Name: exploiting live imaging to track nuclei during myoblast differentiation and fusion
Uploaded: 2019-04-13T14:00:00
Description: Watch this Scientific Journal Video about Exploiting Live Imaging to Track Nuclei During Myoblast Differentiation and Fusion at JoVE.com

This work was supported by the AFM-Telethon to E.V. (#21545) and by the Ospedale San Raffaele (OSR) Seed Grant to S.Z. (ZAMBRA5X1000). Dr. Jean-Yves Tinevez from the Image Analysis Hub of the Institut Pasteur is acknowledged for publicly sharing his &#34;Simple Tracker&#34; MATLAB routines.

All procedures involving animal subjects were approved by the San Raffaele Institutional Animal Care and Use Committee.
1. Dissection of mouse hindlimb muscles
<ol>
	<li>Sterilize tweezers and scissors (both straight and curved) by autoclaving.</li>
	<li>Prepare and filter (0.22 &#181;m) all the media (blocking medium, digestion medium, proliferating medium, and differentiating medium) before starting the experiment (see Table of Materials).</li>
	<li>Put 5 mL of phosphate-b...

<ol>
	<li>Janssen, I., Heymsfield, S. B., Wang, Z. M., Ross, R. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Skeletal+muscle+mass+and+distribution+in+468+men+and+women+aged+18-88+yr.">Skeletal muscle mass and distribution in 468 men and women aged 18-88 yr.</a> Journal of Applied physiology. 89 (1), 81-88 (2000).</li><li>Ten Broek, R. W., Grefte, S., Von den Hoff, J. W. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Regulatory+factors+and+cell+populations+involved+in+skeletal+muscle+regeneration.">Regulatory factors and cell populations involved in skeletal muscle regeneration.</a> Journal of Cellular Physiology. 224 (1), 7-16 (2010).</li><li>Bentzinger, C. F., Wang, Y. X., Dumont, N. A., Rudnicki, M. 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(120), e55047 (2017).</li><li>Roman, W., Gomes, E. R. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Nuclear+positioning+in+skeletal+muscle.">Nuclear positioning in skeletal muscle.</a> Seminars in Cell &amp; Developmental Biology. , (2017).</li><li>Pimentel, M. R., Falcone, S., Cadot, B., Gomes, E. R. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=In+Vitro+Differentiation+of+Mature+Myofibers+for+Live+Imaging.">In Vitro Differentiation of Mature Myofibers for Live Imaging.</a> Journal of Visualized Experiments. (119), e55141 (2017).</li><li>Foudi, 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=Analysis+of+histone+2B-GFP+retention+reveals+slowly+cycling+hematopoietic+stem+cells.">Analysis of histone 2B-GFP retention reveals slowly cycling hematopoietic stem cells.</a> Nature Biotechnology. 27 (1), 84-90 (2009).</li><li>Tirone, 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=High+mobility+group+box+1+orchestrates+tissue+regeneration+via+CXCR4.">High mobility group box 1 orchestrates tissue regeneration via CXCR4.</a> The Journal of Experimental Medicine. 215 (1), 303-318 (2018).</li><li>Zambrano, S., De Toma, I., Piffer, A., Bianchi, M. E., Agresti, A. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=NF-kappaB+oscillations+translate+into+functionally+related+patterns+of+gene+expression.">NF-kappaB oscillations translate into functionally related patterns of gene expression.</a> eLife. 5, e09100 (2016).</li><li>Adamski, D., 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=Effects+of+Hoechst+33342+on+C2C12+and+PC12+cell+differentiation.">Effects of Hoechst 33342 on C2C12 and PC12 cell differentiation.</a> FEBS Letters. 581 (16), 3076-3080 (2007).</li><li>Otsu, N. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=A+Threshold+Selection+Method+from+Gray-Level+Histograms.">A Threshold Selection Method from Gray-Level Histograms.</a> IEEE Transactions on Systems, Man, and Cybernetics. 9 (1), 62-66 (1979).</li><li>. Simpel Tracker - File Exchange - MATLAB Central Available from: <a target="_blank" href="https://it.mathworks.com/matlabcentral/fileexchange/34040-simple-tracker">https://it.mathworks.com/matlabcentral/fileexchange/34040-simple-tracker</a> (2016)</li><li>Burkard, R., Dell'Amico, M., Martello, S. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=.">.</a> Assignment Problems, Revised Reprint. , (2009).</li><li>Falcone, 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=N-WASP+is+required+for+Amphiphysin-2/BIN1-dependent+nuclear+positioning+and+triad+organization+in+skeletal+muscle+and+is+involved+in+the+pathophysiology+of+centronuclear+myopathy.">N-WASP is required for Amphiphysin-2/BIN1-dependent nuclear positioning and triad organization in skeletal muscle and is involved in the pathophysiology of centronuclear myopathy.</a> EMBO Molecular Medicine. 6 (11), 1455-1475 (2014).</li><li>Syverud, B. C., Lee, J. D., VanDusen, K. W., Larkin, L. M. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Isolation+and+Purification+of+Satellite+Cells+for+Skeletal+Muscle+Tissue+Engineering.">Isolation and Purification of Satellite Cells for Skeletal Muscle Tissue Engineering.</a> Journal of Regenerative Medicine. 3 (2), (2014).</li><li>Liu, L., Cheung, T. H., Charville, G. W., Rando, T. A. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Isolation+of+skeletal+muscle+stem+cells+by+fluorescence-activated+cell+sorting.">Isolation of skeletal muscle stem cells by fluorescence-activated cell sorting.</a> Nature Protocols. 10 (10), 1612-1624 (2015).</li></ol>

