1. Recommendations Before Starting
<ol>
	<li>Do not use PSCs contaminated with mycoplasma because they will not differentiate properly into sinus node cells. Test for mycoplasma contamination before starting the protocol. Do this using a PCR kit for rapid, highly sensitive detection of mycoplasmas and follow the manufacturer`s protocol.</li>
	<li>For each Petri dish (step 2.3.4), coat one 10 cm2 cell culture dish with sterile 7 ml 0.1 % gelatin from cold water fish skin for 1 hr at 37 &#176;C. Remove the gelatin and let the dish dry under sterile conditions in a sterile bench.</li>
	<li>Before you can start the differentiation protocol you need a double transfected stable mouse ES cell line clone containing the following features: i) Constitutive over-expression of TBX3 using a mammalian expression vector. Ii) The G418 resistance gene under the control of the Myh6-promoter5.</li>
	<li>The undifferentiated PSCs cells should be co-cultivated with irradiated feeder cells under standard conditions as described 1.</li>
</ol>
2. Differentiation Procedure
<ol>
	<li>Two Days before Differentiation - Remove PSCs from feeder cells.
	<ol>
		<li>Aspirate the medium, wash the cells with 10 ml phosphate buffered saline PBS, add 7 ml Collagenase IV solution and incubate the cells for 10 min at 37 &#176;C. Place a sterile 40 &#181;m Filter in a 50 ml tube.</li>
		<li>Carefully rinse the PSC colonies (avoid to remove the feeder cells) by pipetting the collagenase solution up and down 5 times.</li>
		<li>Transfer the cell suspension to a 40 &#181;m filter, rinse the filter three times with 8 ml PBS. Turn around the filter and place it upside down in a petri dish. Remove the PSC cell colonies by pipetting 10 ml PBS to the bottom of the filter.</li>
		<li>Transfer the cell suspension to a 15 ml tube and centrifuge for 5 min at 300 x g.</li>
		<li>Remove the PBS, suspend the cells in 1 ml Accutase and incubate at 37 &#176;C for 5 min.</li>
		<li>Add 10 ml PBS, mix the cell solution by pipetting it up and down 5 times and centrifuge for 5 min at 300 x g.</li>
		<li>Remove the PBS, suspend the cells in 10 ml cultivation medium and determine the cell number.</li>
		<li>Seed 15,000 cells/ cm2 on a 75 cm2 filter flask and cultivate them for 2 days at 37 &#176;C, 5% CO2. After 2 days the flask should be 50-70% confluent.</li>
	</ol>
	</li>
	<li>Day 0 - Start of Differentiation
	<ol>
		<li>Remove the medium and wash the cells with 10 ml PBS.</li>
		<li>Aspirate the PBS, add 2 ml Accutase and incubate the cells at 37 &#176;C for 5 min. Place a sterile 40 &#181;m Filter in a 50 ml tube.</li>
		<li>Add 10 ml PBS, transfer the cell suspension to the 40 &#181;m filter, rinse the filter via addition of 10 ml PBS and centrifuge the flow-through for 5 min at 300 x g.</li>
		<li>Suspend the cells in 10 ml differentiation medium and determine the cell number.</li>
		<li>Dilute the cell suspension with differentiation medium to a final concentration of 20,000 cells/ml.</li>
		<li>Pipette 20 ml water and 5 ml hanging drop (HD) solution in a quadratic Petri dish to avoid drying-out of the HDs. 
		NOTE: For each 24 well plate containing iSABs (see section 2.8.6.4/2.8.7) start with 16 Petri dishes.</li>
		<li>Pipette up to 50 ml cell suspension in a tray .</li>
		<li>Turn around the lid of the petri dish. Place 180 HDs each containing 20 &#181;l (400 cells/HD) cell suspension onto the lid using a 12 channel pipette.</li>
		<li>Carefully turn around the lid and place it onto the Petri dish. 
		NOTE: The speed of turning around the lid is very important. If the lid is turned around too slow or too fast, the surface tension of the cell suspension is not high enough to retain the hanging drops on the lid. Before trying to produce HDs for first time practice turning around the lid with 20 &#181;l drops of medium.</li>
		<li>Cultivate the cells for 2 days at 37 &#176;C, 5% CO2 to let them form EBs. 
		NOTE: Place one petri dish filled with water on the top of a stack of 5 Petri dishes. Otherwise the HD in the upper petri dish will dry.</li>
	</ol>
	</li>
	<li>Day 2
	<ol>
		<li>Carefully turn around the lid of the quadratic Petri dish and transfer the EBs derived from two Petri dishes (360 EBs) to a 50 ml tube.</li>
		<li>Wait 10 min to let the EBs settle at the bottom of the tube (Do not centrifuge the EBs).</li>
		<li>Aspirate as much medium as possible, suspend the EBs in 10 ml differentiation medium and transfer the suspension to a 10 cm Petri dish.</li>
	</ol>
	</li>
	<li>Day 2-6 Suspension culture
	<ol>
		<li>Cultivate the EBs in suspension for 4 days at 37 &#176;C, 5% CO2, change medium after 2 days. 
		NOTE: Even though the petri dish is not coated (as opposed to a cell culture dish) the EBs often attach to the surface. Control the petri dishes for attached EBs every day and if necessary detach the EBs from the surface by gentle pipetting. Optional: Shake the petri dishes continuously during the suspension culture period. Be careful with the speed of the shaker. The EBs should neither accumulate in the middle nor float to the border of the Petri dishes.</li>
	</ol>
	</li>
	<li>Day 6
	<ol>
		<li>Transfer the EBs from one Petri dish to one gelatin coated 10 cm2 cell culture dish.</li>
	</ol>
	</li>
	<li>Day 7-12
	<ol>
		<li>The cells should start to beat after 8-12 days. Check for beating foci of the cells daily under a microscope. The cells start to form a layer.</li>
		<li>Change medium daily. 
		NOTE: After changing medium, the cells require 3-4 hr to recover and to start beating again.</li>
	</ol>
	</li>
	<li>Day 12-15 Selection of sinus nodal cells.
	<ol>
		<li>Three days after the cells have started beating (around day 12-15), aspirate the medium and pipette 10 ml of fresh differentiation medium containing 400 &#181;g/ ml G418 to the cells.</li>
	</ol>
	</li>
	<li>Four days after the beginning of the selection dissociate the cell layer. 
	NOTE: It is possible that the cell layer is already detached from the surface.
	<ol>
		<li>Remove the medium carefully without aspirating the cell layer.</li>
		<li>Add 10 ml of PBS and remove the PBS carefully without aspirating the cell layer.</li>
		<li>Add 10 ml of Collagenase IV solution, transfer the cells to a 50 ml tube and incubate the cells at 37 &#176;C for 5 min.</li>
		<li>Vigorously mix the suspension by pipetting up and down 10 times and incubate the cells at 37 &#176;C for 5 min. A suspension of small clusters should occur. If there are still huge parts of the layer left, then repeat step 2.8.4 two more times.</li>
		<li>Add 20 ml of PBS and centrifuge for 10 min at 300 x g.</li>
		<li>Aspirate the PBS carefully. 
		NOTE: If iSABs are to be generated proceed with step 2.8.7. If iSAB derived sinus nodal single cells are to be generated go on with step 2.9.</li>
		<li>Suspend the cells in 12 ml differentiation medium containing 400 &#181;g/ml G418 and seed them on 6 wells of gelatin coated 24 wells (2 ml/well).</li>
	</ol>
	</li>
	<li>Generation of single nodal cell.
	<ol>
		<li>Suspend the cells from step 2.8.6 in 5 ml Accutase and incubate at 37 &#176;C for 5 min.</li>
		<li>Vigorously mix the suspension by pipetting up and down 10 times and incubate the cells at 37 &#176;C for 5 min.</li>
		<li>Add 20 ml of PBS and centrifuge for 5 min at 300 x g.</li>
		<li>Suspend the cells in 12 ml differentiation medium containing 400 &#181;g/ml G418 and seed them on 6 wells of a gelatin coated 24 wells (2 ml/well).</li>
	</ol>
	</li>
	<li>Day 2 after dissociation, aspirate the medium and wash the cells three times with PBS. Add 1 ml differentiation medium/well.</li>
	<li>Day 4-8 after dissociation, change Medium every 2nd day. On day 10 after Dissociation use iSABs or iSAB derived sinus nodal single cells are available for further analysis.</li>
</ol>

