Diese Arbeit wurde von NIH R01 EB014869 unterstützt.

1. Vorbereitung der Zellen für die Bildgebung
Hinweis: Die unmittelbaren Zwangs-Sonde (DFP) kann für adhärente Zelltypen jeglicher Art verwendet werden. Hier werden NIH-3 t 3-Maus-Fibroblasten als die Modell-Zell-Linie für dieses Protokoll verwendet.
<ol><li>Kultur NIH-3 t 3-fibroblastenzellen in Dulbeccos geändert Eagle Medium (DMEM) ergänzt mit 10 % Spender Rinderserum und 1 % Penicillin-Streptomycin auf einem 35-mm-Glasboden Schale bis zum gewünschten Konfluenz. Zellen bei 37 ° C und 5 % CO2zu erhalten.<ol>
<li>Achten Sie darauf, alle 35 mm unten Glasschalen mit 5 µg/mL Fibronektin (oder ähnliche ECM-Protein), Mantel vor der Aussaat NIH-3 t 3-Zellen für die Bildgebung. Hinweis: Die Zellen müssen vollständig verteilt und Anhänger auf dem Teller für das Experiment. Es gibt keine Einschränkungen in Bezug auf die Konfluenz für die DFP-Methode zu arbeiten.</li>
	</ol>
</li>
	<li>Unmittelbar vor dem Experiment waschen Sie die Zellen zweimal mit PBS gefolgt von einem einzigen waschen mit vollständigen Wachstumsmedium.</li>
	<li>Die untere Glasschale 3 mL komplette Wachstumsmedium hinzufügen.</li>
</ol>2. Mikroskopie und Bildaufnahme
Hinweis: Ein umgekehrtes Fluoreszenz Mikroskop (oder Äquivalent) mit Mikromanipulator auf den Seitenarm, entsprechend den Empfehlungen des Herstellers installiert. Das Mikroskop sollte auch mit einer Klimakammer weiterhin die Temperatur bei 37 ° C und CO-2 -Ebene mit 5 % ausgestattet werden. Ein Mikromanipulator und Microinjector mit dem Mikroskop verbunden ist ebenfalls erforderlich. Ein Öl-Immersion 40 X / 1,3 NA oder 60 X / 1,49 NA (oder gleichwertige Ziele) werden empfohlen für die Experimente. Das Mikroskop sollte auf einem Rütteltisch isoliert montiert werden.
<img alt="Figure 1" class="xfigimg" src="/files/ftp_upload/58038/58038fig1.jpg"> Abbildung 1 . Nukleare Verformung und Mikroskop mit Schwerpunkt A. maximale nukleare Verformung und Entspannung der nuklearen Verformung. Vor der Berechnung maximale nukleare Deformation, wurden die hinteren Kanten der nuklearen Formen zuerst fiel um für die Übersetzung von deformierten Kern zu korrigieren. Die Form des Kerns zum Zeitpunkt der Mikropipette Tipp Ablösung war vor dem abziehen auf nukleare Ausgangsform überlagert. Der Unterschied im Bereich zwischen den beiden Formen als Δ gemessen wurdeeine1. Die maximale nukleare Verformung wurde als ΔA1 geteilt durch die ursprünglichen nuklearen Bereich definiert. Auch ein zweiter Parameter, Δ2, kann durch die Überlagerung der endgültigen Steady-State nuclear Form nach Mikropipette Ablösung auf die nukleare Originalform definiert werden. B. konzentrieren sich die Zelle auf der Fläche A und Verschieben der Brennebene bis Ebene B Mikropipette Tipp zu finden. Während der Aufnahme, wurde die Mikropipette nach rechts (Richtung oranger Pfeil) übersetzt. Diese Zahl wurde von Neelam Et al.modifiziert. 15. <a href="https://www.jove.com/files/ftp_upload/58038/58038fig1large.jpg" target="_blank">Bitte klicken Sie hier für eine größere Version dieser Figur.</a>
<ol><li>Schalten Sie die Microinjector pro des Herstellers Protokoll.</li>
	<li>Tragen Sie mit einer eintauchen Öl Pipette einen einzigen Tropfen Immersionsöl auf das Objektiv.</li>
	<li>Klemmen Sie die Schüssel fest in die Schale Halter und laden Sie die Schale Halter auf die Bühne. Hinweis: Die Zellen bei 37 ° C und 5 % CO2 während des Experiments einzuhalten.</li>
	<li>Passen Sie die Höhe des Ziels, die Zellen in den Fokus (Ebene A, Abbildung 1 b) bringen.</li>
	<li>Bewegen Sie den Mikroskoptisch, eine Zelle von Interesse zu finden.</li>
	<li>Drehen Sie den Joystick auf der Mikromanipulator, pipettieren Halter an die oberste Position zu bewegen. Laden Sie die 0,5 µm Durchmesser Spitze Mikropipette auf den Halter pipettieren.<ol>