Muscle fibers (myofibers) are multinucleated cells that are formed by the fusion of muscle precursors cells (myoblasts) derived from muscle stem cells (satellite cells) that undergo proliferation and differentiation2,3,4. To assess myoblast differentiation, the common procedure consists of culturing myoblasts in differentiating medium and fixing the cells at different time points to perform immunofluorescence staining for MyHC, ...

Skeletal muscle is the largest tissue in the human body, totaling 35%-40% of body mass1. Satellite cells are muscle stem cells, anatomically characterized by their position (juxtaposed to the plasma membrane, underneath the basal lamina of muscle fibers), that give rise to proliferating myoblasts (myogenic progenitor cells), which eventually differentiate and integrate into existing myofibers and/or fuse to form new myofibers2,3,4. Their discovery and the progress in the study of their biology has led to significant insights into muscle development and regeneration.
Protocols to isolate and differentiate myoblasts into myotubes have been developed many years ago and are still widely used to study skeletal muscle differentiation5,6,7. However, most of these methods represent static procedures that rely on the analysis of fixed cells and, consequently, do not allow scientists to fully explore highly dynamic processes, such as myoblast fusion and myofiber maturation. The most striking example is nuclear positioning, which is tightly regulated, with nuclei initially in the center of the myofiber and, then, located at the periphery after myofiber maturation8,9. Live imaging is the most appropriate technique to obtain further insights into such a peculiar phenomenon.
Here, we describe a method that enables scientists to record myoblast differentiation and myotube formation by time-lapse microscopy and to perform quantitative analyses from the automatic tracking of myoblast nuclei. This method provides a high-throughput quantitative characterization of nuclear dynamics and myoblast behavior during differentiation and fusion. The protocol is divided into four different parts, namely (1) the collection of muscles from the hindlimbs of mice, (2) the isolation of primary myoblasts that consists in mechanical and enzymatic digestion, (3) myoblast proliferation and differentiation, and (4) live imaging to track nuclei within the first 16 h of myoblast differentiation.
In the following procedure, myoblasts are isolated from H2B-GFP mice and treated with 1 &#181;g/mL of doxycycline to induce H2B-GFP expression, as previously described10. Alternatively, it is possible to isolate the myoblasts from other transgenic mice that express a fluorescent protein in the nucleus or to transfect the cells isolated from wild-type mice to express a fluorescent protein in the nucleus, as described by Pimentel et al.9.

