Improve Research Reproducibility A Bio-protocol resource
- Protocols
- Articles and Issues
- For Authors
- About
- Become a Reviewer
Past Issue in 2015
Volume: 5, Issue: 11
Cell Biology
Dictyostelium Cultivation, Transfection, Microscopy and Fractionation
The real time visualisation of fluorescently tagged proteins in live cells using ever more sophisticated microscopes has greatly increased our understanding of the dynamics of key proteins during fundamental physiological processes such as cell locomotion, chemotaxis, cell division and membrane trafficking. In addition the fractionation of cells and isolation of organelles or known compartments can often verify any subcellular localisation and the use of tagged proteins as bait for the immunoprecipitation of material from cell fractions can identify specific binding partners and multiprotein complexes thereby helping assign a function to the tagged protein. We have successfully applied these techniques to the Dictyostelium discoideum protein TSPOON that is part of an ancient heterohexamer membrane trafficking complex (Hirst et al., 2013). TSPOON is the product of the tstD gene in Dictyostelium and is not required for growth or the developmental cycle in this organism. Dictyostelium amoebae will exist in a vegetative phase where growth is sustained by the phagocytosis of bacteria. When this food source is spent they enter a developmental phase where the amoebae aggregate, via chemotaxis to extracellular waves of cAMP, into multicellular structures that subsequently form a fruiting body containing viable spores (Muller-Taubenberger et al., 2013). In the laboratory this cycle takes less than 24 h to complete and as a further aid to manipulation the requirement for a bacterial food source has been circumvented by the derivatisation of the wild type and isolation of axenic strains that can also grow in a nutrient rich broth. Axenic strains like Ax2 are the mainstay of laboratory research using Dictyostelium (Muller-Taubenberger et al., 2013). A description of Dictyostelium cell cultivation, the generation of cell lines that overexpress TSPOON-GFP and TSPOON null cells, and subsequent analysis (Muller-Taubenberger and Ishikawa-Ankerhold, 2013) is detailed below.
FRAP Analysis of LET-23::GFP in the Vulval Epithelial Cells of Living Caenorhabditis elegans Larvae
The Caenorhabditis elegans (C. elegans) vulva is a well-established system to study organ development as the molecular mechanisms that govern its formation are conserved in animals. Of special interest is the EGFR/RAS/MAPK signaling pathway that is required for fate acquisition and morphogenesis of the vulva. let-23 encodes the sole homologue of the epidermal growth factor receptor (EGFR), is expressed at the plasma membrane of the vulval precursor cells (VPCs) and is activated by LIN-3 EGF at the end of the L3 larval stage to initiate vulva development. LET-23 activity can be modulated through altering its subcellular and plasma membrane localization. To study the trafficking of EGF receptor in a living organism, we created a functional LET-23::GFP translational reporter worm line (Haag et al., 2014) and quantified the mobile fraction of LET-23::GFP at the basolateral membrane of the VPCs by fluorescence recovery after photobleaching (FRAP). Here we describe the protocol for LET-23::GFP FRAP at the basolateral membrane of the VPCs and the data analysis using FIJI (ImageJ).
Immunology
Cytokine-stimulated Phosphoflow of PBMC Using CyTOF Mass Cytometry
Phosphorylation of tyrosine, serine, and threonine residues is critical for the control of protein activity involved in various cellular events. An assortment of kinases and phosphatases regulate intracellular protein phosphorylation in many different cell signaling pathways. These pathways include T and B cell signaling, regulating growth and cell cycle control, plus cytokine, chemokine, and stress responses. Phosphoflow assays combine phosphoprotein-specific antibodies with the power of flow cytometry to enhance phosphoprotein study. In our assay, peripheral blood mononuclear cells are stimulated by cytokines, fixed, surface-stained with a cocktail of antibodies labeled with MAXPAR (brand name) metal-chelating polymers and permeabilized with methanol. They are then stained with intracellular phospho-specific antibodies. We use a CyTOFTM mass cytometer to acquire the ICP-MS (inductively coupled plasma mass spectrometry) data. The current mass window selected is approximately AW 103-203, which includes the lanthanides used for most antibody labeling, as well as iridium and rhodium for DNA intercalators. Subsequent analysis of the dual count signal data using FlowJo software allows for cell types to be analyzed based on the dual count signal in each mass channel. The percentage of each cell type is determined and reported as a percent of the parent cell type. Median values are reported to quantitate the level of phosphorylation of each protein in response to stimulation. Comparing the level of phosphorylation between samples can offer insight to the status of the immune system.
