Name: improved protocol for chromatin immunoprecipitation from mouse skeletal muscle
Uploaded: 2017-11-06T17:00:00
Description: Watch this Scientific Journal Video about Improved Protocol for Chromatin Immunoprecipitation from Mouse Skeletal Muscle at JoVE.com

We thank all the staff of the IGBMC high throughput sequencing facility, a member of &#34;France G&#233;nomique&#34; consortium (ANR10-INBS-09-08) and all IGBMC general services in particular the staff of the IGBMC animal facility. This work was supported by grants from the CNRS, the INSERM, the AFM, the Ligue Nationale contre le Cancer, the French state fund through the ANR under the programme Investissements d&#39;Avenir labelled ANR-10-IDEX-0002-02, the Labex INRT ANR-10-IDEX-0001-02 and the ANR-AR2GR-16-CE11-009-01. The funders had no role in study design, data collection and analysis, decision to publish, or preparation of the manuscript. S.J was supported by the Ligue Nationale contre le Cancer and the ANR-AR2GR-16-CE11-009-01, and V.U by the Minist&#232;re de l&#39;Enseignement et de la Recherche. ID is an &#39;&#233;quipe labellis&#233;e&#39; of the Ligue Nationale contre le Cancer.

Mice were kept in accordance with the institutional guidelines regarding the care and use of laboratory animals and in accordance with National Animal Care Guidelines (European Commission directive 86/609/CEE; French decree no.87-848). All procedures were approved by the French national ethics committee.
1. Isolation of Muscle Tissue
<ol>
	<li>Sacrifice one adult 6 to 8-week-old mouse by cervical dislocation. Sterlise the limb by rinsing it with 70% ethanol and dissect the hind limb muscles ...

<ol>
	<li>Johnson, D. S., Mortazavi, A., Myers, R. M., Wold, B. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Genome-wide+mapping+of+in+vivo+protein-DNA+interactions.">Genome-wide mapping of in vivo protein-DNA interactions.</a> Science. 316 (5830), 1497-1502 (2007).</li><li>Furey, T. S. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=ChIP-seq+and+beyond:+new+and+improved+methodologies+to+detect+and+characterize+protein-DNA+interactions.">ChIP-seq and beyond: new and improved methodologies to detect and characterize protein-DNA interactions.</a> Nat Rev Genet. 13 (12), 840-852 (2012).</li><li>Wade, J. T. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Mapping+Transcription+Regulatory+Networks+with+ChIP-seq+and+RNA-seq.">Mapping Transcription Regulatory Networks with ChIP-seq and RNA-seq.</a> Adv Exp Med Biol. 883, 119-134 (2015).</li><li>Alpern, D., 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=TAF4,+a+subunit+of+transcription+factor+II+D,+directs+promoter+occupancy+of+nuclear+receptor+HNF4A+during+post-natal+hepatocyte+differentiation.">TAF4, a subunit of transcription factor II D, directs promoter occupancy of nuclear receptor HNF4A during post-natal hepatocyte differentiation.</a> Elife. 3, e03613 (2014).</li><li>Martianov, I., 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=Cell-specific+occupancy+of+an+extended+repertoire+of+CREM+and+CREB+binding+loci+in+male+germ+cells.">Cell-specific occupancy of an extended repertoire of CREM and CREB binding loci in male germ cells.</a> BMC Genomics. 11, 530 (2010).</li><li>Achour, 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=Neuronal+identity+genes+regulated+by+super-enhancers+are+preferentially+down-regulated+in+the+striatum+of+Huntington's+disease+mice.">Neuronal identity genes regulated by super-enhancers are preferentially down-regulated in the striatum of Huntington's disease mice.</a> Hum Mol Genet. 24 (12), 3481-3496 (2015).</li><li>Joshi, 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=TEAD+transcription+factors+are+required+for+normal+primary+myoblast+differentiation+in+vitro+and+muscle+regeneration+in+vivo.">TEAD transcription factors are required for normal primary myoblast differentiation in vitro and muscle regeneration in vivo.</a> PLoS Genet. 13 (2), e1006600 (2017).</li><li>Ohkawa, Y., Mallappa, C., Dacwag-Vallaster, C. S., Imbalzano, A. N., DiMario, J. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=.">.</a> Myogenesis: Methods and protocols. 798, 517-531 (2012).</li><li>Dimauro, I., Pearson, T., Caporossi, D., Jackson, M. J. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=A+simple+protocol+for+the+subcellular+fractionation+of+skeletal+muscle+cells+and+tissue.">A simple protocol for the subcellular fractionation of skeletal muscle cells and tissue.</a> BMC Res Notes. 5, 513 (2012).</li><li>Thomas, J. L., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=PAK1+and+CtBP1+Regulate+the+Coupling+of+Neuronal+Activity+to+Muscle+Chromatin+and+Gene+Expression.">PAK1 and CtBP1 Regulate the Coupling of Neuronal Activity to Muscle Chromatin and Gene Expression.</a> Mol Cell Biol. 35 (24), 4110-4120 (2015).</li><li>Kuo, T., 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=Genome-wide+analysis+of+glucocorticoid+receptor-binding+sites+in+myotubes+identifies+gene+networks+modulating+insulin+signaling.">Genome-wide analysis of glucocorticoid receptor-binding sites in myotubes identifies gene networks modulating insulin signaling.</a> Proc Natl Acad Sci U S A. 109 (28), 11160-11165 (2012).</li><li>Whyte, W. A., 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=Master+transcription+factors+and+mediator+establish+super-enhancers+at+key+cell+identity+genes.">Master transcription factors and mediator establish super-enhancers at key cell identity genes.</a> Cell. 153 (2), 307-319 (2013).</li><li>Benhaddou, A., Keime, C., Ye, T., Morlon, A., Michel, I., Jost, B., Mengus, G., Davidson, I. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Transcription+factor+TEAD4+regulates+expression+of+myogenin+and+the+unfolded+protein+response+genes+during+C2C12+cell+differentiation.">Transcription factor TEAD4 regulates expression of myogenin and the unfolded protein response genes during C2C12 cell differentiation.</a> Cell Death and Differentiation. 19 (2), 220-231 (2011).</li><li>Cowling, B. 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=Reducing+dynamin+2+expression+rescues+X-linked+centronuclear+myopathy.">Reducing dynamin 2 expression rescues X-linked centronuclear myopathy.</a> J Clin Invest. 124 (3), 1350-1363 (2014).</li><li>. ChIP Analysis Available from: <a target="_blank" href="https://www.thermofisher.com/fr/fr/home/life-science/epigenetics-noncoding-rna-research/chromatin-remodeling/chromatin-immunoprecipitation-chip/chip-analysis.html">https://www.thermofisher.com/fr/fr/home/life-science/epigenetics-noncoding-rna-research/chromatin-remodeling/chromatin-immunoprecipitation-chip/chip-analysis.html</a> (2017)</li></ol>

