We thank Karyn Esser, Nobuya Koike and Noheon Park for helpful advice. This work was in part supported by NIH/NIGMS (R01GM114424) to S.-H.Y., and the Robert A. Welch Foundation (AU-1731) and NIH/NIA (R01AG045828) to Z.C.

Animal care was performed under Institutional Animal Care and Use Committee (IACUC) guidelines, and the procedures were conducted according to an animal protocol approved by the University of Texas Health Science Center at Houston.
1. Nuclei Isolation from Cross-linked Skeletal Muscle
<ol>
	<li>Weigh and mince hind limb skeletal muscle, isolated from approximately 20-week old C57BL/6 male mice, in ice-cold phosphate buffered saline (PBS) as described in detail previously22<...

<ol>
	<li>Bouzakri, K., 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=siRNA-based+gene+silencing+reveals+specialized+roles+of+IRS-1/Akt2+and+IRS-2/Akt1+in+glucose+and+lipid+metabolism+in+human+skeletal+muscle.">siRNA-based gene silencing reveals specialized roles of IRS-1/Akt2 and IRS-2/Akt1 in glucose and lipid metabolism in human skeletal muscle.</a> Cell Metab. 4 (1), 89-96 (2006).</li><li>Boucher, J., Kleinridders, A., Kahn, C. R. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Insulin+receptor+signaling+in+normal+and+insulin-resistant+states.">Insulin receptor signaling in normal and insulin-resistant states.</a> Cold Spring Harb Perspect Biol. 6 (1), (2014).</li><li>Green, C. B., Takahashi, J. S., Bass, J. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=The+meter+of+metabolism.">The meter of metabolism.</a> Cell. 134 (5), 728-742 (2008).</li><li>Liu, A. C., Lewis, W. G., Kay, S. A. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Mammalian+circadian+signaling+networks+and+therapeutic+targets.">Mammalian circadian signaling networks and therapeutic targets.</a> Nat Chem Biol. 3 (10), 630-639 (2007).</li><li>Harfmann, B. D., Schroder, E. A., Esser, K. A. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Circadian+rhythms,+the+molecular+clock,+and+skeletal+muscle.">Circadian rhythms, the molecular clock, and skeletal muscle.</a> J Biol Rhythms. 30 (2), 84-94 (2015).</li><li>Nohara, K., Yoo, S. H., Chen, Z. J. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Manipulating+the+circadian+and+sleep+cycles+to+protect+against+metabolic+disease.">Manipulating the circadian and sleep cycles to protect against metabolic disease.</a> Front Endocrinol (Lausanne). 6, 35 (2015).</li><li>Harfmann, B. 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=Muscle-specific+loss+of+Bmal1+leads+to+disrupted+tissue+glucose+metabolism+and+systemic+glucose+homeostasis.">Muscle-specific loss of Bmal1 leads to disrupted tissue glucose metabolism and systemic glucose homeostasis.</a> Skelet Muscle. 6, 12 (2016).</li><li>Pedersen, B. K., Febbraio, M. A. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Muscles,+exercise+and+obesity:+skeletal+muscle+as+a+secretory+organ.">Muscles, exercise and obesity: skeletal muscle as a secretory organ.</a> Nat Rev Endocrinol. 8 (8), 457-465 (2012).</li><li>Solomon, M. J., Varshavsky, A. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Formaldehyde-mediated+DNA-protein+crosslinking:+a+probe+for+in+vivo+chromatin+structures.">Formaldehyde-mediated DNA-protein crosslinking: a probe for in vivo chromatin structures.</a> Proc Natl Acad Sci U S A. 82 (19), 6470-6474 (1985).</li><li>Jackson, V. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Studies+on+histone+organization+in+the+nucleosome+using+formaldehyde+as+a+reversible+cross-linking+agent.">Studies on histone organization in the nucleosome using formaldehyde as a reversible cross-linking agent.