<li>Zur Vermeidung von Zelladhäsion, die Mikropipette Vorbehandeln der Mikropipette Spitze mit 0,3 mg/mL PLL-g-PEG-Lösung für 1 h bei Raumtemperatur. Haftung durch Berühren der Mikropipette in den Zellkern ohne Saug Druck, und dann übersetzen die Mikropipette vom Nucleus testen. Keine Haftung kann von einem völligen Mangel an nuklearen Verformung und Übersetzung erkannt werden. Hinweis: Führen Sie Herstellung Vorschläge, um das Paket zu öffnen.</li>
	</ol>
</li>
	<li>Erhöhen die objektiven Brennebene über Flugzeug A und am oberen Rand der Zelle nach Flugzeug B durch die Feinsteuerung einstellen (Abbildung 1 b, siehe Punkt 2.4).</li>
	<li>Legen Sie die Mikromanipulator auf grob Kontrolle. Bringen Sie langsam die Mikropipette bis Flugzeug B durch die Beobachtung für die Silhouette des mikropipette, bis die Mikropipette voll ins Blickfeld kommt.</li>
	<li>Sobald die Mikropipette Tipp korrekt ausgerichtet ist, soll der Mikromanipulator Feinsteuerung .</li>
	<li>Senken Sie das Ziel, die äquatorialebene der Zelle (Ebene A, Abbildung 1 b) und senken Sie die Mikropipette bis etwa 15 µm über Ebene A (Abb. 1 b, gestrichelten Mikropipette).</li>
	<li>Die Entschädigung Druck (P-c) auf die Microinjector auf den gewünschten Druck einstellen; warten Sie einige Sekunden für den Druck zu stabilisieren. Hinweis: Der optimale Druck-Sollwert richtet sich nach Zelltyp und die spezifischen Ziele des Experiments. In den meisten Fällen wäre 300 hPa ein guter Ausgangspunkt.</li>
	<li>Stellen Sie sicher, dass die Mikropipette nicht verstopft ist, mit Hilfe der Clean -Einstellung im Feld Mikromanipulator und überprüfen, um sicherzustellen, dass Luftblasen aus der Mikropipette Spitze entstehen.</li>
	<li>Führen Sie die Spitze in die Zelle durch eine schrittweise Senkung der Mikropipette bis die Spitze die nuklearen Oberfläche leicht berührt. Hinweis: Wenn die Mikropipette absenken, die Silhouette der Mikropipette Spitze wird klar, wie es in den Fokus kommt. Bevor die Mikropipette den Kern berührt, erhöhen Sie den Objektive Fokus zu und richten Sie die Mikropipette Spitze mit Kern (gleichen X-y-Koordinate, höheren Z-Ebene). Im Mittelpunkt der Äquatorebene des Kerns (Ebene A, Abbildung 1 b) zurück wieder und senken Sie allmählich die Mikropipette Spitze.</li>
	<li>Erstellen Sie eine Dichtung zwischen der Mikropipette Spitze und die Kernmembran durch das Trennen der Druck-Zuleitung von der Mikroinjektion System, und eröffnet damit die Mikropipette Rohrende in die Atmosphäre. Dieser Schritt schafft einen negativen Druck gleich Pc an der nuklearen Oberfläche.</li>
	<li>Bilder mit den Mikroskopen Bild Datenerfassungs-Software zu erwerben. Eine Avi-Erwerb (Video) oder Nd-Erwerb (Bilder) in der Bild-Datenerfassungs-Software einrichten. Hinweis: Für jede Imaging Software zu erwerben, eingerichtet in Echtzeit video Bildgebung oder Zeitraffer Bild Akquisitionen mit einem kurzen Zeitintervall.</li>
	<li>Umschalten auf das entsprechende Leuchtstoff imaging Channel (z. B. GFP, RFP, etc.) und Bildgebung zu beginnen.</li>
	<li>Übersetzen die Mikropipette Spitze vom Körper der Zelle (nach rechts, Abbildung 1 b) bis der Kern aus der Mikropipette löst. Hinweis: Ziehen Sie die Spitze entlang der positiven X-Richtung (nach rechts in das Blickfeld). Die ziehende Rate kann programmiert und gesteuert durch Computer oder der Joystick kann manuell verschoben werden. Haben wir nicht gefunden, eine Korrelation zwischen der ziehen-Rate und nukleare Verformung15 schlägt eine in erster Linie elastische Reaktion zu zwingen.</li>
</ol>(3) Datenanalyse
<ol><li>Führen Sie Bildanalyse mit grundlegenden Bildverarbeitungs-Software zur Verfügung. Das Ausmaß der nuklearen Verformung kann durch die Länge Belastung (Ɛ) oder der Bereich Belastung (Abbildung 1A) quantifiziert werden. Quantifizieren, Länge Belastung mit Formel 1, wo L und L0 darstellen bzw. die Länge des Kerns auf maximale Deformation und die ursprüngliche Position. <img alt="Equation 1" src="/files/ftp_upload/58038/58038eq1.jpg">(Gleichung 1)</li>
</ol>

