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Past Issue in 2016
Volume: 6, Issue: 24
Biochemistry
Activity-based Pull-down of Proteolytic Standard and Immunoproteasome Subunits
Activity-based probes (ABP) are small organic molecules that irreversibly bind to the active center of a specific enzyme family and may be coupled to a fluorophore or an affinity tag (Li et al., 2013). Here, we describe a method to pull-down active catalytic standard and immunoproteasome subunits in cell lysates using the biotinylated, proteasome-specific ABP Biotin-Epoxomicin (Bio-EP). Covalent labeling of the active catalytic subunits with Bio-EP is followed by a pull-down using streptavidin-coated beads. After elution from the beads, enriched subunits may be detected via Western blot, tandem mass spectrometry (Li et al., 2013), or alternative techniques.
Cancer Biology
Affinity Pulldown of Biotinylated RNA for Detection of Protein-RNA Complexes
RNA-binding proteins (RBPs) have recently emerged as crucial players in the regulation of gene expression. The interactions of RBPs with target mRNAs control the levels of gene products by altering different regulatory steps, including pre-mRNA splicing and maturation, nuclear mRNA export, and mRNA stability and translation (Glisovic et al., 2008). There are several methodologies available today to identify RNAs bound to specific RBPs; some detect only recombinant molecules in vitro, others detect recombinant and endogenous molecules, while others detect only endogenous molecules. Examples include systematic evolution of ligands by exponential enrichment (SELEX), biotinylated RNA pulldown assay, RNA immunoprecipitation (RIP) assay, electrophoretic mobility shift assay (EMSA), RNA footprinting analysis, and various UV crosslinking and immunoprecipitation (CLIP) methods such as CLIP, PAR-CLIP, and iCLIP (Popova et al., 2015). Here, we describe a simple and informative method to study and identify the RNA region of interaction between an RBP and its target transcript (Panda et al., 2014 and 2016). Its reproducibility and ease of use make this protocol a fast and useful method to identify interactions between RBPs and specific RNAs.
In vitro Assays for the Detection of Calreticulin Exposure, ATP and HMGB1 Release upon Cell Death
Accumulating evidence is revealing the essential role of immune system in cancer treatment. Certain chemotherapeutic drugs can potently induce the release of ‘cell death associated molecular patterns’ (CDAMPs), which accompanies cancer cell demise. CDAMPs can engage corresponding receptors on immune cells and stimulate immune responses to achieve long-term tumor control (Ma et al., 2013; Ma et al., 2014; Yang et al., 2015). Among reported CDAMPs, calreticulin (CALR), ATP and HMGB1 are well known for their immune-stimulatory effect. Here we describe the assays that we applied to measure cell death and these CDAMPs. Briefly, cell death can be analyzed by co-staining of 4’,6-diamidino-2-phenylindole (DAPI) with 3,3’-Dihexyloxacarbocyanine Iodide [DiOC6(3)] or Annexin V. CALR exposure on the cell membrane can be detected by flow cytometry. ATP and HMGB1 release can be quantified by luminescence assay and ELISA assay respectively.
Cell Biology
Isolation of THY1+ Undifferentiated Spermatogonia from Mouse Postnatal Testes Using Magnetic-activated Cell Sorting (MACS)
In mammals, homeostasis of many tissues rely on a subpopulation of cells, referred to as stem cells, to sustain an appropriate number of undifferentiated and differentiated cells. Spermatogonial stem cells (SSCs) provide the fundamental cellular source for spermatogenesis and are responsible for the lifelong maintenance of the germline pool in testes throughout the reproductive lifespan of males. To gain insight into germline stem cell biology and develop strategies for infertility treatment, several germ cell isolation methods have been reported in order to acquire good quality and quantity of undifferentiated spermatogonia. Among them, magnetic-activated cell sorting (MACS) is an efficient cell isolation method that requires less time and less initial cell numbers to obtain an enriched cell population using an antigen-antibody reaction. Thymus cell antigen 1 (THY1, CD90.2) is recognized as a surface marker of undifferentiated spermatogonia in mouse neonatal and adult testes. Here, we describe a protocol for the isolation of one-week-old THY1+ cells and four-week-old THY1+ cells from mouse testes. The isolation procedure consists of three steps: testis collection and single cell suspension, cell labeling using a biotin-conjugated anti-THY1 antibody and magnetic cell separation. Note, this isolation protocol should be completed within five hours to maximize the quality and the amount of living cells.
