I thank Jeannie T. Lee for supervision of this project when I was in the Lee laboratory and Tyler Broering for editing the manuscript. This work was supported by the Basil O&#8217;Connor Starter Scholar Award from the March of Dimes Foundation and the NIH Grant GM098605.

1. 3D Slide Preparation
<ol>
	<li>Prepare the following reagents:
	<ol>
		<li>CSK buffer: 100 mM NaCl, 300 mM sucrose, 10 mM PIPES, 3 mM MgCl2. Adjust pH to 6.8 with 1 M NaOH. Store the CSK buffer at 4 &#176;C.</li>
		<li>CSK buffer with 0.5% Triton X-100: Add 200 &#956;l of Triton X-100 to 40 ml of CSK buffer. Mix the solution using magnetic stirrer until Triton X-100 is completely dissolved. Store the CSK buffer with 0.5% Triton X-100 at 4 &#176;C.</li>
		<li>4% Paraformaldehyde (PFA)&#8211;PBS, pH 7.4: Dissolve 4 g of PFA in approximately 70-80 ml of water. In order to expedite the dissolving process, add approximately 20 &#956;l of 4 N NaOH and keep the solution in a water bath at 60 &#176;C until the PFA has completely dissolved and the solution is transparent. This process takes approximately 1 hr. After PFA has completely dissolved, add 10 ml of 10x PBS. Adjust the final volume to 100 ml with water and cool down the solution to room temperature (25 &#176;C). Use freshly prepared solution for each new experiment. 
		Note: Obtain institutional permission for all animal work and adhere to relevant animal care guidelines.</li>
	</ol>
	</li>
	<li>Euthanize male mice. Using forceps and scissors, excise the testis from the mouse. Place the testis in PBS (or RPMI 1640). After the removal of testis, quickly carry out the following steps 1.3-1.4 in order to prevent the degradation of RNA.</li>
	<li>Rupture the testis on a small Petri dish and remove the tunica albuginea. Unravel the seminiferous tubules in PBS on ice using forceps.</li>
	<li>Using forceps, transfer several tubules (several pieces of tubules approximately 5-10 mm in length) into one well of a 4-well dish containing 500 ml of CSK buffer + 0.5% Triton X-100 on ice, and incubate for 6 min. Overexposure to CSK buffer may result in the disruption of cells.</li>
	<li>Using forceps, transfer all the tubules to one well of a 4-well dish containing 4% PFA-PBS solution. This step can be preformed without a stereomicroscope, but optionally it can be used. Incubate for 10 min at room temperature. Simultaneously begin preparing 12 cytospin chambers during the incubation periods.</li>
	<li>Using forceps, transfer all the tubules to one well of a 4-well dish containing PBS. Incubate for 5 min at room temperature.</li>
	<li>On the backside of a glass slide, transfer all the tubules into 30 &#956;l of PBS (the top of the slide should be avoided due to cationic charge). Using the tips of two forceps, tear the tubules to pieces. Chop the tubules in a horizontal direction by clipping tubules between tips of two forceps and pulling the forceps horizontally. Continue with this step for approximately 10-20 sec.</li>
	<li>Mix the suspension by pipetting using a P20 pipette.</li>
	<li>Transfer the suspension to a microcentrifuge tube, dilute with PBS to approximately 1.3 ml. Apply 100 &#956;l of suspension to each of the 12 cytospin chambers (1.2 ml total). At this step, the concentration of cells does not need to be determined.</li>
	<li>Cytospin the samples at 2,000 rpm for 10 min at room temperature. After cytospinning, dry slides on lab bench for a few minutes at room temperature. After slides have been allowed to dry completely for few minutes, go to the next step.</li>
	<li>Using a Coplin jar containing PBS, wash the slides for 5 min at room temperature.</li>
	<li>Transfer slides to a Coplin jar containing 70% ethanol and wait at least 2 min prior to initiation of RNA FISH. Slides are stable for a few weeks in 70% ethanol at 4 &#176;C. For long-term storage, dehydrate slides using serial treatment with 80% and 100% ethanol in Coplin jars for 2 min each and air-dry completely dehydrate the slides. Store at -80 &#176;C in a slide box.</li>
</ol>
2. Cot-1 DNA Probe Preparation by Random Priming
<ol>
	<li>Prepare the following reagents:
	<ol>
		<li>Hybridization buffer: Mix the proceeding components to prepare 900 ml of hybridization buffer stock; this solution will be used to stock probes. This hybridization buffer stock allows for the addition of 10% volume of RNase inhibitor solution (Ribonucleoside Vanadyl Complex) prior to hybridization.
		<table>
			<tbody>
				<tr>
					<td>Component</td>
					<td>Amount (&#956;l)</td>
					<td>Final concentration</td>
				</tr>
				<tr>
					<td>Formamide</td>
					<td>500</td>
					<td>50% (v/v)</td>
				</tr>
				<tr>
					<td>50% Dextran</td>
					<td>200</td>
					<td>10% (w/v)</td>
				</tr>
				<tr>
					<td>20x SSC</td>
					<td>100</td>
					<td>2x</td>
				</tr>
				<tr>
					<td>1% BSA</td>
					<td>100</td>
					<td>0.1%</td>
				</tr>
			</tbody>
		</table>
		Prior to hybridization, add &#8530; vol of 200 mM Ribonucleoside Vanadyl Complex or water to the hybridization buffer stock to match the final concentration. At -20 &#176;C, this mixture is stable for more than a year.</li>
