The work in this manuscript was supported by funds from Dept. of Radiation Oncology and Huntsman Cancer Institute and the National Institute of Health grant (R01-CA188520) to SB. I thank Danielle Johnson and Steven Bennett in my lab for demonstrating the protocol and explaining its benefits. I am grateful to Dr. Mahesh Chandrasekharan (Huntsman Cancer Institute) for critical comments on the manuscript.

1. Chromatin immunoprecipitation (ChIP) following BrdU Labeling
<ol>
	<li>Culture NIH3T3 cells in the presence of either DMSO or HDAC1,2-selective inhibitors as described previously6.</li>
	<li>Following treatment with DMSO or HDAC1,2 selective inhibitors, add BrdU to the cells in a sterile tissue culture hood. Incubate 2 x 106 NIH3T3 cells plated in 10 ml NIH3T3 media with a 20 &#181;M final concentration of bromodeoxyuridine (BrdU) for 60 min in a sterile 37 &#176;C tissue culture incubator.</li...

<ol>
	<li>Podhorecka, M., Skladanowski, A., Bozko, P. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=H2AX+Phosphorylation:+Its+Role+in+DNA+Damage+Response+and+Cancer+Therapy.">H2AX Phosphorylation: Its Role in DNA Damage Response and Cancer Therapy.</a> J nucleic acids. , (2010).</li><li>Groth, A., Rocha, W., Verreault, A., Almouzni, G. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Chromatin+challenges+during+DNA+replication+and+repair.">Chromatin challenges during DNA replication and repair.</a> 128, 721-733 (2007).</li><li>Demeret, C., Vassetzky, Y., Mechali, M. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Chromatin+remodelling+and+DNA+replication:+from+nucleosomes+to+loop+domains.">Chromatin remodelling and DNA replication: from nucleosomes to loop domains.</a> Oncogene. 20, 3086-3093 (2001).</li><li>Bhaskara, 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=Deletion+of+histone+deacetylase+3+reveals+critical+roles+in+S+phase+progression+and+DNA+damage+control.">Deletion of histone deacetylase 3 reveals critical roles in S phase progression and DNA damage control.</a> Mol Cell. 30, 61-72 (2008).</li><li>Bhaskara, S., Hiebert, S. W. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Role+for+histone+deacetylase+3+in+maintenance+of+genome+stability.">Role for histone deacetylase 3 in maintenance of genome stability.</a> Cell Cycle. 10, 727-728 (2011).</li><li>Bhaskara, 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=Histone+deacetylases+1+and+2+maintain+S-phase+chromatin+and+DNA+replication+fork+progression.">Histone deacetylases 1 and 2 maintain S-phase chromatin and DNA replication fork progression.</a> Epigenetics Chromatin. 6, 27 (2013).</li><li>Bhaskara, 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=Hdac3+is+essential+for+the+maintenance+of+chromatin+structure+and+genome+stability.">Hdac3 is essential for the maintenance of chromatin structure and genome stability.</a> Cancer Cell. 18, 436-447 (2010).</li><li>Johnson, D. P., 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=HDAC1,2+inhibition+impairs+EZH2-+and+BBAP-mediated+DNA+repair+to+overcome+chemoresistance+in+EZH2+gain-of-function+mutant+diffuse+large+B-cell+lymphoma.">HDAC1,2 inhibition impairs EZH2- and BBAP-mediated DNA repair to overcome chemoresistance in EZH2 gain-of-function mutant diffuse large B-cell lymphoma.</a> Oncotarget. 6, 4863-4887 (2015).</li><li>Bhaskara, S. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Histone+deacetylases+1+and+2+regulate+DNA+replication+and+DNA+repair:+potential+targets+for+genome+stability-mechanism-based+therapeutics+for+a+subset+of+cancers.">Histone deacetylases 1 and 2 regulate DNA replication and DNA repair: potential targets for genome stability-mechanism-based therapeutics for a subset of cancers.</a> Cell Cycle. 14, 1779-1785 (2015).</li><li>Taddei, A., Roche, D., Sibarita, J. B., Turner, B. M., Almouzni, G. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Duplication+and+maintenance+of+heterochromatin+domains.">Duplication and maintenance of heterochromatin domains.</a> J Cell Biol. 147, 1153-1166 (1999).</li><li>Alabert, C., Groth, A. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Chromatin+replication+and+epigenome+maintenance.">Chromatin replication and epigenome maintenance.</a> Nat Rev Mol Cell Biol. 13, 153-167 (2012).</li><li>Clapier, C. R., Cairns, B. R. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Regulation+of+ISWI+involves+inhibitory+modules+antagonized+by+nucleosomal+epitopes.">Regulation of ISWI involves inhibitory modules antagonized by nucleosomal epitopes.</a> Nature. 492, 280-284 (2012).</li><li>Sirbu, B. M., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Analysis+of+protein+dynamics+at+active,+stalled,+and+collapsed+replication+forks.">Analysis of protein dynamics at active, stalled, and collapsed replication forks.</a> Genes Dev. 25, 1320-1327 (2011).</li></ol>

The protocol described in this manuscript is a relatively quick method to demonstrate the presence of proteins or their post-translationally modified forms on newly replicated or nascent DNA. Additionally, this technique permits one to measure the association-dissociation kinetics of a protein or its modified form with nascent DNA. This technique is complementary to the elegant iPOND technology13. In the iPOND technology, newly synthesized DNA is labeled with ethyl deoxyuridine (EdU). A biotin conjugate is the...

