Name: live-cell imaging of fungal cells to investigate modes of entry and subcellular localization of antifungal plant defensins
Uploaded: 2017-12-24T12:30:00
Description: Watch this Scientific Journal Video about Live-cell Imaging of Fungal Cells to Investigate Modes of Entry and Subcellular Localization of Antifungal Plant Defensins at JoVE.com

We thank Dr. R. Howard Berg, Director of the Integrated Microscopy Facility at the Donald Danforth Plant Science Center, for his guidance and help with confocal microscopy. The authors have no conflict of interest to declare.

1. Labeling of Defensins with Fluorophores
<ol>
	<li>Select a fluorophore that has minimum effect on the antimicrobial properties as well as the uptake and localization of defensin inside the living cell. 
	NOTE: Selecting optimal fluorophore depends on specific experimental objectives. The spectral and chemical properties, photostability, size and charge of the fluorophore should also be considered.</li>
	<li>Label defensin with the selected fluorophore using an appropriate peptide labeling kit available from com...

<ol>
	<li>Jones, J. D. G., Dangl, J. L. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=The+plant+immune+system.">The plant immune system.</a> Nature. 444 (7117), 323-329 (2006).</li><li>Tavormina, P., De Coninck, B., Nikonorova, N., De Smet, I., Cammue, B. P. A. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=The+Plant+Peptidome:+An+expanding+repertoire+of+structural+features+and+biological+functions.">The Plant Peptidome: An expanding repertoire of structural features and biological functions.</a> Plant cell. 27 (8), 2095-2118 (2015).</li><li>Van Der Weerden, N. L., Bleackley, M. R., Anderson, M. A. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Properties+and+mechanisms+of+action+of+naturally+occurring+antifungal+peptides.">Properties and mechanisms of action of naturally occurring antifungal peptides.</a> Cell. and Mol. Life Sci. 70 (19), 3545-3570 (2013).</li><li>Van der Weerden, N. L., Anderson, M. A. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Plant+defensins:+Common+fold,+multiple+functions.">Plant defensins: Common fold, multiple functions.</a> Fungal Biol Rev. 26 (4), 121-131 (2013).</li><li>De Coninck, B., Cammue, B. P. A., Thevissen, K. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Modes+of+antifungal+action+and+in+planta+functions+of+plant+defensins+and+defensin-like+peptides.">Modes of antifungal action and in planta functions of plant defensins and defensin-like peptides.</a> Fungal Biol Rev. 26 (4), 109-120 (2013).</li><li>Kaur, J., Sagaram, U. S., Shah, D. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Can+plant+defensins+be+used+to+engineer+durable+commercially+useful+fungal+resistance+in+crop+plants?.">Can plant defensins be used to engineer durable commercially useful fungal resistance in crop plants?.</a> Fungal Biol. Rev. 25 (3), 128-135 (2011).</li><li>Vriens, K., Cammue, B. P. A., Thevissen, K. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Antifungal+plant+defensins:+Mechanisms+of+action+and+production.">Antifungal plant defensins: Mechanisms of action and production.</a> Molecules. 19 (8), 12280-12303 (2014).</li><li>Sagaram, U. S., Kaur, J., Shah, D. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Antifungal+plant+defensins:+Structure-activity+relationships,+modes+of+action,+and+biotech+applications.">Antifungal plant defensins: Structure-activity relationships, modes of action, and biotech applications.</a> ACS Symp. Ser. 1095, 317-336 (2012).</li><li>Thevissen, K., Francois, I. E. J. A., Aerts, A. M., Cammue, B. P. A. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Fungal+sphingolipids+as+targets+for+the+development+of+selective+antifungal+therapeutics.">Fungal sphingolipids as targets for the development of selective antifungal therapeutics.</a> Curr. Drug Targets. 6 (8), 923-928 (2005).</li><li>Thevissen, K., Kristensen, H. H., Thomma, B. P. H. J., Cammue, B. P. A., Francois, I. E. J. A. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Therapeutic+potential+of+antifungal+plant+and+insect+defensins.">Therapeutic potential of antifungal plant and insect defensins.</a> Drug Discov. Today. 12 (21-22), 966-971 (2007).</li><li>Aerts, A. M., Fran&#231;ois, I. E. J. A., Cammue, B. P. A., Thevissen, K. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=The+mode+of+antifungal+action+of+plant,+insect+and+human+defensins.">The mode of antifungal action of plant, insect and human defensins.</a> Cell. Mol. Life Sci. 65 (13), 2069-2079 (2008).</li><li>Van Der Weerden, N. L., Lay, F. T., Anderson, M. A. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=The+plant+defensin,+NaD1,+enters+the+cytoplasm+of+Fusarium+oxysporum+hyphae.">The plant defensin, NaD1, enters the cytoplasm of Fusarium oxysporum hyphae.</a> J. Biol. Chem. 283 (21), 14445-14452 (2008).</li><li>Lobo, D. S., Pereira, I. 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=Antifungal+Pisum+sativum+Defensin+1+Interacts+with+Neurospora+crassa+Cyclin+F+Related+to+the+Cell+Cycle.">Antifungal Pisum sativum Defensin 1 Interacts with Neurospora crassa Cyclin F Related to the Cell Cycle.</a> Biochemistry. 46 (4), 987-996 (2007).</li><li>El-Mounadi, K., Islam, K. T., Hernandez-Ortiz, P., Read, N. D., Shah, D. M. