We thank the Single Cell Open Lab (scOpenLab) at the German Cancer Center (DKFZ) for helpful discussions. This research was supported by the German Cancer Aid, Max-Eder Program grant number 70111964 (S.T.).

Fresh frozen glioma samples were obtained from the National Center for Tumor diseases (NCT)-tissue bank in Heidelberg, Germany. The use of patient material was approved by the Institutional Review Board at the Medical Faculty of Heidelberg, and informed consent was obtained from all patients included in the study.
1. Experimental preparation
<ol>
	<li>Perform all steps on ice or at 4 &#176;C.</li>
	<li>Pre-chill tubes, dishes, razor blades, Douncers and pestles to 4 &#176;C.</li>
	<li>Prepare all buffers in advance. These buffers are stable at room temperature. Sterile filtration is recommended, especially for sucrose. The stock preparations are modified from Corces et al.19. See Tables 1-7.</li>
	<li>Remove samples from liquid nitrogen or -80 &#176;C freezer storage and keep on dry ice until Step 2.1.</li>
</ol>
2. Tissue dissection and dissociation
<ol>
	<li>Transfer fresh frozen tissue sample (10-60 mg) to a pre-chilled Petri dish. Mince/chop fresh frozen tissue with a razor blade to small pieces on ice.</li>
	<li>Add 500 &#181;L of chilled nuclei lysis buffer to a pre-chilled 1.5 mL tube. Place the tissue pieces in the 1.5 mL tube containing the nuclei lysis buffer, and transfer to a Douncer (Table of Materials). 
	NOTE: There are two Dounce homogenizer pestles: &#8220;loose&#8221; or &#8220;A&#8221; pestle for initial sample reduction and &#8220;tight&#8221; or &#8220;B&#8221; pestle for complete sample homogenization.</li>
	<li>Dounce the tissue pieces with the &#8220;loose&#8221; pestle for about 20 strokes, until friction is reduced. If debris is present, the sample may be pre-cleared by filtration with a 100 mm strainer.</li>
	<li>Dounce with the &#8220;tight&#8221; pestle for 20 strokes to achieve complete tissue homogenization.</li>
	<li>Transfer the homogenate (about 500 &#181;L) into a pre-chilled 2 mL tube. Add 1 mL of chilled lysis buffer. Mix gently and incubate on ice for 5 min. Gently mix with a wide-bore pipette tip and repeat 1-2 times during the incubation.</li>
	<li>Filter the entire homogenate using a 30 &#181;m strainer mesh, collect into a 15 mL Falcon&#160;tube and transfer back into a new pre-chilled 2 mL tube. A single strainer is typically sufficient for the entire homogenate.</li>
	<li>Check under a light microscope to verify the removal of large debris and the intactness of the nuclear membrane. Nuclei need to be round and the nuclear membrane should not be distorted. If debris is present, nuclei can be re-filtered.</li>
	<li>Centrifuge the nuclei at 500 x g for 5 min at 4 &#176;C on a bench top centrifuge. Remove the supernatant, leaving behind ~50 &#181;L with pellet containing the nuclei. Gently resuspend the pellet in another 1 mL of nuclei lysis buffer and incubate for 5 min on ice.</li>
	<li>Centrifuge the nuclei at 500 x g for 5 min at 4&#176;C. Remove the supernatant without disturbing pellet, add 500 mL of 1x homogenization buffer (HB) (Table 4) and incubate for 5 min without resuspending. Then, resuspend the nuclei in another 1.0 mL of 1x HB.</li>
	<li>Centrifuge the nuclei at 500 x g for 5 min at 4 &#176;C. Remove the supernatant and gently resuspend the nuclei in 200 &#181;L of 1x HB into a new 2.0 mL tube.</li>
</ol>
3. Gradient centrifugation
<ol>
	<li>Add 200 &#181;L of 50% iodixanol solution (Table 5) to give a final concentration of 25% iodixanol. Mix well 10 times with pipette set on 300 mL.</li>
	<li>Add 300 &#181;L of 29% iodixanol solution (Table 6) under the 25% mixture. Use a P1000 fine tip to avoid mixture of the layers.</li>
	<li>Add 300 &#181;l of 35% Iodixanol solution (Table 7) under the 29% mixture. Use a P1000 fine tip to avoid mixture of the layers. 
	Caution: This step requires gradual removal of the pipette tip during pipetting to avoid excessive volume displacement.</li>
	<li>Place the samples in a swinging bucket centrifuge, spin for 20 min at 3,500 x g at 4&#176;C with the brake off.</li>
	<li>Gently remove the samples without shaking and observe under light. A clear white band of 95% pure nuclei should be visible between the second and third layer (Figure 1).</li>
</ol>
4. Isolation of nuclei
<ol>
	<li>Aspirate the top layers until the white nuclei band at the interphase of 29%-35%.</li>
	<li>Collect the nuclei band in a 200 mL volume, transfer to a fresh tube and filter with a 20 &#181;m filter (Table of Materials). 
	NOTE: The nuclei do not need to be resuspended prior to filtration.</li>
	<li>Check under a light microscope to verify the removal of large debris and the intactness of the nuclear membrane. Nuclei need to be round and the nuclear membrane should not be distorted.</li>
	<li>Count nuclei using Trypan blue staining on a hemocytometer and aliquot nuclei for snRNA-seq/snATAC-seq.</li>
</ol>
5. Single nuclei RNA and ATAC seq
<ol>
	<li>Immediately process the nuclei using the single cell gene expression and single cell ATAC reagent kits (Table of Materials). 
	NOTE: The nuclei sample concentrations for the 10x Genomics system are 1500-3000 nuclei per &#181;L for snRNA-seq, and 3500-7000 nuclei per m &#181;L for snATAC-seq. The nuclei can be diluted using 1x PBS.</li>
	<li>Sequence the resulting libraries at the Genomics Core Facility.</li>
	<li>Perform quality control analysis of the data. Nuclei are included for further analysis if they contain Unique Molecular Identifier (UMI) &#62;1000, number of genes &#62;500 and percent of mitochondrial genes &#60;5%, and are within mean + three standard deviations of the UMIs and genes.</li>
</ol>

