Agradecemos al Dr. Till Böcking por el protocolo original de preparación de una sola molécula. 
Este trabajo fue apoyado por la subvención NSF 1121972(SS).

<ol>
	<li>Pang, H. -. B., 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=Virion+stiffness+regulates+immature+HIV-1+entry.">Virion stiffness regulates immature HIV-1 entry.</a> Retrovirology. 10, 4 (2013).</li><li>Kol, N., 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=A+Stiffness+Switch+in+Human+Immunodeficiency+Virus.">A Stiffness Switch in Human Immunodeficiency Virus.</a> Biophys. J. 92, 1777-1783 (2007).</li><li>Ortega-Esteban, A., 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=Minimizing+tip&#8211;sample+forces+in+jumping+mode+atomic+force+microscopy+in+liquid.">Minimizing tip&#8211;sample forces in jumping mode atomic force microscopy in liquid.</a> Ultramicroscopy. 114, 56-61 (2012).</li><li>Ortega-Esteban, A., 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=Monitoring+dynamics+of+human+adenovirus+disassembly+induced+by+mechanical+fatigue.">Monitoring dynamics of human adenovirus disassembly induced by mechanical fatigue.</a> Sci. Rep. 3, (2013).</li><li>Hernando-P&#233;rez, M., 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=Physical+Virology:+Direct+Measurement+of+Phage.">Physical Virology: Direct Measurement of Phage.</a> phi29 Stiffness Provides Evidence of Internal Pressure (Small 15/2012). Small. 8, 2365-2365 (2012).</li><li>Carrasco, C., 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=DNA-mediated+anisotropic+mechanical+reinforcement+of+a+virus.">DNA-mediated anisotropic mechanical reinforcement of a virus.</a> Proc. Natl. Acad. Sci. U.S.A. 103, 13706-13711 (2006).</li><li>Sofia, S. J., Premnath, V. V., Merrill, E. W. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Poly(ethylene+oxide)+Grafted+to+Silicon+Surfaces:+Grafting+Density+and+Protein+Adsorption.">Poly(ethylene oxide) Grafted to Silicon Surfaces: Grafting Density and Protein Adsorption.</a> Macromolecules. 31, 5059-5070 (1998).</li><li>Visnapuu, M. -. L., Duzdevich, D., Greene, E. C. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=The+importance+of+surfaces+in+single-molecule+bioscience.">The importance of surfaces in single-molecule bioscience.</a> Mol. Biosyst. 4, 394-403 (2008).</li><li>Elenko, M. P., Szostak, J. W., Van Oijen, A. M. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Single-molecule+binding+experiments+on+long+time+scales.">Single-molecule binding experiments on long time scales.</a> Rev. Sci. Instrum. 81, (2010).</li><li>van Oijen, A. M., 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=Single-Molecule+Kinetics+of+&#955;+Exonuclease+Reveal+Base+Dependence+and+Dynamic+Disorder.">Single-Molecule Kinetics of &#955; Exonuclease Reveal Base Dependence and Dynamic Disorder.</a> Science. 301, 1235-1238 (2003).</li><li>B&#246;cking, T., Aguet, F., Harrison, S. C., Kirchhausen, T. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Single-molecule+analysis+of+a+molecular+disassemblase+reveals+the+mechanism+of+Hsc70-driven+clathrin+uncoating.">Single-molecule analysis of a molecular disassemblase reveals the mechanism of Hsc70-driven clathrin uncoating.</a> Nat. Struct. Mol. Biol. 18, 295-301 (2011).</li><li>Cocucci, E., Aguet, F., Boulant, S., Kirchhausen, T. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=The+First+Five+Seconds+in+the+Life+of+a+Clathrin-Coated+Pit.">The First Five Seconds in the Life of a Clathrin-Coated Pit.</a> Cell. 150, 495-507 (2012).</li><li>Rust, M. J., Bates, M., Zhuang, X. W. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Sub-diffraction-limit+imaging+by+stochastic+optical+reconstruction+microscopy.">Sub-diffraction-limit imaging by stochastic optical reconstruction microscopy.</a> 3, 793-795 (2006).</li><li>Betzig, E., 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=Imaging+intracellular+fluorescent+proteins+at+nanometer+resolution.">Imaging intracellular fluorescent proteins at nanometer resolution.</a> Science. 313, 1642-1645 (2006).</li><li>Hess, S. T., Girirajan, T. P. K., Mason, M. D. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Ultra-High+Resolution+Imaging+by+Fluorescence+Photoactivation+Localization+Microscopy.">Ultra-High Resolution Imaging by Fluorescence Photoactivation Localization Microscopy.</a> Biophys. J. 91, 4258-4272 (2006).</li><li>Juette, M. F., 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=Three-dimensional+sub-100+nm+resolution+fluorescence+microscopy+of+thick+samples.">Three-dimensional sub-100 nm resolution fluorescence microscopy of thick samples.</a> Nat. Methods. 5, 527-529 (2008).</li><li>Xu, K., Zhong, G., Zhuang, X. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Actin,+Spectrin,+and+Associated+Proteins+Form+a+Periodic+Cytoskeletal+Structure+in+Axons.">Actin, Spectrin, and Associated Proteins Form a Periodic Cytoskeletal Structure in Axons.</a> Science. 339, 452-456 (2013).</li><li>Huang, B., Wang, W., Bates, M., Zhuang, X. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Three-Dimensional+Super-Resolution+Imaging+by+Stochastic+Optical+Reconstruction+Microscopy.">Three-Dimensional Super-Resolution Imaging by Stochastic Optical Reconstruction Microscopy.</a> Science. 319, 810-813 (2008).</li><li>Hodges, 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=Asymmetric+packaging+of+polymerases+within+vesicular+stomatitis+virus.">Asymmetric packaging of polymerases within vesicular stomatitis virus.</a> Biochemical and Biophysical Research Communications. 440, 271-276 (2013).</li><li>Lawson, N. D., Stillman, E. A., Whitt, M. A., Rose, J. K. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Recombinant+vesicular+stomatitis+viruses+from+DNA.">Recombinant vesicular stomatitis viruses from DNA.</a> Proc. Natl. Acad. Sci. U.S.A. 92, 4477-4481 (1995).</li></ol>