<ol>
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M., Gruenbaum, Y. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=The+nuclear+lamina+and+heterochromatin:+a+complex+relationship.">The nuclear lamina and heterochromatin: a complex relationship.</a> Biochemical Society Transactions. 39 (6), 1705-1709 (2011).</li><li>Lammerding, J., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Lamins+A+and+C+but+not+lamin+B1+regulate+nuclear+mechanics.">Lamins A and C but not lamin B1 regulate nuclear mechanics.</a> Journal of Biological Chemistry. 281 (35), 25768-25780 (2006).</li><li>Dahl, K. N., Engler, A. J., Pajerowski, J. D., Discher, D. 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U. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=LINC+complexes+form+by+binding+of+three+KASH+peptides+to+domain+interfaces+of+trimeric+SUN+proteins.">LINC complexes form by binding of three KASH peptides to domain interfaces of trimeric SUN proteins.</a> Cell. 149 (5), 1035-1047 (2012).</li><li>Tapley, E. C., Starr, D. A. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Connecting+the+nucleus+to+the+cytoskeleton+by+SUN-KASH+bridges+across+the+nuclear+envelope.">Connecting the nucleus to the cytoskeleton by SUN-KASH bridges across the nuclear envelope.</a> Current Opinion in Cell Biology. 25 (1), 57-62 (2013).</li><li>Arsenovic, P. T., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Nesprin-2G,+a+Component+of+the+Nuclear+LINC+Complex,+Is+Subject+to+Myosin-Dependent+Tension.">Nesprin-2G, a Component of the Nuclear LINC Complex, Is Subject to Myosin-Dependent Tension.</a> Biophysical Journal. 110 (1), 34-43 (2016).</li><li>Rowat, A. C., Lammerding, J., Ipsen, J. H. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Mechanical+properties+of+the+cell+nucleus+and+the+effect+of+emerin+deficiency.">Mechanical properties of the cell nucleus and the effect of emerin deficiency.</a> Biophysical Journal. 91 (12), 4649-4664 (2006).</li><li>Rowat, A. C., Foster, L. J., Nielsen, M. M., Weiss, M., Ipsen, J. H. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Characterization+of+the+elastic+properties+of+the+nuclear+envelope.">Characterization of the elastic properties of the nuclear envelope.</a> Journal of the Royal Society Interface. 2 (2), 63-69 (2005).</li><li>Pagliara, S., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Auxetic+nuclei+in+embryonic+stem+cells+exiting+pluripotency.">Auxetic nuclei in embryonic stem cells exiting pluripotency.</a> Nature Materials. 13 (6), 638-644 (2014).</li><li>Liu, H., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=In+situ+mechanical+characterization+of+the+cell+nucleus+by+atomic+force+microscopy.">In situ mechanical characterization of the cell nucleus by atomic force microscopy.</a> ACS Nanotechnology. 8 (4), 3821-3828 (2014).</li><li>Krause, M., Te Riet, J., Wolf, K. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Probing+the+compressibility+of+tumor+cell+nuclei+by+combined+atomic+force-confocal+microscopy.">Probing the compressibility of tumor cell nuclei by combined atomic force-confocal microscopy.</a> Physical Biology. 10 (6), 065002 (2013).</li><li>Neelam, S., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Direct+force+probe+reveals+the+mechanics+of+nuclear+homeostasis+in+the+mammalian+cell.">Direct force probe reveals the mechanics of nuclear homeostasis in the mammalian cell.</a> Proceedings of the National Academy of Sciences of the United States of America. 112 (18), 5720-5725 (2015).</li><li>Pajerowski, J. D., Dahl, K. N., Zhong, F. L., Sammak, P. J., Discher, D. E. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Physical+plasticity+of+the+nucleus+in+stem+cell+differentiation.">Physical plasticity of the nucleus in stem cell differentiation.</a> Proceedings of the National Academy of Sciences of the United States of America. 104 (40), 15619-15624 (2007).</li><li>Lammerding, J., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Lamin+A/C+deficiency+causes+defective+nuclear+mechanics+and+mechanotransduction.">Lamin A/C deficiency causes defective nuclear mechanics and mechanotransduction.</a> Journal of Clinical Investigation. 113 (3), 370-378 (2004).</li><li>Chancellor, T. J., Lee, J., Thodeti, C. K., Lele, T. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Actomyosin+tension+exerted+on+the+nucleus+through+nesprin-1+connections+influences+endothelial+cell+adhesion,+migration,+and+cyclic+strain-induced+reorientation.">Actomyosin tension exerted on the nucleus through nesprin-1 connections influences endothelial cell adhesion, migration, and cyclic strain-induced reorientation.</a> Biophysical Journal. 99 (1), 115-123 (2010).</li><li>Neelam, S., Dickinson, R. B., Lele, T. P. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=New+approaches+for+understanding+the+nuclear+force+balance+in+living,+adherent+cells.">New approaches for understanding the nuclear force balance in living, adherent cells.</a> Methods. 94, 27-32 (2016).</li></ol>

