The authors thank all previous and present members of the department of Reproduction and Development of the Erasmus MC for helpful and stimulating discussions during the past years. We also want to thank the three anonymous reviewers for providing helpful feedback. Work in the Gribnau lab is supported by funding from the Dutch research council (NWO-VICI) and an ERC starting grant.

1. Induction of Differentiation in Female Embryonic Stem Cells to Induce X Chromosome Inactivation
NOTE: Female mouse embryonic stem cells (available upon request) are grown under standard ES cell conditions on gelatinized culture dishes coated with mouse embryonic fibroblasts (MEFs). We here assume that the reader is familiar with standard cell culture techniques39-41. To induce differentiation, ES cells grown in T25 dishes will be separated from the MEFs, and will be plated in diffe...

<ol>
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Combined DNA-RNA FISH can be technically challenging, as conditions suitable for DNA FISH can be too harsh for less stable RNA molecules. Several approaches have been applied to study both DNA and RNA in the same cell, circumventing the need for simultaneous incubation with probes detecting both the DNA and RNA. For example, in a superimposition approach, first RNA FISH is performed, and cells are imaged, and coordinates are taken. Subsequently, the same slides are used for DNA FISH, during which the signal of RNA FISH i...

Studying cells and tissues by means of fluorescent in situ hybridization (FISH) has, since its introduction in the late 1970s1, allowed researchers to study genes, chromatin organization and gene expression at the subcellular level. DNA FISH is frequently used in cytogenetics, karyotyping2, cancer diagnostics3 and pre-implantation genetic screening4, and has an important role in molecular research5-6 since it allows the detection of nucleic acids in their native environment. Single cell expression analysis by RNA FISH can detect native primary transcripts and noncoding RNAs being transcribed from chromosomes, and offers advantages to other techniques which assess gene expression at a population level, including for example quantitative RT-PCR, genome wide expression analysis or Northern blotting. By visualizing RNA transcripts originating directly from their sites of origin, it has for example been noticed that gene expression is stochastic7, and can sometimes be allele specific8. Improvements in the technique have even allowed the detection and quantification of single mRNA molecules within cells9-11.
The basic principle of FISH consists of hybridization of nucleic acids within the cell to a nucleic acid probe by means of highly specific Watson and Crick base-pairing. The probe can be either directly or indirectly detected, resulting in a signal which can be microscopically visualized. Initial attempts consisted of radioactively labeled probes, which had drawbacks based on safety issues, limited spatial resolution and the ability to detect only one target at a time12-14. The subsequent development of nonradioactive labels, including fluorochromes, haptens, and enzymes, has allowed the wide spread use of FISH as a routine molecular biology technique. The FISH probe can either be directly labeled with fluorochromes by chemical linking of fluorescent molecules to nucleic acid sequences15 and integration of fluorescently labeled nucleotides16-19, or the probe can be indirectly visualized after integration of haptens (including biotin and digoxigenin) and immunological detection of haptens by hapten specific antibodies conjugated to fluorescent reporter molecules20-21. The latter approach allows signal amplification by using several layers of fluorescently labeled antibodies which are used to enhance the original signal, and enables the detection of RNA species which are expressed at low levels. By combining direct and indirect labeling techniques and various haptens, several targets can be simultaneously visualized within the same cell.
One of the most important steps in FISH protocols is the hybridization of the probe to its target. Although in theory, a probe will specifically bind only to its target, in practice, this specificity is not always achieved, as probes may bind to homologous regions, and hybridization conditions will not always be ideal for a certain DNA region or RNA species. Post-hybridization washes are therefore of particular importance, as they can increase the stringency of the FISH procedure, and can prevent nonspecific binding of FISH probes, which would result in a high level of background noise. As RNA molecules are single stranded they can easily be hybridized to a FISH probe. In contrast, the double stranded DNA molecule first needs a denaturation step, after which a probe can hybridize. This is usually achieved by heating of the specimen, which results in denaturation of the DNA. However, under these harsh conditions, fragile, single stranded RNA molecules might be lost. Therefore, combined DNA-RNA FISH requires significant optimization of the conditions, and is more technically challenging compared to the separate detection of only RNA or DNA.
Here we present a detailed protocol of combined, simultaneous DNA-RNA FISH which has allowed us to study X chromosome inactivation (XCI) in differentiating female mouse embryonic stem cells22-24. XCI is a crucial epigenetic mechanism for female embryonic development25, and results in heterochromatinization and hence silencing of one of the two X chromosomes in female individuals26-27. Essential to this process is the noncoding RNA Xist28-30, which is regulated by the RNF1222-23 and REX124 proteins. Xist expression becomes upregulated on the future inactive X chromosome (Xi) during embryonic development or upon ES cell differentiation in vitro, and can spread along the X chromosome and thereby attract chromatin remodeling enzymes which result in the transcriptional shutdown of the X chromosome31. This spreading of Xist RNA can be visualized by RNA FISH as a coating of the X chromosome, which is also referred to as an Xist cloud. Since female ES cells can lose one of their X chromosomes due to genomic instability, we and others have employed combined DNA-RNA FISH to study XCI, to make sure that only karyotypically stable cells are assessed in the analysis of this important process22,32-34. As with every molecular biology technique, several different excellent protocols have been published35-38. Here we present our method, starting from the induction of differentiation in mouse ES cells, fixation of cells, labeling of FISH probes by Nick-translation, pre-treatment of fixed cells to allow permeabilization and subsequent probe uptake, hybridization of the probe to the target, and finally detection of the probe by fluorescently labeled antibodies. The herein presented protocol allows the faithful detection of Xist RNA and the X chromosome within a period of two days, and the basics of this technique can likely be adapted to other systems and areas of research.