		<li>20x&#160;SSC: Dissolve 88.2 g of sodium citrate and 175.3 g of NaCl in approximately 800 ml of water. Adjust the pH to 7.0 using a few drops of 1 M HCl. Add water to adjust the final volume to 1 L. Sterilize by autoclaving. After preparation, 20x&#160;SSC can be stored at room temperature.</li>
		<li>50% (w/v) Dextran: Stir water and slowly add 50 g of dextran sulfate. Keep stirring overnight at room temperature. Add water to adjust final volume to 100 ml. Store at room temperature.</li>
	</ol>
	</li>
	<li>Add the following constituents listed below to a PCR tube. Using a PCR machine, mix and incubate the solution for 5 min at 95 &#176;C.
	<table>
		<tbody>
			<tr>
				<td>Component</td>
				<td align="center">Amount per reaction (&#956;l)</td>
				<td align="center">Final</td>
			</tr>
			<tr>
				<td>Cot-1 DNA: 1 mg/ml</td>
				<td align="center">1</td>
				<td align="center">1 &#956;g</td>
			</tr>
			<tr>
				<td>Random 9mer primer (from kit)</td>
				<td align="center">10</td>
				<td align="center"></td>
			</tr>
			<tr>
				<td>Water</td>
				<td align="center">27</td>
				<td align="center"></td>
			</tr>
		</tbody>
	</table>
	</li>
	<li>Centrifuge briefly and place on ice.</li>
	<li>Add the following components. Mix and incubate for 30 min at 37 &#176;C using a PCR machine. (For details of the kit used see the table of reagents and equipment).
	<table>
		<tbody>
			<tr>
				<td>Component</td>
				<td align="center">Amount per reaction (&#956;l)</td>
				<td align="center">Final concentration</td>
			</tr>
			<tr>
				<td>Mixture prepared from step 2.2</td>
				<td align="center">38</td>
				<td align="center"></td>
			</tr>
			<tr>
				<td>5x nucleotide buffer (from kit)</td>
				<td align="center">9.2</td>
				<td align="center"></td>
			</tr>
			<tr>
				<td>Cy3-dUTP (1 mM)</td>
				<td align="center">0.8</td>
				<td align="center">16 &#956;M</td>
			</tr>
			<tr>
				<td>Klenow (from kit)</td>
				<td align="center">2</td>
				<td align="center"></td>
			</tr>
		</tbody>
	</table>
	</li>
	<li>Add 2 &#956;l of stop buffer (from kit) to discontinue the reaction.</li>
	<li>Purify the stopped reaction using microspin columns.</li>
	<li>Add 50 &#956;g (5 &#956;l) of herring sperm DNA (50 fold excess of template Cot-1 DNA) to the purified fraction.</li>
	<li>Measure the total volume using a pipette. Add 0.7x volume of 100% ethanol and 0.1x volume of 3 M sodium acetate (pH 5.2), mix well, and centrifuge for 15 min at maximum speed (17,000 x g) using a microcentrifuge at 4 &#176;C.</li>
	<li>Remove the liquid, and add 200 &#956;l of 70% ethanol, mix well and centrifuge for 5 min at maximum speed at 4 &#176;C.</li>
	<li>Remove the excess liquid. Dry the precipitate for 10-30 min at room temperature.</li>
	<li>Dissolve the pellet in 20 &#956;l of hybridization buffer stock. Because the pellet is often difficult to dissolve, pipette repeatedly. As an alternate option, a vortex mixer can also be used to efficiently dissolve the pellet. Probes can be kept at -20 &#176;C until use.</li>
</ol>
3. Cot-1 RNA FISH
<ol>
	<li>Add the components listed below to a PCR tube. Using a PCR machine, incubate for 10 min at 80 &#176;C, followed by a preannealing step of approximately 10-30 min at 42 &#176;C. Keep at 42 &#176;C until hybridization. Ribonucleoside Vanadyl Complex is optional; it can be replaced with water.
	<table>
		<tbody>
			<tr>
				<td>Component</td>
				<td align="center">Amount per reaction (&#956;l)</td>
				<td align="center">Final</td>
			</tr>
			<tr>
				<td>Cot-1 DNA probe (50 ng/&#956;l)</td>
				<td align="center">2</td>
				<td align="center">100 ng</td>
			</tr>
			<tr>
				<td>Ribonucleoside Vanadyl Complex (200 mM)</td>
				<td align="center">2</td>
				<td align="center">20 mM</td>
			</tr>
			<tr>
				<td>Hybridization buffer</td>
				<td align="center">added to 20</td>
				<td align="center"></td>
			</tr>
		</tbody>
	</table>
	</li>
	<li>Dehydrate slides in a Coplin jar containing 80% ethanol for 2 min, followed by a Coplin jar containing 100% ethanol for 2 min. Dry slides completely on lab bench at room temperature.</li>
	<li>Preheat a tip box chamber (filled with 2-3 cm of water) in a 42 &#176;C incubator in advance. Place the slide on the tip box chamber. Briefly centrifuge the preannealed probes and pipette directly onto the dehydrated slides. Avoid making bubbles. Gently cover the slide with a cover slip.</li>
	<li>Hybridize for 6 hr to overnight (14-15 hr) at 42 &#176;C.</li>
	<li>Prepare wash solutions in Coplin jars (two jars with both 2x SSC and 50% formamide, and two jars with 2x SSC). Preheat at 42 &#176;C for 30 min in a water bath.</li>
	<li>Use a razor blade to remove the cover slip from the edge of the slide. Avoid scratching samples. Wash slides in a Coplin jar containing 2x SSC and 50% formamide for 5 min at 45 &#176;C. Repeat this step once.</li>
	<li>Wash slides in a Coplin jar containing 2x SSC for 5 min at 45 &#176;C. Repeat this step once.</li>
	<li>Add 20 &#956;l of DAPI-mounting media to the slides, and cover with a cover slip. Gently press cover glass to remove extra mounting media. Blot extra mounting media with cleaning tissue. The slides are ready for microscopy evaluation.</li>
</ol>

