Name: sample preparation and imaging of exosomes by transmission electron microscopy
Uploaded: 2018-01-04T13:00:00
Description: Watch this Scientific Journal Video about Sample Preparation and Imaging of Exosomes by Transmission Electron Microscopy at JoVE.com

This research was supported by the Bio &#38; Medical Technology Development Program of the National Research Foundation (NRF) &#38; funded by the Korean government (MSIP&#38;MOHW) (No. 2016M3A9B6904244). We also thank members of the Medicinal Bioconvergence Research Center for purification of exosome.

1. Block Preparation, Sectioning, Staining and Imaging of the Exosome
<ol>
	<li>Pellet the exosomes from culture supernatant of HCT116 cells by centrifugation at 100,000 x g for 1.5 h23. Remove the culture supernatant and carefully fix the purified exosome pellet with 1 mL of 2.5% glutaraldehyde in 0.1 M sodium cacodylate solution (pH 7.0) for 1 h at 4 &#176;C. For 0.1 M sodium cacodylate, dissolve 4.28 g cacodylic acid in 160 mL of distilled water (DW). Adjust pH to 7.4 with 0.1 M HCl then make...

<ol>
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This article presents a protocol for observing the detailed exosome&#39;s structure and labeling of its specific proteins. Negative staining has been considered as the best method for exosome imaging17. This conventional technique has shown exosomes&#39; cup-shaped structure. However, this cup shape is a form of artefact that can occur due to the drying process. Cryo-TEM results have shown that exosomes have a perfectly spherical structure in aqueous solution25,<...

Extracellular vesicles (EVs) are lipid bilayer vesicles secreted by cells, and their size ranges between 30 and 300 nm. EVs were first reported in 1978, with evidence from vesicles of patients with Hodgkin&#39;s disease1. These vesicles were reported to be 40 to 120 nanometers in size. In 1980, it was reported that EVs are involved in the coagulation system and thrombosis, formation of a blood clot inside a blood vessel in cancer patients2. After 30 years, EVs have been reported to be an important factor to promote tumor invasion, immune escape, and angiogenesis3. In addition, the functions of EVs have been studied as regulators in cellular interactions in the areas of inflammation, immune disorder, neurological disease, and cancer4. Since EVs contain specific biomolecules such as protein, mRNA, and microRNA5, their potential application in diagnostics and therapeutics has been analyzed6,7. EVs are a category composed of subgroups including exosomes, prostasomes, oncosomes, dexosomes, microparticles, promininosomes, argosomes, and exosome-like vesicles, depending on their cellular origin and biological function3. In addition, based on their biogenesis, these EVs can be divided into microvesicles (shed microvesicles, 100 - 1000 nm) and exosomes (30 - 300 nm)8,9. Among these, the exosome has been reported as a cell communicator for immune response10, cancer11,12, and infectious disease13.
Interest in the exosomes as a biomarker for early diagnosis is increasing rapidly, and the purification and characterization of exosomes must be accompanied with molecular imaging techniques. The varying sizes and morphologies of exosomes, depending on their origin and function14, can be distinguished by microscopy techniques with high resolution, such as electron microscopy. Most exosomes were visualized by negative stained Transmission Electron Microscopy (TEM)15,16,17, and these results were confirmed by immunolabeling of a specific protein in whole mount vesicle18. Several research groups have reported the structure through Scanning Electron Microscopy, Atomic Force Microscopy19,20, and Cryo-TEM21,22. However, while these techniques are useful for studying the exosome structure, they are insufficient for observing the position of specific proteins located inside the exosome. Therefore, we introduced a protocol for imaging exosomes with a specific protein&#39;s labelling. We applied block preparation, ultrathin sectioning, and immunostaining for ascertaining the protein&#39;s detailed location in the exosome. This was compared with negative staining and whole mount immunostaining, which is traditionally used for characterization of the exosome.

