This work is supported by the University of Virginia, the University of Virginia Cancer Center and The Thomas F. and Kate Miller Jeffress Memorial Trust. We thank the James E. Darnell Lab (Rockefeller University) the Robert Ross Lab (Fordham University) for cell lines.

PLANNING
The day before a ChIP experiment is planned, cells should be cultured so that a sufficient number is available. Assume that each ChIP assay will require ~1-1.5 x 107 cells. Always plan to do both the negative (IgG) and positive (pan histone antibody) controls and duplicate experiments. 
 Tip - For 2FTGH cells, each ChIP assay requires about one 15 cm tissue culture dish at 80% confluency.
PART 1: PREPARE CHROMATIN AND PERFORM ChIP
<ol>
 <li>Remove culture media and induce cells for the times required with 20 mL of 10% cosmic calf serum (CCS)/DMEM containing IFN-gamma at 5 ng/mL. Replace the media on the uninduced plates with 20 mL of 10% CCS/DMEM as well.</li>
 <li>In a fume hood, add 540 &mu;L 37% formaldehyde to 20 mL of media (1% final concentration) in the 15 cm dish. 
 Tip - Tilt plate and add the formaldehyde to the media pool - then rock plate to spread it evenly.
 </li>
 <li>Allow crosslinking to proceed for 10 minutes at room temperature.</li>
 <li>Add glycine to 0.125 M final concentration to stop crosslinking.</li>
 <li>Vacuum aspirate the media and wash cells once with 10 mL ice cold phosphate buffered saline (PBS).</li>
 <li>Collect cells with a cell scraper in ~ 7 mL PBS and combine cells (from 6 plates) that were treated identically in 50 mL conical tube on ice.</li>
 <li>Centrifuge (Beckman Coutler Allegra 12-R Centrifuge) at 1800 rpm at 4&deg;C for 5 minutes and aspirate the PBS. 
 Tip - Snap freeze the cell pellet if stopping here and store at -80&deg;C.</li>
 <li>Resuspend the cell pellet in 4 mL Swelling Buffer (25 mM HEPES pH 7.8, 1.5 mM MgCl2, 10 mM KCl, 0.1% NP40. Add 1 mM DTT, Complete protease inhibitors and chill on ice prior to use) and transfer to a 15 mL conical tube. 
 Tip - This swelling buffer volume is appropriate for a 6 plate pooling (~6-9 x 107 cells). More or less buffer might change the douncing efficiency.
 </li>
 <li>Incubate the cell suspension on ice for 10 minutes.</li>
 <li>Transfer suspension to a pre-chilled 15 mL douncer (Wheaton) and dounce 20 strokes with pestle A.</li>
 <li>Transfer dounced cells back to a 15 mL conical tube on ice.</li>
 <li>Centrifuge at 2500 rpm for 5 minutes at 4&deg;C and discard the supernatant.</li>
 <li>Resuspend the nuclear pellet (~ 200 &mu;L from 6 plates) in 3 mL (15 pellet volumes) of Sonication Buffer (50 mM HEPES pH 7.9, 140 mM NaCl, 1 mM EDTA, 1% Triton X-100, 0.1% Sodium deoxycholate, 0.1% SDS. Add Complete protease inhibitors and chill on ice just prior to use). 
 Tip - This sonication buffer volume is appropriate for a 6 plate pooling (~6-9 x 107 cells). More or less buffer might change the sonication efficiency.</li>
 <li>Sonicate nuclei suspension on ice for 10 cycles (20 seconds on/40 seconds off /amplitude setting of 8) using a Misonix Sonicator 3000 equipped with the microtip. This typically results in chromatin fragments averaging 200-1000 bps in size. 
 Tip - Because sonicators will vary, the sonication efficiency must be determined empirically. To do so, take aliquots of 20 &mu;L before sonication and after each sonication cycle. Heat these samples at 65&deg;C for 4 hours. Add DNA loading buffer and run a standard 1% agarose/TBE gel to visualize DNA fragments.) 
 </li>
 <li>Transfer sonicated material to an SS34 centrifuge tube and centrifuge for 20 minutes at 4&deg;C at 13000 rpm in an SS34 rotor (Sorvall RC6 Plus Centrifuge) to pellet what is usually a small amount of cell debris.</li>
 <li>Carefully transfer the supernatant to a 15 mL conical tube on ice.</li>
 <li>Pre-clear by adding 360 &mu;L Salmon Sperm DNA/Protein A or G agarose beads slurry and rocking at 4&deg;C for at least 30 minutes. 
 Tip - This step decreases the noise in the assay that arises from non-specific binding events.</li>
 <li>Centrifuge at 1000 rpm at 4&deg;C for 5 minutes to pellet the agarose beads.</li>
 <li>Transfer pre-cleared supernatant to another 15 mL conical tube on ice.</li>
 <li>Measure the A260 units of the pre-cleared chromatin and adjust the volume with Sonication Buffer to four (4) A260 units (0.2 mg/mL assuming 1 A260 unit = .050 mg/ml) 
 Tip - To measure the A260 units, dilute 10 &mu;L of pre-cleared chromatin in 190 &mu;L DDW; blank spectrophotometer with 10 &mu;L sonication buffer in 190 &mu;L DDW. 
 </li>
 <li>Save 75 &mu;L of the chromatin (at 4 A260 units) as the Input Sample and store at 20&deg;C until ready to reverse crosslinks. Tip - This step is crucial for data analysis. Do not neglect to take the input aliquot. </li>
 <li>Aliquot the prepared chromatin to 1.7 mL microfuge tubes on ice as 1 mL aliquots. Tip - If stopping here, snap freeze the prepared chromatin on dry ice and store at -80&deg;C. NB: stored chromatin can degrade, producing less than optimal results, so avoid if possible. </li>
 <li>Add the ChIP-grade antibodies to the induced and uninduced samples sets in duplicate. Add IgG (2 &mu;g) and pan Histone H3 antibody (15 &mu;L) as the negative and positive controls to induced and uninduced samples sets. 
