This work was supported by the European Research Council (ERG) and EMBO installation (ERG) and by a PhD fellowship from the Funda&#231;&#227;o para a Ci&#234;ncia e Tecnologia (MP).

NOTE: One mouse yields sufficient myoblasts for approximately two 35 mm dishes or two live-imaging dishes, so plan mattings, dissection, and coating (step 2.6) accordingly. Since myoblasts are isolated through sequential centrifugations and preplating, the protocol should be done in batches of 5 - 10 animals.
All procedures involving animal subjects were approved by the Animal Ethics Committee at Instituto de Medicina Molecular and University Pierre et Marie Curie&#160;
1. Dissection of Neonatal Mice Hind-limb Muscles
<ol>
	<li>Prepare all solutions in advance (Materials Table) and sterilize by filtration (0.22 &#181;m filter). Make sure all media are at 37 &#176;C before addition to the cells, except the formulations containing basement membrane matrix (e.g., Matrigel).</li>
	<li>Sterilize the dissection material (one each of: curved scissors, straight scissors, regular forceps, and fine-tip forceps) and the work bench by wiping them with 70% ethanol.</li>
	<li>Prepare a 100 mm Petri dish with 5 mL of Dulbecco&#39;s Phosphate Buffered Saline (DPBS) for muscle collection and keep it on ice until the mincing step.</li>
	<li>Decapitate P6 - P8 mice with straight scissors and sterilize the skin with 70% ethanol.</li>
	<li>Make an incision in the back skin and pull it gently towards the hind limbs until it is removed, completely exposing the hind-limb musculature.</li>
	<li>Use the forceps to remove fat tissue without damaging the muscles.</li>
	<li>To remove the dorsal hind-limb muscles, keep the limb stretched and bend the paw to expose the heel tendons. Use the curved scissors to separate muscle from bone, starting from the tendons, by gently sliding and cutting upwards. Excise the muscles and place them in iced DPBS.</li>
	<li>Isolate the quadriceps by pinching the muscle with fine-tip forceps and cutting around it without damaging the femur or the knee joint.</li>
	<li>After dissecting all animals, proceed to a sterile laminar flow cell culture hood, where all the following steps should be performed.</li>
</ol>
2. Myoblast Isolation
<ol>
	<li>Remove the excess of DPBS. Mince the tissue with sterilized curved scissors in order to obtain a uniform mass.</li>
	<li>Collect the minced tissue in a 50 mL conical centrifuge tube using 5 mL of digestion mix and incubate it with agitation at 37 &#176;C for 90 min.</li>
	<li>Stop the digestion by adding 6 mL of dissection medium and centrifuge the suspension for 5 min at 75 x g to pellet the remaining tissue.</li>
	<li>Carefully collect the supernatant. Make sure to not collect tissue debris. Centrifuge it at 350 x g for 5 min; resuspend it in 5 mL of dissection medium.</li>
	<li>Filter the cell suspension through a 40 &#181;m cell strainer. Add 25 mL of dissection medium and preplate it in a 150 mm dish for 4 h in a cell culture incubator (37 &#176;C and 5% CO2) to allow the fibroblasts to adhere.</li>
	<li>While preplating, coat dishes with 500 &#181;L of basement membrane matrix diluted 1:100 in cold IMDM for 1 h at RT. Wash once with DPBS and plate the cells immediately (step 2.8) or leave with growth medium until plating.</li>
	<li>After preplating, collect the supernatant and centrifuge it at 350 x g for 10 min.</li>
	<li>Resuspend it in growth medium and count the cells on a hemocytometer. Adjust the volume so that between 150,000 and 250,000 cells are plated per basement membrane matrix-coated dish. Keep the cells in a cell culture incubator.</li>
</ol>
3. Myofiber Differentiation
NOTE: After 3 d, the cells should start to fuse and form myotubes at around 70% confluency (Figure 1B).
<ol>
	<li>At this point, transfect the cells, if desired, with a siRNA or DNA of interest. If the cells are not to be transfected, change directly to differentiation medium and skip to step 3.4.</li>
	<li>Transfect with transfection reagents following the manufacturer&#39;s instructions. Incubate the cells for 5 h with siRNA-lipid complexes (20 nM + 1 &#181;L of reagent) or DNA-lipid complexes (1 &#181;g + 1 &#181;L of reagent). Optimize the siRNA and DNA concentrations if necessary.</li>
	<li>Wash them once with differentiation medium and then switch to new differentiation medium.</li>
	<li>The following day, dilute the basement membrane matrix 1:2 in ice-cold differentiation medium. Remove the existing medium and add 200 &#181;L of ice-cold matrix to each dish.</li>
	<li>Incubate for 30 min in a cell culture incubator.</li>
	<li>Supplement the differentiation medium with agrin (100 ng/mL) and carefully add 2 mL to the cells.</li>
	<li>Carefully change half of the medium every 2 d, always supplementing with agrin to a final concentration of 100 ng/&#181;L.</li>
	<li>Monitor cell differentiation and viability. Depending on a variety of factors (such as FBS and chicken embryo extract origins), the cells might take between 5 -&#160;10 differentiation d&#160;to reach full maturation (Figure 2).</li>
</ol>
4. Immunostaining in Glass-bottom Dishes
<ol>
	<li>For immunostaining, at any time-point of interest, wash the cells once with DPBS and fix them with 4% PFA at RT for 10 min.</li>
	<li>Wash them twice with DPBS. At this point, the cells can be stored at 4 &#176;C.</li>
	<li>Permeabilize them with 0.5% Triton X-100 for 5 min at RT.</li>
	<li>Wash them twice with PBS and block with blocking solution for 30 min at RT.</li>
	<li>Incubate them with primary antibody diluted in blocking solution O/N at 4 &#176;C.</li>
	<li>Wash 3x with DPBS for 5 min at RT.</li>
	<li>Incubate them with the secondary antibody and 0.2 &#181;g/mL of DAPI for 1 h at RT.</li>
	<li>Wash 3x with DPBS for 5 min at RT.</li>
	<li>Add 200 &#181;L of mounting medium and proceed to imaging.</li>
</ol>