Die Autoren haben nichts preisgeben.

Messung der mechanischen Integration des Kerns mit dem Zytoskelett ist eine Herausforderung für die aktuellsten Methoden, z. B. Mikropipette Anspruch16, weil sie entweder einzelne Kerne erfordern (wo ist der Kern von dem Zytoskelett entkoppelt) oder Kerne in den suspendierten Zellen (wo extrazelluläre Kräften wie Zugkräfte, fehlen). Auf den Kern wurde Kraft angewandt, indem biaxiale Beanspruchung auf Zellen Anhänger auf eine Membran17,18</s...

Krankheiten wie Krebs betreffen Änderungen an nuklearen Form und Struktur1,2, die in der Regel von einer Erweichung der Kern3,4begleitet werden. Nukleare Widerstand gegen mechanische Verformung hat in der Regel durch Krafteinwirkung auf isolierten Kernen5gekennzeichnet.
Kern in Zellen ist Molekular mit dem Zytoskelett der Linker Nucleoskeleton und Cytoskelett (LINC) komplexe6,7,8,9verbunden. Infolgedessen ist der Kern mechanisch mit dem Zytoskelett und durch Zelle-Substrat Verwachsungen, die extrazelluläre Matrix integriert. Mechanisch sondieren des Kerns im Inneren adhärente Zellen bieten einen Einblick in diese mechanischen Integration. Methoden der Kerne in lebenden Zellen zu manipulieren zählen Mikropipette Anspruch10,11und atomic Force Microscopy12,13,14. Wir beschrieben vor kurzem eine unmittelbaren Zwangs-Sonde (DFP), die mechanische Kräfte direkt auf den Kern in einem lebendigen adhärente Zellen15gilt.
Hier beschreiben wir das Verfahren für die Nutzung einer Mikroinjektion Systems, die häufig in Mikroskopie Einrichtungen, eine bekannte, Nano-Maßstab mechanische Kraft direkt in den Zellkern in eine adhärente Zellen anzuwenden. Ein Femtotip (0,5 µm Durchmesser Mikropipette Spitze) ist montiert und die Mikroinjektion System durch ein Rohr verbunden. Der Tipp, positioniert in einem 45° Winkel relativ zur Oberfläche der Kulturschale sinkt bis angrenzend an der nuklearen Oberfläche. Das Rohr ist dann nicht getrennt und die Atmosphäre, die schafft eines negativen Saugdruck an der nuklearen Oberfläche und dichtet die Mikropipette Spitze gegen die nukleare Oberfläche eröffnet. Durch die Übersetzung der Mikropipette Spitze ist der Kern verformt und schließlich (abhängig von der Größe der Krafteinwirkung), losgelöst von der Mikropipette. Diese Abteilung tritt auf, wenn die Rückstellkräfte (widerstehen), ausgeübt durch den Kern und die Zelle, die Saugkraft durch die Mikropipette aufgetragen gleich. Analyse kann erfolgen durch die Verschiebung des Kerns, Messung der Länge Dehnung (Gleichung 1) oder der Bereich Belastung (Abb. 1A).

<table><tbody><tr><td>FluoroDish</td><td>WPI</td><td>FD35</td><td></td></tr><tr><td>SYTO 59</td><td>ThermoFisher Scientific</td><td>S11341</td><td></td></tr><tr><td>Femtotips&amp;nbsp;</td><td>Eppendorf</td><td>930000043</td><td></td></tr><tr><td>InjectMan NI2</td><td>Eppendorf</td><td>NA</td><td>discontinued, current equivalent model: InjectMan 4</td></tr><tr><td>FemtoJet</td><td>Eppendorf</td><td>NA</td><td>Current model FemtoJet 4i</td></tr><tr><td>Plan Fluor oil immersion 40x</td><td>Nikon</td><td>NA</td><td></td></tr><tr><td>Apo TIRF oil immersion 60x</td><td>Nikon</td><td>NA</td><td></td></tr><tr><td>Donor Bovine Serum (DBS)</td><td>ThermoFisher Scientific</td><td>16030074</td><td>NIH 3T3 serum</td></tr><tr><td>Dulbecco&#039;s Modification of Eagle&#039;s (DMEM)</td><td>Mediatech cellgro</td><td>MT10013CVRF</td><td>NIH 3T3 medium</td></tr><tr><td>Penicillin-Streptomycin&amp;nbsp;</td><td>Mediatech</td><td>MT30004CIRF</td><td>NIH 3T3 medium supplement</td></tr><tr><td>Immersion Oil Type LDF Non-Fluorescing</td><td>Nikon</td><td>77007</td><td>Immersion oil for objective lens&amp;nbsp;</td></tr></tbody></table>

a direct force probe for measuring mechanical integration between the nucleus and the cytoskeleton

Die mechanischen Eigenschaften des Kerns bestimmen seine Reaktion auf mechanische Kräfte, die in den Zellen erzeugt. Da der Kern mit dem Zytoskelett Molekular kontinuierlich ist, werden Methoden benötigt, das mechanische Verhalten in adhärenten Zellen zu untersuchen. Hier diskutieren wir die unmittelbaren Zwangs-Sonde (DFP) als Instrument zur Kraft direkt in den Zellkern in lebenden adhärente Zellen anwenden. Wir legen einen schmalen Mikropipette zur nuklearen Oberfläche mit Absaugung. Die Mikropipette wird vom Nucleus, übersetzt, was bewirkt, den Kern dass zu verformen und zu übersetzen. Wenn die Rückstellkraft der Saugkraft entspricht, wird der Kern löst und elastisch entspannt. Da der Saugdruck genau bekannt ist, wird die Kraft auf die nukleare Oberfläche bezeichnet. Diese Methode hat ergeben, dass Nano-Maßstab Kräfte ausreichen, um zu verformen und übersetzen den Zellkern in adhärenten Zellen und identifiziert Zellskelett Elemente, mit die den Kern Kräften widerstehen können. Die DFP kann verwendet werden, um die Beiträge der zellulären und nuklearen Komponenten zur nuklearen mechanischen Eigenschaften in lebenden Zellen zu sezieren.