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Antifungal+mechanisms+of+a+plant+defensin+MtDef4+are+not+conserved+between+the+ascomycete+fungi+Neurospora+crassa+and+Fusarium+graminearum.">Antifungal mechanisms of a plant defensin MtDef4 are not conserved between the ascomycete fungi Neurospora crassa and Fusarium graminearum.</a> Mol. Microbiol. 100 (3), 542-559 (2016).</li><li>Baxter, A. 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=The+Tomato+Defensin+TPP3+Binds+Phosphatidylinositol+(4,5)-Bisphosphate+via+a+Conserved+Dimeric+Cationic+Grip+Conformation+To+Mediate+Cell+Lysis.">The Tomato Defensin TPP3 Binds Phosphatidylinositol (4,5)-Bisphosphate via a Conserved Dimeric Cationic Grip Conformation To Mediate Cell Lysis.</a> Mol. and Cell. Biol. 35 (11), 1964-1978 (2015).</li><li>Kvansakul, 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=Binding+of+phosphatidic+acid+by+NsD7+mediates+the+formation+of+helical+defensin-lipid+oligomeric+assemblies+and+membrane+permeabilization.">Binding of phosphatidic acid by NsD7 mediates the formation of helical defensin-lipid oligomeric assemblies and membrane permeabilization.</a> Proc. Natl. Acad. Sci. 113, 11202-11207 (2016).</li><li>Poon, I. K. H., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Phosphoinositide-mediated+oligomerization+of+a+defensin+induces+cell+lysis.">Phosphoinositide-mediated oligomerization of a defensin induces cell lysis.</a> eLife. 3, e01808 (2014).</li><li>Mu&#241;oz, A., Read, N. D. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Live-cell+imaging+and+analysis+shed+light+on+the+complexity+and+dynamics+of+antimicrobial+Peptide+action.">Live-cell imaging and analysis shed light on the complexity and dynamics of antimicrobial Peptide action.</a> Front. Immunol. 3, 248 (2012).</li><li>Hayes, B. M. 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=Identification+and+mechanism+of+action+of+the+plant+defensin+NaD1+as+a+new+member+of+the+antifungal+drug+arsenal+against+candida+albicans.">Identification and mechanism of action of the plant defensin NaD1 as a new member of the antifungal drug arsenal against candida albicans.</a> Antimicrob. Agents Chemother. 57 (8), 3667-3675 (2013).</li><li>Mu&#241;oz, A., Marcos, J. F., Read, N. D. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Concentration-dependent+mechanisms+of+cell+penetration+and+killing+by+the+de+novo+designed+antifungal+hexapeptide+PAF26.">Concentration-dependent mechanisms of cell penetration and killing by the de novo designed antifungal hexapeptide PAF26.</a> Mol. Microbiol. 85 (1), 89-106 (2012).</li><li>Eaton, C. 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=The+guanine+nucleotide+exchange+factor+RIC8+regulates+conidial+germination+through+G&#945;+proteins+in+Neurospora+crassa.">The guanine nucleotide exchange factor RIC8 regulates conidial germination through G&#945; proteins in Neurospora crassa.</a> PLoS One. 7 (10), e48026 (2012).</li><li>Leslie, J. F., Summerell, 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=.">.</a> The Fusarium. laboratory manual. , (2006).</li><li>Broekaert, W. F., Terras, F. R. G., Cammue, B. P. A., Vanderleyden, J. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=An+automated+quantitative+assay+for+fungal+growth+inhibition.">An automated quantitative assay for fungal growth inhibition.</a> FEMS Microbiol.Lett. 69 (1-2), 55-59 (1990).</li><li>Sagaram, U. S., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Structural+and+functional+studies+of+a+phosphatidic+acid-binding+antifungal+plant+defensin+MtDef4:+Identification+of+an+RGFRRR+motif+governing+fungal+cell+entry.">Structural and functional studies of a phosphatidic acid-binding antifungal plant defensin MtDef4: Identification of an RGFRRR motif governing fungal cell entry.</a> PLoS One. 8 (12), 1-22 (2013).</li><li>Uchida, 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=Soft+X-ray+tomography+of+phenotypic+switching+and+the+cellular+response+to+antifungal+peptoids+in+Candida+albicans.">Soft X-ray tomography of phenotypic switching and the cellular response to antifungal peptoids in Candida albicans.</a> Proc. Natl. Acad. Sci. 106 (46), 19375-19380 (2009).</li><li>Nair, R., 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=Better+prediction+of+sub-cellular+localization+by+combining+evolutionary+and+structural+information.">Better prediction of sub-cellular localization by combining evolutionary and structural information.</a> Proteins Struct. Funct. Bioinform. 53 (4), 917-930 (2003).</li><li>Scott, M. S., Calafell, S. J., Thomas, D. Y., Hallett, M. T. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Refining+protein+subcellular+localization.">Refining protein subcellular localization.</a> PLoS Comput. Biol. 1 (6), e66 (2005).</li><li>Shagaghi, N., Bhave, M., Palombo, E., Clayton, A. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Revealing+the+sequence+of+interactions+of+PuroA+peptide+with+Candida+albicans+cells+by+live-cell+imaging.">Revealing the sequence of interactions of PuroA peptide with Candida albicans cells by live-cell imaging.</a> Sci. Rep. 7, 43542 (2017).</li></ol>

In this study, a reliable live-cell imaging methodology with the use of fluorescently labeled antifungal defensins was described to study the kinetics of the internalization of these peptides into fungal cells and to determine their subcellular targets. This method is a powerful tool to visualize the dynamics of the interaction between defensins and fungal cells temporally and spatially.
Various methods have been used to study the internalization and intracellular localization of plant defensi...

