Name: freezing and thawing human embryonic stem cells
Uploaded: 2009-12-24T13:00:00
Duration: 8 min 49 s
Description: Watch this Scientific Journal Video about Freezing and Thawing Human Embryonic Stem Cells at JoVE.com

1. Thawing hES cells
Pre-experimental Set-up
<ol>
 <li>One day prior to thawing hES cells, plate a feeder layer of irradiated mouse embryonic fibroblasts (MEF), CF1 strain, on one well of a gelatin-coated 6-well tissue culture plate in MEF culture medium (D-MEM basal medium supplemented with 10% heat-inactivated FBS and 1% non-essential amino acids). Incubate overnight at 37&deg;C and 5% CO2. </li>
 <li>Before removing the hES cells from liquid nitrogen, be sure to have all necessary equipment and reagents in place and ready to use to ensure an efficient and successful thaw.</li>
</ol>
Thawing the hES Cells
 <ol start="3">
 <li>Remove a cryogenic vial of hES cells from the liquid nitrogen storage tank using metal forceps.</li>
 <li>Roll the vial between gloved hands for 3-5 seconds to remove the frost.</li>
 <li>Record the information on the label of the vial.</li>
 <li>Using metal forceps, immerse the vial into a 37&deg;C water bath. Swirl the vial gently and observe the progress of the thaw often (but quickly!) by holding the vial up to the light to see the size of the ice crystal. Do not submerge the cap of the vial in the water bath as this could contaminate the cells.</li>
 <li>When only a small ice crystal remains, submerge the entire vial in ethanol to sterilize. </li>
 <li>In a sterile biological safety cabinet, transfer the contents of the cryogenic vial directly to the bottom of a 15 mL conical tube.</li>
 <li>Slowly add 4 mL of hES cell culture medium (D-MEM/F-12 basal medium supplemented with 20% Knockout serum replacement, 1% non-essential amino acids, 1% L-glutamine, 0.2% &beta;- mercaptoethanol and 4 ng/mL bFGF) to the tube. Gently rock to continually mix the cells as the new medium is added to the tube.</li>
 <li>Centrifuge the cells for 5 minutes at 200 x g.</li>
 </ol>
Plating the hES Cells
<ol start="11">
 <li>While the hES cells are in the centrifuge, prepare the MEF feeder plate by labeling with the appropriate hES cell information: cell line, passage number, and thaw date.</li>
 <li>When there is approximately 2 minutes left on the spin time, aspirate the MEF culture medium and add 1.0 mL of PBS to the well.</li>
 <li>Bring the pelleted hES cells back to the biological safety cabinet, and carefully aspirate the supernatant. Be careful not to aspirate the cell pellet, but remove as much supernatant as possible, as this solution contains DMSO from the freezing medium.</li>
 <li>Re-suspend the pellet very gently by adding 2.5 mL of hES cell culture medium using a 5 mL glass pipet and pipetting 3-4 times.</li>
 <li>Aspirate the PBS from the MEF feeder well and slowly add all 2.5 mL of the hES cell suspension to the prepared well of the 6-well plate.</li>
 <li>Place the plate into the 37&deg;C incubator and carefully slide the plate forward to back, and side to side to evenly distribute the cells throughout the well. Do not swirl the plate in a circular pattern to avoid concentrating the colonies in the center.</li>
 <li>Allow the cells to attach at 37&deg;C and 5% CO2 overnight.</li>
 <li>The day after the thaw, remove the medium (with any floating cells) and add 2.5 ml of fresh hES cell culture medium to the well.</li>
 <li>Optional: The removed medium and cells can be transferred to a separate prepared MEF feeder plate. This step often generates new colonies that can be cultured in parallel with cells from the original thaw.</li>
 <li>Incubate the plates at 37&deg;C and 5% CO2 overnight.</li>
</ol>
2. Freezing the hES Cells
<ol>
 <li>While the hES cells are in the centrifuge, label the cryogenic vials inside the biological safety cabinet, including the cell line, passage number, and freezing date. The typical density for freezing hES cells is one well of cells (from a 6-well plate) per cryogenic vial. </li>
 <li>When the hES cells are finished centrifuging, bring the tubes back to the biological safety cabinet. Aspirate the supernatant from the tube, being careful not to disturb the loosely-packed cell pellet.</li>
 <li>Resuspend the cell pellet with the appropriate amount of hES cell culture medium: 0.5 mL hES cell culture medium per cryogenic vial. Be very gentle when pipetting, as the hES cells recover better when frozen in relatively large colony pieces.</li>
 <li>Slowly, while gently shaking the tube, add the appropriate amount (0.5 mL per cryovial) of 2X hES cell freezing medium (60% defined FBS, 20% hES cell culture medium, and 20% DMSO) to the cells. Once the freezing medium is added, pipet the solution extremely gently one to two times to mix.</li>
 <li>Quickly but gently, add 1 mL of the cell suspension to each cryogenic vial.</li>
 <li>Transfer the vials into an isopropanol freezing container and place in a -80&deg;C freezer overnight. The cells will freeze at 1&deg;C per minute in the isopropanol freezing container.</li>
 <li>The following day, quickly transfer the frozen vials to a liquid nitrogen storage tank using metal forceps. </li>
</ol>
Representative Results
The first day after human ES cells are thawed, small colonies may appear transparent and may be difficult to see under the microscope. Since newly thawed ES cells tend to proliferate slowly, they may take a few days to appear as established colonies (Figure 1).
Figure 1. Cell recovery and growth. hES cells thawed from liquid nitrogen were imaged &nbsp;1, 7 and 11 days after thawing.