Abbildung 2A zeigt einem NIH-3 t 3 Maus Fibroblasten Kern zu zwingen. Die Mikropipette Spitze auf der rechten Seite übersetzt wird, der Kern verformt sich und löst sich schließlich von der Mikropipette Spitze. Die Länge Belastung des Kerns wird gesehen, mit zunehmender Saugkraft (Abb. 2 b) zu erhöhen. Die Vorderkante des Kerns (Mikropipette Kante ziehen) bildet eine nukleare Vorwölbung und die Hinterkante ist von seiner urs...

Watch this Scientific Journal Video about A Direct Force Probe for Measuring Mechanical Integration Between the Nucleus and the Cytoskeleton at JoVE.com

A Direct Force Probe for Measuring Mechanical Integration Between the Nucleus and the Cytoskeleton

Eine direkte Kraft-Sonde zur Messung der mechanischen Integration zwischen dem Kern und dem Zytoskelett

In diesem Protokoll beschreiben wir eine Mikropipette-Methode, um eine kontrollierte Kraft direkt in den Zellkern in einer lebenden Zelle anwenden. Dieser Test ermöglicht Verhör der nuklearen mechanischen Eigenschaften in der lebendigen, anhaftende Zelle.

The mechanical properties of the nucleus determine its response to mechanical forces generated in cells. Because the nucleus is molecularly continuous ...

a-direct-force-probe-for-measuring-mechanical-integration-between

Research

JoVE Journal

Biochemistry

15.1K Aufrufe.  University of Florida. In diesem Protokoll beschreiben wir eine Mikropipette-Methode, um eine kontrollierte Kraft direkt in den Zellkern in einer lebenden Zelle anwenden. Dieser Test ermöglicht Verhör der nuklearen mechanischen Eigenschaften in der lebendigen, anhaftende Zelle.

Serie: A Direct Force Probe for Measuring Mechanical Integration Between the Nucleus and the Cytoskeleton

Fluorescence Biomembrane Force Probe: Concurrent Quantitation of Receptor-ligand Kinetics and Binding-induced Intracellular Signaling on a Single Cell

Membrane receptor-ligand interactions mediate many cellular functions. Binding kinetics and downstream signaling triggered by these molecular interactions are likely affected by the mechanical environment in which binding and signaling take place. A recent study demonstrated that mechanical force can regulate antigen recognition by and triggering of the T-cell receptor (TCR). This was made possible by a new technology we developed and termed fluorescence biomembrane force probe (fBFP), which combines single-molecule force spectroscopy with fluorescence microscopy. Using an ultra-soft human red blood cell as the sensitive force sensor, a high-speed camera and real-time imaging tracking techniques, the fBFP is of ~1 pN (10-12 N), ~3 nm and ~0.5 msec in force, spatial and temporal resolution. With the fBFP, one can precisely measure single receptor-ligand binding kinetics under force regulation and simultaneously image binding-triggered intracellular calcium signaling on a single live cell. This new technology can be used to study other membrane receptor-ligand interaction and signaling in other cells under mechanical regulation.

We describe a technique for concurrently measuring force-regulated single receptor-ligand binding kinetics and real-time imaging of calcium signaling in a single T lymphocyte.

Fluoreszenz Biomembrane Kraft Sonde: Concurrent Quantifizierung von Rezeptor-Ligand-Kinetik und Binding-induzierte intrazelluläre Signaling auf Einzelzell

Membrane receptor-ligand interactions mediate many cellular functions. Binding kinetics and downstream signaling triggered by these molecular interactions ...

Forschung

Biotechnik

A Protocol for Using F&#246;rster Resonance Energy Transfer (FRET)-force Biosensors to Measure Mechanical Forces across the Nuclear LINC Complex

The LINC complex has been hypothesized to be the critical structure that mediates the transfer of mechanical forces from the cytoskeleton to the nucleus. Nesprin-2G is a key component of the LINC complex that connects the actin cytoskeleton to membrane proteins (SUN domain proteins) in the perinuclear space. These membrane proteins connect to lamins inside the nucleus. Recently, a F&#246;rster Resonance Energy Transfer (FRET)-force probe was cloned into mini-Nesprin-2G (Nesprin-TS (tension sensor)) and used to measure tension across Nesprin-2G in live NIH3T3 fibroblasts. This paper describes the process of using Nesprin-TS to measure LINC complex forces in NIH3T3 fibroblasts. To extract FRET information from Nesprin-TS, an outline of how to spectrally unmix raw spectral images into acceptor and donor fluorescent channels is also presented. Using open-source software (ImageJ), images are pre-processed and transformed into ratiometric images. Finally, FRET data of Nesprin-TS is presented, along with strategies for how to compare data across different experimental groups.

A number of FRET-based force biosensors have recently been developed, enabling the protein-specific resolution of intracellular force. In this protocol, we demonstrate how one of these sensors, designed for the linker of the nucleoskeleton-cytoskeleton (LINC) complex protein Nesprin-2G can be used to measure actomyosin forces on the nuclear LINC complex.

