Name: study of the actin cytoskeleton in live endothelial cells expressing gfp-actin
Uploaded: 2011-11-18T13:00:00
Duration: 8 min 37 s
Description: Watch this Scientific Journal Video about Study of the Actin Cytoskeleton in Live Endothelial Cells Expressing GFP-Actin at JoVE.com

The GFP-&beta;-actin plasmid was generously provided by Dr. Wayne Orr, LSUHSC-S Department of Pathology, and was amplified in the laboratory of Dr. Becky Worthylake, LSUHSC-NO Department of Pharmacology. This work was supported by grants from the National Institutes of Health (P20 RR-018766) and the American Heart Association (05835386N).

<ol>
	<li>Spindler, V., Schlegel, N., Waschke, J. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Role+of+GTPases+in+control+of+microvascular+permeability.">Role of GTPases in control of microvascular permeability.</a> Cardiovasc. Res. 87, 243-253 (2010).</li><li>Wojciak-Stothard, B., Ridley, A. J. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Rho+GTPases+and+the+regulation+of+endothelial+permeability.">Rho GTPases and the regulation of endothelial permeability.</a> Vascul. Pharmacol. 39, 187-199 (2002).</li><li>Yuan, S. Y. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Signal+transduction+pathways+in+enhanced+microvascular+permeability.">Signal transduction pathways in enhanced microvascular permeability.</a> Microcirculation. 7, 395-403 (2000).</li><li>Birukov, K. G. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Small+GTPases+in+mechanosensitive+regulation+of+endothelial+barrier.">Small GTPases in mechanosensitive regulation of endothelial barrier.</a> Microvasc. Res. 77, 46-52 (2009).</li><li>Duran, W. N., Sanchez, F. A., Breslin, J. W., Tuma, R. F., Duran, W. N., Ley, K. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Microcirculatory+Exchange+Function.">Microcirculatory Exchange Function.</a> Handbook of Physiology: Microcirculation. , 81-124 (2008).</li><li>Hu, Y. L., Chien, S. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Dynamic+motion+of+paxillin+on+actin+filaments+in+living+endothelial+cells.">Dynamic motion of paxillin on actin filaments in living endothelial cells.</a> Biochem. Biophys. Res. Commun. 357, 871-876 (2007).</li><li>Borm, B., Requardt, R. P., Herzog, V., Kirfel, G. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Membrane+ruffles+in+cell+migration:+indicators+of+inefficient+lamellipodia+adhesion+and+compartments+of+actin+filament+reorganization.">Membrane ruffles in cell migration: indicators of inefficient lamellipodia adhesion and compartments of actin filament reorganization.</a> Exp. Cell. Res. 302, 83-95 (2005).</li><li>Hotulainen, P., Lappalainen, P. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Stress+fibers+are+generated+by+two+distinct+actin+assembly+mechanisms+in+motile+cells.">Stress fibers are generated by two distinct actin assembly mechanisms in motile cells.</a> J. Cell. Biol. 173, 383-394 (2006).</li><li>Pellegrin, S., Mellor, H. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Actin+stress+fibres.">Actin stress fibres.</a> J. Cell. Sci. 120, 3491-3499 (2007).</li><li>Ballestrem, C., Wehrle-Haller, B., Imhof, B. A. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Actin+dynamics+in+living+mammalian+cells.">Actin dynamics in living mammalian cells.</a> J. Cell. Sci. 111, 1649-1658 (1998).</li><li>Helmke, B. P., Rosen, A. B., Davies, P. F. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Mapping+mechanical+strain+of+an+endogenous+cytoskeletal+network+in+living+endothelial+cells.">Mapping mechanical strain of an endogenous cytoskeletal network in living endothelial cells.</a> Biophys. J. 84, 2691-2699 (2003).</li><li>Birukova, A. A., Smurova, K., Birukov, K. G., Kaibuchi, K., Garcia, J. G., Verin, A. D. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Role+of+Rho+GTPases+in+thrombin-induced+lung+vascular+endothelial+cells+barrier+dysfunction.">Role of Rho GTPases in thrombin-induced lung vascular endothelial cells barrier dysfunction.</a> Microvasc. Res. 67, 64-77 (2004).</li><li>van Nieuw Amerongen, G. P., van Delft, S., Vermeer, M. A., Collard, J. G., van Hinsbergh, V. W. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Activation+of+RhoA+by+thrombin+in+endothelial+hyperpermeability:+role+of+Rho+kinase+and+protein+tyrosine+kinases.">Activation of RhoA by thrombin in endothelial hyperpermeability: role of Rho kinase and protein tyrosine kinases.</a> Circ. Res. 87, 335-340 (2000).</li><li>Moy, A. B., Blackwell, K., Kamath, A. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Differential+effects+of+histamine+and+thrombin+on+endothelial+barrier+function+through+actin-myosin+tension.">Differential effects of histamine and thrombin on endothelial barrier function through actin-myosin tension.</a> Am J Physiol Heart Circ Physiol. 282, H21-H29 (2002).</li><li>Wittman, T., Littlefield, R., Waterman-Storer, C., Goldman, R. D., Spector, D. L. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Fluorescent+speckle+microscopy+of+cytoskeletal+dynamics+in+living+cells.">Fluorescent speckle microscopy of cytoskeletal dynamics in living cells.</a> Live Cell Imaging: A Laboratory Manual. , 184-204 (2005).</li><li>Rabut, G., Ellenberg, J., Goldman, R. D., Spector, D. L. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Photobleaching+techniques+to+study+mobility+and+molecular+dynamics+of+proteins+in+live+cells:+FRAP,+iFRAP,+and+FLIP.">Photobleaching techniques to study mobility and molecular dynamics of proteins in live cells: FRAP, iFRAP, and FLIP.</a> Live Cell Imaging: A Laboratory Manual. , 101-126 (2005).</li></ol>