Los autores no tienen intereses financieros contrapuestos en este trabajo.

La proyección de imagen del solo virión con AFM y proyección de imagen de alta resolución de la fluorescencia se puede utilizar como metodología alternativa a la tomografía de CryoEM. Cada una de estas metodologías tiene sus fortalezas específicas. Por ejemplo, AFM se puede hacer en viriones WT sin necesidad de etiquetar la muestra o las proteínas virales internas. La localización de las estructuras virales se desconvía de sus contribuciones a las propiedades elásticas del virión.
Las imágenes de super-resolución de virión único en combinación con los enfoques genéticos inversos virales recientemente desarrollados se convierten en una técnica poderosa para localizar proteínas virales de bajo número de copias20. Los virus recombinantes con el reemplazo de sus proteínas con las proteínas fundidas a las proteínas fluorescentes se pueden hacer y purificar usando estos acercamientos genéticos reversos. Aunque las imágenes de súper resolución tienen especificidad en parte debido al etiquetado genético, requiere el uso de los virus mutantes.
AFM y la proyección de imagen de la super-resolución son los métodos complementarios que utilizan preparaciones muy similares de la muestra. Los métodos descritos en este documento, que se adoptan forman ensayos anteriores de imágenes de molécula única, permiten el anclaje de viriones individuales con pocos efectos sobre la topología de los viriones.

Las interacciones inespecíficas basadas en la carga se utilizan rutinariamente para la adhesión de viriones en microscopía de fuerza atómica1,2. Estas técnicas funcionan especialmente bien cuando se utilizan en viriones no enredados con cápsides muy rígidas3-6. Aunque estas técnicas son muy eficaces en la inmovilización de la muestra, no evitan la unión inespecífica de proteínas a la superficie. La unión inespecífica puede crear un problema al intentar obtener imágenes de viriones con AFM y técnicas de fluorescencia de súper resolución que requieren incubaciones de la muestra con varios anticuerpos. Aquí se describe un método de preparación de la muestra para la inmovilización específica de viriones.
Poli(etilenglicol) (PEG) injertado a poli(L-lisina) (PLL) y adsorbido sobre una superficie de vidrio proporciona un bloque significativo para las interacciones electrostáticas de proteínas con vidrio7. Los ensayos de moléculas individuales que requieren inmovilización de moléculas individuales en superficies de vidrio han aprovechado esta propiedad y la han utilizado para crear una técnica específica de inmovilización de molécula única basada en PEG8-10. Esta preparación también se utilizó para inmovilizar jaulas de clatrina en la superficie de vidrio11, así como para crear un recubrimiento homogéneo de fibronectina para el control de la adhesión celular 12.
Hemos adoptado el método de la preparación de la muestra basado en la adsorción de PLL-g-PEG a las superficies de cristal de metodologías de la proyección de imagen de una sola molécula y lo hemos aplicado a los solos viriones de la proyección de imagen del virus vesicular de la estomatitis (VSV). Estos viriones individuales fueron fotomicadas usando la microscopia de la fuerza atómica (AFM). También se realizaron experimentos similares en perlas funcionalizadas como control. Los viriones también fueron foto fotomicadas por microscopía de fluorescencia de súper resolución si se utilizó un anticuerpo VSV-G etiquetado con Alexa 647 para crear una imagen de la envoltura de viriones individuales. Imágenes fluorescentes de alta resolución utiliza la localización de moléculas individuales para crear una imagen13-15. La imagen biplanar de fPALM permite la localización de moléculas individuales con 20 nm en plano y 50 nm de resolución a lo largo del eje óptico15,16. Esta técnica bi-planar fue utilizada para las imágenes fluorescentes de la super-resolución de la imagen presentes en este estudio. Una técnica alternativa que tiene resultados similares es STORM13,17,18.
Tanto AFM como imágenes fluorescentes de súper resolución de VSV ancladas al vidrio por los procedimientos descritos en este trabajo, mostraron una unión específica de viriones al vidrio con mínimas interacciones inespecíficas19. Aquí presentamos los protocolos de preparación de muestras para el AFM y experimentos de imágenes fluorescentes de súper resolución. En resumen: Las tapas de vidrio limpio se funcionalizan mediante la adsorber una mezcla de PLL-g-PEG y PLL-g-PEG-biotina. Es típico que esta película delgada esté diseñada para proporcionar entre un 15-25% de biotina funcionalizada en una superficie recubierta. Los cubrebocas se incuban además con avidina tetramérica. Un anticuerpo viral biotinilado entonces se utiliza para crear un sitio de unión único para los viriones. La unión del anticuerpo se puede hacer de dos maneras.
El primer método está optimizado para AFM, sin embargo, sigue siendo adecuado para imágenes de fluorescencia de súper resolución. En este método la superficie recubierta de avidina se trata con anticuerpos biotinilados antes de la adhesión viral. Los viriones inmovilizados se tratan con el anticuerpo etiquetado Alexa 647 para cubrir la envoltura y permitir imágenes de fluorescencia de súper resolución de los viriones.
El segundo método es atacar el virus en solución con el anticuerpo biotinilado y el anticuerpo etiquetado alexa 647 antes de adherir los virus a la superficie tratada con avidina; este método está optimizado para experimentos de imágenes de fluorescencia de súper resolución en los que la recuperación de la envoltura viral es importante. Este método tiene la ventaja de permitir un recubrimiento uniforme de anticuerpos en la superficie viral. El anticuerpo biotinilado se puede mezclar con anticuerpos virales etiquetados alexa 647 en proporciones que permiten suficiente adsorción del virus a la superficie tratada con avidina mientras se mantiene una alta concentración de etiqueta fluorescente en el exterior de la envoltura viral. Estos anticuerpos virales etiquetados con Alexa 647 no están biotinilados y su exceso puede enjuagarse para reducir el ruido de fondo.