Ein Protokoll für die Verwendung von Förster Resonance Energy Transfer (FRET) -force Biosensoren mechanische Kräfte über den Kern LINC-Komplex zu messen

The LINC complex has been hypothesized to be the critical structure that mediates the transfer of mechanical forces from the cytoskeleton to the nucleus. ...

Direct Force Measurements of Subcellular Mechanics in Confinement using Optical Tweezers

During the development of a multicellular organism, a single fertilized cell divides and gives rise to multiple tissues with diverse functions. Tissue morphogenesis goes in hand with molecular and structural changes at the single cell level that result in variations of subcellular mechanical properties. As a consequence, even within the same cell, different organelles and compartments resist differently to mechanical stresses; and mechanotransduction pathways can actively regulate their mechanical properties. The ability of a cell to adapt to the microenvironment of the tissue niche thus is in part due to the ability to sense and respond to mechanical stresses. We recently proposed a new mechanosensation paradigm in which nuclear deformation and positioning enables a cell to gauge the physical 3D environment and endows the cell with a sense of proprioception to decode changes in cell shape. In this article, we describe a new method to measure the forces and material properties that shape the cell nucleus inside living cells, exemplified on adherent cells and mechanically confined cells. The measurements can be performed non-invasively with optical traps inside cells, and the forces are directly accessible through calibration-free detection of light momentum. This allows measuring the mechanics of the nucleus independently from cell surface deformations and allowing dissection of exteroceptive and interoceptive mechanotransduction pathways. Importantly, the trapping experiment can be combined with optical microscopy to investigate the cellular response and subcellular dynamics using fluorescence imaging of the cytoskeleton, calcium ions, or nuclear morphology. The presented method is straightforward to apply, compatible with commercial solutions for force measurements, and can easily be extended to investigate the mechanics of other subcellular compartments, e.g., mitochondria, stress-fibers, and endosomes.

Here, we present a protocol to investigate the intracellular mechanical properties of isolated embryonic zebrafish cells in three-dimensional confinement with direct force measurement by an optical trap.

Direkte Kraftmessungen der subzellulären Mechanik im Einschluss mit optischen Pinzetten

During the development of a multicellular organism, a single fertilized cell divides and gives rise to multiple tissues with diverse functions. Tissue ...

Entwicklungsbiologie

Measurement of Force-Sensitive Protein Dynamics in Living Cells Using a Combination of Fluorescent Techniques

Cells sense and respond to physical cues in their environment by converting mechanical stimuli into biochemically-detectable signals in a process called mechanotransduction. A crucial step in mechanotransduction is the transmission of forces between the external and internal environments. To transmit forces, there must be a sustained, unbroken physical linkage created by a series of protein-protein interactions. For a given protein-protein interaction, mechanical load can either have no effect on the interaction, lead to faster disassociation of the interaction, or even stabilize the interaction. Understanding how molecular load dictates protein turnover in living cells can provide valuable information about the mechanical state of a protein, in turn elucidating its role in mechanotransduction. Existing techniques for measuring force-sensitive protein dynamics either lack direct measurements of protein load or rely on the measurements performed outside of the cellular context. Here, we describe a protocol for the F&#246;rster resonance energy transfer-fluorescence recovery after photobleaching (FRET-FRAP) technique, which enables the measurement of force-sensitive protein dynamics within living cells. This technique is potentially applicable to any FRET-based tension sensor, facilitating the study of force-sensitive protein dynamics in variety of subcellular structures and in different cell types.

Here, we present a protocol for the simultaneous use of F&#246;rster resonance energy transfer-based tension sensors to measure protein load and fluorescence recovery after photobleaching to measure protein dynamics enabling the measurement of force-sensitive protein dynamics within living cells.

Messung von Kraft-und Kleinschreibung Proteindynamik in lebenden Zellen mit einer Kombination von fluoreszierenden Techniken

Cells sense and respond to physical cues in their environment by converting mechanical stimuli into biochemically-detectable signals in a process called ...

Biophysical Assays to Probe the Mechanical Properties of the Interphase Cell Nucleus: Substrate Strain Application and Microneedle Manipulation

In most eukaryotic cells, the nucleus is the largest organelle and is typically 2 to 10 times stiffer than the surrounding cytoskeleton; consequently, the physical properties of the nucleus contribute significantly to the overall biomechanical behavior of cells under physiological and pathological conditions. For example, in migrating neutrophils and invading cancer cells, nuclear stiffness can pose a major obstacle during extravasation or passage through narrow spaces within tissues.1 On the other hand, the nucleus of cells in mechanically active tissue such as muscle requires sufficient structural support to withstand repetitive mechanical stress. Importantly, the nucleus is tightly integrated into the cellular architecture; it is physically connected to the surrounding cytoskeleton, which is a critical requirement for the intracellular movement and positioning of the nucleus, for example, in polarized cells, synaptic nuclei at neuromuscular junctions, or in migrating cells.2 Not surprisingly, mutations in nuclear envelope proteins such as lamins and nesprins, which play a critical role in determining nuclear stiffness and nucleo-cytoskeletal coupling, have been shown recently to result in a number of human diseases, including Emery-Dreifuss muscular dystrophy, limb-girdle muscular dystrophy, and dilated cardiomyopathy.3 To investigate the biophysical function of diverse nuclear envelope proteins and the effect of specific mutations, we have developed experimental methods to study the physical properties of the nucleus in single, living cells subjected to global or localized mechanical perturbation. Measuring induced nuclear deformations in response to precisely applied substrate strain application yields important information on the deformability of the nucleus and allows quantitative comparison between different mutations or cell lines deficient for specific nuclear envelope proteins. Localized cytoskeletal strain application with a microneedle is used to complement this assay and can yield additional information on intracellular force transmission between the nucleus and the cytoskeleton. Studying nuclear mechanics in intact living cells preserves the normal intracellular architecture and avoids potential artifacts that can arise when working with isolated nuclei. Furthermore, substrate strain application presents a good model for the physiological stress experienced by cells in muscle or other tissues (e.g., vascular smooth muscle cells exposed to vessel strain). Lastly, while these tools have been developed primarily to study nuclear mechanics, they can also be applied to investigate the function of cytoskeletal proteins and mechanotransduction signaling.