No conflicts of interest declared.

The imaging of GFP-actin in live endothelial cells enables a detailed analysis of the dynamics of the actin cytoskeleton in response to inflammatory stimuli. This method may also be useful to build upon previous findings showing remodeling of the cytoskeleton in response to physical forces like shear stress11. In addition, this method allows a detailed assessment of the contribution of actin cytoskeletal dynamics to various endothelial cell activities, including migration, mitosis, formation of intercellular junctions and junctional maturation, and maintenance of barrier function. 
In the data shown, the behavior of the endothelial actin cytoskeleton can be observed before and after treatment with thrombin. Local lamellipodia all along the edges of endothelial cells were observed forming and regressing over time in both nonconfluent and confluent cell monolayers. Treatment with thrombin briefly interrupted lamellipodia formation and turnover. Thrombin also caused the cells to contract slightly, in agreement with previous reports that thrombin causes actin stress fiber formation and increased centripetal tension development in endothelial cells12-14. However, from live cell imaging studies such as this, the origin of the stress fibers can now be determined. In HUVEC, most of the stress fibers originate at the cell periphery and resemble transverse arc fibers in migrating cells8, 9. Another strength of this method over using fixed cells is that the number of stress fibers can be quantified in individual cells before and after thrombin treatment, eliminating selection bias between experimental groups. 
With this protocol we evaluate dynamic motion of the cell edge and actin stress fibers. To understand actin monomer dynamics in endothelial cells, more advanced techniques such as fluorescence recovery after photobleaching (FRAP) or fluorescence speckle microscopy (FSM) can be applied15, 16. In addition, because microvascular endothelial cells may represent a better model of microvascular barrier function, optimization of transfection protocols to effectively express GFP-actin in microvascular endothelial cells represents a logical future direction.
In summary, imaging of live endothelial cells expressing GFP-actin represents a powerful tool to determine how the endothelial cell actin cytoskeleton responds to various types of stimuli. Studies using tightly confluent endothelial monolayers will help determine the roles of dynamic structures such as actin-rich lamellipodia and transverse arc stress fibers in endothelial barrier function. In addition, live cell imaging of endothelial cells expressing GFP-actin or other fusion proteins that allow visualization of other subcellular structures will provide detailed spatiotemporal information needed to understand the signaling and structural mechanisms that determine barrier integrity.