<ol>
	<li>Huse, J. T., Holland, 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=Targeting+brain+cancer:+advances+in+the+molecular+pathology+of+malignant+glioma+and+medulloblastoma.">Targeting brain cancer: advances in the molecular pathology of malignant glioma and medulloblastoma.</a> Nature Reviews Cancer. 10 (5), 319-331 (2010).</li><li>Kreso, A., Dick, 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=Evolution+of+the+cancer+stem+cell+model.">Evolution of the cancer stem cell model.</a> Cell Stem Cell. 14 (3), 275-291 (2014).</li><li>Filbin, M. G., Suva, M. L. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Gliomas+Genomics+and+Epigenomics:+Arriving+at+the+Start+and+Knowing+It+for+the+First+Time.">Gliomas Genomics and Epigenomics: Arriving at the Start and Knowing It for the First Time.</a> Annual Review of Pathology. 11, 497-521 (2016).</li><li>Ferris, S. P., Hofmann, J. W., Solomon, D. A., Perry, A. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Characterization+of+gliomas:+from+morphology+to+molecules.">Characterization of gliomas: from morphology to molecules.</a> Virchows Archive. 471 (2), 257-269 (2017).</li><li>Louis, D. 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=The+2016+World+Health+Organization+Classification+of+Tumors+of+the+Central+Nervous+System:+a+summary.">The 2016 World Health Organization Classification of Tumors of the Central Nervous System: a summary.</a> Acta Neuropathologica. 131 (6), 803-820 (2016).</li><li>Eckel-Passow, J. E., 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=Glioma+Groups+Based+on+1p/19q,+IDH,+and+TERT+Promoter+Mutations+in+Tumors.">Glioma Groups Based on 1p/19q, IDH, and TERT Promoter Mutations in Tumors.</a> The New England Journal of Medicine. 372 (26), 2499-2508 (2015).</li><li>Suzuki, H., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Mutational+landscape+and+clonal+architecture+in+grade+II+and+III+gliomas.">Mutational landscape and clonal architecture in grade II and III gliomas.</a> Nature Genetics. 47 (5), 458-468 (2015).</li><li>Cancer Genome Atlas Research. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Comprehensive,+Integrative+Genomic+Analysis+of+Diffuse+Lower-Grade+Gliomas.">Comprehensive, Integrative Genomic Analysis of Diffuse Lower-Grade Gliomas.</a> The New England Journal of Medicine. 372 (26), 2481-2498 (2015).</li><li>Noushmehr, H., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Identification+of+a+CpG+island+methylator+phenotype+that+defines+a+distinct+subgroup+of+glioma.">Identification of a CpG island methylator phenotype that defines a distinct subgroup of glioma.</a> Cancer Cell. 17 (5), 510-522 (2010).</li><li>Yan, H., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=IDH1+and+IDH2+mutations+in+gliomas.">IDH1 and IDH2 mutations in gliomas.</a> The New England Journal of Medicine. 360 (8), 765-773 (2009).</li><li>Yan, H., Bigner, D. D., Velculescu, V., Parsons, D. W. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Mutant+metabolic+enzymes+are+at+the+origin+of+gliomas.">Mutant metabolic enzymes are at the origin of gliomas.</a> Cancer Research. 69 (24), 9157-9159 (2009).</li><li>Gawad, C., Koh, W., Quake, S. R. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Single-cell+genome+sequencing:+current+state+of+the+science.">Single-cell genome sequencing: current state of the science.</a> Nature Reviews Genetics. 17 (3), 175-188 (2016).</li><li>Tanay, A., Regev, A. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Scaling+single-cell+genomics+from+phenomenology+to+mechanism.">Scaling single-cell genomics from phenomenology to mechanism.</a> Nature. 541 (7637), 331-338 (2017).</li><li>Wu, M., Singh, A. K. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Microfluidic+Flow+Cytometry+for+Single-Cell+Protein+Analysis.">Microfluidic Flow Cytometry for Single-Cell Protein Analysis.</a> Methods in Molecular Biology. 1346, 69-83 (2015).</li><li>Schwartzman, O., Tanay, A. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Single-cell+epigenomics:+techniques+and+emerging+applications.">Single-cell epigenomics: techniques and emerging applications.</a> Nature Reviews Genetics. 16 (12), 716-726 (2015).</li><li>Macaulay, I. C., Ponting, C. P., Voet, T. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Single-Cell+Multiomics:+Multiple+Measurements+from+Single+Cells.">Single-Cell Multiomics: Multiple Measurements from Single Cells.</a> Trends in Genetics. 33 (2), 155-168 (2017).</li><li>Buenrostro, J. 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=Single-cell+chromatin+accessibility+reveals+principles+of+regulatory+variation.">Single-cell chromatin accessibility reveals principles of regulatory variation.