The fundamental biological and clinical importance of integral membrane proteins prompted the development of a yeast-based system for the high-throughput identification of protein-protein interactions (PPI) for full-length transmembrane proteins. To this end, our lab developed the split-ubiquitin based Membrane Yeast Two-Hybrid (MYTH) system. This technology allows for the sensitive detection of transient and stable protein interactions using Saccharomyces cerevisiae as a host organism. MYTH takes advantage of the observation that ubiquitin can be separated into two stable moieties: the C-terminal half of yeast ubiquitin (Cub) and the N-terminal half of the ubiquitin moiety (Nub). In MYTH, this principle is adapted for use as a 'sensor' of protein-protein interactions. Briefly, the integral membrane bait protein is fused to Cub which is linked to an artificial transcription factor. Prey proteins, either in individual or library format, are fused to the Nub moiety. Protein interaction between the bait and prey leads to reconstitution of the ubiquitin moieties, forming a full-length 'pseudo-ubiquitin' molecule. This molecule is in turn recognized by cytosolic deubiquitinating enzymes, resulting in cleavage of the transcription factor, and subsequent induction of reporter gene expression. The system is highly adaptable, and is particularly well-suited to high-throughput screening. It has been successfully employed to investigate interactions using integral membrane proteins from both yeast and other organisms.
25 Related JoVE Articles!
Immunohistochemistry: Paraffin Sections Using the Vectastain ABC Kit from Vector Labs
Institutions: University of California, Irvine (UCI).
Immunohistochemistry (IHC) is a valuable technique utilized to localize/visualize protein expression in a mounted tissue section using specific antibodies. There are two methods: the direct and indirect method. In this experiment, we will only describe the use of indirect IHC staining. Indirect IHC staining utilizes highly specific primary and biotin-conjugated secondary antibodies. Primary antibodies are utilized to discretely identify proteins of interest by binding to a specific epitope, while secondary antibodies subtract for non-specific background staining and amplify signal by forming complexes to the primary antibody. Slides can either be generated from frozen sections, or paraffin embedded sections mounted on glass slides. In this protocol, we discuss the preparation of paraffin-embedded sections by dewaxing, hydration using an alcohol gradient, heat induced antigen retrieval, and blocking of endogenous peroxidase activity and non-specific binding sites. Some sections are then stained with antibodies specific for T cell marker CD8 and while others are stained for tyrosine hydroxylase. The slides are subsequently treated with appropriate secondary antibodies conjugated to biotin, then developed utilizing avidin-conjugated horseradish peroxidase (HRP) with Diaminiobenzidine (DAB) as substrate. Following development, the slides are counterstained for contrast, and mounted under coverslips with permount. After adequate drying, these slides are then ready for imaging.
Basic Protocols, Issue 8, Staining, Antibody, Immunohistochemistry
Identifying DNA Mutations in Purified Hematopoietic Stem/Progenitor Cells
Institutions: UT Health Science Center at San Antonio, UT Health Science Center at San Antonio, UT Health Science Center at San Antonio, UT Health Science Center at San Antonio, UT Health Science Center at San Antonio.
In recent years, it has become apparent that genomic instability is tightly related to many developmental disorders, cancers, and aging. Given that stem cells are responsible for ensuring tissue homeostasis and repair throughout life, it is reasonable to hypothesize that the stem cell population is critical for preserving genomic integrity of tissues. Therefore, significant interest has arisen in assessing the impact of endogenous and environmental factors on genomic integrity in stem cells and their progeny, aiming to understand the etiology of stem-cell based diseases.
transgenic mice carry a recoverable λ phage vector encoding the LacI
reporter system, in which the LacI
gene serves as the mutation reporter. The result of a mutated LacI
gene is the production of β-galactosidase that cleaves a chromogenic substrate, turning it blue. The LacI
reporter system is carried in all cells, including stem/progenitor cells and can easily be recovered and used to subsequently infect E. coli
. After incubating infected E. coli
on agarose that contains the correct substrate, plaques can be scored; blue plaques indicate a mutant LacI
gene, while clear plaques harbor wild-type. The frequency of blue (among clear) plaques indicates the mutant frequency in the original cell population the DNA was extracted from. Sequencing the mutant LacI
gene will show the location of the mutations in the gene and the type of mutation.
transgenic mouse model is well-established as an in vivo
mutagenesis assay. Moreover, the mice and the reagents for the assay are commercially available. Here we describe in detail how this model can be adapted to measure the frequency of spontaneously occurring DNA mutants in stem cell-enriched Lin-
(LSK) cells and other subpopulations of the hematopoietic system.
Infection, Issue 84, In vivo mutagenesis, hematopoietic stem/progenitor cells, LacI mouse model, DNA mutations, E. coli
Methods for Studying the Mechanisms of Action of Antipsychotic Drugs in Caenorhabditis elegans
Institutions: Harvard Medical School, McLean Hospital.
is a simple genetic organism amenable to large-scale forward and reverse genetic screens and chemical genetic screens. The C. elegans
genome includes potential antipsychotic drug (APD) targets conserved in humans, including genes encoding proteins required for neurotransmitter synthesis and for synaptic structure and function. APD exposure produces developmental delay and/or lethality in nematodes in a concentration-dependent manner. These phenotypes are caused, in part, by APD-induced inhibition of pharyngeal pumping1,2
. Thus, the developmental phenotype has a neuromuscular basis, making it useful for pharmacogenetic studies of neuroleptics. Here we demonstrate detailed procedures for testing APD effects on nematode development and pharyngeal pumping. For the developmental assay, synchronized embryos are placed on nematode growth medium (NGM) plates containing APDs, and the stages of developing animals are then scored daily. For the pharyngeal pumping rate assay, staged young adult animals are tested on NGM plates containing APDs. The number of pharyngeal pumps per unit time is recorded, and the pumping rate is calculated. These assays can be used for studying many other types of small molecules or even large molecules.
