Name: assessing cardiomyocyte subtypes following transcription factor-mediated reprogramming of mouse embryonic fibroblasts
Uploaded: 2017-03-22T14:00:00
Description: Watch this Scientific Journal Video about Assessing Cardiomyocyte Subtypes Following Transcription Factor-mediated Reprogramming of Mouse Embryonic Fibroblasts at JoVE.com

A.F.-P. was supported by the National Science Foundation Graduate Research Fellowship under Grant No.2015165336. N.V.M was supported by grants from the NIH (HL094699), Burroughs Wellcome Fund (1009838), and the March of Dimes (#5-FY14-203). We acknowledge Young-Jae Nam, Christina Lubczyk, and Minoti Bhakta for their important contributions to protocol development and data analysis. We also thank John Shelton for valuable technical input and members of the Munshi lab for scientific discussion.

All experimental procedures involving animal practices were approved by the Institutional Animal Care and Use Committee at UT Southwestern Medical Center.
1. Isolation of Hcn4-GFP E12.5 Mouse Embryonic Fibroblast (MEFs)
<ol>
	<li>Set up timed matings between homozygous Hcn4-GFP males and CD-1 females.</li>
	<li>Sacrifice pregnant female at E12.5 by carbon dioxide euthanasia and subsequent cervical dislocation.
	<ol>
		<li>Remove uterine horns with dissecting forceps as described previously<s...

<ol>
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The present study provides a direct-reprogramming strategy for conversion of MEFs into a diverse set of cardiac subtypes via retrovirus-mediated expression of the cardiac transcription factors Gata4, Mef2c, Tbx5, and Hand2 (GHMT). Using a multiplex immunostaining approach in combination with a PM-specific reporter mouse, we are able to identify iAM, iVMs, and iPMs at single cell resolution. Such an assay allows for an experimental in vitro system capable of isolating the contributions of individual transcription...

The heart is the first functional organ to develop in the embryo1,2. In conjunction with the circulatory system, it supplies oxygen, nutrients, and a waste disposal mechanism during development. Three weeks after fertilization, the human heart beats for the first time and its proper regulation is maintained by cardiomyocytes (CMs). The irreversible loss of these specialized cells is therefore the fundamental issue underlying progressive heart failure. While some organisms such as the zebrafish and Xenopus have the potential for cardiac regeneration, the adult mammalian heart is more limited3,5,6. Thus, given the critical function of the heart, it is not astonishing that heart disease is the leading cause of death in the world, accounting for 600,000 deaths in the United States alone7. Therefore, cell-based therapies to efficiently repair or replace the injured myocardium are of great clinical interest.
The seminal study of Yamanaka and colleagues8 showed that forced expression of four transcription factors is sufficient to convert fully differentiated fibroblast cells to pluripotent stem cells. However, the tumorigenic capacity of all pluripotent stem cell strategies has been a critical concern in their use for therapeutic purposes. This motivated the scientific field to search for alternative methods to transdifferentiate cells while avoiding a pluripotent stage. Recently, several groups have shown the feasibility of this strategy by displaying direct conversion of mouse fibroblasts to induced cardiomyocyte-like cells (iCLMs) with the ectopic expression of the transcription factors Gata4, Mef2c, Tbx5, and later on, Hand2 (GMT and GHMT, respectively)9,10. Furthermore, the same strategy can be performed in vivo and in human-derived tissues9,11,12. Recent studies have highlighted additional factors or signaling pathways that can be modulated to further improve cardiac reprogramming efficiency13,14,15. Taken together, these studies demonstrate the potential of directed transdifferentiation for regenerative therapies. However, the low efficiency of CM reprogramming, the unknown molecular mechanisms, inconsistent reproducibility due to methodological differences16, and the heterogeneous nature of iCLMs remain unaddressed.
In order to directly evaluate iCLM heterogeneity, we designed a discrete and robust single-cell assay for the identification of sarcomere development and cardiac lineage specification-two necessary characteristics of functional cardiomyocytes. There are at least three major types of CM in the heart as defined by their location and unique electrical properties: atrial (AM), ventricular (VM) and pacemaker (PM)17,18,19,20. In an orchestrated combination, they allow the proper pumping of blood. During heart injury, one or all subtypes might be affected, and the type of cell therapy would need to be addressed on a case-by-case basis. Currently, most strategies focus on the overall generation of cardiomyocytes, while little work is being done to study the molecular mechanisms that regulates subtype specification.
The following study details how to properly quantify well-organized sarcomeres and identify a diverse set of cardiomyocyte subtypes. Using a pacemaker (PM)-specific reporter mouse, we are able to apply an immunocytochemical approach to distinguish induced atrial-like myocytes (iAM), induced ventricular-like myocytes (iVM), and induced PM-like myocytes (iPMs)21. Based on our observations, only cells that exhibit sarcomere organization are capable of spontaneous beating. This unique reprogramming platform allows for assessing the role of certain parameters in sarcomere organization, subtype specification, and efficiency of CM reprogramming at single-cell resolution.

