We thank the Scientific Genomics Platform at the Max Delbr&#252;ck Center for Molecular Medicine in the Helmholtz Association, Berlin for technical support.
JL and KMSO were supported by the German Research Foundation (DFG) Research Training Group GRK 2318 and by Research Unit FOR 2841. KMSO was supported by Collaborative Research Grant 1365. AB was supported by funding from the Gottfried Wilhelm Leibniz Prize of the DFG awarded to NR.

All animal experiments were conducted in accordance with the Animal Welfare Act (TierSchG) and the Animal Welfare Experimental Animal Regulation (TierSchVersV) and were authorized by local authorities and the Animal Welfare Officers at our institution (MDC).
1. Tissue preparation
<ol>
	<li>Prepare a 6-well plate containing 2 mL of 1x phosphate-buffered saline (PBS) per well for each kidney that will be obtained. Prepare a 6-well plate containing 2 mL of RNA stabilization solution per well and kidney. Pre-cool both plates on ice.</li>
	<li>Euthanize a 3- to 6-month-old male C57BL/6 mouse. Place the mouse on a dissecting tray, pin down the extremities and sterilize the abdomen with 70% ethanol.</li>
	<li>Open the abdomen up to the ribcage using forceps and scissors. Lift the intestine and other organs to the side and remove the kidneys by carefully cutting the ureter, renal artery, and vein with a scissor. Wash the kidney in the previously prepared, ice-cold 1x PBS and remove the renal fascia and any remaining fat from the kidney until all white tissue is removed (Figure 2A).</li>
	<li>Place the kidney on a cold dissecting plate and use a sharp scalpel or razor blade to obtain a middle slice of 1-2 mm. Make sure the tissue piece contains the entire corticomedullary axis (Figure 2B). Use microdissection scissors and forceps to carefully trim the cortex from the sides of the center piece. Within the dissected tissue piece, the three segments cortex, outer medulla, and inner medulla should be clearly visible (Figure 2C). 
	&#8203;NOTE: The slice should not exceed a thickness of 2 mm or a weight of 20 mg to ensure sufficient buffer amounts for effective tissue lysis and in order to minimize ambient background RNA in the cDNA libraries. Ambient RNA wastes sequence capacity, as it is not associated with single nuclei.</li>
	<li>Transfer the kidney piece to the previously prepared RNA stabilization solution and incubate for 24 h at 4 &#176;C to avoid RNA degradation. After 24 h, remove the RNA stabilization solution and store the tissue at -80 &#176;C until further use. Carefully remove the excess solution with tissue paper.</li>
</ol>
2. Nuclei isolation
<ol>
	<li>Cleaning and preparation steps
	<ol>
		<li>Clean benchtops and pipettes with 70% ethanol and RNase decontamination solution.</li>
		<li>Clean a round-bottomed, 2 mL tissue grinder tube and matching pestle A and B with RNase decontamination solution, followed by 70% ethanol and RNase-free water (1 grinder tube and pestle set per sample). Let it dry completely.</li>
		<li>Pre-cool the centrifuge to 4 &#176;C.</li>
		<li>Label and pre-cool three 15 mL collection tubes, a 1.5 mL collection tube, a 5 mL fluorescence-activated cell sorting (FACS) collection tube, and a dry grinder tube for each sample on ice.</li>
	</ol>
	</li>
	<li>Buffer preparation
	<ol>
		<li>Warm up the Ribonucleoside-vanadyl complex stock solution to 65 &#176;C until reconstituted to a green-black clear solution according to manufacturer&#39;s instructions.11</li>
		<li>Prepare 1x PBS containing 4% bovine serum albumin (BSA) as described in Table 1A. Additionally, prepare 1x PBS with 0.04% BSA (Table 1B). Filter both solutions using a 0.2 &#181;m surfactant-free cellulose acetate (SFCA) membrane syringe filter and keep on ice until further use.</li>
		<li>Prepare Nuclei Lysis Buffer 1 (NLB1, Table 1C). Add 4 mL of EZ lysis buffer for Nuclei Lysis Buffer 2 (NLB2, Table 1D) and 2 mL of 0.04 % BSA / PBS for the Nuclei Suspension Buffer (NSB, Table 1E) to 15 mL tubes. Add the RNase inhibitor solution to NLB2 and NSB directly before use as indicated below in the protocol. Keep on ice until further use.</li>
		<li>Prepare EZ lysis buffer with 10% sucrose (Sucrose Gradient Buffer, Table 1F). Mix well and filter the buffer into a fresh 15 mL tube using a 0.2 &#181;m SFCA membrane syringe filter. Keep on ice until further use.</li>
	</ol>
	</li>
	<li>Tissue homogenization and cell lysis 
	NOTE: In order to minimize RNA degradation, all steps are carried out on ice. The grinder tube, Petri dish, and all buffers need to be pre-cooled. All resuspension steps are done by carefully pipetting the nuclei suspension. Do not vortex the sample to avoid shearing forces and damage to nuclei.
	<ol>
		<li>Take the frozen kidney piece and transfer it to a 60 mm polystyrene Petri dish on ice containing 1 mL of NLB1.</li>
		<li>Mince the tissue thoroughly using a razor blade or scalpel (Figure 3A).</li>
		<li>Cut off the tip of a 1 mL pipette tip and transfer the minced tissue and buffer to the grinder tube. Make sure to transfer all tissue pieces. Wash the Petri dish 5-10 times with the buffer, if necessary.</li>
		<li>Homogenize the suspension on ice by slowly moving pestle A, 25x up and down in the grinder tube. Avoid air bubbles caused by rapid movement (Figure 3B).</li>
		<li>Pass the homogenate through a 100 &#181;m strainer in a pre-cooled 15 mL collection tube and wash the filter with another 1 mL of NLB1.</li>
		<li>Wash the grinder tube with cold EZ nuclei lysis buffer and discard the buffer.</li>
		<li>Transfer the homogenate back into the grinder tube and homogenize the suspension on ice by slowly moving pestle B, 15x up and down in the grinder tube. Avoid air bubbles caused by rapid movement (Figure 3C).</li>
		<li>Transfer the homogenate to a pre-cooled 15 mL collection tube. Wash the grinder tube with another 2 mL of NLB1 and make sure to transfer all tissue fragments to the collection tube. Incubate the homogenate (total volume of 4 mL) for 5 min on ice to lyse the cells.</li>
	</ol>
	</li>
	<li>Nuclei purification
	<ol>
		<li>Pass the homogenate through a 40 &#181;m strainer into a pre-cooled 15 mL collection tube. Spin the collection tube for 5 min at 500 x g at 4 &#176;C in a centrifuge with a swinging-bucket rotor. In the meantime, add RNase inhibitor solution to NLB2 (Table 1D).</li>
		<li>Remove the supernatant without disturbing the pellet. Carefully resuspend the pellet in 4 mL of NLB2.</li>
		<li>Carefully underlay the suspension with a 1 mL cushion of Sucrose Gradient Buffer. Centrifuge at 500 x g for 5 min at 4 &#176;C in a centrifuge with a swinging-bucket rotor. In the meantime, add RNase inhibitor solution to NSB (Table 1E).</li>
		<li>After centrifugation, gently remove the collection tube from the centrifuge and be careful not to disturb the two layers when handling the collection tube. Cell debris is visible between the two layers. Remove the supernatant carefully starting with the debris. Remove the remaining supernatant without disturbing the nuclei pellet and carefully resuspend the pellet in 1 mL of NSB. 
		NOTE: The resuspension volume depends on the amount of tissue used for the isolation and pellet size gained after the last centrifugation step. The volume might need to be adapted to the expected number of nuclei.</li>
		<li>Pass the homogenate through a 20 &#181;m strainer into the pre-cooled 5 mL FACS collection tube.</li>
	</ol>
	</li>
</ol>
3. Nuclei sorting
<ol>
	<li>Add 20 &#181;L of 4&#8242;,6-diamidino-2-phenylindole (DAPI) per mL of NSB to a final concentration of 2 &#181;M to the homogenate in the FACS collection tube and mix carefully. Incubate for 5 min on ice.</li>
	<li>Prepare the pre-cooled 1.5 mL collection tube with 20 &#181;L of 4% BSA /1x PBS and add 0.5 &#181;L RNase inhibitor solution to a final concentration of 1 U/&#181;L. Immediately proceed to sorting.</li>
	<li>Sort the nuclei using a cell sorter.
	<ol>
		<li>Mix the nuclei suspension briefly before inserting the FACS collection tube into the sorter.</li>
		<li>Set a first gate P1 based on the forward scatter (FSC) and side scatter (SSC) to exclude debris and aggregates (Figure 4A).</li>
		<li>To exclude empty or damaged nuclei and multiplets, set a subsequent gate based on the DAPI-Area versus DAPI-Height (DAPI-A vs DAPI-H) (Figure 4B).</li>
		<li>Sort single nuclei into the 1.5 mL collection tube containing 4% BSA /1x PBS with 1 U/&#181;L RNase inhibitor solution prepared in 3.2.</li>
	</ol>
	</li>
</ol>
4. Quality control
<ol>
	<li>Measure the final nuclei concentration under a fluorescence microscope or in an automated counting chamber in at least two independent counts and assess the suspension quality (Figure 5). 
	NOTE: Optimal concentrations are between 700 - 1,200 nuclei/&#181;L. Lower cell concentrations such as 700 nuclei/&#181;L may be preferable as resulting cDNA libraries contained less ambient background RNA (transcripts not associated with individual nuclei).</li>
	<li>Calculate the required volume of nuclei suspension for the desired recovery of sequenced single nuclei. In order to avoid nuclei aggregation and RNA degradation, proceed immediately to library preparation.</li>
</ol>