<table border="0" cellpadding="0" cellspacing="0" width="583">
	<tbody>
		<tr height="22">
			<td height="22" style="height:22px;width:216px;">Glutaraldehyde</td>
			<td style="width:81px;">EMS</td>
			<td style="width:119px;">16200</td>
			<td style="width:167px;"></td>
		</tr>
		<tr height="22">
			<td height="22" style="height:22px;width:216px;">Sodium cacodylate&#160;</td>
			<td>EMS</td>
			<td style="width:119px;">12300</td>
			<td></td>
		</tr>
		<tr height="22">
			<td height="22" style="height:22px;width:216px;">Osmium tetroxide 1 g crystal</td>
			<td>EMS</td>
			<td style="width:119px;">19100</td>
			<td>Use only in fume hood</td>
		</tr>
		<tr height="22">
			<td height="22" style="height:22px;width:216px;">acetone</td>
			<td>JUNSEI</td>
			<td>1B2031</td>
			<td></td>
		</tr>
		<tr height="22">
			<td height="22" style="height:22px;width:216px;">Spurr medium</td>
			<td>TED PELLA</td>
			<td style="width:119px;">18108</td>
			<td></td>
		</tr>
		<tr height="22">
			<td height="22" style="height:22px;width:216px;">Ultra-microtome</td>
			<td style="width:81px;">Leica</td>
			<td style="width:119px;">UCT</td>
			<td></td>
		</tr>
		<tr height="22">
			<td height="22" style="height:22px;width:216px;">Uranyl acetate</td>
			<td>EMS</td>
			<td style="width:119px;">22400</td>
			<td>Hazardous chemical</td>
		</tr>
		<tr height="22">
			<td height="22" style="height:22px;width:216px;">Lead citrate</td>
			<td>EMS</td>
			<td style="width:119px;">17900</td>
			<td></td>
		</tr>
		<tr height="43">
			<td height="43" style="height:43px;width:216px;">Transmission Electron Microscopy</td>
			<td style="width:81px;">Hitachi</td>
			<td style="width:119px;">H7600</td>
			<td></td>
		</tr>
		<tr height="22">
			<td height="22" style="height:22px;width:216px;">nickel grid</td>
			<td style="width:81px;">EMS</td>
			<td style="width:119px;">G200-Ni</td>
			<td></td>
		</tr>
		<tr height="22">
			<td height="22" style="height:22px;width:216px;">Copper grid</td>
			<td>EMS</td>
			<td style="width:119px;">G200-Cu</td>
			<td></td>
		</tr>
		<tr height="22">
			<td height="22" style="height:22px;width:216px;">glycine</td>
			<td>SIGMA</td>
			<td>022K5404</td>
			<td></td>
		</tr>
		<tr height="22">
			<td height="22" style="height:22px;width:216px;">Phosphate buffer saline</td>
			<td style="width:81px;">SIGMA</td>
			<td style="width:119px;">P4417</td>
			<td></td>
		</tr>
		<tr height="22">
			<td height="22" style="height:22px;width:216px;">Bovine serum albumin</td>
			<td style="width:81px;">Aurion</td>
			<td style="width:119px;">25557</td>
			<td></td>
		</tr>
		<tr height="22">
			<td height="22" style="height:22px;width:216px;">1st Antibody</td>
			<td style="width:81px;"></td>
			<td style="width:119px;"></td>
			<td style="width:167px;">purification in manually&#160;</td>
		</tr>
		<tr height="43">
			<td height="43" style="height:43px;width:216px;">Purified anti-human CD274 (B7-H1, PD-L1) Antibody</td>
			<td style="width:81px;">BioLegend</td>
			<td style="width:119px;">329710</td>
			<td style="width:167px;">Whole mount Immumogold</td>
		</tr>
		<tr height="43">
			<td height="43" style="height:43px;width:216px;">Purified Mouse IgG2b, &#954; Isotype Ctrl</td>
			<td style="width:81px;">BioLegend</td>
			<td style="width:119px;">401202</td>
			<td style="width:167px;">Whole mount Immumogold (Control)</td>
		</tr>
		<tr height="43">
			<td height="43" style="height:43px;width:216px;">2nd Anti-mouse igG conjugated 9-11 nm gold particle</td>
			<td style="width:81px;">sigma</td>
			<td style="width:119px;">G7652</td>
			<td></td>
		</tr>
		<tr height="22">
			<td height="22" style="height:22px;width:216px;">silver paint</td>
			<td style="width:81px;">CANS</td>
			<td style="width:119px;">CTP100</td>
			<td></td>
		</tr>
		<tr height="22">
			<td height="22" style="height:22px;width:216px;">aluminum stub</td>
			<td style="width:81px;">EMS</td>
			<td style="width:119px;">75622</td>
			<td></td>
		</tr>
		<tr height="22">
			<td height="22" style="height:22px;width:216px;">FIB-SEM</td>
			<td style="width:81px;">Zeiss</td>
			<td style="width:119px;">AURIGA</td>
			<td></td>
		</tr>
		<tr height="43">
			<td height="43" style="height:43px;width:216px;">Transmission Electron Microscopy</td>
			<td style="width:81px;">JEOL</td>
			<td style="width:119px;">JEM2200FS</td>
			<td></td>
		</tr>
		<tr height="22">
			<td height="22" style="height:22px;width:216px;">Glow discharger</td>
			<td style="width:81px;">JEOL</td>
			<td style="width:119px;">JFC1100E</td>
			<td></td>
		</tr>
		<tr height="22">
			<td height="22" style="height:22px;width:216px;">Carbon grid</td>
			<td>EMS</td>
			<td style="width:119px;">121119</td>
			<td></td>
		</tr>
		<tr height="22">
			<td height="22" style="height:22px;width:216px;">Paraformaldehyde</td>
			<td>EMS</td>
			<td style="width:119px;">19210</td>
			<td></td>
		</tr>
		<tr height="41">
			<td height="41" style="height:41px;width:216px;">Formvar carbon coated Copper Grid (200 meh)</td>
			<td style="width:81px;">EMS</td>
			<td style="width:119px;">FCF200-CU</td>
			<td style="width:167px;"></td>
		</tr>
		<tr height="41">
			<td height="41" style="height:41px;width:216px;">Formvar carbon coated&#160; Nickel Grid (200 mesh)</td>
			<td style="width:81px;">EMS</td>
			<td style="width:119px;">FCF200-NI</td>
			<td style="width:167px;"></td>
		</tr>
	</tbody>
</table>

