The authors would like to thank Integrated Imaging Core facility at Johns Hopkins University for microscopes and data analysis software. We thank J. Snedeker and Q. E. Yu for proofreading and suggestions, and X.C. lab members for helpful discussions and suggestions. Supported by NIGMS/NIH R35GM127075, the Howard Hughes Medical Institute, the David and Lucile Packard Foundation, and Johns Hopkins University startup funds (X.C.).

1. Preparation of live cell imaging cocktail (live cell media)
<ol>
	<li>Supplement Schneider&#8217;s Drosophila medium with 15% fetal bovine serum (FBS) and 0.6x penicillin/streptomycin. Adjust the pH to approximately 7.0.</li>
	<li>Just before using the medium, add insulin to a final concentration of 200 &#181;g/mL. 
	NOTE: This media is critical for maintaining normal cell division and development of the Drosophila testis during time-lapse imaging10,14.</li>
</ol>
2. Preparation of glass bottom cell culture dish
<ol>
	<li>Use a poly L-lysine coated glass-bottom cell culture dish with a diameter of 35 mm for the Drosophila testis. The inner well of the dish has a glass bottom with a diameter of 23 mm and a side with an elevation of 1 mm (Figure 1A-a). 
	NOTE: Choose a glass-bottom dish that allows for a shorter working distance, larger numerical aperture, and higher magnification objective; these features are crucial to obtain a super-resolution image.</li>
	<li>Use a dialysis membrane (MWCO: 12&#8211;14kD) that allows for the gaseous exchange. Cut the membrane into small pieces. 
	NOTE: The membrane pieces should be smaller than the glass area of the dish but large enough to cover the specimen.</li>
	<li>Soak the membrane with 100 &#181;L of live cell media for ~5 min. Do not use a dry membrane on the sample, as it may damage it. Membrane helps prevent hypoxic stress.</li>
	<li>Prepare 2&#8211;3 light-weight glass or plastic pieces to put onto the membrane so that the tissue will not float. To do this, first take the outer ring of the 50 mL centrifuge tube and cut it into small pieces. Then, sterilize the pieces with 70% ethanol before use. 
	NOTE: This step ensures that the sample remains on the surface during imaging and does not float, which is crucial for obtaining optimal results.</li>
	<li>Prepare a ring ~25 mm in diameter and place it at the elevated side of the dish. Put a coverslip on it to generate two chambers. The bottom chamber will contain the sample while the top chamber will serve as a humidity chamber to prevent the sample from drying.
	<ol>
		<li>To make this ring, cut off the outer ring from a 50 mL centrifuge tube, which will allow it to fit securely on the elevated side of the 35 mm dish. A similar ring can be made in other ways, for example, by using a rubber band or plastic twist tie to fit on the elevated side of the dish to properly hold the coverslip without interfering with the sample. 
		NOTE: This step is critical, especially for samples sensitive to stresses such as hypoxic conditions, and changes in temperature and humidity.</li>
	</ol>
	</li>
</ol>
3. Dissection of testes from male flies and mounting
<ol>
	<li>Take ~10 young male flies (2&#8211;3 day old) and dissect the testes in the live cell media to obtain ~10 pairs of Drosophila adult testes.
	<ol>
		<li>Dissect the flies under a dissection microscope in a dissection dish using fine forceps. 
		NOTE: The Drosophila melanogaster (fruit fly) strain carries UAS-&#945;-Tubulin-GFP transgene driven by an early germ cell driver nanos-Gal4.</li>
		<li>Generate the following knock-in Drosophila melanogaster strains using the CRISPR-Cas9 technology: Lamin-mCherry (C-terminal tag) and CENP-A-Dendra2-CENP-A [tag at the internal site (between 118th - 119th codon)]. 