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L., Kim, J., Susztak, K. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Understanding+the+kidney+one+cell+at+a+time.">Understanding the kidney one cell at a time.</a> Kidney International. 96 (4), 862-870 (2019).</li><li>Clark, A. R., Greka, A. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=The+power+of+one:+advances+in+single-cell+genomics+in+the+kidney.">The power of one: advances in single-cell genomics in the kidney.</a> Nature Reviews Nephrology. 16 (2), 73-74 (2020).</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=A+single-nucleus+RNA-sequencing+pipeline+to+decipher+the+molecular+anatomy+and+pathophysiology+of+human+kidneys.">A single-nucleus RNA-sequencing pipeline to decipher the molecular anatomy and pathophysiology of human kidneys.</a> Nature Communications. 10 (1), 2832 (2019).</li><li>Wu, H., Kirita, Y., Donnelly, E. L., Humphreys, B. D. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Advantages+of+single-nucleus+over+single-cell+RNA+sequencing+of+adult+kidney:+Rare+cell+types+and+novel+cell+states+revealed+in+fibrosis.">Advantages of single-nucleus over single-cell RNA sequencing of adult kidney: Rare cell types and novel cell states revealed in fibrosis.</a> Journal of the American Society of Nephrology. 30 (1), 23-32 (2019).</li><li>Adam, M., Potter, A. S., Potter, S. S. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Psychrophilic+proteases+dramatically+reduce+single-cell+RNA-seq+artifacts:+a+molecular+atlas+of+kidney+development.">Psychrophilic proteases dramatically reduce single-cell RNA-seq artifacts: a molecular atlas of kidney development.</a> Development. 144 (19), 3625-3632 (2017).</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>Muto, Y., 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+transcriptional+and+chromatin+accessibility+profiling+redefine+cellular+heterogeneity+in+the+adult+human+kidney.">Single cell transcriptional and chromatin accessibility profiling redefine cellular heterogeneity in the adult human kidney.</a> Nature Communications. 12 (1), 2190 (2021).</li><li>Hinze, 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=Kidney+single-cell+transcriptomes+predict+spatial+corticomedullary+gene+expression+and+tissue+osmolality+gradients.">Kidney single-cell transcriptomes predict spatial corticomedullary gene expression and tissue osmolality gradients.</a> Journal of the American Society of Nephrology. 32 (2), 291 (2021).</li><li>Berger, S. 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+cytoplasmic+RNA:+ribonucleoside-vanadyl+complexes.">Isolation of cytoplasmic RNA: ribonucleoside-vanadyl complexes.</a> Methods in Enzymology. 152, 227-234 (1987).</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. 36 (5), 411-420 (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>Park, J., 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+of+the+mouse+kidney+reveals+potential+cellular+targets+of+kidney+disease.">Single-cell transcriptomics of the mouse kidney reveals potential cellular targets of kidney disease.</a> Science. 360 (6390), 758-763 (2018).</li><li>Kirita, Y., Wu, H., Uchimura, K., Wilson, P. 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The authors have nothing to disclose.