 Tip - The amount of antibody to use must be determined empirically or see the supplier's product sheet for suggested amounts. Typically 1-2 &mu;g of a ChIP-grade antibody works well. The appropriate volume must be determined empirically for antibodies that are supplied as serum. 
 </li>
 <li>Rock all tubes overnight at 4&deg;C.</li>
</ol>
PART 2: COLLECT IMMUNOCOMPLEXES
<ol>
 <li>Add 60 &mu;L of Salmon Sperm DNA/Protein A or Protein G agarose beads slurry to all tubes. 
 Tip Use Protein A for rabbit polyclonal antibodies and Protein G for mouse monoclonal antibodies.</li>
 <li>Rock at 4&deg;C for at least 60 minutes.</li>
 <li>Pellet the immunocomplexes (agarose beads) by microfuging gently at 2000 rpm at 4&deg;C for 3 minutes.</li>
 <li>Aspirate the supernatant.</li>
 <li>Wash the immunocomplexes with 1 mL of each of the following Wash Buffers for 10 minutes with rocking at 4&deg;C. Microfuge for 3 minutes at 2000 rpm at 4&deg;C between each wash and aspirate supernatant. Keep samples chilled on ice. Add PMSF just prior to use.
 <ul>
 <li>Low Salt Wash - 0.1% SDS, 1% Triton X-100, 2 mM EDTA, 20 mM Tris-Cl, pH 8.0, 150 mM NaCl, 1 mM PMSF</li>
 <li>High Salt Wash - 0.1% SDS, 1% Triton X-100, 2 mM EDTA, 20 mM Tris-Cl, pH 8.0, 500 mM NaCl, 1 mM PMSF</li>
 <li>LiCl Wash - 0.25 M LiCl, 1% NP-40, 1% Sodium deoxycholate, 1 mM EDTA, 10 mM Tris-Cl, pH 8.0, 1 mM PMSF</li>
 <li>TE Wash - TWO Washes with TE Buffer -10 mM Tris-Cl, pH 8.0, 1 mM EDTA, 1 mM PMSF</li>
 </ul>
 </li>
 <li>Remove the final TE Buffer wash and to the beads, add 500 &mu;L Elution Buffer (50 mM Tris-Cl, pH 8.0, 10 mM EDTA, 1% SDS). 
 Tip - The Elution Buffer should be prepared freshly. 
 </li>
 <li>Vortex to mix agarose beads in Elution Buffer and heat for 30 minutes at 65&deg;C. 
 Tip - vortex each tube at least every 10 minutes during this 30 minutes.</li>
 <li>Microfuge for 30 seconds at 2000 rpm and transfer the eluent to a new microfuge tube. 
 Tip - During the elution, thaw your input samples and add 500 &mu;L Elution Buffer to each one. Include these samples in all steps going forward. 
 </li>
 <li>Add 5 M NaCl to a final concentration of 200 mM to all samples and vortex.</li>
 <li>Incubate at 65&deg;C overnight (or at least 4 hours).</li>
</ol>
PART 3: PURIFY ChIP'd AND INPUT DNA
<ol>
 <li>Microfuge all samples for 30 seconds to collect condensation on lids.</li>
 <li>Add 1&mu;L of RNAse A (10 U/&mu;L) to each tube and incubate at room temperature for 15 minutes.</li>
 <li>Add 10 &mu;L 0.5 M EDTA, 40 &mu;L 0.5 M Tris-Cl pH 6.5, 2 &mu;L Proteinase K (10 mg/mL) and incubate at 45&deg;C for 60 minutes. Tip Prepare a master mix of these reagents and add 52 &mu;L to each tube.</li>
 <li>Phenol/chloroform/isoamyl alcohol extract and then chloroform/isoamyl alcohol extract the samples. </li>
 <li>Add 2 &mu;L glycogen (25 &mu;g/&mu;L) and 0.1 volumes of 3M Na Acetate pH 5.2 and vortex.</li>
 <li>Add 2.5 volumes of 100% ethanol and vortex. </li>
 <li>Incubate at 20&deg;C overnight.</li>
</ol>
PART 4: PURIFY ChIP'd AND INPUT DNA CONTINUED
<ol>
 <li>Microfuge samples for a minimum of 20 minutes at 13000 rpm at 4&deg;C to precipitate the DNA/glycogen pellets.</li>
 <li>Wash with DNA/glycogen pellets with 1 mL of 70% Ethanol.</li>
 <li>Air dry the pellets or quickly dry in DNA Savant speed vacuum centrifuge. 
 Tip - Do not over dry the DNA.</li>
 <li>Resuspend DNA/glycogen pellets in 200 &mu;L TE Buffer.</li>
 <li>DNA (1 &mu;L) is ready for quantification via real-time PCR. Store remaining DNA at 20&deg;C. 
 Tip - Using more than 1 &mu;L of DNA can inhibit the real-time PCR reactions, so scale up with caution.</li>
</ol>
Part 5: REPRESENTATIVE RESULTS:
ChIP and Input DNA samples are quantified with Real-Time PCR 7,8 (Applied Biosystems 7500 Fast Real-Time PCR System) using primers specific to the gene locus of interest. Primers that target genomic sequence known to be enriched in or lacking in the histone modifications being assayed can be used as positive and negative controls as well. Data is presented as Percent of Input. The ChIP procedure should be wholly repeated with three biological replicates to ensure reported changes in histone modifications are statistically significant.
There are several important issues to consider when using real-time PCR to quantify DNA, including primer design, PCR efficiency, and the appropriate way to calculate the percent of input and normalization procedures. When profiling histone modification occupancy across a gene, the PCR efficiency must be consistent among all primer pairs. The real-time PCR system manufacturer can provide the necessary information and training.
Figure 1 shows representative results of chromatin immunoprecipitated during STAT1 activation of the IRF1 gene9, triggered by IFN-&gamma;.
<img src="/files/ftp_upload/2053/2053fig1.jpg" alt="Figure 1" /> 
 Figure 1. Occupancy of STAT1, RNA Polymerase II and H3K36me3 is dynamic during STAT1 activation of the IRF1 gene. (A, B, C) ChIP with &alpha;-H3K36me3, &alpha;-STAT1 and &alpha;-Pol II of chromatin collected from 2FTGH cells induced with IFN-&gamma; for 30 minutes (red squares), 1.5 hours (blue circles), 5 hours (green triangles) or uninduced (black diamonds). IgG is the negative control (grey crosses). (D) Pan H3 is the positive control and shows the histone occupancy across the locus in the induced (blue circles) and uninduced conditions (black diamonds). The dip around -5 bp is due to the nucleosome depletion that is found at transcription start sites.