		NOTE: While only one testis of excellent quality is needed for each experiment, mounting enough number of tissues (15&#8211;20) or cells will ensure that there will be at least one healthy sample with excellent fluorescence signals for time-lapse imaging.</li>
	</ol>
	</li>
	<li>Wash the testes twice in live cell media in the dissection dish.
	<ol>
		<li>Use a pipette to add media followed by removing the live cell media as a washing step.</li>
		<li>Remove excess tissue using forceps. Any extra tissue will interfere with imaging. 
		NOTE: Do not use phosphate-buffered saline (PBS) for washing, because it may affect the dynamics of certain cellular components.</li>
	</ol>
	</li>
	<li>Add 100&#8211;150 &#181;L of live cell media into the dish (prepared in step 2.1) and spread it on the glass surface using a pipette tip. Spreading the media on the surface will allow the tissue to properly stick to the dish.</li>
	<li>Transfer the testes to the dish using fine forceps and bring them to the center of the dish (Figure 1A-b). 
	NOTE: Avoid transferring debris because it will interfere with imaging and could reduce the quality of the image.</li>
	<li>Remove excess live cell media (leave approximately 10 &#181;L of media) to allow for the tissue to flatten and stick properly to the dish. Perform this step quickly to avoid drying the sample.</li>
	<li>Place the pre-wet membrane (prepared in step 2.2 and 2.3) on top of the testes (Figure 1A-c).</li>
	<li>Put 2&#8211;3 small plastic weights (prepared in Step 2.4) on the membrane so that the sample will not float and quickly add 100&#8211;150 &#181;L of live cell media (Figure 1A-d). 
	NOTE: Adding media quickly and gently ensures that the sample will not dry out or become displaced.</li>
	<li>Place the plastic ring (prepared in step 2.5) on the elevated side of the dish (Figure 1B-a).</li>
	<li>Place a 22 mm x 22 mm coverslip on top of the ring (Figure 1B-b). This generates two chambers.</li>
	<li>Take a piece of tissue paper, dampen it with water, then swirl it and put it on the coverslip, to create a humid chamber (Figure 1B-c). Close the lid of the dish (Figure 1B-d) and begin live cell imaging. 
	NOTE: If the sample is light sensitive, perform section 3 in the dark.</li>
</ol>
4. Live cell imaging of Drosophila male germline stem cells (GSC) in situ
<ol>
	<li>Place the dish under the super-resolution microscope and secure it with the stage clamps.
	<ol>
		<li>Open the imaging software, turn on the transmitted light, and use 63x objective to focus on the testis tissue with the focus knob. 
		NOTE: If there is a difficulty in locating a sample with the 63x objective, then first use the 40x or 20x objective before switching to the 63x.</li>
		<li>Turn on the lasers, click Live, and find the GSC with the optimal position and condition. Avoid testes that have a low fluorescence signal or have the hub (niche) away from the surface. 
		NOTE: In Drosophila testes, the GSCs are attached to the hub.</li>
	</ol>
	</li>
	<li>Adjust the focus for the GSCs and identify the right settings for the sample, including laser power, electron-multiplying (EM) gain, averaging, and zoom for the Airyscan mode. Use the following settings as an example for Drosophila testes expressing EGFP tagged &#945;-tubulin in early-stage germ cells.
	<ol>
		<li>Set the frame size between 512 x 512 pixels and 1024 x 1024 pixels by clicking Frame Size.</li>
		<li>Set the frame average to 1 or 2 by clicking Averaging. 
		NOTE: Increasing the frame size (&#62;1024 x 1024 pixels) and performing more averaging (i.e., more than 2) could result in photobleaching or phototoxicity.</li>
		<li>Set the laser power to 1%&#8211;2% by clicking Lasers. 
		NOTE: Boosting the laser power may also lead to photobleaching or phototoxicity.</li>
		<li>Set the EM gain below the recommended level (&#60; 800) by clicking Master Gain. 
		NOTE: A higher EM gain may generate artifacts.</li>