Defective DNA repair and/or DNA replication are a major cause of genome instability, which can trigger cell death. A single unrepaired double strand break is sufficient to cause cell death1. Chromatin organization is transiently altered during both replication and repair2,3, and failure to maintain epigenetic information during these processes will result in a threat to genome integrity. Loss of HDAC3 or HDAC1,2 function impedes S-phase progression,&#160;DNA replication and repair leading to genotoxic stress (DNA damage) and cell&#160;death4-9. It is therefore a practical strategy to use selective HDAC inhibitors to disrupt replication, repair and chromatin in cancer cells and cause DNA damage, which in turn can stop growth and induce cell death selectively in rapidly growing cancer cells.
During DNA replication, chromatin is rapidly disassembled and then reassembled following DNA duplication. Newly synthesized histone H4 is acetylated at K5 and K12 residues (H4K5K12ac) and following deposition onto chromatin, they are rapidly deacetylated by histone deacetylases (HDACs)10,11. Failure of cells to maintain nascent chromatin integrity by histone deacetylation can lead to fork collapse, which in turn can result in DNA damage and cell death. We recently showed that selective inhibition of HDAC1,2 increases histone acetylation (H4K5ac, H4K12ac and H4K16ac) and inhibits SMARCA5 chromatin remodeler activity on nascent chromatin, which correlates with reduced replication fork progression, increased fork collapse and increased replication stress-induced DNA damage6. Thus, HDAC inhibitor treatment can alter nascent chromatin structure to trigger DNA damage and death very quickly in cancer cells, as these cells cycle rapidly and pass many times through the S-phase. It is therefore important to understand how HDACs function to regulate histone acetylation and protein binding to maintain DNA replication in mammalian cells.
To quantitatively measure the amount of histone acetylation and SMARCA5 chromatin remodeler associated with nascent DNA during DNA replication, we devised a modified ChIP assay called the BrdU-ChIP-Slot-Western technique. Following chromatin immunoprecipitation (ChIP) of a desired protein or histone modification, the amount of nascent DNA (labeled using thymidine analog, BrdU) in the ChIP sample can be detected using western analysis of BrdU-labeled ChIP DNA transferred onto a membrane using a Slot Blot apparatus. Using this technique, we showed that H4K16ac (a mark involved in chromatin packaging) and the ISWI family member SMARCA5 (SWI/SNF-related matrix-associated actin-dependent regulator of chromatin) chromatin remodeler are associated with nascent DNA in S-phase cells6. We also found that the nascent H4K16ac mark is deacetylated by HDAC1,2 during DNA replication6. H4K16ac inhibits chromatin remodeler activity of the ISWI family member SMARCA512. Hence, using the BrdU-CHIP-Slot-Western technique, we could connect the functions for HDAC1,2 in regulating chromatin remodeling during DNA replication. Hence, the BrdU-ChIP-Slot-Western Blot technique is a powerful approach to quantitatively measure the association and dissociation dynamics of proteins or their post-translational modifications that are bound to nascent DNA.