<ol>
	<li>Levy, D., Darnell, J. E. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Signalling:+Stats:+transcriptional+control+and+biological+impact.">Signalling: Stats: transcriptional control and biological impact.</a> Nature Reviews Molecular Cell Biology. 3, 651-662 (2002).</li><li>Bromberg, J., Darnell, J. E. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=The+role+of+STATs+in+transcriptional+control+and+their+impact+on+cellular+function.">The role of STATs in transcriptional control and their impact on cellular function.</a> Oncogene. 19, 2468-2473 (2000).</li><li>Hu, X., Ivashkiv, L. B. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Cross-regulation+of+signaling+pathways+by+interferon-gamma:+implications+for+immune+responses+and+autoimmune+diseases.">Cross-regulation of signaling pathways by interferon-gamma: implications for immune responses and autoimmune diseases.</a> Immunity. 31, 539-550 (2009).</li><li>Campos, E. I., Reinberg, D. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Histones:+annotating+chromatin.">Histones: annotating chromatin.</a> Annu Rev Genet. 43, 559-599 (2009).</li><li>Kouzarides, T. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Chromatin+Modifications+and+Their+Function.">Chromatin Modifications and Their Function.</a> Cell. 128, 693-705 (2007).</li><li>Jenuwein, T., Allis, C. D. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Translating+the+histone+code.">Translating the histone code.</a> Science. 293, 1074-1080 (2001).</li><li>Wittwer, C. T., Herrmann, M. G., Moss, A. A., Rasmussen, R. P. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Continuous+fluorescence+monitoring+of+rapid+cycle+DNA+amplification.">Continuous fluorescence monitoring of rapid cycle DNA amplification.</a> Biotechniques. 22 (130-131), 134-138 (1997).</li><li>Higuchi, R., Dollinger, G., Walsh, P. S., Griffith, R. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Simultaneous+amplification+and+detection+of+specific+DNA+sequences.">Simultaneous amplification and detection of specific DNA sequences.</a> Biotechnology (N Y). 10, 413-417 (1992).</li><li>Kroger, A., Koster, M., Schroeder, K., Hauser, H., Mueller, P. P. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Activities+of+IRF-1.">Activities of IRF-1.</a> J Interferon Cytokine Res. 22, 5-14 (2002).</li><li>Ross, R. A., Spengler, B. A. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Human+neuroblastoma+stem+cells.">Human neuroblastoma stem cells.</a> Seminars in cancer biology. 17, 241-247 (2007).</li></ol>

No conflicts of interest declared.

