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Evidence for a retroviral insertion in TRPM1 as the cause of congenital stationary night blindness and leopard complex spotting in the horse.
PUBLISHED: 01-01-2013
Leopard complex spotting is a group of white spotting patterns in horses caused by an incompletely dominant gene (LP) where homozygotes (LP/LP) are also affected with congenital stationary night blindness. Previous studies implicated Transient Receptor Potential Cation Channel, Subfamily M, Member 1 (TRPM1) as the best candidate gene for both CSNB and LP. RNA-Seq data pinpointed a 1378 bp insertion in intron 1 of TRPM1 as the potential cause. This insertion, a long terminal repeat (LTR) of an endogenous retrovirus, was completely associated with LP, testing 511 horses (?(2)=1022.00, p<0.0005), and CSNB, testing 43 horses (?(2)=43, p<0.0005). The LTR was shown to disrupt TRPM1 transcription by premature poly-adenylation. Furthermore, while deleterious transposable element insertions should be quickly selected against the identification of this insertion in three ancient DNA samples suggests it has been maintained in the horse gene pool for at least 17,000 years. This study represents the first description of an LTR insertion being associated with both a pigmentation phenotype and an eye disorder.
Authors: Richard Gabriel, Ina Kutschera, Cynthia C Bartholomae, Christof von Kalle, Manfred Schmidt.
Published: 06-25-2014
Linear-amplification mediated PCR (LAM-PCR) has been developed to study hematopoiesis in gene corrected cells of patients treated by gene therapy with integrating vector systems. Due to the stable integration of retroviral vectors, integration sites can be used to study the clonal fate of individual cells and their progeny. LAM- PCR for the first time provided evidence that leukemia in gene therapy treated patients originated from provirus induced overexpression of a neighboring proto-oncogene. The high sensitivity and specificity of LAM-PCR compared to existing methods like inverse PCR and ligation mediated (LM)-PCR is achieved by an initial preamplification step (linear PCR of 100 cycles) using biotinylated vector specific primers which allow subsequent reaction steps to be carried out on solid phase (magnetic beads). LAM-PCR is currently the most sensitive method available to identify unknown DNA which is located in the proximity of known DNA. Recently, a variant of LAM-PCR has been developed that circumvents restriction digest thus abrogating retrieval bias of integration sites and enables a comprehensive analysis of provirus locations in host genomes. The following protocol explains step-by-step the amplification of both 3’- and 5’- sequences adjacent to the integrated lentiviral vector.
24 Related JoVE Articles!
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Development of an in vitro model system for studying the interaction of Equus caballus IgE with its high-affinity receptor FcεRI
Authors: Sari Sabban, Hongtu Ye, Birgit Helm.
Institutions: King Abdulaziz University, The University of Sheffield.
The interaction of IgE with its high-affinity Fc receptor (FcεRI) followed by an antigenic challenge is the principal pathway in IgE mediated allergic reactions. As a consequence of the high affinity binding between IgE and FcεRI, along with the continuous production of IgE by B cells, allergies usually persist throughout life, with currently no permanent cure available. Horses, especially race horses, which are commonly inbred, are a species of mammals that are very prone to the development of hypersensitivity responses, which can seriously affect their performance. Physiological responses to allergic sensitization in horses mirror that observed in humans and dogs. In this paper we describe the development of an in situ assay system for the quantitative assessment of the release of mediators of the allergic response pertaining to the equine system. To this end, the gene encoding equine FcεRIα was transfected into and expressed onto the surface of parental Rat Basophil Leukemia (RBL-2H3.1) cells. The gene product of the transfected equine α-chain formed a functional receptor complex with the endogenous rat β- and γ-chains 1. The resultant assay system facilitated an assessment of the quantity of mediator secreted from equine FcεRIα transfected RBL-2H3.1 cells following sensitization with equine IgE and antigenic challenge using β-hexosaminidase release as a readout 2, 3. Mediator release peaked at 36.68% ± 4.88% at 100 ng ml-1 of antigen. This assay was modified from previous assays used to study human and canine allergic responses 4, 5. We have also shown that this type of assay system has multiple applications for the development of diagnostic tools and the safety assessment of potential therapeutic intervention strategies in allergic disease 6, 2, 3.