<ol>
	<li>Freshney, R. I. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=.">.</a> Culture of Animal Cells: A Manual of Basic Technique. , (2005).</li><li>Thomson, J. A., Itskovitz-Eldor, J., Shapiro, S. S., Waknitz, M. A., Swiergiel, J. J., Marshall, V. S., Jones, J. M. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Embryonic+stem+cell+lines+derived+from+human+blastocysts.">Embryonic stem cell lines derived from human blastocysts.</a> Science. 282 (5391), 1145-1147 (1998).</li></ol>

The accompanying video demonstrates a method for thawing and freezing hES cells. Cells frozen in liquid nitrogen should be thawed bath as quickly as possible to obtain the best possible recovery. Remember to be extremely careful when pipetting thawing cells: minimize handling of the cells and pipette gently. One vial of hES cells can be plated onto either one well of a 6-well plate, or all wells of a 4-well plate and immediately placed in the incubator. Since culturing in four separate wells reduces the possibility of losing the entire culture to contamination, and makes it easier to locate hES cell colonies on the smaller surface area, the 4-well plate is recommended when thawing hES cells for the first time.
The first day after thawing hES cells, colonies are small and may be transparent. Replenish the hES cell culture medium every day, even if the colonies are not apparent under the microscope since it may take a few days in culture for hES cells to appear as established colonies. It is important to use a freshly plated MEF feeder layer when thawing cells, as the colonies often do not reach an appropriate size for passaging until 10 12 days after the thaw.
When thawing a low passage vial of hES cells, it is good practice to expand and freeze additional vials to maintain a stock of low passage cells for future culture and experiments. It is also a good idea to routinely freeze all "extra" healthy hES cells to maintain frozen stocks. The most successful thaws and subsequent cultures were frozen as high-quality, undifferentiated, actively dividing hES cell colonies. hES cells recover from a freeze more efficiently if handled gently as larger cell aggregates. The final aggregate size should be similar to (or slightly larger than) the size of aggregates plated after a routine passage.

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		<div>
		<table border="1">
		<thead>
		<tr>
		<th>Material Name</th>
		<th>Type</th>
		<th>Company</th>
		<th>Catalogue Number</th>
		<th>Comment</th>
		</tr>
		</thead>
		<tbody>
		