<table>
	<tbody>
		<tr>
			<td>chicken embryos extract</td>
			<td>Seralab</td>
			<td>CE-650-J</td>
			<td></td>
		</tr>
		<tr>
			<td>collagenase</td>
			<td>Sigma</td>
			<td>C9263-1G</td>
			<td>125units/mg</td>
		</tr>
		<tr>
			<td>collagen from calf skin</td>
			<td>Sigma</td>
			<td>C8919</td>
			<td></td>
		</tr>
		<tr>
			<td>dispase</td>
			<td>Gibco</td>
			<td>17105-041</td>
			<td>1.78 units/mg</td>
		</tr>
		<tr>
			<td>doxyciclin</td>
			<td>Sigma</td>
			<td>D1515</td>
			<td></td>
		</tr>
		<tr>
			<td>DMEM</td>
			<td>Sigma</td>
			<td>D5671</td>
			<td></td>
		</tr>
		<tr>
			<td>fetal bovine serum</td>
			<td>Life technologies</td>
			<td>10270106</td>
			<td></td>
		</tr>
		<tr>
			<td>gentamicin</td>
			<td>Sigma</td>
			<td>G1397</td>
			<td></td>
		</tr>
		<tr>
			<td>Horse serum</td>
			<td>Invitrogen</td>
			<td>16050-098</td>
			<td></td>
		</tr>
		<tr>
			<td>Hoechst</td>
			<td>life technologies</td>
			<td>33342</td>
			<td></td>
		</tr>
		<tr>
			<td>IMDM</td>
			<td>Sigma</td>
			<td>I3390</td>
			<td></td>
		</tr>
		<tr>
			<td>L-glutamine</td>
			<td>Sigma</td>
			<td>G7513</td>
			<td></td>
		</tr>
		<tr>
			<td>Matrigel</td>
			<td>Corning</td>
			<td>356231</td>
			<td></td>
		</tr>
		<tr>
			<td>penicillin-streptomycin</td>
			<td>Sigma</td>
			<td>P0781</td>
			<td></td>
		</tr>
		<tr>
			<td>red blood cells lysis medium</td>
			<td>Biolegend</td>
			<td>420301</td>
			<td></td>
		</tr>
		<tr>
			<td>Digestion medium</td>
			<td></td>
			<td></td>
			<td></td>
		</tr>
		<tr>
			<td>collagenase</td>
			<td>40 mg</td>
			<td></td>
			<td></td>
		</tr>
		<tr>
			<td>dispase</td>
			<td>70 mg</td>
			<td></td>
			<td></td>
		</tr>
		<tr>
			<td>PBS</td>
			<td>20 ml</td>
			<td></td>
			<td></td>
		</tr>
		<tr>
			<td>filtered 0.22um</td>
			<td></td>
			<td></td>
			<td></td>
		</tr>
		<tr>
			<td>Blocking medium</td>
			<td></td>
			<td></td>
			<td></td>
		</tr>
		<tr>
			<td>DMEM</td>
			<td></td>
			<td></td>
			<td></td>
		</tr>
		<tr>
			<td>Fetal bovine serum</td>
			<td>10%</td>
			<td></td>
			<td></td>
		</tr>
		<tr>
			<td>L-glutammine</td>
			<td>1%</td>
			<td></td>
			<td></td>
		</tr>
		<tr>
			<td>penicillin-streptomycin</td>
			<td>1%</td>
			<td></td>
			<td></td>
		</tr>
		<tr>
			<td>gentamicin</td>
			<td>1 &#8240;</td>
			<td></td>
			<td></td>
		</tr>
		<tr>
			<td>filtered 0.22um</td>
			<td></td>
			<td></td>
			<td></td>
		</tr>
		<tr>
			<td>proliferation medium</td>
			<td></td>
			<td></td>
			<td></td>
		</tr>
		<tr>
			<td>IMDM</td>
			<td></td>
			<td></td>
			<td></td>
		</tr>
		<tr>
			<td>Fetal bovine serum</td>
			<td>20%</td>
			<td></td>
			<td></td>
		</tr>
		<tr>
			<td>L-glutammine</td>
			<td>1%</td>
			<td></td>
			<td></td>
		</tr>
		<tr>
			<td>penicillin-streptomycin</td>
			<td>1%</td>
			<td></td>
			<td></td>
		</tr>
		<tr>
			<td>gentamicin</td>
			<td>1 &#8240;</td>
			<td></td>
			<td></td>
		</tr>
		<tr>
			<td>chichen embryo extract</td>
			<td>3%</td>
			<td></td>
			<td></td>
		</tr>
		<tr>
			<td>filtered 0.22um</td>
			<td></td>
			<td></td>
			<td></td>
		</tr>
		<tr>
			<td>differentiation medium</td>
			<td></td>
			<td></td>
			<td></td>
		</tr>
		<tr>
			<td>IMDM</td>
			<td></td>
			<td></td>
			<td></td>
		</tr>
		<tr>
			<td>Horse serum</td>
			<td>2%</td>
			<td></td>
			<td></td>
		</tr>
		<tr>
			<td>L-glutammine</td>
			<td>1%</td>
			<td></td>
			<td></td>
		</tr>
		<tr>
			<td>penicillin-streptomycin</td>
			<td>1%</td>
			<td></td>
			<td></td>
		</tr>
		<tr>
			<td>gentamicin</td>
			<td>1 &#8240;</td>
			<td></td>
			<td></td>
		</tr>
		<tr>
			<td>chichen embryo extract</td>
			<td>1%</td>
			<td></td>
			<td></td>
		</tr>
		<tr>
			<td>filtered 0.22um</td>
			<td></td>
			<td></td>
			<td></td>
		</tr>
	</tbody>
</table>

