purification of nuclei from mouse brain for single-cell multiome analysis

High-Quality Sample Preparation for Multiome 10X Genomics Analysis

For many years, single-cell techniques have been the gold standard for the analysis of biological processes. They were initially restricted to single-cell phenotyping through microscopy, flow cytometry, and similar assays. A breakthrough in single-cell analysis came with the development of approaches for single-cell molecular profiling, in particular single-cell RNA sequencing (scRNA-Seq) that enabled characterizing the entire transcriptome of individual cells. Highly powerful, scRNA-Seq generates information about the transcriptional status of a cell in a specific condition and time point. However, it does not provide visibility on the gene regulation that drives transcription, or on the molecular modifications that occur over time. To overcome this limitation, many efforts have been invested in the development of single-cell multi-omics assays that enable the analysis of multiple factors and processes from the same cell1,2,3,4. The first successful measurement of two modalities within single cells came through linking multiplex surface protein expression patterns with the full transcriptome of individual cells in the CITE-Seq approach5. More recent evolutions combine gene expression with chromatin accessibility (Assay for Transposase-Accessible Chromatin using sequencing, ATAC-Seq), thereby simultaneously capturing transcriptomic and epigenomic modalities in the same cells (e.g., sci-CAR)6. The first commercial solutions that allowed associating transcriptomics with cell phenotype or with epigenetic changes of the same cell came from 10X Genomics.
Experiments for single-cell molecular profiling contain the following steps: (1) tissue dissociation or preparation of single-cell suspensions; (2) cell purification and/or nuclei isolation; (3) partitioning and barcoding; (4) library construction and quality control; (5) next-generation sequencing; (6) data analysis. While steps (3)-(6) may significantly vary depending on the technology employed, the initial steps are generally common to all of them. The quality of the prepared cell/nuclei suspension will determine the overall outcome of the experiment. Depending on the type of tissue, obtaining high-quality single-cell/nuclei suspensions may be challenging. The particularities of some tissues, such as the heart, the muscle, the brain, the lung, the intestine, and others, require methods for tissue disruption and nuclei isolation adapted to each type of sample in order to guarantee the production of high-quality nuclei for molecular analysis7,8,9,10. The tissue disruption methods and dissociation protocols can be mechanical, enzymatic (e.g., a mix of collagenases and DNase), or a combination of the two, and can be performed manually or by instruments (e.g., Qiagen DSC-400, gentleMACS).
Single-cell techniques have become a tool of choice for biomedical research. In neurobiology, the cell diversity in the brain and the complexity of their functions require high-resolution and high-throughput analysis for visualization of rare cell populations and for assessing their heterogeneity11,12,13,14. Linking cellular identity and gene regulatory mechanisms of individual cells provides insights into brain development and physiology. Another example is studies of immune response in the context of infectious, autoimmune, or cancer diseases, which strongly rely on single-cell analyses. The heterogeneity of immune cell subsets and the complexity of their activity and interactions with other cell types require single-cell resolution in deciphering the mechanisms underlying immune response. The immune cells originate from the bone marrow, where hematopoietic progenitors are composed of gradually differentiating cells that acquire and lose cell surface markers throughout a stepwise process prior to exiting the bone marrow to home in the periphery. Single-cell analysis allows for minute characterization of cellular developmental stages. It can be achieved through single-cell phenotyping, conventionally performed by multi-parameter flow cytometry. However, single-cell transcriptomic signatures have been shown to reveal a more precise identification of progenitor cell subtypes since these cells are distributed in clusters that fall into one another and can therefore be misidentified when using a coarse cell surface marker approach15. An increasing number of studies uncover the epigenetic modifications that hematopoietic stem and progenitor cells (HSPCs) can acquire from exposure to various agents, leading to a significant impact on the long-term responsiveness of the immune system16,17,18,19. The novel multi-omics technologies enable studying these processes with single-cell resolution.
Many protocols for cell and nuclei isolation have been described for brain11,20,21,22 and bone marrow samples23,24. To minimize bias due to experimental variability, it is necessary to validate optimized single-nuclei preparation protocols for joint single-cell transcriptomic and epigenomic sequencing, thereby ensuring the reproducibility of single-cell multiomic assays.
Here, two robust protocols for nuclei preparation from (1) fresh-frozen brain tissue and (2) fresh bone marrow HSPCs for downstream single-cell Multiome analysis are described (Figure 1).
<img alt="Figure 1" class="xfigimg" src="/files/ftp_upload/65715/65715fig01.jpg" /> 
Figure 1: Schematic representation of protocols for nuclei isolation from fresh-frozen brain and bone marrow tissues. <a href="https://www.jove.com/files/ftp_upload/65715/65715fig01large.jpg" target="_blank">Please click here to view a larger version of this figure.</a>