<table border="0" cellpadding="0" cellspacing="0" width="608">
	<tbody>
		<tr height="21">
			<td height="21" style="height:21px;width:216px;">Anti-BrdU (westerns)</td>
			<td style="width:107px;">BD Biosciences</td>
			<td style="width:119px;">B555627</td>
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			<td height="21" style="height:21px;">Anti-SMARCA5</td>
			<td>Abcam</td>
			<td style="width:119px;">ab3749</td>
			<td></td>
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			<td height="21" style="height:21px;width:216px;">Anti-H4K16ac</td>
			<td style="width:107px;">Active Motif</td>
			<td>39167</td>
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			<td height="21" style="height:21px;width:216px;">Zeta-Probe GT Membrane</td>
			<td style="width:107px;">Bio-Rad</td>
			<td style="width:119px;">162-0197</td>
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			<td height="21" style="height:21px;width:216px;">Formaldehyde</td>
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			<td style="width:119px;">BP531-500</td>
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			<td height="21" style="height:21px;width:216px;">Protein A agarose</td>
			<td style="width:107px;">Millipore</td>
			<td style="width:119px;">16-156</td>
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			<td height="21" style="height:21px;width:216px;">Rnase A</td>
			<td style="width:107px;">Qiagen</td>
			<td style="width:119px;">19101</td>
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			<td height="21" style="height:21px;width:216px;">Proteinase K</td>
			<td style="width:107px;">Sigma</td>
			<td style="width:119px;">P4850</td>
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			<td height="21" style="height:21px;width:216px;">PCR Purification Kit</td>
			<td style="width:107px;">Qiagen</td>
			<td style="width:119px;">28106</td>
			<td></td>
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			<td height="21" style="height:21px;width:216px;">Glycine</td>
			<td style="width:107px;">Sigma</td>
			<td style="width:119px;">G7403</td>
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			<td height="21" style="height:21px;width:216px;">Protease inhibitor cocktail</td>
			<td style="width:107px;">Roche</td>
			<td style="width:119px;">11836170001</td>
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			<td height="21" style="height:21px;width:216px;">BrdU</td>
			<td style="width:107px;">Sigma</td>
			<td style="width:119px;">B9285</td>
			<td></td>
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			<td height="21" style="height:21px;width:216px;">Rabbit IgG&#160;</td>
			<td style="width:107px;">Millipore</td>
			<td style="width:119px;">12-370</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:216px;">HEPES</td>
			<td style="width:107px;">Sigma</td>
			<td style="width:119px;">H3375</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:216px;">NaCl</td>
			<td style="width:107px;">Sigma</td>
			<td style="width:119px;">S-3014</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:216px;">Triton-X-100</td>
			<td style="width:107px;">Sigma</td>
			<td style="width:119px;">93443</td>
			<td></td>
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			<td height="42" style="height:42px;width:216px;">NP40</td>
			<td style="width:107px;">USB Corporation</td>
			<td style="width:119px;">19628</td>
			<td></td>
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			<td height="21" style="height:21px;width:216px;">Sodium deoxycholate</td>
			<td style="width:107px;">Sigma</td>
			<td style="width:119px;">D6750</td>
			<td></td>
		</tr>
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			<td height="21" style="height:21px;width:216px;">Sodium bicarbonate</td>
			<td style="width:107px;">Sigma</td>
			<td style="width:119px;">S-4019</td>
			<td></td>
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			<td height="42" style="height:42px;width:216px;">Ethanol</td>
			<td style="width:107px;">Decon Laboratories</td>
			<td style="width:119px;">04-355-222</td>
			<td></td>
		</tr>
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			<td height="21" style="height:21px;width:216px;">DEPC-treated water</td>
			<td style="width:107px;">Sigma</td>
			<td style="width:119px;">95284</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:216px;">Tris</td>
			<td style="width:107px;">Fisher</td>
			<td style="width:119px;">BP-152-5</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:216px;">EDTA</td>
			<td style="width:107px;">Invitrogen</td>
			<td style="width:119px;">15575-020</td>
			<td></td>
		</tr>
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			<td height="21" style="height:21px;width:216px;">SDS</td>
			<td style="width:107px;">Ambion</td>
			<td style="width:119px;">AM9820</td>
			<td></td>
		</tr>
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			<td height="42" style="height:42px;width:216px;">Sodium hydroxide</td>
			<td style="width:107px;">Mallinckrodt GenAR&#160;</td>
			<td style="width:119px;">MAL7772-06</td>
			<td></td>
		</tr>
		<tr height="42">
			<td height="42" style="height:42px;width:216px;">20X SSC</td>
			<td style="width:107px;">Life Technologies</td>
			<td style="width:119px;">15557-036</td>
			<td></td>
		</tr>
		<tr height="42">
			<td height="42" style="height:42px;width:216px;">Non-fat dry milk</td>
			<td style="width:107px;">Lab Scientific Inc</td>
			<td style="width:119px;">M0841</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:216px;">ECL</td>
			<td style="width:107px;">Thermo Fisher</td>
			<td style="width:119px;">80196</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:216px;">X-ray film</td>
			<td style="width:107px;">Genesee Sci</td>
			<td style="width:119px;">30-101</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:216px;">Developer</td>
			<td style="width:107px;">Konica Minolta</td>
			<td style="width:119px;">SRX-101A</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:216px;">UV Crosslinker</td>
			<td style="width:107px;">Stratagene</td>
			<td style="width:119px;">XLE-1000</td>
			<td></td>
		</tr>
		<tr height="84">
			<td height="84" style="height:84px;width:216px;">Sonicator</td>
			<td style="width:107px;">Branson Sonifier&#160; Digital Ultrasonic Cell Disruptor</td>
			<td style="width:119px;">Model: 450</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:216px;">Centrifuge</td>
			<td style="width:107px;">Eppendorf</td>
			<td style="width:119px;">Model: 5810R</td>
			<td></td>
		</tr>
		<tr height="42">
			<td height="42" style="height:42px;width:216px;">Water bath</td>
			<td style="width:107px;">Fisher Scientific Isotemp</td>
			<td style="width:119px;">Model: 2322</td>
			<td></td>
		</tr>
		<tr height="42">
			<td height="42" style="height:42px;width:216px;">NanoDrop 1000 spectrophotometer</td>
			<td style="width:107px;">ThermoScientific</td>
			<td style="width:119px;">Model: 1000</td>
			<td></td>
		</tr>
		<tr height="63">
			<td height="63" style="height:63px;width:216px;">Slot Blot apparatus&#160;</td>
			<td style="width:107px;">Schleicher and Schuell Minifold II</td>
			<td style="width:119px;">44-27570</td>
			<td></td>
		</tr>
		<tr height="63">
			<td height="63" style="height:63px;width:216px;">Tissue Culture Incubator</td>
			<td style="width:107px;">Thermo Scientific</td>
			<td style="width:119px;">Series II 3110 Water-Jacketed CO2 Incubators</td>
			<td></td>
		</tr>
	</tbody>
</table>

examination of proteins bound to nascent dna in mammalian cells using  brdu-chip-slot-western technique