exploiting live imaging to track nuclei during myoblast differentiation and fusion

Nuclear positioning within cells is important for multiple cellular processes in development and regeneration. The most intriguing example of nuclear positioning occurs during skeletal muscle differentiation. Muscle fibers (myofibers) are multinucleated cells formed by the fusion of muscle precursor cells (myoblasts) derived from muscle stem cells (satellite cells) that undergo proliferation and differentiation. Correct nuclear positioning within myofibers is required for the proper muscle regeneration and function. The common procedure to assess myoblast differentiation and myofiber formation relies on fixed cells analyzed by immunofluorescence, which impedes the study of nuclear movement and cell behavior over time. Here, we describe a method for the analysis of myoblast differentiation and myofiber formation by live cell imaging. We provide a software for automated nuclear tracking to obtain a high-throughput quantitative characterization of nuclear dynamics and myoblast behavior (i.e., the trajectory) during differentiation and fusion.

To automatically follow nuclear movement during myoblast differentiation in live imaging, the nuclei should preferentially be fluorescently labeled. It is important to note that using DNA-intercalating molecules is not feasible because these molecules interfere with the proliferation and differentiation of primary myoblasts13. As an example, proliferation and differentiation have been analyzed in primary myoblasts cultured with or without Hoechst (<strong class="xf...

Watch this Scientific Journal Video about Exploiting Live Imaging to Track Nuclei During Myoblast Differentiation and Fusion at JoVE.com

Exploiting Live Imaging to Track Nuclei During Myoblast Differentiation and Fusion

Skeletal muscle differentiation is a highly dynamic process, which particularly relies on nuclear positioning. Here, we describe a method to track nuclei movements by live cell imaging during myoblast differentiation and myotube formation and to perform a quantitative characterization of nuclei dynamics by extracting information from automatic tracking.

Nuclear positioning within cells is important for multiple cellular processes in development and regeneration. The most intriguing example of nuclear ...