<table border="0" cellpadding="0" cellspacing="0" width="573">
	<colgroup>
		<col />
		<col />
		<col />
		<col />
	</colgroup>
	<tbody>
		<tr height="84">
			<td height="84" style="height:84px;width:216px;">Glass coverslips (fPALM)</td>
			<td style="width:71px;">Electron Microscopy Services</td>
			<td style="width:119px;">72225-01</td>
			<td style="width:167px;">25 mm Coverslips</td>
		</tr>
		<tr height="42">
			<td height="42" style="height:42px;width:216px;">PLL(20)-g[3.5]-PEG(2)/PEG(3.4)-Biotin (20%)&#160;</td>
			<td style="width:71px;">SuSoS&#160;</td>
			<td style="width:119px;">-</td>
			<td style="width:167px;">Stock: 0.5 mg/ml in PBS</td>
		</tr>
		<tr height="42">
			<td height="42" style="height:42px;width:216px;">NeutrAvidin biotin-binding protein</td>
			<td style="width:71px;">Invitrogen</td>
			<td style="width:119px;">A2666</td>
			<td style="width:167px;">Stock: 0.25 mg/ml in PBS</td>
		</tr>
		<tr height="60">
			<td height="60" style="height:60px;width:216px;">Alexa Fluor 647 goat anti-rabbit IgG (H+L)&#160;</td>
			<td style="width:71px;">Invitrogen</td>
			<td style="width:119px;">A21245</td>
			<td style="width:167px;">1:200 in 0.2 M KPO4, 0.15 M NaCl, 10% Glycol, pH 7.2 buffer</td>
		</tr>
		<tr height="84">
			<td height="84" style="height:84px;width:216px;">&#945;-VSV-G&#160;</td>
			<td style="width:71px;">Invitrogen</td>
			<td style="width:119px;">ab34774</td>
			<td style="width:167px;">1:200 in 0.2 M KPO4, 0.15 M NaCl, 10% Glycol, pH 7.2 buffer</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;">Gluox</td>
			<td style="width:71px;">Sigma</td>
			<td>G2133-250KU&#160;</td>
			<td>Glucose oxidase type seven from Aspergillius&#160;</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;">Catalase</td>
			<td style="width:71px;">Sigma</td>
			<td style="width:119px;">C40-100mg&#160;</td>
			<td>Catalase from Bovine liver&#160;</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;">MEA</td>
			<td style="width:71px;">Sigma</td>
			<td>30070-10G&#160;</td>
			<td>Cysteamine (MEA</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;">Stock Buffer</td>
			<td style="width:71px;"></td>
			<td style="width:119px;"></td>
			<td>50 mM Tris-HCl (pH 8.0) + 10 mM NaCl + 10% glucose</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:216px;">NTE</td>
			<td style="width:71px;"></td>
			<td style="width:119px;"></td>
			<td>10 mM Tris pH 7.4, 100 mM NaCl, 66 mM EDTA</td>
		</tr>
		<tr height="42">
			<td height="42" style="height:42px;">Slide-A-Lyzer, mini dialysis unit</td>
			<td style="width:71px;">Thermo Scientific</td>
			<td style="width:119px;"></td>
			<td>10,000 MW</td>
		</tr>
		<tr height="42">
			<td height="42" style="height:42px;">Microscope Cover Glass: 35 CIRCLE #1</td>
			<td style="width:71px;">Fisherbrand</td>
			<td style="width:119px;">35 CIRCLE #1</td>
			<td style="width:167px;"></td>
		</tr>
	</tbody>
</table>

sample preparation for single virion atomic force microscopy and super-resolution fluorescence imaging