Cytokine-Stimulated Phosphoflow of Whole Blood Using CyTOF Mass Cytometry
The ability to assess the function of a range of cytokine, antigen receptor, and Toll-like receptor (TLR) signaling pathways in a range of immune cells could provide a kind of fingerprint of the state of the human immune system. The mass cytometry or CyTOF, platform allows for the parallel application of about 40 labeled antibodies to a single sample, creating the possibility to read out many cell types and signaling pathways in a single small blood sample. We developed such a mass cytometry panel, consisting of 22 antibodies to cell surface lineage markers and 8 antibodies to phospho-specific epitopes of signaling proteins. These antibodies were chosen to discriminate all major white blood cell lineages, to a level of detail that includes subsets such as naïve, central memory, effector memory, and late effector CD4+ and CD8+T cells, naïve, transitional, and switched memory B cells, plasmablasts, myeloid and plasmacytoid dendritic cells, CD16+ and CD16+CD56+ NK cells, CD16+ and classical monocytes etc. 32 such cell subsets are defined in our standard gating scheme. The eight phospho-specific antibodies were chosen to represent major signaling nodes responsive to cytokine, TLR, and antigen receptor signaling. This antibody panel is used with 8 standard stimulation conditions (unstimulated, IFNa, IL-6, IL-7, IL-10, IL-21, LPS, PMA+ ionomycin), although other stimuli can be added. Comparison of healthy controls to subjects with immune deficiencies of unknown etiology may help elucidate the mechanisms of such deficiencies. Phosphorylation of tyrosine, serine, and threonine residues is critical for the control of protein activity involved in various cellular events. An assortment of kinases and phosphatases regulate intracellular protein phosphorylation in many different cell signaling pathways, such as T and B cell signaling, those regulating apoptosis, growth and cell cycle control, plus those involved with cytokine, chemokine, and stress responses. Phosphoflow assays combine phospho-specific antibodies with the power of flow cytometry to enhance phospho protein study. In our assay, peripheral blood mononuclear cells are stimulated by cytokines, fixed, surface-stained with a cocktail of antibodies labeled with MAXPAR (Brand Name) metal-chelating polymers and permeabilized with methanol. They are then stained with intracellular phospho-specific antibodies. We use a CyTOFTM mass cytometer to acquire the ICP-MS data. The current mass window selected is approximately AW 103-203, which includes the lanthanides used for most antibody labeling, as well as iridium and rhodium for DNA intercalators. Subsequent analysis of the dual count signal data using FlowJo software allows for cell types to be analyzed based on the dual count signal in each mass channel. The percentage of each cell type is determined and reported as a percent of the parent cell type. Median values are reported to quantitate the level of phosphorylation of each protein in response to stimulation. Comparing the level of phosphorylation between samples can offer insight to the status of the immune system. Whole blood stimulation is the closest to the in vivo condition and it allows for assessment of granulocyte population as well as lymphocytes and monocytes.