<table border="1">
<tbody>
	<tr>
		<td colspan="4">1. Ringer 5x Stock</td>
	</tr>
	<tr>
		<td>Chemical</td>
		<td>Company</td>
		<td>Catalog Number</td>
		<td>Amount</td>
	</tr>
	<tr>
		<td>Sodium Chloride</td>
		<td>EMD</td>
		<td>SX0420-3</td>
		<td>35 g</td>
	</tr>
	<tr>
		<td>Potassium Chloride</td>
		<td>J.T. Baker</td>
		<td>3040</td>
		<td>1.75 g</td>
	</tr>
	<tr>
		<td>Calcium Chloride</td>
		<td>Sigma</td>
		<td>C-3881</td>
		<td>1.47 g</td>
	</tr>
	<tr>
		<td>Magnesium Sulfate</td>
		<td>Sigma</td>
		<td>M-9397</td>
		<td>1.44 g</td>
	</tr>
	<tr>
		<td>Sterile Filtered Water</td>
		<td>N/A</td>
		<td>N/A</td>
		<td>Bring to 1 L</td>
	</tr>
	<tr>
		<td colspan="4">Sterile filter into autoclaved bottles and stores at 4&deg;C</td>
	</tr>
	<tr>
		<td colspan="4">&nbsp;</td>
	</tr>
	<tr>
		<td colspan="4">2. MOPS buffer</td>
	</tr>
	<tr>
		<td>Chemical</td>
		<td>Company</td>
		<td>Catalog Number</td>
		<td>Amount </td>
	</tr>
	<tr>
		<td>MOPS</td>
		<td>Sigma</td>
		<td>M3183</td>
		<td>125.6 g</td>
	</tr>
	<tr>
		<td>Sterile Filtered Water</td>
		<td>N/A</td>
		<td>N/A</td>
		<td>Bring to 1 L</td>
	</tr>
	<tr>
		<td colspan="4">Sterile filter into autoclaved bottles and stores at 4&deg;C</td>
	</tr>
	<tr>
		<td colspan="4">&nbsp;</td>
	</tr>
	<tr>
		<td colspan="4">3. Albumin Physiological Salt Solution (APSS)</td>
	</tr>
	<tr>
		<td>Chemical</td>
		<td>Company</td>
		<td>Catalog Number</td>
		<td>Amount </td>
	</tr>
	<tr>
		<td>Ringer stock (5x)</td>
		<td>N/A</td>
		<td>N/A</td>
		<td>200 mL </td>
	</tr>
	<tr>
		<td>Mops Buffer</td>
		<td>N/A</td>
		<td>N/A</td>
		<td>5 mL </td>
	</tr>
	<tr>
		<td>Sodium Phosphate</td>
		<td>Sigma</td>
		<td>S-9638</td>
		<td>0.168 g</td>
	</tr>
	<tr>
		<td>Sodium Pyruvate</td>
		<td>Sigma</td>
		<td>P5280</td>
		<td>0.22 g</td>
	</tr>
	<tr>
		<td>EDTA sodium salt</td>
		<td>Sigma</td>
		<td>ED2SS</td>
		<td>0.0074 g</td>
	</tr>
	<tr>
		<td>Glucose</td>
		<td>Sigma</td>
		<td>G7528</td>
		<td>0.901 g</td>
	</tr>
	<tr>
		<td>Albumin, Bovine</td>
		<td>USB</td>
		<td>10856</td>
		<td>10 g</td>
	</tr>
	<tr>
		<td>Sterile Filtered Water</td>
		<td>N/A</td>
		<td>N/A</td>
		<td>Bring to 1 L</td>
	</tr>
	<tr>
		<td colspan="4">Adjust pH to 7.4 at 37&deg;C, then sterile filter into autoclaved bottles and store at 4&deg;C.</td>
	</tr>
	<tr>
		<td colspan="4">&nbsp;</td>
	</tr>
	<tr>
		<td colspan="4">4. 0.9% Saline</td>
	</tr>
	<tr>
		<td>Chemical</td>
		<td>Company</td>
		<td>Catalog Number</td>
		<td>Amount </td>
	</tr>
	<tr>
		<td>Sodium Chloride</td>
		<td>EMD</td>
		<td>SX0420-3</td>
		<td>9 g</td>
	</tr>
	<tr>
		<td>Sterile Filtered Water</td>
		<td>N/A</td>
		<td>N/A</td>
		<td>Bring to 1 L</td>
	</tr>
	<tr>
		<td colspan="4">Sterile filter into autoclaved bottles and stores at 4&deg;C</td>
	</tr>
	<tr>
		<td colspan="4">&nbsp;</td>
	</tr>
	<tr>
		<td colspan="4">5. 1.5 % Gelatin Solution</td>
	</tr>
	<tr>
		<td>Gelatin from porcine skin</td>
		<td>Sigma</td>
		<td>G2500</td>
		<td>15 g</td>
	</tr>
	<tr>
		<td>0.9% Saline</td>
		<td>N/A</td>
		<td>N/A</td>
		<td>Bring to 1 L</td>
	</tr>
	<tr>
		<td colspan="4">Warm the solution to 37&deg;C to dissolve gelatin sufficiently. While still warm, sterile filter into autoclaved bottles and store at 4&deg;C</td>
	</tr>	
</tbody>
</table>

