We thank Hongjae Sunwoo for helpful advice for oligonucleotide design in RNA FISH. We also thank Serenity Curtis for editing the manuscript. N.Y. was supported by a Postdoctoral Fellowship for Research Abroad of the Japan Society for the Promotion of Science (JSPS). This work was supported by the NIH (RO1-GM102184), the March of Dimes Research Foundation (#6-FY12-337), and the Developmental Fund and Trustee Grant at Cincinnati Children's Hospital Medical Center to Y.O.

1. Probe Preparation
<ol>
	<li>Obtain multiple unique oligonucleotides in Xist (20-30 nucleotide-length oligonucleotides, 63-65 &#186;C melting temperature, Table 1) with a 5&#8217;-amino modification and suspend in water.</li>
	<li>Pool equimolar amounts of oligonucleotides with 5&#8217;-amino modification (total 4.5 &#181;g) and label with amine-reactive fluorescent dye following the manufacturer&#8217;s instruction.
	<ol>
		<li>Dissolve the pooled oligonucleotides in final 5 &#181;l of nuclease-free...

<ol>
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No conflicts of interest declared.

In this paper, we have presented a quick immuno-FISH protocol that takes less than 5 hr to complete slide preparation, Xist RNA FISH, and immunofluorescence for H3K27me3. In comparison with the general immuno-FISH approach for Xist RNA detection, which usually needs overnight incubation for RNA FISH, this protocol not only significantly reduces time spent but also improves the sensitivity of immune-FISH using oligonucleotide probes.
Since Xist is highly transcribed during X-chromosome inactiva...

Mammalian X-chromosome inactivation (XCI) is a strategy to compensate for the imbalance in X-linked gene dosage between XX and XY, wherein one of the two X-chromosomes in females is transcriptionally inactivated1. X-chromosome inactivation is a great model system for long non-coding RNA (lncRNA) research. X-chromosome inactivation is regulated by multiple lncRNAs, and has been extensively studied over the past few decades to uncover the crosstalk mechanisms between lncRNAs, transcription, chromatin structure and nuclear organization2,3.
The X inactivation center (XIC) located on the X-chromosome is a complex genetic locus comprised of a number of genes producing non-coding RNAs4. X-inactive specific transcript (Xist) lncRNA in eutherian mammals is one such lncRNA which plays a crucial role in X-chromosome inactivation5,6. Xist transcripts surround the location of the future Xi to initiate X-chromosome inactivation, and appear as a cloud when visualized using RNA FISH; this formation is referred to as the &#8220;Xist Cloud&#8221;7. Since Xist RNA interacts with various chromatin-modifying enzymes, co-localization of the Xist clouds with different epigenetic modifications for silent chromatin and repressive transcription is observed during X-chromosome inactivation8. For example, Xist RNA interacts with polycomb repressive complex 2 (PRC2) which is responsible for H3K27me3 and induces a repressive chromatin state9. The occurrence of the Xist cloud on the Xi and its co-localization with the intensive H3K27me3 modification represents a facultative heterochromatin landscape of the Xi10,11.
Cytogenetic techniques, such as DNA/RNA FISH have come a long way from the traditional method using radiolabelled probes12 to recent and advanced techniques with enhanced sensitivity and fluorescent imaging using multiple oligonucleotide probes13,14. DNA/RNA FISH coupled with immunofluorescence has been routinely used as a cytological tool to understand spatiotemporal nuclear organization, RNA localization, chromatin structure and modifications. The most standard probe preparation for RNA FISH involves the use of plasmid or bacterial artificial chromosome (BAC) clones and their subsequent labeling either with nick translation or random priming15. However, nearly 70% of genes in mice and 40% of genes in humans show an overlap of sense and antisense transcripts16, hence requiring a strand-specific FISH method in order to distinguish sense and antisense transcripts. In vitro transcribed RNA probes (riboprobe) are often used for strand-specific RNA FISH17,18; however, this involves preparing a plasmid clone or PCR product with T7, SP6, or T3 promoter and synthesizing riboprobes. Furthermore, riboprobes derived from genomic DNA or cDNA often contain non-specific regions and repetitive elements, which result in high background noise. Another issue is that riboprobes, which are a few hundred nucleotides in length and contain multiple fluorophores, cannot efficiently penetrate into the nucleus. To circumvent this, multiple shorter oligonucleotide probes labeled with a single fluorophore at the end have been developed that have good sensitivity, uniform signal strength, and ease of purification and handling14. In addition, DNA oligonucleotides are generally more stable than RNA. We applied a similar strategy of using oligonucleotides in Xist RNA FISH19 with immunofluorescence to understand the epigenetic dynamics of the Xi induced by Xist lncRNA during the process of X-chromosome inactivation. This protocol describes the creation of oligonucleotide probes and proper preparation of cells, as well as utilization of immunofluorescence and RNA FISH. Xist RNA FISH using multiple oligonucleotides is cost effective approach in the long-term if Xist RNA FISH is performed routinely in one&#8217;s laboratory. This technique can be used to identify lncRNAs in cells while simultaneously mapping its co-localization with epigenetic modifications or factors. One major advantage of the protocol is the ability to easily modify it to suit one&#8217;s research interests.