<ol>
	<li>Wobus, A. M., Wallukat, G., Hescheler, J. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Pluripotent+mouse+embryonic+stem+cells+are+able+to+differentiate+into+cardiomyocytes+expressing+chronotropic+responses+to+adrenergic+and+cholinergic+agents+and+Ca2++channel+blockers.">Pluripotent mouse embryonic stem cells are able to differentiate into cardiomyocytes expressing chronotropic responses to adrenergic and cholinergic agents and Ca2+ channel blockers.</a> Differentiation. 48 (3), 173-182 (1991).</li><li>David, R., 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=MesP1+drives+vertebrate+cardiovascular+differentiation+through+Dkk-1-mediated+blockade+of+Wnt-signalling.">MesP1 drives vertebrate cardiovascular differentiation through Dkk-1-mediated blockade of Wnt-signalling.</a> Nat Cell Biol. 10, 338-345 (2008).</li><li>David, R., 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=Forward+programming+of+pluripotent+stem+cells+towards+distinct+cardiovascular+cell+types.">Forward programming of pluripotent stem cells towards distinct cardiovascular cell types.</a> Cardiovasc Res. 84 (2), 263-272 (2009).</li><li>Hoogaars, W. M., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Tbx3+controls+the+sinoatrial+node+gene+program+and+imposes+pacemaker+function+on+the+atria.">Tbx3 controls the sinoatrial node gene program and imposes pacemaker function on the atria.</a> Genes Dev. 21 (9), 1098-1112 (2007).</li><li>Klug, M. G., Soonpaa, M. H., Koh, G. Y., Field, L. J. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Genetically+selected+cardiomyocytes+from+differentiating+embronic+stem+cells+form+stable+intracardiac+grafts.">Genetically selected cardiomyocytes from differentiating embronic stem cells form stable intracardiac grafts.</a> J Clin Invest. 98 (1), 216-224 (1996).</li><li>Marger, 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=Pacemaker+activity+and+ionic+currents+in+mouse+atrioventricular+node+cells.">Pacemaker activity and ionic currents in mouse atrioventricular node cells.</a> Channels (Austin). 5 (3), 241-250 (2011).</li><li>Jung, J. J., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Programming+and+isolation+of+highly+pure+physiologically+and+pharmacologically+functional+sinus-nodal+bodies+from+pluripotent+stem+cells).">Programming and isolation of highly pure physiologically and pharmacologically functional sinus-nodal bodies from pluripotent stem cells).</a> Stem cell reports. 2 (5), 592-605 (2014).</li><li>Maltsev, V. A., Wobus, A. M., Rohwedel, J., Bader, M., Hescheler, J. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Cardiomyocytes+differentiated+in+vitro+from+embryonic+stem+cells+developmentally+express+cardiac-specific+genes+and+ionic+currents.">Cardiomyocytes differentiated in vitro from embryonic stem cells developmentally express cardiac-specific genes and ionic currents.</a> Circulation research. 75 (2), 233-244 (1994).</li><li>He, J. Q., Ma, Y., Lee, Y., Thomson, J. A., Kamp, T. 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The authors have nothing to disclose.