Plants have evolved a sophisticated innate immune system for defense against the microbial plant pathogens1. They express numerous gene-encoded host defense peptides with putative antimicrobial activity2. Indeed, many of these peptides display antimicrobial activity in vitro3. Defensins comprise one of the largest groups of host defense peptides in the plant kingdom4. These cysteine-rich, cationic peptides exhibit potent growth inhibitory activity against fungal and oomycete pathogens at micromolar concentrations and represent one of the first lines of defense against these pathogens5,6. Because of their potent antifungal activity, defensins can be exploited in agribiotechnological applications to generate disease resistant crops. Constitutive overexpression of several plant defensins has been shown to enhance disease resistance in the greenhouse and field tests of transgenic crops6. It is important to unravel the mechanisms of action (MOA) of these antifungal peptides in order to fully harness their potential as effective tools for crop protection. However, the MOA of these plant defensins are poorly understood. Current evidence suggests that they exhibit different MOA5,6,7,8. Some defensins act extracellularly on fungi and target specific cell wall/plasma membrane resident sphingolipids, disrupt membrane integrity and activate cellular toxicity pathways9,10,11. Recently, however, antifungal defensins that translocate into fungal cells have been discovered12,13,14. Some of these defensins bind to membrane-resident bioactive phospholipids, form oligomeric complexes and permeabilize plasma membranes15,16,17. Thus, some aspects of the MOA of plant defensins have been elucidated. However, the MOA of plant defensins likely involve a complex set of events which have not yet been identified and integrated into a comprehensive model. In particular, there remains a major gap in our understanding of the cellular targets of these peptides.
With recent advances in microscopy technologies and the development of new fluorescent probes, live-cell imaging techniques are now frequently used to study the MOA of antimicrobial peptides (AMPs). These techniques complement widely used methods such as immunolocalization, electron microscopy, atomic force microscopy or X-ray tomography18, which have been employed mostly to analyze the effects of antifungal peptides on the morphology and growth of fungal cells including the study of cell wall integrity, alterations in cell growth/branching patterns, as well as plasma membrane permeabilization and killing. Nevertheless, these studies have been limited to imaging cells at a certain time point after treatment with the peptides instead of performing time-lapse imaging on the same cells to monitor their dynamic changes in response to defensin challenge. In recent years, use of fluorescently labeled peptides in conjunction with live cell imaging using confocal microscopy has enabled real-time visualization of the dynamics of AMP&#8211;microbe interactions. Both naturally purified and chemically synthesized antifungal peptides can be tagged with fluorescent labels (e.g., DyLight, rhodamine, BODIPY, or Alexa Fluor based dyes) and directly observed during their interaction with cells by time-lapse live-cell imaging. The use of these labeled peptides has significantly increased our understanding of the different aspects of their MOA including mode of entry, subcellular localization, intracellular trafficking, and sites of antifungal action within living fungal cells18.
Recently, several studies have shown that various antifungal peptides including plant defensins are internalized by living fungal cells12,14,19,20. The MOA of these defensins likely involve interaction with intracellular targets. We have recently reported the antifungal action of a plant defensin MtDef4 in two ascomycete fungi, Neurospora crassa and Fusarium graminearum. MtDef4 was shown to use different pathways for fungal cell entry and subcellular localization in these fungi14. This study used chemically synthesized tetramethyl rhodamine (TAMRA)-labeled MtDef4 in combination with vital fluorescent dyes (the membrane selective dye, FM4-64; membrane-permeant dye, SYTOX Green; the cell death reporter dye, propidium iodide) and metabolic inhibitors. These analyses demonstrated the kinetics of the internalization of MtDef4, its mechanisms of intracellular transportation and its subcellular targets14.
Here, a protocol for live-cell imaging using confocal microscopy is presented. The protocol utilizes fluorescently labeled peptides in combination with vital fluorescent dyes to study plant defensin-fungal interactions, in particular, the pathways of translocation and the intracellular targets of defensins in fungal cells.