The ChIP protocol outlined has been used successfully in the lab to assay more than twenty different histone modifications. In addition, we have characterized changes in the occupancy of transcription factors, histone-modifying enzymes, proteins that recognize histone modifications and the RNA Polymerase II transcription machinery, at several IFN-&gamma; induced genes. We have also used the procedure to characterize changes in histone modifications during the differentiation of a cancer stem cell10. <p cla...

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		<div>
		<table border="1">
		<thead>
		<tr>
		<th>Material Name</th>
		<th>Type</th>
		<th>Company</th>
		<th>Catalogue Number</th>
		<th>Comment</th>
		</tr>
		</thead>
		<tbody>
		
<tr>
<td>37% Formaldehyde</td>
<td>&nbsp;</td>
<td>Fisher</td>
<td>BP531-500</td>
<td>&nbsp;</td>
<tr>
<td>Chloroform/Isoamyl alcohol</td>
<td>&nbsp;</td>
<td>Acros</td>
<td>AC32715-5000</td>
<td>&nbsp;</td>
<tr>
<td>Complete Mini Protease Inhibitors</td>
<td>&nbsp;</td>
<td>Roche</td>
<td>1836153</td>
<td>&nbsp;</td>
<tr>
<td>Cosmic Calf Serum</td>
<td>&nbsp;</td>
<td>Hyclone</td>
<td>SH30087.04N</td>
<td>&nbsp;</td>
<tr>
<td>DMEM</td>
<td>&nbsp;</td>
<td>Hyclone</td>
<td>SH30243</td>
<td>&nbsp;</td>
<tr>
<td>DTT</td>
<td>&nbsp;</td>
<td>Sigma</td>
<td>D0632</td>
<td>&nbsp;</td>
<tr>
<td>EDTA</td>
<td>&nbsp;</td>
<td>Fisher</td>
<td>BP118-500</td>
<td>&nbsp;</td>
<tr>
<td>Ethanol</td>
<td>&nbsp;</td>
<td>Pharmco</td>
<td>zp1110EP</td>
<td>&nbsp;</td>
<tr>
<td>Glycine</td>
<td>&nbsp;</td>
<td>Roche</td>
<td>100149</td>
<td>&nbsp;</td>
<tr>
<td>Glycogen</td>
<td>&nbsp;</td>
<td>Roche</td>
<td>901393</td>
<td>&nbsp;</td>
<tr>
<td>HEPES</td>
<td>&nbsp;</td>
<td>Sigma</td>
<td>H3784</td>
<td>&nbsp;</td>
<tr>
<td>IFN-gamma</td>
<td>&nbsp;</td>
<td>R&amp;D Systems</td>
<td>285-IF-100</td>
<td>&nbsp;</td>
<tr>
<td>IgG</td>
<td>&nbsp;</td>
<td>Jackson Immunoresearch</td>
<td> 109-005-003</td>
<td>&nbsp;</td>
<tr>
<td>KCl</td>
<td>&nbsp;</td>
<td>MP Biologicals</td>
<td>&nbsp;</td>
<td>&nbsp;</td>
<tr>
<td>LiCl</td>
<td>&nbsp;</td>
<td>Sigma</td>
<td>L4408</td>
<td>&nbsp;</td>
<tr>
<td>MgCl2</td>
<td>&nbsp;</td>
<td>Sigma</td>
<td>M8266</td>
<td>&nbsp;</td>
<tr>
<td>Sodium Acetate</td>
<td>&nbsp;</td>
<td>Fisher</td>
<td>BP333-500</td>
<td>&nbsp;</td>
<tr>
<td>Deoxycholic Acid Sodium Salt</td>
<td>&nbsp;</td>
<td>Fisher</td>
<td>BP349-100</td>
<td>&nbsp;</td>
<tr>
<td>NaCl</td>
<td>&nbsp;</td>
<td>Fisher</td>
<td>7647-14-5</td>
<td>&nbsp;</td>
<tr>
<td>NP40</td>
<td>&nbsp;</td>
<td>US Biological</td>
<td>N3500</td>
<td>&nbsp;</td>
<tr>
<td>Anti-Histone H3, CT, pan</td>
<td>&nbsp;</td>
<td>Millipore</td>
<td>07-690</td>
<td>&nbsp;</td>
<tr>
<td>Phenol/chloroform/isoamyl</td>
<td>&nbsp;</td>
<td>Fisher</td>
<td>108-95-2</td>
<td>&nbsp;</td>
<tr>
<td>Phosphate Buffered Saline</td>
<td>&nbsp;</td>
<td>Fisher</td>
<td>7647-14-5</td>
<td>&nbsp;</td>
<tr>
<td>PMSF</td>
<td>&nbsp;</td>
<td>EMD</td>
<td>50-230-0316</td>
<td>&nbsp;</td>
<tr>
<td>Proteinase K</td>
<td>&nbsp;</td>
<td>5-Prime</td>
<td>2500140</td>
<td>&nbsp;</td>
<tr>
<td>RNAse A</td>
<td>&nbsp;</td>
<td>5-Prime</td>
<td>2500130</td>
<td>&nbsp;</td>
<tr>
<td>Salmon Sperm DNA/Protein A Agarose</td>
<td>&nbsp;</td>
<td>Millipore</td>
<td>16-157</td>
<td>&nbsp;</td>
<tr>
<td>Salmon Sperm DNA/Protein G Agaorse</td>
<td>&nbsp;</td>
<td>Millipore</td>
<td>16-201</td>
<td>&nbsp;</td>
<tr>
<td>SDS</td>
<td>&nbsp;</td>
<td>Fisher</td>
<td>BP166-500</td>
<td>&nbsp;</td>
<tr>
<td>Tris-Cl</td>
<td>&nbsp;</td>
<td>Sigma</td>
<td>T5941</td>
<td>&nbsp;</td>
<tr>
<td>Triton X-100</td>
<td>&nbsp;</td>
<td>Acros</td>
<td>327372500</td>
<td>&nbsp;</td>
<tr>
<td>Anti-K36me3</td>
<td>&nbsp;</td>
<td>Abcam</td>
<td>ab9050</td>
<td>&nbsp;</td>
<tr>
<td>Anti-STAT1</td>
<td>&nbsp;</td>
<td>Santa Cruz</td>
<td>sc-345X</td>
<td>&nbsp;</td>
<tr>
<td>Anti-RNA Polymerase II</td>
<td>&nbsp;</td>
<td>Santa Cruz</td>
<td>sc-899</td>
<td>&nbsp;</td>		</tbody>
		</table>
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chromatin immunoprecipitation (chip) to assay dynamic histone modification in activated gene expression in human cells