Neuroscience, Issue 84, antipsychotic drug, Caenorhabditis elegans, clozapine, developmental delay, lethality, nematode, pharmacogenetics, pharyngeal pumping, schizophrenia
Gene-environment Interaction Models to Unmask Susceptibility Mechanisms in Parkinson's Disease
Institutions: SRI International, University of California-Santa Cruz.
Lipoxygenase (LOX) activity has been implicated in neurodegenerative disorders such as Alzheimer's disease, but its effects in Parkinson's disease (PD) pathogenesis are less understood. Gene-environment interaction models have utility in unmasking the impact of specific cellular pathways in toxicity that may not be observed using a solely genetic or toxicant disease model alone. To evaluate if distinct LOX isozymes selectively contribute to PD-related neurodegeneration, transgenic (i.e.
5-LOX and 12/15-LOX deficient) mice can be challenged with a toxin that mimics cell injury and death in the disorder. Here we describe the use of a neurotoxin, 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP), which produces a nigrostriatal lesion to elucidate the distinct contributions of LOX isozymes to neurodegeneration related to PD. The use of MPTP in mouse, and nonhuman primate, is well-established to recapitulate the nigrostriatal damage in PD. The extent of MPTP-induced lesioning is measured by HPLC analysis of dopamine and its metabolites and semi-quantitative Western blot analysis of striatum for tyrosine hydroxylase (TH), the rate-limiting enzyme for the synthesis of dopamine. To assess inflammatory markers, which may demonstrate LOX isozyme-selective sensitivity, glial fibrillary acidic protein (GFAP) and Iba-1 immunohistochemistry are performed on brain sections containing substantia nigra, and GFAP Western blot analysis is performed on striatal homogenates. This experimental approach can provide novel insights into gene-environment interactions underlying nigrostriatal degeneration and PD.
Medicine, Issue 83, MPTP, dopamine, Iba1, TH, GFAP, lipoxygenase, transgenic, gene-environment interactions, mouse, Parkinson's disease, neurodegeneration, neuroinflammation
A New Approach for the Comparative Analysis of Multiprotein Complexes Based on 15N Metabolic Labeling and Quantitative Mass Spectrometry
Institutions: University of Münster, Carnegie Institution for Science.
The introduced protocol provides a tool for the analysis of multiprotein complexes in the thylakoid membrane, by revealing insights into complex composition under different conditions. In this protocol the approach is demonstrated by comparing the composition of the protein complex responsible for cyclic electron flow (CEF) in Chlamydomonas reinhardtii
, isolated from genetically different strains. The procedure comprises the isolation of thylakoid membranes, followed by their separation into multiprotein complexes by sucrose density gradient centrifugation, SDS-PAGE, immunodetection and comparative, quantitative mass spectrometry (MS) based on differential metabolic labeling (14
N) of the analyzed strains. Detergent solubilized thylakoid membranes are loaded on sucrose density gradients at equal chlorophyll concentration. After ultracentrifugation, the gradients are separated into fractions, which are analyzed by mass-spectrometry based on equal volume. This approach allows the investigation of the composition within the gradient fractions and moreover to analyze the migration behavior of different proteins, especially focusing on ANR1, CAS, and PGRL1. Furthermore, this method is demonstrated by confirming the results with immunoblotting and additionally by supporting the findings from previous studies (the identification and PSI-dependent migration of proteins that were previously described to be part of the CEF-supercomplex such as PGRL1, FNR, and cyt f
). Notably, this approach is applicable to address a broad range of questions for which this protocol can be adopted and e.g.
used for comparative analyses of multiprotein complex composition isolated from distinct environmental conditions.
Microbiology, Issue 85, Sucrose density gradients, Chlamydomonas, multiprotein complexes, 15N metabolic labeling, thylakoids
Lignin Down-regulation of Zea mays via dsRNAi and Klason Lignin Analysis
Institutions: University of Arizona, Michigan State University, The Institute for Advanced Learning and Research, Michigan State University.
To facilitate the use of lignocellulosic biomass as an alternative bioenergy resource, during biological conversion processes, a pretreatment step is needed to open up the structure of the plant cell wall, increasing the accessibility of the cell wall carbohydrates. Lignin, a polyphenolic material present in many cell wall types, is known to be a significant hindrance to enzyme access. Reduction in lignin content to a level that does not interfere with the structural integrity and defense system of the plant might be a valuable step to reduce the costs of bioethanol production. In this study, we have genetically down-regulated one of the lignin biosynthesis-related genes, cinnamoyl-CoA reductase (ZmCCR1
) via a double stranded RNA interference technique. The ZmCCR1_RNAi
construct was integrated into the maize genome using the particle bombardment method. Transgenic maize plants grew normally as compared to the wild-type control plants without interfering with biomass growth or defense mechanisms, with the exception of displaying of brown-coloration in transgenic plants leaf mid-ribs, husks, and stems. The microscopic analyses, in conjunction with the histological assay, revealed that the leaf sclerenchyma fibers were thinned but the structure and size of other major vascular system components was not altered. The lignin content in the transgenic maize was reduced by 7-8.7%, the crystalline cellulose content was increased in response to lignin reduction, and hemicelluloses remained unchanged. The analyses may indicate that carbon flow might have been shifted from lignin biosynthesis to cellulose biosynthesis. This article delineates the procedures used to down-regulate the lignin content in maize via RNAi technology, and the cell wall compositional analyses used to verify the effect of the modifications on the cell wall structure.
Bioengineering, Issue 89, Zea mays, cinnamoyl-CoA reductase (CCR), dsRNAi, Klason lignin measurement, cell wall carbohydrate analysis, gas chromatography (GC)
Production of Haploid Zebrafish Embryos by In Vitro Fertilization
Institutions: University of Notre Dame.
The zebrafish has become a mainstream vertebrate model that is relevant for many disciplines of scientific study. Zebrafish are especially well suited for forward genetic analysis of developmental processes due to their external fertilization, embryonic size, rapid ontogeny, and optical clarity – a constellation of traits that enable the direct observation of events ranging from gastrulation to organogenesis with a basic stereomicroscope. Further, zebrafish embryos can survive for several days in the haploid state. The production of haploid embryos in vitro
is a powerful tool for mutational analysis, as it enables the identification of recessive mutant alleles present in first generation (F1) female carriers following mutagenesis in the parental (P) generation. This approach eliminates the necessity to raise multiple generations (F2, F3, etc.