The ability to produce stem cell derived cardiac pacemaker cells may allow reconstitution of the proper cardiac rhythm in the sense of &#8220;biological pacemakers&#8221;. Likewise, drug testing in vitro will benefit from their availability. PSCs can give rise to any cell type of the mammalian body including cardiomyocytes with pacemaker cell properties8,9,10,11,12,13. However, typically the cell populations within &#8220;Embryoid Bodies&#8221; are highly heterogeneous, which inevitably leads to the requiremen...

The term &#8220;sick sinus syndrome&#8221; summarizes multiple diseases leading to the deterioration of the cardiac pacemaker system. It comprises pathological, symptomatic sinus bradycardia, sinoatrial block, sinus arrest as well as the tachycardia-bradycardia syndrome. Thereby, a &#8220;sick sinus syndrome&#8221; is often accompanied by general cardiac diseases such as an ischemic heart disease, cardiomyopathies or myocarditis. At present, therapeutic approaches are based on the implantation of electrical pacemakers. However, this goes along with a number of risks such as infections and battery failure. Overall, the incidence of complications is still very high in patients having implanted an artificial pacemaker. Furthermore, as opposed to the endogenous pacemaker, these devices do not respond to hormone stimulation.
A future alternative may rely on the availability of &#8220;biological pacemakers&#8221; for which PSCs could serve as a suitable cellular source and which would also be highly valuable for in vitro drug testing. Yet, a major problem lies in the very rare appearance of sinus nodal cells within embryoid bodies (EBs) - this typically does not exceed ~0.5%1.
Previously, it was shown that &#8220;forward programming&#8221; towards specific cardiomyocyte subtypes is feasible via overexpression of distinct early cardiovascular transcription factors such as Mesoderm-specific-posterior 1 (MesP1) and NK2 transcription factor related, locus 5 (Nkx2.5)2,3. For normal size and function of the sinoatrial node (SAN), the T-box transcription factor Tbx3 is crucial, which has been shown to initiate the pacemaker gene program and to control differentiation of the SAN4. While this enhanced the appearance of functional pacemaker cells, the content still did not exceed ~40% within the entire cardiomyocytic cell population.
Therefore, an additional Myh6-promoter based antibiotic selection step5 was introduced by us. This ultimately leads to yet unobserved cardiomyocyte aggregates (&#8220;induced sino-atrial bodies; &#8220;iSABs&#8221;) which exhibit highly increased beating frequencies (&#62;400 bpm) in vitro, for the first time approximating those of a murine heart and comparable to in vitro cultivated sinus nodal cells isolated from a murine heart6. Under Isoprenaline administration even beating frequencies of 550 bpm are achieved. Notably, iSABs consist of over 80% functional nodal cells as evident from extensive physiological analyses7. Recently, several approaches to generate sinus nodal cells using direct reprogramming19, surface markers14 or pharmacological treatment with small molecules16,17 were described. Yet, none of these methods led to such a high purity of pacemaker cells and beating frequencies close to the murine heart as observed in iSABs.
Moreover, in an ex vivo model of cultivated adult mouse ventricular slices which have lost their spontaneous beating activity, the iSABs are capable of integrating into the slice tissue, thereby remaining spontaneously active and robustly pacing the heart slices to contractions7. A detailed protocol for the generation of these iSABs is described in this paper.