Author Spotlight: Advancing Biomedical Research Through Single Cell Analysis 

High-Quality Brain and Bone Marrow Nuclei Preparation for Single Nuclei Multiome Assays

The Cytometry and Biomarkers Technology Unit supports biomedical projects through state-of-the-art technologies and pipelines for cell phenotyping and molecular profiling with single-cell resolution. In this context, we use different tools for single-cell multiomic analysis to obtain insights into gene expression and gene regulation in health and disease. Flow cytometry identify and source individual cells based on unique characteristic.Recent advance include high-throughput, image-based spectral sorters, and those technology offer flexibility in panel design, enable simultaneous use of similar dyes, and the managing of autofluorescence. A major experimental challenge when using cutting-edge, single-cell technologies is working with particularly fragile or rare cell populations. Each tissue or cell type needs to undergo fine-tuned protocol optimization to obtain enough highly viable cells that translate into high-quality sequencing data.Our modified single nuclei preparation protocol improves nuclei recovery and minimizes stress on the nuclei. It is specifically optimized for brain and bone marrow tissues and covers all the steps from sample dissociation to nuclei purification.

Watch this Scientific Journal Video about Purification of Nuclei from Mouse Brain for Single-Cell Multiome Analysis at JoVE.com

Purification of Nuclei from Mouse Brain for Single-Cell Multiome Analysis  

To begin, fill a glass Dounce with two milliliters of ice-cold nuclei lysis buffer containing 0.01%digitonin, and add the dissected mouse brain tissue pieces into it. Using a glass Dounce tissue homogenizer, homogenize the tissue 25 times each with pestles A and B, and transfer the resulting homogenate into a 15-milliliter tube. Add two milliliters of ice-cold nuclei lysis buffer containing 0.01%digitonin to the homogenate and incubate on ice for five minutes.Then, centrifuge the nuclei at 500 G for five minutes at four degrees Celsius. Using a micropipette, remove the supernatant and add four milliliters of ice-cold nuclei lysis buffer containing 0.01%digitonin. Filter the nuclei suspension through a 40-micrometer cell strainer.Centrifuge the nuclei again, remove the supernatant and add four milliliters of staining buffer to wash the nuclei. After filtering the suspension through a 40-micrometer cell strainer, pellet the nuclei by centrifugation and resuspend the nuclei in one milliliter of PBS containing 0.04%BSA and RNase inhibitors. To count the cells, mix 10 microliters of 0.4%trypan blue with 10 microliters of the nuclei in a 0.5-milliliter tube.Count the nuclei using an automated cell counter. Transfer 100 microliters of the nuclei to a FACS tube for the unstained control. Add 10 microliters of 7-AAD to the remaining nuclei and incubate for five minutes at four degrees Celsius, and proceed with nuclei sorting using FACS.Then, transfer 10 microliters of the sorted nuclei into a new FACS tube containing 90 microliters of DPBS with 2%heat-inactivated FBS. After centrifuging the sorted nuclei, remove the supernatant using a micropipette and resuspend the nuclei in 100 microliters of diluted nuclei buffer. Before sorting, the sample contains substantial debris with over 99%of singlets positive for nuclear stain, indicating effective cell lysis.Brain nuclei after sorting demonstrated an increase in purity from the initial 36%to nearly 100%

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356 Views.  Institut Pasteur, Université Paris Cité. To begin, fill a glass Dounce with two milliliters of ice-cold nuclei lysis buffer containing 0.01%digitonin, and add the dissected mouse brain tissue pieces into it. Using a glass Dounce tissue homogenizer, homogenize the tissue 25 times each with pestles A and B, and transfer the resulting homogenate into a 15-milliliter tube. Add two milliliters of ice-cold nuclei lysis buffer containing 0.01%digitonin to the homogenate and incubate on ice for five minutes.Then, centrifuge the nucle...