</a> Cell. 15 (3), 945-954 (1978).</li><li>Gilmour, D. S., Lis, 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=Detecting+protein-DNA+interactions+in+vivo:+distribution+of+RNA+polymerase+on+specific+bacterial+genes.">Detecting protein-DNA interactions in vivo: distribution of RNA polymerase on specific bacterial genes.</a> Proc Natl Acad Sci U S A. 81 (14), 4275-4279 (1984).</li><li>Takahashi, J. 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=ChIP-seq+and+RNA-seq+methods+to+study+circadian+control+of+transcription+in+mammals.">ChIP-seq and RNA-seq methods to study circadian control of transcription in mammals.</a> Methods Enzymol. 551, 285-321 (2015).</li><li>Kuo, M. H., 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=In+vivo+cross-linking+and+immunoprecipitation+for+studying+dynamic+Protein:DNA+associations+in+a+chromatin+environment.">In vivo cross-linking and immunoprecipitation for studying dynamic Protein:DNA associations in a chromatin environment.</a> Methods. 19 (3), 425-433 (1999).</li><li>Chen, Z., Manley, J. L. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Core+promoter+elements+and+TAFs+contribute+to+the+diversity+of+transcriptional+activation+in+vertebrates.">Core promoter elements and TAFs contribute to the diversity of transcriptional activation in vertebrates.</a> Mol Cell Biol. 23 (20), 7350-7362 (2003).</li><li>Menet, J. S., Abruzzi, K. C., Desrochers, J., Rodriguez, J., Rosbash, M. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Dynamic+PER+repression+mechanisms+in+the+Drosophila+circadian+clock:+from+on-DNA+to+off-DNA.">Dynamic PER repression mechanisms in the Drosophila circadian clock: from on-DNA to off-DNA.</a> Genes Dev. 24 (4), 358-367 (2010).</li><li>Miki, T., Matsumoto, T., Zhao, Z., Lee, C. C. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=p53+regulates+Period2+expression+and+the+circadian+clock.">p53 regulates Period2 expression and the circadian clock.</a> Nat Commun. 4, 2444 (2013).</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>Koike, N., 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=Transcriptional+architecture+and+chromatin+landscape+of+the+core+circadian+clock+in+mammals.">Transcriptional architecture and chromatin landscape of the core circadian clock in mammals.</a> Science. 338 (6105), 349-354 (2012).</li><li>Zhou, J., Yu, W., Hardin, P. E. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=ChIPping+away+at+the+Drosophila+clock.">ChIPping away at the Drosophila clock.</a> Methods Enzymol. 551, 323-347 (2015).</li><li>Takahashi, J. S. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Transcriptional+architecture+of+the+mammalian+circadian+clock.">Transcriptional architecture of the mammalian circadian clock.</a> Nat Rev Genet. , (2016).</li><li>Edelman, J. C., Edelman, P. M., Kniggee, K. M., Schwartz, I. L. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Isolation+of+skeletal+muscle+nuclei.">Isolation of skeletal muscle nuclei.</a> J Cell Biol. 27 (2), 365-377 (1965).</li><li>Ohkawa, Y., Mallappa, C., Vallaster, C. S., Imbalzano, A. N. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Isolation+of+nuclei+from+skeletal+muscle+satellite+cells+and+myofibers+for+use+in+chromatin+immunoprecipitation+assays.">Isolation of nuclei from skeletal muscle satellite cells and myofibers for use in chromatin immunoprecipitation assays.</a> Methods Mol Biol. 798, 517-530 (2012).