Single-cell transcriptomics advance the understanding of cell type-specific gene expression in renal physiology and disease. Here, we provided a simple and reproducible method to isolate high-quality single nuclei from frozen mouse kidney tissue for snRNA-seq in a standardized way.
For snRNA-seq, it is critical to use high-quality nuclei as input for library generation and to avoid RNA degradation during tissue processing. Therefore, the incubation of tissue pieces in RNA stabilization solution immediately after dissection is essential to protect and stabilize cellular RNA and allows to store samples at - 80 &#176;C indefinitely. When applying this protocol to frozen tissue without RNA stabilization solution treatment, such as archival material, a trial run is required, and the RNA quality needs to be assessed as we observed a significant loss of RNA integrity in snap-frozen tissue without prior incubation in RNA stabilization solution.
In general, appropriate sample handling is crucial to maximizing the recovery of intact, single nuclei. All resuspension steps should be carried out by pipetting carefully to avoid shear stress and physical damage. Buffers for the final nuclei resuspension and nuclei sorting should contain BSA to avoid nuclei loss and aggregation.
Buffer volumes in this protocol are optimized for very small tissue samples (~15 mg). It is critical to ensure complete cell lysis and sufficient washing to generate high-quality suspensions. Larger tissue blocks or whole kidney samples will result in excessive nuclei concentrations that lead to clumping and aggregation, high abundance of ambient RNA, and overall poor suspension quality. If larger samples or other tissues are processed, it is highly recommended to perform trial runs to determine optimal buffer volumes for minimal ambient RNA levels. Nuclei and RNA quality and concentrations need to be examined carefully as overloading results in overall poor performance.
In addition, large amounts of cell debris, causing high levels of ambient RNA not associated with single nuclei influence the sequencing results negatively. Clarification of the nuclei suspension by centrifugation through a sucrose cushion mitigates this problem to some extent, but it can also lead to bias in cell type representation by counter selecting against dense, small nuclei present, for instance, in immune cells16. If this is of concern, the sucrose gradient should be omitted. By contrast, we found that flow cytometry based on DAPI staining was critical to reduce the amount of cell debris in order to produce a high-quality single nuclei suspension.
The isolation of single nuclei has considerable advantages when compared to single-cell approaches8. It is compatible with properly frozen tissue, making the tissue collection more flexible, and circumvents the need of enzyme-based tissue dissociation, which can introduce transcriptional stress responses6,17. Furthermore, it overcomes the dissociation bias that favors the selection of easily dissociable cell types of the renal cortex, which may lead to an underrepresentation of medullary cell types in some enzyme-based approaches5,6,10.
Using a central kidney piece instead of whole kidney tissue further saves resources and corrects for the overrepresentation of abundant cell types as described earlier10. However, depending on the mouse model or phenotype investigated, it may be beneficial to use whole kidney samples instead of a single middle slice. Whole kidney samples may be more representative of true cell proportions, or changes occurring in the whole kidney, whereas a trimmed middle slice proved advantageous for medullary phenotypes or when sample material was limited. This decision, therefore, is highly user-specific and should be considered carefully.

Kidneys display a highly complex tissue architecture. They consist of functionally and anatomically distinct segments along a corticomedullary axis and mediate biological functions, such as regulation of extracellular fluid volume, electrolyte balance, or acid-base homeostasis1.
Advances in single-cell transcriptomics have enabled the in-depth characterization of complex tissues and accelerated the understanding of segment and cell type-specific gene expression in renal physiology, development, and disease2,3,4.
However, the enzyme-based dissociation protocols that are frequently utilized for scRNA-seq display several drawbacks and constraints. Depending on the protocol, they generate transcriptional stress responses and tissue dissociation bias towards easier-to-dissociate cortical cell types5,6. Although protocols using cold-active proteases for embryonic kidneys are able to mitigate stress-related transcriptional alterations, they fail to overcome the dissociation bias towards cortical cells and might not be readily adaptable to different kinds of diseased kidney tissues7. In addition, single-cell approaches are not easily compatible with frozen tissue samples, limiting their application mostly to non-archived, fresh tissue, thus making the tissue collection a restricting factor6.
Single-nuclei RNA sequencing (snRNA-seq) can circumvent these limitations8,9. Here, we present a protocol for nuclei isolation from a central slice of frozen adult mouse kidney tissue (Figure 1)10. Our protocol is simple and provides a standardized approach to obtain RNA sequencing libraries with a balanced representation of diverse kidney cell types for experimental models that do not involve strong regional tissue changes. In the latter case, our protocol can also be performed with whole kidneys.