<table border="0" cellpadding="0" cellspacing="0" width="873">
	<tbody>
		<tr height="34">
			<td height="34" style="height:34px;width:319px;">DMEM</td>
			<td style="width:91px;">Sigma</td>
			<td style="width:119px;">D5796</td>
			<td style="width:347px;">Component of iCLM media, Plat-E media, fibroblast, and Transfection media</td>
		</tr>
		<tr height="34">
			<td height="34" style="height:34px;width:319px;">Medium 199</td>
			<td style="width:91px;">Thermo Fisher Scientific</td>
			<td style="width:119px;">11150059</td>
			<td style="width:347px;">Component of iCLM media</td>
		</tr>
		<tr height="34">
			<td height="34" style="height:34px;width:319px;">Fetal bovine serrum (FBS)</td>
			<td style="width:91px;">Sigma</td>
			<td style="width:119px;">F2442</td>
			<td style="width:347px;">Component of iCLM media, Plat-E media, fibroblast, and Transfection media</td>
		</tr>
		<tr height="34">
			<td height="34" style="height:34px;width:319px;">Insulin-Transferrin-Selenium G</td>
			<td style="width:91px;">Thermo Fisher Scientific</td>
			<td style="width:119px;">41400-045</td>
			<td style="width:347px;">Component of iCLM media</td>
		</tr>
		<tr height="34">
			<td height="34" style="height:34px;width:319px;">MEM vitamin solution</td>
			<td style="width:91px;">Thermo Fisher Scientific</td>
			<td style="width:119px;">11120-052</td>
			<td style="width:347px;">Component of iCLM media</td>
		</tr>
		<tr height="34">
			<td height="34" style="height:34px;width:319px;">MEM amino acids</td>
			<td style="width:91px;">Thermo Fisher Scientific</td>
			<td style="width:119px;">1601149</td>
			<td style="width:347px;">Component of iCLM media</td>
		</tr>
		<tr height="34">
			<td height="34" style="height:34px;width:319px;">Non-Essential amino acids</td>
			<td style="width:91px;">Thermo Fisher Scientific</td>
			<td style="width:119px;">11140-050</td>
			<td style="width:347px;">Component of iCLM media</td>
		</tr>
		<tr height="34">
			<td height="34" style="height:34px;width:319px;">Antibiotic-Antimycotics</td>
			<td style="width:91px;">Thermo Fisher Scientific</td>
			<td style="width:119px;">15240062</td>
			<td style="width:347px;">Component of iCLM media</td>
		</tr>
		<tr height="34">
			<td height="34" style="height:34px;width:319px;">B-27 supplement</td>
			<td style="width:91px;">Thermo Fisher Scientific</td>
			<td style="width:119px;">17504044</td>
			<td style="width:347px;">Component of iCLM media</td>
		</tr>
		<tr height="34">
			<td height="34" style="height:34px;width:319px;">Heat-Inactivated Horse Serum</td>
			<td style="width:91px;">Thermo Fisher Scientific</td>
			<td style="width:119px;">26050-088</td>
			<td style="width:347px;">Component of iCLM media</td>
		</tr>
		<tr height="34">
			<td height="34" style="height:34px;width:319px;">NaPyruvate</td>
			<td style="width:91px;">Thermo Fisher Scientific</td>
			<td style="width:119px;">11360-70</td>
			<td style="width:347px;">Component of iCLM media</td>
		</tr>
		<tr height="34">
			<td height="34" style="height:34px;">Penicillin/Streptomycin</td>
			<td style="width:91px;">Thermo Fisher Scientific</td>
			<td style="width:119px;">1514022</td>
			<td style="width:347px;">Component of Plat-E media and fibroblast media</td>
		</tr>
		<tr height="34">
			<td height="34" style="height:34px;">Puromycin&#160;</td>
			<td style="width:91px;">Thermo Fisher Scientific</td>
			<td>A11139-03</td>
			<td>Component of Plat-E media</td>
		</tr>
		<tr height="35">
			<td height="35" style="height:35px;">Blasticidin&#160;&#160;</td>
			<td style="width:91px;">Gemini Bio-Products</td>
			<td>400-128P</td>
			<td>Component of Plat-E media</td>
		</tr>
		<tr height="34">
			<td height="34" style="height:34px;width:319px;">Glutamax</td>
			<td style="width:91px;">Thermo Fisher Scientific</td>
			<td>35050-061</td>
			<td>Component of Fibroblast media</td>
		</tr>
		<tr height="20">
			<td height="20" style="height:20px;width:319px;">Confocal laser scanning LSM700</td>
			<td style="width:91px;">Zeiss</td>
			<td style="width:119px;"></td>
			<td>For confocal analysis</td>
		</tr>
		<tr height="20">
			<td height="20" style="height:20px;width:319px;">FuGENE 6 transfection Reagent</td>
			<td style="width:91px;">Promega</td>
			<td style="width:119px;">E2692</td>
			<td>Transfection reagent&#160;</td>
		</tr>
		<tr height="34">
			<td height="34" style="height:34px;width:319px;">Opti-MEM Reduced Serum Medium</td>
			<td style="width:91px;">Thermo Fisher Scientific</td>
			<td style="width:119px;">31985-070</td>
			<td>Transfection reagent&#160;</td>
		</tr>
		<tr height="20">
			<td height="20" style="height:20px;width:319px;">Polybrene</td>
			<td style="width:91px;">Millipore</td>
			<td style="width:119px;">TR-1003-G</td>
			<td>Induction reagent. Use at a final concentration of 8um/mL</td>
		</tr>
		<tr height="35">
			<td height="35" style="height:35px;width:319px;">Platinium-E (PE) Retroviral Packagin Cell Line, Ecotropic</td>
			<td style="width:91px;">CellBiolabs</td>
			<td style="width:119px;">RV-101</td>
			<td>Retroviral pacaking cell line</td>
		</tr>
		<tr height="34">
			<td height="34" style="height:34px;width:319px;">Trypsin 0.25% EDTA</td>
			<td style="width:91px;">Thermo Fisher Scientific</td>
			<td style="width:119px;"></td>
			<td>For MEFs and Plat-E dissociation</td>
		</tr>
		<tr height="20">
			<td height="20" style="height:20px;">Mouse anti &#945;-Actinin (Clone EA-53)</td>
			<td style="width:91px;">Sigma</td>
			<td>A7811</td>
			<td>Antibody for confocal analysis. Use at 1:200</td>
		</tr>
		<tr height="34">
			<td height="34" style="height:34px;">Chicken anti-GFP IgY</td>
			<td style="width:91px;">Thermo Fisher Scientific</td>
			<td>A10262</td>