</li><li>Wilkie, G. S., Schirmer, E. C. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Purification+of+nuclei+and+preparation+of+nuclear+envelopes+from+skeletal+muscle.">Purification of nuclei and preparation of nuclear envelopes from skeletal muscle.</a> Methods Mol Biol. 463, 23-41 (2008).</li><li>Hahn, C. G., Covault, J. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Isolation+of+transcriptionally+active+nuclei+from+striated+muscle+using+Percoll+density+gradients.">Isolation of transcriptionally active nuclei from striated muscle using Percoll density gradients.</a> Anal Biochem. 190 (2), 193-197 (1990).</li><li>Jeong, K., 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=Dual+attenuation+of+proteasomal+and+autophagic+BMAL1+degradation+in+Clock+Delta19/++mice+contributes+to+improved+glucose+homeostasis.">Dual attenuation of proteasomal and autophagic BMAL1 degradation in Clock Delta19/+ mice contributes to improved glucose homeostasis.</a> Scientific reports. 5, 12801 (2015).</li><li>Nohara, K., 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=Ammonia-lowering+activities+and+carbamoyl+phosphate+synthetase+1+(Cps1)+induction+mechanism+of+a+natural+flavonoid.">Ammonia-lowering activities and carbamoyl phosphate synthetase 1 (Cps1) induction mechanism of a natural flavonoid.</a> Nutrition &amp; metabolism. 12, 23 (2015).</li><li>Zhang, L., Rubins, N. E., Ahima, R. S., Greenbaum, L. E., Kaestner, K. H. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Foxa2+integrates+the+transcriptional+response+of+the+hepatocyte+to+fasting.">Foxa2 integrates the transcriptional response of the hepatocyte to fasting.</a> Cell Metab. 2 (2), 141-148 (2005).</li><li>Gade, P., Kalvakolanu, D. V. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Chromatin+immunoprecipitation+assay+as+a+tool+for+analyzing+transcription+factor+activity.">Chromatin immunoprecipitation assay as a tool for analyzing transcription factor activity.</a> Methods Mol Biol. 809, 85-104 (2012).</li><li>Kondratov, R. V., 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=BMAL1-dependent+circadian+oscillation+of+nuclear+CLOCK:+posttranslational+events+induced+by+dimerization+of+transcriptional+activators+of+the+mammalian+clock+system.">BMAL1-dependent circadian oscillation of nuclear CLOCK: posttranslational events induced by dimerization of transcriptional activators of the mammalian clock system.</a> Genes Dev. 17 (15), 1921-1932 (2003).</li><li>Ripperger, J. A., Schibler, U. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Rhythmic+CLOCK-BMAL1+binding+to+multiple+E-box+motifs+drives+circadian+Dbp+transcription+and+chromatin+transitions.">Rhythmic CLOCK-BMAL1 binding to multiple E-box motifs drives circadian Dbp transcription and chromatin transitions.</a> Nat Genet. 38 (3), 369-374 (2006).</li><li>Laplante, 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=DEPTOR+cell-autonomously+promotes+adipogenesis,+and+its+expression+is+associated+with+obesity.">DEPTOR cell-autonomously promotes adipogenesis, and its expression is associated with obesity.</a> Cell Metab. 16 (2), 202-212 (2012).</li><li>Blechman, J., Amir-Zilberstein, L., Gutnick, A., Ben-Dor, S., Levkowitz, G. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=The+metabolic+regulator+PGC-1alpha+directly+controls+the+expression+of+the+hypothalamic+neuropeptide+oxytocin.">The metabolic regulator PGC-1alpha directly controls the expression of the hypothalamic neuropeptide oxytocin.</a> J Neurosci. 31 (42), 14835-14840 (2011).</li></ol>

