We would like to thank Dr. Alengo Nyamay'antu and Dr. Ilse Timmerman for their advices about lentiviral packaging. This work is supported by an American Heart Association Scientist Development Grant 10SDG4170137.

<ol>
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The authors have nothing to disclose.

Primary cardiomyocytes isolated from neonatal rats have long been used to study cardiomyocyte functions in vitro. This protocol describes a method for the isolation of neonatal cardiomyocytes from rat pups using a two-step enzyme digestion method, first digesting with trypsin O/N at 4 &#176;C and then purified collagenase. One advantage of employing the purified collagenase step is that the same grade of enzyme is used for all isolations. Thus, the quality and amount of isolated cells is consistent from experiment to experiment.
Given the higher transduction efficiencies associated with adenovirus, if a high efficiency of transduction of the cell culture is necessary for a given experiment, it is better to use an adenovirus. However, if high levels of transduction are not necessary, a lentiviral vector can be used. Having the option of using either adenoviral or lentiviral vectors makes it easier to achieve appropriate transduction and expression levels for different types of genes. If the fluorescent intensity detected by live-cell imaging using the confocal spinning disk microscope or ICC is very low after lentiviral transduction, using another lentiviral transfer vector that uses a different promoter to express the gene of interest may resolve this problem. With adenoviral vectors, if the band detected by WB is weak after adenoviral transduction, this may indicate a low titer viral stock. In that case, it is better to prepare a higher titer adenoviral solution by propagation in cells before proceeding.
One limitation of this technique is that the yield of isolated viable cardiomyocytes is not highly consistent from experiment to experiment, even when using purified collagenase. In order to perform reproducible imaging experiments it is best to count viable cells after the selection of isolated cardiomyocytes in the supernatant at step 1.2.13. in the protocol section. Then, seed cardiomyocytes on glass bottom dishes at varying dilutions. Once the cells have attached, select dishes with the appropriate cell concentration for the experiment planned.
There are many advantages of using neonatal cardiomyocytes, but there are also some disadvantages. The major drawback is their clear difference from adult cardiomyocytes. Fully differentiated adult cardiomyocytes are rod-shape and isolated adult primary cardiomyocytes maintain their rod-shaped morphology, whereas isolated neonatal primary cardiomyocytes spread in all directions36. The phenotypic differences between isolated adult and neonatal cardiomyocytes are also reflected in their patterns of gene expression 37. Therefore, for experiments in which differentiated cardiomyocytes are required, a protocol for the isolation of adult cardiomyocytes will be needed4.
Employing adenoviral and lentiviral transduction of recombinant proteins into primary rat neonatal cardiomyocytes in combination with confocal spinning disk microscopy allows us to analyze the functions of proteins in cultured live primary cells. Relative to existing methods, which utilize transfection to introduce the gene of interest into cells, a significant advantage of this protocol is that adenoviruses and lentiviruses are very efficiently taken up by the cells resulting in the expression of the gene of interest in almost all cells in the culture. Furthermore, the use of two different types of viruses for gene expression makes it easier to achieve appropriate transduction rates and expression levels for multiple genes. siRNAs and chemical agonists and antagonists can also be used in this system to further perturb and analyze the functions of genes and the proteins they encode.
Preparation of the hearts is an extremely important step in the protocol. Remove the hearts from the body as quickly as possible. Be sure to put them on ice immediately to keep cell viability high. Another important step is the preparation of high quality, and titer, lentiviral/adenoviral stocks. If poor quality viral stocks are used, transduction and expression levels of the gene of interest will be low. Therefore, they may not be suitable for imaging studies.
An important future application of this technique will be its&#8217; use in mouse cardiomyocytes. Pilot studies testing whether this method can be used for the isolation of mouse neonatal cardiomyocytes have yielded promising results. Due to the relatively small size of mouse hearts compared to those of rats, less tissue is obtained initially. Thus, fewer cells are isolated in a single procedure using the same number of animals but simply using more mice for the isolation should eliminate this obstacle. The ability to isolate mouse cardiomyocytes allows researchers to investigate the functions of cells isolated from genetically modified mice (transgenic, knock-out, knock-in) that have been produced in order to study a particular form of the gene of interest.
One of the major hurdles in cardiovascular research has been the difficulty associated with investigating the expression and function of a given gene expressed in heart tissue in vivo in real time. However the ability to isolate functional beating cardiomyocytes, modulate cell functions using viral transduction, and then study them in real time using the confocal spinning disk microscope helps to shed light on the role of cardiomyocytes in vivo and bridge this gap. This method provides a simplified system for understanding cardiomyocyte function at the cellular level. It allows for real time analysis of how perturbations in gene expression alter cardiomyocyte function. Live cell imaging of cardiomyocytes will provide further insights into cardiomyocyte function. Such insights will lead to advances in basic cardiovascular research, resulting in novel therapies for the treatment of cardiovascular disease.