study of the actin cytoskeleton in live endothelial cells expressing gfp-actin

The microvascular endothelium plays an important role as a selectively permeable barrier to fluids and solutes. The adhesive junctions between endothelial cells regulate permeability of the endothelium, and many studies have indicated the important contribution of the actin cytoskeleton to determining junctional integrity1-5. A cortical actin belt is thought to be important for the maintenance of stable junctions1, 2, 4, 5. In contrast, actin stress fibers are thought to generate centripetal tension within endothelial cells that weakens junctions2-5. Much of this theory has been based on studies in which endothelial cells are treated with inflammatory mediators known to increase endothelial permeability, and then fixing the cells and labeling F-actin for microscopic observation. However, these studies provide a very limited understanding of the role of the actin cytoskeleton because images of fixed cells provide only snapshots in time with no information about the dynamics of actin structures5. 
Live-cell imaging allows incorporation of the dynamic nature of the actin cytoskeleton into the studies of the mechanisms determining endothelial barrier integrity. A major advantage of this method is that the impact of various inflammatory stimuli on actin structures in endothelial cells can be assessed in the same set of living cells before and after treatment, removing potential bias that may occur when observing fixed specimens. Human umbilical vein endothelial cells (HUVEC) are transfected with a GFP-&beta;-actin plasmid and grown to confluence on glass coverslips. Time-lapse images of GFP-actin in confluent HUVEC are captured before and after the addition of inflammatory mediators that elicit time-dependent changes in endothelial barrier integrity. These studies enable visual observation of the fluid sequence of changes in the actin cytoskeleton that contribute to endothelial barrier disruption and restoration. 
Our results consistently show local, actin-rich lamellipodia formation and turnover in endothelial cells. The formation and movement of actin stress fibers can also be observed. An analysis of the frequency of formation and turnover of the local lamellipodia, before and after treatment with inflammatory stimuli can be documented by kymograph analyses. These studies provide important information on the dynamic nature of the actin cytoskeleton in endothelial cells that can used to discover previously unidentified molecular mechanisms important for the maintenance of endothelial barrier integrity.

Watch this Scientific Journal Video about Study of the Actin Cytoskeleton in Live Endothelial Cells Expressing GFP-Actin at JoVE.com

Study of the Actin Cytoskeleton in Live Endothelial Cells Expressing GFP-Actin

Microscopic imaging of live endothelial cells expressing GFP-actin allows characterization of dynamic changes in cytoskeletal structures. Unlike techniques that use fixed specimens, this method provides a detailed assessment of temporal changes in the actin cytoskeleton in the same cells before, during, and after various physical, pharmacological, or inflammatory stimuli.

The microvascular endothelium plays an important role as a selectively permeable barrier to fluids and solutes. The adhesive junctions between endothelial ...