<table><tbody><tr><td>Cell sorter</td><td>-</td><td>-</td><td>For fluorescence-activated cell sorting (FACS); e.g. BD FACSAria Cell Sorter.</td></tr><tr><td>Centrifuge 5810 R</td><td>Eppendorf</td><td>5811000015</td><td></td></tr><tr><td>Countess Cell Counting Chamber Slides</td><td>Invitrogen</td><td>C10228</td><td></td></tr><tr><td>Countess II FL Automated Cell Counter</td><td>Invitrogen</td><td>AMQAF1000</td><td>Needs to contain DAPI light cube to count nuclei. Alternatively, nuclei can be counted manually under fluorescence microscope.</td></tr><tr><td>4&amp;prime;,6-Diamidino-2-phenyl-indol-dihydrochlorid (DAPI)</td><td>Biotrend</td><td>40043/b</td><td>Stock solution prepared with a concentration of 100 &amp;micro;M. Used for nuclei staining in a final concentration of 2 &amp;micro;M.</td></tr><tr><td>D(+)-Sucrose &amp;ge;99.9%, ultrapure DNAse-, RNAse-free</td><td>VWR</td><td>0335-500G</td><td></td></tr><tr><td>DNA LoBind Microcentrifuge Tubes (1.5 mL)</td><td>Eppendorf</td><td>22431021</td><td></td></tr><tr><td>Ethanol, 70 %</td><td>-</td><td>-</td><td></td></tr><tr><td>FACS tubes</td><td>pluriSelect</td><td>43-10100-46</td><td></td></tr><tr><td>KIMBLE Dounce tissue grinder set 2 mL complete</td><td>Sigma-Aldrich</td><td>D8938-1SET</td><td></td></tr><tr><td>Minisart Syringe Filters 0.2 &amp;micro;m</td><td>Sartorius</td><td>16534-GUK</td><td></td></tr><tr><td>Nuclease-free Water</td><td>Invitrogen</td><td>AM9937</td><td></td></tr><tr><td>Nuclei EZ Prep Nuclei Isolation Kit</td><td>Sigma-Aldrich</td><td>NUC-101</td><td>Nuclei EZ Lysis Buffer (Product No. N3408) needed for buffer preparation.</td></tr><tr><td>PBS (Phosphate-Buffered Saline) 1X without calcium or magnesium</td><td>Corning</td><td>21-040-CV</td><td></td></tr><tr><td>Petri dishes, polystyrene 60 mm</td><td>Sigma-Aldrich</td><td>P5481</td><td></td></tr><tr><td>Phosphate-Buffered Saline (PBS) with 10% Bovine Albumin</td><td>Sigma-Aldrich</td><td>SRE0036</td><td></td></tr><tr><td>pluriStrainer Mini 100 &amp;micro;m</td><td>pluriSelect</td><td>43-10100-46</td><td></td></tr><tr><td>pluriStrainer Mini 20 &amp;micro;m</td><td>pluriSelect</td><td>43-10020-40</td><td></td></tr><tr><td>pluriStrainer Mini 40 &amp;micro;m</td><td>pluriSelect</td><td>43-10040-40</td><td></td></tr><tr><td>Polystyrene Centrifuge Tube (15 mL)</td><td>Falcon</td><td>352099</td><td></td></tr><tr><td>Razor blades</td><td>-</td><td>-</td><td></td></tr><tr><td>RiboLock RNase Inhibitor (40 U/&amp;micro;L)</td><td>Thermo Fisher</td><td>EO0384</td><td></td></tr><tr><td>Ribonucleoside-vanadyl complex</td><td>New England Biolabs</td><td>S1402S</td><td>Follow manufacturer&#039;s instructions (https://international.neb.com/products/s1402-ribonucleoside-vanadyl-complex#Product%20Information). Upon use the 200 mM stock solution is reconstituted to a green-black clear solution by incubating at 65 &amp;deg;C.</td></tr><tr><td>RNA&lt;em&gt;later&lt;/em&gt; Stabilization Solution</td><td>Invitrogen</td><td>AM7020</td><td></td></tr><tr><td>RNase AWAY</td><td>Fisher Scientific</td><td>11952385</td><td></td></tr></tbody></table>

nuclei isolation from adult mouse kidney for single-nucleus rna-sequencing

The kidneys regulate diverse biological processes such as water, electrolyte, and acid-base homeostasis. Physiological functions of the kidney are executed by multiple cell types arranged in a complex architecture across the corticomedullary axis of the organ. Recent advances in single-cell transcriptomics have accelerated the understanding of cell type-specific gene expression in renal physiology and disease. However, enzyme-based tissue dissociation protocols, which are frequently utilized for single-cell RNA-sequencing (scRNA-seq), require mostly fresh (non-archived) tissue, introduce transcriptional stress responses, and favor the selection of abundant cell types of the kidney cortex resulting in an underrepresentation of cells of the medulla.
Here, we present a protocol that avoids these problems. The protocol is based on nuclei isolation at 4 &#176;C from frozen kidney tissue. Nuclei are isolated from a central piece of the mouse kidney comprised of the cortex, outer medulla, and inner medulla. This reduces the overrepresentation of cortical cells typical for whole-kidney samples for the benefit of medullary cells such that data will represent the entire corticomedullary axis at sufficient abundance. The protocol is simple, rapid, and adaptable and provides a step towards the standardization of single-nuclei transcriptomics in kidney research.