			<td>Antibody for confocal analysis. Use at 1:200</td>
		</tr>
		<tr height="20">
			<td height="20" style="height:20px;">Rabbit Pab anti-NPPA&#160;</td>
			<td style="width:91px;">Abgent</td>
			<td>AP8534A</td>
			<td>Antibody for confocal analysis. Use at 1:400</td>
		</tr>
		<tr height="20">
			<td height="20" style="height:20px;">Rabbit Pab anti Myl2 IgG&#160;</td>
			<td style="width:91px;">ProteinTech</td>
			<td>10906-1-AP</td>
			<td>Antibody for confocal analysis. Use at 1:200</td>
		</tr>
		<tr height="35">
			<td height="35" style="height:35px;width:319px;">Vectashield solution with DAPI (4&#39;,6-Diamidino-2-Phenylindole, Dihydrochloride)</td>
			<td style="width:91px;">Vector Labs</td>
			<td style="width:119px;">H-1500</td>
			<td>Dye for confocal analysis</td>
		</tr>
		<tr height="34">
			<td height="34" style="height:34px;width:319px;">Superfrost Plus Microscope slides</td>
			<td style="width:91px;">Thermo Fisher Scientific</td>
			<td style="width:119px;">12-550-15</td>
			<td>25 x 75 x 1.0 mm</td>
		</tr>
		<tr height="20">
			<td height="20" style="height:20px;width:319px;">BioCoat Fibronectin 12mm coverslips</td>
			<td style="width:91px;">NeuVitro Corp</td>
			<td>GG-12-1.5</td>
			<td>Coverslips for confocal analysis</td>
		</tr>
		<tr height="35">
			<td height="35" style="height:35px;width:319px;">100um cell strainer</td>
			<td style="width:91px;">Thermo Fisher Scientific</td>
			<td>08-771-19</td>
			<td></td>
		</tr>
		<tr height="35">
			<td height="35" style="height:35px;width:319px;">0.45um Syringes filters SFCA 25MM</td>
			<td style="width:91px;">Thermo Fisher Scientific</td>
			<td style="width:119px;">09-740-106</td>
			<td>For virus filtration</td>
		</tr>
		<tr height="20">
			<td height="20" style="height:20px;width:319px;">6ml Syringes</td>
			<td style="width:91px;">Covidien</td>
			<td>8881516937</td>
			<td>For virus filtration</td>
		</tr>
		<tr height="20">
			<td height="20" style="height:20px;">Goat anti-Chicken IgY (H&#38;L) A488</td>
			<td style="width:91px;">Abcam</td>
			<td>AB150169</td>
			<td style="width:347px;">Secondary antibody for confocal analysis. Use at 1:400</td>
		</tr>
		<tr height="35">
			<td height="35" style="height:35px;">Donkey anti-rabbit A647 IgG(H+L)&#160;</td>
			<td style="width:91px;">Thermo Fisher Scientific</td>
			<td>A31573</td>
			<td style="width:347px;">Secondary antibody for confocal analysis. Use at 1:400</td>
		</tr>
		<tr height="35">
			<td height="35" style="height:35px;">Goat anti-mouse IgG(H+L) A555</td>
			<td style="width:91px;">Thermo Fisher Scientific</td>
			<td>A21422</td>
			<td style="width:347px;">Secondary antibody for confocal analysis. Use at 1:400</td>
		</tr>
		<tr height="20">
			<td height="20" style="height:20px;width:319px;">Triton X-100</td>
			<td style="width:91px;">Sigma</td>
			<td style="width:119px;">93443-100ml</td>
			<td>For cell permeabilization&#160;</td>
		</tr>
		<tr height="20">
			<td height="20" style="height:20px;width:319px;">Dulbecco&#39;s PBS without CaCl2 and MgCl2 (D-PBS)</td>
			<td style="width:91px;">Sigma</td>
			<td style="width:119px;">D8537</td>
			<td></td>
		</tr>
		<tr height="35">
			<td height="35" style="height:35px;width:319px;">Power Block 10X Universal Blocking reagent</td>
			<td style="width:91px;">Thermo Fisher Scientific</td>
			<td style="width:119px;">NC9495720</td>
			<td>Dilute to 1X in H20</td>
		</tr>
		<tr height="52">
			<td height="52" style="height:52px;width:319px;">16% Paraformaldehyde aqueous solution (PFA)</td>
			<td style="width:91px;">Electro Microscopy Sciences&#160;</td>
			<td style="width:119px;">15710</td>
			<td>Use at 4% diluted in dH20</td>
		</tr>
		<tr height="20">
			<td height="20" style="height:20px;width:319px;">6 cm&#160; plates</td>
			<td style="width:91px;">Olympus</td>
			<td style="width:119px;">25-260</td>
			<td></td>
		</tr>
		<tr height="35">
			<td height="35" style="height:35px;width:319px;">6-well plates</td>
			<td style="width:91px;">Genesee Scientific</td>
			<td style="width:119px;">25-105</td>
			<td></td>
		</tr>
		<tr height="35">
			<td height="35" style="height:35px;width:319px;">24-well plates</td>
			<td style="width:91px;">Genesee Scientific</td>
			<td style="width:119px;">25-107</td>
			<td></td>
		</tr>
		<tr height="20">
			<td height="20" style="height:20px;width:319px;">10 cm Tissue culture dishes</td>
			<td style="width:91px;">Corning</td>
			<td>4239</td>
			<td></td>
		</tr>
		<tr height="35">
			<td height="35" style="height:35px;width:319px;">15 cm&#160; Tissue culture dishes</td>
			<td style="width:91px;">Thermo Fisher Scientific</td>
			<td>5442</td>
			<td></td>
		</tr>
		<tr height="20">
			<td height="20" style="height:20px;width:319px;">15 ml Conical tubes</td>
			<td style="width:91px;">Corning</td>
			<td style="width:119px;">4308</td>
			<td></td>
		</tr>
		<tr height="20">
			<td height="20" style="height:20px;width:319px;">50 ml Conical tubes</td>
			<td style="width:91px;">Corning</td>
			<td style="width:119px;">4249</td>
			<td></td>
		</tr>
		<tr height="20">
			<td height="20" style="height:20px;width:319px;">0.4% Trypan blue solution</td>
			<td style="width:91px;">Sigma</td>
			<td style="width:119px;">T8154</td>
			<td>For viability</td>
		</tr>
		<tr height="35">
			<td height="35" style="height:35px;width:319px;">Ethyl Alcohol 200 proof</td>
			<td style="width:91px;">Thermo Fisher Scientific</td>
			<td style="width:119px;">7005</td>
			<td></td>
		</tr>
		<tr height="35">
			<td height="35" style="height:35px;width:319px;">Bleach</td>
			<td style="width:91px;">Thermo Fisher Scientific</td>
			<td style="width:119px;">6009</td>
			<td></td>
		</tr>
	</tbody>
</table>