Primary rat neonatal cardiomyocytes have long been used for investigating cardiomyocyte function in vitro1. They are easy to isolate from rat pups by several well established methods2-4. The most common method employs collagenase or trypsin to digest connective tissue of the heart prior to cell isolation. Researchers have also developed methods for isolating cardiomyocytes from adult rodents5-8 as well as neonatal mice9,10.
This protocol describes a method for isolating cardiomyocytes from neonatal rat pups, employing a two-step enzyme digestion procedure. Trypsin is first used O/N at 4&#160;&#176;C, and then purified collagenase at 37&#160;&#176;C. Incubation of the heart tissue with trypsin O/N at 4&#160;&#176;C&#160;reduces the steps necessary to harvest cells compared to methods using sequential incubations in a warm enzyme solution2. In addition, by using purified collagenase rather than crude enzymes, lot-to-lot variability can be eliminated, thus providing enhanced reproducibility.
Functional studies of a particular protein often employ a protein expression system using an adenovirus11-13 and/or a lentivirus14-16. [CAUTIONARY NOTE] The viral production and manipulation should be carried out according to the NIH guidelines.
The adenovirus does not integrate into the host genome. It has a very high efficiency of transduction in most cell types, including dividing cells and non-dividing cells, as well as primary cells and established cell lines. This makes the adenovirus a reliable vector for gene expression. High levels of the protein encoded by the adenovirus vector develop within 48 hr following transduction, and they can last for several weeks17. However, one drawback to using an adenovirus for protein expression is that the development of a recombinant adenovirus is both complicated and time consuming. This drawback explains in part why many researchers have been turning to lentiviruses for recombinant gene expression. Unlike adenoviral constructs, generating a lentiviral construct is quick and easy. Although lentiviruses generally have lower efficiencies of transduction than adenoviruses, in both dividing and non-dividing cells, they do integrate into the host genome. Consequently, expression of the transduced gene is more stable for lentiviruses than for adenoviruses.
Due to technological advances in the field of microscopy, it is much easier to capture live cell images of cells expressing recombinant proteins. This holds true even at video rate speeds of acquisition. This allows the investigator to determine how particular alterations in the protein of interest functionally impact the cell in real time. The confocal spinning disk microscope has several key features that make it an optimal technique for live cell imaging18,19. The Yokogawa spinning disc allows for much more rapid image acquisition, while at the same time utilizing far less laser power than point scanning confocal microscopes. Both of these special features are due to the spinning disk, which contains numerous confocal holes through which the laser passes simultaneously to the samples. During acquisition, the disk itself spins quickly and continuously18-20. By using the autofocus system of the microscope, stable focus is maintained over long periods of time. This allows researchers to take well-focused live cell images. Acquired images are played back as a movie file. The images are analyzed using image analysis software such as ImageJ21,22, FIJI23, or other commercially available software.

