Cell Biology


Protocols in Current Issue
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0 Q&A 368 Views Jun 5, 2024

Extracellular vesicles (EVs) are a heterogeneous group of nanoparticles possessing a lipid bilayer membrane that plays a significant role in intercellular communication by transferring their cargoes, consisting of peptides, proteins, fatty acids, DNA, and RNA, to receiver cells. Isolation of EVs is cumbersome and time-consuming due to their nano size and the co-isolation of small molecules along with EVs. This is why current protocols for the isolation of EVs are unable to provide high purity. So far, studies have focused on EVs derived from cell supernatants or body fluids but are associated with a number of limitations. Cell lines with a high passage number cannot be considered as representative of the original cell type, and EVs isolated from those can present distinct properties and characteristics. Additionally, cultured cells only have a single cell type and do not possess any cellular interactions with other types of cells, which normally exist in the tissue microenvironment. Therefore, studies involving the direct EVs isolation from whole tissues can provide a better understanding of intercellular communication in vivo. This underscores the critical need to standardize and optimize protocols for isolating and characterizing EVs from tissues. We have developed a differential centrifugation-based technique to isolate and characterize EVs from whole adipose tissue, which can be potentially applied to other types of tissues. This may help us to better understand the role of EVs in the tissue microenvironment in both diseased and normal conditions.

0 Q&A 754 Views Dec 5, 2023

Exosomes are a subpopulation of the heterogenous pool of extracellular vesicles that are secreted to the extracellular space. Exosomes have been purported to play a role in intercellular communication and have demonstrated utility as biomarkers for a variety of diseases. Despite broad interest in exosome biology, the conditions that regulate their secretion are incompletely understood. The goal of this procedure is to biochemically reconstitute exosome secretion in Streptolysin O (SLO)-permeabilized mammalian cells. This protocol describes the reconstitution of lyophilized SLO, preparation of cytosol and SLO-permeabilized cells, assembly of the biochemical reconstitution reaction, and quantification of exosome secretion using a sensitive luminescence-based assay. This biochemical reconstitution reaction can be utilized to characterize the molecular mechanisms by which different gene products regulate exosome secretion.

Key features

• This protocol establishes a functional in vitro system to reconstitute exosome secretion in permeabilized mammalian cells upon addition of cytosol, ATP, GTP, and calcium (Ca2+).

Graphical overview

Schematic overview of the exosome secretion biochemical reconstitution protocol. Streptolysin O (SLO) is prepared as described in Procedure A. Cytosol is isolated from HCT116 WT cells as described in Procedure B. HCT116 CD63-Nluc cells are permeabilized by SLO as detailed in Procedure C. The assembly of the exosome secretion reactions are described in Procedure D. Quantification of CD63-Nluc secretion is detailed in Procedure E (Modified from Williams et al., 2023).
0 Q&A 1133 Views Sep 5, 2023

Circular RNA (circRNA) is an intriguing class of non-coding RNA that exists as a continuous closed loop. With the improvements in high throughput sequencing, biochemical analysis, and bioinformatic algorithms, studies on circRNA expression became abundant in recent years. However, functional studies of circRNA are still limited. Subcellular localization of circRNA may provide some clues in elucidating its biological functions by performing subcellular fractionation assay. Notably, circRNAs that are predominantly found in the cytoplasm are more likely to be involved in post-transcriptional gene regulation, e.g., acting as micoRNA sponge, whereas nuclear-retained circRNAs are predicted to play a role in transcriptional regulation. Subcellular fractionation could help researchers to narrow down and prioritize downstream experiments. The majority of the currently available protocols describe the steps for subcellular fractionation followed by western blot analysis for protein molecules. Here, we present a protocol for the subcellular fractionation of cells to detect circRNA via RT-qPCR with divergent primers. Moreover, detailed steps for the generation of specific circRNAs-enriched cDNA included in this protocol will enhance the amplification and detection of low-abundance circRNAs. This will be useful for researchers studying low-abundance circRNAs.

Key features

• This protocol builds upon the method developed by Gagnon et al. (2014) and extends its application to circRNA study.

• Protocol for amplification of low levels of circRNA expression.

• Analysis takes into consideration the ratio of cytoplasmic RNA concentration to nuclear RNA concentration.

Graphical overview

1 Q&A 791 Views Sep 5, 2023

The subfractionation of the endoplasmic reticulum (ER) is a widely used technique in cell biology. However, current protocols present limitations such as low yield, the use of large number of dishes, and contamination with other organelles. Here, we describe an improved method for ER subfractionation that solves other reported methods' main limitations of being time consuming and requiring less starting material. Our protocol involves a combination of different centrifugations and special buffer incubations as well as a fine-tuned method for homogenization followed by western blotting to confirm the purity of the fractions. This protocol contains a method to extract clean ER samples from cells using only five (150 mm) dishes instead of over 50 plates needed in other protocols. In addition, in this article we not only propose a new cell fractionation approach but also an optimized method to isolate pure ER fractions from one mouse liver instead of three, which are commonly used in other protocols. The protocols described here are optimized for time efficiency and designed for seamless execution in any laboratory, eliminating the need for special/patented reagents.

Key features

• Subcellular fractionation from cells and mouse liver.

• Uses only five dishes (150 mm) or one mouse liver to extract highly enriched endoplasmic reticulum without mitochondrial-associated membrane contamination.

• These protocols require the use of ultracentrifuges, dounce homogenizers, and/or Teflon Potter Elvehjem.

• As a result, highly enriched/clean samples are obtained.