<ol>
	<li>Janssen, I., Heymsfield, S. B., Wang, Z., 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> J Appl Physiol. 89 (1), 81-88 (2000).</li><li>Manring, H., Abreu, E., Brotto, L., Weisleder, N., Brotto, M. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Novel+excitation-contraction+coupling+related+genes+reveal+aspects+of+muscle+weakness+beyond+atrophy-new+hopes+for+treatment+of+musculoskeletal+diseases.">Novel excitation-contraction coupling related genes reveal aspects of muscle weakness beyond atrophy-new hopes for treatment of musculoskeletal diseases.</a> Front Physiol. 5, 37 (2014).</li><li>Yaffe, D., Saxel, O. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Serial+passaging+and+differentiation+of+myogenic+cells+isolated+from+dystrophic+mouse+muscle.">Serial passaging and differentiation of myogenic cells isolated from dystrophic mouse muscle.</a> Nature. 270 (5639), 725-727 (1977).</li><li>Pasut, A., Jones, A. E., Rudnicki, M. A. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Isolation+and+Culture+of+Individual+Myofibers+and+their+Satellite+Cells+from+Adult+Skeletal+Muscle.">Isolation and Culture of Individual Myofibers and their Satellite Cells from Adult Skeletal Muscle.</a> J Vis Exp. (73), (2013).</li><li>Meng, H., Janssen, P. M. L., 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=Tissue+Triage+and+Freezing+for+Models+of+Skeletal+Muscle+Disease.">Tissue Triage and Freezing for Models of Skeletal Muscle Disease.</a> J Vis Exp. (89), (2014).</li><li>Demonbreun, A. R., McNally, E. M. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=DNA+Electroporation,+Isolation+and+Imaging+of+Myofibers.">DNA Electroporation, Isolation and Imaging of Myofibers.</a> J Vis Exp. (106), (2015).</li><li>Falcone, S., Roman, W., 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 Mol Med. 6 (11), 1455-1475 (2014).</li><li>Flucher, B. E., Phillips, J. L., Powell, J. A. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Dihydropyridine+receptor+alpha+subunits+in+normal+and+dysgenic+muscle+in+vitro:+expression+of+alpha+1+is+required+for+proper+targeting+and+distribution+of+alpha+2.">Dihydropyridine receptor alpha subunits in normal and dysgenic muscle in vitro: expression of alpha 1 is required for proper targeting and distribution of alpha 2.</a> J Cell Biol. 115 (5), 1345-1356 (1991).</li><li>Cooper, S. T., Maxwell, A. L., 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=C2C12+co-culture+on+a+fibroblast+substratum+enables+sustained+survival+of+contractile,+highly+differentiated+myotubes+with+peripheral+nuclei+and+adult+fast+myosin+expression.">C2C12 co-culture on a fibroblast substratum enables sustained survival of contractile, highly differentiated myotubes with peripheral nuclei and adult fast myosin expression.</a> Cell Motil Cytoskeleton. 58 (3), 200-211 (2004).</li><li>Al-Qusairi, L., Laporte, J. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=T-tubule+biogenesis+and+triad+formation+in+skeletal+muscle+and+implication+in+human+diseases.">T-tubule biogenesis and triad formation in skeletal muscle and implication in human diseases.</a> Skelet Muscle. 1, 26 (2011).</li><li>Vilmont, V., Cadot, B., Ouanounou, G., 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=A+system+to+study+mechanisms+of+neuromuscular+junction+development+and+maintenance.">A system to study mechanisms of neuromuscular junction development and maintenance.</a> Development. , (2016).</li><li>Vilmont, V., Cadot, B., Vezin, E., Le Grand, F., 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=Dynein+disruption+perturbs+post-synaptic+components+and+contributes+to+impaired+MuSK+clustering+at+the+NMJ:+implication+in+ALS.">Dynein disruption perturbs post-synaptic components and contributes to impaired MuSK clustering at the NMJ: implication in ALS.</a> Sci Rep. 6, 27804 (2016).</li></ol>

The authors have nothing to disclose.