</a> Nature. 523 (7561), 486-490 (2015).</li><li>Habib, 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=Massively+parallel+single-nucleus+RNA-seq+with+DroNc-seq.">Massively parallel single-nucleus RNA-seq with DroNc-seq.</a> Nature Methods. 14 (10), 955-958 (2017).</li><li>Corces, M. R., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=An+improved+ATAC-seq+protocol+reduces+background+and+enables+interrogation+of+frozen+tissues.">An improved ATAC-seq protocol reduces background and enables interrogation of frozen tissues.</a> Nature Methods. 14 (10), 959-962 (2017).</li><li>Slyper, 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=A+single-cell+and+single-nucleus+RNA-Seq+toolbox+for+fresh+and+frozen+human+tumors.">A single-cell and single-nucleus RNA-Seq toolbox for fresh and frozen human tumors.</a> Nature Medicine. 26 (5), 792-802 (2020).</li><li>Mathys, H., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Single-cell+transcriptomic+analysis+of+Alzheimer's+disease.">Single-cell transcriptomic analysis of Alzheimer's disease.</a> Nature. 570 (7761), 332-337 (2019).</li><li>Krishnaswami, S. R., 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=Using+single+nuclei+for+RNA-seq+to+capture+the+transcriptome+of+postmortem+neurons.">Using single nuclei for RNA-seq to capture the transcriptome of postmortem neurons.</a> Nature Protocols. 11 (3), 499-524 (2016).</li><li>Al-Dalahmah, O., 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=Single-nucleus+RNA-seq+identifies+Huntington+disease+astrocyte+states.">Single-nucleus RNA-seq identifies Huntington disease astrocyte states.</a> Acta Neuropathologica Communications. 8 (1), 19 (2020).</li><li>Jakel, 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=Altered+human+oligodendrocyte+heterogeneity+in+multiple+sclerosis.">Altered human oligodendrocyte heterogeneity in multiple sclerosis.</a> Nature. 566 (7745), 543-547 (2019).</li><li>Butler, A., Hoffman, P., Smibert, P., Papalexi, E., Satija, R. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Integrating+single-cell+transcriptomic+data+across+different+conditions,+technologies,+and+species.">Integrating single-cell transcriptomic data across different conditions, technologies, and species.</a> Nature Biotechnology. , (2018).</li><li>Lake, B. B., 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=Integrative+single-cell+analysis+of+transcriptional+and+epigenetic+states+in+the+human+adult+brain.">Integrative single-cell analysis of transcriptional and epigenetic states in the human adult brain.</a> Nature Biotechnology. 36 (1), 70-80 (2018).</li><li>Stuart, 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=Comprehensive+Integration+of+Single-Cell+Data.">Comprehensive Integration of Single-Cell Data.</a> Cell. 177 (7), 1888-1902 (2019).</li><li>Bready, D., Placantonakis, D. G. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Molecular+Pathogenesis+of+Low-Grade+Glioma.">Molecular Pathogenesis of Low-Grade Glioma.</a> Neurosurgery Clinics of North America. 30 (1), 17-25 (2019).</li><li>Venteicher, A. 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=Decoupling+genetics,+lineages,+and+microenvironment+in+IDH-mutant+gliomas+by+single-cell+RNA-seq.">Decoupling genetics, lineages, and microenvironment in IDH-mutant gliomas by single-cell RNA-seq.</a> Science. 355 (6332), (2017).</li><li>Tirosh, 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=Single-cell+RNA-seq+supports+a+developmental+hierarchy+in+human+oligodendroglioma.">Single-cell RNA-seq supports a developmental hierarchy in human oligodendroglioma.</a> Nature. 539 (7628), 309-313 (2016).</li><li>Weng, Q., 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=Single-Cell+Transcriptomics+Uncovers+Glial+Progenitor+Diversity+and+Cell+Fate+Determinants+during+Development+and+Gliomagenesis.">Single-Cell Transcriptomics Uncovers Glial Progenitor Diversity and Cell Fate Determinants during Development and Gliomagenesis.</a> Cell Stem Cell. 24 (5), 707-723 (2019).</li><li>Neftel, C., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=An+Integrative+Model+of+Cellular+States,+Plasticity,+and+Genetics+for+Glioblastoma.">An Integrative Model of Cellular States, Plasticity, and Genetics for Glioblastoma.</a> Cell. 178 (4), 835-849 (2019).</li><li>Al-Ali, R., 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=Single-nucleus+chromatin+accessibility+reveals+intratumoral+epigenetic+heterogeneity+in+IDH1+mutant+gliomas.">Single-nucleus chromatin accessibility reveals intratumoral epigenetic heterogeneity in IDH1 mutant gliomas.</a> Acta Neuropathologica Communications. 7 (1), 201 (2019).</li></ol>