<ol>
	<li>Peters, A. H., Plug, A. W., van Vugt, M. J., de Boer, P. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=A+drying-down+technique+for+the+spreading+of+mammalian+meiocytes+from+the+male+and+female+germline.">A drying-down technique for the spreading of mammalian meiocytes from the male and female germline.</a> Chromosome Res. 5, 66-68 (1997).</li><li>Namekawa, S. H., 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=Postmeiotic+sex+chromatin+in+the+male+germline+of+mice.">Postmeiotic sex chromatin in the male germline of mice.</a> Curr Biol. 16, 660-667 (2006).</li><li>Namekawa, S. H., Lee, J. T. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Detection+of+nascent+RNA,+single-copy+DNA+and+protein+localization+by+immunoFISH+in+mouse+germ+cells+and+preimplantation+embryos.">Detection of nascent RNA, single-copy DNA and protein localization by immunoFISH in mouse germ cells and preimplantation embryos.</a> Nat Protoc. 6, 270-284 (2011).</li><li>Mahadevaiah, S. K., Costa, Y., Turner, 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=Using+RNA+FISH+to+study+gene+expression+during+mammalian+meiosis.">Using RNA FISH to study gene expression during mammalian meiosis.</a> Methods in molecular biology. 558, 433-444 (2009).</li><li>Hall, L. 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=An+ectopic+human+XIST+gene+can+induce+chromosome+inactivation+in+postdifferentiation+human+HT-1080+cells.">An ectopic human XIST gene can induce chromosome inactivation in postdifferentiation human HT-1080 cells.</a> Proc Natl Acad Sci U S A. 99, 8677-8682 (2002).</li><li>Huynh, K. D., Lee, J. T. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Inheritance+of+a+pre-inactivated+paternal+X+chromosome+in+early+mouse+embryos.">Inheritance of a pre-inactivated paternal X chromosome in early mouse embryos.</a> Nature. 426, 857-862 (2003).</li><li>Namekawa, S. H., VandeBerg, J. L., McCarrey, J. R., Lee, J. T. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Sex+chromosome+silencing+in+the+marsupial+male+germ+line.">Sex chromosome silencing in the marsupial male germ line.</a> Proceedings of the National Academy of Sciences of the United States of America. 104, 9730-9735 (2007).</li><li>Namekawa, S. H., Payer, B., Huynh, K. D., Jaenisch, R., Lee, J. T. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Two-step+imprinted+X+inactivation:+repeat+versus+genic+silencing+in+the+mouse.">Two-step imprinted X inactivation: repeat versus genic silencing in the mouse.</a> Mol Cell Biol. 30, 3187-3205 (2010).</li><li>Ichijima, Y., 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=MDC1+directs+chromosome-wide+silencing+of+the+sex+chromosomes+in+male+germ+cells.">MDC1 directs chromosome-wide silencing of the sex chromosomes in male germ cells.</a> Genes Dev. 25, 959-971 (2011).</li><li>Sin, H. S., 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=RNF8+regulates+active+epigenetic+modifications+and+escape+gene+activation+from+inactive+sex+chromosomes+in+post-meiotic+spermatids.">RNF8 regulates active epigenetic modifications and escape gene activation from inactive sex chromosomes in post-meiotic spermatids.</a> Genes Dev. 26, 2737-2748 (2012).</li></ol>

The author has nothing to disclose.

In 3D slide preparation, the permeabilization step precedes the fixation step. These steps are performed directly on seminiferous tubules, thereby preserving the three-dimensional chromatin structure. An alternate option to preserving chromatin structure for RNA/DNA FISH is to perform the permeabilization step and the fixation step simultaneously. This alternate technique has been performed in marsupial germ cells and in mouse preimplantation embryos7,8. However, if the fixation step precedes the permeabilizat...

In testes, germ cells differentiate from diploid spermatogonia through meiosis into mature, haploid spermatozoa. During this process, the nuclear chromatin structure of germ cells is continuously and dynamically remodeled. Surface spreads are commonly used for the cytological examination of individual spermatogenic cells. A prevailing method of surface spreads employs hypotonic treatment by which individual spermatogenic cells are spread and flattened1. These conditions are optimal for detailed analysis of meiotic chromosomes. Chromosomal features such as synaptic status and recombination foci are easily observed using this method. However, the hypotonic treatment disrupts subnuclear chromatin architecture, thus this technique is not suitable for structural analysis of nuclei. Consequently, an improved method has been designed to preserve the three-dimensional chromatin structure of testicular germ cells. This method has been termed as the three-dimensional (3D) slide method (Figure 1). The 3D slide method has enabled the detection of nascent RNA localization in nuclei because it was initially optimized to examine gene expression and chromatin states during testicular germ cell differentiation by RNA fluorescence in situ hybridization (FISH)2,3. This 3D method is also applicable to the combination of immunofluorescence, DNA, and RNA FISH. Additionally, this method has aided in the discovery of postmeiotic sex chromatin (PMSC), a silent compartment of the sex chromosomes found in postmeiotic spermatids2.
The 3D slide method was originally optimized through the combination of two essential steps of slide preparation commonly used for nuclear staining: the fixation step designed to fix nuclear materials&#160;and the permeabilization step intended to remove cytoplasmic materials in order to improve the accessibility of staining reagents, such as antibodies and FISH probes. As previously described in another publication3, it has been determined that the permeabilization step must precede the fixation step in order to obtain optimal results with low cytoplasmic background. In this 3D slide method, the permeabilization step and subsequent fixation step are performed directly on seminiferous tubules&#160;and are followed by the mechanical dissociation of germ cells with forceps prior to cytospinning onto slides. An alternative method for RNA FISH of spermatogenic cells was developed in another laboratory4. In this method, consistent with the 3D method, the permeabilization step must precede the fixation step in order to obtain optimal results of RNA FISH.
The following protocol describes the 3D slide method and provides an example of a possible application, Cot-1 RNA FISH for the detection of nuclear nascent RNAs. Cot-1 DNA consists of repetitive elements in the genome. Here, a Cot-1 DNA probe is hybridized to an intron and UTR of the nascent transcripts, thereby detecting the transcriptionally active regions in nucleus5,6. 3D slides are versatile and can be applied to a combination of immunofluorescence, DNA and RNA FISH techniques in order to obtain detailed examination of spatial relationships between chromatin architecture.