The use of this protocol for the cultivation of primary myoblasts gives rise to a special niche that greatly nurtures the development of myofibers. This is partially due to other cell types that are also present in very small numbers. A balance between myoblast concentration and culture purity must be achieved. A good cell culture also depends on the quality of the products used for the medium formulation. All products derived from animal sources should be thoroughly tested. In our experience, the digestion conditions should also be monitored.
As usual for primary cultures, experimental variability can be higher than in studies with isolated fibers or immortalized myoblasts. This variability can be diminished by the standardization of medium and digestion components, mice age and size, and the time points for culture manipulation and results collection. Nevertheless, the advantage of scrutinizing in real time the intricate mechanisms necessary for myofiber development greatly surpasses the variability drawback.
This protocol confers the advantages of in vitro approaches without compromising cell differentiation. Myofibers mature until triads are formed and contractions are coupled to calcium sparks. These functional outputs can be accessed in different experimental conditions. Furthermore, there can be many technical variations made to the protocol. Myoblasts can be harvested from neonatal mice with mutations of interest relating to muscle development. Cells can be lysed for biochemical analysis at different differentiation time points. Calcium indicators can be added to the culture to follow its dynamics. Optogenetic constructs can be used to enforce certain signaling pathways or to induce specific local responses. Finally, the myofibers can be cocultured with other cells types to study their interactions.

Skeletal muscle composes up to 40% of the human body weight1. Muscle-associated disorders represent an immense health and economic burden2. How this highly complex and organized tissue is formed, maintained, and regenerated constitutes an extensive and well-established research field. Depending on the specific scientific interest, the most suited approach can range from simple myotube cultures to complex in vivo models3-6.
The goal of this protocol is to provide an in vitro system that allows for the monitoring of myogenesis through live imaging and immunofluorescence. Compared to traditional approaches, this system offers a very complete and dynamic insight into the mouse myogenic process. Cells can be followed from the myoblast stage to the mature, multinucleated myofiber displaying transversal triads and peripheral nuclei7. This maturation level can be achieved using regular cell culture equipment, without the need for complex stimulatory or mechanical apparatuses. Although some successful in vitro systems have been reported8,9, to our knowledge, this is the only protocol generating mature mouse myofibers with T-tubules transversally paired with Sarcoplasmic Reticulum (SR). Thus, this in vitro system can be used to study the molecular mechanisms of triad formation, which are still poorly understood10.
A further advantage of using this system is the availability of validated mouse-targeted resources, such as antibodies, drugs, and RNAi tools. The relatively simple protocol does not require laborious steps, highly skilled manipulation, or expensive and dedicated equipment. Matured myofibers start appearing after 5 d of culture differentiation7, displaying contractility coupled with calcium sparks (unpublished data). In one week, the different developmental stages of one of the most complex cells in the mammalian body can be studied in combination with a variety of in vitro assays.