		<li>Zoom in to the region or cell of interest to reduce the image acquisition time and reduce photobleaching. This also allows the specimen to survive for a longer time.</li>
	</ol>
	</li>
	<li>Start the time-lapse image capture using the Airyscan mode by clicking Start Experiment.
	<ol>
		<li>Before clicking Start Experiment, make sure that the acquisition is optimally configured.</li>
		<li>If it displays a warning with the notice &#8220;Airyscan acquisition is not configured optimally&#8221;, then click Optimal in frame size section, click Optimal in z-stack section, and click Optimal for scan area section (a minimum of 1.3 zoom is required for super-resolution imaging).</li>
	</ol>
	</li>
	<li>Optimize the time interval, number of z-slices, and duration of the time-lapse imaging according to the experimental design and the type of specimen, so that the quality of the image is not compromised and the cells will not be arrested at particular stages of the cell cycle.
	<ol>
		<li>As an example, the parameters for the time-lapse imaging of Drosophila testes expressing EGFP-tagged &#945;-tubulin in early germline are shown in the following steps.</li>
		<li>For more than 5 h time-lapse imaging, image at a 10 min interval with 1% laser power and take up to 30 z-slices at each time point.</li>
		<li>For highly dynamic cellular processes, such as microtubule dynamics, set a 2 min interval between time points, perform 1&#8211;2 h time-lapse imaging at 1% laser power, and take up to 30 z-slices at each time point.</li>
		<li>For rare cellular events, such as anaphase to early telophase chromatin dynamics (2&#8211;3 min events), set live cell imaging with a 1 min interval between time points, perform 30 min time-lapse imaging at 1% laser power, and take up to 30 z-slices at each time point. 
		NOTE: These parameters may vary for different samples, so alteration will be needed for optimal use for the specific sample.</li>
	</ol>
	</li>
	<li>Perform either time-lapse imaging or live snapshot imaging, depending on the sensitivity of the sample and the experimental design. 
	NOTE: A short movie is 15&#8211;30 min, and a long movie is more than 5 h.</li>
	<li>If the sample is very sensitive and cannot be studied by time-lapse imaging with a super-resolution microscope, as is often the case with Drosophila male GSCs, perform a super-resolution live snapshot (SRLS) of the sample at different cell cycle stages (as shown in Figure 2, Figure 3, Figure 4).
	<ol>
		<li>If a rare cell biological event is being captured or the protein of interest has low expression level, then perform SRLS.</li>
		<li>For SRLS, find a cell at the specific cell cycle stage you are interested in. For example, if focusing on microtubules-kinetochore binding, then use a cell at prometaphase or metaphase. 
		NOTE: This will help ensure that you get a high-quality image of the cell of interest at the right time without risking phototoxicity to the sample or bleaching of the fluorophores, which may occur during a longer movie.</li>
		<li>If using SRLS, image different cell cycle stages of interest across multiple cells and arrange these images in chronological order. 
		NOTE: This can be used to construct a temporal order of events while maximizing signal and tissue health, to obtain excellent temporal resolution of the event for particularly sensitive samples or samples with low signal.</li>
	</ol>
	</li>
</ol>
5. Airyscan processing of the live cell images
<ol>
	<li>After image acquisition with the imaging software, select Processing, click Batch, and then select Airyscan Processing.
	<ol>
		<li>Select the images to be processed and then click Run/Process to obtain the super-resolution images.</li>
		<li>Perform the processing using the default setting. 
		NOTE: Airyscan processing will only work if the imaging settings are properly established for Airyscan imaging.</li>
	</ol>
	</li>
</ol>