In response to a variety of extracellular ligands, the STAT (signal transducer and activator of transcription) transcription factors are rapidly recruited from their latent state in the cytoplasm to cell surface receptors where they are activated by phosphorylation at a single tyrosine residue1. They then dimerize and translocate to the nucleus to drive the transcription of target genes, affecting growth, differentiation, homeostasis and the immune response. Not surprisingly, given their widespread involvement in normal cell processes, dysregulation of STAT function contributes to human disease, particularly to cancers2 and autoimmune diseases3. It is well established that transcription is regulated by alterations to the chromatin template4,5. These alterations include the activities of ATP-dependent complexes, as well as covalent histone modifications and DNA methylation6. Because STAT activation of gene expression is both rapid and transient, it requires specific mechanisms for modulating the chromatin template at STAT-dependent gene loci. To define these mechanisms, we characterize the histone modifications and the enzymatic activities that generate them at gene loci that respond to STAT signaling. This protocol describes chromatin immunoprecipitation, a method that is valuable for the study of STAT signaling to chromatin in activated gene expression.

Watch this Scientific Journal Video about Chromatin Immunoprecipitation ChIP to Assay Dynamic Histone Modification in Activated Gene Expression in Human Cells at JoVE.com

Chromatin Immunoprecipitation ChIP to Assay Dynamic Histone Modification in Activated Gene Expression in Human Cells

This protocol describes how chromatin immunoprecipitation (ChIP) is used to study the dynamic alterations to the chromatin template that regulate transcription induced by a signal transduction pathway.

Chromatin Immunoprecipitation (ChIP) to Assay Dynamic Histone Modification in Activated Gene Expression in Human Cells

In response to a variety of extracellular ligands, the STAT (signal transducer and activator of transcription) transcription factors are rapidly recruited ...

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28.6K visualizações.  University of Virginia. Este protocolo descreve como imunoprecipitação da cromatina (chip) é usado para estudar as alterações dinâmicas ao modelo de cromatina que regulam a transcrição induzida por uma via de transdução de sinal.

Vídeo: Chromatin Immunoprecipitation ChIP to Assay Dynamic Histone Modification in Activated Gene Expression in Human Cells

Chromatin Immunoprecipitation from Human Embryonic Stem Cells

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

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

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

Using the Gene Pulser MXcell Electroporation System to Transfect Primary Cells with High Efficiency

It is becoming increasingly apparent that electroporation is the most effective way to introduce plasmid DNA or siRNA into primary cells. The Gene Pulser MXcell electroporation system and Gene Pulser electroporation buffer (Bio-Rad) were specifically developed to easily transfect nucleic acids into mammalian cells and difficult-to-transfect cells, such as primary and stem cells. We will demonstrate how to perform a simple experiment to quickly identify the best electroporation conditions. We will demonstrate how to run several samples through a range of electroporation conditions so that an experiment can be conducted at the same time as optimization is performed. We will also show how optimal conditions identified using 96-well electroporation plates can be used with standard electroporation cuvettes, facilitating the switch from electroporation plates to electroporation cuvettes while maintaining the same electroporation efficiency. In the video, we will also discuss some of the key factors that can lead to the success or failure of electroporation experiments.

This procedure shows how to use the Gene Pulser MXcell electroporation system to rapidly and easily identify the best electroporation conditions for mouse embryonic fibroblasts (MEFs) or other primary cells. Considerations for troubleshooting are also discussed in the associated video.