The authors have nothing to disclose.

The field of intra-tumoral heterogeneity is at an exciting stage, with novel assays and platforms being developed to challenge and expand the existing knowledge. Intra-tumoral heterogeneity is a crucial factor that contributes to disease progression and resistance to current treatment modalities in gliomas28. Recent studies on brain tumors have focused on this important aspect by using single cell transcriptomic and epigenomic assays to better characterize the cellular heterogeneity within the sam...

Diffuse lower grade gliomas (LGG), the most common primary brain tumor in adults, are infiltrative neoplasms that often arise in the cerebral hemisphere. LGGs exhibit both inter- and intra-tumor heterogeneity, which is not only driven by the tumor population but also by the non-malignant cells intricately involved in tumor development and progression1,2,3,4,5.
Over the last decade, there has been an avalanche of genomic data gathered in the field of gliomas. These data mainly come from bulk tumor sequencing studies and have contributed immensely to the molecular characterization, and the current classification of brain tumors5,6,7,8,9,10,11. However, even though these studies revealed the broad molecular landscape associated with gliomas, there is still a disappointing lack of progress regarding therapeutic intervention. One of the obstacles to treatment resistance in brain tumors is intra-tumor heterogeneity. To address this issue, various studies have been focusing on the genomic, transcriptomic, proteomic, and epigenetic heterogeneity present within a tumor at a single cell level12,13,14,15,16,17.
Although there have been remarkable technological advancements in the single cell field over the last couple of years, one of the major limiting factors is the availability of fresh specimens needed to isolate the cells and perform these experiments. To overcome this limitation, there have been several successful attempts at performing assays, such as snRNA-seq and snATAC-seq from frozen tissues, using nuclei rather than cells18,19. The majority of these methods rely on either fluorescence-activated cell sorting (FACS) or filtration strategies. Both single cell and single nuclei approaches have their strengths and drawbacks. Single cell approaches maintain mitochondrial transcripts, which although may be informative, can also reduce transcriptome coverage due to their high abundance. Single nuclei isolation approaches eliminate a high percentage of the mitochondrial fraction, thereby allowing a more in-depth coverage of the nuclear transcripts20.
There are various commercially available platforms that have been used over the recent years to assay single cell genomics data, including RNA-seq and ATAC-seq. One of the most prominent platforms is the 10x Genomics Chromium platform for single cell gene expression and single cell ATAC profiling. As the platform works with the help of microfluidic chambers, any debris or aggregates can clog the system leading to loss of data, reagents, and valuable clinical samples. Therefore, the success of single cell studies depends largely on the accurate isolation of single cells/nuclei.
The protocol that we will demonstrate herein is a slightly modified combination of the DroNc-seq and Omni-ATAC-seq protocols, and utilizes a similar approach to recent studies that utilize snRNA-seq to understand neurological disorders and neuronal cell types in the human brain18,19,21,22,23,24. The protocol uses a combination of enzymatic/mechanical dissociation of frozen samples followed by filtration and gradient centrifugation and allows for fast and accurate isolation of single nuclei from fresh frozen glioma tissues. We have successfully used this protocol to generate snRNA-seq and snATAC-seq data from the same nuclei preparation from brain tumor specimens.

<table>
	<tbody>
		<tr>
			<td>2-Mercaptoethanol</td>
			<td>Sigma</td>
			<td>M6250</td>
			<td></td>
		</tr>
		<tr>
			<td>CaCl2</td>
			<td>Sigma</td>
			<td>21115-100ML</td>
			<td></td>
		</tr>
		<tr>
			<td>Dounce Homogenizer</td>
			<td>Active motif</td>
			<td>40401</td>
			<td></td>
		</tr>
		<tr>
			<td>EDTA (0.5 M)</td>
			<td>Thermo Scientific</td>
			<td>R1021</td>
			<td></td>
		</tr>
		<tr>
			<td>Falcon 5 mL Round Bottom Polystyrene Test Tube</td>
			<td>Corning</td>
			<td>352235</td>
			<td></td>
		</tr>
		<tr>
			<td>Iodixanol (aka Optiprep)</td>
			<td>Stem cell technologies</td>
			<td>07820</td>
			<td></td>
		</tr>
		<tr>
			<td>MACs Smart Strainers (30 &#181;m)</td>
			<td>Miltenyi Biotec</td>
			<td>130-098-458</td>
			<td></td>
		</tr>
		<tr>
			<td>MACS SmartStrainers (100 &#181;m)</td>
			<td>Miltenyi Biotec</td>
			<td>130-098-463</td>
			<td></td>
		</tr>
		<tr>
			<td>Mg(Ac)2</td>
			<td>Sigma</td>
			<td>63052-100ML</td>
			<td></td>
		</tr>
		<tr>
			<td>NP-40</td>
			<td>Abcam</td>
			<td>ab142227</td>
			<td></td>
		</tr>
		<tr>
			<td>Nuclei Isolation Kit: Nuclei EZ Prep</td>
			<td>Sigma</td>
			<td>NUC101-1KT</td>
			<td></td>
		</tr>
		<tr>
			<td>Phenylmethanesulfonyl fluoride (PMSF)</td>
			<td>Sigma</td>
			<td>P7626</td>
			<td></td>
		</tr>
		<tr>
			<td>Pre-Separation Filters (20 &#181;m)</td>
			<td>Miltenyi Biotec</td>
			<td>130-101-812</td>
			<td></td>
		</tr>
		<tr>
			<td>Safe lock tubes 1.5 mL</td>
			<td>Eppendorf</td>
			<td>0030120086</td>
			<td></td>
		</tr>
		<tr>
			<td>Safe lock tubes 2.0 mL</td>
			<td>Eppendorf</td>
			<td>0030120094</td>
			<td></td>
		</tr>
		<tr>
			<td>Single Cell ATAC</td>
			<td>10x Genomics</td>
			<td></td>
			<td></td>
		</tr>
		<tr>
			<td>Single Cell Gene Expression</td>
			<td>10x Genomics</td>
			<td></td>
			<td></td>
		</tr>
		<tr>
			<td>Sucrose</td>
			<td>Sigma</td>
			<td>S0389</td>
			<td></td>
		</tr>
		<tr>
			<td>Wide Bore pipette tips (1000 &#181;L)</td>
			<td>Themo Fisher Scientific</td>
			<td>2079GPK</td>
			<td></td>
		</tr>
		<tr>
			<td>Wide Bore pipette tips (200 &#181;L)</td>
			<td>Themo Fisher Scientific</td>
			<td>2069GPK</td>
			<td></td>
		</tr>
	</tbody>
</table>