Immunology, Issue 93, Allergy, Immunology, IgE, Fcε, RI, horse (Equus caballus), Immunoassay
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Specific Marking of HIV-1 Positive Cells using a Rev-dependent Lentiviral Vector Expressing the Green Fluorescent Protein
Authors: Jia Guo, Clinton Enos, Yuntao Wu.
Institutions: George Mason University.
Most of HIV-responsive expression vectors are based on the HIV promoter, the long terminal repeat (LTR). While responsive to an early HIV protein, Tat, the LTR is also responsive to cellular activation states and to the local chromatin activity where the integration has occurred. This can result in high HIV-independent activity, and has restricted the usefulness of LTR-based reporter to mark HIV positive cells 1,2,3. Here, we constructed an expression lentiviral vector that possesses, in addition to the Tat-responsive LTR, numerous HIV DNA sequences that include the Rev-response element and HIV splicing sites 4,5,6. The vector was incorporated into a lentiviral reporter virus, permitting highly specific detection of replicating HIV in living cell populations. The activity of the vector was measured by expression of the green fluorescence protein (GFP). The application of this vector as reported here offers a novel alternative approach to existing methods, such as in situ PCR or HIV antigen staining, to identify HIV-positive cells. The vector can also express therapeutic genes for basic or clinical experimentation to target HIV-positive cells.
Infectious Disease, Issue 43, HIV-1, Rev, GFP, lentiviral vector, RRE
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Identification of Novel Genes Associated with Alginate Production in Pseudomonas aeruginosa Using Mini-himar1 Mariner Transposon-mediated Mutagenesis
Authors: T. Ryan Withers, Yeshi Yin, Hongwei D. Yu.
Institutions: Marshall University.
Pseudomonas aeruginosa is a Gram-negative, environmental bacterium with versatile metabolic capabilities. P. aeruginosa is an opportunistic bacterial pathogen which establishes chronic pulmonary infections in patients with cystic fibrosis (CF). The overproduction of a capsular polysaccharide called alginate, also known as mucoidy, promotes the formation of mucoid biofilms which are more resistant than planktonic cells to antibiotic chemotherapy and host defenses. Additionally, the conversion from the nonmucoid to mucoid phenotype is a clinical marker for the onset of chronic infection in CF. Alginate overproduction by P. aeruginosa is an endergonic process which heavily taxes cellular energy. Therefore, alginate production is highly regulated in P. aeruginosa. To better understand alginate regulation, we describe a protocol using the mini-himar1 transposon mutagenesis for the identification of novel alginate regulators in a prototypic strain PAO1. The procedure consists of two basic steps. First, we transferred the mini-himar1 transposon (pFAC) from host E. coli SM10/λpir into recipient P. aeruginosa PAO1 via biparental conjugation to create a high-density insertion mutant library, which were selected on Pseudomonas isolation agar plates supplemented with gentamycin. Secondly, we screened and isolated the mucoid colonies to map the insertion site through inverse PCR using DNA primers pointing outward from the gentamycin cassette and DNA sequencing. Using this protocol, we have identified two novel alginate regulators, mucE (PA4033) and kinB (PA5484), in strain PAO1 with a wild-type mucA encoding the anti-sigma factor MucA for the master alginate regulator AlgU (AlgT, σ22). This high-throughput mutagenesis protocol can be modified for the identification of other virulence-related genes causing change in colony morphology.
Immunology, Issue 85, Pseudomonas aeruginosa, alginate, mucoidy, mutagenesis, mini-himar1 mariner transposon, pFAC
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Investigating Tissue- and Organ-specific Phytochrome Responses using FACS-assisted Cell-type Specific Expression Profiling in Arabidopsis thaliana
Authors: Sankalpi N. Warnasooriya, Beronda L. Montgomery.
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 expression4. 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
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Using an α-Bungarotoxin Binding Site Tag to Study GABA A Receptor Membrane Localization and Trafficking
Authors: Megan L. Brady, Charles E. Moon, Tija C. Jacob.
Institutions: University of Pittsburgh School of Medicine.