<table border="1" fo:keep-together.within-page="1" fo:keep-with-next.within-page="always">
	<tbody>
		<tr>
			<td>Dispase II</td>
			<td>Gibco</td>
			<td>17105041</td>
			<td></td>
		</tr>
		<tr>
			<td>Collagenase&#160;type V</td>
			<td>Sigma-Aldrich-Aldrich</td>
			<td>C9263</td>
			<td></td>
		</tr>
		<tr>
			<td>IMDM, Glutamax supplemented</td>
			<td>Gibco</td>
			<td>31980022</td>
			<td></td>
		</tr>
		<tr>
			<td>Matrigel Growth reduced factor</td>
			<td>Corning</td>
			<td>354230</td>
			<td>protein concentration of the lot should be around 10mg/ml and endotoxin result should be &#60;1.5</td>
		</tr>
		<tr>
			<td>Chicken Embryo Extract</td>
			<td>MP biomedical</td>
			<td>2850145</td>
			<td>it is also possible to prepare in the lab (Danoviz ME, Yablonka-Reuveni Z. Methods Mol Biol (2012))</td>
		</tr>
		<tr>
			<td>Recombinant rat agrin</td>
			<td>R&#38;D systems</td>
			<td>550-AG-100</td>
			<td></td>
		</tr>
		<tr>
			<td>Penicillin-Streptomycin</td>
			<td>Thermo Fisher Scientific</td>
			<td>15140122</td>
			<td></td>
		</tr>
		<tr>
			<td>Horse Serum</td>
			<td>GE Healthcare&#160;</td>
			<td>11581831</td>
			<td></td>
		</tr>
		<tr>
			<td>Lipofectamine RNAiMAX</td>
			<td>Invitrogen</td>
			<td>13778-150</td>
			<td>used to transfect siRNA</td>
		</tr>
		<tr>
			<td>Lipofectamine LTX</td>
			<td>Invitrogen</td>
			<td>15338-100</td>
			<td>used to transfect DNA</td>
		</tr>
		<tr>
			<td>Lipofectamine 2000</td>
			<td>Invitrogen</td>
			<td>11668030</td>
			<td>used to transfect siRNA plus DNA</td>
		</tr>
		<tr>
			<td>DPBS</td>
			<td>Gibco</td>
			<td>14190094&#160;</td>
			<td></td>
		</tr>
		<tr>
			<td>Fetal Bovine Serum</td>
			<td>Eurobio</td>
			<td>CVFSVF0001</td>
			<td></td>
		</tr>
		<tr>
			<td>Cell strainer</td>
			<td>Corning</td>
			<td>21008-949</td>
			<td></td>
		</tr>
		<tr>
			<td>Fluorodishes</td>
			<td>World precision instruments</td>
			<td>FD35-100</td>
			<td>dishes used to cultivate cells for live imaging</td>
		</tr>
		<tr>
			<td>Triton X-100</td>
			<td>Sigma-Aldrich</td>
			<td>T9284</td>
			<td></td>
		</tr>
		<tr>
			<td>16% PFA (Paraformaldehyde)</td>
			<td>Science Services GmbH</td>
			<td>E15710</td>
			<td></td>
		</tr>
		<tr>
			<td>Goat Serum</td>
			<td>Sigma-Aldrich</td>
			<td>G9023</td>
			<td></td>
		</tr>
		<tr>
			<td>BSA (Bovine Serum Albumine)</td>
			<td>Sigma-Aldrich</td>
			<td>A7906</td>
			<td></td>
		</tr>
		<tr>
			<td>Saponine</td>
			<td>Sigma-Aldrich</td>
			<td>47036</td>
			<td></td>
		</tr>
		<tr>
			<td>DAPI</td>
			<td>Sigma-Aldrich</td>
			<td>D9542</td>
			<td>use at 200ng/ul</td>
		</tr>
		<tr>
			<td>Fluoromount-G</td>
			<td>SouthernBiotech</td>
			<td>0100-01&#160;</td>
			<td></td>
		</tr>
		<tr>
			<td>Name</td>
			<td>Company</td>
			<td>Catalog Number</td>
			<td>Comments</td>
		</tr>
		<tr>
			<td>Solutions and Media</td>
			<td></td>
			<td></td>
			<td></td>
		</tr>
		<tr>
			<td>Digestion Mix</td>
			<td></td>
			<td></td>
			<td>in DPBS 
			5 mg/ml collagenase 
			3.5 mg/ml dispase 
			sterile filtered, can be stored in working aliquotes for 2 weeks at -20 &#176;C</td>
		</tr>
		<tr>
			<td>Dissection Medium</td>
			<td></td>
			<td></td>
			<td>in IMDM Glutamax supplemented 
			10% FBS 
			1% Penicillin-Streptomycin 
			sterile filtered</td>
		</tr>
		<tr>
			<td>Growth Medium</td>
			<td></td>
			<td></td>
			<td>in IMDM Glutamax supplemented 
			20% FBS 
			1% Chicken Embryo Extract 
			1% Penicillin-Streptomycin1% Penicillin-Streptomycin 
			sterile filtered</td>
		</tr>
		<tr>
			<td>Differentiation Medium</td>
			<td></td>
			<td></td>
			<td>in IMDM Glutamax supplemented 
			2% Horse Serum 
			1% Penicillin-Streptomycin 
			sterile filtered</td>
		</tr>
		<tr>
			<td>Blocking Solution</td>
			<td></td>
			<td></td>
			<td>in DPBS 
			10% Goat Serum 
			5% BSA 
			add 0.1% saponine when incubating with primary and secondary antibodies</td>
		</tr>
	</tbody>
</table>

in vitro differentiation of mature myofibers for live imaging

Skeletal muscles are composed of myofibers, the biggest cells in the mammalian body and one of the few syncytia. How the complex and evolutionarily conserved structures that compose it are assembled remains under investigation. Their size and physiological features often constrain manipulation and imaging applications. The culture of immortalized cell lines is widely used, but it can only replicate the early steps of differentiation.
Here, we describe a protocol that enables easy genetic manipulation of myofibers originating from primary mouse myoblasts. After one week of differentiation, the myofibers display contractility, aligned sarcomeres and triads, as well as peripheral nuclei. The entire differentiation process can be followed by live imaging or immunofluorescence. This system combines the advantages of the existing ex vivo and in vitro protocols. The possibility of easy and efficient transfection as well as the ease of access to all differentiation stages broadens the potential applications. Myofibers can subsequently be used not only to address relevant developmental and cell biology questions, but also to reproduce muscle disease phenotypes for clinical applications.