<table>
	<tbody>
		<tr>
			<td>FM4-64 Dye</td>
			<td>Life Technologies</td>
			<td>T13320</td>
			<td></td>
		</tr>
		<tr>
			<td>DyLight 550 Antibody Labeling Kit</td>
			<td>Thermo Scientific</td>
			<td>84530</td>
			<td></td>
		</tr>
		<tr>
			<td>Glass Bottom Microwell Dishes</td>
			<td>Mat TeK</td>
			<td>P35G-1.5-10-C</td>
			<td></td>
		</tr>
		<tr>
			<td>Mira cloth</td>
			<td>EMD Millipore Corp</td>
			<td>475855-1R</td>
			<td></td>
		</tr>
		<tr>
			<td>SP8-X confocal microscope</td>
			<td>Leica</td>
			<td></td>
			<td></td>
		</tr>
		<tr>
			<td>ImageJ software</td>
			<td>FiJi</td>
			<td></td>
			<td>For Image analysis</td>
		</tr>
		<tr>
			<td>Imaris software</td>
			<td>Bitplane</td>
			<td></td>
			<td>For Image analysis</td>
		</tr>
	</tbody>
</table>

live-cell imaging of fungal cells to investigate modes of entry and subcellular localization of antifungal plant defensins

Small cysteine-rich defensins are one of the largest groups of host defense peptides present in all plants. Many plant defensins exhibit potent in vitro antifungal activity against a broad-spectrum of fungal pathogens and therefore have the potential to be used as antifungal agents in transgenic crops. In order to harness the full potential of plant defensins for diseases control, it is crucial to elucidate their mechanisms of action (MOA). With the advent of advanced microscopy techniques, live-cell imaging has become a powerful tool for understanding the dynamics of the antifungal MOA of plant defensins. Here, a confocal microscopy based live-cell imaging method is described using two fluorescently labeled plant defensins (MtDef4 and MtDef5) in combination with vital fluorescent dyes. This technique enables real-time visualization and analysis of the dynamic events of MtDef4 and MtDef5 internalization into fungal cells. Importantly, this assay generates a wealth of information including internalization kinetics, mode of entry and subcellular localization of these peptides. Along with other cell biological tools, these methods have provided critical insights into the dynamics and complexity of the MOA of these peptides. These tools can also be used to compare the MOA of these peptides against different fungi.

Live cell imaging was carried out to track and compare the internalization and subcellular localization of two defensins, MtDef4 and MtDef5, from Medicago truncatula; in fungal cells. TMR-MtDef4 was chemically synthesized while MtDef5 was labeled with Dylight550 (Dylight550-MtDef5). Conidia were incubated with either defensin in combination with the membrane selective dye FM4-64. Figure 1 shows that TMR-MtDef4 has different trafficking pathways in <e...

Watch this Scientific Journal Video about Live-cell Imaging of Fungal Cells to Investigate Modes of Entry and Subcellular Localization of Antifungal Plant Defensins at JoVE.com

Live-cell Imaging of Fungal Cells to Investigate Modes of Entry and Subcellular Localization of Antifungal Plant Defensins

Plant defensins play an important role in plant defense against pathogens. For effective use of these antifungal peptides as antifungal agents, understanding their modes of action (MOA) is critical. Here, a live-cell imaging method is described to study critical aspects of the MOA of these peptides.

Small cysteine-rich defensins are one of the largest groups of host defense peptides present in all plants. Many plant defensins exhibit potent in vitro ...