It is becoming increasingly apparent that electroporation is the most effective way to introduce plasmid DNA or siRNA into primary cells. The Gene Pulser ...

Robotics and Dynamic Image Analysis for Studies of Gene Expression in Plant Tissues

Gene expression in plant tissues is typically studied by destructive extraction of compounds from plant tissues for in vitro analyses. The methods presented here utilize the green fluorescent protein (gfp) gene for continual monitoring of gene expression in the same pieces of tissues, over time. The gfp gene was placed under regulatory control of different promoters and introduced into lima bean cotyledonary tissues via particle bombardment. Cotyledons were then placed on a robotic image collection system, which consisted of a fluorescence dissecting microscope with a digital camera and a 2-dimensional robotics platform custom-designed to allow secure attachment of culture dishes. Images were collected from cotyledonary tissues every hour for 100 hours to generate expression profiles for each promoter. Each collected series of 100 images was first subjected to manual image alignment using ImageReady to make certain that GFP-expressing foci were consistently retained within selected fields of analysis. Specific regions of the series measuring 300 x 400 pixels, were then selected for further analysis to provide GFP Intensity measurements using ImageJ software. Batch images were separated into the red, green and blue channels and GFP-expressing areas were identified using the threshold feature of ImageJ. After subtracting the background fluorescence (subtraction of gray values of non-expressing pixels from every pixel) in the respective red and green channels, GFP intensity was calculated by multiplying the mean grayscale value per pixel by the total number of GFP-expressing pixels in each channel, and then adding those values for both the red and green channels. GFP Intensity values were collected for all 100 time points to yield expression profiles. Variations in GFP expression profiles resulted from differences in factors such as promoter strength, presence of a silencing suppressor, or nature of the promoter. In addition to quantification of GFP intensity, the image series were also used to generate time-lapse animations using ImageReady. Time-lapse animations revealed that the clear majority of cells displayed a relatively rapid increase in GFP expression, followed by a slow decline. Some cells occasionally displayed a sudden loss of fluorescence, which may be associated with rapid cell death. Apparent transport of GFP across the membrane and cell wall to adjacent cells was also observed. Time lapse animations provided additional information that could not otherwise be obtained using GFP Intensity profiles or single time point image collections.

We report a method for introduction, tracking and quantitative analysis of GFP expression in plant cells. This method utilizes a custom-designed robotics system for semi-continuous image collection from large numbers of samples, over time. We also demonstrate the use of ImageJ and ImageReady for analysis of image series.

Gene expression in plant tissues is typically studied by destructive extraction of compounds from plant tissues for in vitro analyses. The methods ...

Using an Automated Cell Counter to Simplify Gene Expression Studies: siRNA Knockdown of IL-4 Dependent Gene Expression in Namalwa Cells

The use of siRNA mediated gene knockdown is continuing to be an important tool in studies of gene expression.  siRNA studies are being conducted not only to study the effects of downregulating single genes, but also to interrogate signaling pathways and other complex interaction networks.  These pathway analyses require both the use of relevant cellular models and methods that cause less perturbation to the cellular physiology.  Electroporation is increasingly being used as an effective way to introduce siRNA and other nucleic acids into difficult to transfect cell lines and primary cells without altering the signaling pathway under investigation. There are multiple critical steps to a successful siRNA experiment, and there are ways to simplify the work while improving the data quality at several experimental stages.  To help you get started with your siRNA mediated gene knockdown project, we will demonstrate how to perform a pathway study complete from collecting and counting the cells prior to electroporation through post transfection real-time PCR gene expression analysis.  The following study investigates the role of the transcriptional activator STAT6 in IL-4 dependent gene expression of CCL17 in a Burkitt lymphoma cell line (Namalwa).  The techniques demonstrated are useful for a wide range of siRNA-based experiments on both adherent and suspension cells.  We will also show how to streamline cell counting with the TC10 automated cell counter, how to electroporate multiple samples simultaneously using the MXcell electroporation system, and how to simultaneously assess RNA quality and quantity with the Experion automated electrophoresis system.

This procedure describes a quick and easy workflow to introduce siRNA into difficult to transfect cell lines and follow gene expression by real-time PCR. Use of an automated cell counter, multi-well electroporation plate, and automated electrophoresis station provide quick and reliable results without the need for expensive robotic handling.

The use of siRNA mediated gene knockdown is continuing to be an important tool in studies of gene expression.  siRNA studies are being conducted not only ...