The extent of myofiber development is mostly determined by the purity and viability of the isolated myoblasts. The adhesion, proliferation, and fusion capacity can be used to empirically access those parameters (Figure 1 A, B). At proliferation D2, myoblasts should have adhered and should display the typical fusiform shape. Proliferation is expected to happen extensively at this stage, leading to spontaneous myotube formation the following day (Figure 1B).
Cell confluency might need slight adjustments. It should be increased if myoblasts take more than 3 d to proliferate and fuse. It should be decreased if myofibers are not allowed to grow and elongate relatively straight due to their density. Confluency typically decreases from the center to the periphery of the dish, so the best myofibers should be found towards the outer regions.
Myotubes will quickly elongate and display multiple centrally aligned nuclei (Figure 1C). By D5, some cells start acquiring striations and moving their nuclei to the periphery. The number of myofibers with mature characteristics will increase with time as well as with cell thickness (Figure 1D).
The degree of differentiation can be further observed by immunofluorescence. Myofibers fixed at differentiation D8 present transversal triads. This can be confirmed by imaging components of the T-tubules (DPHR) and the SR (triadin), which are expected to colocalize at the triads (Figure 2).
The functionality of myofibers can be addressed by live imaging. From differentiation D3 onwards, the cells display spontaneous twitching. By transfecting a calcium sensor (e.g., GCaMP6f11), it is possible to observe that the contractions are coupled with calcium peaks (Figure 3).
Using this system, we were able to identify a novel molecular pathway that is disrupted in centronuclear myopathies and myotonic dystrophies, which can therefore be a novel target for innovative molecular therapies7. We have also adapted this method to study the development of the neuromuscular junction (NMJ)12. Through the coculture with rat spinal cord explants, we have described a role for dynein in NMJ formation13.
<img alt="Figure 1" src="/files/ftp_upload/55141/55141fig1.jpg" /> 
Figure 1: Developmental Stages of the Myoblast Culture. A) At proliferation D2, myoblasts have adhered and started proliferating. B) At proliferation D3, a confluency of 60 - 80% is reached, and myoblasts start fusing spontaneously. C) At differentiation D3, myotubes containing centrally located nuclei are predominant. D) From differentiation D5 onwards (e.g., day 8), myofibers start exhibiting striations and peripheral nuclei and begin to thicken. Scale bar: 50 &#181;m. <a href="http://cloudflare.jove.com/files/ftp_upload/55141/55141fig1large.jpg" target="_blank">Please click here to view a larger version of this figure.</a>
<img alt="Figure 2" src="/files/ftp_upload/55141/55141fig2.jpg" /> 
Figure 2: Representative Confocal Image of a D8 Myofiber Immunostain. A) Immunostaining for dihydropyridine receptor (DHPR, top panel) and triadin (TRDN, middle panel). An overlay of the DHPR, TRDN, and DAPI channels shows colocalization of the triad components. B) An intensity profile of the yellow line drawn in A. C) A 3D image of volume rendering of myofibers stained for &#945;-actinin (green) and DAPI (blue). Scale bar and grid width: 5 &#181;m. <a href="http://cloudflare.jove.com/files/ftp_upload/55141/55141fig2large.jpg" target="_blank">Please click here to view a larger version of this figure.</a>
<img alt="Figure 3" src="/files/ftp_upload/55141/55141fig3.jpg" /> 
Figure 3: Live Imaging of Calcium Levels in Myofibers with Spontaneous Twitching. A) High-speed time-lapse (20 ms frames) microscopy of a calcium spark in a twitching myofiber. Calcium was detected through the expression of GCaMP6f (Addgene plasmid #40755). B) Quantification of the fluorescence intensity over time for the calcium sensor in panel A. <a href="http://cloudflare.jove.com/files/ftp_upload/55141/55141fig3large.jpg" target="_blank">Please click here to view a larger version of this figure.</a>

Watch this Scientific Journal Video about In Vitro Differentiation of Mature Myofibers for Live Imaging at JoVE.com

In Vitro Differentiation of Mature Myofibers for Live Imaging

Muscle cells are among the most complex eukaryotic cells. We present a protocol for the in vitro differentiation of highly mature myofibers that allows for genetic manipulation and clear imaging during all developmental stages.

In Vitro Differentiation of Mature Myofibers for Live Imaging

Skeletal muscles are composed of myofibers, the biggest cells in the mammalian body and one of the few syncytia. How the complex and evolutionarily ...

in-vitro-differentiation-of-mature-myofibers-for-live-imaging

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JoVE Journal

Developmental Biology

10.2K Views.  Universidade de Lisboa. Muscle cells are among the most complex eukaryotic cells. We present a protocol for the in vitro differentiation of highly mature myofibers that allows for genetic manipulation and clear imaging during all developmental stages.