Here we describe a novel protocol for preparing chromatin from adult mouse skeletal muscles and show that this chromatin is suitable for ChIP experiments that detect transcription factor binding and covalent histone modifications in the muscle fiber nuclei. This protocol involves several critical steps. The first is tissue disruption that can be performed either by dounce or by mechanical shearing. Mechanical shearing is faster and more reproducible, and is therefore the method of choice. Nevertheless, if no suitable app...

Chromatin immunoprecipitation (ChIP) coupled to quantitative polymerase chain reaction (qPCR) and high throughput sequencing (ChIP-seq) have become the methods of choice to study transcription and epigenetic regulation of gene expression in various tissues and cell-types1. This technique allows genome-wide profiling of covalent chromatin modifications, histone variant occupancy, and transcription factor binding2,3.
While performing ChIP from cultured cells is well established, ChIP from mammalian tissues remains more challenging. Preparing chromatin for ChIP involves several critical steps that need to be optimized for every tissue and cell type. Chromatin can be prepared from the cellular lysates of cultured cells or following purification of their nuclei. In the case of mammalian tissues, efficient lysis, formaldehyde fixation, and purification of nuclei are critical in order to ensure optimal recovery of the chromatin. Moreover, the choice of whether to fix the nuclei before or after their purification has to be experimentally determined. Despite these hurdles, ChIP has been successfully performed from tissues such as the liver, testis, or brain4,5,6. In the case of skeletal muscle, disruption of such a physically resistant tissue, which exhibits a high content of structural proteins, and isolation of its nuclei is particularly challenging. Given this specificity, protocols optimized for other tissues do not give satisfactory results for skeletal muscles.
Here we describe a protocol to isolate ChIP-grade chromatin from mouse skeletal muscle tissue that involves physically disrupting the tissue, formaldehyde fixation, and then the isolation of nuclei and sonication. The efficiency of this method to prepare chromatin suitable for ChIP from this tissue was demonstrated by performing ChIP-qPCR and ChIP-seq for various transcription factors, RNA polymerase II, and covalent histone modifications7.
This new technique is much faster than a previously reported protocol8 comprising long collagenase digestion steps during which time, changes in genomic localisation of transcription factors and alterations in gene expression may take place. The rapidity with which the nuclei are isolated and fixed makes the method described here particularly attractive to prepare chromatin that more faithfully captures the native genomic occupancy state. Moreover, although other methods for chromatin isolation or protein extraction from muscle tissue have have been described8,9,10 and used for ChIP-qPCR experiments on selected genes, no ChIP-seq data has been reported using them. The method reported here is suitable for transcription factor and histone modification ChIP-seq, and hence should be also suitable for 3/4C or HiC chromatin conformation capture applications.