Histone deacetylases 1 and 2 (HDAC1,2) localize to the sites of DNA replication. In the previous study, using a selective inhibitor and a genetic knockdown system, we showed novel functions for HDAC1,2 in replication fork progression and nascent chromatin maintenance in mammalian cells. Additionally, we used a BrdU-ChIP-Slot-Western technique that combines chromatin immunoprecipitation (ChIP) of bromo-deoxyuridine (BrdU)-labeled DNA with slot blot and Western analyses to quantitatively measure proteins or histone modification associated with nascent DNA.
Actively dividing cells were treated with HDAC1,2 selective inhibitor or transfected with siRNAs against Hdac1 and Hdac2 and then newly synthesized DNA was labeled with the thymidine analog bromodeoxyuridine (BrdU). The BrdU labeling was done at a time point when there was no significant cell cycle arrest or apoptosis due to the loss of HDAC1,2 functions. Following labeling of cells with BrdU, chromatin immunoprecipitation (ChIP) of histone acetylation marks or the chromatin-remodeler was performed with specific antibodies. BrdU-labeled input DNA and the immunoprecipitated (or ChIPed) DNA was then spotted onto a membrane using the slot blot technique and immobilized using UV. The amount of nascent DNA in each slot was then quantitatively assessed using Western analysis with an anti-BrdU antibody. The effect of loss of HDAC1,2 functions on the levels of newly synthesized DNA-associated histone acetylation marks and chromatin remodeler was then determined by normalizing the BrdU-ChIP signal obtained from the treated samples to the control samples.

To determine the specificity of HDAC1,2-selective inhibitors, Hdac1,2FL/FL and Hdac3FL/FL fibrosarcoma cells were used. Adenovirus-containing Cre recombinase (Ad-Cre) was used to delete Hdac1,2 and Hdac3 in these cells. Following Ad-Cre infection of Hdac1,2FL/FL cells, a robust increase in H4K5ac was observed. Treatment of Hdac1,2&#160;knockout cells with 233 or 898 did not result in...

Watch this Scientific Journal Video about Examination of Proteins Bound to Nascent DNA in Mammalian Cells Using  BrdU-ChIP-Slot-Western Technique at JoVE.com

Examination of Proteins Bound to Nascent DNA in Mammalian Cells Using  BrdU-ChIP-Slot-Western Technique

In this protocol, we describe a novel BrdU-ChIP-Slot-Western technique to examine proteins and histone modifications associated with newly synthesized or nascent DNA.

Histone deacetylases 1 and 2 (HDAC1,2) localize to the sites of DNA replication. In the previous study, using a selective inhibitor and a genetic ...

The overall goal of this procedure is to rapidly examine proteins bound to nascent DNA with accuracy using BrdU labeling and chromatin precipitation. This method can answer key questions in the replication, repair in chromatin field, such as, what proteins are bound to nascent DNA during DNA replication and what repair proteins are bound to nascent DNA during replication stress. The main advantage of this technique is that it is a relatively quick method to detect proteins bound to nascent DNA in a highly quantitative manner.To begin, set up cultures of two million NIH 3T3 cells in 10 milliliters of media with either DMSO or inhibitors. Also, add BrdU to a final concentration of 20 micromolar. Once plated, incubate the cells for 60 minutes.After an hour, crosslink the intracellular proteins to the DNA by adding formaldehyde directly to the culture medium to a concentration of 1%by volume. Then, let the cells incubate at room temperature for 10 minutes with agitation. After 10 minutes, quench the reaction by adding glycine to the media to 125 millimolar and continue the incubation for five more minutes.Next, collect the cells in PBS and wash them twice with PBS using centrifugation. The pellet can be frozen at 80 degrees Celsius per storage if desired. Now, prepare the lysate from the crosslinked cells, add 500 microliters of FA140 buffer supplemented with the protease inhibitor cocktail to the pellet and shear the chromatin using five 15-second pulses of sonication.Keep the cells chilled between the pulses. Then, run 10 microliters of sample out on a 1.5%gel to diagnose the efficiency of the shearing. Once sheared, centrifuge the samples for 10 minutes, and transfer the supernatant to a new tube.Then, estimate the protein concentration in the supernatant using a kit. Next, prepare a 50%slurry of Protein A Agarose beads with FA140 buffer containing protease inhibitor. Add 50 microliters of the slurry to each sample and incubate the samples at 4 degrees Celsius with constant end-over-end rotation for 30 minutes.After half an hour, spin down the samples for a minute around 1000 G's in a refrigerated centrifuge. Then, collect the supernatant containing the labelled chromatin. Before proceeding, save 1/10th of the extract at 20 degrees Celsius to later serve as the input control.To immunoprecipitate the chromatin, add either eight microliters of H4K16ac antibody or five micrograms of SMARCA5 antibody to the supernatants. Also, add five micrograms of rapid IgG to the extract that serves as the negative control sample. Incubate the chromatin at 4 degrees Celsius overnight on a rotisserie mixer.The next day, add 50 microliters of the prepared 50%Protein A Agarose slurry to the immunoprecipitations and incubate the mixtures for an hour at 4 degrees Celsius with rotation. After an hour, pellet the Agarose beads and carefully discard the supernatant. Now, wash the beads using end-over-end rotations at 4 degrees Celsius in three sequential buffers.First, use freshly prepared, low-salt immune complex wash buffer for five minutes. Second, use freshly prepared, high-salt immune complex wash buffer for five minutes. Third, use freshly prepared, Lithium chloride immune complex wash buffer for five minutes.Following washes, add elution solution to the samples as described in the text. Spin the samples and transfer the eluate to a new 1.5 milliliter tube. Now, incubate the samples at 65 degrees Celsius for 5 hours to reverse the crosslinking.Later, precipitate the DNA. Add one milliliter of 100%ethanol to the samples and mix well. Then, incubate them at 80 degrees Celsius for two to three hours or overnight at 20 degrees Celsius.After the precipitation, remove the ethanol with a 15-minute ceintrifugation at 18000 G's. Then, following the text protocol, wash the pellet, treat the samples with RNase, then Proteinase K, purify DNA as described in the text, and finally, store at 20 degrees Celsius. To begin, measure the yield of input and ChIP DNA on a spectrophotometer.Then, denature the samples. Add 2.5 volumes of 0.4 normal sodium hydroxide, briefly vortex and centrifuge and incubate the samples at room temperature for 30 minutes. Next, neutralize the denatured DNA by adding 175 microliters of one molar Tris hydochloride pH 6.8.Vortex, centrifuge, and place the samples on ice. Now, prepare serial dilutions of the input and immunoprecipitated DNA and proceed with the slot-blot assay as described in the text protocol. After the DNA on the blot has been UV immobilized, detect the BrdU on the slot blot using western blotting.First, block the membrane with 5%nonfat dry milk in PBST for an hour at room temperature to prevent nonspecific binding. Next, prepare a bath of 1%nonfat dry milk in PBST with added 1:500 diluted anti-BrdU antibody. Incubate the blot in this bath for three hours at room temperature on a shaker.Afterwards, wash the membrane with PBST three times. Then, submerge the blot in a 1:5000 dilution of HRP conjugated anti-mouse secondary antibody in PBST. Incubate at room temperature for an hour with shaking.Use three washes with PBST to remove the secondary and analyse the result. The BrdU H4K16ac ChIP slot western technique was used to determine the amount of H4K16ac associated with nascent DNA. A robust enrichment in H4K16ac associated with nascent DNA was observed when compared to the rapid IgG control.Following inhibition of HDAC1/2 with compound 233, an increase in nascent-DNA-associated H4K16ac was observed. The same result was obtained using compound 898. Finally, the level of SMARCA5 chromatin remodeler on nascent DNA was determined using the BrdU SMARCA5 ChIP slot western technique.Indeed, SMARCA5 associated with nascent DNA and compound 898 did not change the levels of SMARCA5. After watching this video, you should have a good understanding of the changes that occur in chromatin and chromatin-modifying enzymes during DNA replication in mammalian cells. After its development, this technique paved the way for researchers in the field of replication to explore chromatin changes on nascent DNA as well as dynamics of DNA repair proteins on nascent DNA.In the future, this technique could also be used to study the dynamics of the DNA damage response and DNA repair proteins at the stalled fork in addition to studying the histone modifications and chromatin modifying enzymes at the fork.