Video: In Vitro Differentiation of Mature Myofibers for Live Imaging

Live-imaging of the Drosophila Pupal Eye

Inherent processes of Drosophila pupal development can shift and distort the eye epithelium in ways that make individual cell behavior difficult to track during live cell imaging. These processes include: retinal rotation, cell growth and organismal movement. Additionally, irregularities in the topology of the epithelium, including subtle bumps and folds often introduced as the pupa is prepared for imaging, make it challenging to acquire in-focus images of more than a few ommatidia in a single focal plane. The workflow outlined here remedies these issues, allowing easy analysis of cellular processes during Drosophila pupal eye development. Appropriately-staged pupae are arranged in an imaging rig that can be easily assembled in most laboratories. Ubiquitin-DE-Cadherin:GFP and GMR-GAL4&#8211;driven UAS-&#945;-catenin:GFP are used to visualize cell boundaries in the eye epithelium 1-3. After deconvolution is applied to fluorescent images captured at multiple focal planes, maximum projection images are generated for each time point and enhanced using image editing software. Alignment algorithms are used to quickly stabilize superfluous motion, making individual cell behavior easier to track.

Live-imaging of the Drosophila Pupal Eye

This protocol presents an efficient method for imaging the live Drosophila pupal eye neuroepithelium. This method compensates for tissue movement and uneven topology, enhances visualization of cell boundaries through the use of multiple GFP-tagged junction proteins, and uses an easily-assembled imaging rig.

Inherent processes of Drosophila pupal development can shift and distort the eye epithelium in ways that make individual cell behavior difficult to track ...

Analysis of Zebrafish Larvae Skeletal Muscle Integrity with Evans Blue Dye

The zebrafish model is an emerging system for the study of neuromuscular disorders. In the study of neuromuscular diseases, the integrity of the muscle membrane is a critical disease determinant. To date, numerous neuromuscular conditions display degenerating muscle fibers with abnormal membrane integrity; this is most commonly observed in muscular dystrophies. Evans Blue Dye (EBD) is a vital, cell permeable dye that is rapidly taken into degenerating, damaged, or apoptotic cells; in contrast, it is not taken up by cells with an intact membrane. EBD injection is commonly employed to ascertain muscle integrity in mouse models of neuromuscular diseases. However, such EBD experiments require muscle dissection and/or sectioning prior to analysis. In contrast, EBD uptake in zebrafish is visualized in live, intact preparations. Here, we demonstrate a simple and straightforward methodology for performing EBD injections and analysis in live zebrafish. In addition, we demonstrate a co-injection strategy to increase efficacy of EBD analysis. Overall, this video article provides an outline to perform EBD injection and characterization in zebrafish models of neuromuscular disease.

In this study, we describe a straightforward method to perform Evans Blue Dye (EBD) analysis on zebrafish larvae. This technique is a powerful tool for the characterization of skeletal muscle integrity and delineation of zebrafish models of muscular dystrophy, and is a valuable method for the development of novel therapeutics.

The zebrafish model is an emerging system for the study of neuromuscular disorders.  In the study of neuromuscular diseases, the integrity of the muscle ...

Live Confocal Imaging of Developing Arabidopsis Flowers

The study of plant growth and development has long relied on experimental techniques using dead, fixed tissues and lacking proper cellular resolution. Recent advances in confocal microscopy, combined with the development of numerous fluorophores, have overcome these issues and opened the possibility to study the expression of several genes simultaneously, with a good cellular resolution, in live samples. Live confocal imaging provides plant biologists with a powerful tool to study development, and has been extensively used to study root growth and the formation of lateral organs on the flanks of the shoot apical meristem. However, it has not been widely applied to the study of flower development, in part due to challenges that are specific to imaging flowers, such as the sepals that grow over the flower meristem, and filter out the fluorescence from underlying tissues. Here, we present a detailed protocol to perform live confocal imaging on live, developing Arabidopsis flower buds, using either an upright or an inverted microscope.

Live confocal imaging provides biologists with a powerful tool to study development. Here, we present a detailed protocol for the live confocal imaging of developing Arabidopsis flowers.

The study of plant growth and development has long relied on experimental techniques using dead, fixed tissues and lacking proper cellular resolution. ...

In Vitro Differentiation of Human Pluripotent Stem Cells into Trophoblastic Cells

The placenta is the first organ to develop during embryogenesis and is required for the survival of the developing embryo. The placenta is comprised of various trophoblastic cells that differentiate from the extra-embryonic trophectoderm cells of the preimplantation blastocyst. As such, our understanding of the early differentiation events of the human placenta is limited because of ethical and legal restrictions on the isolation and manipulation of human embryogenesis. Human pluripotent stem cells (hPSCs) are a robust model system for investigating human development and can also be differentiated in vitro into trophoblastic cells that express markers of the various trophoblast cell types. Here, we present a detailed protocol for differentiating hPSCs into trophoblastic cells using bone morphogenic protein 4 and inhibitors of the Activin/Nodal signaling pathways. This protocol generates various trophoblast cell types that can be transfected with siRNAs for investigating loss-of-function phenotypes or can be infected with pathogens. Additionally, hPSCs can be genetically modified and then differentiated into trophoblast progenitors for gain-of-function analyses. This in vitro differentiation method for generating human trophoblasts starting from hPSCs overcomes the ethical and legal restrictions of working with early human embryos, and this system can be used for a variety of applications, including drug discovery and stem cell research.