nuclei isolation from fresh frozen brain tumors for single-nucleus rna-seq and atac-seq

Adult diffuse gliomas exhibit inter- and intra-tumor heterogeneity. Until recently, the majority of large-scale molecular profiling efforts have focused on bulk approaches that led to the molecular classification of brain tumors. Over the last five years, single cell sequencing approaches have highlighted several important features of gliomas. The majority of these studies have utilized fresh brain tumor specimens to isolate single cells using flow cytometry or antibody-based separation methods. Moving forward, the use of fresh-frozen tissue samples from biobanks will provide greater flexibility to single cell applications. Furthermore, as the single-cell field advances, the next challenge will be to generate multi-omics data from either a single cell or the same sample preparation to better unravel tumor complexity. Therefore, simple and flexible protocols that allow data generation for various methods such as single-nucleus RNA sequencing (snRNA-seq) and single nucleus Assay for Transposase-Accessible Chromatin with high-throughput sequencing (snATAC-seq) will be important for the field.
Recent advances in the single cell field coupled with accessible microfluidic instruments such as the 10x genomics platform have facilitated single cell applications in research laboratories. To study brain tumor heterogeneity, we developed an enhanced protocol for the isolation of single nuclei from fresh frozen gliomas. This protocol merges existing single cell protocols and combines a homogenization step followed by filtration and buffer mediated gradient centrifugation. The resulting samples are pure single nuclei suspensions that can be used to generate single nucleus gene expression and chromatin accessibility data from the same nuclei preparation.

Single nucleus&#160;genomics is an evolving field with limited data and protocols. A critical factor that influences the outcome of single nuclei assays is the isolation of pure and intact nuclei. We combined two published protocols (DroNc-seq and Omni-ATAC-seq protocols) to isolate high-quality and pure nuclei from fresh frozen glioma tissue blocks in a relatively short time thereby maintaining the stability of the transcripts (Figure 1).
The use of various filtr...

Watch this Scientific Journal Video about Nuclei Isolation from Fresh Frozen Brain Tumors for Single-Nucleus RNA-seq and ATAC-seq at JoVE.com

Nuclei Isolation from Fresh Frozen Brain Tumors for Single-Nucleus RNA-seq and ATAC-seq

Intra-tumoral heterogeneity is an inherent feature of tumors, including gliomas. We developed a simple and efficient protocol that utilizes a combination of buffers and gradient centrifugation to isolate single nuclei from fresh frozen glioma tissues for single nucleus RNA and ATAC sequencing studies.

Adult diffuse gliomas exhibit inter- and intra-tumor heterogeneity. Until recently, the majority of large-scale molecular profiling efforts have focused ...

nuclei-isolation-from-fresh-frozen-brain-tumors-for-single-nucleus

Research

JoVE Journal

Cancer Research

11.9K Views.  University Hospital Heidelberg. Intra-tumoral heterogeneity is an inherent feature of tumors, including gliomas. We developed a simple and efficient protocol that utilizes a combination of buffers and gradient centrifugation to isolate single nuclei from fresh frozen glioma tissues for single nucleus RNA and ATAC sequencing studies.

Video: Nuclei Isolation from Fresh Frozen Brain Tumors for Single-Nucleus RNA-seq and ATAC-seq

Next Generation Sequencing for the Detection of Actionable Mutations in Solid and Liquid Tumors

As our understanding of the driver mutations necessary for initiation and progression of cancers improves, we gain critical information on how specific molecular profiles of a tumor may predict responsiveness to therapeutic agents or provide knowledge about prognosis. At our institution a tumor genotyping program was established as part of routine clinical care, screening both hematologic and solid tumors for a wide spectrum of mutations using two next-generation sequencing (NGS) panels: a custom, 33 gene hematological malignancies panel for use with peripheral blood and bone marrow, and a commercially produced solid tumor panel for use with formalin-fixed paraffin-embedded tissue that targets 47 genes commonly mutated in cancer. Our workflow includes a pathologist review of the biopsy to ensure there is adequate amount of tumor for the assay followed by customized DNA extraction is performed on the specimen. Quality control of the specimen includes steps for quantity, quality and integrity and only after the extracted DNA passes these metrics an amplicon library is generated and sequenced. The resulting data is analyzed through an in-house bioinformatics pipeline and the variants are reviewed and interpreted for pathogenicity. Here we provide a snapshot of the utility of each panel using two clinical cases to provide insight into how a well-designed NGS workflow can contribute to optimizing clinical outcomes.