) which involves breeding of mutant families, thus saving the researcher time along with reducing the needs for zebrafish colony space, labor, and the husbandry costs. Although zebrafish have been used to conduct forward screens for the past several decades, there has been a steady expansion of transgenic and genome editing tools. These tools now offer a plethora of ways to create nuanced assays for next generation screens that can be used to further dissect the gene regulatory networks that drive vertebrate ontogeny. Here, we describe how to prepare haploid zebrafish embryos. This protocol can be implemented for novel future haploid screens, such as in enhancer and suppressor screens, to address the mechanisms of development for a broad number of processes and tissues that form during early embryonic stages.
Developmental Biology, Issue 89, zebrafish, haploid, in vitro fertilization, forward genetic screen, saturation, recessive mutation, mutagenesis
Enhanced Northern Blot Detection of Small RNA Species in Drosophila Melanogaster
Institutions: Institut de Génétique et de Biologie Moléculaire et Cellulaire, Istituto Italiano di Tecnologia.
The last decades have witnessed the explosion of scientific interest around gene expression control mechanisms at the RNA level. This branch of molecular biology has been greatly fueled by the discovery of noncoding RNAs as major players in post-transcriptional regulation. Such a revolutionary perspective has been accompanied and triggered by the development of powerful technologies for profiling short RNAs expression, both at the high-throughput level (genome-wide identification) or as single-candidate analysis (steady state accumulation of specific species). Although several state-of-art strategies are currently available for dosing or visualizing such fleeing molecules, Northern Blot assay remains the eligible approach in molecular biology for immediate and accurate evaluation of RNA expression. It represents a first step toward the application of more sophisticated, costly technologies and, in many cases, remains a preferential method to easily gain insights into RNA biology. Here we overview an efficient protocol (Enhanced Northern Blot) for detecting weakly expressed microRNAs (or other small regulatory RNA species) from Drosophila melanogaster
whole embryos, manually dissected larval/adult tissues or in vitro
cultured cells. A very limited amount of RNA is required and the use of material from flow cytometry-isolated cells can be also envisaged.
Molecular Biology, Issue 90, Northern blotting, Noncoding RNAs, microRNAs, rasiRNA, Gene expression, Gcm/Glide, Drosophila melanogaster
Strategies for Tracking Anastasis, A Cell Survival Phenomenon that Reverses Apoptosis
Institutions: Johns Hopkins University Bloomberg School of Public Health, Chinese University of Hong Kong, Johns Hopkins University School of Medicine.
Anastasis (Greek for “rising to life”) refers to the recovery of dying cells. Before these cells recover, they have passed through important checkpoints of apoptosis, including mitochondrial fragmentation, release of mitochondrial cytochrome c
into the cytosol, activation of caspases, chromatin condensation, DNA damage, nuclear fragmentation, plasma membrane blebbing, cell shrinkage, cell surface exposure of phosphatidylserine, and formation of apoptotic bodies. Anastasis can occur when apoptotic stimuli are removed prior to death, thereby allowing dying cells to reverse apoptosis and potentially other death mechanisms. Therefore, anastasis appears to involve physiological healing processes that could also sustain damaged cells inappropriately. The functions and mechanisms of anastasis are still unclear, hampered in part by the limited tools for detecting past events after the recovery of apparently healthy cells. Strategies to detect anastasis will enable studies of the physiological mechanisms, the hazards of undead cells in disease pathology, and potential therapeutics to modulate anastasis. Here, we describe effective strategies using live cell microscopy and a mammalian caspase biosensor for identifying and tracking anastasis in mammalian cells.
Cellular Biology, Issue 96, Anastasis, apoptosis, apoptotic bodies, caspase, cell death, cell shrinkage, cell suicide, cytochrome c, DNA damage, genetic alterations, mitochondrial outer membrane permeabilization (MOMP), programmed cell death, reversal of apoptosis
Larval RNA Interference in the Red Flour Beetle, Tribolium castaneum
Institutions: Miami University.
The red flour beetle, Tribolium castaneum
, offers a repertoire of experimental tools for genetic and developmental studies, including a fully annotated genome sequence, transposon-based transgenesis, and effective RNA interference (RNAi). Among these advantages, RNAi-based gene knockdown techniques are at the core of Tribolium
research. T. castaneum
show a robust systemic RNAi response, making it possible to perform RNAi at any life stage by simply injecting double-stranded RNA (dsRNA) into the beetle’s body cavity.
In this report, we provide an overview of our larval RNAi technique in T. castaneum
. The protocol includes (i) isolation of the proper stage of T. castaneum
larvae for injection, (ii) preparation for the injection setting, and (iii) dsRNA injection. Larval RNAi is a simple, but powerful technique that provides us with quick access to loss-of-function phenotypes, including multiple gene knockdown phenotypes as well as a series of hypomorphic phenotypes. Since virtually all T. castaneum
tissues are susceptible to extracellular dsRNA, the larval RNAi technique allows researchers to study a wide variety of tissues in diverse contexts, including the genetic basis of organismal responses to the outside environment. In addition, the simplicity of this technique stimulates more student involvement in research, making T. castaneum
an ideal genetic system for use in a classroom setting.
Molecular Biology, Issue 92, RNA interference, RNAi, gene knockdown, red flour beetle, Tribolium castaneum, injection, double-stranded RNA, functional analysis, teaching laboratories
Isolation and Functional Analysis of Mitochondria from Cultured Cells and Mouse Tissue
Institutions: Elon University, Wake Forest School of Medicine, Wake Forest School of Medicine, Wake Forest School of Medicine.