In Vitro Differentiation of Human Pluripotent Stem Cells into Trophoblastic Cells

Here, we present a protocol to efficiently generate human trophoblastic cells from human pluripotent stem cells using bone morphogenic protein 4 and inhibitors of the Activin/Nodal pathways. This method is suitable for the efficient differentiation of human pluripotent stem cells and can generate large quantities of cells for genetic manipulation.

The placenta is the first organ to develop during embryogenesis and is required for the survival of the developing embryo. The placenta is comprised of ...

Long-term Live Imaging of Drosophila Eye Disc

Live imaging provides the ability to continuously track dynamic cellular and developmental processes in real time. Drosophila larval imaginal discs have been used to study many biological processes, such as cell proliferation, differentiation, growth, migration, apoptosis, competition, cell-cell signaling, and compartmental boundary formation. However, methods for the long-term ex vivo culture and live imaging of the imaginal discs have not been satisfactory, despite many efforts. Recently, we developed a method for the long-term ex vivo culture and live imaging of imaginal discs for up to 18 h. In addition to using a high insulin concentration in the culture medium, a low-melting agarose was also used to embed the disc to prevent it from drifting during the imaging period. This report uses the eye-antennal discs as an example. Photoreceptor R3/4-specific m&#948;0.5-Ga4 expression was followed to demonstrate that photoreceptor differentiation and ommatidial rotation can be observed during a 10 h live imaging period. This is a detailed protocol describing this simple method.

Long-term Live Imaging of Drosophila Eye Disc

This protocol describes a detailed method for the long-term ex vivo culture and live imaging of a Drosophila imaginal disc. It demonstrates photoreceptor differentiation and ommatidial rotation within the 10 h period of live imaging of the eye disc. The protocol is simple and does not require expensive setup.

Live imaging provides the ability to continuously track dynamic cellular and developmental processes in real time. Drosophila larval imaginal discs have ...

In Vitro Ovule Cultivation for Live-cell Imaging of Zygote Polarization and Embryo Patterning in Arabidopsis thaliana

In most flowering plants, the zygote and embryo are hidden deep in the mother tissue, and thus it has long been a mystery of how they develop dynamically; for example, how the zygote polarizes to establish the body axis and how the embryo specifies various cell fates during organ formation. This manuscript describes an in vitro ovule culture method to perform live-cell imaging of developing zygotes and embryos of Arabidopsis thaliana. The optimized cultivation medium allows zygotes or early embryos to grow into fertile plants. By combining it with a poly(dimethylsiloxane) (PDMS) micropillar array device, the ovule is held in the liquid medium in the same position. This fixation is crucial to observe the same ovule under a microscope for several days from the zygotic division to the late embryo stage. The resulting live-cell imaging can be used to monitor the real-time dynamics of zygote polarization, such as nuclear migration and cytoskeleton rearrangement, and also the cell division timing and cell fate specification during embryo patterning. Furthermore, this ovule cultivation system can be combined with inhibitor treatments to analyze the effects of various factors on embryo development, and with optical manipulations such as laser disruption to examine the role of cell-cell communication.

In Vitro Ovule Cultivation for Live-cell Imaging of Zygote Polarization and Embryo Patterning in Arabidopsis thaliana

This manuscript describes an in vitro ovule cultivation method that enables live-cell imaging of Arabidopsis zygotes and embryos. This method is utilized to visualize the intracellular dynamics during zygote polarization and the cell fate specification in developing embryos.

In most flowering plants, the zygote and embryo are hidden deep in the mother tissue, and thus it has long been a mystery of how they develop dynamically; ...

Live Imaging of Mouse Secondary Palate Fusion

The fusion of the secondary palatal shelves to form the intact secondary palate is a key process in mammalian development and its disruption can lead to cleft secondary palate, a common congenital anomaly in humans. Secondary palate fusion has been extensively studied leading to several proposed cellular mechanisms that may mediate this process. However, these studies have been mostly performed on fixed embryonic tissues at progressive timepoints during development or in fixed explant cultures analyzed at static timepoints. Static analysis is limited for the analysis of dynamic morphogenetic processes such a palate fusion and what types of dynamic cellular behaviors mediate palatal fusion is incompletely understood. Here we describe a protocol for live imaging of ex vivo secondary palate fusion in mouse embryos. To examine cellular behaviors of palate fusion, epithelial-specific Keratin14-cre was used to label palate epithelial cells in ROSA26-mTmGflox reporter embryos. To visualize filamentous actin, Lifeact-mRFPruby reporter mice were used. Live imaging of secondary palate fusion was performed by dissecting recently-adhered secondary palatal shelves of embryonic day (E) 14.5 stage embryos and culturing in agarose-containing media on a glass bottom dish to enable imaging with an inverted confocal microscope. Using this method, we have detected a variety of novel cellular behaviors during secondary palate fusion. An appreciation of how distinct cell behaviors are coordinated in space and time greatly contributes to our understanding of this dynamic morphogenetic process. This protocol can be applied to mutant mouse lines, or cultures treated with pharmacological inhibitors to further advance understanding of how secondary palate fusion is controlled.