Without protocol, it is possible to investigate the dynamic process of myoblast differentiation and myofiber formation, in particular nuclear positioning by exploiting live cell imaging. Live cell imaging of myoblast with foreign cell nuclei allow the study of myoblast differentiation in living cells and the automatic tracking of the nuclei. Visual demonstration helps with understanding how to combine primary cell isolation with live imaging and imaging analysis.Demonstrating the procedure with Frederica Colombo, will be Giorga Careccia, a PhD student in our laboratory. Begin by harvesting the tibialis soleus, extensor digitorum longus, gastrocnemius, quadriceps, and triceps muscles from both hind limbs of an adult mouse into a Petri dish of PBS on ice. Use sterile scissors and tweezers to carefully remove the tendons and fat from each muscle and transfer the muscles into an empty Petri dish.Using sterile curved scissors cut and mince the muscles until a uniform mass is obtained and transfer the muscle pieces to a 50 milliliter tube. Then add 10 milliliters of digestion medium to the muscle pieces for a 30 minute incubation in a 37 degree celsius water bath at 250 rotations per minute. At the end of the enzymatic digestion, stop the reaction with 10 milliliters of blocking medium.And spin down the sample by centrifugation. Place the tube on ice and transfer the supernatant into a new 50 milliliter tube. Centrifuge the supernatant again.And re-suspend the pellet in one millimeter of DMEM. Supplement it with ten percent fetal bovine serum, or FBS, on ice. Digest the reserved pellet in 10 milliliters of fresh digestion medium as just demonstrated and combine the digested pellet with the reserve cell suspension, on ice.Strain the pulled cells through a 70 micrometer filter, followed by a 40 micrometer filter. And wash the cells in 15 millimeters of fresh DMEM, supplemented with 10 percent FBS. At the end of the centrifugation, re-suspend the pellet in three milliliters of red blood cell lysis buffer at room temperature.Stopping the lysis after five minutes with 40 milliliters of PBS and an additional centrifugation. Re-suspend the pellet in 20 milliliters of DMEM supplemented with 10 percent FBS and pre-plate the cells in uncoated Petri dish. After one hour at 37 degree celsius and five percent carbon dioxide collect the satellite cell containing supernatant.And pre-plate the cell suspension two more times as demonstrated. After the last plating, collect the satellite cells by centrifugation and re-suspend the pellet in 40 milliliters of fresh proliferation medium. The split the cells between two collagen coated 150 milliliters Petri dishes with one microgram per-milliliter of doxycycline per dish to induce H2BGFP expression.And return the cells to the cell culture incubator for two or three days. When the myoblasts have reached the appropriate experimental density, wash the cells in each dish with five milliliters of PBS and detach the cells from the plate bottoms with two milliliters of Trypsin per dish at 37 degree celsius for five minutes. Confirm detachment by light microscopy and stop the reaction with five milliliters of DMEM plus ten percent FBS per plate.For live cell imaging, plate two times ten to the fifth cells into each well of a 12 well plate coated with 350 microliters of differentiation medium, supplemented with basement membrane matrix per well for two hours. When the cells have adhered to the bottom of the plate, place the plate in a 37 degree celsius and five percent carbon dioxide incubator on a confocal microscope stage and use a 20 times dry objective to obtain fields of view with hundreds of cells to acquire 16 bit images with 1024 by 1024 pixels per frame every six minutes for 16 hours. For each acquired position, generate a multi frame dot tif file and download and extract the dot zip software provided in a selected folder.Open the example of segmentation tracking folder and click do segmentation dot M to open the command window in Matlab. Change the due segmentation dot M scripts so that the variable file name track is the name of the tif file and path input track is the folder where the dot tif is contained. Click run to run the script.The result of the segmentation will be saved as a file dot mat, while the segmentation of the nuclei can be visualized in the output figure. To generate the tracks, first double click generate tracks dot M in the same working folder. Next, change the file name to file name point the appropriate dot Mat file for the segmented nuclei.Click Run to run the script. The result of the tracking will be saved as another dot mat file and the generated tracks will be plotted. To evaluate the quality of the tracks.First double click the check tracking dot M and modify the file name to the appropriate dot tif name. Then click file name track to use the dot mat file of the tracks and click run. In the figure window use the lower scroll bar to select the nucleus.The selected nucleus will be circled in red, and the trajectory of the selected cell can be followed in time using the upper scroll bar. Green crosses indicate the detected nuclei. Proliferation and differentiation are strongly impaired in myoblasts cultured with Hoechst.Compared to myoblast's isolated from H2BGFP mice and cultured with doxycycline or wild type, myosin heavy chain labeled myoblasts. Live cell imaging with primary myoblasts expressing the H2BGFP protein allows tracking of the nuclei during differentiation. Merged images of transmission in GFP channels at the initial and final time points of the differentiation period, allow the identification of myotubes and consequently nuclei that end up integrating into myotubes or that do not fuse into myotubes.After imaging by confocal fluorescence microscopy, the nuclei can be segmented as demonstrated and watershed transform can be used to separate nearby objects. With this approach, most of the nuclei are identified in the image, allowing the nuclei motion to be tracked as demonstrated. For example, it appears that the total length of the trajectories is slightly higher for cells stained with Hoechst.Although the difference is not significant. However, computation of the total displacement during a time lapse reveals that the total displacement of the cells stained with Hoechst is significantly smaller than that of unstained cells. As predicted the total annual variation for the unstained cells is significantly smaller compared to cells stained with Hoechst.It is important to follow the protocol exactly as demonstrated in particular when combining the technical skills from the biological steps with the confocal microscope and software used steps. To study myoblast differentiation and nuclear positioning in another muscle model of interest it is possible to transfer isolated myoblast with fluorescent nuclear protein. This technique paved the way to explore cellular and nuclear dynamics during muscle differentiation and to further investigate defects in this processes.Under various pathological conditions such as Muscular dystrophies.