<table border="0" cellpadding="0" cellspacing="0" width="874">
	<tbody>
		<tr height="21">
			<td height="21" style="height:21px;width:464px;">female mouse embryonic stem cells</td>
			<td style="width:124px;"></td>
			<td style="width:119px;"></td>
			<td style="width:167px;">will be made available upon request</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:464px;">mouse embryonic fibroblasts</td>
			<td style="width:124px;"></td>
			<td style="width:119px;"></td>
			<td>can be derived from E13.5 embryos, or via commercial sources e.g Millipore</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:464px;">ES cell culture medium</td>
			<td style="width:124px;"></td>
			<td style="width:119px;"></td>
			<td>DMEM, 15% foetal calf serum, 100 U ml-1 penicillin, 100 mg ml-1 streptomycin, non-essential amino acids, 0.1 mM &#223;-mercaptoethanol, and 1000 U ml-1 LIF. Filter sterilize and store at 4&#186;C for maximal 2 weeks.&#160;</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:464px;">LIF</td>
			<td style="width:124px;">Chemicon</td>
			<td style="width:119px;">ESG1107</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:464px;">DMEM</td>
			<td style="width:124px;">Invitrogen</td>
			<td align="right" style="width:119px;">11960085</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:464px;">Fetal Calf Serum&#160;</td>
			<td style="width:124px;">Invitrogen</td>
			<td align="right" style="width:119px;">10099141</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:464px;">Penicillin&#8211;streptomycin (100&#215;)</td>
			<td style="width:124px;">Invitrogen</td>
			<td style="width:119px;">15140-122</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:464px;">Non-essential aminoacids&#160;</td>
			<td style="width:124px;">Invitrogen</td>
			<td style="width:119px;">11140-050</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:464px;">&#223;-mercaptoethanol&#160;</td>
			<td style="width:124px;">Sigma-Aldrich</td>
			<td style="width:119px;">M7522</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:464px;">ES cell differentiation medium</td>
			<td style="width:124px;"></td>
			<td style="width:119px;"></td>
			<td>IMDM-Glutamax, 15% heat inactivated foetal calf serum, 100 U ml-1 penicillin, 100 mg ml-1 streptomycin, non-essential amino acids, 37.8 &#956;l/l monothioglycerol and 50 &#956;g/ml ascorbic acid</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:464px;">IMDM-Glutamax</td>
			<td style="width:124px;">Invitrogen</td>
			<td style="width:119px;">31980-030</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:464px;">Ascorbic acid (50 mg/ml)</td>
			<td style="width:124px;">Sigma-Aldrich</td>
			<td>A4403</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:464px;">monothioglycerol</td>
			<td style="width:124px;">Sigma-Aldrich</td>
			<td>M6145</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:464px;">T25 cell culture dishes</td>
			<td style="width:124px;">Greiner Bio-one</td>
			<td align="right" style="width:119px;">690160</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:464px;">6-well cell culture dishes</td>
			<td style="width:124px;">Greiner Bio-one</td>
			<td align="right" style="width:119px;">662160</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:464px;">cell culture grade PBS</td>
			<td style="width:124px;">Sigma-Aldrich</td>
			<td style="width:119px;">D8537</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:464px;">Trypsin-EDTA 0.25% (v/v) trypsin/0.2% (w/v) EDTA in PBS&#160;</td>
			<td style="width:124px;">Gibco</td>
			<td style="width:119px;">25200-056</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:464px;">falcon tubes</td>
			<td style="width:124px;">Falcon</td>
			<td align="right" style="width:119px;">352196</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:464px;">24x24 mm coverslips</td>
			<td style="width:124px;">Menzle</td>
			<td align="right" style="width:119px;">780882</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:464px;">gelatin</td>
			<td style="width:124px;">Sigma-Aldrich</td>
			<td style="width:119px;">G1890-100G</td>