Measurement of Mechanical Tension at cell-cell junctions using two-photon laser ablation
The cortical actomyosin cytoskeleton is found in all non-muscle cells where a key function is to control mechanical force (Salbreux et al., 2012). When coupled to E-cadherin cell-cell adhesion, cortical actomyosin generates junctional tension that influences many aspects of tissue function, organization and morphogenesis (Lecuit and Yap, 2015). Uncovering the molecular mechanisms underlying the generation of junctional tension requires tools for measuring it in live cells with a high spatio-temporal resolution. For this, we have set up a technique of laser ablation, in which we use the high power output of a two-photon laser to physically cut the actin cortex at the sites of cell-cell adhesion labeled with E-cadherin-GFP. Tension, thus is visualized as the outwards recoil of the vertices that define a junction after this was ablated/cut. Analysis of recoil versus time allows extracting parameters related to the amount of contractile force that is applied to the junction before ablation (initial recoil) and the ratio between elasticity of the junction and viscosity of the media (cytoplasm) in which the junctional cortex is immersed. Using this approach we have discovered how Src protein-tyrosine kinase (Gomez et al., 2015); actin-binding proteins such as tropomyosins (Caldwell et al., 2014) and N-WASP (Wu et al., 2014); Myosin II (Priya et al., 2015) and coronin-1B (Michael et al., 2016) contribute to the molecular apparatus responsible for generating tension at the cell-cell junctions. This protocol describes the experimental procedure for setting up laser ablation experiments and how to optimize ablation and acquisition conditions for optimal measurements of junctional tension. It also provides a full description, step by step, of the post-acquisition analysis required to evaluate changes in contractile force as well as cell elasticity and/or cytoplasm viscosity.
Microbiology
Antibiotic Disc Assay for Synechocystis sp. PCC6803
This protocol describes how to investigate the integrity of the outer cell wall in the cyanobacterium Synechocystis sp. PCC6803 using antibiotics. It is adapted to the agar diffusion test (Bauer et al., 1966), in which filter paper discs impregnated with specified concentrations of antibiotics were placed on agar plates inoculated with bacteria. The antibiotics we tested, interfering with the biosynthesis/function of bacterial cell walls, will diffuse into the agar and produce a zone of cyanobacterial growth inhibition around the disc(s). The size of the inhibition zone reflects the sensitivity of the strain to the action of antibiotics, e.g., a mutation in a protein functioning within the cell wall or its construction would render the mutant strain more sensitive to the respective antibiotic. The method has proven to be useful for phenotyping a mutant of Synechocystis sp. PCC6803 lacking all three genes encoding Deg proteases. Deletion of these ATP-independent serine proteases was shown to have impact on the outer cell layers of Synechocystis cells (Cheregi et al., 2015).
Highly Accurate Real-time Measurement of Rapid Hydrogen-peroxide Dynamics in Fungi
Reactive oxygen species (ROS) are unavoidable by-products of aerobic metabolism. Despite beneficial aspects as a signaling molecule, ROS are principally recognized as harmful agents that act on nucleic acids, proteins and lipids. Reactive oxygen species, and, in particular, hydrogen peroxide (H2O2), are deployed as defense molecules across kingdoms, e.g., by plants in order to defeat invading pathogens like fungi. Necrotrophic plant pathogenic fungi themselves secrete H2O2 to induce host cell death and facilitate infection. Hydrogen peroxide is, to a certain extent, freely diffusible through membranes. To be able to monitor intracellular hydrogen peroxide dynamics in fungi, we recently established the versatile HyPer-imaging technique in the filamentous plant pathogen Fusarium graminearum (Mentges and Bormann, 2015). HyPer consists of a circularly permuted yellow fluorescent protein (cpYFP) inserted into the regulatory domain (RD) of the prokaryotic H2O2-sensing protein, OxyR. The OxyR domain renders the sensor highly specific for H2O2. Oxidation of HyPer increases fluorescence of cpYFP excited at 488 nm and decreases fluorescence excited at 405 nm, thereby facilitating ratiometric readouts (Belousov et al., 2006). HyPer turned out to be pH-sensitive. A single amino acid mutation in the H2O2-sensing domain of HyPer renders the sensor insensitive to H2O2. This reporter is called SypHer and serves as a control for pH changes.By using the HyPer-imaging technique, we could demonstrate that: i) HyPer imaging enables the specific and accurate detection of rapid changes in the intracellular H2O2 balance, ii) F. graminearum reacts on external stimuli with the transient production of H2O2, and iii) faces increased H2O2 level during initial infection of wheat.The aim of this protocol is to guide the user through the basic setup of an in vitro HyPer imaging experiment in basically any fungus. It will provide the specific parameter for the fluorescence imaging as well as the construction of customized flow chambers for in vitro applications.