<table border="0" cellpadding="0" cellspacing="0" width="562">
	<colgroup>
		<col />
		<col />
		<col />
	</colgroup>
	<tbody>
		<tr height="21">
			<td height="21" style="height:21px;width:297px;">Cot-1 DNA&#160;</td>
			<td style="width:147px;">Invitrogen</td>
			<td style="width:119px;">18440-016</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;">Stratagene Prime-It Fluor Fluorescence Labeling Kit</td>
			<td style="width:147px;">Agilent</td>
			<td align="right" style="width:119px;">
			300380
			</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;">Herring sperm DNA Solution</td>
			<td style="width:147px;">Invitrogen</td>
			<td>15634-017</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;">Ethanol, 200 proof (absolute)</td>
			<td>Pharmco-AAPER</td>
			<td align="right">111000200</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;">Sodium acetate</td>
			<td>Sigma-Aldrich</td>
			<td style="width:119px;">S2889</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:297px;">Formamide deionized</td>
			<td>American Bioanalytical</td>
			<td>AB00600-00500</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;">Sodium citrate tribasic dihydrate</td>
			<td>Sigma-Aldrich</td>
			<td style="width:119px;">C8532</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:297px;">Bovine serum albumin</td>
			<td style="width:147px;">Lifeblood Medical</td>
			<td style="width:119px;">77110-100</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;">Dextran sulfate sodium salt from Leuconostoc spp.</td>
			<td>Sigma-Aldrich</td>
			<td style="width:119px;">D6001</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;">RPMI 1640</td>
			<td style="width:147px;">Invitrogen</td>
			<td style="width:119px;">A10491-01</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:297px;">Sucrose</td>
			<td>Sigma-Aldrich</td>
			<td style="width:119px;">S0389</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:297px;">PIPES</td>
			<td>Sigma-Aldrich</td>
			<td style="width:119px;">P6757</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;">Magnesium chloride hexahydrate</td>
			<td>Sigma-Aldrich</td>
			<td style="width:119px;">M0250</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:297px;">Triton X-100</td>
			<td>Sigma-Aldrich</td>
			<td style="width:119px;">T8787</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:297px;">Paraformaldehyde</td>
			<td>Sigma-Aldrich</td>
			<td align="right" style="width:119px;">76240</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:297px;">Sodium hydroxide</td>
			<td>Sigma-Aldrich</td>
			<td align="right" style="width:119px;">221465</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:297px;">Phosphate buffered saline</td>
			<td>Sigma-Aldrich</td>
			<td style="width:119px;">P4417</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;">VECTASHIELD Mounting Medium with DAPI</td>
			<td style="width:147px;">Vector Laboratories</td>
			<td style="width:119px;">H1200</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;">Ribonucleoside-vanadyl complex</td>
			<td>New England Biolabs</td>
			<td style="width:119px;">S1402S</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;">Illustra MicroSpin G-50 Columns</td>
			<td>GE Healthcare</td>
			<td style="width:119px;">27-5330-01</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:297px;">Microcentrifuge</td>
			<td style="width:147px;">Eppendorf</td>
			<td align="right" style="width:119px;">5424</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:297px;">Forceps</td>
			<td style="width:147px;">VWR</td>
			<td style="width:119px;">300-050</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:297px;">Microcentrifuge tubes</td>
			<td style="width:147px;">Bioexpress</td>
			<td style="width:119px;">C-3262-1</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:297px;">Cytospin 3</td>
			<td style="width:147px;">Shandon</td>
			<td style="width:119px;"></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:297px;">Coplin jar</td>
			<td style="width:147px;">Fisher</td>
			<td style="width:119px;">08-815</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;">Superfrost /Plus Microscope Slides</td>
			<td>Fisher</td>
			<td>12-550-15</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;">4-well dish</td>
			<td>Fisher</td>
			<td style="width:119px;">12-566-301</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;">Cover glass&#160;</td>
			<td>Fisher</td>
			<td style="width:119px;">12-544-G</td>
		</tr>
		<tr height="42">
			<td height="42" style="height:42px;width:297px;">Air incubator</td>
			<td style="width:147px;">Revolutionary Science</td>
			<td style="width:119px;">RS-IF-203</td>
		</tr>
	</tbody>
</table>

slide preparation method to preserve three-dimensional chromatin architecture of testicular germ cells

During testicular germ cell differentiation, the structure of nuclear chromatin dynamically changes. The following describes a method designed to preserve the three-dimensional chromatin arrangement of testicular germ cells found in mice; this method has been termed as the three-dimensional (3D) slide method. In this method, testicular tubules are directly treated with a permeabilization step that removes cytoplasmic material, followed by a fixation step that fixes nuclear materials. Tubules are then dissociated, the cell suspension is cytospun, and cells adhere to slides. This method improves sensitivity towards detection of subnuclear structures and is applicable for immunofluorescence, DNA, and RNA fluorescence in situ hybridization (FISH) and the combination of these detection methods. As an example of a possible application of the 3D slide method, a Cot-1 RNA FISH is shown to detect nascent RNAs. The 3D slide method will facilitate the detailed examination of spatial relationships between chromatin structure, DNA, and RNA during testicular germ cell differentiation.