<table border="0" cellpadding="0" cellspacing="0" width="597">
	<tbody>
		<tr height="20">
			<td height="20" style="height:20px;width:335px;">Name of the Material/Equipment</td>
			<td style="width:132px;">Company</td>
			<td style="width:131px;">Catalog Number</td>
		</tr>
		<tr height="20">
			<td height="20" style="height:20px;">Iscove&#39;s liquid medium with stable glutamine</td>
			<td>Biochrom AG</td>
			<td>FG 0465</td>
		</tr>
		<tr height="20">
			<td height="20" style="height:20px;">DMEM liquid medium without Na-pyruvate, with stable glutamine</td>
			<td>Biochrom AG</td>
			<td>FG 0435</td>
		</tr>
		<tr height="20">
			<td height="20" style="height:20px;">CLS type IV, CLS IV</td>
			<td>Biochrom AG</td>
			<td>C4-22</td>
		</tr>
		<tr height="20">
			<td height="20" style="height:20px;">Non-essential amino acids</td>
			<td>Biochrom AG</td>
			<td>K 0293</td>
		</tr>
		<tr height="20">
			<td height="20" style="height:20px;">FBS Superior</td>
			<td>Biochrom AG</td>
			<td>S 0615</td>
		</tr>
		<tr height="20">
			<td height="20" style="height:20px;">Sodium pyruvate (100 mM)</td>
			<td>Biochrom AG</td>
			<td>L 0473</td>
		</tr>
		<tr height="20">
			<td height="20" style="height:20px;">G 418-BC liquid (ready-to-use solution), sterile</td>
			<td>Biochrom AG</td>
			<td>A 2912</td>
		</tr>
		<tr height="20">
			<td height="20" style="height:20px;">Reagent reservoir PP f.multichannel pip. 60ml,sterile</td>
			<td>Brand</td>
			<td>703409</td>
		</tr>
		<tr height="20">
			<td height="20" style="height:20px;">Accutase</td>
			<td>eBioscience,Inc.</td>
			<td>00-4555-56</td>
		</tr>
		<tr height="20">
			<td height="20" style="height:20px;">Eppendorf Xplorer/Xplorer plus, electronic pipette</td>
			<td>Eppendorf</td>
			<td>4861000155</td>
		</tr>
		<tr height="20">
			<td height="20" style="height:20px;">Falcon Cell Strainer 40&#181;m</td>
			<td>Falcon</td>
			<td>352340</td>
		</tr>
		<tr height="20">
			<td height="20" style="height:20px;">Penicillin/Streptomycin&#160;</td>
			<td>GE Healthcare</td>
			<td>P11-010</td>
		</tr>
		<tr height="20">
			<td height="20" style="height:20px;">Petri Dishes</td>
			<td>Greiner BioOne</td>
			<td>663102</td>
		</tr>
		<tr height="20">
			<td height="20" style="height:20px;">DPBS without Ca and Mg</td>
			<td>PAN-Biotech</td>
			<td>P04-36500</td>
		</tr>
		<tr height="20">
			<td height="20" style="height:20px;">Fetal bovine serum</td>
			<td>PAN-Biotech</td>
			<td>P30-3302</td>
		</tr>
		<tr height="20">
			<td height="20" style="height:20px;">Leukemia inhibitory factor</td>
			<td>Phoenix Europe GmbH</td>
			<td>LIF-250</td>
		</tr>
		<tr height="20">
			<td height="20" style="height:20px;">Quadratic petri dishes</td>
			<td>Roth</td>
			<td>PX67.1</td>
		</tr>
		<tr height="20">
			<td height="20" style="height:20px;">Gelatin from cold water fish skin</td>
			<td>SigmaAldrich</td>
			<td>G7765</td>
		</tr>
		<tr height="20">
			<td height="20" style="height:20px;">2-Mercaptoethanol</td>
			<td>SigmaAldrich</td>
			<td>M3148&#160;</td>
		</tr>
		<tr height="20">
			<td height="20" style="height:20px;">1-Thioglycerol</td>
			<td>SigmaAldrich</td>
			<td>M6145</td>
		</tr>
		<tr height="20">
			<td height="20" style="height:20px;">Tissue culture dishes</td>
			<td>TPP</td>
			<td>93100</td>
		</tr>
		<tr height="20">
			<td height="20" style="height:20px;">Tissue culture flask</td>
			<td>TPP</td>
			<td>90076</td>
		</tr>
		<tr height="20">
			<td height="20" style="height:20px;">Tissue culture test plates (24 well)</td>
			<td>TPP</td>
			<td>92424</td>
		</tr>
	</tbody>
</table>

generation of murine cardiac pacemaker cell aggregates based on es-cell-programming in combination with myh6-promoter-selection

Treatment of the &#8220;sick sinus syndrome&#8221; is based on artificial pacemakers. These bear hazards such as battery failure and infections. Moreover, they lack hormone responsiveness and the overall procedure is cost-intensive. &#8220;Biological pacemakers&#8221; generated from PSCs may become an alternative, yet the typical content of pacemaker cells in Embryoid Bodies (EBs) is extremely low. The described protocol combines &#8220;forward programming&#8221; of murine PSCs via the sinus node inducer TBX3 with Myh6-promoter based antibiotic selection. This yields cardiomyocyte aggregates consistent of &#62;80% physiologically functional pacemaker cells. These &#8220;induced-sinoatrial-bodies&#8221; (&#8220;iSABs&#8221;) are spontaneously contracting at yet unreached frequencies (400-500 bpm) corresponding to nodal cells isolated from mouse hearts and are able to pace murine myocardium ex vivo. Using the described protocol highly pure sinus nodal single cells can be generated which e.g. can be used for in vitro drug testing. Furthermore, the iSABs generated according to this protocol may become a crucial step towards heart tissue engineering.