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Mouse Mammary Epithelial Cells form Mammospheres During Lactogenic Differentiation

A phenotypic measure commonly used to determine the degree of lactogenic differentiation in mouse mammary epithelial cell cultures is the formation of dome shaped cell structures referred to as mammospheres 1. The HC11 cell line has been employed as a model system for the study of regulation of mammary lactogenic differentiation both in vitro and in vivo 2. The HC11 cells differentiate and synthesize milk proteins in response to treatment with lactogenic hormones. Following the growth of HC11 mouse mammary epithelial cells to confluence, lactogenic differentiation was induced by the addition of a combination of lactogenic hormones including dexamethasone, insulin, and prolactin, referred to as DIP. The HC11 cells induced to differentiate were photographed at times up to 120 hours post induction of differentiation and the number of mammospheres that appeared in each culture was enumerated. The size of the individual mammospheres correlates with the degree of differentiation and this is depicted in the images of the differentiating cells.

HC11 lactogenic differentiation can be characterized by the formation of domed structures referred to as mammospheres. The structures can be enumerated by phase contrast microscopy to aid in quantifying lactogenic differentiation.

A phenotypic measure commonly used to determine the degree of lactogenic differentiation in mouse mammary epithelial cell cultures is the formation of ...

A Practical Approach to Genetic Inducible Fate Mapping: A Visual Guide to Mark and Track Cells In Vivo

Fate maps are generated by marking and tracking cells in vivo to determine how progenitors contribute to specific structures and cell types in developing and adult tissue. An advance in this concept is Genetic Inducible Fate Mapping (GIFM), linking gene expression, cell fate, and cell behaviors in vivo, to create fate maps based on genetic lineage.
GIFM exploits X-CreER lines where X is a gene or set of gene regulatory elements that confers spatial expression of a modified bacteriophage protein, Cre recombinase (CreERT). CreERT contains a modified estrogen receptor ligand binding domain which renders CreERT sequestered in the cytoplasm in the absence of the drug tamoxifen. The binding of tamoxifen releases CreERT, which translocates to the nucleus and mediates recombination between DNA sequences flanked by loxP sites. In GIFM, recombination typically occurs between a loxP flanked Stop cassette preceding a reporter gene such as GFP.
Mice are bred to contain either a region- or cell type-specific CreER and a conditional reporter allele. Untreated mice will not have marking because the Stop cassette in the reporter prevents further transcription of the reporter gene. We administer tamoxifen by oral gavage to timed-pregnant females, which provides temporal control of CreERT release and subsequent translocation to the nucleus removing the Stop cassette from the reporter. Following recombination, the reporter allele is constitutively and heritably expressed. This series of events marks cells such that their genetic history is indelibly recorded. The recombined reporter thus serves as a high fidelity genetic lineage tracer that, once on, is uncoupled from the gene expression initially used to drive CreERT.
We apply GIFM in mouse to study normal development and ascertain the contribution of genetic lineages to adult cell types and tissues. We also use GIFM to follow cells on mutant genetic backgrounds to better understand complex phenotypes that mimic salient features of human genetic disorders.
This video article guides researchers through experimental methods to successfully apply GIFM. We demonstrate the method using our well characterized Wnt1-CreERT;mGFP mice by administering tamoxifen at embryonic day (E)8.5 via oral gavage followed by dissection at E12.5 and analysis by epifluorescence stereomicroscopy. We also demonstrate how to micro-dissect fate mapped domains for explant preparation or FACS analysis and dissect adult fate-mapped brains for whole mount fluorescent imaging. Collectively, these procedures allow researchers to address critical questions in developmental biology and disease models.

A Practical Approach to Genetic Inducible Fate Mapping: A Visual Guide to Mark and Track Cells In Vivo

Genetic Inducible Fate Mapping (GIFM) marks and tracks cells with fine spatial and temporal control in vivo and elucidates how cells from a specific genetic lineage contribute to developing and adult tissues. Demonstrated here are the techniques required to fate map E12.5 mouse embryos for epifluorescent and explant analysis.

Fate maps are generated by marking and tracking cells in vivo to determine how progenitors contribute to specific structures and cell types in developing ...

Live Imaging Of Drosophila melanogaster Embryonic Hemocyte Migrations

Many studies address cell migration using in vitro methods, whereas the physiologically relevant environment is that of the organism itself. Here we present a protocol for the mounting of Drosophila melanogaster embryos and subsequent live imaging of fluorescently labeled hemocytes, the embryonic macrophages of this organism. Using the Gal4-uas system1 we drive the expression of a variety of genetically encoded, fluorescently tagged markers in hemocytes to follow their developmental dispersal throughout the embryo. Following collection of embryos at the desired stage of development, the outer chorion is removed and the embryos are then mounted in halocarbon oil between a hydrophobic, gas-permeable membrane and a glass coverslip for live imaging. In addition to gross migratory parameters such as speed and directionality, higher resolution imaging coupled with the use of fluorescent reporters of F-actin and microtubules can provide more detailed information concerning the dynamics of these cytoskeletal components.