Comparison between two or more distinct groups, such as healthy vs. disease, is necessary to determine cellular status. Mitochondria are at the nexus of cell heath due to their role in both cell metabolism and energy production as well as control of apoptosis. Therefore, direct evaluation of isolated mitochondria and mitochondrial perturbation offers the ability to determine if organelle-specific (dys)function is occurring. The methods described in this protocol include isolation of intact, functional mitochondria from HEK cultured cells and mouse liver and spinal cord, but can be easily adapted for use with other cultured cells or animal tissues. Mitochondrial function assessed by TMRE and the use of common mitochondrial uncouplers and inhibitors in conjunction with a fluorescent plate reader allow this protocol not only to be versatile and accessible to most research laboratories, but also offers high throughput.
Cellular Biology, Issue 97, Mitochondria, TMRE, cytokines, ALS, HEK cells, fluorescence, mitochondrial dysfunction, mitochondrial membrane potential, cytochrome c
A Guided Materials Screening Approach for Developing Quantitative Sol-gel Derived Protein Microarrays
Institutions: McMaster University .
Microarrays have found use in the development of high-throughput assays for new materials and discovery of small-molecule drug leads. Herein we describe a guided material screening approach to identify sol-gel based materials that are suitable for producing three-dimensional protein microarrays. The approach first identifies materials that can be printed as microarrays, narrows down the number of materials by identifying those that are compatible with a given enzyme assay, and then hones in on optimal materials based on retention of maximum enzyme activity. This approach is applied to develop microarrays suitable for two different enzyme assays, one using acetylcholinesterase and the other using a set of four key kinases involved in cancer. In each case, it was possible to produce microarrays that could be used for quantitative small-molecule screening assays and production of dose-dependent inhibitor response curves. Importantly, the ability to screen many materials produced information on the types of materials that best suited both microarray production and retention of enzyme activity. The materials data provide insight into basic material requirements necessary for tailoring optimal, high-density sol-gel derived microarrays.
Chemistry, Issue 78, Biochemistry, Chemical Engineering, Molecular Biology, Genetics, Bioengineering, Biomedical Engineering, Chemical Biology, Biocompatible Materials, Siloxanes, Enzymes, Immobilized, chemical analysis techniques, chemistry (general), materials (general), spectroscopic analysis (chemistry), polymer matrix composites, testing of materials (composite materials), Sol-gel, microarray, high-throughput screening, acetylcholinesterase, kinase, drug discovery, assay
Rapid Protocol for Preparation of Electrocompetent Escherichia coli and Vibrio cholerae
Institutions: University of Texas Brownsville, University of Alberta, University of Texas Brownsville.
Electroporation has become a widely used method for rapidly and efficiently introducing foreign DNA into a wide range of cells. Electrotransformation has become the method of choice for introducing DNA into prokaryotes that are not naturally competent. Electroporation is a rapid, efficient, and streamlined transformation method that, in addition to purified DNA and competent bacteria, requires commercially available gene pulse controller and cuvettes. In contrast to the pulsing step, preparation of electrocompetent cells is time consuming and labor intensive involving repeated rounds of centrifugation and washes in decreasing volumes of sterile, cold water, or non-ionic buffers of large volumes of cultures grown to mid-logarithmic phase of growth. Time and effort can be saved by purchasing electrocompetent cells from commercial sources, but the selection is limited to commonly employed E. coli
laboratory strains. We are hereby disseminating a rapid and efficient method for preparing electrocompetent E. coli
, which has been in use by bacteriology laboratories for some time, can be adapted to V. cholerae
and other prokaryotes. While we cannot ascertain whom to credit for developing the original technique, we are hereby making it available to the scientific community.
Bioengineering, Issue 80, Cell Engineering, Gram-Negative Bacteria, Enterobacteriaceae, Escherichia, Escherichia coli, Vibrionaceae, Vibrio, Vibrio cholerae, Bacteria, Escherichia coli, Vibrio cholerae, electrocompetence, transformation protocol, electroporation
Ratiometric Biosensors that Measure Mitochondrial Redox State and ATP in Living Yeast Cells
Institutions: Columbia University, Columbia University.
Mitochondria have roles in many cellular processes, from energy metabolism and calcium homeostasis to control of cellular lifespan and programmed cell death. These processes affect and are affected by the redox status of and ATP production by mitochondria. Here, we describe the use of two ratiometric, genetically encoded biosensors that can detect mitochondrial redox state and ATP levels at subcellular resolution in living yeast cells. Mitochondrial redox state is measured using redox-sensitive Green Fluorescent Protein (roGFP) that is targeted to the mitochondrial matrix. Mito-roGFP contains cysteines at positions 147 and 204 of GFP, which undergo reversible and environment-dependent oxidation and reduction, which in turn alter the excitation spectrum of the protein. MitGO-ATeam is a Förster resonance energy transfer (FRET) probe in which the ε subunit of the Fo
-ATP synthase is sandwiched between FRET donor and acceptor fluorescent proteins. Binding of ATP to the ε subunit results in conformation changes in the protein that bring the FRET donor and acceptor in close proximity and allow for fluorescence resonance energy transfer from the donor to acceptor.
Bioengineering, Issue 77, Microbiology, Cellular Biology, Molecular Biology, Biochemistry, life sciences, roGFP, redox-sensitive green fluorescent protein, GO-ATeam, ATP, FRET, ROS, mitochondria, biosensors, GFP, ImageJ, microscopy, confocal microscopy, cell, imaging
Obtaining Highly Purified Toxoplasma gondii Oocysts by a Discontinuous Cesium Chloride Gradient
Institutions: Dynamac, Inc., University of Cincinnati, McMicken College of Arts and Science, Agricultural Research Service, U.S. Department of Agriculture, US Environmental Protection Agency.