A representative result of a 3D slide is shown in Figure 2. In this experiment, Cot-1 RNA FISH was performed to detect nascent transcription together with immunostaining using anti CBX1 and &#947;H2AX antibodies. To combine RNA FISH and immunostaining, immunostaining was performed first, followed by RNA FISH as described in3. CBX1 is a heterochromatin protein that localizes to pericentromeric heterochromatin and silent sex chromosomes in meiosis called an XY body (or sex body). &#947;H2AX is a...

Watch this Scientific Journal Video about Slide Preparation Method to Preserve Three-dimensional Chromatin Architecture of Testicular Germ Cells at JoVE.com

Slide Preparation Method to Preserve Three-dimensional Chromatin Architecture of Testicular Germ Cells

The material here describes a method developed to preserve the three-dimensional chromatin structure of testicular germ cells. This has been termed the three-dimensional (3D) slide method. This method improves sensitivity for detection of subnuclear structures and is applicable for immunofluorescence, DNA, and RNA fluorescence in situ hybridization (FISH).

During testicular germ cell differentiation, the structure of nuclear chromatin dynamically changes. The following describes a method designed to preserve ...

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Research

JoVE Journal

Biology

7.3K Views.  Cincinnati Children's Hospital Medical Center. Il materiale qui descrive un metodo sviluppato per preservare la struttura tridimensionale della cromatina delle cellule germinali testicolari. Questo è stato definito il metodo di scorrimento tridimensionale (3D). Questo metodo migliora la sensibilità per il rilevamento di strutture subnucleari ed è applicabile per l'immunofluorescenza, il DNA e la fluorescenza dell'RNA nell'ibridazione in situ (FISH).

Video: Slide Preparation Method to Preserve Three-dimensional Chromatin Architecture of Testicular Germ Cells

Microfabrication of Chip-sized Scaffolds for Three-dimensional Cell cultivation

Using microfabrication technologies is a prerequisite to create scaffolds of reproducible geometry and constant quality for three-dimensional cell cultivation. These technologies offer a wide spectrum of advantages not only for manufacturing but also for different applications. The size and shape of formed cell clusters can be influenced by the exact and reproducible architecture of the microfabricated scaffold and, therefore, the diffusion path length of nutrients and gases can be controlled.1 This is unquestionably a useful tool to prevent apoptosis and necrosis of cells due to an insufficient nutrient and gas supply or removal of cellular metabolites.
Our polymer chip, called CellChip, has the outer dimensions of 2 x 2 cm with a central microstructured area. This area is subdivided into an array of up to 1156 microcontainers with a typical dimension of 300 m edge length for the cubic design (cp- or cf-chip) or of 300 m diameter and depth for the round design (r-chip).2
So far, hot embossing or micro injection moulding (in combination with subsequent laborious machining of the parts) was used for the fabrication of the microstructured chips. Basically, micro injection moulding is one of the only polymer based replication techniques that, up to now, is capable for mass production of polymer microstructures.3 However, both techniques have certain unwanted limitations due to the processing of a viscous polymer melt with the generation of very thin walls or integrated through holes. In case of the CellChip, thin bottom layers are necessary to perforate the polymer and provide small pores of defined size to supply cells with culture medium e.g. by microfluidic perfusion of the containers.
In order to overcome these limitations and to reduce the manufacturing costs we have developed a new microtechnical approach on the basis of a down-scaled thermoforming process. For the manufacturing of highly porous and thin walled polymer chips, we use a combination of heavy ion irradiation, microthermoforming and track etching. In this so called "SMART" process (Substrate Modification And Replication by Thermoforming) thin polymer films are irradiated with energetic heavy projectiles of several hundred MeV introducing so-called "latent tracks" Subsequently, the film in a rubber elastic state is formed into three dimensional parts without modifying or annealing the tracks. After the forming process, selective chemical etching finally converts the tracks into cylindrical pores of adjustable diameter.

We present two processes for the microfabrication of porous polymer chips for three-dimensional cell cultivation. The first one is hot embossing combined with a solvent vapour welding process. The second one uses a recently developed microthermoforming process combined with ion track technology leading to a significant simplification of manufacture.

Using microfabrication technologies is a prerequisite to create scaffolds of reproducible geometry and constant quality for three-dimensional cell ...

Hi-C: A Method to Study the Three-dimensional Architecture of Genomes.