Live Imaging Of Drosophila melanogaster Embryonic Hemocyte Migrations

Drosophila hemocytes disperse over the entirety of the developing embryo. This protocol demonstrates how to mount and image these migrations using embryos with fluorescently labelled hemocytes.

Many studies address cell migration using in vitro methods, whereas the physiologically relevant environment is that of the organism itself. Here we ...

Fluorescent Labeling of COS-7 Expressing SNAP-tag Fusion Proteins for Live Cell Imaging

SNAP-tag and CLIP-tag protein labeling systems enable the specific, covalent attachment of molecules, including fluorescent dyes, to a protein of interest in live cells. These systems offer a broad selection of fluorescent substrates optimized for a range of imaging instrumentation. Once cloned and expressed, the tagged protein can be used with a variety of substrates for numerous downstream applications without having to clone again. There are two steps to using this system: cloning and expression of the protein of interest as a SNAP-tag fusion, and labeling of the fusion with the SNAP-tag substrate of choice. The SNAP-tag is a small protein based on human O6-alkylguanine-DNA-alkyltransferase (hAGT), a DNA repair protein. SNAP-tag labels are dyes conjugated to guanine or chloropyrimidine leaving groups via a benzyl linker. In the labeling reaction, the substituted benzyl group of the substrate is covalently attached to the SNAP-tag. CLIP-tag is a modified version of SNAP-tag, engineered to react with benzylcytosine rather than benzylguanine derivatives. When used in conjunction with SNAP-tag, CLIP-tag enables the orthogonal and complementary labeling of two proteins simultaneously in the same cells.

SNAP-tag and CLIP-tag protein labeling systems enable the specific, covalent attachment of molecules, including fluorescent dyes, to a protein of interest in live cells. Once cloned and expressed, the tagged protein can be used with a variety of substrates for numerous downstream applications without having to clone again.

SNAP-tag and CLIP-tag protein labeling systems enable the specific, covalent attachment of molecules, including fluorescent dyes, to a protein of interest ...

Determining the Contribution of the Energy Systems During Exercise

One of the most important aspects of the metabolic demand is the relative contribution of the energy systems to the total energy required for a given physical activity. Although some sports are relatively easy to be reproduced in a laboratory (e.g., running and cycling), a number of sports are much more difficult to be reproduced and studied in controlled situations. This method presents how to assess the differential contribution of the energy systems in sports that are difficult to mimic in controlled laboratory conditions. The concepts shown here can be adapted to virtually any sport.
The following physiologic variables will be needed: rest oxygen consumption, exercise oxygen consumption, post-exercise oxygen consumption, rest plasma lactate concentration and post-exercise plasma peak lactate. To calculate the contribution of the aerobic metabolism, you will need the oxygen consumption at rest and during the exercise. By using the trapezoidal method, calculate the area under the curve of oxygen consumption during exercise, subtracting the area corresponding to the rest oxygen consumption. To calculate the contribution of the alactic anaerobic metabolism, the post-exercise oxygen consumption curve has to be adjusted to a mono or a bi-exponential model (chosen by the one that best fits). Then, use the terms of the fitted equation to calculate anaerobic alactic metabolism, as follows: ATP-CP metabolism = A1 (mL . s-1) x t1 (s). Finally, to calculate the contribution of the lactic anaerobic system, multiply peak plasma lactate by 3 and by the athlete&#x2019;s body mass (the result in mL is then converted to L and into kJ).
The method can be used for both continuous and intermittent exercise. This is a very interesting approach as it can be adapted to exercises and sports that are difficult to be mimicked in controlled environments. Also, this is the only available method capable of distinguishing the contribution of three different energy systems. Thus, the method allows the study of sports with great similarity to real situations, providing desirable ecological validity to the study.

This protocol allows researchers focused on exercise and sports sciences to determine the relative contribution of three different energy systems to the total energy expenditure during a large variety of exercises.

One of the most important aspects of the metabolic demand is the relative contribution of the energy systems to the total energy required for a given ...

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 ...