It is increasingly evident that neurotransmitter receptors, including ionotropic GABA A receptors (GABAAR), exhibit highly dynamic trafficking and cell surface mobility1-7. To study receptor cell surface localization and endocytosis, the technique described here combines the use of fluorescent α-bungarotoxin with cells expressing constructs containing an α-bungarotoxin (Bgt) binding site (BBS). The BBS (WRYYESSLEPYPD) is based on the α subunit of the muscle nicotinic acetylcholine receptor, which binds Bgt with high affinity8,9. Incorporation of the BBS site allows surface localization and measurements of receptor insertion or removal with application of exogenous fluorescent Bgt, as previously described in the tracking of GABAA and metabotropic GABAB receptors2,10. In addition to the BBS site, we inserted a pH-sensitive GFP (pHGFP11) between amino acids 4 and 5 of the mature GABAAR subunit by standard molecular biology and PCR cloning strategies (see Figure 1)12. The BBS is 3' of the pH-sensitive GFP reporter, separated by a 13-amino acid alanine/proline linker. For trafficking studies described in this publication that are based on fixed samples, the pHGFP serves as a reporter of total tagged GABAAR subunit protein levels, allowing normalization of the Bgt labeled receptor population to total receptor population. This minimizes cell to cell Bgt staining signal variability resulting from higher or lower baseline expression of the tagged GABAAR subunits. Furthermore the pHGFP tag enables easy identification of construct expressing cells for live or fixed imaging experiments.
Neuroscience, Issue 85, α-bungarotoxin, binding site, endocytosis, immunostaining, rodent hippocampal neurons, receptor, trafficking, plasma membrane
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A Semi-quantitative Approach to Assess Biofilm Formation Using Wrinkled Colony Development
Authors: Valerie A. Ray, Andrew R. Morris, Karen L. Visick.
Institutions: Loyola University Medical Center.
Biofilms, or surface-attached communities of cells encapsulated in an extracellular matrix, represent a common lifestyle for many bacteria. Within a biofilm, bacterial cells often exhibit altered physiology, including enhanced resistance to antibiotics and other environmental stresses 1. Additionally, biofilms can play important roles in host-microbe interactions. Biofilms develop when bacteria transition from individual, planktonic cells to form complex, multi-cellular communities 2. In the laboratory, biofilms are studied by assessing the development of specific biofilm phenotypes. A common biofilm phenotype involves the formation of wrinkled or rugose bacterial colonies on solid agar media 3. Wrinkled colony formation provides a particularly simple and useful means to identify and characterize bacterial strains exhibiting altered biofilm phenotypes, and to investigate environmental conditions that impact biofilm formation. Wrinkled colony formation serves as an indicator of biofilm formation in a variety of bacteria, including both Gram-positive bacteria, such as Bacillus subtilis 4, and Gram-negative bacteria, such as Vibrio cholerae 5, Vibrio parahaemolyticus 6, Pseudomonas aeruginosa 7, and Vibrio fischeri 8. The marine bacterium V. fischeri has become a model for biofilm formation due to the critical role of biofilms during host colonization: biofilms produced by V. fischeri promote its colonization of the Hawaiian bobtail squid Euprymna scolopes 8-10. Importantly, biofilm phenotypes observed in vitro correlate with the ability of V. fischeri cells to effectively colonize host animals: strains impaired for biofilm formation in vitro possess a colonization defect 9,11, while strains exhibiting increased biofilm phenotypes are enhanced for colonization 8,12. V. fischeri therefore provides a simple model system to assess the mechanisms by which bacteria regulate biofilm formation and how biofilms impact host colonization. In this report, we describe a semi-quantitative method to assess biofilm formation using V. fischeri as a model system. This method involves the careful spotting of bacterial cultures at defined concentrations and volumes onto solid agar media; a spotted culture is synonymous to a single bacterial colony. This 'spotted culture' technique can be utilized to compare gross biofilm phenotypes at single, specified time-points (end-point assays), or to identify and characterize subtle biofilm phenotypes through time-course assays of biofilm development and measurements of the colony diameter, which is influenced by biofilm formation. Thus, this technique provides a semi-quantitative analysis of biofilm formation, permitting evaluation of the timing and patterning of wrinkled colony development and the relative size of the developing structure, characteristics that extend beyond the simple overall morphology.
Microbiology, Issue 64, Immunology, Biofilm, wrinkled colony, rugose, Vibrio fischeri, Zeiss stemi, dissecting microscope, marine biology
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Isolation and Culture of Neonatal Mouse Cardiomyocytes
Authors: Elisabeth Ehler, Thomas Moore-Morris, Stephan Lange.
Institutions: King’s College London, University of California San Diego .