The overall goal of this live-cell imaging method is to study critical aspects of the mechanisms of action of antifungal plant defensins in fungal cells. With the advent of advanced confocal microscopy techniques, live-cell imaging has become a powerful tool to study the modes of action of antifungal plant defensins. Making use of this technology, here we present a method to help answer key question in understanding the modes of action of antifungal plant defensins.Our focuses are how these peptides are internalized into the fungal cells and how these peptides are localized into the cell organelles or diffused in the cytoplasm. To make a conidial suspension of PH-1 strain of Fusarium graminearum, first set up cultures of the strain on plates containing complete medium. Culture them at 28 degrees Celsius over five days.To produce conidia, inoculate four 10-millimeter diameter plugs of the five-day-old culture into 50 milliliters of carboxymethyl cellulose medium. Culture these plugs for four to seven days at 28 degrees Celsius on a rotary shaker set to 180 rpm. When the cultures have a red color, the conidia have formed.To collect the conidia in a suspension, vortex the liquid culture, and filter one milliliter of it through two layers of filtration material, into a two-milliliter microcentrifuge tube. Centrifuge the suspension for two minutes, and discard the supernatant. Then, wash the pellet with one milliliter of sterile water, and repeat the centrifugation.Next, resuspend the pellet in one milliliter of 2x SFM. Then, count the conidia using a hemocytometer, and adjust the density of the suspension to 100, 000 conidia per milliliter. To make a Neurospora crassa conidial suspension, transfer conidia from stock cultures to a slant tube containing Vogel's agar medium, and incubate the tubes at room temperature under constant light for five days.After five days, transfer a small amount of growing culture, using an inoculation loop, to a microcentrifuge tube containing two milliliters of Vogel's liquid medium. Be sure to mix the conidia off the loop. Then, filter the suspension, centrifuge it, and resuspend the pellet of conidia in Vogel's medium without a wash step.Finally, adjust the final suspension to 100, 000 conidia per milliliter. To make a germlings preparation for confocal microscopy, pipette 50 microliters of conidia suspension onto a 35-millimeter culture dish, and let the conidia germinate for three to six hours at room temperature. For confocal microscopy, pipette 50 microliters of conidial suspension into a 10-millimeter microwell of glass-bottom dish.Then, at the predetermined minimal inhibitory concentration, add 50 microliters of fluorescently labeled defensins to the suspension, and incubate the conidia with the labeled defensins for 2.5 hours at room temperature. After the incubation, add two microliters of the membrane selective dye FM4-64, for a final concentration of five micromolar. Then, incubate the culture for 30 minutes at room temperature prior to examining the conidia.To set up the confocal microscope, select the white light laser. Use the 488-nanometer and 550-nanometer lasers to excite the rhodamine-labeled defensins and the FM4-64 dye, respectively. Set these lasers to an intensity of 1%Then, set the detection wavelengths to 580 to 700 nanometers for the rhodamine-labeled defensin and from 690 to 800 nanometers for the FM4-64 dye.Now, collect the images. For time-lapse imaging, add 50 microliters of conidial suspension into a glass-bottom microwell dish. Next, mount the microwell dish on the microscope, and find the cells under low power.Then, switch to a 100x, 1.44 oil objective. To observe the DyLight550-labeled defensins, set the laser line to 550 nanometers for excitation and from 560 to 600 nanometers for detection. Next, set the scan mode to xyzt.Then, set the Z-position, the zoom, the frequency of image capture, and so forth, as needed. Now, to the conidial suspension, add 50 microliters of fluorophore-labeled defensins at the minimal inhibitory concentration of three micromolar, and add two microliters of membrane selective dye FM4-64 for a final concentration of five micromolar. Then, refocus the optics if needed.Before capturing images, place small pieces of wet filter paper in the microwell dish to prevent evaporation. Then, process with capturing an image every 3.5 minutes over 2.5 hours. Live-cell imaging was carried out to track and compare the internalization and subcellular localization of two defensins from Medicago truncatula.Chemically synthesized rhodamine-labeled defensin four was trafficked differently in Neurospora crassa and Fusarium graminearum. FM4-64 labeled the plasma membranes of both fungi. However, in Fusarium, defensin four is diffused in the cytoplasm.Whereas, in Neurospora, it is transported to vesicular bodies. For comparison, defensin five was visualized using a DyLight550 label in Neurospora crassa, along with plasma membrane labeling by FM4-64. Time-lapse imaging shows that this defensin enters the cells within 30 to 40 minutes and then diffuses through the cytoplasm.This differs from the trafficking of defensin four, which enters the cells and remains trapped within the vesicular bodies even after three hours. In summary, live-cell imaging is a powerful tool to increase our understanding of the modes of action of antifungal plant differences. With other vital fluorescent dyes and cellular markers, it has the flexibility to be modified for other antimicrobial peptides.Ultimately, this technique can help to develop new strategies for use of antimicrobial peptides as an antifungal agent in agriculture and medicine.

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Biology

Live-cell Imaging and Quantitative Analysis of Embryonic Epithelial Cells in Xenopus laevis

Embryonic epithelial cells serve as an ideal model to study morphogenesis where multi-cellular tissues undergo changes in their geometry, such as changes in cell surface area and cell height, and where cells undergo mitosis and migrate. Furthermore, epithelial cells can also regulate morphogenetic movements in adjacent tissues1. A traditional method to study epithelial cells and tissues involve chemical fixation and histological methods to determine cell morphology or localization of particular proteins of interest. These approaches continue to be useful and provide "snapshots" of cell shapes and tissue architecture, however, much remains to be understood about how cells acquire specific shapes, how various proteins move or localize to specific positions, and what paths cells follow toward their final differentiated fate. High resolution live imaging complements traditional methods and also allows more direct investigation into the dynamic cellular processes involved in the formation, maintenance, and morphogenesis of multicellular epithelial sheets. Here we demonstrate experimental methods from the isolation of animal cap tissues from Xenopus laevis embryos to confocal imaging of epithelial cells and simple measurement approaches that together can augment molecular and cellular studies of epithelial morphogenesis.

Live-cell Imaging and Quantitative Analysis of Embryonic Epithelial Cells in Xenopus laevis

Xenopus embryonic epithelia are an ideal model system to study cell behaviors such as polarity development and shape change during epithelial morphogenesis. Traditional histology of fixed samples is increasingly being complemented by live-cell confocal imaging. Here we demonstrate methods to isolate frog tissues and visualize live epithelial cells and their cytoskeleton using live-cell confocal microscopy.

Embryonic epithelial cells serve as an ideal model to study morphogenesis where multi-cellular tissues undergo changes in their geometry, such as changes ...

Fluorescence-based Measurement of Store-operated Calcium Entry in Live Cells: from Cultured Cancer Cell to Skeletal Muscle Fiber