The described protocol allows generation of iSABs with a beating frequency of around 450 bpm from PSCs (shown in the movie) which is near to the mouse heart beating frequency. After dissociation of iSABs (step 2.8.8) the observed single cells show the typical shape of cells of the sinus node (spindle and spider cells) as shown in Figure 1. These cells highly express proteins which are known to be essential for the function of the sinus node like hyperpolarization-activated cyclic nucleotide-gated cation ...

Watch this Scientific Journal Video about Generation of Murine Cardiac Pacemaker Cell Aggregates Based on ES-Cell-Programming in Combination with Myh6-Promoter-Selection at JoVE.com

Generation of Murine Cardiac Pacemaker Cell Aggregates Based on ES-Cell-Programming in Combination with Myh6-Promoter-Selection

This protocol describes how to produce functional sinus nodal tissue from murine pluripotent stem cells (PSC). T-Box3 (TBX3) overexpression plus cardiac Myosin-heavy-chain (Myh6) promoter antibiotic selection leads to highly pure pacemaker cell aggregates. These &#8220;Induced-sinoatrial-bodies&#8221; (&#8220;iSABs&#8221;) contain over 80% pacemaker cells, show highly increased beating rates and are able to pace myocardium ex vivo.

Treatment of the &#8220;sick sinus syndrome&#8221; is based on artificial pacemakers. These bear hazards such as battery failure and infections. Moreover, ...

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Research

JoVE Journal

Developmental Biology

9.6K Views.  University of Rostock. This protocol describes how to produce functional sinus nodal tissue from murine pluripotent stem cells (PSC). T-Box3 (TBX3) overexpression plus cardiac Myosin-heavy-chain (Myh6) promoter antibiotic selection leads to highly pure pacemaker cell aggregates. These “Induced-sinoatrial-bodies” (“iSABs”) contain over 80% pacemaker cells, show highly increased beating rates and are able to pace myocardium ex vivo.

Video: Generation of Murine Cardiac Pacemaker Cell Aggregates Based on ES-Cell-Programming in Combination with Myh6-Promoter-Selection

Generation of Aggregates of Mouse Embryonic Stem Cells that Show Symmetry Breaking, Polarization and Emergent Collective Behaviour In Vitro

We have developed a protocol improving current Embryoid Body (EB) culture which allows the study of self-organization, symmetry breaking, axial elongation and cell fate specification using aggregates of mouse embryonic stem cells (mESCs) in suspension culture. Small numbers of mESCs are aggregated in basal medium for 48 hr in non-tissue-culture-treated, U-bottomed 96-well plates, after which they are competent to respond to experimental signals. Following treatment, these aggregates begin to show signs of polarized gene expression and gradually alter their morphology from a spherical mass of cells to an elongated, well organized structure in the absence of external asymmetry cues. These structures are not only able to display markers of the three germ layers, but actively display gastrulation-like movements, evidenced by a directional dislodgement of individual cells from the aggregate, which crucially occurs at one region of the elongated structure. This protocol provides a detailed method for the reproducible formation of these aggregates, their stimulation with signals such as Wnt/&#946;-Catenin activation and BMP inhibition and their analysis by single time-point or time-lapse fluorescent microscopy. In addition, we describe modifications to current whole-mount mouse embryo staining procedures for immunocytochemical analysis of specific markers within fixed aggregates. The changes in morphology, gene expression and length of the aggregates can be quantitatively measured, providing information on how signals can alter axial fates. It is envisaged that this system can be applied both to the study of early developmental events such as axial development and organization, and more broadly, the processes of self-organization and cellular decision-making. It may also provide a suitable niche for the generation of cell types present in the embryo that are unobtainable from conventional adherent culture such as spinal cord and motor neurones.

Generation of Aggregates of Mouse Embryonic Stem Cells that Show Symmetry Breaking, Polarization and Emergent Collective Behaviour In Vitro

We have developed a protocol to generate aggregates of mouse embryonic stem cells that display self-organization, symmetry breaking and elongation paralleling axial development. This technique allows the study of axial developmental processes and the generation of cell types that are otherwise difficult to perform in monolayer culture.

We have developed a protocol improving current Embryoid Body (EB) culture which allows the study of self-organization, symmetry breaking, axial elongation ...

Aggregate Size Optimization in Microwells for Suspension-based Cardiac Differentiation of Human Pluripotent Stem Cells

Cardiac differentiation of human pluripotent stems cells (hPSCs) is typically carried out in suspension cell aggregates. Conventional aggregate formation of hPSCs involves dissociating cell colonies into smaller clumps, with size control of the clumps crudely controlled by pipetting the cell suspension until the desired clump size is achieved. One of the main challenges of conventional aggregate-based cardiac differentiation of hPSCs is that culture heterogeneity and spatial disorganization lead to variable and inefficient cardiomyocyte yield. We and others have previously reported that human embryonic stem cell (hESC) aggregate size can be modulated to optimize cardiac induction efficiency. We have addressed this challenge by employing a scalable, microwell-based approach to control physical parameters of aggregate formation, specifically aggregate size and shape. The method we describe here consists of forced aggregation of defined hPSC numbers in microwells, and the subsequent culture of these aggregates in conditions that direct cardiac induction. This protocol can be readily scaled depending on the size and number of wells used. Using this method, we can consistently achieve culture outputs with cardiomyocyte frequencies greater than 70%.