La inmovilización de viriones a superficies de vidrio es un paso crítico en la proyección de imagen de un solo virión. Aquí presentamos una técnica adoptada de ensayos de imágenes de una sola molécula que permite la adhesión de viriones individuales a superficies de vidrio con especificidad. Esta preparación se basa en injertar la superficie del vidrio con una mezcla de PLL-g-PEG y PLL-g-PEG-Biotina, añadir una capa de avidina, y finalmente crear anclajes de virión a través de la unión de anticuerpos específicos del virus biotinilado. Hemos aplicado esta técnica a través de una gama de experimentos incluyendo la microscopia de la fuerza atómica (AFM) y la proyección de imagen de la fluorescencia de la super-resolución. Este método de preparación de la muestra da como resultado una adhesión de control de los viriones a la superficie.

Imágenes de virión único usando AFM:
El protocolo de preparación de muestras descrito anteriormente se utilizó en el anclaje de viriones de tipo salvaje a la superficie de vidrio. Los viriones VSV tienen forma de bala de 180 nm de longitud y 80 nm de diámetro. Como hay una variedad de viriones para los que se puede aplicar esta técnica, el concepto también se demuestra aquí en perlas biotiniladas de 36 nm también. Los experimentos AFM resultantes se muestran en la Figura 1. Es importante tener en cuenta que los viriones VSV tienen un módulo de Young más bajo (100 MPa) en comparación con los virus no envopados (GPa). Las imágenes particulares de un solo virión VSV se obtuvieron en modo de tapping en condiciones ambientales con un voladizo rígido. El objetivo ha sido deformar el virus hasta el punto de que la densidad de proteínas adicionales dentro del virus se hace visible como una protuberancia dentro de la imagen AFM. Este método se utiliza para detectar la densidad extra de proteínas dentro de la cavidad del virus19.
Imágenes de super resolución de virión único:
Alexa 647 etiquetado VSV-G anticuerpos se utilizaron para recubrir la envoltura de viriones VSV individuales para experimentos de súper resolución utilizando el método 5A. Para demostrar la densidad de ataduras y la baja unión inespecífica, se muestra un escaneo grande de la muestra en la Figura 2A. La recuperación de la envoltura viral en un virión representativo se muestra en la Figura 2B (isosuperficie azul).
<img alt="Figure 1" fo:content-width="5in" fo:src="/files/ftp_upload/51366/51366fig1highres.jpg" src="/files/ftp_upload/51366/51366fig1.jpg" style="opacity: 0.9; font-size: 14.399999618530273px; line-height: 28px;">
Figura 1. Proyección de imagen de AFM de cuentas y de VSV en la superficie funcionalizada de PEGG. Exploración de AFM de los granos biotinylated de 36 nanómetro(A, B)y de un virion de VSV(c)anclado a la superficie con un anticuerpo biotinylated de VSVG. AFM se realizó en modo de exploración de topografía de aire ac. El radio de la punta es de <25 nm y las mediciones se llevaron a cabo bajo modulación de fuerza y golpecito de luz. La punta tenía una constante de fuerza de 3 N/m y una frecuencia resonante de 75 kHz con una incertidumbre de 15 kHz. Mientras que las perlas conservaron su altura durante la exploración AFM, el virión VSV tiene un módulo de jóvenes significativamente más pequeño y está significativamente deformado en altura. En esta imagen, el virión fue fotoficado específicamente con un voladizo rígido en modo tapping que produjo una pequeña convolución xy (utilizada para determinar la punta vs extremo romo del virus) y la diferencia de altura entre la punta y el extremo romo del virus se utiliza para detectar densidad de proteínas adicionales en el extremo romo del virus19.
<img alt="Figure 2" fo:content-width="5in" fo:src="/files/ftp_upload/51366/51366fig2highres.jpg" src="/files/ftp_upload/51366/51366fig2.jpg"> Figura 2. Fluorescencia basada en imágenes de viriones VSV en la superficie funcionalizada PEGG. A)viriones recombinantes de VSV inmovilizados en la superficie de PEGG utilizando un anticuerpo anti VSVG biotinilado fotoizado en fluorescencia de amplio campo. B)Reconstrucción de fluorescencia de alta resolución de la envoltura de VSV unida a la superficie de PEGG a través de un anticuerpo anti VSVG biotinilado y decorado con anticuerpos anti-VSVG etiquetados con Alexa 647 (se utilizó el Método 5A para la creación de estas imágenes). La superficie azul es una proyección isosuperficial 2D. La izquierda muestra un modelo del virus en forma de bala. 
<table border="0" cellpadding="0" cellspacing="0" width="212"><colgroup>
<col>
<col>
</colgroup>
<tbody>
<tr height="27">
<td height="27" style="height:27px;width:119px;">Tamaño de la la ficha de cubierta</td>
			<td style="width:93px;">fluido</td>
		</tr>
<tr height="20">
<td height="20" style="height:20px;">40 milímetros</td>
			<td>65 μl</td>
		</tr>
<tr height="20">
<td height="20" style="height:20px;">35 milímetros</td>
			<td>50 μl</td>
		</tr>
<tr height="20">
<td height="20" style="height:20px;">30 milímetros</td>
			<td>36 μl</td>
		</tr>
<tr height="20">
<td height="20" style="height:20px;">25 milímetros</td>
			<td>25 μl</td>
		</tr>
<tr height="20">
<td height="20" style="height:20px;">20 milímetros</td>
			<td>16 μl</td>
		</tr>
</tbody></table>Tabla 1. Alícuotas fluidas según el tamaño del cubrecubos.