Analysis of SNARE-mediated Membrane Fusion Using an Enzymatic Cell Fusion Assay

The interactions of SNARE (soluble N-ethylmaleimide-sensitive factor attachment protein receptor) proteins on vesicles (v-SNAREs) and on target membranes (t-SNAREs) catalyze intracellular vesicle fusion1-4. Reconstitution assays are essential for dissecting the mechanism and regulation of SNARE-mediated membrane fusion5. In a cell fusion assay6,7, SNARE proteins are expressed ectopically at the cell surface. These "flipped" SNARE proteins drive cell-cell fusion, demonstrating that SNAREs are sufficient to fuse cellular membranes. Because the cell fusion assay is based on microscopic analysis, it is less efficient when used to analyze multiple v- and t-SNARE interactions quantitatively.
Here we describe a new assay8 that quantifies SNARE-mediated cell fusion events by activated expression of &beta;-galactosidase. Two components of the Tet-Off gene expression system9 are used as a readout system: the tetracycline-controlled transactivator (tTA) and a reporter plasmid that encodes the LacZ gene under control of the tetracycline-response element (TRE-LacZ). We transfect tTA into COS-7 cells that express flipped v-SNARE proteins at the cell surface (v-cells) and transfect TRE-LacZ into COS-7 cells that express flipped t-SNARE proteins at the cell surface (t-cells). SNARE-dependent fusion of the v- and t-cells results in the binding of tTA to TRE, the transcriptional activation of LacZ and expression of &beta;-galactosidase. The activity of &beta;-galactosidase is quantified using a colorimetric method by absorbance at 420 nm.
The vesicle-associated membrane proteins (VAMPs) are v-SNAREs that reside in various post-Golgi vesicular compartments10-15. By expressing VAMPs 1, 3, 4, 5, 7 and 8 at the same level, we compare their membrane fusion activities using the enzymatic cell fusion assay. Based on spectrometric measurement, this assay offers a quantitative approach for analyzing SNARE-mediated membrane fusion and for high-throughput studies.

We have developed a cell fusion assay that quantifies SNARE-mediated membrane fusion events by activated expression of &beta;-galactosidase.

The interactions of SNARE (soluble N-ethylmaleimide-sensitive factor attachment protein receptor)  proteins on vesicles (v-SNAREs) and on target membranes ...

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 ...

Live Imaging of Apoptotic Cell Clearance during Drosophila Embryogenesis

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

Live Imaging of Apoptotic Cell Clearance during Drosophila Embryogenesis

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

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

Live Cell Fluorescence Microscopy to Observe Essential Processes During Microbial Cell Growth

Core cellular processes such as DNA replication and segregation, protein synthesis, cell wall biosynthesis, and cell division rely on the function of proteins which are essential for bacterial survival. A series of target-specific dyes can be used as probes to better understand these processes. Staining with lipophilic dyes enables the observation of membrane structure, visualization of lipid microdomains, and detection of membrane blebs. Use of fluorescent-d-amino acids (FDAAs) to probe the sites of peptidoglycan biosynthesis can indicate potential defects in cell wall biogenesis or cell growth patterning. Finally, nucleic acid stains can indicate possible defects in DNA replication or chromosome segregation. Cyanine DNA stains label living cells and are suitable for time-lapse microscopy enabling real-time observations of nucleoid morphology during cell growth. Protocols for cell labeling can be applied to protein depletion mutants to identify defects in membrane structure, cell wall biogenesis, or chromosome segregation. Furthermore, time-lapse microscopy can be used to monitor morphological changes as an essential protein is removed and can provide additional insights into protein function. For example, the depletion of essential cell division proteins results in filamentation or branching, whereas the depletion of cell growth proteins may cause cells to become shorter or rounder. Here, protocols for cell growth, target-specific labeling, and time-lapse microscopy are provided for the bacterial plant pathogen Agrobacterium tumefaciens. Together, target-specific dyes and time-lapse microscopy enable characterization of essential processes in A. tumefaciens. Finally, the protocols provided can be readily modified to probe essential processes in other bacteria.

Understanding the function of essential processes in bacteria is challenging. Fluorescence microscopy with target-specific dyes can provide key insights into microbial cell growth and cell cycle progression. Here, Agrobacterium tumefaciens is used as a model bacterium to highlight methods for live cell imaging for characterization of essential processes.

Core cellular processes such as DNA replication and segregation, protein synthesis, cell wall biosynthesis, and cell division rely on the function of ...