The authors have nothing to disclose.

Here we describe a robust method where cross-linked skeletal muscle tissues were used to isolate high-quality nuclei. Sequential filtration was carried out to effectively separate nuclei from debris, and ultrasonic acoustic energy from dish-shaped transducer sheared the chromatin for ChIP analysis. The results showed circadian time-specific binding of BMAL1 to target promoters.
ChIP can be employed to capture real-time protein occupancy on genomic DNA when cross-linking takes place. To take ad...

Skeletal muscle plays important roles in physiology and behavior. The multi-nucleated muscle fiber consists of myofibrils where actin and myosin form functional units called sarcomeres to generate contractile force. Skeletal muscle is also the largest metabolic organ in the body, accounting for &#62;80% postprandial glucose intake and regulating insulin response and metabolic homeostasis1,2. Muscle physiology and metabolism are closely regulated by the circadian clock, an intrinsic biological timer3,4,5,6. For example, the skeletal muscle-specific deletion of Bmal1, one of the core circadian clock components, resulted in insulin resistance and diminished glucose uptake in skeletal muscle, and the animals were found to develop type 2 diabetes7. In addition, skeletal muscle is also increasingly being appreciated as an endocrine organ8, secreting myokines to regulate systemic metabolism and physiology. Mechanistic studies are required to fully understand these regulatory functions in skeletal muscle.
ChIP is a powerful approach to delineate promoter recruitment of DNA binding proteins. ChIP was initially developed to identify nucleosome organization on chromatin DNA9,10. A variety of methods have since been reported to cross-link proteins and chromatin DNA using formaldehyde, dimethyl sulfate or ultraviolet irradiation (UV)11,12. Formaldehyde cross-linking is the most commonly used, preserving chromatin structure and DNA-protein interactions9,13,14. Cross-linked chromatin is shredded by sonication and immunoprecipitated with antibody against the particular DNA binding protein of interest15,16. In recent years, ChIP-sequencing (ChIP-seq), a method combining ChIP with NGS, has been developed to interrogate genome-wide transcription factor binding17, and in some cases to monitor dynamic changes over a time course18,19,20. For example, circadian ChIP-seq studies have revealed a highly orchestrated sequence of genomic binding of circadian clock components and histone markers, which drives temporally precise gene expression throughout the ~ 24 h circadian cycle18.
Most available ChIP protocols are designed for soft tissues (e.g. liver, brain, etc.), and very few have been published for hard tissues including skeletal muscle. It is technically challenging to homogenize fiber-rich skeletal muscle and isolate high-quality nuclei21, especially for ChIP experiments which require cross-linking. In a recent muscle ChIP study22, satellite cells were separated from myofibers, and nuclei were prepared from both cell types through a prolonged procedure involving tissue digestion. The entire process took approximately three hours to complete before formaldehyde cross-linking was performed on isolated nuclei. While this procedure avoided cross-linking muscle fiber, which makes muscle tissue even more refractory to efficient homogenization, and was able to produce high-quality nuclei, the significant time-lag from tissue collection to nuclei cross-linking incurs the risk of altered DNA-protein interaction. In contrast, most studies performed cross-linking immediately after experimental treatment or tissue collection in order to preserve the real-time DNA-protein binding12. A second drawback of nuclei isolation before cross-linking is that it precludes time-sensitive applications such as circadian sample collection which typically occurs at 3 - 4 h intervals. Without cross-linking the nuclei, the isolation needs to proceed immediately after dissection, whereas cross-linked samples can be processed together after the entire time course is completed, thus ensuring greater experimental consistency.
Other protocols for nuclei isolation from uncrosslinked skeletal muscle have also been reported. Two studies described the use of gradient ultracentrifugation to separate nuclei from remaining myofibrils and cell debris23,24. While sucrose or colloidal gradient ultracentrifugation is effective with uncrosslinked muscle tissues, our experiments revealed that after crosslinking, gradient ultracentrifugation failed to separate nuclei from cell debris on the gradient.
We therefore developed a procedure to isolate high-quality nuclei using cross-linked mouse skeletal muscle tissues. Rather than gradient ultracentrifugation, we devised a serial filtration method to effectively separate nuclei from debris. Following ultrasonication, the chromatin samples were successfully applied for ChIP studies which showed a circadian pattern of BMAL1 protein binding to target promoters. Our method can be broadly applicable to various mechanistic studies of muscle tissues.