This manuscript describes clinical protocols for two next-generation sequencing panels. One panel interrogates hematologic malignancies while the other panel targets genes commonly mutated in solid tumors. Molecular classification of driver mutations in human malignancies offers valuable prognostic and predictive information.

As our understanding of the driver mutations necessary for initiation and progression of cancers improves, we gain critical information on how specific ...

Transplantation of Zebrafish Pediatric Brain Tumors into Immune-competent Hosts for Long-term Study of Tumor Cell Behavior and Drug Response

Tumor cell transplantation is an important technique to define the mechanisms controlling cancer cell growth, migration, and host response, as well as to assess potential patient response to therapy. Current methods largely depend on using syngeneic or immune-compromised animals to avoid rejection of the tumor graft. Such methods require the use of specific genetic strains that often prevent the analysis of immune-tumor cell interactions and/or are limited to specific genetic backgrounds. An alternative method in zebrafish takes advantage of an incompletely developed immune system in the embryonic brain before 3 days, where tumor cells are transplanted for use in short-term assays (i.e., 3 to 10 days). However, these methods cause host lethality, which prevents the long-term study of tumor cell behavior and drug response. This protocol describes a simple and efficient method for the long-term orthotopic transplantation of zebrafish brain tumor tissue into the fourth ventricle of a 2-day-old immune-competent zebrafish. This method allows: 1) long-term study of tumor cell behaviors, such as invasion and dissemination; 2) durable tumor response to drugs; and 3) re-transplantation of tumors for the study of tumor evolution and/or the impact of different host genetic backgrounds. In summary, this technique allows cancer researchers to assess engraftment, invasion, and growth at distant sites, as well as to perform chemical screens and cell competition assays over many months. This protocol can be extended to studies of other tumor types and can be used to elucidate mechanisms of chemoresistance and metastasis.

The transplantation of cancer cells is an important tool for the identification of cancer mechanisms and therapeutic responses. Current techniques depend on immune-incompetent animals. Here, we describe a method to transplant zebrafish tumor cells into immune-competent embryos for the long-term analysis of tumor cell behavior and in vivo drug responses.

Tumor cell transplantation is an important technique to define the mechanisms controlling cancer cell growth, migration, and host response, as well as to ...

Development of a Human Preclinical Model of Osteoclastogenesis from Peripheral Blood Monocytes Co-cultured with Breast Cancer Cell Lines

The crosstalk between tumor cells and bone cells in the bone microenvironment is crucial to understanding the mechanism of bone metastasis formation. We developed an in vitro fully human preclinical model of a co-culture of breast cancer cells and monocytes undergoing differentiation towards osteoclasts. We optimized a model of osteoclastogenesis starting from a sample of peripheral blood collected from healthy donors. Peripheral blood mononuclear cells (PBMCs) were first separated by density gradient centrifugation, seeded at a high density and induced to differentiate by adding two growth factors (GFs): receptor activator of nuclear factor-&#954;B ligand (RANKL) and macrophage colony-stimulating factor (MCSF). The cells were left in culture for 14 days and then fixed and analyzed by downstream analysis. In osteolytic bone metastases, one of the effects of cancer cell arrival in bone is the induction of osteoclastogenesis. We thus challenged our model with co-cultures of breast cancer cells to study the differentiation power of cancer cells with respect to GFs. A straightforward way of studying cancer cell-osteoclast interaction is to perform indirect co-cultures based on the use of conditioned medium collected from breast cancer cell cultures and mixed with fresh medium. This mixture is then used to induce osteoclast differentiation. We also optimized a method of direct co-culture in which cancer cells and monocytes undergoing differentiation share the medium and exchange secreted factors. This is a significant improvement over the original indirect co-culture method as researchers can observe the reciprocal interactions of the two cell types and perform downstream analyses for both cancer cells and osteoclasts. This method enables us to study the effect of drugs on the metastatic bone microenvironment and to seed cell lines other than those derived from breast cancer. The model can also be used to study other diseases such as osteoporosis or other bone conditions.

This protocol describes development of an in vitro human preclinical model of osteoclastogenesis from peripheral blood monocytes cultured with breast cancer cell lines to mimic the cancer cell-osteoclast interaction. The model could be used to further our understanding of bone metastasis formation and improve therapeutic options.

The crosstalk between tumor cells and bone cells in the bone microenvironment is crucial to understanding the mechanism of bone metastasis formation. We ...

Detection of a CDH1 Rare Transcript Variant in Fresh-frozen Gastric Cancer Tissues by Chip-based Digital PCR

CDH1a, a non-canonical transcript of the CDH1 gene, has been found to be expressed in some gastric cancer (GC) cell lines, whereas it is absent in normal gastric mucosa. Recently, we detected CDH1a transcript variant in fresh-frozen tumor tissues obtained from patients with GC. The expression of this variant in tissue samples was investigated by the chip-based digital PCR (dPCR) approach presented here. dPCR offers the potential for an accurate, robust, and highly sensitive measurement of nucleic acids and is increasingly utilized for many applications in different fields. dPCR is capable of detecting rare targets; in addition, dPCR offers the possibility for absolute and precise quantification of nucleic acids without the need for calibrators and standard curves. In fact, the reaction partitioning enriches the target from the background, which improves amplification efficiency and tolerance to inhibitors. Such characteristics make dPCR an optimal tool for the detection of the CDH1a rare transcript.