assessing cardiomyocyte subtypes following transcription factor-mediated reprogramming of mouse embryonic fibroblasts

Direct reprogramming of one cell type into another has recently emerged as a powerful paradigm for regenerative medicine, disease modeling, and lineage specification. In particular, the conversion of fibroblasts into induced cardiomyocyte-like myocytes (iCLMs) by Gata4, Hand2, Mef2c, and Tbx5 (GHMT) represents an important avenue for generating de novo cardiac myocytes in vitro and in vivo. Recent evidence suggests that GHMT generates a greater diversity of cardiac subtypes than previously appreciated, thus underscoring the need for a systematic approach to conducting additional studies. Before direct reprogramming can be used as a therapeutic strategy, however, the mechanistic underpinnings of lineage conversion must be understood in detail to generate specific cardiac subtypes. Here we present a detailed protocol for generating iCLMs by GHMT-mediated reprogramming of mouse embryonic fibroblasts (MEFs). 
We outline methods for MEF isolation, retroviral production, and MEF infection to accomplish efficient reprogramming. To determine the subtype identity of reprogrammed cells, we detail a step-by-step approach for performing immunocytochemistry on iCLMs using a defined set of compatible antibodies. Methods for confocal microscopy, identification, and quantification of iCLMs and individual atrial (iAM), ventricular (iVM), and pacemaker (iPM) subtypes are also presented. Finally, we discuss representative results of prototypical direct reprogramming experiments and highlight important technical aspects of our protocol to ensure efficient lineage conversion. Taken together, our optimized protocol should provide a stepwise approach for investigators to conduct meaningful cardiac reprogramming experiments that require identification of individual CM subtypes.

Taking advantage of the PM-specific reporter mouse, we developed a multiplex immunostaining strategy to identify diverse endogenous myocytes as depicted in Figure 1. Following the reprogramming steps shown in Figure 2, induction of subtype-specific CMs can be detected as early as day 421, albeit at a low-rate. By day 14, the experiment can be stopped and assessed for sarcomere organization (Figure 3) and subtype-sp...

Watch this Scientific Journal Video about Assessing Cardiomyocyte Subtypes Following Transcription Factor-mediated Reprogramming of Mouse Embryonic Fibroblasts at JoVE.com

Assessing Cardiomyocyte Subtypes Following Transcription Factor-mediated Reprogramming of Mouse Embryonic Fibroblasts

This manuscript describes a step-by-step protocol for the generation and quantification of diverse reprogrammed cardiac subtypes using a retrovirus-mediated delivery of Gata4, Hand2, Mef2c, and Tbx5.

Direct reprogramming of one cell type into another has recently emerged as a powerful paradigm for regenerative medicine, disease modeling, and lineage ...