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Research

JoVE Journal

Biology

Long-term Imaging Mammalian Cells using Wide-Field Microscopy

DNA Transfection of Mammalian Skeletal Muscles using In Vivo Electroporation

A growing interest in cell biology is to express transgenically modified forms of essential proteins (e.g. fluorescently tagged constructs and/or mutant variants) in order to investigate their endogenous distribution and functional relevance. An interesting approach that has been implemented to fulfill this objective in fully differentiated cells is the in vivo transfection of plasmids by various methods into specific tissues such as liver1, skeletal muscle2,3, and even the brain4. We present here a detailed description of the steps that must be followed in order to efficiently transfect genetic material into fibers of the flexor digitorum brevis (FDB) and interosseus (IO) muscles of adult mice using an in vivo electroporation approach. The experimental parameters have been optimized so as to maximize the number of muscle fibers transfected while minimizing tissue damages that may impair the quality and quantity of the proteins expressed in individual fibers. We have verified that the implementation of the methodology described in this paper results in a high yield of soluble proteins, i.e. EGFP and ECFP3, calpain, FKBP12, &beta;2a-DHPR, etc. ; structural proteins, i.e. minidystrophin and &alpha;-actinin; and membrane proteins, i.e. &alpha;1s-DHPR, RyR1, cardiac Na/Ca2+ exchanger , NaV1.4 Na channel, SERCA1, etc., when applied to FDB, IO and other muscles of mice and rats. The efficient expression of some of these proteins has been verified with biochemical3 and functional evidence5. However, by far the most common confirmatory approach used by us are standard fluorescent microscopy and 2-photon laser scanning microscopy (TPLSM), which permit to identify not only the overall expression, but also the detailed intracellular localization, of fluorescently tagged protein constructs. The method could be equally used to transfect plasmids encoding for the expression of proteins of physiological relevance (as shown here), or for interference RNA (siRNA) aiming to suppress the expression of normally expressed proteins (not tested by us yet). It should be noted that the transfection of FDB and IO muscle fibers is particularly relevant for the investigation of mammalian muscle physiology since fibers enzymatically dissociated from these muscles are currently one of the most suitable models to investigate basic mechanisms of excitability and excitation-contraction coupling under current or voltage clamp conditions2,6-8.

DNA Transfection of Mammalian Skeletal Muscles using In Vivo Electroporation

We describe detailed procedures for the efficient transfection of plasmid DNA into the fibers of foot muscles of live mice using electroporation and the subsequent visualization of protein expression using fluorescence microscopy.