<tr>
<td>D-MEM</td>
<td>&nbsp;</td>
<td>Invitrogen</td>
<td>11965-092</td>
<td>For MEF mediumjavascript:void(0);</td>
</tr>
<tr>
<td>Fetal Bovine Serum (FBS), Certified</td>
<td>&nbsp;</td>
<td>Invitrogen</td>
<td>16000-044</td>
<td>Heat-inactivated 
For MEF medium</td>
</tr>
<tr>
<td>D-MEM/F-12</td>
<td>&nbsp;</td>
<td>Invitrogen</td>
<td>11330-057</td>
<td>&nbsp;</td>
<tr>
<td>Knockout Serum Replacement</td>
<td>&nbsp;</td>
<td>Invitrogen</td>
<td>10828-028</td>
<td>Pre-screen to ensure support of hES cells</td>
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<tr>
<td>bFGF</td>
<td>&nbsp;</td>
<td>Stemgent</td>
<td>03-0002</td>
<td>Use at [4 ng/mL] final</td>
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<td>Non-essential Amino Acids</td>
<td>&nbsp;</td>
<td>Invitrogen</td>
<td>11140-050</td>
<td>&nbsp;</td>
<tr>
<td>L-glutamine</td>
<td>&nbsp;</td>
<td>Invitrogen</td>
<td>25030-081</td>
<td>200 mM (100X) 
Use at [1X] final</td>
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<tr>
<td>PBS</td>
<td>&nbsp;</td>
<td>Invitrogen</td>
<td>14190-250</td>
<td>Without Ca2+ or Mg2+</td>
</tr>
<tr>
<td>Collagenase IV</td>
<td>&nbsp;</td>
<td>Invitrogen</td>
<td>17104-019</td>
<td>Make a fresh solution at 1 mg/mL in D-MEM/F-12</td>
</tr>
<tr>
<td>Gelatin</td>
<td>&nbsp;</td>
<td>Sigma</td>
<td>G1890</td>
<td>Type A, Porcine</td>
</tr>
<tr>
<td>DMSO</td>
<td>&nbsp;</td>
<td>Sigma</td>
<td>D2560</td>
<td>For freezing medium</td>
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<tr>
<td>Fetal Bovine Serum (FBS), Defined</td>
<td>&nbsp;</td>
<td>HyClone</td>
<td>SH300.70.01</td>
<td>For freezing medium</td>
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<tr>
<td>6-well plates</td>
<td>&nbsp;</td>
<td>Nunc</td>
<td>140675</td>
<td>For general culture</td>
</tr>
<tr>
<td>4-well plates</td>
<td>&nbsp;</td>
<td>Nunc</td>
<td>176740</td>
<td>For thawing</td>
</tr>
<tr>
<td>5 mL glass pipettes</td>
<td>&nbsp;</td>
<td>Fisher</td>
<td>13-678-27E</td>
<td>Individually wrapped</td>
</tr>
<tr>
<td>15 mL conical tubes</td>
<td>&nbsp;</td>
<td>Corning</td>
<td>430052</td>
<td>Polypropylene</td>
</tr>
<tr>
<td>Cryogenic vials</td>
<td>&nbsp;</td>
<td>Nunc</td>
<td>5000-1020</td>
<td>1.5 mL capacity</td>
</tr>
<tr>
<td>Freezing container</td>
<td>&nbsp;</td>
<td>Nalgene</td>
<td>5100-0001</td>
<td>&#x201C;Mr. Frosty&#x201D;</td>
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freezing and thawing human embryonic stem cells

Since James Thomson et al developed a technique in 1998 to isolate and grow hES in culture, freezing cells for later use and thawing and expanding cells from a frozen stock have become important procedures performed in routine hES cell culture. Since hES cells are very sensitive to the stresses of freezing and thawing, special care must taken. Here we demonstrate the proper technique for rapidly thawing hES cells from liquid nitrogen stocks, plating them on mouse embryonic feeder cells, and slowly freezing them for long-term storage.

Watch this Scientific Journal Video about Freezing and Thawing Human Embryonic Stem Cells at JoVE.com

Freezing and Thawing Human Embryonic Stem Cells

Since James Thomson et al developed a technique in 1998 to isolate and grow hES in culture, freezing cells for later use and thawing and expanding cells from a frozen stock have become important procedures performed in routine hES cell culture. Since hES cells are very sensitive to the stresses of freezing and thawing, special care must taken. Here we demonstrate the proper technique for rapidly thawing hES cells from liquid nitrogen stocks, plating them on mouse embryonic feeder cells, and slowly freezing them for long-term storage.