To determine the performance of our protocol, we used the 10x Genomics Chromium Single Cell 3&#39; Gene Expression Kit v3.1 for library preparation and analyzed the snRNA-seq data with the Seurat package12,13.
Figure 6&#160;shows results from a representative snRNA-seq library. To assess the quality of our nuclei, we plotted the number of genes against the number of transcripts (defined by unique molecular identifiers (UMIs)) colored by the fraction of mitochondrial reads (Figure 6A). Nuclei of good quality generally show higher numbers of reads, correlating UMI and gene numbers, and low mitochondrial read fractions.
For the subsequent analysis, nuclei with less than 500 or more than 4000 counted genes, or more than 5% of mitochondrial RNA were excluded (n = 828). Only genes expressed in a minimum of three nuclei were included. We detected about 20,000 genes in total in the remaining 6,000 nuclei with 1,600 median genes and 2,800 median UMIs per nucleus (Figure 6B).
Clustering was based on highly variable genes. We identified a total of 18 clusters. Cell identities were annotated based on known marker genes (not shown). Subclusters of one cell type were summarized to one cluster resulting in a total of 11 distinct cell types: podocytes, proximal tubule (PT), thin limb (tL), thick ascending limb (TAL), distal convoluted tubule (DCT), connecting tubule (CNT), collecting duct principal and intercalated cells (CD-PC, A-IC, B-IC), deep medullary epithelium of the pelvis (DMEP) and endothelium. Gene expression patterns of cluster-enriched markers were visualized in a dot plot (Figure 6C) and cell type clusters in a t-distributed stochastic neighbor embedding (t-SNE) plot (Figure 6D).
To assess cell type distributions in our sample, the percentage of each cell type was calculated (Figure 6E) and used to determine the ratio of PT to TAL. The PT is mainly located in the kidney cortex and frequently overrepresented in kidney single-cell datasets as cells of the PT are easy to dissociate and highly abundant in whole kidney samples. The TAL on the other hand stretches across the whole outer medulla14. Thus, the ratio of PT and TAL fractions represents a good measure for the enrichment of medullary cell types in a kidney single-cell dataset. In general, the PT/TAL ratio in single-cell whole kidney datasets ranged from 8 (unpublished data from cold-protease-treated whole kidney tissue) to 45 for enzymatically dissociated tissue10,14,15. In the snRNA-seq dataset presented here we were able to reach a PT/TAL ratio of 2. This result illustrates that removal of excess cortex during tissue dissection combined with snRNA-seq results in a strikingly improved kidney cell type representation.
<img alt="Figure 1" class="xfigimg" src="/files/ftp_upload/62901/62901fig01.jpg" /> 
Figure 1: Schematic overview of the workflow. The protocol consists of four major steps that include tissue dissection followed by nuclei isolation, nuclei sorting and a final purity and concentration assessment. Scale bar = 100 &#181;m. <a href="https://www.jove.com/files/ftp_upload/62901/62901fig01large.jpg" target="_blank">Please click here to view a larger version of this figure.</a>
<img alt="Figure 2" class="xfigimg" src="/files/ftp_upload/62901/62901fig02.jpg" /> 
Figure 2: Kidney dissection and tissue preparation. (A) Representative image of dissected whole kidney. The dotted lines indicate the cuts required to obtain a middle slice of 1-2 mm with a representation of all renal cell types. (B) Representative image of obtained middle slice. The dotted lines indicate the cuts for cortex trimming from the side. (C) Representative image of central kidney piece with trimmed cortex. Cortex (C), outer medulla (OM) and inner medulla (IM) are clearly visible. Scale bar = 500 &#181;m. <a href="https://www.jove.com/files/ftp_upload/62901/62901fig02large.jpg" target="_blank">Please click here to view a larger version of this figure.</a>
<img alt="Figure 3" class="xfigimg" src="/files/ftp_upload/62901/62901fig03.jpg" /> 
Figure 3: Tissue homogenization and nuclei purification. (A) Representative image showing sufficiently minced kidney tissue. Scale bar = 500 &#181;m. (B) Homogenate after first homogenization step (25 strokes with pestle A, 2 mL grinder tube). (C) Homogenate after second homogenization step (15 strokes with pestle B, 2 mL grinder tube). <a href="https://www.jove.com/files/ftp_upload/62901/62901fig03large.jpg" target="_blank">Please click here to view a larger version of this figure.</a>
<img alt="Figure 4" class="xfigimg" src="/files/ftp_upload/62901/62901fig04.jpg" /> 
Figure 4: Gating strategy for nuclei sorting. (A) A first gate P1 was set based on forward scatter (FSC) vs side scatter (SSC) to exclude debris and aggregates. (B) A subsequent gate based on DAPI-Area (DAPI-A) vs DAPI-Height (DAPI-H) excluded empty or damaged nuclei and multiplets. <a href="https://www.jove.com/files/ftp_upload/62901/62901fig04large.jpg" target="_blank">Please click here to view a larger version of this figure.</a>
<img alt="Figure 5" class="xfigimg" src="/files/ftp_upload/62901/62901fig05.jpg" /> 
Figure 5: Nuclei suspension before and after nuclei sorting. (A, C) DAPI-stained nuclei (blue). (B, D) Overlay of DAPI and brightfield (BF) channel. Before sorting (upper panel) the nuclei suspension contains cell debris and aggregates (labeled with white arrowheads). After sorting (lower panel) the nuclei suspension appears much cleaner. Examples of DAPI-stained nuclei are labeled with black arrowheads. Good quality nuclei appear round and smooth with an intact membrane and are well-separated, whereas nuclei of poor quality appear wrinkled and show loss of the nuclear membrane. Scale bar = 250 &#181;m. <a href="https://www.jove.com/files/ftp_upload/62901/62901fig05large.jpg" target="_blank">Please click here to view a larger version of this figure.</a>
<img alt="Figure 6" class="xfigimg" src="/files/ftp_upload/62901/62901fig06.jpg" /> 
Figure 6: Quality control and analysis of a representative snRNA-seq dataset. (A) Number of genes (nGene) plotted against the number of unique molecular identifiers (nUMI) colored by the fraction of mitochondrial reads (percent.mt). Low quality nuclei correspond to the bottom left quadrant of the plot (n = 828) and were excluded from subsequent analysis. (B) Distribution and median of nGene and nUMI detected per nucleus in the snRNA-seq dataset, representing 6,177 nuclei (&#62; 500 genes). Libraries were sequenced to a median depth of ~ 8,200 mapped reads per nucleus. (C) Dot plot showing gene expression patterns of cluster-enriched markers (x-axis) for individual cell types (y-axis). The size of the dot corresponds to the proportion of cells expressing the indicated gene. The color corresponds to the average expression. (D) T-distributed stochastic neighbor embedding (t-SNE) plot of identified cell types. (E) Cell type distribution in snRNA-seq dataset. PT, proximal tubule; tL, thin limb; TAL, thick ascending limb, DCT, distal convoluted tubule; CNT, connecting tubule; CD-PC, collecting duct principal cells; A-IC, type A intercalated cells; B-IC, type B intercalated cells; DMEP, deep medullary epithelium of pelvis. <a href="https://www.jove.com/files/ftp_upload/62901/62901fig06large.jpg" target="_blank">Please click here to view a larger version of this figure.</a>
<table border="1" fo:keep-together.within-page="1" fo:keep-with-next.within-page="always">
	<tbody>
		<tr>
			<td colspan="3">Reagent</td>
			<td>Final concentration</td>
			<td>Volume (mL)</td>
		</tr>
		<tr>
			<td colspan="3">(A) 4 % BSA / PBS</td>
			<td></td>
			<td></td>
		</tr>
		<tr>
			<td colspan="3">Phosphate-Buffered Saline (PBS) with 10% Bovine Albumin</td>
			<td>4%</td>
			<td>2</td>
		</tr>
		<tr>
			<td colspan="3">PBS (Phosphate-Buffered Saline) 1X without calcium or magnesium</td>
			<td>-</td>
			<td>3</td>
		</tr>
		<tr>
			<td colspan="3">(B) 0.04 % BSA / PBS</td>
			<td></td>
			<td></td>
		</tr>
		<tr>
			<td colspan="3">4 % BSA / PBS</td>
			<td>0.04 %</td>
			<td>0.5</td>
		</tr>
		<tr>
			<td colspan="3">PBS (Phosphate-Buffered Saline) 1X without calcium or magnesium</td>
			<td>-</td>
			<td>49.5</td>
		</tr>
		<tr>
			<td colspan="3">(C) Nuclei Lysis Buffer 1 (NLB1)</td>
			<td></td>
			<td></td>
		</tr>
		<tr>
			<td colspan="3">Nuclear EZ Lysis Buffer</td>
			<td>-</td>
			<td>4</td>
		</tr>
		<tr>
			<td colspan="3">RiboLock RNase Inhibitor (40 U/&#181;L)</td>
			<td>1 U/&#181;L</td>
			<td>0.1</td>
		</tr>
		<tr>
			<td colspan="3">Ribonucleoside-vanadyl complex (200 mM)</td>
			<td>10 mM</td>
			<td>0.2</td>
		</tr>
		<tr>
			<td colspan="3">(D) Nuclei Lysis Buffer 2 (NLB2)</td>
			<td></td>
			<td></td>
		</tr>
		<tr>
			<td colspan="3">Nuclear EZ Lysis Buffer</td>
			<td>-</td>
			<td>4</td>
		</tr>
		<tr>
			<td colspan="3">RiboLock RNase Inhibitor (40 U/&#181;L)</td>
			<td>1 U/&#181;L</td>
			<td>0.1</td>
		</tr>
		<tr>
			<td colspan="3">(E) Nuclei Suspension Buffer (NSB)</td>
			<td></td>
			<td></td>
		</tr>
		<tr>
			<td colspan="3">0.04 % BSA / PBS</td>
			<td>-</td>
			<td>2</td>
		</tr>
		<tr>
			<td colspan="3">RiboLock RNase Inhibitor (40 U/&#181;L)</td>
			<td>1 U/&#181;L</td>
			<td>0.05</td>
		</tr>
		<tr>
			<td colspan="3">(F) Sucrose Gradient Buffer (10 % Sucrose)</td>
			<td></td>
			<td></td>
		</tr>
		<tr>
			<td colspan="3">Weight 1 g of Sucrose</td>
			<td></td>
			<td></td>
		</tr>
		<tr>
			<td colspan="3">Dissolve in 6 ml of Nuclear EZ Lysis Buffer</td>
			<td></td>
			<td></td>
		</tr>
		<tr>
			<td colspan="3">Fill up to 10 mL with Nuclear EZ Lysis Buffer</td>
			<td></td>
			<td></td>
		</tr>
		<tr>
			<td colspan="3">Filter through a 0.2 &#181;m syringe filter into a fresh tube</td>
			<td></td>
			<td></td>
		</tr>
	</tbody>
</table>
Table 1: Solution recipes: (A) Preparation of 4% BSA/1x PBS. Filter using a 0.2 &#181;m SFCA membrane syringe filter and keep on ice until use. (B) Preparation of 0.04% BSA/1 x PBS. Filter using a 0.2 &#181;m SFCA membrane syringe filter and keep on ice until use. (C) Preparation of Nuclei Lysis Buffer 1 (NLB1). Indicated volumes are provided per sample. Keep on ice until use. (D) Preparation of Nuclei Lysis Buffer 2 (NLB2). Indicated volumes are provided per sample. Add RiboLock RNase Inhibitor to NLB2 directly before use as noted in the protocol. Keep on ice until use. (E) Preparation of Nuclei Suspension Buffer (NSB). Indicated volumes are provided per sample. Add RiboLock RNase Inhibitor to NSB directly before use as noted in the protocol. Keep on ice until use. (F) Preparation of Sucrose Gradient Buffer. Filter using a 0.2 &#181;m SFCA membrane syringe filter and keep on ice until use.