 A growing interest in cell biology is to express transgenically modified forms of essential proteins (e.g. fluorescently tagged constructs and/or mutant ...

Intranuclear Microinjection of DNA into Dissociated Adult Mammalian Neurons

Primary neuronal cell cultures are valuable tools to study protein function since they represent a more biologically relevant system compared to immortalized cell lines. However, the post-mitotic nature of primary neurons prevents effective heterologous protein expression using common procedures such as electroporation or chemically-mediated transfection. Thus, other techniques must be employed in order to effectively express proteins in these non-dividing cells.
In this article, we describe the steps required to perform intranuclear injections of cDNA constructs into dissociated adult sympathetic neurons. This technique, which has been applied to different types of neurons, can successfully induce heterologous protein expression. The equipment essential for the microinjection procedure includes an inverted microscope to visualize cells, a glass injection pipet filled with cDNA solution that is connected to a N2(g) pressure delivery system, and a micromanipulator. The micromanipulator coordinates the injection motion of microinjection pipet with a brief pulse of pressurized N2 to eject cDNA solution from the pipet tip. 
This technique does not have the toxicity associated with many other transfection methods and enables multiple DNA constructs to be expressed at a consistent ratio. The low number of injected cells makes the microinjection procedure well suited for single cell studies such as electrophysiological recordings and optical imaging, but may not be ideal for biochemical assays that require a larger number of cells and higher transfection efficiencies. Although intranuclear microinjections require an investment of equipment and time, the ability to achieve high levels of heterologous protein expression in a physiologically relevant environment makes this technique a very useful tool to investigate protein function.

Direct intranuclear injection of cDNA is an effective transfection technique for post-mitotic cells. This method provides high levels of heterologous protein expression from single or multiple cDNA constructs and enables protein function to be studied in a physiologically relevant environment with a variety of single cell assays.

Primary neuronal cell cultures are valuable tools to study protein function since they represent a more biologically relevant system compared to ...

Analysis of DNA Double-strand Break (DSB) Repair in Mammalian Cells

DNA double-strand breaks are the most dangerous DNA lesions that may lead to massive loss of genetic information and cell death. Cells repair DSBs using two major pathways: nonhomologous end joining (NHEJ) and homologous recombination (HR). Perturbations of NHEJ and HR are often associated with premature aging and tumorigenesis, hence it is important to have a quantitative way of measuring each DSB repair pathway. Our laboratory has developed fluorescent reporter constructs that allow sensitive and quantitative measurement of NHEJ and HR. The constructs are based on an engineered GFP gene containing recognition sites for a rare-cutting I-SceI endonuclease for induction of DSBs. The starting constructs are GFP negative as the GFP gene is inactivated by an additional exon, or by mutations. Successful repair of the I-SceI-induced breaks by NHEJ or HR restores the functional GFP gene. The number of GFP positive cells counted by flow cytometry provides quantitative measure of NHEJ or HR efficiency.

Analysis of DNA Double-strand Break DSB Repair in Mammalian Cells

This article describes GFP-based fluorescence in vivo assays that separately quantify homologous recombination and nonhomologous end joining in mammalian cells.

DNA double-strand breaks are the most dangerous DNA lesions that may lead to massive loss of genetic information and cell death.  Cells repair DSBs using ...

Visualization of DNA Replication in the Vertebrate Model System DT40 using the DNA Fiber Technique

Maintenance of replication fork stability is of utmost importance for dividing cells to preserve viability and prevent disease. The processes involved not only ensure faithful genome duplication in the face of endogenous and exogenous DNA damage but also prevent genomic instability, a recognized causative factor in tumor development.
Here, we describe a simple and cost-effective fluorescence microscopy-based method to visualize DNA replication in the avian B-cell line DT40. This cell line provides a powerful tool to investigate protein function in vivo by reverse genetics in vertebrate cells1. DNA fiber fluorography in DT40 cells lacking a specific gene allows one to elucidate the function of this gene product in DNA replication and genome stability. Traditional methods to analyze replication fork dynamics in vertebrate cells rely on measuring the overall rate of DNA synthesis in a population of pulse-labeled cells. This is a quantitative approach and does not allow for qualitative analysis of parameters that influence DNA synthesis. In contrast, the rate of movement of active forks can be followed directly when using the DNA fiber technique2-4. In this approach, nascent DNA is labeled in vivo by incorporation of halogenated nucleotides (Fig 1A). Subsequently, individual fibers are stretched onto a microscope slide, and the labeled DNA replication tracts are stained with specific antibodies and visualized by fluorescence microscopy (Fig 1B). Initiation of replication as well as fork directionality is determined by the consecutive use of two differently modified analogues. Furthermore, the dual-labeling approach allows for quantitative analysis of parameters that influence DNA synthesis during the S-phase, i.e. replication structures such as ongoing and stalled forks, replication origin density as well as fork terminations. Finally, the experimental procedure can be accomplished within a day, and requires only general laboratory equipment and a fluorescence microscope.

DT40, a model vertebrate genetic system, provides a powerful tool to analyze protein function. Here we describe a simple method that allows qualitative analysis of parameters that influence DNA synthesis during the S-phase in DT40 cells at the single molecule level.

Maintenance of replication fork stability is of utmost importance for dividing cells to preserve viability and prevent disease. The processes involved not ...