<ol>
	<li>Breedijk, R. M. P., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=A+live-cell+super-resolution+technique+demonstrated+by+imaging+germinosomes+in+wild-type+bacterial+spores.">A live-cell super-resolution technique demonstrated by imaging germinosomes in wild-type bacterial spores.</a> Scientific Reports. 10 (1), 5312 (2020).</li><li>Maddox, P. 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=Imaging+the+mitotic+spindle.">Imaging the mitotic spindle.</a> Methods in Enzymology. 505, 81-103 (2012).</li><li>Frigault, M. M., Lacoste, J., Swift, J. L., Brown, C. M. <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+microscopy+-+tips+and+tools.">Live-cell microscopy - tips and tools.</a> Journal of Cell Science. 122 (6), 753-767 (2009).</li><li>Bates, M., Jones, S. A., Zhuang, X. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Stochastic+optical+reconstruction+microscopy+(STORM):+A+method+for+super+resolution+fluorescence+imaging.">Stochastic optical reconstruction microscopy (STORM): A method for super resolution fluorescence imaging.</a> Cold Spring Harbor Protocols. 2013 (6), 075143 (2013).</li><li>Shroff, H., Galbraith, C. G., Galbraith, J. A., Betzig, E. <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+photoactivated+localization+microscopy+of+nanoscale+adhesion+dynamics.">Live-cell photoactivated localization microscopy of nanoscale adhesion dynamics.</a> Nature Methods. 5 (5), 417-423 (2008).</li><li>Vicidomini, G., Bianchini, P., Diaspro, A. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=STED+super-resolved+microscopy.">STED super-resolved microscopy.</a> Nature Methods. 15 (3), 173-182 (2018).</li><li>Huff, J. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=The+Airyscan+detector+from+ZEISS:+confocal+imaging+with+improved+signal-to-noise+ratio+and+super-resolution.">The Airyscan detector from ZEISS: confocal imaging with improved signal-to-noise ratio and super-resolution.</a> Nature Methods. 12 (12), (2015).</li><li>Huff, 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+new+2D+superresolution+mode+for+ZEISS+Airyscan.">The new 2D superresolution mode for ZEISS Airyscan.</a> Nature Methods. 14 (12), 1223 (2017).</li><li>Korobchevskaya, K., Lagerholm, B., Colin-York, H., Fritzsche, M. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Exploring+the+potential+of+Airyscan+microscopy+for+live+cell+imaging.">Exploring the potential of Airyscan microscopy for live cell imaging.</a> Photonics. 4 (4), 41 (2017).</li><li>Ranjan, R., Snedeker, J., Chen, X. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Asymmetric+centromeres+differentially+coordinate+with+mitotic+machinery+to+ensure+biased+sister+chromatid+segregation+in+germline+stem+cells.">Asymmetric centromeres differentially coordinate with mitotic machinery to ensure biased sister chromatid segregation in germline stem cells.</a> Cell Stem Cell. 25 (5), 666-681 (2019).</li><li>Kahney, E. W., Ranjan, R., Gleason, R. J., Chen, X. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Symmetry+from+asymmetry+or+asymmetry+from+symmetry.">Symmetry from asymmetry or asymmetry from symmetry.</a> Cold Spring Harbor Symposia on Quantitative Biology. 82, 305-318 (2017).</li><li>Wooten, M., Ranjan, R., Chen, X. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Asymmetric+histone+inheritance+in+asymmetrically+dividing+stem+cells.">Asymmetric histone inheritance in asymmetrically dividing stem cells.</a> Trends in Genetics. 36 (1), 30-43 (2020).</li><li>Wooten, 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=Asymmetric+histone+inheritance+via+strand-specific+incorporation+and+biased+replication+fork+movement.">Asymmetric histone inheritance via strand-specific incorporation and biased replication fork movement.</a> Nature Structural &amp; Molecular Biology. 26 (8), 732-743 (2019).</li><li>Prasad, M., Jang, A. C. C., Starz-Gaiano, M., Melani, M., Montell, D. J. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=A+protocol+for+culturing+Drosophila+melanogaster+stage+9+egg+chambers+for+live+imaging.">A protocol for culturing Drosophila melanogaster stage 9 egg chambers for live imaging.</a> Nature Protocols. 2 (10), 2467-2473 (2007).</li><li>Schermelleh, L., Heintzmann, R., Leonhardt, H. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=A+guide+to+super-resolution+fluorescence+microscopy.">A guide to super-resolution fluorescence microscopy.</a> Journal of Cell Biology. 190 (2), 165-175 (2010).</li><li>Sivaguru, 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=Comparative+performance+of+airyscan+and+structured+illumination+superresolution+microscopy+in+the+study+of+the+surface+texture+and+3D+shape+of+pollen.">Comparative performance of airyscan and structured illumination superresolution microscopy in the study of the surface texture and 3D shape of pollen.</a> Microscopy Research and Technique. 81 (2), 101-114 (2018).</li></ol>