Single-step Marker Switching in Schizosaccharomyces pombe Using a Lithium Acetate Transformation Protocol
The ability to utilize different selectable markers for tagging or mutating multiple genes in Schizosaccharomyces pombe is hampered by the historical use of only two selectable markers, ura4+ and kanMX6; the latter conferring resistance to the antibiotic G418 (geneticin). More markers have been described recently, but introducing these into yeast cells often requires strain construction from scratch. To overcome this problem we and other groups have created transformation cassettes with flanking homologies to ura4+ and kanMX6 which enable an efficient and time-saving way to exchange markers in existing mutated or tagged fission yeast strains.Here, we present a protocol for single-step marker switching by lithium acetate transformation in fission yeast, Schizosaccharomyces pombe. In the following we describe how to swap the ura4+ marker to a kanMX6, natMX4, or hphMX4 marker, which provide resistance against the antibiotics G418, nourseothricin (clonNAT) or hygromycin B, respectively. We also detail how to exchange any of the MX markers for nutritional markers, such as arg3+, his3+, leu1+ and ura4+.
Molecular Biology
Efficient AAV-mediated Gene Targeting Using 2A-based Promoter-trap System
Adeno-associated virus (AAV)-based targeting vectors have 1-4-log higher gene targeting efficiencies compared with plasmid-based targeting vectors. The efficiency of AAV-mediated gene targeting is further increased by introducing a promoter-trap system into targeting vectors. In addition, we found that the use of ribosome-skipping 2A peptide rather than commonly used internal ribosome entry site (IRES) in the promoter-trap system results in significantly higher AAV-mediated gene targeting efficiencies (Karnan et al., 2016). In this protocol, we describe the procedures for AAV-mediated gene targeting exploiting 2A for promoter trapping, including the construction of a targeting vector based on the platform plasmid pAAV-2Aneo or pAAV-2Aneo v2, production of AAV particles, infection of cells with resulting AAV-based targeting vectors, and isolation and verification of gene-targeted cell clones.
Plant Science
Plant Tissue Trypan Blue Staining During Phytopathogen Infection
In this protocol plant tissue is stained with trypan blue dye allowing the researcher to visualize cell death. Specifically this method avoids the use of the carcinogen compound chloral hydrate, making this classical method of staining safer and faster than ever. The protocol is applied specifically to detect cell death on Arabidopsis leaves during the course of infection with necrotrophic fungus Botrytis cinerea.
Detection of Reactive Oxygen Species in Oryza sativa L. (Rice)
Superoxide ions (O2-) and hydrogen peroxide (H2O2) are the reactive oxygen species (ROS) that play a significant role in regulation of many plant processes. The level of O2- ions is determined qualitatively using nitrobluetetrazolium (NBT) assay while the H2O2 is qualitatively estimated using 3,3-diaminobenzidine (DAB) and 2’,7’-dichlorodihydrofluorescein diacetate (H2DCFDA) assay. Further the aqueous content of H2O2 is estimated quantitatively using ferrous oxidation-xylenol orange (FOX) assay.
Infection of Nicotiana benthamiana Plants with Potato Virus X (PVX)
Potato Virus X (PVX) is the type member of Potexvirus genus, a group of plant viruses with a positive-strand RNA genome (~6.4 kb). PVX is able to establish compatible infections in Nicotiana benthamiana, a commonly used host in plant virology, leading to mild symptoms, such as chlorotic mosaic and mottling. PVX has been widely used as a viral vector for more than two decades (Chapman et al., 1992; Baulcombe et al., 1995; Aguilar et al., 2015). It provides a feasible means for the systemic expression in plants of heterologous proteins, such as avirulence factors, proteins with pharmacological properties, etc., (Hammond-Kosack et al., 1995; Gleba et al., 2014), and also as a tool to help decipher the function of genes in plants by virus-induced gene silencing (VIGS) (Lacomme and Chapman, 2008). Two different protocols, i.e., rubbing (A) and agroinfiltration (B), that allow efficient multiplication and propagation of PVX in N. benthamiana are described here in detail. The rubbing method requires previously infected sap, and infection is achieved by inducing mechanical damages to leaf tissue, allowing viral particles to penetrate the plant surface. Agroinfiltration needs previously modified Agrobacterium to carry and deliver T-DNA with PVX sequences into the plant cell. Agrobacterium is grown until saturation and infection is established by infiltrating it into plant tissue with a syringe. Any of these two methods can be successfully applied, and the choice should be based mainly on the availability of material and time, but it is recommended to use agroinfiltration when chimeric viruses are being used.
Inoculation of Rice with Different Pathogens: Sheath Blight (Rhizoctonia solani), Damping off Disease (Pythium graminicola) and Barley Powdery Mildew (Blumeria graminis f. sp. hordei)
To prevent yield losses in plant cultivation due to plant pathogens, it is an important task to find new disease resistance mechanisms. Recently, Weidenbach et al. (2016) reported about the capacity of the rice gene OsJAC1 to enhance resistance in rice and barley against a broad spectrum of different pathogens. Here, we describe the respective protocols used by Weidenbach and colleagues for inoculation of rice with the basidiomycete Rhizoctonia solani, the oomycete Pythium graminicola and the ascomycete Blumeria graminis f. sp. hordei (Bgh).