Watch this Scientific Journal Video about Sample Preparation for Single Virion Atomic Force Microscopy and Super-resolution Fluorescence Imaging at JoVE.com

Sample Preparation for Single Virion Atomic Force Microscopy and Super-resolution Fluorescence Imaging

La unión de viriones a una superficie es un requisito para la obtención de imágenes de viriones individuales mediante imágenes de fluorescencia de súper resolución o microscopía de fuerza atómica (AFM). Aquí se demuestra un método de preparación de la muestra para la adhesión controlada de viriones a las superficies de vidrio adecuado para su uso en AFM y super-resolución de imágenes de fluorescencia.

Preparación de muestras para microscopía de fuerza atómica de virión único e imágenes de fluorescencia de súper resolución

Immobilization of virions to glass surfaces is a critical step in single virion imaging. Here we present a technique&#160;adopted from single molecule ...

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Biology

9.4K vistas.  University of Utah. La unión de viriones a una superficie es un requisito para la obtención de imágenes de viriones individuales mediante imágenes de fluorescencia de súper resolución o microscopía de fuerza atómica (AFM). Aquí se demuestra un método de preparación de la muestra para la adhesión controlada de viriones a las superficies de vidrio adecuado para su uso en AFM y super-resolución de imágenes de fluorescencia.

Video: Sample Preparation for Single Virion Atomic Force Microscopy and Super-resolution Fluorescence Imaging

Time-lapse Imaging of Mitosis After siRNA Transfection

Changes in cellular organization and chromosome dynamics that occur during mitosis are tightly coordinated to ensure accurate inheritance of genomic and cellular content. Hallmark events of mitosis, such as chromosome movement, can be readily tracked on an individual cell basis using time-lapse fluorescence microscopy of mammalian cell lines expressing specific GFP-tagged proteins. In combination with RNAi-based depletion, this can be a powerful method for pinpointing the stage(s) of mitosis where defects occur after levels of a particular protein have been lowered. In this protocol, we present a basic method for assessing the effect of depleting a potential mitotic regulatory protein on the timing of mitosis. Cells are transfected with siRNA, placed in a stage-top incubation chamber, and imaged using an automated fluorescence microscope. We describe how to use software to set up a time-lapse experiment, how to process the image sequences to make either still-image montages or movies, and how to quantify and analyze the timing of mitotic stages using a cell-line expressing mCherry-tagged histone H2B. Finally, we discuss important considerations for designing a time-lapse experiment. This strategy is complementary to other approaches and offers the advantages of 1) sensitivity to changes in kinetics that might not be observed when looking at cells as a population and 2) analysis of mitosis without the need to synchronize the cell cycle using drug treatments. The visual information from such imaging experiments not only allows the sub-stages of mitosis to be assessed, but can also provide unexpected insight that would not be apparent from cell cycle analysis by FACS.

Here we describe a basic protocol to image and quantify the mitotic timing of live mammalian tissue culture cells after siRNA transfection.

Time-lapse de imágenes de mitosis después de la transfección de siRNA

Changes in cellular organization and chromosome dynamics that occur during mitosis are tightly coordinated to ensure accurate inheritance of genomic and ...