The overall goal of this procedure is to generate and quantify a diverse set of induced cardiomyocyte subtypes. This method can help answer key, fundamental questions regarding subtype-specific lineage conversion during cardiac reprogramming such as the necessary cues that regulate sarcomere assembly and subtype specification. The main advantage of this technique is that it provides the method for quantified effects on cardio subtype specification which is required to perform mechanisis studies.To begin, isolate mouse embryonic fiberblasts from stage E 12.5 embryos. Store them in liquid nitrogen as described in the accompanying text protocol. Next, harvest plat-E cells and plate them at one million cells per well into a six well plate so that the cells reach 70 to 80%confluency in 24 hours.Cover the cells with transfaction media and incubate them under standard culture conditions. On experiment day minus one, take a 15 milliliter conical polystyrene tube and mix 60 microliters of reduced serum media with six microliters of transfection reagent per reaction. Incubate the mixture for five minutes at room temperature.Since the transfection reagent use your add your reagent directly to the reduced serum media to avoid any decrease in transfection efficiency. Next, add a total of two micrograms of GHMT cocktail per reaction, and gently tap the tube to mix it. Incubate the reaction for 15 minutes at room temperature and then add the mixture to the plat-E cells in the drop wise manner.Record the date and time of transfection. Incubate the transfected plat-E cells overnight. One hour before plating the mouse embryonic fibroblast, prepare a 24 well plate for imunno-cytochemistry by first adding 12 millimeter fibronectin coated cover slips to each well.Next, add 300 microliters of bovine collagen solution to each well and incubate the plate for one hour. Near the end of the incubation, thaw a frozen vial of HCN4GFP mouse embryonic fibroblast. Quick thaw the cells, wash them once with pre-warmed fiberblast media and count the concentration of live cells.Then aspirate the coating solution in the 24 well plate and immediately plate 30, 000 cells per well onto the collagen and fibronectin coated cover slips. 24 hours post-transfection, filter the retro-viral medium through a 0.45 micron pore size surfectant free cellulose acetate filter, and transfer it to a 15 milliliter conical tube. Then, add polybrene to a final concentration of eight micrograms per milliliter.Carefully replenish the plat-E cells with two milliliters of fresh transfection medium. Changing the media too rapidly may cause the cells to detatch. Properly maintained plat-E cells produce an average of ten million infection units per milliliter.High GFP expression and intensity in more than 95%of the cells, typically correlates with a successful GHNT mediated generation of induced cardiomyocyte-like myocytes. Next, aspirate the medium of the cultured embryonic fibroblasts and add the freshly collected retroviral medium. Then return meth plate to the incubator and incubate overnight.The next day, again transfer the media from the plat-E cells to the embryonic fibroblasts. Discard the plat-E cells after the second virus collection. 48 hours post induction, aspirate the cell condition media and wash the cells once with PBS.Then add 500 microliters of pre-warmed induced cardio myocyte-like myocyite media per well of the 24 well plate. Replace the media every two to three days for the next 12 days. 14 days post induction, carefully aspirate the media and rinse each well with 300 microliters of ice cold PBS.Then removed the PBS and add 250 microliters of a 4%paraformaldehyde solution per well and incubate the cells for 15 minutes at room temperature. Next, permeabalize the cells by washing the wells three times for five minutes with 300 microliters of 0.1%tritonex 100 and PBS. Aspirate the excess permiableization solution after the last wash, and then add a universal blocking buffer at 300 microliters per well.Block for 10 minutes at room temperature. Stain one pair of slides overnight with mouse anti-alpha actenin, chicken anti-GFP and rabbit anti-NPPA antibodies to identify induced pacemaker-like myocytes in induced atrial-like myocytes. The following day, wash the wells and add the appropriate secondary antibody as described in the accompanying text protocol.Following additional washes, add 2.4 microliters of mounting media to a glass microscope slide. Take a cover slip from the 24 well plate and remove the excess solution. Then transfer it to the glass slide with the mounting media.For each slide, start from one edge and start scanning up and down in the red fluorescent channel to identify alpha-actinin positive sarcomere positive cells. Sarcomere striations are easiest to identify in the 555 nanometer wavelength. Once identified, switch to the green channel and keep note if the cells are positive.Then switch to the computer to asses the far red 647 nanometer wavelength to look for NPPA or MYL2 staining. Cells that are alpha-actinin positive, sarcomere positive, Hnc4-GFP negative and Nppa positive are induced atrial-like myocytes. Nppa staining will appear paranuclear and punctate.First, count the number of cells 24 hours after seeding as described in the accompanying text protocol. Next, visually inspect each cell on a cover slip for proper alpha-actinin and sacromere staining and record the number of cells positively stained for both markers. Then, divide by the actual total cells plated.An average reprogramming experiment will yield approximately one percent of cells that are both alpha-actinin and sarcomere positive. By day 14, the experiment can be stopped and assessed for sarcomere organization. This is identified by the positive alpha-actinin staining shown here in red.Only cells that exhibit sarcomere organization are capable of spontaneous beating, so this is a good first check. Shown here are induced pacemaker-like cardiomyocites from Hcn4-GFP reporter mice. Three cells from this view exhibit sarcomere organization.Three cell clusters positive for Hcn4-GFP are present in the center of the image and can be idenfied as a pacemaker cell type. Once cell at the bottom left can be observed with alpha-actinin staining but no sarcomere organization or identifiable subtype marker. In this population of induced ventricular like cardiomyocytes, the central cell exhibits sarcomere organization, this cell also stains positive for the myocin light chain marker MYL-2 which is a marker for ventricular cardio myocytes.Once mastered, the plating and the transfection of the plat-E cells can be performed in one hour. The induction of the mouse embryonic fibroblasts in one to two hours and the myto quantification of a full 24 well plate in about eight hours. While attempting this procedure, it's important to remember that healthy mouse embryonic fibroblasts and high titer viruses are key for a successful reprogramming experiment.After watching this video, you should have a good understanding of how to generate and quantify individual induced cardiomyocyte subtypes.

assessing-cardiomyocyte-subtypes-following-transcription-factor

Research

JoVE Journal

Developmental Biology

Culture of Embryonic Mouse Cochlear Explants and Gene Transfer by Electroporation