<table>
	<tbody>
		<tr>
			<td>T 25 digital ULTRA-TURRAX</td>
			<td>T 18 ULTRA-TURRAX</td>
			<td>0009022800</td>
			<td></td>
		</tr>
		<tr>
			<td>PMSF</td>
			<td>SIGMA-ALDRICH CHIMIE SARL</td>
			<td>P7626-25G</td>
			<td></td>
		</tr>
		<tr>
			<td>Protease Inhibitor Cocktail-EDTA Free</td>
			<td>Roche Diagnostics</td>
			<td>11873580001</td>
			<td></td>
		</tr>
		<tr>
			<td>Protein G Sepharose beads</td>
			<td>SIGMA-ALDRICH CHIMIE</td>
			<td>P-3296</td>
			<td></td>
		</tr>
		<tr>
			<td>Proteinase K</td>
			<td>SIGMA-ALDRICH CHIMIE</td>
			<td>P-2308</td>
			<td></td>
		</tr>
		<tr>
			<td>Cell Strainers 70um</td>
			<td>Corning BV</td>
			<td>431751</td>
			<td></td>
		</tr>
		<tr>
			<td>Cell Strainers 40um</td>
			<td>Corning BV</td>
			<td>352340</td>
			<td></td>
		</tr>
		<tr>
			<td>Formaldehyde EM grade</td>
			<td>Euromedex</td>
			<td>15710-S</td>
			<td></td>
		</tr>
		<tr>
			<td>Rnase A</td>
			<td>Fischer Scientific</td>
			<td>12091039</td>
			<td></td>
		</tr>
		<tr>
			<td>Phenol:Chloroform:Isoamyl Alcohol 25:24:1</td>
			<td>SIGMA-ALDRICH CHIMIE</td>
			<td>P3803</td>
			<td></td>
		</tr>
		<tr>
			<td>BSA</td>
			<td>SIGMA-ALDRICH CHIMIE</td>
			<td>B4287-25G</td>
			<td></td>
		</tr>
		<tr>
			<td>yeast tRNA</td>
			<td>SIGMA-ALDRICH CHIMIE</td>
			<td>R5636</td>
			<td></td>
		</tr>
		<tr>
			<td>Glycogen Blue</td>
			<td>AMIBION</td>
			<td>AM9516</td>
			<td></td>
		</tr>
		<tr>
			<td>Pol II ChIP Antibody</td>
			<td>Santa Cruz</td>
			<td>SC-9001</td>
			<td></td>
		</tr>
		<tr>
			<td>H3K27ac ChIP Antibody</td>
			<td>Active Motif</td>
			<td>39133</td>
			<td></td>
		</tr>
		<tr>
			<td>Tead4 ChIP Antibody</td>
			<td>Aviva Systems Biology</td>
			<td>(ARP38276_P050)</td>
			<td></td>
		</tr>
		<tr>
			<td>IGEPAL</td>
			<td>SIGMA-ALDRICH CHIMIE</td>
			<td>I-3021</td>
			<td></td>
		</tr>
		<tr>
			<td>E220 Focused Ultrasonicator</td>
			<td>Covaris E220</td>
			<td></td>
			<td></td>
		</tr>
		<tr>
			<td>Name</td>
			<td>Company</td>
			<td>Catalog Number</td>
			<td>Comments</td>
		</tr>
		<tr>
			<td>Additional items</td>
			<td></td>
			<td></td>
			<td></td>
		</tr>
		<tr>
			<td>Scissors</td>
			<td></td>
			<td></td>
			<td></td>
		</tr>
		<tr>
			<td>Loose Dounce</td>
			<td></td>
			<td></td>
			<td></td>
		</tr>
		<tr>
			<td>15 ml and 50 ml falcon tubes</td>
			<td></td>
			<td></td>
			<td></td>
		</tr>
		<tr>
			<td>14 ml round bottom tubes</td>
			<td></td>
			<td></td>
			<td></td>
		</tr>
		<tr>
			<td>1.5 ml and 2 ml Eppendorf tubes</td>
			<td></td>
			<td></td>
			<td></td>
		</tr>
		<tr>
			<td>70 &#956;m and 40 &#956;m cell strainers (Corning)</td>
			<td></td>
			<td></td>
			<td></td>
		</tr>
	</tbody>
</table>

improved protocol for chromatin immunoprecipitation from mouse skeletal muscle

We describe an efficient and reproducible protocol for the preparation of chromatin from adult mouse skeletal muscle, a physically resistant tissue with a high content of structural proteins. Dissected limb muscles from adult mice are physically disrupted by mechanical homogenisation, or a combination of mincing and douncing, in a hypotonic buffer before formaldehyde fixation of the cell lysate. The fixed nuclei are purified by further cycles of mechanical homogenisation or douncing and sequential filtrations to remove cell debris. The purified nuclei can be sonicated immediately or at a later stage after freezing. The chromatin can be efficiently sonicated and is suitable for chromatin immunoprecipitation experiments, as illustrated by the profiles obtained for transcription factors, RNA polymerase II, and covalent histone modifications. The binding events detected using chromatin prepared by this protocol are predominantly those taking place in the muscle fiber nuclei despite the presence of chromatin from other fiber-associated satellite and endothelial cells. This protocol is therefore adapted to study gene regulation in the adult mouse skeletal muscle.