Watch this Scientific Journal Video about Nuclei Isolation from Adult Mouse Kidney for Single-Nucleus RNA-Sequencing at JoVE.com

Nuclei Isolation from Adult Mouse Kidney for Single-Nucleus RNA-Sequencing

Here, we present a protocol to isolate high-quality nuclei from frozen mouse kidneys that improve the representation of medullary kidney cell types and avoids the gene expression artifacts from enzymatic tissue dissociation.

The kidneys regulate diverse biological processes such as water, electrolyte, and acid-base homeostasis. Physiological functions of the kidney are ...

nuclei-isolation-from-adult-mouse-kidney-for-single-nucleus-rna

Research

JoVE Journal

Biology

4.4K Views.  Charité - Universitätsmedizin Berlin, corporate member of Freie Universität Berlin and Humboldt-Universität zu Berlin. Onze methode helpt bij het genereren en begrijpen van genexpressiegegevens van complexe weefsels op eencellig niveau. Onze methode kan op vrijwel elk weefsel op dezelfde manier worden toegepast en leidt tot gegevens van hoge kwaliteit met zeer weinig protocolgerelateerde artefacten. Dr.Janna Leiz en ikzelf van het Schmidt-Ott lab zullen het protocol presenteren.Begin met het plaatsen van de nier op een koude ontleedplaat en gebruik een scherp scalpel of scheermesje om een middelste pla...

Video: Nuclei Isolation from Adult Mouse Kidney for Single-Nucleus RNA-Sequencing

Neuronal Nuclei Isolation from Human Postmortem Brain Tissue

Neurons in the human brain become postmitotic largely during prenatal development, and thus maintain their nuclei throughout the full lifespan. However, little is known about changes in neuronal chromatin and nuclear organization during the course of development and aging, or in chronic neuropsychiatric disease. However, to date most chromatin and DNA based assays (other than FISH) lack single cell resolution. To this end, the considerable cellular heterogeneity of brain tissue poses a significant limitation, because typically various subpopulations of neurons are intermingled with different types of glia and other non-neuronal cells. One possible solution would be to grow cell-type specific cultures, but most CNS cells, including neurons, are ex vivo sustainable, at best, for only a few weeks and thus would provide an incomplete model for epigenetic mechanisms potentially operating across the full lifespan.  Here, we provide a protocol to extract and purify nuclei from frozen (never fixed) human postmortem brain. The method involves extraction of nuclei in hypotonic lysis buffer, followed by ultracentrifugation and immunotagging with anti-NeuN antibody. Labeled neuronal nuclei are then collected separately using fluorescence-activated sorting. This method should be applicable to any brain region in a wide range of species and suitable for chromatin immunoprecipitation studies with site- and modification-specific anti-histone antibodies, and for DNA methylation and other assays. 

The cellular heterogeneity of brain tissue poses a significant limitation for the study of epigenetic markings in chromatin because most assays lack single cell resolution. Neurons typically are intermingled with glia and other non-neuronal cells. We provide a protocol to extract and collect neuronal nuclei from human brain.

Neurons in the human brain become postmitotic largely during prenatal development, and thus maintain their nuclei throughout the full lifespan. However, ...

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.

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 ...