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Unit 1

The Cytoskeleton I: Actin and Microfilaments

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Testing Visual Sensitivity to the Speed and Direction of Motion in Lizards

Testing visual sensitivity in any species provides basic information regarding behaviour, evolution, and ecology. However, testing specific features of the visual system provide more empirical evidence for functional applications. Investigation into the sensory system provides information about the sensory capacity, learning and memory ability, and establishes known baseline behaviour in which to gauge deviations (Burghardt, 1977). However, unlike mammalian or avian systems, testing for learning and memory in a reptile species is difficult. Furthermore, using an operant paradigm as a psychophysical measure of sensory ability is likewise as difficult. Historically, reptilian species have responded poorly to conditioning trials because of issues related to motivation, physiology, metabolism, and basic biological characteristics. Here, I demonstrate an operant paradigm used a novel model lizard species, the Jacky dragon (Amphibolurus muricatus) and describe how to test peripheral sensitivity to salient speed and motion characteristics. This method uses an innovative approach to assessing learning and sensory capacity in lizards. I employ the use of random-dot kinematograms (RDKs) to measure sensitivity to speed, and manipulate the level of signal strength by changing the proportion of dots moving in a coherent direction. RDKs do not represent a biologically meaningful stimulus, engages the visual system, and is a classic psychophysical tool used to measure sensitivity in humans and other animals. Here, RDKs are displayed to lizards using three video playback systems. Lizards are to select the direction (left or right) in which they perceive dots to be moving. Selection of the appropriate direction is reinforced by biologically important prey stimuli, simulated by computer-animated invertebrates.

Testing visual sensitivity in lizards using an operant conditioning paradigm that employs video playback of random-dot kinematograms and computer-generated invertebrates.

Testing visual sensitivity in any species provides basic information regarding behaviour, evolution, and ecology. However, testing specific features of ...

Computer-Generated Animal Model Stimuli

Communication between animals is diverse and complex. Animals may communicate using auditory, seismic, chemosensory, electrical, or visual signals. In particular, understanding the constraints on visual signal design for communication has been of great interest. Traditional methods for investigating animal interactions have used basic observational techniques, staged encounters, or physical manipulation of morphology. Less intrusive methods have tried to simulate conspecifics using crude playback tools, such as mirrors, still images, or models. As technology has become more advanced, video playback has emerged as another tool in which to examine visual communication (Rosenthal, 2000). However, to move one step further, the application of computer-animation now allows researchers to specifically isolate critical components necessary to elicit social responses from conspecifics, and manipulate these features to control interactions. Here, I provide detail on how to create an animation using the Jacky dragon as a model, but this process may be adaptable for other species. In building the animation, I elected to use Lightwave  3D to alter object morphology, add texture, install bones, and provide comparable weight shading that prevents exaggerated movement. The animation is then matched to select motor patterns to replicate critical movement features. Finally, the sequence must rendered into an individual clip for presentation. Although there are other adaptable techniques, this particular method had been demonstrated to be effective in eliciting both conspicuous and social responses in staged interactions.

Computer-generated stimuli using the Jacky dragon as a model.

Communication between animals is diverse and complex. Animals may communicate using auditory, seismic, chemosensory, electrical, or visual signals. In ...

Live Cell Imaging of F-actin Dynamics via Fluorescent Speckle Microscopy (FSM)

In this protocol we describe the use of Fluorescent Speckle Microscopy (FSM) to capture high-resolution images of actin dynamics in PtK1 cells. A unique advantage of FSM is its ability to capture the movement and turnover kinetics (assembly/disassembly) of the F-actin network within living cells. This technique is particularly useful in deriving quantitative measurements of F-actin dynamics when paired with computer vision software (qFSM).  We describe  the selection, microinjection and visualization of fluorescent actin probes in living cells. Importantly, similar procedures are applicable to visualizing other macomolecular assemblies. FSM has been demonstrated for microtubules, intermediate filaments, and adhesion complexes.  