We present two independent, microscope-based tools to measure the induced nuclear and cytoskeletal deformations in single, living adherent cells in response to global or localized strain application. These techniques are used to determine nuclear stiffness (i.e., deformability) and to probe intracellular force transmission between the nucleus and the cytoskeleton.

Biophysikalische Assays auf die mechanischen Eigenschaften der Interphase Zellkern Probe: Substrat Dehnungs-Anwendung und Mikronadel Manipulation

In most eukaryotic cells, the nucleus is the largest organelle and is typically 2 to 10 times stiffer than the surrounding cytoskeleton; consequently, the ...

Biologie

DNA Tension Probes to Map the Transient Piconewton Receptor Forces by Immune Cells

Mechanical forces transmitted at the junction between two neighboring cells and at the junction between cells and the extracellular matrix are critical for regulating many processes ranging from development to immunology. Therefore, developing the tools to study these forces at the molecular scale is critical. Our group developed a suite of molecular tension sensors to quantify and visualize the forces generated by cells and transmitted to specific ligands. The most sensitive class of molecular tension sensors are comprised of nucleic acid stem-loop hairpins. These sensors use fluorophore-quencher pairs to report on the mechanical extension and unfolding of DNA hairpins under force. One challenge with DNA hairpin tension sensors is that they are reversible with rapid hairpin refolding upon termination of the tension and thus transient forces are difficult to record. In this article, we describe the protocols for preparing DNA tension sensors that can be "locked" and prevented from refolding to enable "storing" of mechanical information. This allows for the recording of highly transient piconewton forces, which can be subsequently "erased" by the addition of complementary nucleic acids that remove the lock. This ability to toggle between real-time tension mapping and mechanical information storing reveals weak, short-lived, and less abundant forces, that are commonly employed by T cells as part of their immune functions.

This paper describes a detailed protocol for using DNA-based tension probes to image the receptor forces applied by immune cells. This approach can map receptor forces &gt;4.7pN in real-time and can integrate forces over time.

DNA-Spannungssonden zur Kartierung der transienten Piconewton-Rezeptor-Kräfte durch Immunzellen

Mechanical forces transmitted at the junction between two neighboring cells and at the junction between cells and the extracellular matrix are critical ...

Protrusion Force Microscopy: A Method to Quantify Forces Developed by Cell Protrusions

In numerous biological contexts, animal cells need to interact physically with their environment by developing mechanical forces. Among these, traction forces have been well-characterized, but there is a lack of techniques allowing the measurement of the protrusion forces exerted by cells orthogonally to their substrate. We designed an experimental setup to measure the protrusion forces exerted by adherent cells on their substrate. Cells plated on a compliant Formvar sheet deform this substrate and the resulting topography is mapped by atomic force microscopy (AFM) at the nanometer scale. Force values are then extracted from an analysis of the deformation profile based on the geometry of the protrusive cellular structures. Hence, the forces exerted by the individual protruding units of a living cell can be measured over time. This technique will enable the study of force generation and its regulation in the many cellular processes involving protrusion. Here, we describe its application to measure the protrusive forces generated by podosomes formed by human macrophages.

Here, we detail the experimental techniques used to evaluate the protrusion forces that podosomes apply on a compliant film, from the preparation of the film to the automated analysis of topographical images.

Vorsprung-Kraft-Mikroskopie: Eine Methode, um Kräfte entwickelt von Zelle Vorsprünge zu quantifizieren

In numerous biological contexts, animal cells need to interact physically with their environment by developing mechanical forces. Among these, traction ...