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.

Currently, exosomes are classified into size and shape categories by transmission electron microscopy. Figure 2 shows negative stained exosome and immune-labelled exosome in whole mount status. Figure 3 shows sectioned exosome and immuno-labelled exosomes after thin sectioning. Immuno-gold staining using antibodies of specific proteins is used to positively identify an exosome and classify the types of proteins in the exosome. Th...

Watch this Scientific Journal Video about Sample Preparation and Imaging of Exosomes by Transmission Electron Microscopy at JoVE.com

Sample Preparation and Imaging of Exosomes by Transmission Electron Microscopy

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.

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

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JoVE Journal

Biology

Preparation of embryos for Electron Microscopy of the Drosophila embryonic heart tube

Preparation of embryos for Electron Microscopy of the Drosophila embryonic heart tube

The morphogenesis of the Drosophila  embryonic heart tube has emerged as a valuable model system for studying cell migration, cell-cell adhesion and cell ...

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

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

Cryo-electron Microscopy Specimen Preparation By Means Of a Focused Ion Beam

Here we present a protocol used to prepare cryo-TEM samples of Aspergillus niger spores, but which can easily be adapted for any number of microorganisms ...

In Vivo 4-Dimensional Tracking of Hematopoietic Stem and Progenitor Cells in Adult Mouse Calvarial Bone Marrow

In Vivo 4-Dimensional Tracking of Hematopoietic Stem and Progenitor Cells in Adult Mouse Calvarial Bone Marrow

Through a delicate balance between quiescence and proliferation, self renewal and production of differentiated progeny, hematopoietic stem cells (HSCs) ...

Tandem High-pressure Freezing and Quick Freeze Substitution of Plant Tissues for Transmission Electron Microscopy

Since the 1940s transmission electron microscopy (TEM) has been providing biologists with ultra-high resolution images of biological materials. Yet, ...

Do's and Don'ts of Cryo-electron Microscopy: A Primer on Sample Preparation and High Quality Data Collection for Macromolecular 3D Reconstruction

Cryo-electron microscopy (cryoEM) entails flash-freezing a thin layer of sample on a support, and then visualizing the sample in its frozen hydrated state ...

Preparation and Observation of Thick Biological Samples by Scanning Transmission Electron Tomography

This report describes a protocol for preparing thick biological specimens for further observation using a scanning transmission electron microscope. It ...

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 ...

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 ...