Store operated Ca2+ entry (SOCE), earlier termed capacitative Ca2+ entry, is a tightly regulated mechanism for influx of extracellular Ca2+ into cells to replenish depleted endoplasmic reticulum (ER) or sarcoplasmic reticulum (SR) Ca2+ stores1,2. Since Ca2+ is a ubiquitous second messenger, it is not surprising to see that SOCE plays important roles in a variety of cellular processes, including proliferation, apoptosis, gene transcription and motility. Due to its wide occurrence in nearly all cell types, including epithelial cells and skeletal muscles, this pathway has received great interest3,4. However, the heterogeneity of SOCE characteristics in different cell types and the physiological function are still not clear5-7.
The functional channel properties of SOCE can be revealed by patch-clamp studies, whereas a large body of knowledge about this pathway has been gained by fluorescence-based intracellular Ca2+ measurements because of its convenience and feasibility for high-throughput screening. The objective of this report is to summarize a few fluorescence-based methods to measure the activation of SOCE in monolayer cells, suspended cells and muscle fibers5,8-10. The most commonly used of these fluorescence methods is to directly monitor the dynamics of intracellular Ca2+ using the ratio of F340nm and F380nm (510 nm for emission wavelength) of the ratiometric Ca2+ indicator Fura-2. To isolate the activity of unidirectional SOCE from intracellular Ca2+ release and Ca2+ extrusion, a Mn2+ quenching assay is frequently used. Mn2+ is known to be able to permeate into cells via SOCE while it is impervious to the surface membrane extrusion processes or to ER uptake by Ca2+ pumps due to its very high affinity with Fura-2. As a result, the quenching of Fura-2 fluorescence induced by the entry of extracellular Mn2+ into the cells represents a measurement of activity of SOCE9. Ratiometric measurement and the Mn+2 quenching assays can be performed on a cuvette-based spectrofluorometer in a cell population mode or in a microscope-based system to visualize single cells. The advantage of single cell measurements is that individual cells subjected to gene manipulations can be selected using GFP or RFP reporters, allowing studies in genetically modified or mutated cells. The spatiotemporal characteristics of SOCE in structurally specialized skeletal muscle can be achieved in skinned muscle fibers by simultaneously monitoring the fluorescence of two low affinity Ca2+ indicators targeted to specific compartments of the muscle fiber, such as Fluo-5N in the SR and Rhod-5N in the transverse tubules9,11,12.

The extent of store-operated Ca2+ entry (SOCE) can be monitored using fluorescent Ca2+ indicators. Mn2+ quenching of such indicators assays SOCE in cultured cells and skeletal muscle fibers. A technique allowing spatial and temporal resolution of SOCE by confocal imaging of mechanically skinned muscle fibers is also described.

Store operated Ca2+ entry (SOCE), earlier termed capacitative Ca2+ entry, is a tightly regulated mechanism for influx of extracellular Ca2+ into cells to ...

Live Cell Imaging of Early Autophagy Events: Omegasomes and Beyond

Autophagy is a cellular response triggered by the lack of nutrients, especially the absence of amino acids. Autophagy is defined by the formation of double membrane structures, called autophagosomes, that sequester cytoplasm, long-lived proteins and protein aggregates, defective organelles, and even viruses or bacteria. Autophagosomes eventually fuse with lysosomes leading to bulk degradation of their content, with the produced nutrients being recycled back to the cytoplasm. Therefore, autophagy is crucial for cell homeostasis, and dysregulation of autophagy can lead to disease, most notably neurodegeneration, ageing and cancer.	
	Autophagosome formation is a very elaborate process, for which cells have allocated a specific group of proteins, called the core autophagy machinery. The core autophagy machinery is functionally complemented by additional proteins involved in diverse cellular processes, e.g. in membrane trafficking, in mitochondrial and lysosomal biology. Coordination of these proteins for the formation and degradation of autophagosomes constitutes the highly dynamic and sophisticated response of autophagy. Live cell imaging allows one to follow the molecular contribution of each autophagy-related protein down to the level of a single autophagosome formation event and in real time, therefore this technique offers a high temporal and spatial resolution.	
	Here we use a cell line stably expressing GFP-DFCP1, to establish a spatial and temporal context for our analysis. DFCP1 marks omegasomes, which are precursor structures leading to autophagosomes formation. A protein of interest (POI) can be marked with either a red or cyan fluorescent tag. Different organelles, like the ER, mitochondria and lysosomes, are all involved in different steps of autophagosome formation, and can be marked using a specific tracker dye. Time-lapse microscopy of autophagy in this experimental set up, allows information to be extracted about the fourth dimension, i.e. time. Hence we can follow the contribution of the POI to autophagy in space and time.

Time-lapse microscopy of fluorescently labeled autophagy markers allows monitoring of the dynamic autophagy response with high temporal resolution. Using specific autophagy and organelle markers in a combination of 3 different colors, we can follow the contribution of a protein to autophagosome formation in a robust spatial and temporal context.

Autophagy is a  cellular response triggered by the lack of nutrients, especially the absence of  amino acids. Autophagy is defined by the formation of ...

Utilizing pHluorin-tagged Receptors to Monitor Subcellular Localization and Trafficking

Understanding membrane protein trafficking, assembly, and expression requires an approach that differentiates between those residing in intracellular organelles and those localized on the plasma membrane. Traditional fluorescence-based measurements lack the capability to distinguish membrane proteins residing in different organelles. Cutting edge methodologies transcend traditional methods by coupling pH-sensitive fluorophores with total internal reflection fluorescence microscopy (TIRFM). TIRF illumination excites the sample up to approximately 150 nm from the glass-sample interface, thus decreasing background, increasing the signal to noise ratio, and enhancing resolution. The excitation volume in TIRFM encompasses the plasma membrane and nearby organelles such as the peripheral ER. Superecliptic pHluorin (SEP) is a pH sensitive version of GFP. Genetically encoding SEP into the extracellular domain of a membrane protein of interest positions the fluorophore on the luminal side of the ER and in the extracellular region of the cell. SEP is fluorescent when the pH is greater than 6, but remains in an off state at lower pH values. Therefore, receptors tagged with SEP fluoresce when residing in the endoplasmic reticulum (ER) or upon insertion in the plasma membrane (PM) but not when confined to a trafficking vesicle or other organelles such as the Golgi. The extracellular pH can be adjusted to dictate the fluorescence of receptors on the plasma membrane. The difference in fluorescence between TIRF images at neutral and acidic extracellular pH for the same cell corresponds to a relative number of receptors on the plasma membrane. This allows a simultaneous measurement of intracellular and plasma membrane resident receptors. Single vesicle insertion events can also be measured when the extracellular pH is neutral, corresponding to a low pH trafficking vesicle fusing with the plasma membrane and transitioning into a fluorescent state. This versatile technique can be exploited to study localization, expression, and trafficking of membrane proteins.