Since James Thomson et al developed a technique in 1998 to isolate and grow hES in culture, freezing cells for later use and thawing and expanding cells ...

freezing-and-thawing-human-embryonic-stem-cells

Research

JoVE Journal

Biology

Freezing Human ES Cells

Here we demonstrate how our lab freezes HuES human embryonic stem cell lines.  A healthy, exponentially expanding culture is washed with PBS to remove residual media that could otherwise quench the Trypsin reaction.  Warmed 0.05% Trypsin-EDTA is then added to cover the cells, and the plate allowed to incubate for up to 5 mins at room temperature.  During this time cells can be observed rounding, and colonies lifting off the plate surface.  Gentle repeated pipetting will remove cells and colonies from the plate surface.  Trypsinized cells are placed in a standard conical tube containing pre-warmed hES cell media to quench remaining trypsin, and then spun.  Cells are resuspended growth media at a concentration of approximately one million cells in one mL of media, a concentration such that one frozen aliquot is sufficient to resurrect a culture on a 10cm plate.  After cells are adequately resuspended, ice cold freezing media is added at equal volume.  Cell suspensions are mixed thoroughly, aliquoted into freezing vials, and allowed to slowly freeze to -80C over 24 hours.  Frozen cells can then moved to the vapor phase of liquid nitrogen for long term storage, or remain at -80 for approximately six months.

Here we demonstrate how our lab freezes HuES human embryonic stem cell lines.

Here we demonstrate how our lab freezes HuES human embryonic stem cell lines.  A healthy, exponentially expanding culture is washed with PBS to remove ...

Propagation of Human Embryonic Stem (ES) Cells

Propagation of Human Embryonic Stem ES Cells

Derivation of Hematopoietic Stem Cells from Murine Embryonic Stem Cells

A stem cell is defined as a cell with the capacity to both self-renew and generate multiple differentiated progeny.  Embryonic stem cells (ESC) are derived from the blastocyst of the early embryo and are pluripotent in differentiative ability.  Their vast differentiative potential has made them the focus of much research centered on deducing how to coax them to generate clinically useful cell types.  The successful derivation of hematopoietic stem cells (HSC) from mouse ESC has recently been accomplished and can be visualized in this video protocol.  HSC, arguably the most clinically exploited cell population, are used to treat a myriad of hematopoietic malignancies and disorders.  However, many patients that might benefit from HSC therapy lack access to suitable donors.  ESC could provide an alternative source of HSC for these patients.  The following protocol establishes a baseline from which ESC-HSC can be studied and inform efforts to isolate HSC from human ESC.  In this protocol, ESC are differentiated as embryoid bodies (EBs) for 6 days in commercially available serum pre-screened for optimal hematopoietic differentiation.  EBs are then dissociated and infected with retroviral HoxB4.  Infected EB-derived cells are plated on OP9 stroma, a bone marrow stromal cell line derived from the calvaria of  M-CSF-/- mice, and co-cultured in the presence of hematopoiesis promoting cytokines for ten days.  During this co-culture, the infected cells expand greatly, resulting in the generation a heterogeneous pool of 100s of millions of cells.  These cells can then be used to rescue and reconstitute lethally irradiated mice.

This protocol details the derivation of transplantable hematopoietic stem cells from mouse embryonic stem cells (ESC) and their subsequent injection into lethally irradiated recipient mice. Briefly, ESC are differentiated as embryoid bodies, which are then infected with retroviral HoxB4 and co-cultured with OP9 stromal cells and hematopoietic cytokines.

A stem cell is defined as a cell with the capacity to both self-renew and generate multiple differentiated progeny.  Embryonic stem cells (ESC) are ...

Derivation of Human Embryonic Stem Cells by Immunosurgery

The ability of human embryonic stem cells to self-renew and differentiate into all cell types of 
the body suggests that they hold great promise for both medical applications and as a research 
tool for addressing fundamental questions in development and disease. Here, we provide a 
concise, step-by-step protocol for the derivation of human embryonic stem cells from embryos 
by immunosurgical isolation of the inner cell mass. 


The ability of human embryonic stem cells to self-renew and differentiate into all cell types of 
the body suggests that they hold great promise for both medical applications and as a research 
tool for addressing fundamental questions in development and disease. Here, we provide a 
concise, step-by-step protocol for the derivation of human embryonic stem cells from embryos 
by immunosurgical isolation of the inner cell mass.

The ability of human embryonic stem cells to self-renew and differentiate into all cell types of 
the body suggests that they hold great promise for both ...