Here, we present a protocol for live imaging of mouse secondary palate fusion using confocal microscopy. This protocol can be used in combination with a variety of fluorescent reporter mouse lines, and with pathway inhibitors for mechanistic insight. This protocol can be adapted for live imaging in other developmental systems.

The fusion of the secondary palatal shelves to form the intact secondary palate is a key process in mammalian development and its disruption can lead to ...

Live Cell Imaging of Chromosome Segregation During Mitosis

Chromosomes must be reliably and uniformly segregated into daughter cells during mitotic cell division. Fidelity of chromosomal segregation is controlled by multiple mechanisms that include the Spindle Assembly Checkpoint (SAC). The SAC is part of a complex feedback system that is responsible for prevention of a cell progress through mitosis unless all chromosomal kinetochores have attached to spindle microtubules. Chromosomal lagging and abnormal chromosome segregation is an indicator of dysfunctional cell cycle control checkpoints and can be used to measure the genomic stability of dividing cells. Deregulation of the SAC can result in the transformation of a normal cell into a malignant cell through the accumulation of errors during chromosomal segregation. Implementation of the SAC and the formation of the kinetochore complex are tightly regulated by interactions between kinases and phosphatase such as Protein Phosphatase 2A (PP2A). This protocol describes live cell imaging of lagging chromosomes in mouse embryonic fibroblasts isolated from mice that had a knockout of the PP2A-B56&#947; regulatory subunit. This method overcomes the shortcomings of other cell cycle control imaging techniques such as flow cytometry or immunocytochemistry that only provide a snapshot of a cell cytokinesis status, instead of a dynamic spatiotemporal visualization of chromosomes during mitosis.

This protocol describes an easy and convenient method to label and visualize live chromosomes in mitotic cells using Histone2B-GFP BacMam 2.0 label and a spinning disc confocal microscopy system.

Chromosomes must be reliably and uniformly segregated into daughter cells during mitotic cell division. Fidelity of chromosomal segregation is controlled ...

Confocal Live Imaging of Shoot Apical Meristems from Different Plant Species

The shoot apical meristem (SAM) functions as a conserved stem cell reservoir and it generates almost all aboveground tissues during the postembryonic development. The activity and morphology of SAMs determine important agronomic traits, such as shoot architecture, size and number of reproductive organs, and most importantly, grain yield. Here, we provide a detailed protocol for analyzing both the surface morphology and the internal cellular structure of the living SAMs from different species through laser scanning confocal microscope. The whole procedure from the sample preparation to the acquisition of high resolution three-dimensional (3D) images can be accomplished within as short as 20 minutes. We demonstrate that this protocol is highly efficient for studying not only the inflorescence SAMs of the model species but also the vegetative meristems from different crops, providing a simple but powerful tool to study the organization and development of meristems across different plant species.

This protocol presents how to live image and analyze the shoot apical meristems from different plant species using laser scanning confocal microscopy.

The shoot apical meristem (SAM) functions as a conserved stem cell reservoir and it generates almost all aboveground tissues during the postembryonic ...

Live Imaging and Analysis of Muscle Contractions in Drosophila Embryo

Coordinated muscle contractions are a form of rhythmic behavior seen early during development in Drosophila embryos. Neuronal sensory feedback circuits are required to control this behavior. Failure to produce the rhythmic pattern of contractions can be indicative of neurological abnormalities. We previously found that defects in protein O-mannosylation, a posttranslational protein modification, affect the axon morphology of sensory neurons and result in abnormal coordinated muscle contractions in embryos. Here, we present a relatively simple method for recording and analyzing the pattern of peristaltic muscle contractions by live imaging of late stage embryos up to the point of hatching, which we used to characterize the muscle contraction phenotype of protein O-mannosyltransferase mutants. Data obtained from these recordings can be used to analyze muscle contraction waves, including frequency, direction of propagation and relative amplitude of muscle contractions at different body segments. We have also examined body posture and taken advantage of a fluorescent marker expressed specifically in muscles to accurately determine the position of the embryo midline. A similar approach can also be utilized to study various other behaviors during development, such as embryo rolling and hatching.

Live Imaging and Analysis of Muscle Contractions in Drosophila Embryo

Here, we present a method to record embryonic muscle contractions in Drosophila embryos in a non-invasive and detail-oriented manner.

Coordinated muscle contractions are a form of rhythmic behavior seen early during development in Drosophila embryos. Neuronal sensory feedback circuits ...