The three-dimensional folding of chromosomes compartmentalizes the genome and and can bring distant functional elements, such as promoters and enhancers, into close spatial proximity 2-6. Deciphering the relationship between chromosome organization and genome activity will aid in understanding genomic processes, like transcription and replication. However, little is known about how chromosomes fold. Microscopy is unable to distinguish large numbers of loci simultaneously or at high resolution. To date, the detection of chromosomal interactions using chromosome conformation capture (3C) and its subsequent adaptations required the choice of a set of target loci, making genome-wide studies impossible 7-10.
We developed Hi-C, an extension of 3C that is capable of identifying long range interactions in an unbiased, genome-wide fashion. In Hi-C, cells are fixed with formaldehyde, causing interacting loci to be bound to one another by means of covalent DNA-protein cross-links. When the DNA is subsequently fragmented with a restriction enzyme, these loci remain linked. A biotinylated residue is incorporated as the 5' overhangs are filled in. Next, blunt-end ligation is performed under dilute conditions that favor ligation events between cross-linked DNA fragments. This results in a genome-wide library of ligation products, corresponding to pairs of fragments that were originally in close proximity to each other in the nucleus. Each ligation product is marked with biotin at the site of the junction. The library is sheared, and the junctions are pulled-down with streptavidin beads. The purified junctions can subsequently be analyzed using a high-throughput sequencer, resulting in a catalog of interacting fragments.
Direct analysis of the resulting contact matrix reveals numerous features of genomic organization, such as the presence of chromosome territories and the preferential association of small gene-rich chromosomes. Correlation analysis can be applied to the contact matrix, demonstrating that the human genome is segregated into two compartments: a less densely packed compartment containing open, accessible, and active chromatin and a more dense compartment containing closed, inaccessible, and inactive chromatin regions. Finally, ensemble analysis of the contact matrix, coupled with theoretical derivations and computational simulations, revealed that at the megabase scale Hi-C reveals features consistent with a fractal globule conformation.

The Hi-C method allows unbiased, genome-wide identification of chromatin interactions (1). Hi-C couples proximity ligation and massively parallel sequencing. The resulting data can be used to study genomic architecture at multiple scales: initial results identified features such as chromosome territories, segregation of open and closed chromatin, and chromatin structure at the megabase scale.

The three-dimensional folding of chromosomes compartmentalizes the genome and and can bring distant functional elements, such as promoters and enhancers, ...

Isolation of Mammary Epithelial Cells from Three-dimensional Mixed-cell Spheroid Co-culture

While enormous efforts have gone into identifying signaling pathways and molecules involved in normal and malignant cell behaviors1-2, much of this work has been done using classical two-dimensional cell culture models, which allow for easy cell manipulation. It has become clear that intracellular signaling pathways are affected by extracellular forces, including dimensionality and cell surface tension3-4. Multiple approaches have been taken to develop three-dimensional models that more accurately represent biologic tissue architecture3. While these models incorporate multi-dimensionality and architectural stresses, study of the consequent effects on cells is less facile than in two-dimensional tissue culture due to the limitations of the models and the difficulty in extracting cells for subsequent analysis.
The important role of the microenvironment around tumors in tumorigenesis and tumor behavior is becoming increasingly recognized4. Tumor stroma is composed of multiple cell types and extracellular molecules. During tumor development there are bidirectional signals between tumor cells and stromal cells5. Although some factors participating in tumor-stroma co-evolution have been identified, there is still a need to develop simple techniques to systematically identify and study the full array of these signals6. Fibroblasts are the most abundant cell type in normal or tumor-associated stromal tissues, and contribute to deposition and maintenance of basement membrane and paracrine growth factors7.
Many groups have used three dimensional culture systems to study the role of fibroblasts on various cellular functions, including tumor response to therapies, recruitment of immune cells, signaling molecules, proliferation, apoptosis, angiogenesis, and invasion8-15. We have optimized a simple method for assessing the effects of mammary fibroblasts on mammary epithelial cells using a commercially available extracellular matrix model to create three-dimensional cultures of mixed cell populations (co-cultures)16-22. With continued co-culture the cells form spheroids with the fibroblasts clustering in the interior and the epithelial cells largely on the exterior of the spheroids and forming multi-cellular projections into the matrix. Manipulation of the fibroblasts that leads to altered epithelial cell invasiveness can be readily quantified by changes in numbers and length of epithelial projections23. Furthermore, we have devised a method for isolating epithelial cells out of three-dimensional co-culture that facilitates analysis of the effects of fibroblast exposure on epithelial behavior. We have found that the effects of co-culture persist for weeks after epithelial cell isolation, permitting ample time to perform multiple assays. This method is adaptable to cells of varying malignant potential and requires no specialized equipment. This technique allows for rapid evaluation of in vitro cell models under multiple conditions, and the corresponding results can be compared to in vivo animal tissue models as well as human tissue samples.

A simple method is described for analyzing effects of tissue fibroblasts on associated epithelial cells. The combination of this method and three-dimensional tissue culture can facilitate analysis of cells after isolation from 3D. The technique is applicable to cells of varying malignant potential, allowing systematic study of effects of tumor-associated stroma on tumor cells.

While enormous efforts have gone into identifying signaling pathways and molecules involved in normal and malignant cell behaviors1-2, much of this work ...

Simple and Efficient Technique for the Preparation of Testicular Cell Suspensions

Mammalian testes are very complex organs that contain over 30 different cell types, including somatic testicular cells and different stages of germline cells. This heterogeneity is an important drawback concerning the study of the bases of mammalian spermatogenesis, as pure or enriched cell populations in certain stages of sperm development are needed for most molecular analyses1.
 Various strategies such as Staput2,3, centrifugal elutriation1, and flow cytometry (FC)4,5 have been employed to obtain enriched or purified testicular cell populations in order to enable differential gene expression studies. 
It is required that cells are in suspension for most enrichment/ purification approaches. Ideally, the cell suspension will be representative of the original tissue, have a high proportion of viable cells and few multinucleates - which tend to form because of the syncytial nature of the seminiferous epithelium6,7 - and lack cell clumps1 . Previous reports had evidenced that testicular cell suspensions prepared by an exclusively mechanical method clumped more easily than trypsinized ones1 . On the other hand, enzymatic treatments with RNAses and/or disaggregating enzymes like trypsin and collagenase lead to specific macromolecules degradation, which is undesirable for certain downstream applications. The ideal process should be as short as possible and involve minimal manipulation, so as to achieve a good preservation of macromolecules of interest such as mRNAs. Current protocols for the preparation of cell suspensions from solid tissues are usually time-consuming, highly operator-dependent, and may selectively damage certain cell types1,8 . 
	The protocol presented here combines the advantages of a highly reproducible and extremely brief mechanical disaggregation with the absence of enzymatic treatment, leading to good quality cell suspensions that can be used for flow cytometric analysis and sorting4, and ulterior gene expression studies9 .

