institute of Science, Rehovot 7610001, Israel
| | - Elizabeth Stoops
- Department of Molecular Genetics, Weizmann Institute of Science, Rehovot 7610001, Israel
| | - Adriana Reuveny
- Department of Molecular Genetics, Weizmann Institute of Science, Rehovot 7610001, Israel
| | - Samuel Safran
- Department of Chemical and Biological Physics, Weizmann Institute of Science, Rehovot 7610001, Israel
| | - Talila Volk
- Department of Molecular Genetics, Weizmann Institute of Science, Rehovot 7610001, Israel
| |
Collapse
|
6
|
Deviri D, Safran S. Balance of osmotic pressures determines the volume of the nucleus. Biophys J 2022. [DOI: 10.1016/j.bpj.2021.11.298] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/02/2022] Open
|
7
|
Bajpai G, Safran S. Mesoscale mixing of chromosomes. Biophys J 2022. [DOI: 10.1016/j.bpj.2021.11.941] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/02/2022] Open
|
8
|
Amiad-Pavlov D, Lorber D, Bajpai G, Reuveny A, Roncato F, Alon R, Safran S, Volk T. Live imaging of chromatin distribution reveals novel principles of nuclear architecture and chromatin compartmentalization. Sci Adv 2021; 7:7/23/eabf6251. [PMID: 34078602 PMCID: PMC8172175 DOI: 10.1126/sciadv.abf6251] [Citation(s) in RCA: 31] [Impact Index Per Article: 10.3] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 11/08/2020] [Accepted: 04/15/2021] [Indexed: 05/12/2023]
Abstract
Live imaging of chromatin in an intact organism reveals a novel mode of mesoscale chromatin organization at nuclear periphery.
Collapse
Affiliation(s)
- Daria Amiad-Pavlov
- Department of Molecular Genetics, Weizmann Institute of Science, Rehovot, Israel
| | - Dana Lorber
- Department of Molecular Genetics, Weizmann Institute of Science, Rehovot, Israel
| | - Gaurav Bajpai
- Department of Chemical and Biological Physics, Weizmann Institute of Science, Rehovot, Israel
| | - Adriana Reuveny
- Department of Molecular Genetics, Weizmann Institute of Science, Rehovot, Israel
| | - Francesco Roncato
- Department of Immunology Weizmann Institute of Science, Rehovot, Israel
| | - Ronen Alon
- Department of Immunology Weizmann Institute of Science, Rehovot, Israel
| | - Samuel Safran
- Department of Chemical and Biological Physics, Weizmann Institute of Science, Rehovot, Israel
| | - Talila Volk
- Department of Molecular Genetics, Weizmann Institute of Science, Rehovot, Israel
| |
Collapse
|
9
|
Abstract
Intact-organism imaging of Drosophila larvae reveals and quantifies chromatin-aqueous phase separation. The chromatin can be organized near the lamina layer of the nuclear envelope, conventionally fill the nucleus, be organized centrally, or as a wetting droplet. These transitions are controlled by changes in nuclear volume and the interaction of chromatin with the lamina (part of the nuclear envelope) at the nuclear periphery. Using a simple polymeric model that includes the key features of chromatin self-attraction and its binding to the lamina, we demonstrate theoretically that it is the competition of these two effects that determines the mode of chromatin distribution. The qualitative trends as well as the composition profiles obtained in our simulations compare well with the observed intact-organism imaging and quantification. Since the simulations contain only a small number of physical variables we can identify the generic mechanisms underlying the changes in the observed phase separations.
Collapse
|
10
|
Deviri D, Safran S. Physical Theory of Concentration Buffering in Multi-Component, Phase-Separating Systems. Biophys J 2021. [DOI: 10.1016/j.bpj.2020.11.768] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022] Open
|
11
|
Bajpai G, Pavlov DA, Lorber D, Volk T, Safran S. Mesoscale Phase Separation of Chromatin in the Nucleus. Biophys J 2021. [DOI: 10.1016/j.bpj.2020.11.2014] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022] Open
|
12
|
|
13
|
Deviri D, Strom AR, Karpen G, Safran S. Multivalency of Proteins and their Interactions Predict their Phase Separation. Biophys J 2020. [DOI: 10.1016/j.bpj.2019.11.496] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/13/2022] Open
|
14
|
Dasbiswas K, Hu S, Bershadsky AD, Safran S. Mechanical Force-Driven Registry of Non-Muscle Myosin in Fibroblasts. Biophys J 2020. [DOI: 10.1016/j.bpj.2019.11.2456] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/25/2022] Open
|
15
|
Deviri D, Strom AR, Colmenares S, Wilson S, Hickmann C, Karpen G, Safran S. Phase-Separation Driven Heterochromatin Formation: Experiment and Theory. Biophys J 2019. [DOI: 10.1016/j.bpj.2018.11.422] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/24/2022] Open
|
16
|
Cohen O, Safran S. Slow and Fast Time Scales in Cardiomyocyte Beating. Biophys J 2019. [DOI: 10.1016/j.bpj.2018.11.899] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/27/2022] Open
|
17
|
Hu S, Dasbiswas K, Guo Z, Tee YH, Thiagarajan V, Zaidel-Bar R, Hersen P, Safran S, Bershadsky AD. Two Levels of Myosin-IIA Dynamics in Cells: Turnover of Filaments and Self-Organization of Filament Stacks. Biophys J 2016. [DOI: 10.1016/j.bpj.2015.11.1077] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/22/2022] Open
|
18
|
Zedler U, Hampe N, Born S, Rubner W, Houben S, Kirchgeßner N, Hoffmann B, Safran S, Merkel R. Reaction of Primary Fibroblasts to Well Controlled External Strain. Biophys J 2010. [DOI: 10.1016/j.bpj.2009.12.4006] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022] Open
|
19
|
Gov N, Zilman AG, Safran S. Hydrodynamics of confined membranes. Phys Rev E Stat Nonlin Soft Matter Phys 2004; 70:011104. [PMID: 15324039 DOI: 10.1103/physreve.70.011104] [Citation(s) in RCA: 31] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 10/23/2003] [Revised: 05/03/2004] [Indexed: 05/24/2023]
Abstract
We calculate the hydrodynamic interaction Lambdak (Oseen interaction kernel) and relaxation frequency omegak for the fluctuations of a membrane that is harmonically bounded to a permeable or impermeable wall. We show that due to the confining wall there is an increase in the effective viscosity of the fluid surrounding the membrane. This has been observed in experiments on confined membranes, such as lamellar phases and the red-blood cell membrane. Our results allow a quantitative analysis of these experiments, in terms of the strength of the membrane confining potential and dislocations.