is an obligate intracellular protozoan pathogen that commonly infects humans. It is a well characterized apicomplexan associated with causing food- and water-borne disease outbreaks. The definitive host is the feline species where sexual replication occurs resulting in the development of the highly infectious and environmentally resistant oocyst. Infection occurs via ingestion of tissue cysts from contaminated meat or oocysts from soil or water. Infection is typically asymptomatic in healthy individuals, but results in a life-long latent infection that can reactivate causing toxoplasmic encephalitis and death if the individual becomes immunocompromised. Meat contaminated with T. gondii
cysts have been the primary source of infection in Europe and the United States, but recent changes in animal management and husbandry practices and improved food handling and processing procedures have significantly reduced the prevalence of T. gondii
cysts in meat1, 2
. Nonetheless, seroprevalence in humans remains relatively high suggesting that exposure from oocyst contaminated soil or water is likely. Indeed, waterborne outbreaks of toxoplasmosis have been reported worldwide supporting the theory exposure to the environmental oocyst form poses a significant health risk3-5
. To date, research on understanding the prevalence of T. gondii
oocysts in the water and environment are limited due to the lack of tools to detect oocysts in the environment 5, 6
. This is primarily due to the lack of efficient purification protocols for obtaining large numbers of highly purified T gondii
oocysts from infected cats for research purposes. This study describes the development of a modified CsCl method that easily purifies T. gondii
oocysts from feces of infected cats that are suitable for molecular biological and tissue culture manipulation7
Jove Infectious Diseases, Microbiology, Issue 33, Toxoplasma gondii, cesium chloride, oocysts, discontinuous gradient, apicomplexan
Investigating Tissue- and Organ-specific Phytochrome Responses using FACS-assisted Cell-type Specific Expression Profiling in Arabidopsis thaliana
Institutions: Michigan State University (MSU), Michigan State University (MSU).
Light mediates an array of developmental and adaptive processes throughout the life cycle of a plant. Plants utilize light-absorbing molecules called photoreceptors to sense and adapt to light. The red/far-red light-absorbing phytochrome photoreceptors have been studied extensively. Phytochromes exist as a family of proteins with distinct and overlapping functions in all higher plant systems in which they have been studied1
. Phytochrome-mediated light responses, which range from seed germination through flowering and senescence, are often localized to specific plant tissues or organs2
. Despite the discovery and elucidation of individual and redundant phytochrome functions through mutational analyses, conclusive reports on distinct sites of photoperception and the molecular mechanisms of localized pools of phytochromes that mediate spatial-specific phytochrome responses are limited. We designed experiments based on the hypotheses that specific sites of phytochrome photoperception regulate tissue- and organ-specific aspects of photomorphogenesis, and that localized phytochrome pools engage distinct subsets of downstream target genes in cell-to-cell signaling. We developed a biochemical approach to selectively reduce functional phytochromes in an organ- or tissue-specific manner within transgenic plants. Our studies are based on a bipartite enhancer-trap approach that results in transactivation of the expression of a gene under control of the Upstream Activation Sequence (UAS) element by the transcriptional activator GAL43
. The biliverdin reductase (BVR
) gene under the control of the UAS is silently maintained in the absence of GAL4 transactivation in the UAS-BVR parent4
. Genetic crosses between a UAS-BVR transgenic line and a GAL4-GFP enhancer trap line result in specific expression of the BVR
gene in cells marked by GFP
. BVR accumulation in Arabidopsis plants results in phytochrome chromophore deficiency in planta5-7
. Thus, transgenic plants that we have produced exhibit GAL4-dependent activation of the BVR
gene, resulting in the biochemical inactivation of phytochrome, as well as GAL4-dependent GFP
expression. Photobiological and molecular genetic analyses of BVR
transgenic lines are yielding insight into tissue- and organ-specific phytochrome-mediated responses that have been associated with corresponding sites of photoperception4, 7, 8
. Fluorescence Activated Cell Sorting (FACS) of GFP-positive, enhancer-trap-induced BVR
-expressing plant protoplasts coupled with cell-type-specific gene expression profiling through microarray analysis is being used to identify putative downstream target genes involved in mediating spatial-specific phytochrome responses. This research is expanding our understanding of sites of light perception, the mechanisms through which various tissues or organs cooperate in light-regulated plant growth and development, and advancing the molecular dissection of complex phytochrome-mediated cell-to-cell signaling cascades.
Plant Biology, Issue 39, Arabidopsis thaliana, confocal microscopy, expression profiling, microarray, fluorescence, FACS, photomorphogenesis, phytochrome, protoplasting
Assaying β-amyloid Toxicity using a Transgenic C. elegans Model
Institutions: University of Colorado, University of Colorado.
Accumulation of the β-amyloid peptide (Aβ) is generally believed to be central to the induction of Alzheimer's disease, but the relevant mechanism(s) of toxicity are still unclear. Aβ is also deposited intramuscularly in Inclusion Body Myositis, a severe human myopathy. The intensely studied nematode worm Caenorhabditis elegans
can be transgenically engineered to express human Aβ. Depending on the tissue or timing of Aβ expression, transgenic worms can have readily measurable phenotypes that serve as a read-out of Aβ toxicity. For example, transgenic worms with pan-neuronal Aβ expression have defects is associative learning (Dosanjh et al.
2009), while transgenic worms with constitutive muscle-specific expression show a progressive, age-dependent paralysis phenotype (Link, 1995; Cohen et al.
2006). One particularly useful C. elegans
model employs a temperature-sensitive mutation in the mRNA surveillance system to engineer temperature-inducible muscle expression of an Aβ transgene, resulting in a reproducible paralysis phenotype upon temperature upshift (Link et al.
2003). Treatments that counter Aβ toxicity in this model [e.g., expression of a protective transgene (Hassan et al.
2009) or exposure to Ginkgo biloba extracts (Wu et al.
2006)] reproducibly alter the rate of paralysis induced by temperature upshift of these transgenic worms. Here we describe our protocol for measuring the rate of paralysis in this transgenic C. elegans
model, with particular attention to experimental variables that can influence this measurement.
Neuroscience, Issue 44, Alzheimer's disease, paralysis, compound screening, Inclusion Body Myositis, invertebrate model
Respirometric Oxidative Phosphorylation Assessment in Saponin-permeabilized Cardiac Fibers
Institutions: University of Calgary, University of Calgary.