The authors declare no conflict of interest.

Super-resolution microscopy methods provide spatial resolution as high as 10s of nanometers4,5,6. The STORM and PALM microscopy methods allow resolution up to 20 to 50 nm (XY-resolution), while STED microscopy offers resolution of 20 to 100 nm (XY-resolution). The spatial resolution of SIM microscopy is limited to 100 to 130 nm15. However, due to its high-photon density and lengthy acquisition time, it is extremely ch...

Visualizing subcellular structures and protein dynamics in live cells with resolution beyond the diffraction limit of light is typically very challenging1-3. While multiple super-resolution techniques such as Stochastic-Optical-Reconstruction-Microscopy (STORM), Photo-Activated-Localization-Microscopy (PALM) and Stimulated-Emission-Depletion (STED)4,5,6 microscopy have been developed, complications in specimen preparation as well as the need to maintain viability and activity ex vivo, limit the use of conventional super-resolution microscopy for imaging live samples. Conventional confocal microscopy cannot reach spatial resolution beyond ~230 nm XY-resolution and is often insufficient to observe intricate cellular substructures5,6. However, a recent development in confocal microscopy, Airyscan super-resolution imaging, is able to achieve approximately 140 nm (XY-resolution)7,8 and has a relatively simple sample preparation that is compatible with live imaging. Since this imaging detection system requires a long acquisition time, its high spatial resolution does come at the cost of temporal resolution9. Therefore, a method is needed to ensure that live cell imaging is extended with high spatial resolution.
Here, we developed a method for observing live cells in intact tissue at its optimal resolution to decipher subcellular structures with detailed spatial information. This method is designed as such so that samples can be mounted stably for a long period of time (~ 10 h) without moving or degenerating. The live cell media used in this technique can support cellular function and avoid photobleaching for up to 10 hours under a super-resolution microscope. Finally, this protocol minimizes most stresses caused by the constant illumination of lasers over extended periods of time such as hypoxia, changes in humidity and temperature, as well as nutrient exhaustion.
Using this protocol to image Drosophila male germline stem cells (GSCs), we were able to observe how the asymmetric activity of microtubules allows for preferential interaction with epigenetically distinct sister chromatids10,11,12,13. These types of cellular events are highly dynamic and are very difficult to visualize in live cells using other super-resolution imaging methods such as STORM, PALM, or STED. We anticipate that this method will become highly useful for cell biologists as they aim to understand the dynamic subcellular structures of live cells residing in tissues. There are many areas in which this method can be applied to, such as studying the dynamics of proteins; understanding the movement of cells; and lineage tracing and cellular differentiation processes, among other possible applications.

<table>
	<tbody>
		<tr>
			<td>Adobe Illustrator CS6 (figure making software)</td>
			<td>Adobe</td>
			<td>N/A</td>
			<td></td>
		</tr>
		<tr>
			<td>Dialysis membrane</td>
			<td>Spectra/Por 1-4 Standard RC Dialysis Membrane</td>
			<td>Cat No. 08-67121</td>
			<td></td>
		</tr>
		<tr>
			<td>FBS</td>
			<td>Thermo Fisher Scientific</td>
			<td>Cat. no. 26140079</td>
			<td>15% (V/V)</td>
		</tr>
		<tr>
			<td>Fiji (analysis software)</td>
			<td>NIH</td>
			<td>N/A</td>
			<td>Image fluorescence intensity quantification</td>
		</tr>
		<tr>
			<td>Glass bottom cell culture dishes (FluroDish)</td>
			<td>World Precision Instrument, Inc.</td>
			<td>FD35PDL-100</td>
			<td></td>
		</tr>
		<tr>
			<td>Imaris (image reconstruction software)</td>
			<td>Bitplane</td>
			<td>N/A</td>
			<td>3D image reconstruction</td>
		</tr>
		<tr>
			<td>Imerssion oil</td>
			<td>Zeiss</td>
			<td>Immersol 518F/30 &#176;C</td>
			<td></td>
		</tr>
		<tr>
			<td>Insulin</td>
			<td>Sigma</td>
			<td>Cat. No. 15550</td>
			<td>200 &#181;g/ml</td>
		</tr>
		<tr>
			<td>Penicillin/streptomycin</td>
			<td>Invitrogen</td>
			<td>Cat No. - 15140-122</td>
			<td>0.6x</td>
		</tr>
		<tr>
			<td>Schneider Drosophila media</td>
			<td>Invitrogen</td>
			<td>Cat No. - 11720-034</td>
			<td></td>
		</tr>
		<tr>
			<td>Spinning disc confocal microscope</td>
			<td>Zeiss</td>
			<td>N/A</td>
			<td>equipped with an evolve camera (Photometrics), using a 63x Zeiss objective (1.4 NA).</td>
		</tr>
		<tr>
			<td>Tissue paper</td>
			<td>Kimwipe</td>
			<td>N/A</td>
			<td>Wet to form humid chamber</td>
		</tr>
		<tr>
			<td>LSM 800 confocal microscope with AiryScan super-resolution module</td>
			<td>Zeiss</td>
			<td>N/A</td>
			<td>equipped with highly sensitive GaAsP (Gallium Arsenide Phosphide) detectors using a 63x Zeiss objective (1.4 NA)</td>
		</tr>
		<tr>
			<td>ZEN (imaging software)</td>
			<td>Zeiss</td>
			<td>N/A</td>
			<td></td>
		</tr>
	</tbody>
</table>

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.