<table border="0" cellpadding="0" cellspacing="0">
	<tbody>
		<tr>
			<td>1 scissors for decapitation</td>
			<td>WPI</td>
			<td>501749</td>
			<td>Autoclave before use</td>
		</tr>
		<tr>
			<td>1 fine scissors for heart isolation and chopping</td>
			<td>WPI</td>
			<td>14393</td>
			<td>Autoclave before use</td>
		</tr>
		<tr>
			<td>2 fine forceps (Dumont No. 5)</td>
			<td>Sigma</td>
			<td>F6521</td>
			<td>Autoclave before use</td>
		</tr>
		<tr>
			<td>Three sterilized 10 cm plastic dishes</td>
			<td>Sigma</td>
			<td>CLS430165</td>
			<td>for hearts isolation</td>
		</tr>
		<tr>
			<td>3.5 cm glass bottom culture dishes</td>
			<td>MatTek</td>
			<td>P35G-1.5-20-C</td>
			<td>for final plating of cardiomyocytes for future live cell imaging. micro-Dishes from ibidi are an acceptable alternative.</td>
		</tr>
		<tr>
			<td>3.5 cm glass bottom culture dishes</td>
			<td>MatTek</td>
			<td>P35G-0.17-14-C</td>
			<td>for TIRF or high resolution image</td>
		</tr>
		<tr>
			<td>Ethanol solution, 70 % (v/v) in water</td>
			<td>Sigma</td>
			<td>E7148</td>
			<td></td>
		</tr>
		<tr>
			<td>2% gelatin</td>
			<td>Sigma</td>
			<td>G1393</td>
			<td></td>
		</tr>
		<tr>
			<td>One sterilized 10 cm plastic dish</td>
			<td>Sigma</td>
			<td>CLS430165</td>
			<td>for trypsinization</td>
		</tr>
		<tr>
			<td>Aluminium foil</td>
			<td>any brand</td>
			<td></td>
			<td></td>
		</tr>
		<tr>
			<td>parafilm</td>
			<td>Sigma</td>
			<td>P7543</td>
			<td></td>
		</tr>
		<tr>
			<td>Two 10 cm plastic cell culture dish</td>
			<td>Sigma</td>
			<td>CLS430165</td>
			<td>for selection</td>
		</tr>
		<tr>
			<td>Auto pipette</td>
			<td>Drummond Scientific&#160;</td>
			<td>4-000-300</td>
			<td>for trituration</td>
		</tr>
		<tr>
			<td>Cell counter</td>
			<td></td>
			<td></td>
			<td></td>
		</tr>
		<tr>
			<td>&#160; Cellometer, automated cell counter</td>
			<td>nexcelom</td>
			<td></td>
			<td>to check and count cells</td>
		</tr>
		<tr>
			<td>&#160; Microscope and Hematocytometer</td>
			<td>any brand</td>
			<td></td>
			<td>to check and count cells</td>
		</tr>
		<tr>
			<td>Trypan Blue Solution, 0.4%</td>
			<td>invitrogen</td>
			<td>15250-061</td>
			<td></td>
		</tr>
		<tr>
			<td>CO2 incubator</td>
			<td>Sanyo</td>
			<td>MCO-19AIC</td>
			<td></td>
		</tr>
		<tr>
			<td>incubating orbital shaker</td>
			<td>Sigma</td>
			<td>Z673129</td>
			<td>to shake heart tissue with collagenase at 37 C at 170-200 rpm</td>
		</tr>
		<tr>
			<td>10 mg/ml BrdU solution</td>
			<td>BD Pharmingen</td>
			<td>550891</td>
			<td></td>
		</tr>
		<tr>
			<td>DMEM, High Glucose</td>
			<td>invitrogen</td>
			<td>41965039</td>
			<td>Mix medium as indicated in the protocol and warm before use</td>
		</tr>
		<tr>
			<td>MEM</td>
			<td>invitrogen</td>
			<td>31095029</td>
			<td>Mix medium as indicated in the protocol and warm before use</td>
		</tr>
		<tr>
			<td>Fetal Bovine Serum</td>
			<td>invitrogen</td>
			<td>26140079</td>
			<td></td>
		</tr>
		<tr>
			<td>Penicillin-Streptomycin (10,000 U/mL)&#160;</td>
			<td>invitrogen</td>
			<td>15140-122</td>
			<td></td>
		</tr>
		<tr>
			<td></td>
			<td></td>
			<td></td>
			<td></td>
		</tr>
		<tr>
			<td>Section 2 lentiviral transduction</td>
			<td></td>
			<td></td>
			<td></td>
		</tr>
		<tr>
			<td>three packaging plasmids</td>
			<td></td>
			<td></td>
			<td></td>
		</tr>
		<tr>
			<td>&#160;pMDLg/pRRE</td>
			<td>Addgene</td>
			<td>12251</td>
			<td></td>
		</tr>
		<tr>
			<td>&#160;pRSV-Rev</td>
			<td>Addgene</td>
			<td>12253</td>
			<td></td>
		</tr>
		<tr>
			<td>&#160;pMD2.G</td>
			<td>Addgene</td>