Investigation of mitochondrial function represents an important parameter of cardiac physiology as mitochondria are involved in energy metabolism, oxidative stress, apoptosis, aging, mitochondrial encephalomyopathies and drug toxicity. Given this, technologies to measure cardiac mitochondrial function are in demand. One technique that employs an integrative approach to measure mitochondrial function is respirometric oxidative phosphorylation (OXPHOS) analysis.
The principle of respirometric OXPHOS assessment is centered around measuring oxygen concentration utilizing a Clark electrode. As the permeabilized fiber bundle consumes oxygen, oxygen concentration in the closed chamber declines. Using selected substrate-inhibitor-uncoupler titration protocols, electrons are provided to specific sites of the electron transport chain, allowing evaluation of mitochondrial function. Prior to respirometric analysis of mitochondrial function, mechanical and chemical preparatory techniques are utilized to permeabilize the sarcolemma of muscle fibers. Chemical permeabilization employs saponin to selectively perforate the cell membrane while maintaining cellular architecture.
This paper thoroughly describes the steps involved in preparing saponin-skinned cardiac fibers for oxygen consumption measurements to evaluate mitochondrial OXPHOS. Additionally, troubleshooting advice as well as specific substrates, inhibitors and uncouplers that may be used to determine mitochondria function at specific sites of the electron transport chain are provided. Importantly, the described protocol may be easily applied to cardiac and skeletal tissue of various animal models and human samples.
Physiology, Issue 48, cardiac fibers, mitochondria, oxygen consumption, mouse, methodology
Competitive Genomic Screens of Barcoded Yeast Libraries
Institutions: University of Toronto, University of Toronto, University of Toronto, National Human Genome Research Institute, NIH, Stanford University , University of Toronto.
By virtue of advances in next generation sequencing technologies, we have access to new genome sequences almost daily. The tempo of these advances is accelerating, promising greater depth and breadth. In light of these extraordinary advances, the need for fast, parallel methods to define gene function becomes ever more important. Collections of genome-wide deletion mutants in yeasts and E. coli
have served as workhorses for functional characterization of gene function, but this approach is not scalable, current gene-deletion approaches require each of the thousands of genes that comprise a genome to be deleted and verified. Only after this work is complete can we pursue high-throughput phenotyping. Over the past decade, our laboratory has refined a portfolio of competitive, miniaturized, high-throughput genome-wide assays that can be performed in parallel. This parallelization is possible because of the inclusion of DNA 'tags', or 'barcodes,' into each mutant, with the barcode serving as a proxy for the mutation and one can measure the barcode abundance to assess mutant fitness. In this study, we seek to fill the gap between DNA sequence and barcoded mutant collections. To accomplish this we introduce a combined transposon disruption-barcoding approach that opens up parallel barcode assays to newly sequenced, but poorly characterized microbes. To illustrate this approach we present a new Candida albicans
barcoded disruption collection and describe how both microarray-based and next generation sequencing-based platforms can be used to collect 10,000 - 1,000,000 gene-gene and drug-gene interactions in a single experiment.
Biochemistry, Issue 54, chemical biology, chemogenomics, chemical probes, barcode microarray, next generation sequencing
Single Cell Fate Mapping in Zebrafish
Institutions: Cincinnati Children's Hospital Medical Center, Cincinnati Children's Hospital Medical Center.
The ability to differentially label single cells has important implications in developmental biology. For instance, determining how hematopoietic, lymphatic, and blood vessel lineages arise in developing embryos requires fate mapping and lineage tracing of undifferentiated precursor cells. Recently, photoactivatable proteins which include: Eos1, 2
, and KikGR9, 10
have received wide interest as cell tracing probes. The fluorescence spectrum of these photosensitive proteins can be easily converted with UV excitation, allowing a population of cells to be distinguished from adjacent ones. However, the photoefficiency of the activated protein may limit long-term cell tracking11
. As an alternative to photoactivatable proteins, caged fluorescein-dextran has been widely used in embryo model systems7, 12-14
. Traditionally, to uncage fluorescein-dextran, UV excitation from a fluorescence lamp house or a single photon UV laser has been used; however, such sources limit the spatial resolution of photoactivation. Here we report a protocol to fate map, lineage trace, and detect single labeled cells. Single cells in embryos injected with caged fluorescein-dextran are photoactivated with near-infrared laser pulses produced from a titanium sapphire femtosecond laser. This laser is customary in all two-photon confocal microscopes such as the LSM 510 META NLO microscope used in this paper. Since biological tissue is transparent to near-infrared irradiation15
, the laser pulses can be focused deep within the embryo without uncaging cells above or below the selected focal plane. Therefore, non-linear two-photon absorption is induced only at the geometric focus to uncage fluorescein-dextran in a single cell. To detect the cell containing uncaged fluorescein-dextran, we describe a simple immunohistochemistry protocol16
to rapidly visualize the activated cell. The activation and detection protocol presented in this paper is versatile and can be applied to any model system.
The reagents used in this protocol can be found in the table appended at the end of the article.
Developmental Biology, Issue 56, Zebrafish, Two-photon, photoactivation, immunohistochemistry, caged fluorescent protein, fate mapping
Detection of Rare Genomic Variants from Pooled Sequencing Using SPLINTER
Institutions: Washington University School of Medicine, Washington University School of Medicine, Washington University School of Medicine.
As DNA sequencing technology has markedly advanced in recent years2
, it has become increasingly evident that the amount of genetic variation between any two individuals is greater than previously thought3
. In contrast, array-based genotyping has failed to identify a significant contribution of common sequence variants to the phenotypic variability of common disease4,5
. Taken together, these observations have led to the evolution of the Common Disease / Rare Variant hypothesis suggesting that the majority of the "missing heritability" in common and complex phenotypes is instead due to an individual's personal profile of rare or private DNA variants6-8
. However, characterizing how rare variation impacts complex phenotypes requires the analysis of many affected individuals at many genomic loci, and is ideally compared to a similar survey in an unaffected cohort. Despite the sequencing power offered by today's platforms, a population-based survey of many genomic loci and the subsequent computational analysis required remains prohibitive for many investigators.