Isolating Myofibrils from Skeletal Muscle Biopsies and Determining Contractile Function with a Nano-Newton Resolution Force Transducer

Striated muscle cells are indispensable for the activity of humans and animals. Single muscle fibers are comprised of myofibrils, which consist of serially linked sarcomeres, the smallest contractile units in muscle. Sarcomeric dysfunction contributes to muscle weakness in patients with mutations in genes encoding for sarcomeric proteins. The study of myofibril mechanics allows for the assessment of actin-myosin interactions without potential confounding effects of damaged, adjacent myofibrils when measuring the contractility of single muscle fibers. Ultrastructural damage and misalignment of myofibrils might contribute to impaired contractility. If structural damage is present in the myofibrils, they likely break during the isolation procedure or during the experiment. Furthermore, studies in myofibrils provide the assessment of actin-myosin interactions in the presence of the geometrical constraints of the sarcomeres. For instance, measurements in myofibrils can elucidate whether myofibrillar dysfunction is the primary effect of a mutation in a sarcomeric protein. In addition, perfusion with calcium solutions or compounds is almost instant due to the small diameter of the myofibril. This makes myofibrils eminently suitable to measure the rates of activation and relaxation during force production. The protocol described in this paper employs an optical force probe based on the principle of a Fabry-P&#233;rot interferometer capable of measuring forces in the nano-Newton range, coupled to a piezo length motor and a fast-step perfusion system. This setup enables the study of myofibril mechanics with high resolution force measurements.

Presented here is a protocol to assess the contractile properties of striated muscle myofibrils with nano-Newton resolution. The protocol employs a setup with an interferometry-based, optical force probe. This setup generates data with a high signal-to-noise ratio and enables the assessment of the contractile kinetics of myofibrils.

Isolieren von Myofibrils von Skelettmuskelbiopsien und Bestimmung der Kontraktilenfunktion mit einem Nano-Newton Resolution Force Transducer

Striated muscle cells are indispensable for the activity of humans and animals. Single muscle fibers are comprised of myofibrils, which consist of ...

Directly Measuring Forces Within Reconstituted Active Microtubule Bundles

Microtubule networks are employed in cells to accomplish a wide range of tasks, ranging from acting as tracks for vesicle transport to working as specialized arrays during mitosis to regulate chromosome segregation. Proteins that interact with microtubules include motors such as kinesins and dynein, which can generate active forces and directional motion, as well as non-motor proteins that crosslink filaments into higher-order networks or regulate filament dynamics. To date, biophysical studies of microtubule-associated proteins have overwhelmingly focused on the role of single motor proteins needed for vesicle transport, and significant progress has been made in elucidating the force-generating properties and mechanochemical regulation of kinesins and dyneins. However, for processes in which microtubules act both as cargo and track, such as during filament sliding within the mitotic spindle, much less is understood about the biophysical regulation of ensembles of the crosslinking proteins involved. Here, we detail our methodology for directly probing force generation and response within crosslinked microtubule minimal networks reconstituted from purified microtubules and mitotic proteins. Microtubule pairs are crosslinked by proteins of interest, one microtubule is immobilized to a microscope coverslip, and the second microtubule is manipulated by an optical trap. Simultaneous total internal reflection fluorescence microscopy allows for multichannel visualization of all the components of this microtubule network as the filaments slide apart to generate force. We also demonstrate how these techniques can be used to probe pushing forces exerted by kinesin-5 ensembles and how viscous braking forces arise between sliding microtubule pairs crosslinked by the mitotic MAP PRC1. These assays provide insights into the mechanisms of spindle assembly and function and can be more broadly adapted to study dense microtubule network mechanics in diverse contexts, such as the axon and dendrites of neurons and polar epithelial cells.

Here, we present a protocol for reconstituting microtubule bundles in vitro and directly quantifying the forces exerted within them using simultaneous optical trapping and total internal reflection fluorescence microscopy. This assay allows for nanoscale-level measurement of the forces and displacements generated by protein ensembles within active microtubule networks.

Direkte Messung von Kräften innerhalb rekonstituierter aktiver Mikrotubulibündel

Microtubule networks are employed in cells to accomplish a wide range of tasks, ranging from acting as tracks for vesicle transport to working as ...

Combining 3D Magnetic Force Actuator and Multi-Functional Fluorescence Imaging to Study Nucleus Mechanobiology

A fundamental question in mechanobiology is how living cells sense extracellular mechanical stimuli in the context of cell physiology and pathology. The cellular mechano-sensation of extracellular mechanical stimuli is believed to be through the membrane receptors, the associated protein complex, and the cytoskeleton. Recent advances in mechanobiology demonstrate that the cell nucleus in cytoplasm itself can independently sense mechanical stimuli simultaneously. However, a mechanistic understanding of how the cell nucleus senses, transduces, and responds to mechanical stimuli is lacking, mainly because of the technical challenges in accessing and quantifying the nucleus mechanics by conventional tools. This paper describes the design, fabrication, and implementation of a new magnetic force actuator that applies precise and non-invasive 3D mechanical stimuli to directly deform the cell nucleus. Using CRISPR/Cas9-engineered cells, this study demonstrates that this tool, combined with high-resolution confocal fluorescent imaging, enables the revelation of the real-time dynamics of a mechano-sensitive yes-associated protein (YAP) in single cells as a function of nucleus deformation. This simple method has the potential to bridge the current technology gap in the mechanobiology community and provide answers to the knowledge gap that exists in the relation between nucleus mechanotransduction and cell function.

This study presents a new protocol to directly apply mechanical force on the cell nucleus through magnetic microbeads delivered into the cytoplasm and to conduct simultaneous live-cell fluorescent imaging.

Kombination von 3D-Magnetkraftaktor und multifunktionaler Fluoreszenzbildgebung zur Untersuchung der Kernmechanobiologie

A fundamental question in mechanobiology is how living cells sense extracellular mechanical stimuli in the context of cell physiology and pathology. The ...