			<td>12259</td>
			<td></td>
		</tr>
		<tr>
			<td>The lentiviral transfer vector, pLVX-IRES-Puro</td>
			<td>Clontech</td>
			<td>632183</td>
			<td></td>
		</tr>
		<tr>
			<td>Opti-MEM (serum-free medium)</td>
			<td>invitrogen</td>
			<td>31985070</td>
			<td></td>
		</tr>
		<tr>
			<td>transfection reagent</td>
			<td></td>
			<td></td>
			<td></td>
		</tr>
		<tr>
			<td>&#160; polyethyleneimine&#8220;Max&#8221;, (Mw 40,000) - High Potency Linear PEI (Equivalent to Mw 25,000 in Free Base Form)&#160;</td>
			<td>Polysciences</td>
			<td>24765-2</td>
			<td>It can be substituted with X-tremeGENE 9 from Roche</td>
		</tr>
		<tr>
			<td>&#160; X-tremeGENE 9</td>
			<td>Roche</td>
			<td>6365779001</td>
			<td>substitute for PEI as transfection reagent</td>
		</tr>
		<tr>
			<td>chloroquine</td>
			<td>Sigma</td>
			<td>C6628</td>
			<td>dissolve in water and make 100 mM stock solution. Inhibition of endosomal acidification can be achieved with 10-100 &#956;M Chloroquine.</td>
		</tr>
		<tr>
			<td>HEPES</td>
			<td>Sigma</td>
			<td>H3375</td>
			<td></td>
		</tr>
		<tr>
			<td>10 ml Luer-Lok syringe, sterilized</td>
			<td>BD</td>
			<td>309604</td>
			<td></td>
		</tr>
		<tr>
			<td>0.45 um filters</td>
			<td>Sigma</td>
			<td>F8677</td>
			<td>use only cellulose acetate or polyethersulfone (PES) (low protein binding) filters. Do not use nitrocellulose filters. Nitrocellulose binds surface proteins on the lentiviral envelope and destroys the virus.</td>
		</tr>
		<tr>
			<td>Hexadimethrine bromide</td>
			<td>Sigma</td>
			<td>H9268</td>
			<td>dissolve in water and make 8mg/ml stock solution, then filter it to sterilize.</td>
		</tr>
		<tr>
			<td>polyethylene glicol 6000</td>
			<td>Sigma</td>
			<td>81260</td>
			<td></td>
		</tr>
		<tr>
			<td>Sodium chloride</td>
			<td>Sigma</td>
			<td>S9888</td>
			<td></td>
		</tr>
		<tr>
			<td>sodium hydroxide</td>
			<td>Sigma</td>
			<td>S5881</td>
			<td></td>
		</tr>
		<tr>
			<td></td>
			<td></td>
			<td></td>
			<td></td>
		</tr>
		<tr>
			<td>Section 3 Adenoviral transduction</td>
			<td></td>
			<td></td>
			<td></td>
		</tr>
		<tr>
			<td>HEK 293T cells</td>
			<td>ATCC</td>
			<td>CRL-11268</td>
			<td></td>
		</tr>
		<tr>
			<td>Some 10 cm cell culture dishes</td>
			<td>Sigma</td>
			<td>CLS430165</td>
			<td></td>
		</tr>
		<tr>
			<td>96-Well Microplate with lid, flat-bottom, tissue culture, sterile</td>
			<td>BD Falcon</td>
			<td>353072</td>
			<td>for titration</td>
		</tr>
		<tr>
			<td>Multichannel piptte, 10-100 ul, 8-channel</td>
			<td>eppendorf</td>
			<td>3122 000.035</td>
			<td></td>
		</tr>
		<tr>
			<td></td>
			<td></td>
			<td></td>
			<td></td>
		</tr>
		<tr>
			<td>Section 4 live cell imaging</td>
			<td></td>
			<td></td>
			<td></td>
		</tr>
		<tr>
			<td>Spinning disk confocal microspopy</td>
			<td>PerkinElmer</td>
			<td>L7267000</td>
			<td></td>
		</tr>
		<tr>
			<td>a temperature controlled chamber</td>
			<td>any brand</td>
			<td></td>
			<td>to keep temperature at 37 C</td>
		</tr>
		<tr>
			<td>a CO2 environmental system</td>
			<td>any brand</td>
			<td></td>
			<td>optional to maintain CO2 concentration optimal</td>
		</tr>
		<tr>
			<td>Medium</td>
			<td></td>
			<td></td>
			<td></td>
		</tr>
		<tr>
			<td>&#160; CO2 Independent Medium, No Glutamine</td>
			<td>invitrogen</td>
			<td>18045-054&#160;&#160;</td>
			<td>for long time time-lapse imaging</td>
		</tr>
		<tr>
			<td>&#160; DMEM, High Glucose, HEPES, no Phenol Red&#160;</td>
			<td>invitrogen</td>
			<td>21063-029</td>
			<td>for long time time-lapse imaging</td>
		</tr>
	</tbody>
</table>