Video: Purification of Nuclei from Mouse Brain for Single-Cell Multiome Analysis  

Single-cell analysis has become the approach of choice for unraveling the complexity of biological processes that require assessing the variability of individual cellular responses to treatment or infection with single-cell resolution. 
Many techniques for single-cell molecular profiling have been developed over the past 10 years, and several dedicated technologies have been commercialized. The 10X Genomics droplet-based single-cell profiling is a widespread technology that offers ready-to-use reagents for transcriptomic and multi-omic single-cell profiling. The technology includes workflows for single-cell and single-nuclei RNA sequencing (scRNA-Seq and snRNA-Seq, respectively), scATAC-Seq, single-cell immune profiling (BCR/TCR sequencing), and multiome. The latter combines transcriptional (scRNA-Seq) and epigenetic information (scATAC-Seq) coming from the same cell. 
The quality (viability, integrity, purity) of single-cell or single-nuclei suspensions isolated from tissues and analyzed by any of these approaches is critical for generating high-quality data. Therefore, the sample preparation protocols should be adapted to the particularities of each biological tissue and ensure the generation of high-quality cell and nuclei suspensions.
This article describes two protocols for preparing brain and bone marrow samples for the downstream multiome 10X Genomics pipeline. The protocols are performed stepwise and cover tissue dissociation, cell sorting, nuclei isolation, and quality control of prepared nuclei suspension that is used as starting material for cell partitioning and barcoding, library preparation, and sequencing. These standardized protocols produce high-quality nuclei libraries and robust and reliable data.

The success of single-cell/single-nuclei transcriptomics and multi-omics largely depends on the quality of cells/nuclei. Therefore, isolating cells/nuclei from tissue and their purification must be highly standardized. This protocol describes the preparation of nuclei from the brain and bone marrow for downstream single-nuclei multiome assay.

Single-cell analysis has become the approach of choice for unraveling the complexity of biological processes that require assessing the variability of ...

Purification of Nuclei from Mouse Bone Marrow Hematopoietic Stem and Progenitor Cells (HSPCs)

To begin, take a vial containing the mouse bone marrow hematopoietic stem and progenitor cells. Using a micropipette, resuspend the pellet in one milliliter of ACK lysing buffer and incubate for one to two minutes at room temperature. Transfer the resuspended mixture into a 50 milliliter tube through the pre-wetted 70 micrometer cell strainer.Then add 10 milliliters of FACS buffer to dilute the ACK lysing buffer. Centrifuge the mixture at 400 G for five minutes at four degrees Celsius and resuspend the pellet in 10 milliliters of FACS buffer by first resuspending it in one milliliter of buffer and then topping up with nine milliliters of buffer. Now, mix 10 microliters of 0.4%trypan blue with 10 microliters of the cells in a 0.5 milliliter tube, and count the cells using an automated cell counter.To stain the cells, centrifuge the cells at 400 G for five minutes at four degrees Celsius. Resuspend the pellet in FACS buffer to achieve a final concentration of one times 10 to the seven cells per milliliter by first resuspending the pellet in one milliliter of buffer and then topping up with the remaining volume. Using a P1000 micropipette, transfer the suspension into a FACS tube through a 35 micrometer cell strainer cap.Next, prepare staining mix as shown here. After centrifugation, resuspend the cell suspension in 300 microliters of staining mix one in a sample tube and incubate on ice for 15 minutes protected from light. Then add 300 microliters of mix two into the sample tube and incubate for 20 minutes on ice protected from light.Add three milliliters of the FACS buffer to the single stained and mixed stained sample tubes. Now centrifuge the cell suspension. After discarding the supernatant, resuspend the pellet in 500 microliters of the FACS buffer.Prepare a 1.5 milliliter tube prefilled with 500 microliters of collection medium. Once the FACS instrument has been calibrated, add 500 microliters of FACS buffer to the cell suspension and then transfer one milliliter of the sample through a 35 micrometer cell strainer cap into a new FACS tube. After cell sorting, transfer 10 microliters of the sorted cells into a new FACS tube containing 90 microliters of FACS buffer.Pellet the cell suspension by centrifugation and resuspend in 50 microliters of PBS with 0.04%BSA. Transfer the suspension to a 0.2 milliliter tube and add 50 microliters of PBS with BSA to the original tube to collect any leftover cells. Transfer the cells to the 0.2 milliliter tube to reach a total volume of 100 microliters.Run a pilot experiment to identify the best lysis time for nuclei isolation. After pelleting the nuclei, resuspend the nuclei pellet in 12 microliters of diluted nuclei buffer. Add two microliters of nuclei to a tube containing 0.4%trypan blue and eight microliters of PBS with 0.04%BSA and count the nuclei using an automated cell counter.After completing the nuclei isolation, transfer six microliters of nuclei resuspension into a new FACS tube pre-filled with 150 microliters of FACS buffer. Add three microliters of 7-AAD and incubate for five minutes on ice.