Live Cell Imaging of F-actin Dynamics via Fluorescent Speckle Microscopy FSM

Selection, microinjection, and imaging of fluorescently-labeled F-actin via fluorescent speckle microscopy (FSM).

In this protocol we describe the use of Fluorescent Speckle Microscopy (FSM) to capture high-resolution images of actin dynamics in PtK1 cells. A unique ...

Live Imaging of Cell Motility and Actin Cytoskeleton of Individual Neurons and Neural Crest Cells in Zebrafish Embryos

The zebrafish is an ideal model for imaging cell behaviors during development in vivo. Zebrafish embryos are externally fertilized and thus easily accessible at all stages of development. Moreover, their optical clarity allows high resolution imaging of cell and molecular dynamics in the natural environment of the intact embryo. We are using a live imaging approach to analyze cell behaviors during neural crest cell migration and the outgrowth and guidance of neuronal axons.
Live imaging is particularly useful for understanding mechanisms that regulate cell motility processes. To visualize details of cell motility, such as protrusive activity and molecular dynamics, it is advantageous to label individual cells. In zebrafish, plasmid DNA injection yields a transient mosaic expression pattern and offers distinct benefits over other cell labeling methods. For example, transgenic lines often label entire cell populations and thus may obscure visualization of the fine protrusions (or changes in molecular distribution) in a single cell. In addition, injection of DNA at the one-cell stage is less invasive and more precise than dye injections at later stages.
Here we describe a method for labeling individual developing neurons or neural crest cells and imaging their behavior in vivo. We inject plasmid DNA into 1-cell stage embryos, which results in mosaic transgene expression. The vectors contain cell-specific promoters that drive expression of a gene of interest in a subset of sensory neurons or neural crest cells. We provide examples of cells labeled with membrane targeted GFP or with a biosensor probe that allows visualization of F-actin in living cells1.
Erica Andersen, Namrata Asuri, and Matthew Clay contributed equally to this work.

This protocol describes imaging of individual neurons or neural crest cells in living zebrafish embryos. This method is used to examine cellular behaviors and actin localization using fluorescence confocal time-lapse microscopy.

The zebrafish is an ideal model for imaging cell behaviors during development in vivo. Zebrafish embryos are externally fertilized and thus easily ...

Transplantation of GFP-expressing Blastomeres for Live Imaging of Retinal and Brain Development in Chimeric Zebrafish Embryos

Cells change extensively in their locations and property during embryogenesis. These changes are regulated by the interactions between the cells and their environment. Chimeric embryos, which are composed of cells of different genetic background, are great tools to study the cell-cell interactions mediated by genes of interest. The embryonic transparency of zebrafish at early developmental stages permits direct visualization of the morphogenesis of tissues and organs at the cellular level. Here, we demonstrate a protocol to generate chimeric retinas and brains in zebrafish embryos and to perform live imaging of the donor cells. The protocol covers the preparation of transplantation needles, the transplantation of GFP-expressing donor blastomeres to GFP-negative hosts, and the examination of donor cell behavior under live confocal microscopy. With slight modifications, this protocol can also be used to study the embryonic development of other tissues and organs in zebrafish. The advantages of using GFP to label donor cells are also discussed. 

We demonstrate a protocol to generate chimeric zebrafish embryos for live imaging cellular behavior during embryogenesis.

Cells change extensively in their locations and property during embryogenesis. These changes are regulated by the interactions between the cells and their ...

Do-It-Yourself Device for Recovery of Cryopreserved Samples Accidentally Dropped into Cryogenic Storage Tanks