<table border="0" cellpadding="0" cellspacing="0" width="765">
	<colgroup>
		<col />
		<col />
		<col />
		<col />
	</colgroup>
	<tbody>
		<tr height="20">
			<td height="20" style="height:20px;width:216px;">Materials</td>
			<td style="width:143px;"></td>
			<td style="width:119px;"></td>
			<td style="width:288px;"></td>
		</tr>
		<tr height="20">
			<td height="20" style="height:20px;width:216px;">Formaldehyde solution</td>
			<td style="width:143px;">Sigma Aldrich</td>
			<td style="width:119px;">F8775&#160;</td>
			<td></td>
		</tr>
		<tr height="20">
			<td height="20" style="height:20px;width:216px;">Glycine</td>
			<td style="width:143px;">Fisher Scientific</td>
			<td style="width:119px;">BP381-5</td>
			<td></td>
		</tr>
		<tr height="20">
			<td height="20" style="height:20px;width:216px;">Trypan Blue solution (0.4%)</td>
			<td style="width:143px;">Fisher Scientific</td>
			<td style="width:119px;">15250061</td>
			<td></td>
		</tr>
		<tr height="20">
			<td height="20" style="height:20px;width:216px;">RNase A</td>
			<td style="width:143px;">Sigma Aldrich</td>
			<td style="width:119px;">10109142001</td>
			<td></td>
		</tr>
		<tr height="20">
			<td height="20" style="height:20px;width:216px;">Protease K</td>
			<td style="width:143px;">Sigma Aldrich</td>
			<td style="width:119px;">3115887001</td>
			<td></td>
		</tr>
		<tr height="57">
			<td height="57" style="height:57px;width:216px;">Chicken Anti-BMAL1 antibody</td>
			<td style="width:143px;"></td>
			<td style="width:119px;"></td>
			<td style="width:288px;">Generated in chicken (Cocalico Biologicals) against antigen aa 318-579, and IgY was affinity purified using the same antigen.&#160;</td>
		</tr>
		<tr height="20">
			<td height="20" style="height:20px;width:216px;">Chicken IgY Precipitating Resin</td>
			<td style="width:143px;">GenScript</td>
			<td style="width:119px;">L00405</td>
			<td></td>
		</tr>
		<tr height="20">
			<td height="20" style="height:20px;width:216px;"></td>
			<td style="width:143px;"></td>
			<td style="width:119px;"></td>
			<td></td>
		</tr>
		<tr height="20">
			<td height="20" style="height:20px;width:216px;">Equipment</td>
			<td style="width:143px;"></td>
			<td style="width:119px;"></td>
			<td></td>
		</tr>
		<tr height="38">
			<td height="38" style="height:38px;width:216px;">KINEMATICA&#160;Polytron PT2100 Benchtop Homogenizer</td>
			<td style="width:143px;">Fisher Scientific</td>
			<td style="width:119px;">08-451-178</td>
			<td></td>
		</tr>
		<tr height="20">
			<td height="20" style="height:20px;width:216px;">15mL Dounce tissue grinder</td>
			<td style="width:143px;">Whearton</td>
			<td style="width:119px;">357544</td>
			<td></td>
		</tr>
		<tr height="20">
			<td height="20" style="height:20px;width:216px;">Falcon Cell Strainers 100&#181;m</td>
			<td style="width:143px;">Fisher Scientific</td>
			<td style="width:119px;">08-771-19</td>
			<td></td>
		</tr>
		<tr height="20">
			<td height="20" style="height:20px;width:216px;">Falcon Cell Strainers 70&#181;m</td>
			<td style="width:143px;">Fisher Scientific</td>
			<td style="width:119px;">08-771-1</td>
			<td></td>
		</tr>
		<tr height="20">
			<td height="20" style="height:20px;width:216px;">Falcon Cell Strainers 40&#181;m</td>
			<td style="width:143px;">Fisher Scientific</td>
			<td style="width:119px;">08-771-2</td>
			<td></td>
		</tr>
		<tr height="20">
			<td height="20" style="height:20px;width:216px;">pluriStrainer 30 &#181;m</td>
			<td style="width:143px;">PluriSelect</td>
			<td style="width:119px;">43-50030-03</td>
			<td></td>
		</tr>
		<tr height="20">
			<td height="20" style="height:20px;width:216px;">pluriStrainer 20 &#181;m</td>
			<td style="width:143px;">PluriSelect</td>
			<td style="width:119px;">43-50020-03</td>
			<td></td>
		</tr>
		<tr height="20">
			<td height="20" style="height:20px;width:216px;">pluriStrainer 10 &#181;m</td>
			<td style="width:143px;">PluriSelect</td>
			<td style="width:119px;">43-50010-03</td>
			<td></td>
		</tr>
		<tr height="38">
			<td height="38" style="height:38px;width:216px;">Covaris S2 Focused-ultrasonicator</td>
			<td style="width:143px;">Covaris</td>
			<td style="width:119px;">Model S2</td>
			<td></td>
		</tr>
		<tr height="20">
			<td height="20" style="height:20px;">Labquake&#160;</td>
			<td>Thermo Scientific</td>
			<td>C415110</td>
			<td></td>
		</tr>
		<tr height="20">
			<td height="20" style="height:20px;">CCD Microscope Camera</td>
			<td>&#160;Leica Microsystems</td>
			<td>DFC3000 G</td>
			<td></td>
		</tr>
		<tr height="20">
			<td height="20" style="height:20px;width:216px;"></td>
			<td style="width:143px;"></td>
			<td style="width:119px;"></td>
			<td></td>
		</tr>
		<tr height="20">
			<td height="20" style="height:20px;width:216px;">Reagent Kit</td>
			<td style="width:143px;"></td>
			<td style="width:119px;"></td>
			<td></td>
		</tr>
		<tr height="20">
			<td height="20" style="height:20px;width:216px;">DNA extraction kit</td>
			<td style="width:143px;">Thermo Scientific</td>
			<td style="width:119px;">K0691</td>
			<td></td>
		</tr>
		<tr height="20">
			<td height="20" style="height:20px;width:216px;"></td>
			<td style="width:143px;"></td>
			<td style="width:119px;"></td>
			<td></td>
		</tr>
		<tr height="20">
			<td height="20" style="height:20px;width:216px;">Buffers</td>
			<td style="width:143px;"></td>
			<td style="width:119px;"></td>
			<td></td>
		</tr>
		<tr height="76">
			<td height="76" style="height:76px;width:216px;">All buffer components are discribed in the protocol. Each component was purchased from Sigma Aldrich</td>
			<td style="width:143px;"></td>
			<td style="width:119px;"></td>
			<td></td>
		</tr>
	</tbody>
</table>