			<td>prepare a 0.2% gelatin/cell culture PBS solution, and autoclave</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:464px;">paraformaldehyde</td>
			<td style="width:124px;">Sigma-Aldrich</td>
			<td>P6148</td>
			<td>prepare 4% PFA/PBS solutions, by dissolving PFA in PBS. Stir at 70 &#7484;C until completely dissolved and cool down to room temperature. Aliquots can be stored at -20&#7484;C</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:464px;">absolute 100%&#160; ethanol</td>
			<td style="width:124px;">Sigma-Aldrich</td>
			<td style="width:119px;">32221-2.5L</td>
			<td>use absolute 100% ethanol and RNAse free water to make 70% and 90% ethanol solutions</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:464px;">RNAse free water</td>
			<td style="width:124px;">Baxter</td>
			<td>TKF7114</td>
			<td></td>
		</tr>
		<tr height="42">
			<td height="42" style="height:42px;width:464px;">sterile filter tips</td>
			<td style="width:124px;">Rainin Bio Clean</td>
			<td style="width:119px;">GP-L10F, GP-L200F, RT-1000F</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:464px;">digoxigenin-labeling kit (DIG-Nick translation)</td>
			<td style="width:124px;">Roche</td>
			<td align="right" style="width:119px;">11745816910</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:464px;">biotin-labeling kit (Biotin Nick translation)</td>
			<td style="width:124px;">Roche</td>
			<td align="right" style="width:119px;">11745824910</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:464px;">Sephadex G50</td>
			<td style="width:124px;">Sigma-Aldrich</td>
			<td style="width:119px;">G5080</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:464px;">2 ml syringe</td>
			<td style="width:124px;">BD Plastipak</td>
			<td align="right" style="width:119px;">300013</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:464px;">sterilized cotton</td>
			<td style="width:124px;"></td>
			<td style="width:119px;"></td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:464px;">eppendorf tubes</td>
			<td style="width:124px;">Eppendorf</td>
			<td align="right" style="width:119px;">30120086</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:464px;">yeast tRNA 10 mg/ml</td>
			<td style="width:124px;">Invitrogen</td>
			<td style="width:119px;">15401-029</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:464px;">Salmon Sperm DNA 10 mg/ml</td>
			<td style="width:124px;">Invitrogen</td>
			<td style="width:119px;">15632-011</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:464px;">mouse cot-1 DNA&#160; 1 mg/ml</td>
			<td style="width:124px;">Invitrogen</td>
			<td style="width:119px;">18440-016</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:464px;">eppendorf bench top microcentrifuge</td>
			<td style="width:124px;">Eppendorf</td>
			<td style="width:119px;">Model 5417R&#160;</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:464px;">Eppendorf Refrigerated Centrifuge</td>
			<td style="width:124px;">Eppendorf</td>
			<td style="width:119px;">Model 5810R&#160;</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:464px;">2M NaAc, pH 5.6</td>
			<td style="width:124px;">Sigma-Aldrich</td>
			<td style="width:119px;">S7670</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:464px;">50+ hybridization solution</td>
			<td style="width:124px;"></td>
			<td style="width:119px;"></td>
			<td>50% formamide, 2x SSC, 50 mM phosphate buffer pH 7, 10% dextran sulfate pH 7</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:464px;">formamide</td>
			<td style="width:124px;">Acros organics</td>
			<td align="right" style="width:119px;">3272350000</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:464px;">dextran sulfate</td>
			<td style="width:124px;">Fluka</td>
			<td align="right" style="width:119px;">31403</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:464px;">pepsin</td>
			<td style="width:124px;">Sigma-Aldrich</td>
			<td>P6887</td>
			<td>prepare a 0.2% solution in RNAse free water, and add 84 &#181;l 37% HCL per 100 ml</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:464px;">HCL, 37% solution&#160;</td>
			<td style="width:124px;">Fluka</td>
			<td align="right" style="width:119px;">84422</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:464px;">object glasses</td>