live cell imaging of primary rat neonatal cardiomyocytes following adenoviral and lentiviral transduction using confocal spinning disk microscopy

Primary rat neonatal cardiomyocytes are useful in basic in vitro cardiovascular research because they can be easily isolated in large numbers in a single procedure. Due to advances in microscope technology it is relatively easy to capture live cell images for the purpose of investigating cellular events in real time with minimal concern regarding phototoxicity to the cells. This protocol describes how to take live cell timelapse images of primary rat neonatal cardiomyocytes using a confocal spinning disk microscope following lentiviral and adenoviral transduction to modulate properties of the cell. The application of two different types of viruses makes it easier to achieve an appropriate transduction rate and expression levels for two different genes. Well focused live cell images can be obtained using the microscope&#8217;s autofocus system, which maintains stable focus for long time periods. Applying this method, the functions of exogenously engineered proteins expressed in cultured primary cells can be analyzed. Additionally, this system can be used to examine the functions of genes through the use of siRNAs as well as of chemical modulators.

To illustrate the technique, a lentivirus encoding EGFP (enhanced green fluorescent protein)-tagged Cx43 (Connexin43) or a mutated Cx43 32 was used to express EGFP-tagged proteins in cells, and an adenovirus encoding FGFR1DN (fibroblast growth factor receptor 1 dominant negative) was used to shut down FGF signaling in the cell 33-35. Three days following the isolation of cardiomyocytes, the isolated cardiomyocytes were transduced with lentivirus in order to express EGFP-tagged proteins in the cells. Then after 3 days of lentiviral transduction, the isolated cardiomyocytes were further transduced with an adenovirus encoding FGFR1DN to eliminate FGF signaling in the cells. After allowing enough time for cells to express the transduced exogenous genes, a confocal spinning disk microscope was used to capture live cell images. Acquired images are played back as a movie file and analyzed using image analysis software. For more detailed representative results please see Sakurai&#160;et al32.
The expression of EGFP tagged proteins following lentiviral transduction was confirmed by confocal spinning disk microscopy 72 hr following lentiviral transduction Figures 1A-B. The expression of FGFR1DN by adenoviral transduction was confirmed by WB and ICC after 24 hr of adenoviral transduction Figures 1C-D. The time of adenoviral addition to 3.5 cm dishes was defined as time 0 and time-lapse images were acquired with a 40x air NA 0.9 objective lens every 5 min&#160;for 6 hr using a chamber heater to maintain the temperature at 37 &#730;C. Time-lapse images of EGFP-tagged proteins in the primary cardiomyocytes taken by confocal spinning disk microscopy are shown in Supplemental Movies 1-2.
In cases where the temperature equilibration was not adequate, or the multiple-acquisition mode was not functioning properly, images captured might move in the x-y plane Supplemental Movie 1. However when working properly the autofocus system stably maintained focus and this did not occur. As shown in Supplemental Movie 2, when the temperature equilibration was adequate and only one region of interest was acquired, the images captured are of very high quality.
The beating of cardiomyocytes was assessed after long-term time-lapse live cell imaging in order to confirm cell viability. Even after 16 hr&#160;of time-lapse imaging EGFP expressing cardiomyocytes maintained their functional properties and beat rhythmically Supplemental Movie 3.
<img alt="Figure 1" fo:content-width="5in" src="/files/ftp_upload/51666/51666fig1highres.jpg" width="500" /> 
Figure 1.&#160;Confirmation of protein expression following lentiviral or adenoviral transduction.&#160;(A) Isolated rat neonatal cardiomyocytes expressing Cx43-WT-EGFP transduced with Ad-FGFR1DN 3 days after transduction. See also Supplemental Movie 1. (B) Isolated rat neonatal cardiomyocytes expressing Cx43-S325/328/330E(3SE)-EGFP transduced with Ad-FGFR1DN 3 days after transduction. See also Supplemental Movie 2. (C) Protein expression following adenoviral transduction detected by ICC 24 hr after transduction. Hemagglutinin (HA) protein-tagged FGFR1DN was detected by anti-HA antibody using conventional ICC methods, alpha-actinin was used as a marker for cardiomyocytes. (D) Expression of FGFR1DN protein following adenoviral transduction detected by WB 24 hr after transduction. HA-tagged FGFR1DN was detected by anti-HA antibody by WB, beta-tubulin was used as loading control.
Supplemental Movie 1.&#160;Time-lapse imaging of isolated rat neonatal cardiomyocytes expressing Cx43-WT-EGFP transduced with Ad-FGFR1DN. The time-lapse images were acquired with a 40x objective lens every 5 min&#160;for 6 hr with a confocal spinning disk microscope. Acquired images were played back as a movie at 10 frames per sec. This movie has been modified from Sakurai&#160;et al32. <a href="https://www-jove-com.remotexs.ntu.edu.sg/files/ftp_upload/51666/s_movie1_2.mov" target="_blank">Please click here to view this video.</a>
Supplemental Movie 2.&#160;Time-lapse imaging of isolated rat neonatal cardiomyocytes expressing Cx43-S325/328/330E-EGFP transduced with Ad-FGFR1DN. The time-lapse images were acquired with a 40x objective lens every 5 min for 6 hr with a confocal spinning disk microscope. Acquired images were played back as a movie at 10 frames per sec. This movie has been modified from Sakurai&#160;et al32. <a href="https://www-jove-com.remotexs.ntu.edu.sg/files/ftp_upload/51666/s_movie2_2.mov" target="_blank">Please click here to view this video.</a>
Supplemental Movie 3.&#160;Time-lapse imaging of isolated rat neonatal cardiomyocytes played back at actual speed. The time-lapse images of isolated rat neonatal cardiomyocytes expressing Cx43-EGFP transduced with Ad-FGFR1DN were acquired with a 40x objective lens every 200 msec for 10 sec with a confocal spinning disk microscope following 16 hr of time-lapse acquisition. Acquired images were played back as a movie at 5 frames per sec at actual speed. <a href="https://www-jove-com.remotexs.ntu.edu.sg/files/ftp_upload/51666/s_movie3.MOV" target="_blank">Please click here to view this video.</a>

Watch this Scientific Journal Video about Live Cell Imaging of Primary Rat Neonatal Cardiomyocytes Following Adenoviral and Lentiviral Transduction Using Confocal Spinning Disk Microscopy at JoVE.com

Live Cell Imaging of Primary Rat Neonatal Cardiomyocytes Following Adenoviral and Lentiviral Transduction Using Confocal Spinning Disk Microscopy

This protocol describes a method of live cell imaging using primary rat neonatal cardiomyocytes following lentiviral and adenoviral transduction using confocal spinning disk microscopy. This enables detailed observations of cellular processes in living cardiomyocytes.