Live cell imaging beyond the diffraction limit in Drosophila tissue, especially for GSCs, provides an opportunity to investigate the dynamics of subcellular events in the context of cell cycle progression. Recently, a study utilizing this protocol has shown that microtubule activities at the mother centrosome versus the daughter centrosome are temporally asymmetric in GSCs10. The mother centrosome emanates microtubules approximately 4 hours prior to the mitotic entry, whereas the daughter...

Watch this Scientific Journal Video about Super-Resolution Live Cell Imaging of Subcellular Structures at JoVE.com

Super-Resolution Live Cell Imaging of Subcellular Structures

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 ...

super-resolution-live-cell-imaging-of-subcellular-structures

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4.6K Views.  The Johns Hopkins University. 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.

Video: Super-Resolution Live Cell Imaging of Subcellular Structures

Super-resolution Imaging of the Bacterial Division Machinery

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

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

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

4D Imaging of Protein Aggregation in Live Cells

One of the key tasks of any living cell is maintaining the proper folding of newly synthesized proteins in the face of ever-changing environmental conditions and an intracellular environment that is tightly packed, sticky, and hazardous to protein stability1. The ability to dynamically balance protein production, folding and degradation demands highly-specialized quality control machinery, whose absolute necessity is observed best when it malfunctions. Diseases such as ALS, Alzheimer's, Parkinson's, and certain forms of Cystic Fibrosis have a direct link to protein folding quality control components2, and therefore future therapeutic development requires a basic understanding of underlying processes. Our experimental challenge is to understand how cells integrate damage signals and mount responses that are tailored to diverse circumstances.
The primary reason why protein misfolding represents an existential threat to the cell is the propensity of incorrectly folded proteins to aggregate, thus causing a global perturbation of the crowded and delicate intracellular folding environment1. The folding health, or "proteostasis," of the cellular proteome is maintained, even under the duress of aging, stress and oxidative damage, by the coordinated action of different mechanistic units in an elaborate quality control system3,4. A specialized machinery of molecular chaperones can bind non-native polypeptides and promote their folding into the native state1, target them for degradation by the ubiquitin-proteasome system5, or direct them to protective aggregation inclusions6-9.
In eukaryotes, the cytosolic aggregation quality control load is partitioned between two compartments8-10: the juxtanuclear quality control compartment (JUNQ) and the insoluble protein deposit (IPOD) (Figure 1 - model). Proteins that are ubiquitinated by the protein folding quality control machinery are delivered to the JUNQ, where they are processed for degradation by the proteasome. Misfolded proteins that are not ubiquitinated are diverted to the IPOD, where they are actively aggregated in a protective compartment.
Up until this point, the methodological paradigm of live-cell fluorescence microscopy has largely been to label proteins and track their locations in the cell at specific time-points and usually in two dimensions. As new technologies have begun to grant experimenters unprecedented access to the submicron scale in living cells, the dynamic architecture of the cytosol has come into view as a challenging new frontier for experimental characterization. We present a method for rapidly monitoring the 3D spatial distributions of multiple fluorescently labeled proteins in the yeast cytosol over time. 3D timelapse (4D imaging) is not merely a technical challenge; rather, it also facilitates a dramatic shift in the conceptual framework used to analyze cellular structure.
We utilize a cytosolic folding sensor protein in live yeast to visualize distinct fates for misfolded proteins in cellular aggregation quality control, using rapid 4D fluorescent imaging. The temperature sensitive mutant of the Ubc9 protein10-12 (Ubc9ts) is extremely effective both as a sensor of cellular proteostasis, and a physiological model for tracking aggregation quality control. As with most ts proteins, Ubc9ts is fully folded and functional at permissive temperatures due to active cellular chaperones. Above 30 &deg;C, or when the cell faces misfolding stress, Ubc9ts misfolds and follows the fate of a native globular protein that has been misfolded due to mutation, heat denaturation, or oxidative damage. By fusing it to GFP or other fluorophores, it can be tracked in 3D as it forms Stress Foci, or is directed to JUNQ or IPOD.

Cellular viability depends on timely and efficient management of protein misfolding. Here we describe a method for visualizing the different potential fates of a misfolded protein: refolding, degradation, or sequestration in inclusions. We demonstrate the use of a folding sensor, Ubc9ts, for monitoring proteostasis and aggregation quality control in live cells using 4D microscopy.