To isolate nuclei, we performed mechanical homogenization of the dissected and minced muscle tissue for either 15 or 45 s, at 18,000 and 22,000 rpm (see Table of Materials). In all conditions, nuclei could be separated from the tissue debris, but the yield was optimal using the lower speed (Figure 1A-B). Nuclei could also be prepared by douncing for 3 - 5 min (Figure 1A, and data not shown), but ...

Watch this Scientific Journal Video about Improved Protocol for Chromatin Immunoprecipitation from Mouse Skeletal Muscle at JoVE.com

Improved Protocol for Chromatin Immunoprecipitation from Mouse Skeletal Muscle

A novel protocol for the preparation of chromatin from adult mouse skeletal muscle adapted to the study of gene regulation in muscle fibers by chromatin immunoprecipitation is presented.

We describe an efficient and reproducible protocol for the preparation of chromatin from adult mouse skeletal muscle, a physically resistant tissue with a ...

The overall goal of this procedure is to prepare chromatin from adult mouse skeletal muscle. This method can help answer key questions in gene regulation and skeletal muscle fibers. The main advantage of this technique is that it allows preparation of ChIP-grade chromatin from mouse skeletal muscle.A physically resistant tissue with a high content of structural proteins. We first had the idea of this method when we were seeking to characterize the molecular mechanisms underlying gluco-articulated use muscle atrophy, which requires identification of gluco-articulated receptor, DNA-binding sites in mouse skeletal muscle fibers. Demonstrating the procedure will be Shilpy Joshi, a post-doc from our lab.To begin this procedure, recover frozen or freshly dissected hindlimb muscles. Subsequently, mince the muscles in a two-milliliter test tube, containing one milliliter of ice cold hypotonic buffer to a homogeneous preparation of small pieces, using fine scissors. Afterward, leave the tube shaking on a bench top agitator at four degrees Celsius for five to 10 minutes.Next, transfer the dissected tissue to a 14-milliliter round-bottom tube containing four milliliters of cold hypotonic buffer. Homogenize the minced tissue, using a mechanical tissue homogenizer for 15 to 30 seconds. Afterward, transfer the homogenate to a 15-milliliter tube.Add cold hypotonic buffer to result in 10 milliliters of the sample and fix the homogenate before proceeding with the next mouse. In this procedure, add formaldehyde to the sample to result in 1%final concentration. And then shake for 10 minutes at room temperature.Next, add glycine to result in a final concentration of 0.125 molar in each tube to stop fixation. And shake for five to 10 minutes at room temperature. After that, homogenize the fixed lysate, using a loose dounce.Then, transfer it to a 15-milliliter tube and centrifuge at 1000 g for five minutes at four degrees Celsius to obtain nuclei and cellular debris. After five minutes, remove the supernatant and re-suspend the pellet in five milliliters of fresh hypotonic buffer. Filter the lysate through a 70-micrometer cell strainer into a 50-milliliter tube.Using a pipette tip, wash the filter with one milliliter of cold hypotonic buffer. Following that, refilter the filtrate through a 40-micrometer cell strainer. Subsequently, transfer the filtrate to a 15-milliliter tube.And centrifuge at 1000 g for five minutes at four degrees Celsius to obtain the nuclear pellet. After discarding the supernatant, use one milliliter of hypotonic buffer to pool the three pellets and transfer to a 1.5 to two-milliliter tube. Centrifuge at 1000 g for five minutes.Next, assess the volume of the nuclear pellet by comparison with tubes containing a known volume of liquid and re-suspend it in sonication buffer up to three to four times of packed nuclear volume. Subsequently, sonicate the suspension for 10 to 15 minutes at four degrees Celsius, using a sonicator. Centrifuge the sonicated sample and transfer the chromatin supernatant to a fresh 1.5-milliliter tube.To de-crosslink, take 30 microliters of chromatin in a 1.5-milliliter test tube and add 20 microliters of five molar sodium chloride and 450 microliters of water. Complete the volume to 500 microliters and incubate at 65 degrees Celsius overnight. The next day, perform a treatment with one microliter of Proteinase K, 10 microliters of two molar tris at pH 6.8 and 10 microliters of 0.5 molar EDTA for one hour at 42 degrees Celsius.Then, perform a regular phenol-chloroform chloroform extraction and precipitate the DNA with one volume of sodium acetate and two volumes of 100%ethanol for one hour at negative 80 degrees Celsius or overnight at negative 20 degrees Celsius. Next, pellet the DNA by centrifugation at 13, 500 g for 15 minutes. Decant the supernatant and wash the pellet thoroughly with cold 70%ethanol and centrifuge again for five minutes.Then decant the supernatant and air-dry the pellet. After that re-suspend the pellet in the original volume of tris HCl EDTA buffer. Measure the DNA concentration in a spectrophotometer by absorbents at 260 nanometers, 280 nanometers.Subsequently, pipet 500 to 1000 nanograms of DNA together with a DNA-sized ladder on separate lanes of a 1.5%agarose gel. And perform electrophoresis to assess the fragment size of chromatin. To optimize, homogenization was performed for either 15 seconds or 45 seconds at two speeds, 18, 000 and 22, 000 RPM.In all conditions, nuclei could be separated from the tissue debris, but the yield was optimal using lower speed. Nuclei could also be prepared by douncing for three to five minutes. But mechanical homogenization is the method of choice as optimal yields of nuclei can be achieved in as little as 15 seconds, allowing an important gain of time, especially if multiple samples have to be processed.Using this protocol, up to 2.7 times 10 to the seven nuclei from 500 milligrams of tissue can be isolated to generate 100 micrograms of chromatin. Chromatin prepared in this way gives clean, high-quality results in ChIP sequencing experiments. As illustrated by the high levels of acetylated K27 of histone H3 and RNA polymerase 2 at the muscle-expressed Desmond locus.Specificity for muscle fiber is shown by low or absent signal at the Pecam1 and Vcam1 loci that are not expressed in muscle. While attempting this procedure, it is important to properly immerse the homogenizer probe in the sample to avoid frothing, to clean the probe between samples, and to optimize the chromatin fragmentation. Chromatin prepared in this way has been successfully used for ChIP's sake to map genome-wide transcription factor occupancy and should also be suitable for chromatin confirmation capture techniques.After it's development, this technique paved the way for research in the field of genomics, to explore gene regulation in skeletal muscle from mice. The procedure can also be applied to muscle from rat and biopsies from human patients. After watching this video, you should have a good understanding of how to use mechanical homogenization, followed by purification of formaldehyde-fixed nuclei to prepare chromatin from skeletal muscle for immunoprecipitation.Don't forget that working with formaldehyde, phenol, chloroform, and Proteinase K can be hazardous. Precautions such as wearing of gloves and glasses should be taken. Steps involving these reagents should be performed under a hood.