Auditory hair cells located within the mouse organ of Corti detect and transmit sound information to the central nervous system. The mechanosensory hair cells are aligned in one row of inner hair cells and three rows of outer hair cells that extend along the basal to apical axis of the cochlea. The explant culture technique described here provides an efficient method to isolate and maintain cochlear explants from the embryonic mouse inner ear. Also, the morphology and molecular characteristics of sensory hair cells and nonsensory supporting cells within the cochlear explant cultures resemble those observed in vivo and can be studied within its intrinsic cellular environment. The cochlear explants can serve as important experimental tools for the identification and characterization of molecular and genetic pathways that are involved in cellular specification and patterning. Although transgenic mouse models provide an effective approach for gene expression studies, a considerable number of mouse mutants die during embryonic development thereby hindering the analysis and interpretation of developmental phenotypes. The organ of Corti from mutant mice that die before birth can be cultured so that their in vitro development and responses to different factors can be analyzed. Additionally, we describe a technique for electroporating embryonic cochlear explants ex vivo which can be used to downregulate or overexpress specific gene(s) and analyze their potential endogenous function and test whether specific gene product is necessary or sufficient in a given context to influence mammalian cochlear development1-8.

We present a method that describes isolation and culture of cochlear explants from embryonic mouse inner ear. We also demonstrate a method for gene transfer into cochlear explants via square-wave electroporation. The in vitro explant culture coupled with gene transfer technique enables researchers to study the effects of altering gene expression during development.

Auditory hair cells located within the mouse organ of Corti detect and transmit sound information to the central nervous system. The mechanosensory hair ...

Analysis of Cardiomyocyte Development using Immunofluorescence in Embryonic Mouse Heart

During heart development, the generation of myocardial-specific structural and functional units including sarcomeres, contractile myofibrils, intercalated discs, and costameres requires the coordinated assembly of multiple components in time and space. Disruption in assembly of these components leads to developmental heart defects. Immunofluorescent staining techniques are used commonly in cultured cardiomyocytes to probe myofibril maturation, but this ex vivo approach is limited by the extent to which myocytes will fully differentiate in culture, lack of normal in vivo mechanical inputs, and absence of endocardial cues. Application of immunofluorescence techniques to the study of developing mouse heart is desirable but more technically challenging, and methods often lack sufficient sensitivity and resolution to visualize sarcomeres in the early stages of heart development. Here, we describe a robust and reproducible method to co-immunostain multiple proteins or to co-visualize a fluorescent protein with immunofluorescent staining in the embryonic mouse heart and use this method to analyze developing myofibrils, intercalated discs, and costameres. This method can be further applied to assess cardiomyocyte structural changes caused by mutations that lead to developmental heart defects.

Mutations that lead to congenital heart defects benefit from in vivo investigation of cardiac structure during development, but high-resolution structural studies in the mouse embryonic heart are technically challenging. Here we present a robust immunofluorescence and image analysis method to assess cardiomyocyte-specific structures in the developing mouse heart.

During heart development, the generation of myocardial-specific structural and functional units including sarcomeres, contractile myofibrils, intercalated ...

Neural Differentiation of Mouse Embryonic Stem Cells in Serum-free Monolayer Culture

The ability to differentiate mouse embryonic stem cells (ESC) to neural progenitors allows the study of the mechanisms controlling neural specification as well as the generation of mature neural cell types for further study. In this protocol we describe a method for the differentiation of ESC to neural progenitors using serum-free, monolayer culture. The method is scalable, efficient and results in production of ~70% neural progenitor cells within 4 - 6 days. It can be applied to ESC from various strains grown under a variety of conditions. Neural progenitors can be allowed to differentiate further into functional neurons and glia or analyzed by microscopy, flow cytometry or molecular techniques. The differentiation process is amenable to time-lapse microscopy and can be combined with the use of reporter lines to monitor the neural specification process. We provide detailed instructions on media preparation and cell density optimization to allow the process to be applied to most ESC lines and a variety of cell culture vessels.

This protocol describes in detail the method for generating neural progenitors from embryonic stem cells using a serum-free monolayer method. These progenitors can be used to derive mature neural cell types or to study the process of neural specification and is amenable to multiwell format scaling for compound screening.

The ability to differentiate mouse embryonic stem cells (ESC) to neural progenitors allows the study of the mechanisms controlling neural specification as ...

Stable and Efficient Genetic Modification of Cells in the Adult Mouse V-SVZ for the Analysis of Neural Stem Cell Autonomous and Non-autonomous Effects

Relatively quiescent somatic stem cells support life-long cell renewal in most adult tissues. Neural stem cells in the adult mammalian brain are restricted to two specific neurogenic niches: the subgranular zone of the dentate gyrus in the hippocampus and the ventricular-subventricular zone (V-SVZ; also called subependymal zone or SEZ) in the walls of the lateral ventricles. The development of in vivo gene transfer strategies for adult stem cell populations (i.e. those of the mammalian brain) resulting in long-term expression of desired transgenes in the stem cells and their derived progeny is a crucial tool in current biomedical and biotechnological research. Here, a direct in vivo method is presented for the stable genetic modification of adult mouse V-SVZ cells that takes advantage of the cell cycle-independent infection by LVs and the highly specialized cytoarchitecture of the V-SVZ niche. Specifically, the current protocol involves the injection of empty LVs (control) or LVs encoding specific transgene expression cassettes into either the V-SVZ itself, for the in vivo targeting of all types of cells in the niche, or into the lateral ventricle lumen, for the targeting of ependymal cells only. Expression cassettes are then integrated into the genome of the transduced cells and fluorescent proteins, also encoded by the LVs, allow the detection of the transduced cells for the analysis of cell autonomous and non-autonomous, niche-dependent effects in the labeled cells and their progeny.