Collapse
Affiliation(s)
- N Gov
- Department of Materials and Interfaces, The Weizmann Institute of Science, P.O.B. 26, Rehovot, Israel 76100
| | | | | |
Collapse
|
20
|
Hellweg T, Gradzielski M, Farago B, Langevin D, Safran S. Reply to the comment on “Shape fluctuations of microemulsion droplets. A neutron spin-echo study” by V. Lisy. Colloids Surf A Physicochem Eng Asp 2003. [DOI: 10.1016/s0927-7757(03)00097-9] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [What about the content of this article? (0)] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/16/2022]
|
21
|
Abstract
We analyze theoretically both the static and dynamic fluctuation spectra of the red blood cell in a unified manner, using a simple model of the composite membrane. In this model, the two-dimensional spectrin network that forms the cytoskeleton is treated as a rigid shell, located at a fixed, average distance from the lipid bilayer. The cytoskeleton thereby confines both the static and dynamic fluctuations of the lipid bilayer. The sparse connections of the cytoskeleton and bilayer induce a surface tension, for wavelengths larger than the bilayer persistence length. The predictions of the model give a consistent account for both the wave vector and frequency dependence of the experimental data.
Collapse
Affiliation(s)
- N Gov
- Department of Materials and Interfaces, The Weizmann Institute of Science, P.O.B. 26, Rehovot, Israel 76100
| | | | | |
Collapse
|
22
|
Balaban NQ, Schwarz US, Riveline D, Goichberg P, Tzur G, Sabanay I, Mahalu D, Safran S, Bershadsky A, Addadi L, Geiger B. Force and focal adhesion assembly: a close relationship studied using elastic micropatterned substrates. Nat Cell Biol 2001; 3:466-72. [PMID: 11331874 DOI: 10.1038/35074532] [Citation(s) in RCA: 1406] [Impact Index Per Article: 61.1] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/04/2023]
Abstract
Mechanical forces play a major role in the regulation of cell adhesion and cytoskeletal organization. In order to explore the molecular mechanism underlying this regulation, we have investigated the relationship between local force applied by the cell to the substrate and the assembly of focal adhesions. A novel approach was developed for real-time, high-resolution measurements of forces applied by cells at single adhesion sites. This method combines micropatterning of elastomer substrates and fluorescence imaging of focal adhesions in live cells expressing GFP-tagged vinculin. Local forces are correlated with the orientation, total fluorescence intensity and area of the focal adhesions, indicating a constant stress of 5.5 +/- 2 nNmicrom(-2). The dynamics of the force-dependent modulation of focal adhesions were characterized by blocking actomyosin contractility and were found to be on a time scale of seconds. The results put clear constraints on the possible molecular mechanisms for the mechanosensory response of focal adhesions to applied force.
Collapse
Affiliation(s)
- N Q Balaban
- Department of Molecular Cell Biology, The Weizmann Institute of Science, Rehovot, Israel
| | | | | | | | | | | | | | | | | | | | | |
Collapse
|
23
|
Safran S. Lack of control group deemed problematic in fibromyalgia pilot study. Altern Ther Health Med 1998; 4:114, 116. [PMID: 9737036] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [MESH Headings] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/08/2023]
|
24
|
Abstract
We calculate the membrane-induced interaction between inclusions, in terms of the membrane stretching and bending moduli and the spontaneous curvature. We find that the membrane-induced interaction between inclusions varies nonmonotonically as a function of the inclusion spacing. The location of the energy minimum depends on the spontaneous curvature and the membrane perturbation decay length, where the latter is set by the membrane moduli. The membrane perturbation energy increases with the inclusion radius. The Ornstein-Zernike theory, with the Percus-Yevick closure, is used to calculate the radial distribution function of inclusions. We find that when the spontaneous curvature is zero, the interaction between inclusions due to the membrane deformation is qualitatively similar to the hard-core interaction. However, in the case of finite spontaneous curvature, the effective interaction is dramatically modified.
Collapse
Affiliation(s)
- H Aranda-Espinoza
- Instituto de Físcia, Universidad Autónoma de San Luis Potosi, Mexico.
| | | | | | | | | |
Collapse
|