Labeling the extracellular domain of a membrane protein with a pH sensitive fluorophore, superecliptic pHluorin (SEP), allows subcellular localization, expression, and trafficking to be determined. Imaging SEP-labeled proteins with total internal reflection fluorescence microscopy (TIRFM) enables the quantification of protein levels in the peripheral ER and plasma membrane.

Understanding membrane protein trafficking, assembly, and expression requires an approach that differentiates between those residing in intracellular ...

Live-cell Imaging of Platelet Degranulation and Secretion Under Flow

Blood platelets are essential players in hemostasis, the formation of thrombi to seal vascular breaches. They are also involved in thrombosis, the formation of thrombi that occlude the vasculature and injure organs, with life-threatening consequences. This motivates scientific research on platelet function and the development of methods to track cell-biological processes as they occur under flow conditions.
A variety of flow models are available for the study of platelet adhesion and aggregation, two key phenomena in platelet biology. This work describes a method to study real-time platelet degranulation under flow during activation. The method makes use of a flow chamber coupled to a syringe-pump setup that is placed under a wide-field, inverted, LED-based fluorescence microscope. The setup described here allows for the simultaneous excitation of multiple fluorophores that are delivered by fluorescently labeled antibodies or fluorescent dyes. After live-cell imaging experiments, the cover glasses can be further processed and analyzed using static microscopy (i.e., confocal microscopy or scanning electron microscopy).

This work describes a fluorescence microscopy-based method for the study of platelet adhesion, spreading, and secretion under flow. This versatile platform enables the investigation of platelet function for mechanistic research on thrombosis and hemostasis.

Blood platelets are essential players in hemostasis, the formation of thrombi to seal vascular breaches. They are also involved in thrombosis, 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.

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

Isolation of Culturable Yeasts and Molds from Soils to Investigate Fungal Population Structure

Soil is host to an incredible amount of microbial life, with each gram containing up to billions of bacterial, archaeal, and fungal cells. Multicellular fungi such as molds and unicellular fungi, broadly defined as yeasts, fulfill essential roles in soil ecosystems as decomposers of organic material and as food sources for other soil dwellers. Fungal species diversity in soil is dependent on a multitude of climatic factors such as rainfall and temperature, as well as soil properties including organic matter, pH, and moisture. Lack of adequate environmental sampling, especially in regions of Asia, Africa, South America, and Central America, hinders the characterization of soil fungal communities and the discovery of novel species. 
We characterized soil fungal communities in nine countries across six continents using ~4,000 soil samples and a protocol developed in the laboratory for the isolation of yeasts and molds. This protocol begins with separate selective enrichment for yeasts and the medically relevant mold Aspergillus fumigatus, in liquid media while inhibiting bacterial growth. Resulting colonies are then transferred to solid media and further processed to obtain pure cultures, followed by downstream genetic characterization. Yeast species identity is established via sequencing of their internal transcribed spacer (ITS) region of the nuclear ribosomal RNA gene cluster, while global population structure of A. fumigatus is explored via microsatellite marker analysis. 
The protocol was successfully applied to isolate and characterize soil yeast and A. fumigatus populations in Cameroon, Canada, China, Costa Rica, Iceland, Peru, New Zealand, and Saudi Arabia. These findings revealed much-needed insights on global patterns in soil yeast diversity, as well as global population structure and antifungal resistance profiles of A. fumigatus. This paper presents the method of isolating both yeasts and A. fumigatus from international soil samples.

This protocol is an effective, speedy method of culturing yeasts and the mold Aspergillus fumigatus from large sets of soil samples in as little as 7 days. The methods can be easily modified to accommodate a range of incubation media and temperatures as needed for experiments.

Soil is host to an incredible amount of microbial life, with each gram containing up to billions of bacterial, archaeal, and fungal cells. Multicellular ...