<table border="0" cellpadding="0" cellspacing="0" width="573">
	<tbody>
		<tr height="21">
			<td height="21" style="height:21px;width:267px;">oligonucleotides with 5&#8217;-amine modification</td>
			<td style="width:187px;">IDT</td>
			<td style="width:119px;"></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:267px;">Alexa Fluor 488 Reactive Dye</td>
			<td style="width:187px;">Life Technologies</td>
			<td style="width:119px;">A32750</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:267px;">MicroSpin G-25 columns</td>
			<td style="width:187px;">GE Healthcare</td>
			<td style="width:119px;">27-5325-01</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:267px;">Cytospin 2</td>
			<td style="width:187px;">Shandon</td>
			<td align="right" style="width:119px;">59900102</td>
		</tr>
		<tr height="42">
			<td height="42" style="height:42px;width:267px;">Bovine Serum Albumin, Molecular Biology Grade (for hybridization buffer)</td>
			<td style="width:187px;">Roche</td>
			<td style="width:119px;">10715859103</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:267px;">Histone H3K27me3 antibody</td>
			<td style="width:187px;">Active Motif</td>
			<td style="width:119px;">61017</td>
		</tr>
		<tr height="42">
			<td height="42" style="height:42px;width:267px;">Accutase</td>
			<td style="width:187px;">Innovative Cell Technologies</td>
			<td style="width:119px;">AT104</td>
		</tr>
		<tr height="42">
			<td height="42" style="height:42px;width:267px;">Alexa Fluor 555 Goat Anti-Mouse, highly cross-adsorbed</td>
			<td style="width:187px;">Life Technologies</td>
			<td style="width:119px;">A21424</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:267px;">ProLong Gold antifade reagent</td>
			<td style="width:187px;">Life Technologies</td>
			<td style="width:119px;">P36931</td>
		</tr>
	</tbody>
</table>

quick fluorescent in situ hybridization protocol for xist rna combined with immunofluorescence of histone modification in x-chromosome inactivation

Combining RNA fluorescent in situ hybridization (FISH) with immunofluorescence (immuno-FISH) creates a technique that can be employed at the single cell level to detect the spatial dynamics of RNA localization with simultaneous insight into the localization of proteins, epigenetic modifications and other details which can be highlighted by immunofluorescence. X-chromosome inactivation is a paradigm for long non-coding RNA (lncRNA)-mediated gene silencing. X-inactive specific transcript (Xist) lncRNA accumulation (called an Xist cloud) on one of the two X-chromosomes in mammalian females is a critical step to initiate X-chromosome inactivation. Xist RNA directly or indirectly interacts with various chromatin-modifying enzymes and introduces distinct epigenetic landscapes to the inactive X-chromosome (Xi). One known epigenetic hallmark of the Xi is the Histone H3 trimethyl-lysine 27 (H3K27me3) modification. Here, we describe a simple and quick immuno-FISH protocol for detecting Xist RNA using RNA FISH with multiple oligonucleotide probes coupled with immunofluorescence of H3K27me3 to examine the localization of Xist RNA and associated epigenetic modifications. Using oligonucleotide probes results in a shorter incubation time and more sensitive detection of Xist RNA compared to in vitro transcribed RNA probes (riboprobes). This protocol provides a powerful tool for understanding the dynamics of lncRNAs and its associated epigenetic modification, chromatin structure, nuclear organization and transcriptional regulation.

Representative images of quick immuno-FISH are shown in Figure 1A. Co-localization of the Xist RNA cloud and H3K27me3 signal on the Xi was detected in differentiating female cells. At day 12 upon differentiation, more than 90% of EB cells had an Xist cloud (Figure 1B). Short oligonucleotide probes efficiently penetrated into the nuclei, leading to a visualization of almost all H3K27me3 signals co-localized with Xist RNA (Figure 1C; 97%, n = 150).
<p class="jove_conte...

Watch this Scientific Journal Video about Quick Fluorescent In Situ Hybridization Protocol for Xist RNA Combined with Immunofluorescence of Histone Modification in X-chromosome Inactivation at JoVE.co

Quick Fluorescent In Situ Hybridization Protocol for Xist RNA Combined with Immunofluorescence of Histone Modification in X-chromosome Inactivation

We developed an easily customized strand-specific fluorescent in situ hybridization (FISH) protocol combined with immunofluorescence. This allows for a detailed examination of RNA dynamics with simultaneous insight into the chromatin structure, nuclear organization, and transcriptional regulation at the single cell level.

Quick Fluorescent In Situ Hybridization Protocol for Xist RNA Combined with Immunofluorescence of Histone Modification in X-chromosome Inactivation

Combining RNA fluorescent in situ hybridization (FISH) with immunofluorescence (immuno-FISH) creates a technique that can be employed at the single cell ...

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13.8K vistas.  Cincinnati Children's Hospital Medical Center. We developed an easily customized strand-specific fluorescent in situ hybridization (FISH) protocol combined with immunofluorescence. This allows for a detailed examination of RNA dynamics with simultaneous insight into the chromatin structure, nuclear organization, and transcriptional regulation at the single cell level. 

Video: Quick Fluorescent In Situ Hybridization Protocol for Xist RNA Combined with Immunofluorescence of Histone Modification in X-chromosome Inactivation