Conventional methods to initiate suspension aggregate based cardiac differentiation of human pluripotent stems cells (hPSCs) are plagued with culture heterogeneity with respect to aggregate size and shape. Here, we describe a robust method for cardiac differentiation employing microwells to generate size-controlled hPSC aggregates cultured under cardiac-promoting conditions.

Cardiac differentiation of human pluripotent stems cells (hPSCs) is typically carried out in suspension cell aggregates.  Conventional aggregate formation ...

A Novel Mammary Fat Pad Transplantation Technique to Visualize the Vessel Generation of Vascular Endothelial Stem Cells

Endothelial cells (ECs) are the fundamental building blocks of the vascular architecture and mediate vascular growth and remodeling to ensure proper vessel development and homeostasis. However, studies on endothelial lineage hierarchy remain elusive due to the lack of tools to gain access as well as to directly evaluate their behavior in vivo. To address this shortcoming, a new tissue model to study angiogenesis using the mammary fat pad has been developed. The mammary gland develops mostly in the postnatal stages, including puberty and pregnancy, during which robust epithelium proliferation is accompanied by extensive vascular remodeling. Mammary fat pads provide space, matrix, and rich angiogenic stimuli from the growing mammary epithelium. Furthermore, mammary fat pads are located outside the peritoneal cavity, making them an easily accessible grafting site for assessing the angiogenic potential of exogenous cells. This work also describes an efficient tracing approach using fluorescent reporter mice to specifically label the targeted population of vascular endothelial stem cells (VESCs) in vivo. This lineage tracing method, coupled with subsequent tissue whole-mount microscopy, enable the direct visualization of targeted cells and their descendants, through which the proliferation capability can be quantified and the differentiation commitment can be fate-mapped. Using these methods, a population of bipotent protein C receptor (Procr) expressing VESCs has recently been identified in multiple vascular systems. Procr+ VESCs, giving rise to both new ECs and pericytes, actively contribute to angiogenesis during development, homeostasis, and injury repair. Overall, this manuscript describes a new mammary fat pad transplantation and in vivo lineage tracing techniques that can be used to evaluate the stem cell properties of VESCs.

This work demonstrates a novel approach to assess the proliferation, differentiation, and vessel-forming potential of vascular endothelial stem cells (VESCs) through mammary fat pad transplantation followed by whole-mount tissue preparation for microscopic observation. A lineage tracing strategy to investigate the behavior of VESCs in vivo is also presented.

Endothelial cells (ECs) are the fundamental building blocks of the vascular architecture and mediate vascular growth and remodeling to ensure proper ...

Quantitative Whole-mount Immunofluorescence Analysis of Cardiac Progenitor Populations in Mouse Embryos

The use of ever-advancing imaging techniques has contributed broadly to our increased understanding of embryonic development. Pre-implantation development and organogenesis are two areas of research that have benefitted greatly from these advances, due to the high quality of data that can be obtained directly from imaging pre-implantation embryos or ex vivo organs. While pre-implantation embryos have yielded data with especially high spatial resolution, later stages have been less amenable to three-dimensional reconstruction. Obtaining high-quality 3D or volumetric data for known embryonic structures in combination with fate mapping or genetic lineage tracing will allow for a more comprehensive analysis of the morphogenetic events taking place during embryogenesis.
This protocol describes a whole-mount immunofluorescence approach that allows for the labeling, visualization, and quantification of progenitor cell populations within the developing cardiac crescent, a key structure formed during heart development. The approach is designed in such a way that both cell- and tissue-level information can be obtained. Using confocal microscopy and image processing, this protocol allows for three-dimensional spatial reconstruction of the cardiac crescent, thereby providing the ability to analyze the localization and organization of specific progenitor populations during this critical phase of heart development. Importantly, the use of reference antibodies allows for successive masking of the cardiac crescent and subsequent quantitative measurements of areas within the crescent. This protocol will not only enable a detailed examination of early heart development, but with adaptations should be applicable to most organ systems in the gastrula to early somite stage mouse embryo.

Here, we describe a protocol for whole mount immunofluorescence and image-based quantitative volumetric analysis of early stage mouse embryos. We present this technique as a powerful approach to qualitatively and quantitatively assess cardiac structures during development, and propose that it may be widely adaptable to other organ systems.

The use of ever-advancing imaging techniques has contributed broadly to our increased understanding of embryonic development. Pre-implantation development ...