Primary rat neonatal cardiomyocytes are useful in basic in vitro cardiovascular research because they can be easily isolated in large numbers in a single ...

live-cell-imaging-primary-rat-neonatal-cardiomyocytes-following

Nanyang Technological University

Research

JoVE Journal

Biology

13.5K Views.  Max-Planck-Institute for Molecular Biomedicine and Institute of Cell Biology. This protocol describes a method of live cell imaging using primary rat neonatal cardiomyocytes following lentiviral and adenoviral transduction using confocal spinning disk microscopy. This enables detailed observations of cellular processes in living cardiomyocytes.

Video: Live Cell Imaging of Primary Rat Neonatal Cardiomyocytes Following Adenoviral and Lentiviral Transduction Using Confocal Spinning Disk Microscopy

Two-photon axotomy and time-lapse confocal imaging in live zebrafish embryos

Zebrafish have long been utilized to study the cellular and molecular mechanisms of development by time-lapse imaging of the living transparent embryo. Here we describe a method to mount zebrafish embryos for long-term imaging and demonstrate how to automate the capture of time-lapse images using a confocal microscope. We also describe a method to create controlled, precise damage to individual branches of peripheral sensory axons in zebrafish using the focused power of a femtosecond laser mounted on a two-photon microscope. The parameters for successful two-photon axotomy must be optimized for each microscope. We will demonstrate two-photon axotomy on both a custom built two-photon microscope and a Zeiss 510 confocal/two-photon to provide two examples.

Zebrafish trigeminal sensory neurons can be visualized in a transgenic line expressing GFP driven by a sensory neuron specific promoter 1. We have adapted this zebrafish trigeminal model to directly observe sensory axon regeneration in living zebrafish embryos. Embryos are anesthetized with tricaine and positioned within a drop of agarose as it solidifies. Immobilized embryos are sealed within an imaging chamber filled with phenylthiourea (PTU) Ringers. We have found that embryos can be continuously imaged in these chambers for 12-48 hours. A single confocal image is then captured to determine the desired site of axotomy. The region of interest is located on the two-photon microscope by imaging the sensory axons under low, non-damaging power. After zooming in on the desired site of axotomy, the power is increased and a single scan of that defined region is sufficient to sever the axon. Multiple location time-lapse imaging is then set up on a confocal microscope to directly observe axonal recovery from injury.

Here we describe a method for mounting zebrafish embryos for long-term imaging, two-photon imaging and tissue-damage techniques, and time-lapse confocal imaging.

Zebrafish have long been utilized to study the cellular and molecular mechanisms of development by time-lapse imaging of the living transparent embryo.  ...

Live Imaging of the Zebrafish Embryonic Brain by Confocal Microscopy

In this video, we demonstrate the method our lab has developed to analyze the cell shape changes and rearrangements required to bend and fold the developing zebrafish brain (Gutzman et al, 2008). Such analysis affords a new understanding of the underlying cell biology required for development of the 3D structure of the vertebrate brain, and significantly increases our ability to study neural tube morphogenesis. The embryonic zebrafish brain is shaped beginning at 18 hours post fertilization (hpf) as the ventricles within the neuroepithelium inflate. By 24 hpf, the initial steps of neural tube morphogenesis are complete. Using the method described here, embryos at the one cell stage are injected with mRNA encoding membrane-targeted green fluorescent protein (memGFP). After injection and incubation, the embryo, now between 18 and 24 hpf, is mounted, inverted, in agarose and imaged by confocal microscopy. Notably, the zebrafish embryo is transparent making it an ideal system for fluorescent imaging. While our analyses have focused on the midbrain-hindbrain boundary and the hindbrain, this method could be extended for analysis of any region in the zebrafish to a depth of 
80-100 &mu;m.

In this video, we demonstrate a method by which to analyze the developing vertebrate brain in live zebrafish embryos at single cell resolution by confocal microscopy. This includes the method by which we inject the single-cell zebrafish embryo and subsequently mount and image the developing brain.

In this video, we demonstrate the method our lab has developed to analyze the cell shape changes and rearrangements required to bend and fold the ...

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

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

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

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

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

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 ...