Investigación

Biología

Super-resolution Imaging of the Bacterial Division Machinery

Bacterial cell division requires the coordinated assembly of more than ten essential proteins at midcell1,2. Central to this process is the formation of a ring-like suprastructure (Z-ring) by the FtsZ protein at the division plan3,4. The Z-ring consists of multiple single-stranded FtsZ protofilaments, and understanding the arrangement of the protofilaments inside the Z-ring will provide insight into the mechanism of Z-ring assembly and its function as a force generator5,6. This information has remained elusive due to current limitations in conventional fluorescence microscopy and electron microscopy. Conventional fluorescence microscopy is unable to provide a high-resolution image of the Z-ring due to the diffraction limit of light (~200 nm). Electron cryotomographic imaging has detected scattered FtsZ protofilaments in small C. crescentus cells7, but is difficult to apply to larger cells such as E. coli or B. subtilis. Here we describe the application of a super-resolution fluorescence microscopy method, Photoactivated Localization Microscopy (PALM), to quantitatively characterize the structural organization of the E. coli Z-ring8.
	PALM imaging offers both high spatial resolution (~35 nm) and specific labeling to enable unambiguous identification of target proteins. We labeled FtsZ with the photoactivatable fluorescent protein mEos2, which switches from green fluorescence (excitation = 488 nm) to red fluorescence (excitation = 561 nm) upon activation at 405 nm9. During a PALM experiment, single FtsZ-mEos2 molecules are stochastically activated and the corresponding centroid positions of the single molecules are determined with &lt;20 nm precision. A super-resolution image of the Z-ring is then reconstructed by superimposing the centroid positions of all detected FtsZ-mEos2 molecules.
	Using this method, we found that the Z-ring has a fixed width of ~100 nm and is composed of a loose bundle of FtsZ protofilaments that overlap with each other in three dimensions. These data provide a springboard for further investigations of the cell cycle dependent changes of the Z-ring10 and can be applied to other proteins of interest.

We describe a super-resolution imaging method to probe the structural organization of the bacterial FtsZ-ring, an essential apparatus for cell division. This method is based on quantitative analyses of photoactivated localization microscopy (PALM) images and can be applied to other bacterial cytoskeletal proteins.

Super-resolución de imagen de la maquinaria de división bacteriana

Bacterial cell division requires the coordinated  assembly of more than ten essential proteins at midcell1,2. Central  to this process is the formation of ...

Test Samples for Optimizing STORM Super-Resolution Microscopy

STORM is a recently developed super-resolution microscopy technique with up to 10 times better resolution than standard fluorescence microscopy techniques. However, as the image is acquired in a very different way than normal, by building up an image molecule-by-molecule, there are some significant challenges for users in trying to optimize their image acquisition. In order to aid this process and gain more insight into how STORM works we present the preparation of 3 test samples and the methodology of acquiring and processing STORM super-resolution images with typical resolutions of between 30-50 nm. By combining the test samples with the use of the freely available rainSTORM processing software it is possible to obtain a great deal of information about image quality and resolution. Using these metrics it is then possible to optimize the imaging procedure from the optics, to sample preparation, dye choice, buffer conditions, and image acquisition settings. We also show examples of some common problems that result in poor image quality, such as lateral drift, where the sample moves during image acquisition and density related problems resulting in the 'mislocalization' phenomenon.

We describe the preparation of three test samples and how they can be used to optimize and assess the performance of STORM microscopes. Using these examples we show how to acquire raw data and then process it to acquire super-resolution images in cells of approximately 30-50 nm resolution.

Las muestras de prueba para optimizar STORM Super-Resolución de Microscopía

STORM is a recently developed super-resolution microscopy technique with up to 10 times better resolution than standard fluorescence microscopy ...

Rapid Analysis and Exploration of Fluorescence Microscopy Images

Despite rapid advances in high-throughput microscopy, quantitative image-based assays still pose significant challenges. While a variety of specialized image analysis tools are available, most traditional image-analysis-based workflows have steep learning curves (for fine tuning of analysis parameters) and result in long turnaround times between imaging and analysis. In particular, cell segmentation, the process of identifying individual cells in an image, is a major bottleneck in this regard.
Here we present an alternate, cell-segmentation-free workflow based on PhenoRipper, an open-source software platform designed for the rapid analysis and exploration of microscopy images. The pipeline presented here is optimized for immunofluorescence microscopy images of cell cultures and requires minimal user intervention. Within half an hour, PhenoRipper can analyze data from a typical 96-well experiment and generate image profiles. Users can then visually explore their data, perform quality control on their experiment, ensure response to perturbations and check reproducibility of replicates. This facilitates a rapid feedback cycle between analysis and experiment, which is crucial during assay optimization. This protocol is useful not just as a first pass analysis for quality control, but also may be used as an end-to-end solution, especially for screening. The workflow described here scales to large data sets such as those generated by high-throughput screens, and has been shown to group experimental conditions by phenotype accurately over a wide range of biological systems. The PhenoBrowser interface provides an intuitive framework to explore the phenotypic space and relate image properties to biological annotations. Taken together, the protocol described here will lower the barriers to adopting quantitative analysis of image based screens.

Here we describe a workflow for rapidly analyzing and exploring collections of fluorescence microscopy images using PhenoRipper, a recently developed image-analysis platform.

Análisis rápido y exploración de microscopía de fluorescencia de Imágenes

Despite rapid advances in high-throughput microscopy, quantitative image-based assays still pose significant challenges. While a variety of specialized ...