Generation of Scaffold-free, Three-dimensional Insulin Expressing Pancreatoids from Mouse Pancreatic Progenitors In Vitro

The pancreas is a complex organ composed of many different cell types that work together to regulate blood glucose homeostasis and digestion. These cell types include enzyme-secreting acinar cells, an arborized ductal system responsible for the transportation of enzymes to the gut, and hormone-producing endocrine cells. 
Endocrine beta-cells are the sole cell type in the body that produce insulin to lower blood glucose levels. Diabetes, a disease characterized by a loss or the dysfunction of beta-cells, is reaching epidemic proportions. Thus, it is essential to establish protocols to investigate beta-cell development that can be used for screening purposes to derive the drug and cell-based therapeutics. While the experimental investigation of mouse development is essential, in vivo studies are laborious and time-consuming. Cultured cells provide a more convenient platform for screening; however, they are unable to maintain the cellular diversity, architectural organization, and cellular interactions found in vivo. Thus, it is essential to develop new tools to investigate pancreatic organogenesis and physiology.
Pancreatic epithelial cells develop in the close association with mesenchyme from the onset of organogenesis as cells organize and differentiate into the complex, physiologically competent adult organ. The pancreatic mesenchyme provides important signals for the endocrine development, many of which are not well understood yet, thus difficult to recapitulate during the in vitro culture. Here, we describe a protocol to culture three-dimensional, cellular complex mouse organoids that retain mesenchyme, termed pancreatoids. The e10.5 murine pancreatic bud is dissected, dissociated, and cultured in a scaffold-free environment. These floating cells self-assemble with mesenchyme enveloping the developing pancreatoid and a robust number of endocrine beta-cells developing along with the acinar and the duct cells. This system can be used to study the cell fate determination, structural organization, and morphogenesis, cell-cell interactions during organogenesis, or for the drug, small molecule, or genetic screening.

Generation of Scaffold-free, Three-dimensional Insulin Expressing Pancreatoids from Mouse Pancreatic Progenitors In Vitro

Here, we present a protocol to generate insulin expressing 3D murine pancreatoids from free-floating e10.5 dissociated pancreatic progenitors and the associated mesenchyme.

The pancreas is a complex organ composed of many different cell types that work together to regulate blood glucose homeostasis and digestion. These cell ...

Analysis of Cardiac Chamber Development During Mouse Embryogenesis Using Whole Mount Epifluorescence

The goal of this protocol is to describe a method for the dissection of mouse embryos and visualization of embryonic mouse ventricular chambers during heart development using ventricular specific fluorescent reporter knock-in mice (MLC-2v-tdTomato mice). Heart development involves a linear heart tube formation, the heart tube looping, and four chamber septation. These complex processes are highly conserved in all vertebrates. The mouse embryonic heart has been widely used for heart developmental studies. However, due to their extremely small size, dissecting mouse embryonic hearts is technically challenging. In addition, visualization of cardiac chamber formation often needs in situ hybridization, beta-galactosidase staining using LacZ reporter mice, or immunostaining of sectioned embryonic hearts. Here, we describe how to dissect mouse embryonic hearts and directly visualize ventricular chamber formation of MLC-2v-tdTomato mice using whole mount epifluorescent microscopy. With this method, it is possible to directly examine heart tube formation and looping, and four chamber formation without further experimental manipulation of mouse embryos. Although the MLC-2v-tdTomato reporter knock-in mouse line is used in this protocol as an example, this protocol can be applied to other heart-specific fluorescent reporter transgenic mouse lines.

We present the protocols to examine mouse heart development using whole mount epifluorescent microscopy on mouse embryos dissected from ventricular specific MLC-2v-tdTomato reporter knock-in mice. This method allows us to directly visualize each stage of the ventricular formation during mouse heart development without labor-intensive histochemical methods.

The goal of this protocol is to describe a method for the dissection of mouse embryos and visualization of embryonic mouse ventricular chambers during ...

In Vitro Generation of Heart Field-specific Cardiac Progenitor Cells

Pluripotent stem cells offer great potential for understanding heart development and disease and for regenerative medicine. While recent advances in developmental cardiology have led to generating cardiac cells from pluripotent stem cells, it is unclear if the two cardiac fields - the first and second heart fields (FHF and SHF) &#8212; are induced in pluripotent stem cells systems. To address this, we generated a protocol for in vitro specification and isolation of heart field-specific cardiac progenitor cells. We used embryonic stem cells lines carrying Hcn4-GFP and Tbx1-Cre; Rosa-RFP reporters of the FHF and the SHF, respectively, and live cell immunostaining of the cell membrane protein Cxcr4, a SHF marker. With this approach, we generated progenitor cells which recapitulate the functional properties and transcriptome of their in vivo counterparts. Our protocol can be utilized to study early specification and segregation of the two heart fields and to generate chamber-specific cardiac cells for heart disease modelling. Since this is an in vitro organoid system, it may not provide precise anatomical information. However, this system overcomes the poor accessibility of gastrulation-stage embryos and can be upscaled for high-throughput screens.

The purpose of this method is to generate heart field-specific cardiac progenitor cells in vitro in order to study the progenitor cell specification and functional properties, and to generate chamber specific cardiac cells for heart disease modelling.

Pluripotent stem cells offer great potential for understanding heart development and disease and for regenerative medicine. While recent advances in ...