improved-protocol-for-chromatin-immunoprecipitation-from-mouse

Research

JoVE Journal

Biochemistry

Optimized Protocol for the Extraction of Proteins from the Human Mitral Valve

Analysis of the cellular proteome can help to elucidate the molecular mechanisms underlying diseases due to the development of technologies that permit the large-scale identification and quantification of the proteins present in complex biological systems.The knowledge gained from a proteomic approach can potentially lead to a better understanding of the pathogenic mechanisms underlying diseases, allowing for the identification of novel diagnostic and prognostic disease markers, and, hopefully, of therapeutic targets. However, the cardiac mitral valve represents a very challenging sample for proteomic analysis because of the low cellularity in proteoglycan and collagen-enriched extracellular matrix. This makes it challenging to extract proteins for a global proteomic analysis. This work describes a protocol that is compatible with subsequent protein analysis, such as quantitative proteomics and immunoblotting. This can allow for the correlation of data concerning protein expression with data on quantitative mRNA expression and non-quantitative immunohistochemical analysis. Indeed, these approaches, when performed together, will lead to a more comprehensive understanding of the molecular mechanisms underlying diseases, from mRNA to post-translational protein modification. Thus, this method can be relevant to researchers interested in the study of cardiac valve physiopathology.

The protein composition of the human mitral valve is still partially unknown, because its analysis is complicated by low cellularity and therefore by low protein biosynthesis. This work provides a protocol to efficiently extract protein for the analysis of the mitral valve proteome.

Analysis of the cellular proteome can help to elucidate the molecular mechanisms underlying diseases due to the development of technologies that permit ...

A Filtration-based Method of Preparing High-quality Nuclei from Cross-linked Skeletal Muscle for Chromatin Immunoprecipitation

Chromatin immunoprecipitation (ChIP) is a powerful method to determine protein binding to chromatin DNA. Fiber-rich skeletal muscle, however, has been a challenge for ChIP due to technical difficulty in isolation of high-quality nuclei with minimal contamination of myofibrils. Previous protocols have attempted to purify nuclei before cross-linking, which incurs the risk of altered DNA-protein interaction during the prolonged nuclei preparation process. In the current protocol, we first cross-linked the skeletal muscle tissue collected from mice, and the tissues were minced and sonicated. Since we found that ultracentrifugation was not able to separate nuclei from myofibrils using cross-linked muscle tissue, we devised a sequential filtration procedure to obtain high-quality nuclei devoid of significant myofibril contamination. We subsequently prepared chromatin by using an ultrasonicator, and ChIP assays with anti-BMAL1 antibody revealed robust circadian binding pattern of BMAL1 to target gene promoters. This filtration protocol constitutes an easily applicable method to isolate high-quality nuclei from cross-linked skeletal muscle tissue, allowing consistent sample processing for circadian and other time-sensitive studies. In combination with next-generation sequencing (NGS), our method can be deployed for various mechanistic and genomic studies focusing on skeletal muscle function.