Open-source Single-particle Analysis for Super-resolution Microscopy with VirusMapper

Super-resolution fluorescence microscopy is currently revolutionizing cell biology research. Its capacity to break the resolution limit of around 300 nm allows for the routine imaging of nanoscale biological complexes and processes. This increase in resolution also means that methods popular in electron microscopy, such as single-particle analysis, can readily be applied to super-resolution fluorescence microscopy. By combining this analytical approach with super-resolution optical imaging, it becomes possible to take advantage of the molecule-specific labeling capacity of fluorescence microscopy to generate structural maps of molecular elements within a metastable structure. To this end, we have developed a novel algorithm &#8212; VirusMapper &#8212; packaged as an easy-to-use, high-performance, and high-throughput ImageJ plugin. This article presents an in-depth guide to this software, showcasing its ability to uncover novel structural features in biological molecular complexes. Here, we present how to assemble compatible data and provide a step-by-step protocol on how to use this algorithm to apply single-particle analysis to super-resolution images.

This manuscript uses the Fiji-based open-source software package VirusMapper to apply single-particle analysis to super-resolution microscopy images in order to generate precise models of nanoscale structure.

Análisis de una sola partícula de código abierto para el Super-resolución Microscopía con VirusMapper

Super-resolution fluorescence microscopy is currently revolutionizing cell biology research. Its capacity to break the resolution limit of around 300 nm ...

Ground State Depletion Super-resolution Imaging in Mammalian Cells

Advances in fluorescent microscopy and cell biology are intimately correlated, with the enhanced ability to visualize cellular events often leading to dramatic leaps in our understanding of how cells function. The development and availability of super-resolution microscopy has considerably extended the limits of optical resolution from ~250-20 nm. Biologists are no longer limited to describing molecular interactions in terms of colocalization within a diffraction limited area, rather it is now possible to visualize the dynamic interactions of individual molecules. Here, we outline a protocol for the visualization and quantification of cellular proteins by ground-state depletion microscopy&#160;for fixed cell imaging. We provide examples from two different membrane proteins, an element of the endoplasmic reticulum translocon, sec61&#946;, and a plasma membrane-localized voltage-gated L-type Ca2+ channel (CaV1.2). Discussed are the specific microscope parameters, fixation methods, photo-switching buffer formulation, and pitfalls and challenges of image processing.

This article outlines a protocol for the detection of one or more plasma and/or intracellular membrane proteins using Ground State Depletion (GSD) super-resolution microscopy in mammalian cells. Here, we discuss the benefits and considerations of using such approaches for the visualization and quantification of cellular proteins.

La proyección de imagen de resolución súper Estado de agotamiento de la tierra en células de mamíferos

Advances in fluorescent microscopy and cell biology are intimately correlated, with the enhanced ability to visualize cellular events often leading to ...

Sample Preparation and Imaging of Exosomes by Transmission Electron Microscopy

Exosomes are nano-sized extracellular vesicles secreted by body fluids and are known to represent the characteristics of cells that secrete them. The contents and morphology of the secreted vesicles reflect cell behavior or physiological status, for example cell growth, migration, cleavage, and death. The exosomes&#39; role may depend highly on size, and the size of exosomes varies from 30 to 300 nm. The most widely used method for exosome imaging is negative staining, while other results are based on Cryo-Transmission Electron Microscopy, Scanning Electron Microscopy, and Atomic Force Microscopy. The typical exosome&#39;s morphology assessed through negative staining is a cup-shape, but further details are not yet clear. An exosome well-characterized through structural study is necessary particular in medical and pharmaceutical fields. Therefore, function-dependent morphology should be verified by electron microscopy techniques such as labeling a specific protein in the detailed structure of exosome. To observe detailed structure, ultrathin sectioned images and negative stained images of exosomes were compared. In this protocol, we suggest transmission electron microscopy for the imaging of exosomes including negative staining, whole mount immuno-staining, block preparation, thin section, and immuno-gold labelling.

This protocol describes the various techniques necessary for transmission electron microscopy including negative staining, ultrathin sectioning for detailed structure, and immuno-gold labelling to determine the positions of specific proteins in exosomes.

Preparación de la muestra y proyección de imagen de exosomas por microscopía electrónica de transmisión

Exosomes are nano-sized extracellular vesicles secreted by body fluids and are known to represent the characteristics of cells that secrete them. The ...

Miniaturized Sample Preparation for Transmission Electron Microscopy

Due to recent technological progress, cryo-electron microscopy (cryo-EM) is rapidly becoming a standard method for the structural analysis of protein complexes to atomic resolution. However, protein isolation techniques and sample preparation methods for EM remain a bottleneck. A relatively small number (100,000 to a few million) of individual protein particles need to be imaged for the high-resolution analysis of proteins by the single particle EM approach, making miniaturized sample handling techniques and microfluidic principles feasible.
A miniaturized, paper-blotting-free EM grid preparation method for sample pre-conditioning, EM grid priming and post processing that only consumes nanoliter-volumes of sample is presented. The method uses a dispensing system with sub-nanoliter precision to control liquid uptake and EM grid priming, a platform to control the grid temperature thereby determining the relative humidity above the EM grid, and a pick-and-plunge-mechanism for sample vitrification. For cryo-EM, an EM grid is placed on the temperature-controlled stage and the sample is aspirated into a capillary. The capillary tip is positioned in proximity to the grid surface, the grid is loaded with the sample and excess is re-aspirated into the microcapillary. Subsequently, the sample film is stabilized and slightly thinned by controlled water evaporation regulated by the offset of the platform temperature relative to the dew-point. At a given point the pick-and-plunge mechanism is triggered, rapidly transferring the primed EM grid into liquid ethane for sample vitrification. Alternatively, sample-conditioning methods are available to prepare nanoliter-sized sample volumes for negative stain (NS) EM.
The methodologies greatly reduce sample consumption and avoid approaches potentially harmful to proteins, such as the filter paper blotting used in conventional methods. Furthermore, the minuscule amount of sample required allows novel experimental strategies, such as fast sample conditioning, combination with single-cell lysis for &#34;visual proteomics,&#34; or &#34;lossless&#34; total sample preparation for quantitative analysis of complex samples.