Detection of a CDH1 Rare Transcript Variant in Fresh-frozen Gastric Cancer Tissues by Chip-based Digital PCR

The manuscript describes a chip-based digital PCR assay to detect a rare CDH1 transcript variant (CDH1a) in fresh-frozen normal and tumor tissues obtained from patients with gastric cancer.

CDH1a, a non-canonical transcript of the CDH1 gene, has been found to be expressed in some gastric cancer (GC) cell lines, whereas it is absent in normal ...

Obtaining Cancer Stem Cell Spheres from Gynecological and Breast Cancer Tumors

Cancer stem cells (CSC) are a small population with self-renewal and plasticity which are responsible for tumorigenesis, resistance to treatment and recurrent disease. This population can be identified by surface markers, enzymatic activity and a functional profile. These approaches per se are limited, due to phenotypic heterogeneity and CSC plasticity. Here, we update the sphere-forming protocol to obtain CSC spheres from breast and gynecological cancers, assessing functional properties, CSC markers and protein expression. The spheres are obtained with single-cell seeding at low density in suspension culture, using a semi-solid methylcellulose medium to avoid migration and aggregates. This profitable protocol can be used in cancer cell lines but also in primary tumors. The tridimensional non-adherent suspension culture thought to mimic the tumor microenvironment, particularly the CSC-niche, is supplemented with epidermal growth factor and basic fibroblast growth factor to ensure CSC signaling. Aiming for robust identification of CSC, we propose a complementary approach, combining functional and phenotypic evaluation. Sphere-forming capacity, self-renewal and sphere projection area establish CSC functional properties. Additionally, characterization comprises flow cytometry evaluation of the markers, represented by CD44+/CD24- and CD133, and Western blot, considering ALDH. The presented protocol was also optimized for primary tumor samples, following a sample digestion procedure, useful for translational research.

The aim of this methodology is to identify cancer stem cells (CSC) in cancer cell lines and primary human tumor samples with the sphere-forming protocol, in a robust manner, using functional assays and phenotypic characterization with flow cytometry and Western blot.

Cancer stem cells (CSC) are a small population with self-renewal and plasticity which are responsible for tumorigenesis, resistance to treatment and ...

Generation of Orthotopic Pancreatic Tumors and Ex vivo Characterization of Tumor-Infiltrating T Cell Cytotoxicity

In vivo models of pancreatic cancer provide invaluable tools for studying disease dynamics, immune infiltration and new therapeutic strategies. The orthotopic murine model can be performed on large cohorts of immunocompetent mice simultaneously, is relatively inexpensive and preserves the cognate tissue microenvironment. The quantification of T cell infiltration and cytotoxic activity within orthotopic tumors provides a useful indicator of an antitumoral response.
This protocol describes the methodology for surgical generation of orthotopic pancreatic tumors by injection of a low number of syngeneic tumor cells resuspended in 5 &#181;L basement membrane directly into the pancreas. Mice bearing orthotopic tumors take approximately 30 days to reach endpoint, at which point tumors can be harvested and processed for characterization of tumor-infiltrating T cell activity. Rapid enzymatic digestion using collagenase and DNase allows a single-cell suspension to be extracted from tumors. The viability and cell surface markers of immune cells extracted from the tumor are preserved; therefore, it is appropriate for multiple downstream applications, including flow-assisted cell sorting of immune cells for culture or RNA extraction, flow cytometry analysis of immune cell populations. Here, we describe the ex vivo stimulation of T cell populations for intracellular cytokine quantification (IFN&#947; and TNF&#945;) and degranulation activity (CD107a) as a measure of overall cytotoxicity. Whole-tumor digests were stimulated with phorbol myristate acetate and ionomycin for 5 h, in the presence of anti-CD107a antibody in order to upregulate cytokine production and degranulation. The addition of brefeldin A and monensin for the final 4 h was performed to block extracellular transport and maximize cytokine detection. Extra- and intra-cellular staining of cells was then performed for flow cytometry analysis, where the proportion of IFN&#947;+, TNF&#945;+ and CD107a+ CD4+ and CD8+ T cells was quantified.
This method provides a starting base to perform comprehensive analysis of the tumor microenvironment.

Generation of Orthotopic Pancreatic Tumors and Ex vivo Characterization of Tumor-Infiltrating T Cell Cytotoxicity

This protocol describes the surgical generation of orthotopic pancreatic tumors and the rapid digestion of freshly isolated murine pancreatic tumors. Following digestion, viable immune cell populations can be used for further downstream analysis, including ex vivo stimulation of T cells for intracellular cytokine detection by flow cytometry.

In vivo models of pancreatic cancer provide invaluable tools for studying disease dynamics, immune infiltration and new therapeutic strategies. The ...

Orthotopic Transplantation of Breast Tumors as Preclinical Models for Breast Cancer

Preclinical models that faithfully recapitulate tumor heterogeneity and therapeutic response are critical for translational breast cancer research. Immortalized cell lines are easy to grow and genetically modify to study molecular mechanisms, yet the selective pressure from cell culture often leads to genetic and epigenetic alterations over time. Patient-derived xenograft (PDX) models faithfully recapitulate the heterogeneity and drug response of human breast tumors. PDX models exhibit a relatively short latency after orthotopic transplantation that facilitates the investigation of breast tumor biology and drug response. The transplantable genetically engineered mouse models allow the study of breast tumor immunity. The current protocol describes the method to orthotopically transplant breast tumor fragments into the mammary fat pad followed by drug treatments. These preclinical models provide valuable approaches to investigate breast tumor biology, drug response, biomarker discovery and mechanisms of drug resistance.