To address this need, we have developed a pooled sequencing approach1,9
and a novel software package1
for highly accurate rare variant detection from the resulting data. The ability to pool genomes from entire populations of affected individuals and survey the degree of genetic variation at multiple targeted regions in a single sequencing library provides excellent cost and time savings to traditional single-sample sequencing methodology. With a mean sequencing coverage per allele of 25-fold, our custom algorithm, SPLINTER, uses an internal variant calling control strategy to call insertions, deletions and substitutions up to four base pairs in length with high sensitivity and specificity from pools of up to 1 mutant allele in 500 individuals. Here we describe the method for preparing the pooled sequencing library followed by step-by-step instructions on how to use the SPLINTER package for pooled sequencing analysis (http://www.ibridgenetwork.org/wustl/splinter). We show a comparison between pooled sequencing of 947 individuals, all of whom also underwent genome-wide array, at over 20kb of sequencing per person. Concordance between genotyping of tagged and novel variants called in the pooled sample were excellent. This method can be easily scaled up to any number of genomic loci and any number of individuals. By incorporating the internal positive and negative amplicon controls at ratios that mimic the population under study, the algorithm can be calibrated for optimal performance. This strategy can also be modified for use with hybridization capture or individual-specific barcodes and can be applied to the sequencing of naturally heterogeneous samples, such as tumor DNA.
Genetics, Issue 64, Genomics, Cancer Biology, Bioinformatics, Pooled DNA sequencing, SPLINTER, rare genetic variants, genetic screening, phenotype, high throughput, computational analysis, DNA, PCR, primers
Assessment of Mitochondrial Functions and Cell Viability in Renal Cells Overexpressing Protein Kinase C Isozymes
Institutions: University of Arkansas for Medical Sciences .
The protein kinase C (PKC) family of isozymes is involved in numerous physiological and pathological processes. Our recent data demonstrate that PKC regulates mitochondrial function and cellular energy status. Numerous reports demonstrated that the activation of PKC-a and PKC-ε improves mitochondrial function in the ischemic heart and mediates cardioprotection. In contrast, we have demonstrated that PKC-α and PKC-ε are involved in nephrotoxicant-induced mitochondrial dysfunction and cell death in kidney cells. Therefore, the goal of this study was to develop an in vitro
model of renal cells maintaining active mitochondrial functions in which PKC isozymes could be selectively activated or inhibited to determine their role in regulation of oxidative phosphorylation and cell survival. Primary cultures of renal proximal tubular cells (RPTC) were cultured in improved conditions resulting in mitochondrial respiration and activity of mitochondrial enzymes similar to those in RPTC in vivo
. Because traditional transfection techniques (Lipofectamine, electroporation) are inefficient in primary cultures and have adverse effects on mitochondrial function, PKC-ε mutant cDNAs were delivered to RPTC through adenoviral vectors. This approach results in transfection of over 90% cultured RPTC.
Here, we present methods for assessing the role of PKC-ε in: 1. regulation of mitochondrial morphology and functions associated with ATP synthesis, and 2. survival of RPTC in primary culture. PKC-ε is activated by overexpressing the constitutively active PKC-ε mutant. PKC-ε is inhibited by overexpressing the inactive mutant of PKC-ε. Mitochondrial function is assessed by examining respiration, integrity of the respiratory chain, activities of respiratory complexes and F0
-ATPase, ATP production rate, and ATP content. Respiration is assessed in digitonin-permeabilized RPTC as state 3 (maximum respiration in the presence of excess substrates and ADP) and uncoupled respirations. Integrity of the respiratory chain is assessed by measuring activities of all four complexes of the respiratory chain in isolated mitochondria. Capacity of oxidative phosphorylation is evaluated by measuring the mitochondrial membrane potential, ATP production rate, and activity of F0
-ATPase. Energy status of RPTC is assessed by determining the intracellular ATP content. Mitochondrial morphology in live cells is visualized using MitoTracker Red 580, a fluorescent dye that specifically accumulates in mitochondria, and live monolayers are examined under a fluorescent microscope. RPTC viability is assessed using annexin V/propidium iodide staining followed by flow cytometry to determine apoptosis and oncosis.
These methods allow for a selective activation/inhibition of individual PKC isozymes to assess their role in cellular functions in a variety of physiological and pathological conditions that can be reproduced in in vitro
Cellular Biology, Issue 71, Biochemistry, Molecular Biology, Genetics, Pharmacology, Physiology, Medicine, Protein, Mitochondrial dysfunction, mitochondria, protein kinase C, renal proximal tubular cells, reactive oxygen species, oxygen consumption, electron transport chain, respiratory complexes, ATP, adenovirus, primary culture, ischemia, cells, flow cytometry
Genome-wide Gene Deletions in Streptococcus sanguinis by High Throughput PCR
Institutions: Virginia Commonwealth University.
Transposon mutagenesis and single-gene deletion are two methods applied in genome-wide gene knockout in bacteria 1,2
. Although transposon mutagenesis is less time consuming, less costly, and does not require completed genome information, there are two weaknesses in this method: (1) the possibility of a disparate mutants in the mixed mutant library that counter-selects mutants with decreased competition; and (2) the possibility of partial gene inactivation whereby genes do not entirely lose their function following the insertion of a transposon. Single-gene deletion analysis may compensate for the drawbacks associated with transposon mutagenesis. To improve the efficiency of genome-wide single gene deletion, we attempt to establish a high-throughput technique for genome-wide single gene deletion using Streptococcus sanguinis
as a model organism. Each gene deletion construct in S. sanguinis
genome is designed to comprise 1-kb upstream of the targeted gene, the aphA-3
gene, encoding kanamycin resistance protein, and 1-kb downstream of the targeted gene. Three sets of primers F1/R1, F2/R2, and F3/R3, respectively, are designed and synthesized in a 96-well plate format for PCR-amplifications of those three components of each deletion construct. Primers R1 and F3 contain 25-bp sequences that are complementary to regions of the aphA-3
gene at their 5' end. A large scale PCR amplification of the aphA-3
gene is performed once for creating all single-gene deletion constructs. The promoter of aphA-3
gene is initially excluded to minimize the potential polar effect of kanamycin cassette. To create the gene deletion constructs, high-throughput PCR amplification and purification are performed in a 96-well plate format. A linear recombinant PCR amplicon for each gene deletion will be made up through four PCR reactions using high-fidelity DNA polymerase. The initial exponential growth phase of S. sanguinis
cultured in Todd Hewitt broth supplemented with 2.5% inactivated horse serum is used to increase competence for the transformation of PCR-recombinant constructs. Under this condition, up to 20% of S. sanguinis
cells can be transformed using ~50 ng of DNA. Based on this approach, 2,048 mutants with single-gene deletion were ultimately obtained from the 2,270 genes in S. sanguinis
excluding four gene ORFs contained entirely within other ORFs in S. sanguinis
SK36 and 218 potential essential genes. The technique on creating gene deletion constructs is high throughput and could be easy to use in genome-wide single gene deletions for any transformable bacteria.