Imaging Neutrophil Migration in the Mouse Skin to Investigate Subcellular Membrane Remodeling Under Physiological Conditions

The study of immune cell recruitment and function in tissues has been a very active field over the last two decades. Neutrophils are among the first immune cells to reach the site of inflammation and to participate in the innate immune response during infection or tissue damage. So far, neutrophil migration has been successfully visualized using various in vitro experimental systems based on uniform stimulation, or confined migration under agarose, or micro-fluidic channels. However, these models do not recapitulate the complex microenvironment that neutrophils encounter in vivo. The development of multiphoton microscopy (MPM)-based techniques, such as intravital subcellular microscopy (ISMic), offer a unique tool to visualize and investigate neutrophil dynamics at subcellular resolutions under physiological conditions. In particular, the ear of a live anesthetized mouse provides an experimental advantage to follow neutrophil interstitial migration in real-time due to its ease of accessibility and lack of surgical exposure. ISMic provides the optical resolution, speed, and depth of acquisition necessary to track both cellular and, more importantly, subcellular processes in 3D over time (4D). Moreover, multi-modal imaging of the interstitial microenvironment (i.e., blood vessels, resident cells, extracellular matrix) can be readily accomplished using a combination of transgenic mice expressing select fluorescent markers, exogenous labeling via fluorescent probes, tissue intrinsic fluorescence, and second/third harmonic generated signals. This protocol describes 1) the preparation of neutrophils for adoptive transfer into the mouse ear, 2) different settings for optimal sub-cellular imaging, 3) strategies to minimize motion artifacts while maintaining a physiological response, 4) examples of membrane remodeling observed in neutrophils using ISMic, and 5) a workflow for the quantitative analysis of membrane remodeling in migrating neutrophils in vivo.

Neutrophil migration relies on the rapid and continuous remodeling of the plasma membrane in response to chemoattractant and its interactions with the extracellular microenvironment. Described herein is a procedure based on Intravital Subcellular Microscopy to investigate the dynamic of membrane remodeling in neutrophils injected in the ear of anesthetized mice.

The study of immune cell recruitment and function in tissues has been a very active field over the last two decades. Neutrophils are among the first ...

Visualization of Cellular Interactions Between the Maize Sheaths and Fungi

Detached Maize Sheaths for Live-Cell Imaging of Infection by Fungal Foliar Maize Pathogens

We have optimized a protocol to inoculate maize leaf sheaths with hemibiotrophic and necrotrophic foliar pathogenic fungi. The method is modified from one originally applied to rice leaf sheaths and allows direct microscopic observation of fungal growth and development in living plant cells. Leaf sheaths collected from maize seedlings with two fully emerged leaf collars are inoculated with 20 &#181;L drops of 5 x 105 spores/mL fungal spore suspensions and incubated in humidity chambers at 23 &#176;C under continuous fluorescent light. After 24-72 h, excess tissue is removed with a razor blade to leave a single layer of epidermal cells, an optically clear sample that can be imaged directly without the necessity for chemical fixation or clearing. Plant and fungal cells remain alive for the duration of the experiment and interactions can be visualized in real-time. Sheaths can be stained or subjected to plasmolysis to study the developmental cytology and viability of host and pathogen cells during infection and colonization. Fungal strains transformed to express fluorescent proteins can be inoculated or co-inoculated on the sheaths for increased resolution and to facilitate the evaluation of competitive or synergistic interactions. Fungal strains expressing fluorescent fusion proteins can be used to track and quantify the production and targeting of these individual proteins in planta. Inoculated sheath tissues can be extracted to characterize nucleic acids, proteins, or metabolites. The use of these sheath assays has greatly advanced the detailed studies of the mechanisms of fungal pathogenicity in maize and also of fungal protein effectors and secondary metabolites contributing to pathogenicity.

Author Spotlight: Investigating Fungal Pathogenicity Mechanisms in Maize 

This manuscript details an optimized inoculation protocol that uses detached maize leaf sheaths for reproducible cytological, physiological, and molecular studies of maize interactions with fungal plant pathogens. The leaf sheaths facilitate real-time observation of cellular interactions between the living plant and fungus in unfixed tissues.

We have optimized a protocol to inoculate maize leaf sheaths with hemibiotrophic and necrotrophic foliar pathogenic fungi. The method is modified from one ...

Live Cell Imaging of ATG9A Constructs

For live cell imaging of ATG9A constructs, seed HEK293A cells in two milliliters of high-glucose DMEM into a 60-millimeter tissue culture dish until they reach 65 to 70%confluency. The next day, prepare and add the lipofectamine DNA mixture to the cell culture plate containing four milliliters of growth medium and gently rock the plate back and forth to distribute the mix evenly. Incubate the cells at 37 degrees Celsius and 10%carbon dioxide.After four hours of transfection, replace the growth medium with a fresh medium and incubate the cells overnight at 37 degrees Celsius with 10%carbon dioxide. The next day, trypsinize the cells by adding trypsin EDTA. Then, count the detached cells and re-seed them on a culture dish suitable for live microscopy overnight.The next day, image the cells using a confocal microscope. In basal conditions, ATG9A is mainly localized at the Golgi network as indicated by the immunofluorescence of the endogenous protein and overlaps with GM130, a cis-Golgi marker. eGFP N-terminally-tagged ATG9A and mRFP N-terminally tagged ATG9A were less localized at the Golgi and primarily resided in vesicles.In contrast, eGFPc terminally tagged ATG9A is more prone to aggregate within the cell. Fusing a 3x-FLAG sequence between an N-terminal fluorophore and ATG9A helped the overexpressed protein behave similarly to the endogenous one. The overexpressed mCherry 3x-FLAG ATG9A colocalizes with the Golgi marker GM130 in fed conditions.This localization and the AG9A vesicular compartment were preserved over time, allowing the spatiotemporal study of the trafficking of ATG9A.