A novel protocol for the mechanical preparation of testicular cell suspensions from rodent material, avoiding enzymes and detergents, is described. The method is very simple, fast, reproducible, and renders good quality cell suspensions, which are suitable for flow sorting and RNA extraction.

Mammalian testes are very complex organs that contain over 30 different cell types, including somatic testicular cells and different stages of germline ...

Using High Resolution Computed Tomography to Visualize the Three Dimensional Structure and Function of Plant Vasculature

High resolution x-ray computed tomography (HRCT) is a non-destructive diagnostic imaging technique with sub-micron resolution capability that is now being used to evaluate the structure and function of plant xylem network in three dimensions (3D) (e.g. Brodersen et al. 2010; 2011; 2012a,b). HRCT imaging is based on the same principles as medical CT systems, but a high intensity synchrotron x-ray source results in higher spatial resolution and decreased image acquisition time. Here, we demonstrate in detail how synchrotron-based HRCT (performed at the Advanced Light Source-LBNL Berkeley, CA, USA) in combination with Avizo software (VSG Inc., Burlington, MA, USA) is being used to explore plant xylem in excised tissue and living plants. This new imaging tool allows users to move beyond traditional static, 2D light or electron micrographs and study samples using virtual serial sections in any plane. An infinite number of slices in any orientation can be made on the same sample, a feature that is physically impossible using traditional microscopy methods.
Results demonstrate that HRCT can be applied to both herbaceous and woody plant species, and a range of plant organs (i.e. leaves, petioles, stems, trunks, roots). Figures presented here help demonstrate both a range of representative plant vascular anatomy and the type of detail extracted from HRCT datasets, including scans for coast redwood (Sequoia sempervirens), walnut (Juglans spp.), oak (Quercus spp.), and maple (Acer spp.) tree saplings to sunflowers (Helianthus annuus), grapevines (Vitis spp.), and ferns (Pteridium aquilinum and Woodwardia fimbriata). Excised and dried samples from woody species are easiest to scan and typically yield the best images. However, recent improvements (i.e. more rapid scans and sample stabilization) have made it possible to use this visualization technique on green tissues (e.g. petioles) and in living plants. On occasion some shrinkage of hydrated green plant tissues will cause images to blur and methods to avoid these issues are described. These recent advances with HRCT provide promising new insights into plant vascular function.

High resolution x-ray computed tomography (HRCT) is a non-destructive diagnostic imaging technique that can be used to study the structure and function of plant vasculature in 3D. We demonstrate how HRCT facilitates exploration of xylem networks across a wide range of plant tissues and species.

High resolution x-ray computed tomography (HRCT) is a non-destructive diagnostic imaging technique with sub-micron resolution capability that is now being ...

An Efficient Method for Quantitative, Single-cell Analysis of Chromatin Modification and Nuclear Architecture in Whole-mount Ovules in Arabidopsis

In flowering plants, the somatic-to-reproductive cell fate transition is marked by the specification of spore mother cells (SMCs) in floral organs of the adult plant. The female SMC (megaspore mother cell, MMC) differentiates in the ovule primordium and undergoes meiosis. The selected haploid megaspore then undergoes mitosis to form the multicellular female gametophyte, which will give rise to the gametes, the egg cell and central cell, together with accessory cells. The limited accessibility of the MMC, meiocyte and female gametophyte inside the ovule is technically challenging for cytological and cytogenetic analyses at single cell level. Particularly, direct or indirect immunodetection of cellular or nuclear epitopes is impaired by poor penetration of the reagents inside the plant cell and single-cell imaging is demised by the lack of optical clarity in whole-mount tissues.
Thus, we developed an efficient method to analyze the nuclear organization and chromatin modification at high resolution of single cell in whole-mount embedded Arabidopsis ovules. It is based on dissection and embedding of fixed ovules in a thin layer of acrylamide gel on a microscopic slide. The embedded ovules are subjected to chemical and enzymatic treatments aiming at improving tissue clarity and permeability to the immunostaining reagents. Those treatments preserve cellular and chromatin organization, DNA and protein epitopes. The samples can be used for different downstream cytological analyses, including chromatin immunostaining, fluorescence in situ hybridization (FISH), and DNA staining for heterochromatin analysis. Confocal laser scanning microscopy (CLSM) imaging, with high resolution, followed by 3D reconstruction allows for quantitative measurements at single-cell resolution.

An Efficient Method for Quantitative, Single-cell Analysis of Chromatin Modification and Nuclear Architecture in Whole-mount Ovules in Arabidopsis

We provide here an efficient and reliable protocol for immunostaining, Fluorescence in&#160;situ Hybridization, DNA staining followed by quantitative, high-resolution imaging in whole-mount Arabidopsis thaliana ovules. This method was successfully used to analyze chromatin modifications and nuclear architecture.

In flowering plants, the somatic-to-reproductive cell fate transition is marked by the specification of spore mother cells (SMCs) in floral organs of the ...