Probing for Mitochondrial Complex Activity in Human Embryonic Stem Cells

Mitochondria are cytoplasmic organelles that have a primary role in cellular metabolism and homeostasis, regulation of the cell signaling network, and programmed cell death. Mitochondria produce ATP, regulate the cytoplasmic redox state and Ca2+ balance, catabolize fatty acids, synthesize heme, nucleotides, steroid hormones, amino acids, and help assemble iron-sulfur clusters in proteins. Mitochondria also have an essential role in heat production. Mutations of the mitochondrial genome cause several types of human disorder. The accumulation of mtDNA mutations correlates with aging and is suspected to have an important role in the development of cancer. Due to their vitally important role in all cell types, the function of mitochondria must also be critical for stem cells. Key advances have been made in our understanding of stem cell viability, proliferation, and differentiation capacity. But the functional activity of stem cells, in particular their energy status, was not yet been studied in detail. Almost nothing is known about the mitochondrial properties of human embryonic stem cells (hESCs) and their differentiated precursor progeny. One way to understand and evaluate the role of mitochondria in hESC function and developmental potential is to directly measure the activity of mitochondrial respiratory complexes. Here, we describe high resolution clear native gel electrophoresis and subsequent in gel activity visualization as a method for analyzing the five respiratory chain complexes of hESCs.

In this video, we will show you how the mitochondrial respiratory chain complexes of human embryonic stem cells can be analyzed using in gel activity assays.

Mitochondria are cytoplasmic organelles that have a primary role in cellular metabolism and homeostasis, regulation of the cell signaling network, and ...

Freezing, Thawing, and Packaging Cells for Transport

Cultured mammalian cells are used extensively in cell biology studies. It requires a number of special skills in order to be able to preserve the structure, function, behavior, and biology of the cells in culture. This video describes the basic skills required to freeze and store cells and how to recover frozen stocks. 

Cultured mammalian cells are used extensively in cell biology studies. This video describes the basic skills required to freeze and store cells and how to recover frozen stocks.

Cultured mammalian cells are used extensively in cell biology studies. It requires a number of special skills in order to be able to preserve the ...

Chromatin Immunoprecipitation from Human Embryonic Stem Cells

The functional and structural complexity of the myriad of cells in metazoan organisms arises from a small number of stem cells. Stem cells are characterized by two fundamental properties: self-renewal and multipotency that allows a stem cell to differentiate into virtually any cell type 1. The progression stem cell to differentiated cell is characterized by loss of multipotency, structural and morphological changes and the hierarchic activity of transcription factors and signaling molecules, whose activities establish and maintain cell-type specific gene expression patterns. At the molecular level, cell differentiation involves dynamic changes of the structure and composition of chromatin and the detection of those dynamic changes can provide valuable insights into the functional features of stem cells and the cell differentiation process 2,3. Chromatin is a highly compacted DNA-protein complex that forms when cells package chromosomal DNA with proteins, mainly histones 4. Stemcellness and cell differentiation has been correlated with the presence of specific arrays of regulatory proteins such as epigenetic factors, histone variants, and transcription factors 2,3,5.
 Chromatin immunoprecipitation (ChIP) provides a valuable method to monitor the presence of RNA, proteins, and protein modifications in chromatin 6,7. The comparison of chromatin from different cell types can elucidate dynamic changes in protein-chromatin associations that occur during cell differentiation.
Chromatin immunoprecipitation involves the purification of in vivo cross-linked chromatin. The isolated chromatin is reduced to smaller fragments by enzymatic digestion or mechanical force. Chromatin fragments are precipitated using specific antibodies to target proteins or protein and DNA modifications. The precipitated DNA or RNA is purified and used as a template for PCR or DNA microarray based assays. Prerequisites for a successful ChIP are high quality antibodies to the desired antigen and the availability of chromatin from control cells that do not express the target molecule. ChIP can correlate the presence of proteins, protein and RNA modifications, and RNA with specific target DNA, and depending on the choice of outread tool, detects the association of target molecules at specific target genes or in the context of an entire genome. The comparison of the distribution of proteins in the chromatin of differentiating cells can elucidate the dynamic changes of chromatin composition that coincide with the progression of cells along a cell lineage.