Isolation and Culture of Neonatal Mouse Cardiomyocytes

Cultured neonatal cardiomyocytes have long been used to study myofibrillogenesis and myofibrillar functions. Cultured cardiomyocytes allow for easy investigation and manipulation of biochemical pathways, and their effect on the biomechanical properties of spontaneously beating cardiomyocytes.	
The following 2-day protocol describes the isolation and culture of neonatal mouse cardiomyocytes. We show how to easily dissect hearts from neonates, dissociate the cardiac tissue and enrich cardiomyocytes from the cardiac cell-population. We discuss the usage of different enzyme mixes for cell-dissociation, and their effects on cell-viability. The isolated cardiomyocytes can be subsequently used for a variety of morphological, electrophysiological, biochemical, cell-biological or biomechanical assays. We optimized the protocol for robustness and reproducibility, by using only commercially available solutions and enzyme mixes that show little lot-to-lot variability. We also address common problems associated with the isolation and culture of cardiomyocytes, and offer a variety of options for the optimization of isolation and culture conditions.

Primary mouse cardiomyocyte cultures are one of the pivotal tools for the investigation of myofibrillar organization and function. The following protocol describes the isolation and culture of primary cardiomyocytes from neonatal mouse hearts. The resulting cardiomyocyte cultures may be subsequently used for a variety of biomechanical, biochemical and cell-biological assays.

Cultured neonatal cardiomyocytes have long been used to study  myofibrillogenesis and myofibrillar functions. Cultured cardiomyocytes allow  for easy ...

Analyzing Craniofacial Morphogenesis in Zebrafish Using 4D Confocal Microscopy

Time-lapse imaging is a technique that allows for the direct observation of the process of morphogenesis, or the generation of shape. Due to their optical clarity and amenability to genetic manipulation, the zebrafish embryo has become a popular model organism with which to perform time-lapse analysis of morphogenesis in living embryos. Confocal imaging of a live zebrafish embryo requires that a tissue of interest is persistently labeled with a fluorescent marker, such as a transgene or injected dye. The process demands that the embryo is anesthetized and held in place in such a way that healthy development proceeds normally. Parameters for imaging must be set to account for three-dimensional growth and to balance the demands of resolving individual cells while getting quick snapshots of development. Our results demonstrate the ability to perform long-term in vivo imaging of fluorescence-labeled zebrafish embryos and to detect varied tissue behaviors in the cranial neural crest that cause craniofacial abnormalities. Developmental delays caused by anesthesia and mounting are minimal, and embryos are unharmed by the process. Time-lapse imaged embryos can be returned to liquid medium and subsequently imaged or fixed at later points in development. With an increasing abundance of transgenic zebrafish lines and well-characterized fate mapping and transplantation techniques, imaging any desired tissue is possible. As such, time-lapse in vivo imaging combines powerfully with zebrafish genetic methods, including analyses of mutant and microinjected embryos.

Time-lapse confocal imaging is a powerful technique useful for characterizing embryonic development. Here, we describe the methodology and characterize craniofacial morphogenesis in wild-type, as well as pdgfra, smad5, and smo mutant embryos.

Time-lapse imaging is a technique that allows for the direct observation of the process of morphogenesis, or the generation of shape. Due to their optical ...

Isolation, Culture and Transduction of Adult Mouse Cardiomyocytes

Cultured cardiomyocytes can be used to study cardiomyocyte biology using techniques that are complementary to in vivo systems. For example, the purity and accessibility of in vitro culture enables fine control over biochemical analyses, live imaging, and electrophysiology. Long-term culture of cardiomyocytes offers access to additional experimental approaches that cannot be completed in short term cultures. For example, the in vitro investigation of dedifferentiation, cell cycle re-entry, and cell division has thus far largely been restricted to rat cardiomyocytes, which appear to be more robust in long-term culture. However, the availability of a rich toolset of transgenic mouse lines and well-developed disease models make mouse systems attractive for cardiac research. Although several reports exist of adult mouse cardiomyocyte isolation, few studies demonstrate their long-term culture. Presented here, is a step-by-step method for the isolation and long-term culture of adult mouse cardiomyocytes. First, retrograde Langendorff perfusion is used to efficiently digest the heart with proteases, followed by gravity sedimentation purification. After a period of dedifferentiation following isolation, the cells gradually attach to the culture and can be cultured for weeks. Adenovirus cell lysate is used to efficiently transduce the isolated cardiomyocytes. These methods provide a simple, yet powerful model system to study cardiac biology.

This protocol describes a step-by-step method for the reproducible isolation and long-term culture of adult mouse cardiomyocytes with high yield, purity, and viability.

Cultured cardiomyocytes can be used to study cardiomyocyte biology using techniques that are complementary to in vivo systems. For example, the purity and ...