Here we describe a procedure based on the use of lentiviral particles for the long-term genetic modification of neural stem cells and/or their adjacent ependymal cells in the adult ventricular-subventricular neurogenic niche which allows the separate analysis of cell autonomous and non-autonomous, niche-dependent effects on neural stem cells.

Relatively quiescent somatic stem cells support life-long cell renewal in most adult tissues. Neural stem cells in the adult mammalian brain are ...

Simultaneous Assessment of Cardiomyocyte DNA Synthesis and Ploidy: A Method to Assist Quantification of Cardiomyocyte Regeneration and Turnover

Although it is accepted that the heart has a limited potential to regenerate cardiomyocytes following injury and that low levels of cardiomyocyte turnover occur during normal ageing, quantification of these events remains challenging. This is in part due to the rarity of the process and the fact that multiple cellular sources contribute to myocardial maintenance. Furthermore, DNA duplication within cardiomyocytes often leads to a polyploid cardiomyocyte and only rarely leads to new cardiomyocytes by cellular division. In order to accurately quantify cardiomyocyte turnover discrimination between these processes is essential. The protocol described here employs long term nucleoside labeling in order to label all nuclei which have arisen as a result of DNA replication and cardiomyocyte nuclei identified by utilizing nuclei isolation and subsequent PCM1 immunolabeling. Together this allows the accurate and sensitive identification of the nucleoside labeling of the cardiomyocyte nuclei population. Furthermore, 4&#8242;,6-diamidino-2-phenylindole labeling and analysis of nuclei ploidy, enables the discrimination of neo-cardiomyocyte nuclei from nuclei which have incorporated nucleoside during polyploidization. Although this method cannot control for cardiomyocyte binucleation, it allows a rapid and robust quantification of neo-cardiomyocyte nuclei while accounting for polyploidization. This method has a number of downstream applications including assessing the potential therapeutics to enhance cardiomyocyte regeneration or investigating the effects of cardiac disease on cardiomyocyte turnover and ploidy. This technique is also compatible with additional downstream immunohistological techniques, allowing quantification of nucleoside incorporation in all cardiac cell types.

Quantification of cardiomyocyte turnover is challenging. The protocol described here makes an important contribution to this challenge by enabling accurate and sensitive quantification of neo-cardiomyocyte nuclei generation and nuclei ploidy.

Although it is accepted that the heart has a limited potential to regenerate cardiomyocytes following injury and that low levels of cardiomyocyte turnover ...

Protocol for the Direct Conversion of Murine Embryonic Fibroblasts into Trophoblast Stem Cells

Trophoblast stem cells (TSCs) arise as a consequence of the first cell fate decision in mammalian development. They can be cultured in vitro, retaining the ability to self-renew and to differentiate into all subtypes of the trophoblast lineage, equivalent to the in vivo stem cell population giving rise to the fetal portion of the placenta. Therefore, TSCs offer a unique model to study placental development and embryonic versus extra-embryonic cell fate decision in vitro. From the blastocyst stage onwards, a distinct epigenetic barrier consisting of DNA methylation and histone modifications tightly separates both lineages. Here, we describe a protocol to fully overcome this lineage barrier by transient over-expression of trophoblast key regulators Tfap2c, Gata3, Eomes and Ets2 in murine embryonic fibroblasts. The induced trophoblast stem cells are able to self-renew and are almost identical to blastocyst derived trophoblast stem cells in terms of morphology, marker gene expression and methylation pattern. Functional in vitro and in vivo assays confirm that these cells are able to differentiate along the trophoblast lineage generating polyploid trophoblast giant cells and chimerizing the placenta when injected into blastocysts. The induction of trophoblast stem cells from somatic tissue opens new avenues to study genetic and epigenetic characteristics of this extra-embryonic lineage and offers the possibility to generate trophoblast stem cell lines without destroying the respective embryo.

Here we present a protocol for the direct conversion of murine embryonic fibroblasts into fully functional and stable trophoblast stem cells by ten day over-expression of Tfap2c, Gata3, Eomes and Ets2.

Trophoblast stem cells (TSCs) arise as a consequence of the first cell fate decision in mammalian development. They can be cultured in vitro, retaining ...

Reprogramming Mouse Embryonic Fibroblasts with Transcription Factors to Induce a Hemogenic Program

This protocol details the induction of a hemogenic program in mouse embryonic fibroblasts (MEFs) via overexpression of transcription factors (TFs). We first designed a reporter screen using MEFs from human CD34-tTA/TetO-H2BGFP (34/H2BGFP) double transgenic mice. CD34+ cells from these mice label H2B histones with GFP, and cease labeling upon addition of doxycycline (DOX). MEFS were transduced with candidate TFs and then observed for the emergence of GFP+ cells that would indicate the acquisition of a hematopoietic or endothelial cell fate. Starting with 18 candidate TFs, and through a process of combinatorial elimination, we obtained a minimal set of factors that would induce the highest percentage of GFP+ cells. We found that Gata2, Gfi1b, and cFos were necessary and the addition of Etv6 provided the optimal induction. A series of gene expression analyses done at different time points during the reprogramming process revealed that these cells appeared to go through a precursor cell that underwent an endothelial to hematopoietic transition (EHT). As such, this reprogramming process mimics developmental hematopoiesis "in a dish," allowing study of hematopoiesis in vitro and a platform to identify the mechanisms that underlie this specification. This methodology also provides a framework for translation of this work to the human system in the hopes of generating an alternative source of patient-specific hematopoietic stem cells (HSCs) for a number of applications in the treatment and study of hematologic diseases.