We present a filtration-based protocol to isolate high-quality nuclei from cross-linked mouse skeletal muscle wherein we removed the need for ultracentrifugation, making it easily applicable. We show that chromatin prepared from the nuclei is suitable for chromatin immunoprecipitation and likely chromatin immunoprecipitation sequencing studies.

Chromatin immunoprecipitation (ChIP) is a powerful method to determine protein binding to chromatin DNA. Fiber-rich skeletal muscle, however, has been a ...

Quantification of Protein Interaction Network Dynamics using Multiplexed Co-Immunoprecipitation

Dynamic protein-protein interactions control cellular behavior, from motility to DNA replication to signal transduction. However, monitoring dynamic interactions among multiple proteins in a protein interaction network is technically difficult. Here, we present a protocol for Quantitative Multiplex Immunoprecipitation (QMI), which allows quantitative assessment of fold changes in protein interactions based on relative fluorescence measurements of Proteins in Shared Complexes detected by Exposed Surface epitopes (PiSCES). In QMI, protein complexes from cell lysates are immunoprecipitated onto microspheres, and then probed with a labeled antibody for a different protein in order to quantify the abundance of PiSCES. Immunoprecipitation antibodies are conjugated to different MagBead spectral regions, which allows a flow cytometer to differentiate multiple parallel immunoprecipitations and simultaneously quantify the amount of probe antibody associated with each. QMI does not require genetic tagging and can be performed using minimal biomaterial compared to other immunoprecipitation methods. QMI can be adapted for any defined group of interacting proteins, and has thus far been used to characterize signaling networks in T cells and neuronal glutamate synapses. Results have led to new hypothesis generation with potential diagnostic and therapeutic applications. This protocol includes instructions to perform QMI, from the initial antibody panel selection through to running assays and analyzing data. The initial assembly of a QMI assay involves screening antibodies to generate a panel, and empirically determining an appropriate lysis buffer. The subsequent reagent preparation includes covalently coupling immunoprecipitation antibodies to MagBeads, and biotinylating probe antibodies so they can be labeled by a streptavidin-conjugated fluorophore. To run the assay, lysate is mixed with MagBeads overnight, and then beads are divided and incubated with different probe antibodies, and then a fluorophore label, and read by flow cytometry. Two statistical tests are performed to identify PiSCES that differ significantly between experimental conditions, and results are visualized using heatmaps or node-edge diagrams.

Quantitative Multiplex Immunoprecipitation (QMI) uses flow cytometry for sensitive detection of differences in the abundance of targeted protein-protein interactions between two samples. QMI can be performed using a small amount of biomaterial, does not require genetically engineered tags, and can be adapted for any previously defined protein interaction network.

Dynamic protein-protein interactions control cellular behavior, from motility to DNA replication to signal transduction. However, monitoring dynamic ...

Label-Free Immunoprecipitation Mass Spectrometry Workflow for Large-scale Nuclear Interactome Profiling

Immunoaffinity purification mass spectrometry (IP-MS) has emerged as a robust quantitative method of identifying protein-protein interactions. This publication presents a complete interaction proteomics workflow designed for identifying low abundance protein-protein interactions from the nucleus that could also be applied to other subcellular compartments. This workflow includes subcellular fractionation, immunoprecipitation, sample preparation, offline cleanup, single-shot label-free mass spectrometry, and downstream computational analysis and data visualization. Our protocol is optimized for detecting compartmentalized, low abundance interactions that are difficult to identify from whole cell lysates (e.g., transcription factor interactions in the nucleus) by immunoprecipitation of endogenous proteins from fractionated subcellular compartments. The sample preparation pipeline outlined here provides detailed instructions for the preparation of HeLa cell nuclear extract, immunoaffinity purification of endogenous bait protein, and quantitative mass spectrometry analysis. We also discuss methodological considerations for performing large-scale immunoprecipitation in mass spectrometry-based interaction profiling experiments and provide guidelines for evaluating data quality to distinguish true positive protein interactions from nonspecific interactions. This approach is demonstrated here by investigating the nuclear interactome of the CMGC kinase, DYRK1A, a low abundance protein kinase with poorly defined interactions within the nucleus.

Described is a proteomics workflow for identifying protein interaction partners from a nuclear subcellular fraction using immunoaffinity enrichment of a given protein of interest and label-free mass spectrometry. The workflow includes subcellular fractionation, immunoprecipitation, filter aided sample preparation, offline cleanup, mass spectrometry, and a downstream bioinformatics pipeline.

Immunoaffinity purification mass spectrometry (IP-MS) has emerged as a robust quantitative method of identifying protein-protein interactions. This ...