FRET Imaging in Three-dimensional Hydrogels

Imaging of F&#246;rster resonance energy transfer (FRET)&#160;is a powerful tool for examining cell biology in real-time. Studies utilizing FRET commonly employ two-dimensional (2D) culture, which does not mimic the three-dimensional (3D) cellular microenvironment. A method to perform quenched emission FRET imaging using conventional widefield epifluorescence microscopy of cells within a 3D hydrogel environment is presented. Here an analysis method for ratiometric FRET probes that yields linear ratios over the probe activation range is described. Measurement of intracellular cyclic adenosine monophosphate (cAMP) levels is demonstrated in chondrocytes under forskolin stimulation using a probe for EPAC1 activation (ICUE1) and the ability to detect differences in cAMP signaling dependent on hydrogel material type, herein a photocrosslinking hydrogel (PC-gel, polyethylene glycol dimethacrylate) and a thermoresponsive hydrogel (TR-gel). Compared with 2D FRET methods, this method requires little additional work. Laboratories already utilizing FRET imaging in 2D can easily adopt this method to perform cellular studies in a 3D microenvironment. It can further be applied to high throughput drug screening in engineered 3D microtissues. Additionally, it is compatible with other forms of FRET imaging, such as anisotropy measurement and fluorescence lifetime imaging (FLIM), and with advanced microscopy platforms using confocal, pulsed, or modulated illumination.

F&#246;rster resonance energy transfer (FRET) imaging is a powerful tool for real-time cell biology studies. Here a method for FRET imaging cells in physiologic three-dimensional (3D) hydrogel microenvironments using conventional epifluorescence microscopy is presented. An analysis for ratiometric FRET probes that yields linear ratios over the activation range is described.

Imaging of F&#246;rster resonance energy transfer (FRET)&#160;is a powerful tool for examining cell biology in real-time. Studies utilizing FRET commonly ...

Three-dimensional Reconstruction of the Vascular Architecture of the Passive CLARITY-cleared Mouse Ovary

The ovary is the main organ of the female reproductive system and is essential for the production of female gametes and for controlling the endocrine system, but the complex structural relationships and three-dimensional (3D) vasculature architectures of the ovary are not well described. In order to visualize the 3D connections and architecture of blood vessels in the intact ovary, the first important step is to make the ovary optically clear. In order to avoid tissue shrinkage, we used the hydrogel fixation-based passive CLARITY (Clear Lipid-exchanged Acrylamide-hybridized Rigid Imaging/ Immunostaining/In situ-hybridization-compatible Tissue Hydrogel) protocol method to clear an intact ovary. Immunostaining, advanced multiphoton confocal microscopy, and 3D image-reconstructions were then used for the visualization of ovarian vessels and follicular capillaries. Using this approach, we showed a significant positive correlation (P &#60;0.01) between the length of the follicular capillaries and volume of the follicular wall.

Here we present an adaptation of the passive CLARITY and 3D reconstruction method for visualization of the ovarian vasculature and follicular capillaries in intact mouse ovaries.

The ovary is the main organ of the female reproductive system and is essential for the production of female gametes and for controlling the endocrine ...

Adipo-Clear: A Tissue Clearing Method for Three-Dimensional Imaging of Adipose Tissue

Adipose tissue plays a central role in energy homeostasis and thermoregulation. It is composed of different types of adipocytes, as well as adipocyte precursors, immune cells, fibroblasts, blood vessels, and nerve projections. Although the molecular control of cell type specification and how these cells interact have been increasingly delineated, a more comprehensive understanding of these adipose-resident cells can be achieved by visualizing their distribution and architecture throughout the whole tissue. Existing immunohistochemistry and immunofluorescence approaches to analyze adipose histology rely on thin paraffin-embedded sections. However, thin sections capture only a small portion of tissue; as a result, the conclusions can be biased by what portion of tissue is analyzed. We have therefore developed an adipose tissue clearing technique, Adipo-Clear, to permit comprehensive three-dimensional visualization of molecular and cellular patterns in whole adipose tissues. Adipo-Clear was adapted from iDISCO/iDISCO+, with specific modifications made to completely remove the lipid stored in the tissue while preserving native tissue morphology. In combination with light-sheet fluorescence microscopy, we demonstrate here the use of the Adipo-Clear method to obtain high-resolution volumetric images&#160;of an entire adipose tissue.

Due to the high lipid content, adipose tissue has been challenging to visualize using traditional histological methods. Adipo-Clear is a tissue clearing technique that allows robust labeling and high-resolution volumetric fluorescent imaging of adipose tissue. Here, we describe the methods for sample preparation, pretreatment, staining, clearing, and mounting for imaging.

Adipose tissue plays a central role in energy homeostasis and thermoregulation. It is composed of different types of adipocytes, as well as adipocyte ...

Single-Cell Resolution Three-Dimensional Imaging of Intact Organoids

Organoid technology, in vitro 3D culturing of miniature tissue, has opened a new experimental window for cellular processes that govern organ development and function as well as disease. Fluorescence microscopy has played a major role in characterizing their cellular composition in detail and demonstrating their similarity to the tissue they originate from. In this article, we present a comprehensive protocol for high-resolution 3D imaging of whole organoids upon immunofluorescent labeling. This method is widely applicable for imaging of organoids differing in origin, size and shape. Thus far we have applied the method to airway, colon, kidney, and liver organoids derived from healthy human tissue, as well as human breast tumor organoids and mouse mammary gland organoids. We use an optical clearing agent, FUnGI, which enables the acquisition of whole 3D organoids with the opportunity for single-cell quantification of markers. This three-day protocol from organoid harvesting to image analysis is optimized for 3D imaging using confocal microscopy.

The entire 3D structure and cellular content of organoids, as well as their phenotypic resemblance to the original tissue can be captured using the single-cell resolution 3D imaging protocol described here. This protocol can be applied to a wide range of organoids varying in origin, size and shape.

Organoid technology, in vitro 3D culturing of miniature tissue, has opened a new experimental window for cellular processes that govern organ development ...