Analysis of Cell Cycle Position in Mammalian Cells

The regulation of cell proliferation is central to tissue morphogenesis during the development of multicellular organisms. Furthermore, loss of control of cell proliferation underlies the pathology of diseases like cancer. As such there is great need to be able to investigate cell proliferation and quantitate the proportion of cells in each phase of the cell cycle. It is also of vital importance to indistinguishably identify cells that are replicating their DNA within a larger population. Since a cell&prime;s decision to proliferate is made in the G1 phase immediately before initiating DNA synthesis and progressing through the rest of the cell cycle, detection of DNA synthesis at this stage allows for an unambiguous determination of the status of growth regulation in cell culture experiments.
DNA content in cells can be readily quantitated by flow cytometry of cells stained with propidium iodide, a fluorescent DNA intercalating dye. Similarly, active DNA synthesis can be quantitated by culturing cells in the presence of radioactive thymidine, harvesting the cells, and measuring the incorporation of radioactivity into an acid insoluble fraction. We have considerable expertise with cell cycle analysis and recommend a different approach. We Investigate cell proliferation using bromodeoxyuridine/fluorodeoxyuridine (abbreviated simply as BrdU) staining that detects the incorporation of these thymine analogs into recently synthesized DNA. Labeling and staining cells with BrdU, combined with total DNA staining by propidium iodide and analysis by flow cytometry1 offers the most accurate measure of cells in the various stages of the cell cycle. It is our preferred method because it combines the detection of active DNA synthesis, through antibody based staining of BrdU, with total DNA content from propidium iodide. This allows for the clear separation of cells in G1 from early S phase, or late S phase from G2/M. Furthermore, this approach can be utilized to investigate the effects of many different cell stimuli and pharmacologic agents on the regulation of progression through these different cell cycle phases.
In this report we describe methods for labeling and staining cultured cells, as well as their analysis by flow cytometry. We also include experimental examples of how this method can be used to measure the effects of growth inhibiting signals from cytokines such as TGF-&beta;1, and proliferative inhibitors such as the cyclin dependent kinase inhibitor, p27KIP1. We also include an alternate protocol that allows for the analysis of cell cycle position in a sub-population of cells within a larger culture5. In this case, we demonstrate how to detect a cell cycle arrest in cells transfected with the retinoblastoma gene even when greatly outnumbered by untransfected cells in the same culture. These examples illustrate the many ways that DNA staining and flow cytometry can be utilized and adapted to investigate fundamental questions of mammalian cell cycle control.

Determining the cell cycle position of a population of cells, or understanding how signals affect proliferation, can be readily measured by flow cytometry using this protocol. We report a simple experimental approach to staining cells and quantifying their position in the cell cycle.

The regulation of cell proliferation is central to tissue morphogenesis during the development of multicellular organisms. Furthermore, loss of control of ...

Isolation of Ribosome Bound Nascent Polypeptides in vitro to Identify Translational Pause Sites Along mRNA

The rate of translational elongation is non-uniform. mRNA secondary structure, codon usage and mRNA associated proteins may alter ribosome movement on the messagefor review see 1. However, it's now widely accepted that synonymous codon usage is the primary cause of non-uniform translational elongation rates1. Synonymous codons are not used with identical frequency. A bias exists in the use of synonymous codons with some codons used more frequently than others2. Codon bias is organism as well as tissue specific2,3. Moreover, frequency of codon usage is directly proportional to the concentrations of cognate tRNAs4. Thus, a frequently used codon will have higher multitude of corresponding tRNAs, which further implies that a frequent codon will be translated faster than an infrequent one. Thus, regions on mRNA enriched in rare codons (potential pause sites) will as a rule slow down ribosome movement on the message and cause accumulation of nascent peptides of the respective sizes5-8. These pause sites can have functional impact on the protein expression, mRNA stability and protein foldingfor review see 9. Indeed, it was shown that alleviation of such pause sites can alter ribosome movement on mRNA and subsequently may affect the efficiency of co-translational (in vivo) protein folding1,7,10,11. To understand the process of protein folding in vivo, in the cell, that is ultimately coupled to the process of protein synthesis it is essential to gain comprehensive insights into the impact of codon usage/tRNA content on the movement of ribosomes along mRNA during translational elongation.
Here we describe a simple technique that can be used to locate major translation pause sites for a given mRNA translated in various cell-free systems6-8. This procedure is based on isolation of nascent polypeptides accumulating on ribosomes during in vitro translation of a target mRNA. The rationale is that at low-frequency codons, the increase in the residence time of the ribosomes results in increased amounts of nascent peptides of the corresponding sizes. In vitro transcribed mRNA is used for in vitro translational reactions in the presence of radioactively labeled amino acids to allow the detection of the nascent chains. In order to isolate ribosome bound nascent polypeptide complexes the translation reaction is layered on top of 30% glycerol solution followed by centrifugation. Nascent polypeptides in polysomal pellet are further treated with ribonuclease A and resolved by SDS PAGE. This technique can be potentially used for any protein and allows analysis of ribosome movement along mRNA and the detection of the major pause sites. Additionally, this protocol can be adapted to study factors and conditions that can alter ribosome movement and thus potentially can also alter the function/conformation of the protein.