Liquid nitrogen is colorless, odorless, extremely cold (-196 &deg;C) liquid kept under pressure. It is commonly used as a cryogenic fluid for long term storage of biological materials such as blood, cells and tissues 1,2. The cryogenic nature of liquid nitrogen, while ideal for sample preservation, can cause rapid freezing of live tissues on contact - known as 'cryogenic burn'2, which may lead to severe frostbite in persons closely involved in storage and retrieval of samples from Dewars. Additionally, as liquid nitrogen evaporates it reduces the oxygen concentration in the air and might cause asphyxia, especially in confined spaces2.
In laboratories, biological samples are often stored in cryovials or cryoboxes stacked in stainless steel racks within the Dewar tanks1. These storage racks are provided with a long shaft to prevent boxes from slipping out from the racks and into the bottom of Dewars during routine handling. All too often, however, boxes or vials with precious samples slip out and sink to the bottom of liquid nitrogen filled tank. In such cases, samples could be tediously retrieved after transferring the liquid nitrogen into a spare container or discarding it. The boxes and vials can then be relatively safely recovered from emptied Dewar. However, the cryogenic nature of liquid nitrogen and its expansion rate makes sunken sample retrieval hazardous. It is commonly recommended by Safety Offices that sample retrieval be never carried out by a single person. Another alternative is to use commercially available cool grabbers or tongs to pull out the vials3. However, limited visibility within the dark liquid filled Dewars poses a major limitation in their use.
In this article, we describe the construction of a Cryotolerant DIY retrieval device, which makes sample retrieval from Dewar containing cryogenic fluids both safe and easy.

Here we present a low cost, durable cryotolerant device for sample retrieval from Dewar tanks filled with liquid nitrogen. The ease of construction and modular design of the device makes the process of sample retrieval from cryogenic tanks safe and easy.

Liquid nitrogen is colorless, odorless, extremely cold (-196 &deg;C) liquid kept under pressure. It is commonly used as a cryogenic fluid for long term ...

Live Imaging of Apoptotic Cell Clearance during Drosophila Embryogenesis

The proper elimination of unwanted or aberrant cells through apoptosis and subsequent phagocytosis (apoptotic cell clearance) is crucial for normal development in all metazoan organisms. Apoptotic cell clearance is a highly dynamic process intimately associated with cell death; unengulfed apoptotic cells are barely seen in vivo under normal conditions. In order to understand the different steps of apoptotic cell clearance and to compare 'professional' phagocytes - macrophages and dendritic cells to 'non-professional' - tissue-resident neighboring cells, in vivo live imaging of the process is extremely valuable. Here we describe a protocol for studying apoptotic cell clearance in live Drosophila embryos. To follow the dynamics of different steps in phagocytosis we use specific markers for apoptotic cells and phagocytes. In addition, we can monitor two phagocyte systems in parallel: 'professional' macrophages and 'semi-professional' glia in the developing central nervous system (CNS). The method described here employs the Drosophila embryo as an excellent model for real time studies of apoptotic cell clearance.

Live Imaging of Apoptotic Cell Clearance during Drosophila Embryogenesis

Here we describe an effective method for studying dynamics of apoptotic cell clearance in vivo. This method employs live Drosophila embryos as a powerful model for monitoring phagocytosis of apoptotic cells using specific labeling of apoptotic cells and phagocytes.

The  proper elimination of unwanted or aberrant cells through apoptosis and  subsequent phagocytosis (apoptotic cell clearance) is crucial for normal  ...

Intravital Microscopy for Imaging Subcellular Structures in Live Mice Expressing Fluorescent Proteins

Here we describe a procedure to image subcellular structures in live rodents that is based on the use of confocal intravital microscopy. As a model organ, we use the salivary glands of live mice since they provide several advantages. First, they can be easily exposed to enable access to the optics, and stabilized to facilitate the reduction of the motion artifacts due to heartbeat and respiration. This significantly facilitates imaging and tracking small subcellular structures. Second, most of the cell populations of the salivary glands are accessible from the surface of the organ. This permits the use of confocal microscopy that has a higher spatial resolution than other techniques that have been used for in vivo imaging, such as two-photon microscopy. Finally, salivary glands can be easily manipulated pharmacologically and genetically, thus providing a robust system to investigate biological processes at a molecular level.
In this study we focus on a protocol designed to follow the kinetics of the exocytosis of secretory granules in acinar cells and the dynamics of the apical plasma membrane where the secretory granules fuse upon stimulation of the beta-adrenergic receptors. Specifically, we used a transgenic mouse that co-expresses cytosolic GFP and a membrane-targeted peptide fused with the fluorescent protein tandem-Tomato. However, the procedures that we used to stabilize and image the salivary glands can be extended to other mouse models and coupled to other approaches to label in vivo cellular components, enabling the visualization of various subcellular structures, such as endosomes, lysosomes, mitochondria, and the actin cytoskeleton.