Live Cell Imaging and 3D Analysis of Angiotensin Receptor Type 1a Trafficking in Transfected Human Embryonic Kidney Cells Using Confocal Microscopy

Live-cell imaging is used to simultaneously capture time-lapse images of angiotensin type 1a receptors (AT1aR) and intracellular compartments in transfected human embryonic kidney-293 (HEK) cells following stimulation with angiotensin II (Ang II). HEK cells are transiently transfected with plasmid DNA containing AT1aR tagged with enhanced green fluorescent protein (EGFP). Lysosomes are identified with a red fluorescent dye. Live-cell images are captured on a laser scanning confocal microscope after Ang II stimulation and analyzed by software in three dimensions (3D, voxels) over time. Live-cell imaging enables investigations into receptor trafficking and avoids confounds associated with fixation, and in particular, the loss or artefactual displacement of EGFP-tagged membrane receptors. Thus, as individual cells are tracked through time, the subcellular localization of receptors can be imaged and measured. Images must be acquired sufficiently rapidly to capture rapid vesicle movement. Yet, at faster imaging speeds, the number of photons collected is reduced. Compromises must also be made in the selection of imaging parameters like voxel size in order to gain imaging speed. Significant applications of live-cell imaging are to study protein trafficking, migration, proliferation, cell cycle, apoptosis, autophagy and protein-protein interaction and dynamics, to name but a few.

Here we present a protocol to image cells expressing green fluorescent protein-tagged angiotensin type 1a receptors during endocytosis initiated by angiotensin II treatment. This technique includes labeling lysosomes with a second fluorescent marker, and then utilizing software to analyze the co-localization of receptor and lysosome in three dimensions over time.

Live-cell imaging is used to simultaneously capture time-lapse images of angiotensin type 1a receptors (AT1aR) and intracellular compartments in ...

Confocal Microscopy Reveals Cell Surface Receptor Aggregation Through Image Correlation Spectroscopy

Confocal microscopy provides an accessible methodology to capture sub-cellular interactions critical for the characterization and further development of pre-clinical agents labeled with fluorescent probes. With recent advancements in antibody based cytotoxic drug delivery systems, understanding the alterations induced by these agents within the realm of receptor aggregation and internalization is of critical importance. This protocol leverages the well-established methodology of fluorescent immunocytochemistry and the open source FIJI distribution of ImageJ, with its inbuilt autocorrelation and image mathematical functions, to perform spatial image correlation spectroscopy (ICS). This protocol quantitates the fluorescent intensity of labeled receptors as a function of the beam area of the confocal microscope. This provides a quantitative measure of the state of target molecule aggregation on the cell surface. This methodology is focused on the characterization of static cells with potential to expand into temporal investigations of receptor aggregation. This protocol presents an accessible methodology to provide quantification of clustering events occurring at the cell surface, utilizing well established techniques and non-specialized imaging apparatus.

Antibodies that bind to target receptors on the cell surface can confer conformation and clustering alterations. These dynamic changes have implications for characterizing drug development in target cells. This protocol utilizes confocal microscopy and image correlation spectroscopy through ImageJ/FIJI to quantify the extent of receptor clustering on the cell surface.

Confocal microscopy provides an accessible methodology to capture sub-cellular interactions critical for the characterization and further development of ...

Live Cell Imaging to Assess the Dynamics of Metaphase Timing and Cell Fate Following Mitotic Spindle Perturbations

Live cell time-lapse imaging is an important tool in cell biology that provides insight into cellular processes that might otherwise be overlooked, misunderstood, or misinterpreted by the fixed-cell analysis. While the fixed cell imaging and analysis is robust and sufficient to observe cellular steady-state, it can be limited in defining a temporal order of events at the cellular level and is ill-equipped to assess the transient nature of dynamic processes including mitotic progression. In contrast, live cell imaging is an eloquent tool that can be used to observe cellular processes at the single-cell level over time and has the capacity to capture the dynamics of processes that would otherwise be poorly represented in fixed cell imaging. Here we describe an approach to generate cells carrying fluorescently labeled markers of chromatin and microtubules and their use in live cell imaging approaches to monitor metaphase chromosome alignment and mitotic exit. We describe imaging-based techniques to assess the dynamics of spindle formation and mitotic progression, including the identification of cells at various stages in mitosis, identification&#160;and tracking of mitotic defects, and analysis of spindle dynamics and mitotic cell fate following the treatment with mitotic inhibitors.

Here we present a protocol to assess the dynamics of spindle formation and mitotic progression. Our application of time-lapse imaging enables the user to identify cells at various stages of mitosis, track and identify mitotic defects, and analyze spindle dynamics and mitotic cell fate upon exposure to anti-mitotic drugs.

Live cell time-lapse imaging is an important tool in cell biology that provides insight into cellular processes that might otherwise be overlooked, ...