Patient-derived xenograft (PDX) models and transplantable genetically engineered mouse models faithfully recapitulate human disease and are preferred models for basic and translational breast cancer research. Here, a method is described to orthotopically transplant breast tumor fragments into the mammary fat pad to study tumor biology and evaluate drug response.

Preclinical models that faithfully recapitulate tumor heterogeneity and therapeutic response are critical for translational breast cancer research. ...

A Rapid Screening Workflow to Identify Potential Combination Therapy for GBM using Patient-Derived Glioma Stem Cells

The glioma stem cells (GSCs) are a small fraction of cancer cells which play essential roles in tumor initiation, angiogenesis, and drug resistance in glioblastoma (GBM), the most prevalent and devastating primary brain tumor. The presence of GSCs makes the GBM very refractory to most of individual targeted agents, so high-throughput screening methods are required to identify potential effective combination therapeutics. The protocol describes a simple workflow to enable rapid screening for potential combination therapy with synergistic interaction. The general steps of this workflow consist of establishing luciferase-tagged GSCs, preparing matrigel coated plates, combination drug screening, analyzing, and validating the results.

The glioma stem cells (GSCs) are a small fraction of cancer cells which play essential roles in tumor initiation, angiogenesis, and drug resistance in ...

ATAC-Seq Optimization for Cancer Epigenetics Research

The assay for transposase-accessible chromatin with high-throughput sequencing (ATAC-seq) probes deoxyribonucleic acid (DNA) accessibility using the hyperactive Tn5 transposase. Tn5 cuts and ligates adapters for high-throughput sequencing within accessible chromatin regions. In eukaryotic cells, genomic DNA is packaged into chromatin, a complex of DNA, histones, and other proteins, which acts as a physical barrier to the transcriptional machinery. In response to extrinsic signals, transcription factors recruit chromatin remodeling complexes to enable access to the transcriptional machinery for gene activation. Therefore, identifying open chromatin regions is useful when monitoring enhancer and gene promoter activities during biological events such as cancer progression. Since this protocol is easy to use and has a low cell input requirement, ATAC-seq has been widely adopted to define open chromatin regions in various cell types, including cancer cells. For successful data acquisition, several parameters need to be considered when preparing ATAC-seq libraries. Among them, the choice of cell lysis buffer, the titration of the Tn5 enzyme, and the starting volume of cells are crucial for ATAC-seq library preparation in cancer cells. Optimization is essential for generating high-quality data. Here, we provide a detailed description of the ATAC-seq optimization methods for epithelial cell types.

ATAC-seq is a DNA sequencing method that uses the hyperactive mutant transposase, Tn5, to map changes in chromatin accessibility mediated by transcription factors. ATAC-seq enables the discovery of the molecular mechanisms underlying phenotypic alterations in cancer cells. This protocol outlines optimization procedures for ATAC-seq in epithelial cell types, including cancer cells.

The assay for transposase-accessible chromatin with high-throughput sequencing (ATAC-seq) probes deoxyribonucleic acid (DNA) accessibility using the ...

Pancreatic Cancer-Derived Tumor Organoids and Fibroblasts from Fresh Tissue

Establishment of Pancreatic Cancer-Derived Tumor Organoids and Fibroblasts From Fresh Tissue

Tumor organoids are three-dimensional (3D) ex vivo tumor models that recapitulate the biological key features of the original primary tumor tissues. Patient-derived tumor organoids have been used in translational cancer research and can be applied to assess treatment sensitivity and resistance, cell-cell interactions, and tumor cell interactions with the tumor microenvironment. Tumor organoids are complex culture systems that require advanced cell culture techniques and culture media with specific growth factor cocktails and a biological basement membrane that mimics the extracellular environment. The ability to establish primary tumor cultures highly depends on the tissue of origin, the cellularity, and the clinical features of the tumor, such as the tumor grade. Furthermore, tissue sample collection, material quality and quantity, as well as correct biobanking and storage are crucial elements of this procedure. The technical capabilities of the laboratory are also crucial factors to consider. Here, we report a validated SOP/protocol that is technically and economically feasible for the culture of ex vivo tumor organoids from fresh tissue samples of pancreatic adenocarcinoma origin, either from fresh primary resected patient donor tissue or patient-derived xenografts (PDX). The technique described herein can be performed in laboratories with basic tissue culture and mouse facilities and is tailored for wide application in the translational oncology field.

Author Spotlight: Establishment of Pancreatic Cancer-Derived Tumor Organoids and Fibroblasts From Fresh Tissue  

Tumor organoids have revolutionized cancer research and the approach to personalized medicine. They represent a clinically relevant tumor model that allows researchers to stay one step ahead of the tumor in the clinic. This protocol establishes tumor organoids from fresh pancreatic tumor tissue samples and patient-derived xenografts of pancreatic adenocarcinoma origin.

Tumor organoids are three-dimensional (3D) ex vivo tumor models that recapitulate the biological key features of the original primary tumor tissues. ...