An Allele-specific Gene Expression Assay to Test the Functional Basis of Genetic Associations

The number of significant genetic associations with common complex traits is constantly increasing. However, most of these associations have not been understood at molecular level. One of the mechanisms mediating the effect of DNA variants on phenotypes is gene expression, which has been shown to be particularly relevant for complex traits1.
This method tests in a cellular context the effect of specific DNA sequences on gene expression. The principle is to measure the relative abundance of transcripts arising from the two alleles of a gene, analysing cells which carry one copy of the DNA sequences associated with disease (the risk variants)2,3. Therefore, the cells used for this method should meet two fundamental genotypic requirements: they have to be heterozygous both for DNA risk variants and for DNA markers, typically coding polymorphisms, which can distinguish transcripts based on their chromosomal origin (Figure 1). DNA risk variants and DNA markers do not need to have the same allele frequency but the phase (haplotypic) relationship of the genetic markers needs to be understood. It is also important to choose cell types which express the gene of interest. This protocol refers specifically to the procedure adopted to extract nucleic acids from fibroblasts but the method is equally applicable to other cells types including primary cells.
DNA and RNA are extracted from the selected cell lines and cDNA is generated. DNA and cDNA are analysed with a primer extension assay, designed to target the coding DNA markers4. The primer extension assay is carried out using the MassARRAY (Sequenom)5 platform according to the manufacturer's specifications. Primer extension products are then analysed by matrix-assisted laser desorption/ionization time of-flight mass spectrometry (MALDI-TOF/MS). Because the selected markers are heterozygous they will generate two peaks on the MS profiles. The area of each peak is proportional to the transcript abundance and can be measured with a function of the MassARRAY Typer software to generate an allelic ratio (allele 1: allele 2) calculation. The allelic ratio obtained for cDNA is normalized using that measured from genomic DNA, where the allelic ratio is expected to be 1:1 to correct for technical artifacts. Markers with a normalised allelic ratio significantly different to 1 indicate that the amount of transcript generated from the two chromosomes in the same cell is different, suggesting that the DNA variants associated with the phenotype have an effect on gene expression. Experimental controls should be used to confirm the results.

Genetic associations often remain unexplained at a functional level. This method aims to assess the effect of phenotype-associated genetic markers on gene expression by analyzing cells heterozygous for transcribed SNPs. The technology allows accurate measurement by MALDI-TOF mass spectrometry to quantify allele-specific primer extension products.

The number of significant genetic associations with common complex traits is constantly increasing. However, most of these associations have not been ...

Chromatin Immunoprecipitation Assay for Tissue-specific Genes using Early-stage Mouse Embryos

Chromatin immunoprecipitation (ChIP) is a powerful tool to identify protein:chromatin interactions that occur in the context of living cells 1-3. This technique has been widely exploited in tissue culture cells, and to a lesser extent, in primary tissue. The application of ChIP to rodent embryonic tissue, especially at early times of development, is complicated by the limited amount of tissue and the heterogeneity of cell and tissue types in the embryo. Here we present a method to perform ChIP using a dissociated embryonic day 8.5 (E8.5) embryo. Sheared chromatin from a single E8.5 embryo can be divided into up to five aliquots, which allows the investigator sufficient material for controls and for investigation of specific protein:chromatin interactions.
We have utilized this technique to begin to document protein:chromatin interactions during the specification of tissue-specific gene expression programs. The heterogeneity of cell types in an embryo necessarily restricts the application of this technique because the result is the detection of protein:chromatin interactions without distinguishing whether the interactions occur in all, a subset of, or a single cell type(s). However, examination of tissue-specific genes during or following the onset of tissue-specific gene expression is feasible for two reasons. First, immunoprecipitation of tissue specific factors necessarily isolates chromatin from the cell type where the factor is expressed. Second, immunoprecipitation of coactivators and histones containing post-translational modifications that are associated with gene activation should only be found at genes and gene regulatory sequences in the cell type where the gene is being or has been activated. The technique should be applicable to the study of most tissue-specific gene activation events.
In the example described below, we utilized E8.5 and E9.5 mouse embryos to examine factor binding at a skeletal muscle specific gene promoter. Somites, which are the precursor tissues from which the skeletal muscles of the trunk and limbs will form, are present at E8.5-9.54,5. Myogenin is a regulatory factor required for skeletal muscle differentiation 6-9. The data demonstrate that myogenin is associated with its own promoter in E8.5 and E9.5 embryos. Because myogenin is only expressed in somites at this stage of development 6,10, the data indicate that myogenin interactions with its own promoter have already occurred in skeletal muscle precursor cells in E8.5 embryos.

We demonstrate a chromatin immunoprecipitation (ChIP) method to identify factor interactions at tissue-specific genes during or after the onset of tissue-specific gene expression in mouse embryonic tissue. This protocol should be widely applicable for the study of tissue-specific gene activation as it occurs during normal embryonic development.

Chromatin immunoprecipitation (ChIP) is a powerful tool to identify protein:chromatin interactions that occur in the context of living cells 1-3. This ...