			<td style="width:124px;">Starfrost</td>
			<td style="width:119px;">8037/1</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:464px;">20x SSC</td>
			<td style="width:124px;">Invitrogen</td>
			<td style="width:119px;">AM9763</td>
			<td>dilute to 2x SSC in RNAse free water</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:464px;">10 mM Phosphate buffer, pH 7</td>
			<td style="width:124px;"></td>
			<td style="width:119px;"></td>
			<td>add 57.7 ml of 1M Na2HPO4 and 42.3 ml 1M NaH2PO4; use DEPC treated water and autoclave</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:464px;">denaturation buffer</td>
			<td style="width:124px;"></td>
			<td style="width:119px;"></td>
			<td>70% Formamide/2xSSC/10mM phosphate buffer pH 7</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:464px;">Tween-20</td>
			<td style="width:124px;">Sigma-Aldrich</td>
			<td>P2287</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:464px;">2M Tris pH 7.5 solution</td>
			<td style="width:124px;"></td>
			<td style="width:119px;"></td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:464px;">Tris-Saline-Tween washing solution (TST)</td>
			<td style="width:124px;"></td>
			<td style="width:119px;"></td>
			<td>100 ml 10x Saline, 50 ml 2M Tris, 500 &#181;l Tween-20, add RNAse free water till 1 liter&#160;</td>
		</tr>
		<tr height="25">
			<td height="25" style="height:25px;width:464px;">10x Saline solution</td>
			<td style="width:124px;"></td>
			<td style="width:119px;"></td>
			<td>dissolve 85 g NaCl in 1 liter RNAse free H2O, and autoclave</td>
		</tr>
		<tr height="25">
			<td height="25" style="height:25px;width:464px;">Tris-Saline-BSA (TSBSA)</td>
			<td style="width:124px;"></td>
			<td style="width:119px;"></td>
			<td>500 &#956;l 10x Saline, 250 &#956;l 2 M Tris, 1 ml 100x BSA, 3,25 ml RNAse free H2O</td>
		</tr>
		<tr height="42">
			<td height="42" style="height:42px;width:464px;">BSA, purified, 100x&#160;</td>
			<td style="width:124px;">New England Biolabs</td>
			<td style="width:119px;">B9001S</td>
			<td></td>
		</tr>
		<tr height="42">
			<td height="42" style="height:42px;">sheep-anti-dig antibody</td>
			<td style="width:124px;">Roche diagnostics</td>
			<td style="width:119px;"></td>
			<td>use 1:500 diluted in TSBSA</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;">rabbit-anti-sheep antibody conjugated with FITC</td>
			<td style="width:124px;">Jackson labs</td>
			<td style="width:119px;"></td>
			<td>use 1:250 diluted in TSBSA</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;">goat-anti-rabbit antibody conjugated with FITC</td>
			<td style="width:124px;">Jackson labs</td>
			<td style="width:119px;"></td>
			<td>use 1:250 diluted in TSBSA</td>
		</tr>
		<tr height="42">
			<td height="42" style="height:42px;">mouse-anti-biotin antibody</td>
			<td style="width:124px;">Roche diagnostics</td>
			<td style="width:119px;"></td>
			<td>use 1:200 diluted in TSBSA</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;">donkey-anti-mouse antibody conjugated with Rhodamine</td>
			<td style="width:124px;">Jackson labs</td>
			<td style="width:119px;"></td>
			<td>use 1:250 diluted in TSBSA</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;">goat-anti-horse antibody conjugated with Rhodamine</td>
			<td style="width:124px;">Jackson labs</td>
			<td style="width:119px;"></td>
			<td>use 1:250 diluted in TSBSA</td>
		</tr>
		<tr height="25">
			<td height="25" style="height:25px;width:464px;">Tris-Saline washing solution (TS)</td>
			<td style="width:124px;"></td>
			<td style="width:119px;"></td>
			<td>10 ml 10x Saline, 5 ml 2 M Tris, 85 ml RNAse free H2O</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;">Vectashield mounting medium with DAPI</td>
			<td style="width:124px;">Vectorlabs</td>
			<td>H-1200</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;">nail-varnish</td>
			<td style="width:124px;"></td>
			<td style="width:119px;"></td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:464px;">fluorescent miscroscope</td>
			<td style="width:124px;"></td>
			<td style="width:119px;"></td>
			<td></td>
		</tr>
	</tbody>
</table>