Cancer Research

Nuclei Isolation from Mouse Cardiac Progenitor Cells at Single-Cell Resolution

Nuclei Isolation from Mouse Cardiac Progenitor Cells for Epigenome and Gene Expression Profiling at Single-Cell Resolution

The developing heart is a complex structure containing various progenitor cells controlled by complex regulatory mechanisms. The examination of the gene expression and chromatin state of individual cells allows the identification of the cell type and state. Single-cell sequencing approaches have revealed a number of important characteristics of cardiac progenitor cell heterogeneity. However, these methods are generally restricted to fresh tissue, which limits studies with diverse experimental conditions, as the fresh tissue must be processed at once in the same run to reduce the technical variability. Therefore, easy and flexible procedures to produce data from methods such as single-nucleus RNA sequencing (snRNA-seq) and the single-nucleus assay for transposase-accessible chromatin with high-throughput sequencing (snATAC-seq) are needed in this area. Here, we present a protocol to rapidly isolate nuclei for subsequent single-nuclei dual-omics (combined snRNA-seq and snATAC-seq). This method allows the isolation of nuclei from frozen samples of cardiac progenitor cells and can be combined with platforms that use microfluidic chambers.

Author Spotlight: Nuclei Isolation from Mouse Cardiac Progenitor Cells for Epigenome and Gene Expression Profiling at Single-Cell Resolution  

Here, we present a protocol describing cell nuclei preparation. After microdissection and enzymatic dissociation of cardiac tissue into single cells, the progenitor cells were frozen, followed by isolation of pure viable cells, which were used for single-nucleus RNA sequencing and the single-nucleus assay for transposase-accessible chromatin with high-throughput sequencing analyses.

The developing heart is a complex structure containing various progenitor cells controlled by complex regulatory mechanisms. The examination of the gene ...

Developmental Biology

Isolation of Adult Spinal Cord Nuclei for Massively Parallel Single-nucleus RNA Sequencing

Probing an individual cell&#39;s gene expression enables the identification of cell type and cell state. Single-cell RNA sequencing has emerged as a powerful tool for studying transcriptional profiles of cells, particularly in heterogeneous tissues such as the central nervous system. However, dissociation methods required for single cell sequencing can lead to experimental changes in the gene expression and cell death. Furthermore, these methods are generally restricted to fresh tissue, thus limiting studies on archival and bio-bank material. Single nucleus RNA sequencing (snRNA-Seq) is an appealing alternative for transcriptional studies, given that it accurately identifies cell types, permits the study of tissue that is frozen or difficult to dissociate, and reduces dissociation-induced transcription. Here, we present a high-throughput protocol for rapid isolation of nuclei for downstream snRNA-Seq. This method enables isolation of nuclei from fresh or frozen spinal cord samples and can be combined with two massively parallel droplet encapsulation platforms.

Here, we present a protocol to rapidly isolate high-quality nuclei from the fresh or frozen tissue for downstream massively parallel RNA sequencing. We include detergent-mechanical and hypotonic-mechanical tissue disruption and cell lysis options, both of which can be used for isolation of nuclei.

Probing an individual cell&#39;s gene expression enables the identification of cell type and cell state. Single-cell RNA sequencing has emerged as a ...

Neuroscience

Gentle Isolation of Nuclei from the Brain Tissue of Adult African Turquoise Killifish, a Naturally Short-Lived Model for Aging Research

Studying brain aging at single-cell resolution in vertebrate systems remains challenging due to cost, time, and technical constraints. Here, we demonstrate a protocol to generate single-nucleus RNA sequencing (snRNA-seq) libraries from the brains of the naturally short-lived vertebrate African turquoise killifish Nothobranchius furzeri. The African turquoise killifish has a lifespan of 4-6 months and can be housed in a cost-effective manner, thus reducing cost and time barriers to study vertebrate brain aging. However, tailored protocols are needed to isolate nuclei of sufficient quality for downstream single-cell experiments from the brain of young and aged fish. Here, we demonstrate an empirically optimized protocol for the isolation of high-quality nuclei from the brain of adult African turquoise killifish, a critical step in the generation of high-quality single nuclei omic libraries. Furthermore, we show that the steps to reduce contaminating background RNA are important to clearly distinguish cell types. In summary, this protocol demonstrates the feasibility of studying brain aging in non-traditional vertebrate model organisms.

Here we present a protocol to isolate nuclei from the brains of the short-lived vertebrate model Nothobranchius furzeri for downstream applications such as single-nucleus RNA sequencing or single-nucleus assay for transposase-accessible chromatin with sequencing (ATAC-seq).

Studying brain aging at single-cell resolution in vertebrate systems remains challenging due to cost, time, and technical constraints. Here, we ...

Low-input Nucleus Isolation and Multiplexing with Barcoded Antibodies of Mouse Sympathetic Ganglia for Single-nucleus RNA Sequencing

The cardiac autonomic nervous system is crucial in controlling cardiac function, such as heart rate and cardiac contractility, and is divided into sympathetic and parasympathetic branches. Normally, there is a balance between these two branches to maintain homeostasis. However, cardiac disease states such as myocardial infarction, heart failure, and hypertension can induce the remodeling of cells involved in cardiac innervation, which is associated with an adverse clinical outcome.
Although there are vast amounts of data for the histological structure and function of the cardiac autonomic nervous system, its molecular biological architecture in health and disease is still enigmatic in many aspects. Novel technologies such as single-cell RNA sequencing (scRNA-seq) hold promise for the genetic characterization of tissues at single-cell resolution. However, the relatively large size of neurons may impede the standardized use of these techniques. Here, this protocol exploits droplet-based single-nucleus RNA sequencing (snRNA-seq), a method to characterize the biological architecture of cardiac sympathetic neurons in health and disease. A stepwise approach is demonstrated to perform snRNA-seq of the bilateral superior cervical (SCG) and stellate ganglia (StG) dissected from adult mice.
This method enables long-term sample preservation, maintaining an adequate RNA quality when samples from multiple individuals/experiments cannot be collected all at once within a short period of time. Barcoding the nuclei with hashtag oligos (HTOs) enables demultiplexing and the trace-back of distinct ganglionic samples post sequencing. Subsequent analyses revealed successful nuclei capture of neuronal, satellite glial, and endothelial cells of the sympathetic ganglia, as validated by snRNA-seq. In summary, this protocol provides a stepwise approach for snRNA-seq of sympathetic extrinsic cardiac ganglia, a method that has the potential for broader application in studies of the innervation of other organs and tissues.

This protocol describes the detailed, low-input sample preparation for single-nucleus sequencing, including the dissection of mouse superior cervical and stellate ganglia, cell dissociation, cryopreservation, nucleus isolation, and hashtag barcoding.