Extraction and Identification of T Cell Stimulatory Self-lipid Antigens
Autoreactive T cells restricted to CD1 molecules and specific for endogenous lipids are abundant in human blood (de Jong et al., 2010; de Lalla et al., 2011). A few self-lipid molecules recognized by diverse individual T cell clones and accumulated within APCs following stress signals or cell transformation have been identified so far (de Jong et al., 2010; Chang et al., 2008; Lepore et al., 2014). These findings suggested that auto-reactive CD1-restricted T cells display broad lipid specificities and may play critical roles in different types of immune responses including cancer immune surveillance, autoimmunity and antimicrobial immunity. Therefore, the identification of the repertoire of self-lipid molecules recognized by T cells is important to study the physiologic functions of this T cell population and to assess their therapeutic potential (Lepore et al., 2014). Here we describe the protocol we established to isolate and identify endogenous lipids derived from leukemia cells, which stimulate specific autoreactive CD1c-restricted T lymphocytes (Lepore et al., 2014). This protocol can be applied to isolate lipid antigens from any type of target cells and to investigate the self-lipid antigen specificity of autoreactive T cells restricted to all CD1 isoforms (Facciotti et al., 2012).
Microbiology
Quantification of Total and 2-LTR (Long terminal repeat) HIV DNA, HIV RNA and Herpesvirus DNA in PBMCs
Almost all individuals infected with human immunodeficiency virus (HIV) are also infected with cytomegalovirus (CMV) and Epstein Barr virus (EBV). The aims of our studies have included characterizing and measuring the latent HIV reservoir and understanding the association between asymptomatic replication of CMV (and other herpesvirus, including EBV) and this HIV reservoir (Gianella et al., 2014). This protocol was designed to simultaneously co-extract DNA and RNA from the same peripheral blood mononuclear cell (PBMC) aliquot and quantify HIV, CMV and EBV DNA, as well as HIV RNA using droplet digital PCR (ddPCR). For collection and processing of male genital secretions and quantification of HIV RNA and DNA from seven human herpesviruses from seminal plasma, refer to protocol “Quantification of HIV RNA and Human Herpesvirus DNA in Seminal Plasma” (Vargas-Meneses et al., 2015).
Molecular Biology
DNA Damage Sensitivity Assays in Caenorhabditis elegans
C. elegans has served as a genetically tractable multicellular model system to examine DNA damage-induced genotoxic stress which threatens genome integrity. Importantly, the high degree of conservation shared between worms and humans offers the advantage that findings about DNA damage-induced cell cycle arrest/checkpoint response and DNA double-strand break repair in worms are applicable to human studies. Here, we describe simple DNA damage sensitivity assays to quantify the response of C. elegans to diverse types of DNA damaging agents. These assays have provided important insights into the mechanisms of function for factors such as ZTF-8 that are involved in DNA damage repair and response in the C. elegans germline. These DNA damage sensitivity assays rely on the straightforward readouts of either egg or larval lethality and involve the use of various DNA damaging agents. We use γ-irradiation (γ-IR), which produces DNA double-strand breaks (DSBs), camptothecin (CPT), which induces single-strand breaks, nitrogen mustard (HN2), which produces interstrand crosslinks (ICLs), hydroxyurea (HU), which results in replication fork arrest thus preventing DNA synthesis, and UV-C, which causes photoproducts (pyrimidine dimers). See Table 1. Comparisons between the relative sensitivity/resistance observed in, for example, mutants compared to wild type, for various DNA damaging agents allows for inferences regarding potential repair pathways being affected.
Enzymatic Activity Assays for Base Excision Repair Enzymes in Cell Extracts from Vertebrate Cells
We previously reported enzymatic activity assays for the base excision repair (BER) enzymes DNA polymerase β (pol β), aprataxin (APTX), and flap endonuclease 1 (FEN1) in cell extracts from Saccharomyces cerevisiae (Çağlayan and Wilson, 2014). Here, we describe a method to prepare cell extracts from vertebrate cells to investigate these enzymatic activities for the processing of the 5´-adenylated-sugar phosphate-containing BER intermediate. This new protocol complements our previous publication. The cell lines used are wild-type and APTX-deficient human lymphoblast cells from an Ataxia with Oculomotor Apraxia Type 1 (AOA1) disease patient, wild-type and APTX-null DT40 chicken B cells, and mouse embryonic fibroblast (MEF) cells. This protocol is a quick and efficient way to make vertebrate cell extracts without using commercial kits.