An instrument and methods for the preparation of nanoliter-sized sample volumes for transmission electron microscopy is presented. No paper-blotting steps are required, thus avoiding the detrimental consequences this can have for proteins, significantly reducing sample loss and enabling the analysis of single cell lysate for visual proteomics.

Preparación de muestras miniatura para microscopia electrónica de transmisión

Due to recent technological progress, cryo-electron microscopy (cryo-EM) is rapidly becoming a standard method for the structural analysis of protein ...

Biological Sample Preparation by High-pressure Freezing, Microwave-assisted Contrast Enhancement, and Minimal Resin Embedding for Volume Imaging

The described sample preparation technique is designed to combine the best quality of ultrastructural preservation with the most suitable contrast for the imaging modality in a focused ion beam scanning electron microscope (FIB-SEM), which is used to obtain stacks of sequential images for 3D reconstruction and modelling. High-pressure freezing (HPF) allows close to native structural preservation, but the subsequent freeze substitution often does not provide sufficient contrast, especially for a bigger specimen, which is needed for high-quality imaging in the SEM required for 3D reconstruction. Therefore, in this protocol, after the freeze substitution, additional contrasting steps are carried out at room temperature. Although these steps are performed in a microwave, it is also possible to follow traditional bench processing, which requires longer incubation times.The subsequent embedding in minimal amounts of resin allows for faster and more precise targeting and preparation inside the FIB-SEM. This protocol is especially useful for samples that require preparation by high-pressure freezing for a reliable ultrastructural preservation but do not gain enough contrast during the freeze substitution for volume imaging using FIB-SEM. In combination with the minimal resin embedding, this protocol provides an efficient workflow for the acquisition of high-quality volume data.

Here we present a protocol for combining two sample processing techniques, high-pressure freezing and microwave-assisted sample processing, followed by minimal resin embedding for acquiring data with a focused ion beam scanning electron microscope (FIB-SEM). This is demonstrated using a mouse tibial nerve sample and Caenorhabditis elegans.

Preparación de muestras biológicas por congelación de alta presión, realce del contraste asistida por microondas y mínima inclusión de proyección de imagen de volumen

The described sample preparation technique is designed to combine the best quality of ultrastructural preservation with the most suitable contrast for the ...

Super-Resolution Live Cell Imaging of Subcellular Structures

There has long been a crucial tradeoff between spatial and temporal resolution in imaging. Imaging beyond the diffraction limit of light has traditionally been restricted to be used only on fixed samples or live cells outside of tissue labeled with strong fluorescent signal. Current super-resolution live cell imaging techniques require the use of special fluorescence probes, high illumination, multiple image acquisitions with post-acquisition processing, or often a combination of these processes. These prerequisites significantly limit the biological samples and contexts that this technique can be applied to.
Here we describe a method to perform super-resolution (~140 nm XY-resolution) time-lapse fluorescence live cell imaging in situ. This technique is also compatible with low fluorescent intensity, for example, EGFP or mCherry endogenously tagged at lowly expressed genes. As a proof-of-principle, we have used this method to visualize multiple subcellular structures in the Drosophila testis. During tissue preparation, both the cellular structure and tissue morphology are maintained within the dissected testis. Here, we use this technique to image microtubule dynamics, the interactions between microtubules and the nuclear membrane, as well as the attachment of microtubules to centromeres.
This technique requires special procedures in sample preparation, sample mounting and immobilizing of specimens. Additionally, the specimens must be maintained for several hours after dissection without compromising cellular function and activity. While we have optimized the conditions for live super-resolution imaging specifically in Drosophila male germline stem cells (GSCs) and progenitor germ cells in dissected testis tissue, this technique is broadly applicable to a variety of different cell types. The ability to observe cells under their physiological conditions without sacrificing either spatial or temporal resolution will serve as an invaluable tool to researchers seeking to address crucial questions in cell biology.

Presented here is a protocol for super-resolution live-cell imaging in intact tissue. We have standardized the conditions for imaging a highly sensitive adult stem cell population in its native tissue environment. This technique involves balancing temporal and spatial resolution to allow for the direct observation of biological phenomena in live tissue.

Super-Resolución De Imágenes De Células Vivas De Estructuras Subcelulares

There has long been a crucial tradeoff between spatial and temporal resolution in imaging. Imaging beyond the diffraction limit of light has traditionally ...