Generation of Mosaic Mammary Organoids by Differential Trypsinization

Organoids offer self-organizing, three-dimensional tissue structures that recapitulate physiological processes in the convenience of a dish. The murine mammary gland is composed of two distinct epithelial cell compartments, serving different functions: the outer, contractile myoepithelial compartment and the inner, secretory luminal compartment. Here, we describe a method by which the cells comprising these compartments are isolated and then combined to investigate their individual lineage contributions to mammary gland morphogenesis and differentiation. The method is simple and efficient and does not require sophisticated separation technologies such as fluorescence activated cell sorting. Instead, we harvest and enzymatically digest the tissue, seed the epithelium on adherent tissue culture dishes, and then use differential trypsinization to separate myoepithelial from luminal cells with ~90% purity. The cells are then plated in an extracellular matrix where they organize into bilayered, three-dimensional (3D) organoids that can be differentiated to produce milk after 10 days in culture. To test the effects of genetic mutations, cells can be harvested from wild type or genetically engineered mouse models, or they can be genetically manipulated prior to 3D culture. This technique can be used to generate mosaic organoids that allow investigation of gene function specifically in the luminal or myoepithelial compartment.

The mammary gland is a bilayered structure, comprising outer myoepithelial and inner luminal epithelial cells. Presented is a protocol to prepare organoids using differential trypsinization. This efficient method allows researchers to separately manipulate these two cell types to explore questions concerning their roles in mammary gland form and function.

Organoids offer self-organizing, three-dimensional tissue structures that recapitulate physiological processes in the convenience of a dish. The murine ...

Generation of a Human iPSC-Based Blood-Brain Barrier Chip

The blood brain barrier (BBB) is formed by neurovascular units (NVUs) that shield the central nervous system (CNS) from a range of factors found in the blood that can disrupt delicate brain function. As such, the BBB is a major obstacle to the delivery of therapeutics to the CNS. Accumulating evidence suggests that the BBB plays a key role in the onset and progression of neurological diseases. Thus, there is a tremendous need for a BBB model that can predict penetration of CNS-targeted drugs as well as elucidate the BBB&#39;s role in health and disease.
We have recently combined organ-on-chip and induced pluripotent stem cell (iPSC) technologies to generate a BBB chip fully personalized to humans. This novel platform displays cellular, molecular, and physiological properties that are suitable for the prediction of drug and molecule transport across the human BBB. Furthermore, using patient-specific BBB chips, we have generated models of neurological disease and demonstrated the potential for personalized predictive medicine applications. Provided here is a detailed protocol demonstrating how to generate iPSC-derived BBB chips, beginning with differentiation of iPSC-derived brain microvascular endothelial cells (iBMECs) and resulting in mixed neural cultures containing neural progenitors, differentiated neurons, and astrocytes. Also described is a procedure for seeding cells into the organ chip and culturing of the BBB chips under controlled laminar flow. Lastly, detailed descriptions of BBB chip analyses are provided, including paracellular permeability assays for assessing drug and molecule permeability as well as immunocytochemical methods for determining the composition of cell types within the chip.

The blood-brain barrier (BBB) is a multicellular neurovascular unit tightly regulating brain homeostasis. By combining human iPSCs and organ-on-chip technologies, we have generated a personalized BBB chip, suitable for disease modeling and CNS drug penetrability predictions. A detailed protocol is described for the generation and operation of the BBB chip.

The blood brain barrier (BBB) is formed by neurovascular units (NVUs) that shield the central nervous system (CNS) from a range of factors found in the ...

Extra Cellular Matrix-Based and Extra Cellular Matrix-Free Generation of Murine Testicular Organoids

Testicular organoids provide a tool for studying testicular development, spermatogenesis, and endocrinology in vitro. Several methods have been developed in order to create testicular organoids. Many of these methods rely upon extracellular matrix (ECM) to promote de novo tissue assembly, however, there are differences between methods in terms of biomimetic morphology and function of tissues. Moreover, there are few direct comparisons of published methods. Here, a direct comparison is made by studying differences in organoid generation protocols, with provided outcomes. Four archetypal generation methods: (1) 2D ECM-free, (2) 2D ECM, (3) 3D ECM-free, and (4) 3D ECM culture are described. Three primary benchmarks were used to assess the testicular organoid generation. These are cellular self-assembly, inclusion of major cell types (Sertoli, Leydig, germ, and peritubular cells), and appropriately compartmentalized tissue architecture. Of the four environments tested, 2D ECM and 3D ECM-free cultures generated organoids with internal morphologies most similar to native testes, including the de novo compartmentalization of tubular versus interstitial cell types, the development of tubule-like-structures, and an established long-term endocrine function. All methods studied utilized unsorted, primary murine testicular cell suspensions and used commonly accessible culture resources. These testicular organoid generation techniques provide a highly accessible and reproducible toolkit for research initiatives into testicular organogenesis and physiology in vitro.

Here, four methods for generating testicular organoids from primary neonatal murine testicular cells are described i.e., extracellular matrix (ECM) and ECM-free 2D and 3D culture environments. These techniques have multiple research applications and are especially useful for studying testicular development and physiology in vitro.

Testicular organoids provide a tool for studying testicular development, spermatogenesis, and endocrinology in vitro. Several methods have been developed ...