In vitro Reconstitution of the Active T. castaneum Telomerase

Efforts to isolate the catalytic subunit of telomerase, TERT, in sufficient quantities for structural studies, have been met with limited success for more than a decade. Here, we present methods for the isolation of the recombinant Tribolium castaneum TERT (TcTERT) and the reconstitution of the active T. castaneum telomerase ribonucleoprotein (RNP) complex in vitro.
Telomerase is a specialized reverse transcriptase1 that adds short DNA repeats, called telomeres, to the 3' end of linear chromosomes2 that serve to protect them from end-to-end fusion and degradation. Following DNA replication, a short segment is lost at the end of the chromosome3 and without telomerase, cells continue dividing until eventually reaching their Hayflick Limit4. Additionally, telomerase is dormant in most somatic cells5 in adults, but is active in cancer cells6 where it promotes cell immortality7.
The minimal telomerase enzyme consists of two core components: the protein subunit (TERT), which comprises the catalytic subunit of the enzyme and an integral RNA component (TER), which contains the template TERT uses to synthesize telomeres8,9. Prior to 2008, only structures for individual telomerase domains had been solved10,11. A major breakthrough in this field came from the determination of the crystal structure of the active12, catalytic subunit of T. castaneum telomerase, TcTERT1.
Here, we present methods for producing large quantities of the active, soluble TcTERT for structural and biochemical studies, and the reconstitution of the telomerase RNP complex in vitro for telomerase activity assays. An overview of the experimental methods used is shown in Figure 1.

In vitro Reconstitution of the Active T. castaneum Telomerase

Efforts to isolate the catalytic subunit of telomerase, TERT, in sufficient quantities for structural studies, have been met with limited success for more than a decade. Here, we present methods for the isolation of the recombinant Tribolium castaneum TERT (TcTERT) and the reconstitution of the active T. castaneum telomerase ribonucleoprotein (RNP) complex in vitro.

Efforts to isolate the catalytic subunit of telomerase, TERT, in sufficient quantities for structural studies, have been met with limited success for more ...

Chromatin Immunoprecipitation (ChIP) using Drosophila tissue

Epigenetics remains a rapidly developing field that studies how the chromatin state contributes to differential gene expression in distinct cell types at different developmental stages. Epigenetic regulation contributes to a broad spectrum of biological processes, including cellular differentiation during embryonic development and homeostasis in adulthood. A critical strategy in epigenetic studies is to examine how various histone modifications and chromatin factors regulate gene expression. To address this, Chromatin Immunoprecipitation (ChIP) is used widely to obtain a snapshot of the association of particular factors with DNA in the cells of interest.
ChIP technique commonly uses cultured cells as starting material, which can be obtained in abundance and homogeneity to generate reproducible data. However, there are several caveats: First, the environment to grow cells in Petri dish is different from that in vivo, thus may not reflect the endogenous chromatin state of cells in a living organism. Second, not all types of cells can be cultured ex vivo. There are only a limited number of cell lines, from which people can obtain enough material for ChIP assay.
Here we describe a method to do ChIP experiment using Drosophila tissues. The starting material is dissected tissue from a living animal, thus can accurately reflect the endogenous chromatin state. The adaptability of this method with many different types of tissue will allow researchers to address a lot more biologically relevant questions regarding epigenetic regulation in vivo1, 2. Combining this method with high-throughput sequencing (ChIP-seq) will further allow researchers to obtain an epigenomic landscape.

Chromatin Immunoprecipitation ChIP using Drosophila tissue

Recently high-throughput sequencing technology has greatly increased sensitivity of Chromatin Immunoprecipitation (ChIP) experiment and prompted its application using purified cells or dissected tissue. Here we delineate a method to use ChIP technique with Drosophila tissue, which can address the endogenous chromatin state in a well-characterized biological system.

Epigenetics remains a rapidly developing field that studies how the chromatin state contributes to differential gene expression in distinct cell types at ...

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 ...

Generation of High Quality Chromatin Immunoprecipitation DNA Template for High-throughput Sequencing (ChIP-seq)

ChIP-sequencing (ChIP-seq) methods directly offer whole-genome coverage, where combining chromatin immunoprecipitation (ChIP) and massively parallel sequencing can be utilized to identify the repertoire of mammalian DNA sequences bound by transcription factors in vivo. "Next-generation" genome sequencing technologies provide 1-2 orders of magnitude increase in the amount of sequence that can be cost-effectively generated over older technologies thus allowing for ChIP-seq methods to directly provide whole-genome coverage for effective profiling of mammalian protein-DNA interactions.
For successful ChIP-seq approaches, one must generate high quality ChIP DNA template to obtain the best sequencing outcomes. The description is based around experience with the protein product of the gene most strongly implicated in the pathogenesis of type 2 diabetes, namely the transcription factor transcription factor 7-like 2 (TCF7L2). This factor has also been implicated in various cancers.
Outlined is how to generate high quality ChIP DNA template derived from the colorectal carcinoma cell line, HCT116, in order to build a high-resolution map through sequencing to determine the genes bound by TCF7L2, giving further insight in to its key role in the pathogenesis of complex traits.

Generation of High Quality Chromatin Immunoprecipitation DNA Template for High-throughput Sequencing ChIP-seq

The combination of chromatin immunoprecipitation and ultra-high-throughput sequencing (ChIP-seq) can identify and map protein-DNA interactions in a given tissue or cell line. Outlined is how to generate a high quality ChIP template for subsequent sequencing, using experience with the transcription factor TCF7L2 as an example.

ChIP-sequencing (ChIP-seq) methods directly  offer whole-genome coverage, where combining chromatin immunoprecipitation  (ChIP) and massively parallel ...