Plant Science
Magnaporthe oryzae Inoculation of Rice Seedlings by Spraying with a Spore Suspension
Fungal blast caused by Magnaporthe oryzae (M. oryzae) leads to a serious yield loss of rice. Appropriate assessment of disease occurrence is necessary to investigate the nature of the disease and plant strategies to resist the disease. We describe our assay method of disease severity of M. oryzae on intact rice leaves grown on soil.
Simple Digital Photography for Assessing Biomass and Leaf Area Index in Cereals
These instructions refer to obtaining fast and low-labour estimates of ground cover, leaf area index and green biomass for a large number of plots, as those encountered in cereal breeding programs. The procedure includes obtaining the pictures in the field and processing them once downloaded to a computer.
Determination of the Developmental Origin of Seeds Containing Endosperm Using Flow Cytometric Analysis
Seeds derived from a diploid, sexual plant typically contain a 2n embryo (n+n) and 3n endosperm, a ratio characteristic for most flowering plants. However, this ratio is altered in apomictic species, which reproduce asexually through seeds (Koltunow and Grossniklaus, 2003). Apomixis is usually a facultative trait and encompasses several developmental steps: (1) apomeiosis (avoidance of meiosis), (2) parthenogenesis (embryo development without fertilization), and (3) functional endosperm formation (autonomous without fertilization or pseudogamous requiring fertilization). If all three steps occur, this process results in maternal offspring (2n+0), which is genetically identical to the mother plant (clonal). Moreover, sexual and apomictic pathways can occur in the same plant and sometimes they cross over, producing polyhaploid offspring (n+0; resulting from meiosis and parthenogenesis) or BIII hybrids (2n+n; resulting from apomeiosis and fertilization) (Rutishauser, 1947). The different types of offspring can be determined in a flow cytometric seed screen (FCSS), in which the relative chromatin content of stained nuclei is determined by measuring their fluorescence intensity. This allows a comparison of the ploidy of the endosperm to the ploidy of the embryo and, thus, an inference of the pathway by which a seed was formed (Matzk et al., 2000). This method is particularly useful to characterize the developmental origin of seeds in apomictic plants or reproductive mutants of sexual species. Here, we present the protocol for an FCSS in Brassicaceae that has specifically been adapted to plants of the genus Boechera. However, in principle this protocol can be applied to any species producing seeds that contain endosperm.
Cell Wall Biomass Preparation and Fourier Transform Mid-infrared (FTIR) Spectroscopy to Study Cell Wall Composition
Plant cell wall biomass is an abundant and renewable organic resource. Of the polymers it encloses, cellulose and hemicellulose are regarded as a raw material for the production of fuels and other products (Klemm et al., 2005; Slavov et al., 2013). Nonetheless, current usage of lignocellulosic biomass is still below its full potential due to a series of limiting factors mainly related to the cell wall recalcitrance to saccharification, a severe constraint to maximum biomass usability in downstream processing (Pauly and Keegstra, 2008).As a strategy to optimise bio-energy and bio-refining applications, an increasing amount of effort is being put into the advancement of our knowledge concerning the cell wall compositional roots of recalcitrance. Fourier transform mid-infrared spectroscopy (FTIR) represents a very useful tool on this enterprise, as it allows for a high-throughput, non-destructive and low unit cost procedure for the examination of cell wall biomass (Allison et al., 2009; Carpita and McCann, 2015). Furthermore, the use of Attenuated Total Reflection (ATR) in conjunction with infrared spectroscopy (IR) enables cell wall biomass samples to be examined in solid state without extensive preparation. Nonetheless, the analysis of purified cell wall preparations instead of the intact plant biomass is highly recommended, as it minimises or even eradicates interference from biomass components which are not part of the cell wall. Further information regarding the fundamentals of FTIR may be found elsewhere (Smith, 2011). Datasets generated from FTIR spectroscopy can be extensive and complex. In these situations, data-driven modelling techniques are often used as exploratory approaches to identify the most distinctive features of the collected spectra. Here we suggest the use of Principal Component Analysis (PCA), a frequently employed method to transform a large set of variables into a smaller set of new variables (principal components), effectively reducing dataset dimensionality. When the aim is a complete and detailed biomass characterisation, the FTIR-PCA method here described does not exclude the need for parallel wet gravimetric and analytical procedures. However, it does lead to a rapid identification of the major compositional shifts across large sets of samples; thus contributing to steer research pathways, minimise time-draining analytical procedures and reduce overall research costs.