Genetics, Issue 69, Microbiology, Molecular Biology, Biomedical Engineering, Genomics, Streptococcus sanguinis, Streptococcus, Genome-wide gene deletions, genes, High-throughput, PCR
Identification of Sleeping Beauty Transposon Insertions in Solid Tumors using Linker-mediated PCR
Institutions: University of Minnesota, Minneapolis, University of Minnesota, Minneapolis.
Genomic, proteomic, transcriptomic, and epigenomic analyses of human tumors indicate that there are thousands of anomalies within each cancer genome compared to matched normal tissue. Based on these analyses it is evident that there are many undiscovered genetic drivers of cancer1
. Unfortunately these drivers are hidden within a much larger number of passenger anomalies in the genome that do not directly contribute to tumor formation. Another aspect of the cancer genome is that there is considerable genetic heterogeneity within similar tumor types. Each tumor can harbor different mutations that provide a selective advantage for tumor formation2
. Performing an unbiased forward genetic screen in mice provides the tools to generate tumors and analyze their genetic composition, while reducing the background of passenger mutations. The Sleeping Beauty
(SB) transposon system is one such method3
. The SB system utilizes mobile vectors (transposons) that can be inserted throughout the genome by the transposase enzyme. Mutations are limited to a specific cell type through the use of a conditional transposase allele that is activated by Cre Recombinase
. Many mouse lines exist that express Cre Recombinase
in specific tissues. By crossing one of these lines to the conditional transposase allele (e.g.
Lox-stop-Lox-SB11), the SB system is activated only in cells that express Cre Recombinase
. The Cre Recombinase
will excise a stop cassette that blocks expression of the transposase allele, thereby activating transposon mutagenesis within the designated cell type. An SB screen is initiated by breeding three strains of transgenic mice so that the experimental mice carry a conditional transposase allele, a concatamer of transposons, and a tissue-specific Cre Recombinase
allele. These mice are allowed to age until tumors form and they become moribund. The mice are then necropsied and genomic DNA is isolated from the tumors. Next, the genomic DNA is subjected to linker-mediated-PCR (LM-PCR) that results in amplification of genomic loci containing an SB transposon. LM-PCR performed on a single tumor will result in hundreds of distinct amplicons representing the hundreds of genomic loci containing transposon insertions in a single tumor4
. The transposon insertions in all tumors are analyzed and common insertion sites (CISs) are identified using an appropriate statistical method5
. Genes within the CIS are highly likely to be oncogenes or tumor suppressor genes, and are considered candidate cancer genes. The advantages of using the SB system to identify candidate cancer genes are: 1) the transposon can easily be located in the genome because its sequence is known, 2) transposition can be directed to almost any cell type and 3) the transposon is capable of introducing both gain- and loss-of-function mutations6
. The following protocol describes how to devise and execute a forward genetic screen using the SB transposon system to identify candidate cancer genes (Figure 1
Genetics, Issue 72, Medicine, Cancer Biology, Biomedical Engineering, Genomics, Mice, Genetic Techniques, life sciences, animal models, Neoplasms, Genetic Phenomena, Forward genetic screen, cancer drivers, mouse models, oncogenes, tumor suppressor genes, Sleeping Beauty transposons, insertions, DNA, PCR, animal model
Forward Genetics Screens Using Macrophages to Identify Toxoplasma gondii Genes Important for Resistance to IFN-γ-Dependent Cell Autonomous Immunity
Institutions: New York Medical College.
the causative agent of toxoplasmosis, is an obligate intracellular protozoan pathogen. The parasite invades and replicates within virtually any warm blooded vertebrate cell type. During parasite invasion of a host cell, the parasite creates a parasitophorous vacuole (PV) that originates from the host cell membrane independent of phagocytosis within which the parasite replicates. While IFN-dependent-innate and cell mediated immunity is important for eventual control of infection, innate immune cells, including neutrophils, monocytes and dendritic cells, can also serve as vehicles for systemic dissemination of the parasite early in infection. An approach is described that utilizes the host innate immune response, in this case macrophages, in a forward genetic screen to identify parasite mutants with a fitness defect in infected macrophages following activation but normal invasion and replication in naïve macrophages. Thus, the screen isolates parasite mutants that have a specific defect in their ability to resist the effects of macrophage activation. The paper describes two broad phenotypes of mutant parasites following activation of infected macrophages: parasite stasis versus parasite degradation, often in amorphous vacuoles. The parasite mutants are then analyzed to identify the responsible parasite genes specifically important for resistance to induced mediators of cell autonomous immunity. The paper presents a general approach for the forward genetics screen that, in theory, can be modified to target parasite genes important for resistance to specific antimicrobial mediators. It also describes an approach to evaluate the specific macrophage antimicrobial mediators to which the parasite mutant is susceptible. Activation of infected macrophages can also promote parasite differentiation from the tachyzoite to bradyzoite stage that maintains chronic infection. Therefore, methodology is presented to evaluate the importance of the identified parasite gene to establishment of chronic infection.
Immunology, Issue 97, Toxoplasma, macrophages, innate immunity, intracellular pathogen, immune evasion, infectious disease, forward genetics, parasite