Graphical overview

0 Q&A 1032 Views Jun 20, 2023

Cell-based carrier exhibits inherent advantages as the next generation of drug delivery system, namely high biocompatibility and physiological function. Current cell-based carriers are constructed via direct payload internalization or conjugation between cell and payload. However, the cells involved in these strategies must be firstly extracted from the body and the cell-based carrier must be prepared in vitro. Herein, we synthesize bacteria-mimetic gold nanoparticles (GNPs) for the construction of cell-based carrier in mice. Both β-cyclodextrin (β-CD)-modified GNPs and adamantane (ADA)-modified GNPs are coated by E. coli outer membrane vesicles (OMVs). The E. coli OMVs induce the phagocytosis of GNPs by circulating immune cells, leading to intracellular degradation of OMVs and subsequent supramolecular self-assembly of GNPs driven by β-CD-ADA host–guest interactions. In vivo construction of cell-based carrier based on bacteria-mimetic GNPs avoids the immunogenicity induced by allogeneic cells and restriction by the number of separated cells. Due to the inflammatory tropism, endogenous immune cells carry the intracellular GNP aggregates to the tumor tissues in vivo.

Graphical overview

Collect the outer membrane vesicles (OMVs) of E. coli by gradient centrifugation (a) and coat on gold nanoparticles (GNP) surface (b) to prepare OMV-coated cyclodextrin (CD)-GNPs and OMV-coated adamantane (ADA)-GNPs (c) via ultrasonic method

0 Q&A 937 Views Feb 5, 2023

Single-nucleus RNA sequencing (snRNA-seq) provides a powerful tool for studying cell type composition in heterogenous tissues. The liver is a vital organ composed of a diverse set of cell types; thus, single-cell technologies could greatly facilitate the deconvolution of liver tissue composition and various downstream omics analyses at the cell-type level. Applying single-cell technologies to fresh liver biopsies can, however, be very challenging, and snRNA-seq of snap-frozen liver biopsies requires some optimization given the high nucleic acid content of the solid liver tissue. Therefore, an optimized protocol for snRNA-seq specifically targeted for the use of frozen liver samples is needed to improve our understanding of human liver gene expression at the cell-type resolution. We present a protocol for performing nuclei isolation from snap-frozen liver tissues, as well as guidance on the application of snRNA-seq. We also provide guidance on optimizing the protocol to different tissue and sample types.

0 Q&A 1736 Views Jul 20, 2022

Cilia and flagella are microtubule-based hair-like organelles protruding from the surface of most eukaryotic cells, and play essential roles in cell locomotion, left-right asymmetry, embryo development, and tissue homeostasis. With isolated cilia and flagella, great progress has been made in understanding the composition, structure, and function of cilia. However, the current cilia/flagella isolation methods are deficient in the integrity or productivity of purified cilia when applied to mammalian motile cilia. Here, we describe a new protocol that isolates cilia shafts from mouse ependymal cells, by horizontal shear force and mild detergent. This method enables the production of virtually integral cilia with high yields and less cell body contamination. It is suitable for immunostaining, puromycin labeling assay, and proximity ligation assay of mammalian motile cilia.

Graphical abstract:

0 Q&A 1943 Views Jul 5, 2022

Lysosome isolation is a preresiquite for identifying lysosomal protein composition by mass spectroscopic analysis, to reveal lysosome functions, and their involvement in some diseases. Magnetic nanoparticle-based fractionation has received great attention for lysosome isolation, owing to its high efficiency, purity, and preservation of lysosomal structures. Understanding the intracellular trafficking of magnetic probes is the key point of this technique, to determine the appropriate time for magnetic isolation of lysosomes, because this parameter changes depending on different cell lines used. The traditional magnetic probes, such as superparamagnetic iron oxide nanoparticles (SPIONs), require surface modification by fluorescent dyes to enable the investigation of their intracellular trafficking, which has some disadvantages, including the possible alternation of their bio-interaction, and the instability of fluorescence properties in the lysosomal environment. To overcome those limitations, we present a protocol that employs magnetic-plasmonic nanoparticles (MPNPs) to investigate intracellular trafficking using their intrinsic imaging capability, followed by quick lysosome isolation using a magnetic column. This protocol can be easily applied to isolate the intact lysosomes of any adherent cell lines.

Graphical abstract:

0 Q&A 3647 Views Jun 20, 2022

Extracellular vesicles (EVs), such as exosomes, are produced by all known eukaryotic cells, and constitute essential means of intercellular communication. Recent studies have unraveled the important roles of EVs in migrating to specific sites and cells. Functional studies of EVs using in vivo and in vitro systems require tracking these organelles using fluorescent dyes or, alternatively, transfected and fluorescent-tagged proteins, located either intravesicularly or anchored to the EV bilayer membrane. Due to design simplicity, the fluorescent dye might be a preferred method if the cells are difficult to modify by transfection or when the genetic alteration of the mother cells is not desired. This protocol describes techniques to label cultured cell-derived EVs, using lipophilic DiR [DiIC18(7) (1,1'-Dioctadecyl-3,3,3',3'-Tetramethylindotricarbocyanine Iodide)] fluorophore. This technique can be used to study the cellular uptake and intracellular localization of EVs, and their biodistribution in vivo, which are crucial evaluations of any isolated EVs.

0 Q&A 1632 Views May 5, 2022

Endosomal recycling is essential for the appropriate function of the endosome. During this process, endosomal coat complexes (i.e., retromer, and Mvp1) are recruited to the endosome, and deform its membrane to form recycling vesicles. To further analyze this, we developed a protocol for the immunoisolation of recycling vesicles from budding yeast. This method is a powerful way to characterize endosomal recycling pathways.

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