Measurement of Protein Import Capacity of Skeletal Muscle Mitochondria

Mitochondria are key metabolic and regulatory organelles that determine the energy supply as well as the overall health of the cell. In skeletal muscle, mitochondria exist in a series of complex morphologies, ranging from small oval organelles to a broad, reticulum-like network. Understanding how the mitochondrial reticulum expands and develops in response to diverse stimuli such as alterations in energy demand has long been a topic of research. A key aspect of this growth, or biogenesis, is the import of precursor proteins, originally encoded by the nuclear genome, synthesized in the cytosol, and translocated into various mitochondrial sub-compartments. Mitochondria have developed a sophisticated mechanism for this import process, involving many selective inner and outer membrane channels, known as the protein import machinery (PIM). Import into the mitochondrion is dependent on viable membrane potential and the availability of organelle-derived ATP through oxidative phosphorylation. Therefore its measurement can serve as a measure of organelle health. The PIM also exhibits a high level of adaptive plasticity in skeletal muscle that is tightly coupled to the energy status of the cell. For example, exercise training has been shown to increase import capacity, while muscle disuse reduces it, coincident with changes in markers of mitochondrial content. Although protein import is a critical step in the biogenesis and expansion of mitochondria, the process is not widely studied in skeletal muscle. Thus, this paper outlines how to use isolated and fully functional mitochondria from skeletal muscle to measure protein import capacity in order to promote a greater understanding of the methods involved and an appreciation of the importance of the pathway for organelle turnover in exercise, health, and disease.

Mitochondria are key metabolic organelles that exhibit a high level of phenotypic plasticity in skeletal muscle. The import of proteins from the cytosol is a critical pathway for organelle biogenesis, essential for the expansion of the reticulum and the maintenance of mitochondrial function. Therefore, protein import serves as a barometer of cellular health.

Mitochondria are key metabolic and regulatory organelles that determine the energy supply as well as the overall health of the cell. In skeletal muscle, ...

Extraction and Purification of FAHD1 Protein from Swine Kidney and Mouse Liver

Fumarylacetoacetate hydrolase domain-containing protein 1 (FAHD1) is the first identified member of the FAH superfamily in eukaryotes, acting as oxaloacetate decarboxylase in mitochondria. This article presents a series of methods for the extraction and purification of FAHD1 from swine kidney and mouse liver. Covered methods are ionic exchange chromatography with fast protein liquid chromatography (FPLC), preparative and analytical gel filtration with FPLC, and proteomic approaches. After total protein extraction, ammonium sulfate precipitation and ionic exchange chromatography were explored, and FAHD1 was extracted via a sequential strategy using ionic exchange and size-exclusion chromatography. This representative approach may be adapted to other proteins of interest (expressed at significant levels) and modified for other tissues. Purified protein from tissue may support the development of high-quality antibodies, and/or potent and specific pharmacological inhibitors.

This protocol describes how to extract fumarylacetoacetate hydrolase domain-containing protein 1 (FAHD1) from swine kidney and mouse liver. The listed methods may be adapted to other proteins of interest and modified for other tissues.

Fumarylacetoacetate hydrolase domain-containing protein 1 (FAHD1) is the first identified member of the FAH superfamily in eukaryotes, acting as ...

Quantification of Subcellular Glycogen Distribution in Skeletal Muscle Fibers using Transmission Electron Microscopy

With the use of transmission electron microscopy, high-resolution images of fixed samples containing individual muscle fibers can be obtained. This enables quantifications of ultrastructural aspects such as volume fractions, surface area to volume ratios, morphometry, and physical contact sites of different subcellular structures. In the 1970s, a protocol for enhanced staining of glycogen in cells was developed and paved the way for a string of studies on the subcellular localization of glycogen and glycogen particle size using transmission electron microscopy. While most analyses interpret glycogen as if it is homogeneously distributed within the muscle fibers, providing only a single value (e.g., an average concentration), transmission electron microscopy has revealed that glycogen is stored as discrete glycogen particles located in distinct subcellular compartments. Here, the step-by-step protocol from tissue collection to the quantitative determination of the volume fraction and particle diameter of glycogen in the distinct subcellular compartments of individual skeletal muscle fibers is described. Considerations on how to 1) collect and stain tissue specimens, 2) perform image analyses and data handling, 3) evaluate the precision of estimates, 4) discriminate between muscle fiber types, and 5) methodological pitfalls and limitations are included.

A modified post-fixation procedure increases the contrast of glycogen particles in tissue. This paper provides a step-by-step protocol describing how to handle the tissue, conduct the imaging, and use stereological methods to obtain unbiased and quantitative data on fiber type-specific subcellular glycogen distribution in skeletal muscle.

With the use of transmission electron microscopy, high-resolution images of fixed samples containing individual muscle fibers can be obtained. This ...

Isolation of Mitochondrial Contact Sites

An Improved Method to Isolate Mitochondrial Contact Sites

Mitochondria are present in virtually all eukaryotic cells and perform essential functions that go far beyond energy production, for instance, the synthesis of iron-sulfur clusters, lipids, or proteins, Ca2+ buffering, and the induction of apoptosis. Likewise, mitochondrial dysfunction results in severe human diseases such as cancer, diabetes, and neurodegeneration. In order to perform these functions, mitochondria have to communicate with the rest of the cell across their envelope, which consists of two membranes. Therefore, these two membranes have to interact constantly. Proteinaceous contact sites between the mitochondrial inner and outer membranes are essential in this respect. So far, several contact sites have been identified. In the method described here, Saccharomyces cerevisiae mitochondria are used to isolate contact sites and, thus, identify candidates that qualify for contact site proteins. We used this method to identify the mitochondrial contact site and cristae organizing system (MICOS) complex, one of the major contact site-forming complexes in the mitochondrial inner membrane, which is conserved from yeast to humans. Recently, we further improved this method to identify a novel contact site consisting of Cqd1 and the Por1-Om14 complex.