The protocol described here details the induction of a hemogenic program in mouse embryonic fibroblasts via overexpression of a minimal set of transcription factors. This technology may be translated to the human system to provide platforms for future study of hematopoiesis, hematologic disease, and hematopoietic stem cell transplant.

This protocol details the induction of a hemogenic program in mouse embryonic fibroblasts (MEFs) via overexpression of transcription factors (TFs). We ...

Dissection and Culture of Mouse Embryonic Kidney

The goal of this protocol is to describe a method for the dissection, isolation, and culture of mouse metanephric rudiments. 
During mammalian kidney development, the two progenitor tissues, the ureteric bud and the metanephric mesenchyme, communicate and reciprocally induce cellular mechanisms to eventually form the collecting system and the nephrons of the kidney. As mammalian embryos grow intrauterine and therefore are inaccessible to the observer, an organ culture has been developed. With this method, it is possible to study epithelial-mesenchymal interactions and cellular behavior during kidney organogenesis. Furthermore, the origin of congenital kidney and urogenital tract malformations can be investigated. After careful dissection, the metanephric rudiments are transferred onto a filter that floats on culture medium and can be kept in a cell culture incubator for several days. However, one must be aware that the conditions are artificial and could influence the metabolism in the tissue. Also, the penetration of test substances could be limited due to the extracellular matrix and basal membrane present in the explant.
One main advantage of organ culture is that the experimenter can gain direct access to the organ. This technology is cheap, simple, and allows a large number of modifications, such as the addition of biologically active substances, the study of genetic variants, and the application of advanced imaging techniques.

This protocol describes a method for isolating and culturing metanephric rudiments from mouse embryos.

The goal of this protocol is to describe a method for the dissection, isolation, and culture of mouse metanephric rudiments. 
During mammalian kidney ...

Suppression of Pro-fibrotic Signaling Potentiates Factor-mediated Reprogramming of Mouse Embryonic Fibroblasts into Induced Cardiomyocytes

Trans-differentiation of one somatic cell type into another has enormous potential to model and treat human diseases. Previous studies have shown that mouse embryonic, dermal, and cardiac fibroblasts can be reprogrammed into functional induced-cardiomyocyte-like cells (iCMs) through overexpression of cardiogenic transcription factors including GATA4, Hand2, Mef2c, and Tbx5 both in vitro and in vivo. However, these previous studies have shown relatively low efficiency. In order to restore heart function following injury, mechanisms governing cardiac reprogramming must be elucidated to increase efficiency and maturation of iCMs.
We previously demonstrated that inhibition of pro-fibrotic signaling dramatically increases reprogramming efficiency. Here, we detail methods to achieve a reprogramming efficiency of up to 60%. Furthermore, we describe several methods including flow cytometry, immunofluorescent imaging, and calcium imaging to quantify reprogramming efficiency and maturation of reprogrammed fibroblasts. Using the protocol detailed here, mechanistic studies can be undertaken to determine positive and negative regulators of cardiac reprogramming. These studies may identify signaling pathways that can be targeted to promote reprogramming efficiency and maturation, which could lead to novel cell therapies to treat human heart disease.

Here we present a robust method to reprogram primary embryonic fibroblasts into functional cardiomyocytes through overexpression of GATA4, Hand2, Mef2c, Tbx5, miR-1, and miR-133 (GHMT2m) alongside inhibition of TGF-&#946; signaling. Our protocol generates beating cardiomyocytes as early as 7 days post-transduction with up to 60% efficiency.

Trans-differentiation of one somatic cell type into another has enormous potential to model and treat human diseases. Previous studies have shown that ...

Direct Lineage Reprogramming of Adult Mouse Fibroblast to Erythroid Progenitors

Erythroid cell commitment and differentiation proceed through activation of a lineage-restricted transcriptional network orchestrated by a group of cell fate determining and maturing factors. We previously set out to define the minimal set of factors necessary for instructing red blood cell development using direct lineage reprogramming of fibroblasts into induced erythroid progenitors/precursors (iEPs). We showed that overexpression of Gata1, Tal1, Lmo2, and c-Myc (GTLM) can rapidly convert murine and human fibroblasts directly to iEPs that resemble bona fide erythroid cells in terms of morphology, phenotype, and gene expression. We intend that iEPs will provide an invaluable tool to study erythropoiesis and cell fate regulation. Here we describe the stepwise process of converting murine tail tip fibroblasts into iEPs via transcription factor-driven direct lineage reprogramming (DLR). In this example, we perform the reprogramming in fibroblasts from erythroid lineage-tracing mice that express the yellow fluorescent protein (YFP) under the control of the erythropoietin receptor gene (EpoR) promoter, enabling visualization of erythroid cell fate induction upon reprogramming. Following this protocol, fibroblasts can be reprogrammed into iEPs within five to eight days. 
While improvements can still be made to the process, we show that GTLM-mediated reprogramming is a rapid and direct process, yielding cells with properties of bona fide erythroid progenitor and precursor cells.

Here we present our protocol for producing induced erythroid progenitors (iEPs) from mouse adult fibroblasts using transcription factor-driven direct lineage reprogramming (DLR).

Erythroid cell commitment and differentiation proceed through activation of a lineage-restricted transcriptional network orchestrated by a group of cell ...