The cardiac autonomic nervous system is crucial in controlling cardiac function, such as heart rate and cardiac contractility, and is divided into ...

Medicine

Nuclei Isolation from Whole Tissue using a Detergent and Enzyme-Free Method

High-throughput transcriptome and epigenome profiling requires preparation of a single cell or single nuclei suspension. Preparation of the suspension with&#160;intact cell or nuclei involves dissociation and permeabilization, steps that can introduce unwanted noise and undesirable damage. Particularly, certain cell-types such as neurons are challenging to dissociate into individual cells. Additionally, permeabilization of the cellular membrane to release nuclei requires optimization by trial-and-error, which can be time consuming, labor intensive and financially nonviable. To enhance the robustness and reproducibility of sample preparation for high-throughput sequencing, we describe a rapid enzyme and detergent-free column-based nuclei isolation method. The protocol enables efficient isolation of nuclei from the entire zebrafish brain within 20 minutes. The isolated nuclei display intact nuclear morphology and low propensity to aggregate. Further, flow cytometry allows nuclei enrichment and clearance of cellular debris for downstream application. The protocol, which should work on soft tissues and cultured cells, provides a simple and accessible method for sample preparation that can be utilized for high-throughput profiling, simplifying the steps required for successful single-nuclei RNA-seq and ATAC-seq experiments.

Single nuclei isolation relies on dissociation and detergent-based permeabilization of the cell membrane, steps that need optimization and are prone to introducing technical artifacts. We demonstrate a detergent and enzyme-free protocol for rapid isolation of intact nuclei directly from whole tissue, yielding nuclei suitable for single-nucleus RNA-seq (snRNA-Seq) or ATAC-seq.

High-throughput transcriptome and epigenome profiling requires preparation of a single cell or single nuclei suspension. Preparation of the suspension ...

Isolation of Nuclei from Flash-Frozen Liver Tissue for Single-Cell Multiomics

The liver is a complex and heterogenous tissue responsible for carrying out many critical physiological functions, such as the maintenance of energy homeostasis and the metabolism of xenobiotics, among others. These tasks are performed through tight coordination between hepatic parenchymal and non-parenchymal cells. Additionally, various metabolic activities are confined to specific areas of the hepatic lobule-a phenomenon called liver zonation. Recent advances in single-cell sequencing technologies have empowered researchers to investigate tissue heterogeneity at a single-cell resolution. In many complex tissues, including the liver, harsh enzymatic and/or mechanical dissociation protocols can negatively affect the viability or the quality of the single-cell suspensions needed to comprehensively characterize this organ in health and disease.
This paper describes a robust and reproducible protocol for isolating nuclei from frozen, archived liver tissues. This method yields high-quality nuclei that are compatible with downstream, single-cell omics approaches, including single-nucleus RNA-seq, assay for transposase-accessible chromatin with high-throughput sequencing (ATAC-seq), as well as multimodal omics (joint RNA-seq and ATAC-seq). This method has been successfully used for the isolation of nuclei from healthy and diseased human, mouse, and non-human primate frozen liver samples. This approach allows the unbiased isolation of all the major cell types in the liver and, therefore, offers a robust methodology for studying the liver at the single-cell resolution.

Here, we present a protocol for isolating nuclei from flash-frozen, archived liver tissues for single-nucleus RNA-seq, ATAC-seq, and joint multiomics (RNA-seq and ATAC-seq).

The liver is a complex and heterogenous tissue responsible for carrying out many critical physiological functions, such as the maintenance of energy ...

Stria Vascularis Microdissection for Single-Nucleus Sequencing or Immunostaining

Dissection of Adult Mouse Stria Vascularis for Single-Nucleus Sequencing or Immunostaining

Endocochlear potential, which is generated by the stria vascularis, is essential to maintain an environment conducive to appropriate hair cell mechanotransduction and ultimately hearing. Pathologies of the stria vascularis can result in a decreased hearing. Dissection of the adult stria vascularis allows for focused single-nucleus capture and subsequent single-nucleus sequencing and immunostaining. These techniques are used to study stria vascularis pathophysiology at the single-cell level. 
Single-nucleus sequencing can be used in the setting of transcriptional analysis of the stria vascularis. Meanwhile, immunostaining continues to be useful in identifying specific populations of cells. Both methods require proper stria vascularis dissection as a prerequisite, which can prove to be technically challenging.

Author Spotlight: Dissection of Adult Mouse Stria Vascularis for Single-Nucleus Sequencing or Immunostaining  

The stria vascularis is vital to the generation of endocochlear potential. Here, we present the dissection of the adult mouse stria vascularis for single-nucleus sequencing or immunostaining.

Endocochlear potential, which is generated by the stria vascularis, is essential to maintain an environment conducive to appropriate hair cell ...

Isolation and Profiling of Single Nuclei from Frozen Mammalian Tissues

A Simple, Quick, and Partially Automated Protocol for the Isolation of Single Nuclei from Frozen Mammalian Tissues for Single Nucleus Sequencing

Single-cell and single-nucleus RNA sequencing have become common laboratory applications due to the wealth of transcriptomic information that they provide. Single nucleus RNA sequencing, particularly, is useful for investigating gene expression in difficult-to-dissociate tissues. Furthermore, this approach is also compatible with frozen (archival) material. Here, we describe a protocol to isolate high-quality single nuclei from frozen mammalian tissues for downstream single nucleus RNA sequencing in a partially-automated manner using commercially available instruments and reagents. Specifically, a robotic dissociator is used to automate and standardize tissue homogenization, followed by an optimized chemical gradient to filter the nuclei. Lastly, we accurately and automatically count the nuclei using an automated fluorescent cell counter. The performance of this protocol is demonstrated on mouse brain, rat kidney, and cynomolgus liver and spleen tissue. This protocol is straightforward, rapid, and readily adaptable to various mammalian tissues without requiring extensive optimization and provides good quality nuclei for downstream single nuclei RNA sequencing.

Author Spotlight: Enhancing Drug Discovery - Development of Automated, Standardized Protocols for Nuclei Extraction from Frozen Tissues 

The study describes a simple, quick, and partially automated protocol to isolate high-quality nuclei from frozen mammalian tissues for downstream single nuclei RNA sequencing.

Nuclei Isolation from Adult Mouse Kidney for Single-Nucleus RNA-Sequencing

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