The differentiation of ESC coincides with cell-type specific changes in the structure and composition of chromatin. The detection of those changes provides valuable insights into the mechanisms that define stemcellness and cell differentiation. Chromatin immunoprecipitation (ChIP) represents a valuable method to dissect the molecular mechanisms underlying stem cell differentiation.

The functional and structural complexity of the myriad of cells in metazoan organisms arises from a small number of stem cells. Stem cells are ...

In vitro Labeling of Human Embryonic Stem Cells for Magnetic Resonance Imaging

Human embryonic stem cells (hESC) have demonstrated the ability to restore the injured myocardium. Magnetic resonance imaging (MRI) has emerged as one of the predominant imaging modalities to assess the restoration of the injured myocardium. Furthermore, ex-vivo labeling agents, such as iron-oxide nanoparticles, have been employed to track and localize the transplanted stem cells. However, this method does not monitor a fundamental cellular biology property regarding the viability of transplanted cells. It has been known that manganese chloride (MnCl2) enters the cells via voltage-gated calcium (Ca2+) channels when the cells are biologically active, and accumulates intracellularly to generate T1 shortening effect. Therefore, we suggest that manganese-guided MRI can be useful to monitor cell viability after the transplantation of hESC into the myocardium.
In this video, we will show how to label hESC with MnCl2 and how those cells can be clearly seen by using MRI in vitro. At the same time, biological activity of Ca2+-channels will be modulated utilizing both Ca2+-channel agonist and antagonist to evaluate concomitant signal changes.

In this video, we are showing how to label human embryonic stem cells (hESC) with manganese chloride (MnCl2) which can enter cells via voltage-gated calcium channels when the cells are biologically active. Additionally, we show the use of MnCl2 as cellular MRI contrast agent to determine the in vitro viability of hESC.

Human embryonic stem cells (hESC) have demonstrated the ability to restore the injured myocardium. Magnetic resonance imaging (MRI) has emerged as one of ...

Culture and Maintenance of Human Embryonic Stem Cells  

Human embryonic stem (hES) cells must be monitored and cared for in order to maintain healthy, undifferentiated cultures. At minimum, the cultures must be  fed  every day by performing a complete medium change to replenish lost nutrients and to keep the cultures free of unwanted differentiation factors. Although a small amount of differentiation is normal and expected in stem cell cultures, the culture should be routinely cleaned up by manually removing, or "picking" differentiated areas. Identifying and removing excess differentiation from hES cell cultures are essential techniques in the maintenance of a healthy population of cells.

Culture and Maintenance of Human Embryonic Stem Cells

This protocol demonstrates how to maintain healthy, undifferentiated human embryonic stem (ES) cells.

Human embryonic stem (hES) cells must be monitored and cared for in order to maintain healthy, undifferentiated cultures. At minimum, the cultures must be ...

Chromosomal Spread Preparation of Human Embryonic Stem Cells for Karyotyping

Although human embryonic stem cells (hESC) have been shown to present a stable diploid karyotype 1, many studies have reported that depending on culture conditions they become prone to acquire chromosomal anomalies such as addition of whole or parts of chromosomes. Indeed, during long-term culture, karyotypic alterations are observed when enzymatic or chemical dissociation are used 2,3,4, while manual dissection of colonies for passaging retains a stable karyotype 5. Besides, changes in the environment such as the removal of feeder cells also seem to compromise the genetic integrity of hESC 3,6. Once chromosomal alterations could affect cellular physiology, the characterization of the genetic integrity of hESC in vitro is crucial considering hESC as an essential tool in embryogenesis studies and drug testing. Furthermore, for future therapeutic purposes chromosomal changes are a real concern as it is frequently associated to carcinogenesis.
Here we show a simple and useful method to obtain high quality chromosome spreads for subsequent analysis of chromosome set by G-banding, FISH, SKY or CGH techniques 7,8. We recommend checking the chromosomal status routinely with intervals of 5 passages in order to monitor the appearance of translocations and aneuploidies
Priscila Britto and Rafaela Sartore contributed equally to the paper.

Karyotyping is a simple and useful technique widely used for detecting genetic alterations. Here we describe a step by step protocol for chromosome spread preparation of human embryonic stem cells for monitoring the chromosomal status of these cells maintained in culture.

Although human embryonic stem cells (hESC) have been shown to present a stable diploid karyotype 1, many studies have reported that depending on culture ...