One of the key tasks of any living cell is maintaining the proper folding of newly synthesized proteins in the face of ever-changing environmental ...

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, ...

Test Samples for Optimizing STORM Super-Resolution Microscopy

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

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

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

Imaging Cell Membrane Injury and Subcellular Processes Involved in Repair

The ability of injured cells to heal is a fundamental cellular process, but cellular and molecular mechanisms involved in healing injured cells are poorly understood. Here assays are described to monitor the ability and kinetics of healing of cultured cells following localized injury. The first protocol describes an end point based approach to simultaneously assess cell membrane repair ability of hundreds of cells. The second protocol describes a real time imaging approach to monitor the kinetics of cell membrane repair in individual cells following localized injury with a pulsed laser. As healing injured cells involves trafficking of specific proteins and subcellular compartments to the site of injury, the third protocol describes the use of above end point based approach to assess one such trafficking event (lysosomal exocytosis) in hundreds of cells injured simultaneously and the last protocol describes the use of pulsed laser injury together with TIRF microscopy to monitor the dynamics of individual subcellular compartments in injured cells at high spatial and temporal resolution. While the protocols here describe the use of these approaches to study the link between cell membrane repair and lysosomal exocytosis in cultured muscle cells, they can be applied as such for any other adherent cultured cell and subcellular compartment of choice.

The process of healing injured cells involves trafficking of specific proteins and subcellular compartments to the site of cell membrane injury. This protocol describes assays to monitor these processes.

The ability of injured cells to heal is a fundamental cellular process, but cellular and molecular mechanisms involved in healing injured cells are poorly ...

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 imaging assays which allows adhesion of single virions to glass surfaces with specificity. This preparation is based on grafting the surface of the glass with a mixture of PLL-g-PEG and PLL-g-PEG-Biotin, adding a layer of avidin, and finally creating virion anchors through attachment of biotinylated virus specific antibodies. We have applied this technique across a range of experiments including atomic force microscopy (AFM) and super-resolution fluorescence imaging. This sample preparation method results in a control adhesion of the virions to the surface.

The attachment of virions to a surface is a requirement for single virion imaging by Super-resolution fluorescence imaging or atomic force microscopy (AFM). Here we demonstrate a sample preparation method for controlled adhesion of virions to glass surfaces suitable for use in AFM 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 ...

Super-resolution Imaging of the Cytokinetic Z Ring in Live Bacteria Using Fast 3D-Structured Illumination Microscopy (f3D-SIM)

Imaging of biological samples using fluorescence microscopy has advanced substantially with new technologies to overcome the resolution barrier of the diffraction of light allowing super-resolution of live samples. There are currently three main types of super-resolution techniques &#8211; stimulated emission depletion (STED), single-molecule localization microscopy (including techniques such as PALM, STORM, and GDSIM), and structured illumination microscopy (SIM). While STED and single-molecule localization techniques show the largest increases in resolution, they have been slower to offer increased speeds of image acquisition. Three-dimensional SIM (3D-SIM) is a wide-field fluorescence microscopy technique that offers a number of advantages over both single-molecule localization and STED. Resolution is improved, with typical lateral and axial resolutions of 110 and 280 nm, respectively and depth of sampling of up to 30 &#181;m from the coverslip, allowing for imaging of whole cells. Recent advancements (fast 3D-SIM) in the technology increasing the capture rate of raw images allows for fast capture of biological processes occurring in seconds, while significantly reducing photo-toxicity and photobleaching. Here we describe the use of one such method to image bacterial cells harboring the fluorescently-labelled cytokinetic FtsZ protein to show how cells are analyzed and the type of unique information that this technique can provide.

Super-resolution Imaging of the Cytokinetic Z Ring in Live Bacteria Using Fast 3D-Structured Illumination Microscopy f3D-SIM

Spatiotemporal information about dynamic proteins inside live cells is crucial for understanding biology. A type of super-resolution microscopy called fast 3D-structured illumination microscopy (f3D-SIM) reveals unique information about the cytokinetic Z ring in bacteria: both its bead-like appearance and the rapid dynamics of FtsZ within the ring.

Imaging of biological samples using fluorescence microscopy has advanced substantially with new technologies to overcome the resolution barrier of the ...

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

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

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

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

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.

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 ...

Ground State Depletion Super-resolution Imaging in Mammalian Cells

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

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

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