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.

Here we performed formaldehyde cross-linking immediately after tissue collection to preserve real-time DNA-protein interaction. However, we found that sucrose or colloidal gradient, commonly used for nuclei isolation23,24, was not effective in separating nuclei from myofibrils (data not shown). The reason may be that cross-linking conferred similar gravity for nuclei and myofibrils. Therefore, we developed a serial filtration proc...

Watch this Scientific Journal Video about A Filtration-based Method of Preparing High-quality Nuclei from Cross-linked Skeletal Muscle for Chromatin Immunoprecipitation at JoVE.com

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

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 ...

The overall goal of this experimental procedure is to allow preparation of high-quality nuclei from cross-linked skeletal muscle which can then be used for chromatin immunoprecipitation studies. This method can help answer key questions in muscle and circadian field such as genomic studies using muscle tissues and cells in circadian or other time-sensitive context. The main advantage of this technique is that it allow immediate cross-linking of samples and the filtration-based procedure can be reliably conducted to isolate high-quality nuclei with minimal myofibril contamination.Although this method can provide insight into skeletal muscle, it can also be applied to other systems such as cardiac and smooth muscles. Weigh and mince hind limb skeletal muscle isolated from approximately 20-week-old C57 black six male mice in ice cold phosphate-buffered saline as described previously. Place the minced skeletal muscle tissue in a 50 milliliter conical tube containing 10 milliliters of PBS on ice.Then centrifuge the sample at 300 times g at four degrees Celsius for five minutes. Carefully remove the PBS supernatant by aspiration. Estimate the pellet volume in each 50 milliliter tube by using reference tubes with one, two, three, and four milliliters of water.Add seven volumes of ice cold 1%formaldehyde and PBS and homogenize the samples on ice using a probe tissue homogenizer. Next, cross-link the sample by incubating it at room temperature for 10 minutes. Quench the cross-linking reaction through the addition of one molar glycine to a final concentration of 0.125 molar followed by incubation for five minutes at room temperature.After centrifuging the sample at 3, 000 times g for five minutes at four degrees Celsius, remove the supernatant via aspiration. Rinse the pellet by resuspending it in 10 milliliters of ice cold base buffer containing freshly added protease inhibitors. Centrifuge the sample again and carefully remove the supernatant by aspiration.Then resuspend the pellet in six milliliters of lysis buffer containing freshly added protease inhibitors. Transfer the sample to a pre-chilled 15 milliliter Dounce homogenizer and incubate for 10 minutes on ice. Dounce homogenize each sample on ice with 15 slow strokes using a loose pestle followed by 15 strokes with a tight pestle to release the nuclei.The following filtration steps are the key to isolation of high-quality nuclei. Filter the homogenate through a cell strainer and rinse with four milliliters of lysis buffer. Then centrifuge the samples at 1, 000 times g for 10 minutes at four degrees Celsius.Resuspend the pellet in five milliliters of ice cold base buffer and Dounce 10 times with a tight pestle to release the nuclei. Then filter the suspension through a cell strainer and rinse the tube with two milliliters of base buffer and filter again. Repeat the filtration with cell strainers of gradually reduced pore size.Finally, centrifuge at 1, 000 times g at four degrees Celsius for 10 minutes. Remove the supernatant and resuspend the pellet in 500 microliters of base buffer before centrifuging again. Discard the supernatant and store the pellet at minus 80 degrees Celsius.Thaw the samples in 500 microliters of SDS lysis buffer and resuspend with gentle pipetting. Transfer the nuclei DNA suspension to a glass vial on ice. Choosing the right sonication platform and condition is critical for chromatin preparation from isolated nuclei.Run the sonication with focused bursts of ultrasonic acoustic energy from a disc-shaped transducer using the settings outlined in the text protocol. Transfer the sonicated chromatin to a 1.5 milliliter tube. Then centrifuge at 12, 000 