Isolation of Ribosome Bound Nascent Polypeptides in vitro to Identify Translational Pause Sites Along mRNA

A technique to identify translational pause sites on mRNA is described. This procedure is based on isolation of nascent polypeptides accumulating on ribosomes during in vitro translation of a target mRNA, followed by the size analysis of the nascent chains using a denaturing gel electrophoresis.

The rate of translational elongation is non-uniform. mRNA secondary structure, codon usage and mRNA associated proteins may alter ribosome movement on the ...

Using SecM Arrest Sequence as a Tool to Isolate Ribosome Bound Polypeptides

Extensive research has provided ample evidences suggesting that protein folding in the cell is a co-translational process1-5. However, the exact pathway that polypeptide chain follows during co-translational folding to achieve its functional form is still an enigma. In order to understand this process and to determine the exact conformation of the co-translational folding intermediates, it is essential to develop techniques that allow the isolation of RNCs carrying nascent chains of predetermined sizes to allow their further structural analysis.
SecM (secretion monitor) is a 170 amino acid E. coli protein that regulates expression of the downstream SecA (secretion driving) ATPase in the secM-secA operon6. Nakatogawa and Ito originally found that a 17 amino acid long sequence (150-FSTPVWISQAQGIRAGP-166) in the C-terminal region of the SecM protein is sufficient and necessary to cause stalling of SecM elongation at Gly165, thereby producing peptidyl-glycyl-tRNA stably bound to the ribosomal P-site7-9. More importantly, it was found that this 17 amino acid long sequence can be fused to the C-terminus of virtually any full-length and/or truncated protein thus allowing the production of RNCs carrying nascent chains of predetermined sizes7. Thus, when fused or inserted into the target protein, SecM stalling sequence produces arrest of the polypeptide chain elongation and generates stable RNCs both in vivo in E. coli cells and in vitro in a cell-free system. Sucrose gradient centrifugation is further utilized to isolate RNCs.
The isolated RNCs can be used to analyze structural and functional features of the co-translational folding intermediates. Recently, this technique has been successfully used to gain insights into the structure of several ribosome bound nascent chains10,11. Here we describe the isolation of bovine Gamma-B Crystallin RNCs fused to SecM and generated in an in vitro translation system.

We describe here a technique that is now routinely used to isolate stably bound ribosome nascent chain complexes (RNCs). This technique takes advantage of the discovery that a 17 amino acid long SecM "arrest sequence" can halt translation elongation in a prokaryotic (E. coli) system, when inserted into (or fused to the C-terminus) of virtually any protein.

Extensive research has provided ample evidences suggesting that protein folding in the cell is a co-translational process1-5. However, the exact pathway ...

Real-time Imaging of Single Engineered RNA Transcripts in Living Cells Using Ratiometric Bimolecular Beacons

The growing realization that both the temporal and spatial regulation of gene expression can have important consequences on cell function has led to the development of diverse techniques to visualize individual RNA transcripts in single living cells. One promising technique that has recently been described utilizes an oligonucleotide-based optical probe, ratiometric bimolecular beacon (RBMB), to detect RNA transcripts that were engineered to contain at least four tandem repeats of the RBMB target sequence in the 3&#8217;-untranslated region. RBMBs are specifically designed to emit a bright fluorescent signal upon hybridization to complementary RNA, but otherwise remain quenched. The use of a synthetic probe in this approach allows photostable, red-shifted, and highly emissive organic dyes to be used for imaging. Binding of multiple RBMBs to the engineered RNA transcripts results in discrete fluorescence spots when viewed under a wide-field fluorescent microscope. Consequently, the movement of individual RNA transcripts can be readily visualized in real-time by taking a time series of fluorescent images. Here we describe the preparation and purification of RBMBs, delivery into cells by microporation and live-cell imaging of single RNA transcripts.

Ratiometric bimolecular beacons (RBMBs) can be used to image single engineered RNA transcripts in living cells. Here, we describe the preparation and purification of RBMBs, delivery of RBMBs into cells by microporation and fluorescent imaging of single RNA transcripts in real-time.

The growing realization that both the temporal and spatial regulation of gene expression can have important consequences on cell function has led to the ...

Measurement of Heme Synthesis Levels in Mammalian Cells

Heme serves as the prosthetic group for a wide variety of proteins known as hemoproteins, such as hemoglobin, myoglobin and cytochromes. It is involved in various molecular and cellular processes such as gene transcription, translation, cell differentiation and cell proliferation. The biosynthesis levels of heme vary across different tissues and cell types and is altered in diseased conditions such as anemia, neuropathy and cancer. This technique uses [4-14C] 5-aminolevulinic acid ([14C] 5-ALA), one of the early precursors in the heme biosynthesis pathway to measure the levels of heme synthesis in mammalian cells. This assay involves incubation of cells with [14C] 5-ALA followed by extraction of heme and measurement of the radioactivity incorporated into heme. This procedure is accurate and quick. This method measures the relative levels of heme biosynthesis rather than the total heme content. To demonstrate the use of this technique the levels of heme biosynthesis were measured in several mammalian cell lines.

Altered intracellular heme levels are associated with common diseases such as cancer. Thus, there is a need to measure heme biosynthesis levels in diverse cells. The goal of this protocol is to provide a fast and sensitive method to measure and compare the levels of heme synthesis in different cells.

Heme serves as the prosthetic group for a wide variety of proteins known as hemoproteins, such as hemoglobin, myoglobin and cytochromes. It is involved in ...