Author Spotlight: Unveiling Mitochondrial Contact Sites and Architectural Insights 

Mitochondrial contact sites are protein complexes that interact with mitochondrial inner and outer membrane proteins. These sites are essential for the communication between the mitochondrial membranes and, thus, between the cytosol and the mitochondrial matrix. Here, we describe a method to identify candidates qualifying for this specific class of proteins.

Mitochondria are present in virtually all eukaryotic cells and perform essential functions that go far beyond energy production, for instance, the ...

MyDoBID- A Novel Technique for Identifying Muscle Fiber Types Efficiently

Fiber Type Identification of Human Skeletal Muscle

The technique described here can be used to identify specific myosin heavy chain (MHC) isoforms in segments of individual muscle fibers using dot blotting, hereafter referred to as Myosin heavy chain detection by Dot Blotting for IDentification of muscle fiber type (MyDoBID). This protocol describes the process of freeze-drying human skeletal muscle and isolating segments of single muscle fibers. Using MyDoBID, type I and II fibers are classified with MHCI- and IIa-specific antibodies, respectively. Classified fibers are then combined into fiber type-specific samples for each biopsy.
The total protein in each sample is determined by Sodium Dodecyl-Sulfate Polyacrylamide Gel Electrophoresis (SDS-PAGE) and UV-activated gel technology. The fiber type of samples is validated using western blotting. The importance of performing protein loading normalization to enhance target protein detection across multiple western blots is also described. The benefits of consolidating classified fibers into fiber type-specific samples compared to single-fiber western blots, include sample versatility, increased sample throughput, shorter time investment, and cost-saving measures, all while retaining valuable fiber type-specific information that is frequently overlooked using homogenized muscle samples. The purpose of the protocol is to achieve accurate and efficient identification of type I and type II fibers isolated from freeze-dried human skeletal muscle samples.
These individual fibers are subsequently combined to create type I and type II fiber type-specific samples. Furthermore, the protocol is extended to include the identification of type IIx fibers, using Actin as a marker for fibers that were negative for MHCI and MHCIIa, which are confirmed as IIx fibers by western blotting. Each fiber type-specific sample is then used to quantify the expression of various target proteins using western blotting techniques.

Author Spotlight: Deciphering the Mysteries of Skeletal Muscle Fiber Types Using the MyDoBID Technique 

This protocol demonstrates single-fiber isolation from freeze-dried human skeletal muscle and fiber-type classification according to Myosin heavy chain (MHC) isoform using the dot blotting technique. Identified MHC I and II fiber samples can then be further analyzed for fiber type-specific differences in protein expression using western blotting.

The technique described here can be used to identify specific myosin heavy chain (MHC) isoforms in segments of individual muscle fibers using dot ...

Locus-Specific Chromatin Isolation from Yeast Cells

Single-Copy Gene Locus Chromatin Purification in Saccharomyces cerevisiae

The basic organizational unit of eukaryotic chromatin is the nucleosome core particle (NCP), which comprises DNA wrapped ~1.7 times around a histone octamer. Chromatin is defined as the entity of NCPs and numerous other protein complexes, including transcription factors, chromatin remodeling and modifying enzymes. It is still unclear how these protein-DNA interactions are orchestrated at the level of specific genomic loci during different stages of the cell cycle. This is mainly due to the current technical limitations, which make it challenging to obtain precise measurements of such dynamic interactions. Here, we describe an improved method combining site-specific recombination with an efficient single-step affinity purification protocol to isolate a single-copy gene locus of interest in its native chromatin state. The method allows for the robust enrichment of the target locus over genomic chromatin, making this technique an effective strategy for identifying and quantifying protein interactions in an unbiased and systematic manner, for example by mass spectrometry. Further to such compositional analyses, native chromatin purified by this method likely reflects the in vivo situation regarding nucleosome positioning and histone modifications and is, therefore, amenable to further structural and biochemical analyses of chromatin derived from virtually any genomic locus in yeast.

Author Spotlight: Advancing Chromatin Research and Overcoming Limitations with a High-Enrichment Locus-Specific Chromatin Isolation Protocol 

This protocol presents a locus-specific chromatin isolation method based on site-specific recombination to purify a single-copy gene locus of interest in its native chromatin context from budding yeast, Saccharomyces cerevisiae.

The basic organizational unit of eukaryotic chromatin is the nucleosome core particle (NCP), which comprises DNA wrapped ~1.7 times around a histone ...