times g for 15 minutes and transfer the supernatant to a new tube.Next, transfer 50 microliters of the sonicated sample into a new 1.5 milliliter tube for reverse cross-linking overnight at 65 degrees Celsius. Harvesting of the DNA samples is described in the following section. Following evaluation of sonication and quantitation as described in the text protocol, aliquot the thawed chromatin to approximately 100 to 120 micrograms per tube.Then dilute the chromatin one to 10 with immunoprecipitation buffer. Next, add 40 microliters of a 50%slurry of BSA pre-blocked protein HE agarose or IgY beads and incubate on a rotator for three hours at four degrees Celsius. After centrifuging the sample at 1, 000 times g for 10 minutes, carefully transfer the supernatant to new tubes.Then add antibodies at one microgram of antibody per 25 to 100 micrograms of chromatin DNA. Rotate gently overnight at four degrees Celsius and approximately 15 rpm. Then add 10 microliters of BSA pre-blocked protein HE agarose or IgY beads and mix.Rotate the bead suspension in the cold room for two hours. Next, wash the beads with RIPA buffer followed by high salt buffer, lithium chloride buffer, and Tris EDTA as detailed in the text protocol. Following washing, elute the DNA from the beads by first centrifuging at 1, 000 times g for one minute and carefully removing the supernatant.Resuspend the beads with 50 microliters of elution buffer. Then incubate for 10 minutes at 65 degrees Celsius. Following incubation, centrifuge at 12, 000 times g for five minutes.Remove the supernatant and add another 50 microliters of elution buffer before centrifuging once again at 12, 000 times g for five minutes. The final elution volume will be 100 microliters. To reverse cross-link and perform DNA elution, first incubate the eluted chromatin overnight at 65 degrees Celsius.Then add one microliter of RNase A before incubating for 30 minutes at 37 degrees Celsius. Subsequently, incubate with eight microliters of 10 milligrams per milliliter protease K for 30 minutes at 55 degrees Celsius. Harvest the DNA by using a PCR cleanup kit with an elution volume of 50 microliters according to the manufacturer's protocol.Finally, analyze the profiles by real-time QPCR as previously described. Sequential filtration effectively removed tissue debris. Representative images of samples after the initial filtration and after serial filtration are shown here for comparison.Progressive chromatin shredding through 10 cycles of sonication is revealed through running an agarose gel. 10 cycles of sonication with the digested chromatin resulted in DNA of approximately 500 base pairs. Here, representative QPCR results for B males one chIP with mouse skeletal muscle samples collected at ZT6 and ZT18 are shown.Analysis of the Dbp locations elements on the Dbp gene revealed that consistent with previous results binding peaks at around ZT6. Once mastered, preparation of nuclei can be done in five to six hours if it's performed properly. After watching this video, you should have a good understanding of how to use the filtration-based methods to purify high-quality nuclei and chromatin DNA from cross-linked muscle tissue.While attempting this procedure, it's important to remember to maintain samples on ice or in a cold room and save sample aliquots for microscopic checking before and after the filtration steps. After its development, this technique paved the way for the researchers in the field of muscle and genomics to explore circadian or time-sensitive dynamics of chromatin-protein interaction in various muscle tissues. Following this procedure, other methods like chIP sequencing can be performed in order to answer additional questions like look for patterns of transcription factor binding in muscle tissues.

a-filtration-based-method-preparing-high-quality-nuclei-from-cross

Research

JoVE Journal

Biochemistry

8.8K vistas.  University of Texas Health Science Center at Houston. The overall goal of this experimental procedure is to allow preparation of high-quality nuclei from cross-linked skeletal muscle which can then be used for chromatin immunoprecipitation studies. This method can help answer key questions in muscle and circadian field such as genomic studies using muscle tissues and cells in circadian or other time-sensitive context. The main advantage of this technique is that it allow immediate cross-linking of samples and the filtration-based procedure can b...