combined dna-rna fluorescent in situ hybridization (fish) to study x chromosome inactivation in differentiated female mouse embryonic stem cells

Fluorescent in situ hybridization (FISH) is a molecular technique which enables the detection of nucleic acids in cells. DNA FISH is often used in cytogenetics and cancer diagnostics, and can detect aberrations of the genome, which often has important clinical implications. RNA FISH can be used to detect RNA molecules in cells and has provided important insights in regulation of gene expression. Combining DNA and RNA FISH within the same cell is technically challenging, as conditions suitable for DNA FISH might be too harsh for fragile, single stranded RNA molecules. We here present an easily applicable protocol which enables the combined, simultaneous detection of Xist RNA and DNA encoded by the X chromosomes. This combined DNA-RNA FISH protocol can likely be applied to other systems where both RNA and DNA need to be detected.

Using the above mentioned protocol for combined DNA-RNA FISH, we have been able to visualize X chromosome inactivation in differentiating female embryonic stem cells. Figure 1 shows a representative example of an DNA-RNA FISH experiment, where we detected both Xist (which is visible as an so-called Xist RNA cloud on the inactive X chromosome and a basal transcription pinpoint on the active X chromosome), and a region of the X chromosome, which is visible as a pinpoint signal. Note that ...

Watch this Scientific Journal Video about Combined DNA-RNA Fluorescent In situ Hybridization FISH to Study X Chromosome Inactivation in Differentiated Female Mouse Embryonic Stem Cells at JoVE.com

Combined DNA-RNA Fluorescent In situ Hybridization FISH to Study X Chromosome Inactivation in Differentiated Female Mouse Embryonic Stem Cells

Fluorescent in situ hybridization (FISH) allows the detection of nucleic acids in their native environment within cells. We here describe a protocol for the combined, simultaneous detection of RNA and DNA by means of FISH, which can be used to study X chromosome inactivation in mouse embryonic stem cells.

Combined DNA-RNA Fluorescent In situ Hybridization (FISH) to Study X Chromosome Inactivation in Differentiated Female Mouse Embryonic Stem Cells

Fluorescent in situ hybridization (FISH) is a molecular technique which enables the detection of nucleic acids in cells. DNA FISH is often used in ...

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27.4K Views.  Erasmus MC - University Medical Center. Fluorescent in situ hybridization (FISH) allows the detection of nucleic acids in their native environment within cells. We here describe a protocol for the combined, simultaneous detection of RNA and DNA by means of FISH, which can be used to study X chromosome inactivation in mouse embryonic stem cells.