Intravital microscopy is a powerful tool that enables imaging various biological processes in live animals. In this article, we present a detailed method for imaging the dynamics of subcellular structures, such as the secretory granules, in the salivary glands of live mice.

Here we describe a procedure to image subcellular structures in live rodents that is based on the use of confocal intravital microscopy. As a model organ, ...

Endothelial Cell Tube Formation Assay for the In Vitro Study of Angiogenesis

Angiogenesis is a vital process for normal tissue development and wound healing, but is also associated with a variety of pathological conditions. Using this protocol, angiogenesis may be measured in vitro in a fast, quantifiable manner. Primary or immortalized endothelial cells are mixed with conditioned media and plated on basement membrane matrix. The endothelial cells form capillary like structures in response to angiogenic signals found in conditioned media. The tube formation occurs quickly with endothelial cells beginning to align themselves within 1&#160;hr and lumen-containing tubules beginning to appear within 2 hr. Tubes can be visualized using a phase contrast inverted microscope, or the cells can be treated with calcein AM prior to the assay and tubes visualized through fluorescence or confocal microscopy. The number of branch sites/nodes, loops/meshes, or number or length of tubes formed can be easily quantified as a measure of in vitro angiogenesis. In summary, this assay can be used to identify genes and pathways that are involved in the promotion or inhibition of angiogenesis in a rapid, reproducible, and quantitative manner.

Endothelial Cell Tube Formation Assay for the In Vitro Study of Angiogenesis

The tube formation assay is a fast, quantifiable method for measuring in vitro angiogenesis. Endothelial cells are combined with conditioned media and plated on basement membrane extract. Tube formation occurs within hours and newly formed tubules easily quantified.

Angiogenesis is a vital process for normal tissue development and wound healing, but is also associated with a variety of pathological conditions. Using ...

Isolation of Murine Valve Endothelial Cells

Normal valve structures consist of stratified layers of specialized extracellular matrix (ECM) interspersed with valve interstitial cells (VICs) and surrounded by a monolayer of valve endothelial cells (VECs). VECs play essential roles in establishing the valve structures during embryonic development, and are important for maintaining life-long valve integrity and function. In contrast to a continuous endothelium over the surface of healthy valve leaflets, VEC disruption is commonly observed in malfunctioning valves and is associated with pathological processes that promote valve disease and dysfunction. Despite the clinical relevance, focused studies determining the contribution of VECs to development and disease processes are limited. The isolation of VECs from animal models would allow for cell-specific experimentation. VECs have been isolated from large animal adult models but due to their small population size, fragileness, and lack of specific markers, no reports of VEC isolations in embryos or adult small animal models have been reported. Here we describe a novel method that allows for the direct isolation of VECs from mice at embryonic and adult stages. Utilizing the Tie2-GFP reporter model that labels all endothelial cells with Green Fluorescent Protein (GFP), we have been successful in isolating GFP-positive (and negative) cells from the semilunar and atrioventricular valve regions using fluorescence activated cell sorting (FACS). Isolated GFP-positive VECs are enriched for endothelial markers, including CD31 and von Willebrand Factor (vWF), and retain endothelial cell expression when cultured; while, GFP-negative cells exhibit molecular profiles and cell shapes consistent with VIC phenotypes. The ability to isolate embryonic and adult murine VECs allows for previously unattainable molecular and functional studies to be carried out on a specific valve cell population, which will greatly improve our understanding of valve development and disease mechanisms.

The ability to isolate heart valve endothelial cells (VECs) is critical for understanding mechanisms of valve development, maintenance, and disease. Here we describe the isolation of VECs from embryonic and adult Tie2-GFP mice using FACS that will allow for studies determining the contribution of VECs in developmental and disease processes.

Normal valve structures consist of stratified layers of specialized extracellular matrix (ECM) interspersed with valve interstitial cells (VICs) and ...