Quantitative Image Analysis of Membrane Microdomains Labelled by Fluorescently Tagged Proteins in Arabidopsis thaliana and Nicotiana benthamiana
We have recently characterized co-existing membrane microdomains that are labeled by different proteins in living plant cells (Jarsch et al., 2014). For this approach we first created a digital fingerprint for each of the twenty marker proteins using quantitative image analysis. Here we recorded parameters such as domain size, density and shape based on image segmentation. We found highly reproducible patterns of any of the proteins over a large number of biological replicates. Furthermore we exclusively acquired images from lowly expressing cells and chose our imaging conditions in a way that resulted in images where no pixel was saturated.This protocol describes in detail the methods that have been used to analyze quantitative differences in localization of members of the remorin protein family in membrane microdomains of Arabidopsis thaliana and Nicotiana benthamiana (Jarsch et al., 2014). The proteins were either individually or pairwise expressed as fluorophore fusions in the respective plant. Image acquisition was performed using standard Confocal Laser Scanning Microscopy (CLSM) and image analysis was performed using ImageJ.[Introduction] Since confocal laser-scanning or other state-of-the-art fluorescence microscopes are nowadays often regarded as standard equipment a modern research institution should have, the amount of published cell biological data has massively increased over the last years. This certainly also correlates with the availability of an increasing number of fluorophores and corresponding expression vectors that have made it comparably easy to generate large numbers of tagged proteins. One main concern about showing microscopy images in publications is the subjectivity they have been selected with. In addition, and certainly very unfortunate in several cases, the scientific community as well as reviewers of manuscripts have requested ‘no background-high fluorescence’ images from the authors. As a consequence researchers often started selecting the images based on aesthetic aspects rather than showing the most representative ones. Furthermore the majority of images are based on strong over-expression of proteins. Therefore quantitative image analysis has become an absolute requirement in order to make robust statements on cell biological observations and the frequency with which they have been observed. However, this does not only require gaining novel skills but also high numbers of biological repetitions in a standardized way. Furthermore, it should be the ultimate goal to work under conditions where the protein of interest is expressed at native levels. While this may have to be overcome for lowly abundant proteins, researchers should nevertheless aim for similar levels and may thus accept more background noise in the images.It should be noted that all parameters and protocol specifications provided within this protocol have been optimized for the expression we used in a current study (Jarsch et al., 2014). Most likely they have to be adapted for any analyses in different laboratories.
Measurement of Net High-affinity Urea Uptake in Maize Plants
Despite its extensive use as a nitrogen fertilizer, the role of urea as a directly accessible nitrogen source for crop plants is still poorly understood. So far, the physiological and molecular aspects of urea acquisition have been investigated only in a few plant species highlighting the importance of a urea transporter in roots, DUR3 (Kojima et al., 2007; Wang et al., 2012; Zanin et al., 2014a). Regarding maize plants, a crop that needs a large amount of urea fertilizer, the capability to take up urea via an inducible and high-affinity transport system has been recently characterized (Zanin et al., 2014a; Zanin et al., 2014b). Here, we described a small-scale protocol suitable for the measurement of urea net high-affinity uptake in roots of intact maize plants.