Assessment of Wheat Resistance to Fusarium graminearum by Automated Image Analysis of Detached Leaves Assay
Fusarium head blight (FHB) caused by Fusarium pathogens is a globally important cereal disease. To study Fusarium pathogenicity and host disease resistance, robust methods for disease assessment and quantification are needed. Here we describe the procedure of a detached leaves assay emphasizing the image analysis. The protocol provides the different steps of a rapid, automatic and quantitative image analysis to evaluate leaf area infected by Fusarium graminearum.
Electro-fusion of Gametes and Subsequent Culture of Zygotes in Rice
Electro-fusion system with isolated gametes has been utilized to dissect fertilization-induced events in angiosperms, such as egg activation, zygote development and early embryogenesis, since the female gametophytes of plants are deeply embedded within ovaries. In this protocol, procedures for isolation of rice gametes, electro-fusion of gametes, and culture of the produced zygotes are described.
Bacterial Growth Inhibition Assay for Xanthomonas oryzae pv. oryzae or Escherichia coli K12 Grown together with Plant Leaf Extracts
We performed a growth inhibition assay to test antibacterial compounds in leaf extracts from transgenic rice plants. The assay is based on over-night co-incubation of a defined concentration of colony forming units (cfu) of the respective bacteria together with aqueous extracts of ground leaf tissue.
Quantitative Determination of Ascorbate from the Green Alga Chlamydomonas reinhardtii by HPLC
Ascorbate (Asc, also called vitamin C) is of vital importance to the cellular functions of both animals and plants. During evolution, Asc has become one of the most abundant metabolites in seed plants; however, Asc contents in cyanobacteria, green algae and bryophytes are very low. Here we describe a sensitive and reliable HPLC method for the quantitative determination of cellular Asc content in the green alga Chlamydomonas reinhardtii.
Expression, Purification and Crystallization of Recombinant Arabidopsis Monogalactosyldiacylglycerol Synthase (MGD1)
In plant cells, galactolipids are predominant, representing up to 50% of the lipid content in photosynthetic tissues. Galactolipid synthesis is initiated by MGDG synthases (MGDs), which use UDP-galactose as a donor sugar and diacylglycerol (DAG) as acceptor, to form monogalactosyldiacylglycerol (MGDG). This protocol is used to produce a recombinant form of Arabidopsis thaliana (A. thaliana) monogalactosyldiacylglycerol synthase 1 (MGD1) protein, in Escherichia coli (E. coli), using a two-step chromatographic purification procedure. The protein is easily expressed and purified to milligram quantities, suitable for biochemical and structural studies. The crystallization of MGD1 is also described.
Protocol for Increasing Carotenoid Levels in the Roots of Citrus Plants
Carotenoids in plants play several key functions such as acting as light-harvesters, antioxidants (Lado et al., 2016) or being precursors of strigolactones, abscisic acid, volatiles and other signaling compounds (Arbona et al., 2013). Although those functions are well-known in light-exposed tissues, information in belowground organs is limited because of reduced abundance of these pigments. In order to better understand the role of carotenoids in roots, we developed a methodology to increase the abundance of these pigments in underground tissues. We took advantage of the fact that citrus roots exposed to light develop pigmentation in order to increase the carotenoid content. Therefore, here we describe a simple method to increase carotenoids in citrus roots.
Stem Cell
Gene Expression Analysis of Sorted Cells by RNA-seq in Drosophila Intestine
RNA sequencing (RNA-seq) has become a popular method for profiling gene expression. Among many applications, one common purpose is to identify differentially expressed genes and pathways in different biological or pathological conditions. This protocol provides detailed procedure for RNA-seq analysis of ~250,000 sorted Drosophila intestinal cells (Chen et al., 2016), in which RNA amplification is not required.
Quantitative 3D Time Lapse Imaging of Muscle Progenitors in Skeletal Muscle of Live Mice
For non-optically clear mammalian tissues, it is now possible to use multi-photon microscopy to penetrate deep into the tissue and obtain detailed single cell images in a live animal, i.e., intravital imaging. This technique is in principle applicable to any fluorescently marked cell, and we have employed it to observe stem cells during the regenerative process. Stem cell-mediated skeletal muscle regeneration in the mouse model has been classically studied at specific time points by sacrificing the animal and harvesting the muscle tissue for downstream analyses. A method for direct visualization of muscle stem cells to gain real-time information over a long period in a live mammal has been lacking. Here we describe a step-by-step protocol adapted from Webster et al. (2016) to quantitatively measure the behaviors of fluorescently labeled (GFP, EYFP) muscle stem and progenitor cells during homeostasis as well as following muscle injury.