Cultured neonatal cardiomyocytes have long been used to study myofibrillogenesis and myofibrillar functions. Cultured cardiomyocytes allow for easy investigation and manipulation of biochemical pathways, and their effect on the biomechanical properties of spontaneously beating cardiomyocytes. The following 2-day protocol describes the isolation and culture of neonatal mouse cardiomyocytes. We show how to easily dissect hearts from neonates, dissociate the cardiac tissue and enrich cardiomyocytes from the cardiac cell-population. We discuss the usage of different enzyme mixes for cell-dissociation, and their effects on cell-viability. The isolated cardiomyocytes can be subsequently used for a variety of morphological, electrophysiological, biochemical, cell-biological or biomechanical assays. We optimized the protocol for robustness and reproducibility, by using only commercially available solutions and enzyme mixes that show little lot-to-lot variability. We also address common problems associated with the isolation and culture of cardiomyocytes, and offer a variety of options for the optimization of isolation and culture conditions.
Cellular Biology, Issue 79, Biomedical Engineering, Bioengineering, Molecular Biology, Cell Culture Techniques, Primary Cell Culture, Cell Culture Techniques, Primary Cell Culture, Cell Culture Techniques, Primary Cell Culture, Cell Culture Techniques, Disease Models, Animal, Models, Cardiovascular, Cell Biology, neonatal mouse, cardiomyocytes, isolation, culture, primary cells, NMC, heart cells, animal model
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Analysis of Nephron Composition and Function in the Adult Zebrafish Kidney
Authors: Kristen K. McCampbell, Kristin N. Springer, Rebecca A. Wingert.
Institutions: University of Notre Dame.
The zebrafish model has emerged as a relevant system to study kidney development, regeneration and disease. Both the embryonic and adult zebrafish kidneys are composed of functional units known as nephrons, which are highly conserved with other vertebrates, including mammals. Research in zebrafish has recently demonstrated that two distinctive phenomena transpire after adult nephrons incur damage: first, there is robust regeneration within existing nephrons that replaces the destroyed tubule epithelial cells; second, entirely new nephrons are produced from renal progenitors in a process known as neonephrogenesis. In contrast, humans and other mammals seem to have only a limited ability for nephron epithelial regeneration. To date, the mechanisms responsible for these kidney regeneration phenomena remain poorly understood. Since adult zebrafish kidneys undergo both nephron epithelial regeneration and neonephrogenesis, they provide an outstanding experimental paradigm to study these events. Further, there is a wide range of genetic and pharmacological tools available in the zebrafish model that can be used to delineate the cellular and molecular mechanisms that regulate renal regeneration. One essential aspect of such research is the evaluation of nephron structure and function. This protocol describes a set of labeling techniques that can be used to gauge renal composition and test nephron functionality in the adult zebrafish kidney. Thus, these methods are widely applicable to the future phenotypic characterization of adult zebrafish kidney injury paradigms, which include but are not limited to, nephrotoxicant exposure regimes or genetic methods of targeted cell death such as the nitroreductase mediated cell ablation technique. Further, these methods could be used to study genetic perturbations in adult kidney formation and could also be applied to assess renal status during chronic disease modeling.
Cellular Biology, Issue 90, zebrafish; kidney; nephron; nephrology; renal; regeneration; proximal tubule; distal tubule; segment; mesonephros; physiology; acute kidney injury (AKI)
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Tissue Triage and Freezing for Models of Skeletal Muscle Disease
Authors: Hui Meng, Paul M.L. Janssen, Robert W. Grange, Lin Yang, Alan H. Beggs, Lindsay C. Swanson, Stacy A. Cossette, Alison Frase, Martin K. Childers, Henk Granzier, Emanuela Gussoni, Michael W. Lawlor.
Institutions: Medical College of Wisconsin, The Ohio State University, Virginia Tech, University of Kentucky, Boston Children's Hospital, Harvard Medical School, Cure Congenital Muscular Dystrophy, Joshua Frase Foundation, University of Washington, University of Arizona.
Skeletal muscle is a unique tissue because of its structure and function, which requires specific protocols for tissue collection to obtain optimal results from functional, cellular, molecular, and pathological evaluations. Due to the subtlety of some pathological abnormalities seen in congenital muscle disorders and the potential for fixation to interfere with the recognition of these features, pathological evaluation of frozen muscle is preferable to fixed muscle when evaluating skeletal muscle for congenital muscle disease. Additionally, the potential to produce severe freezing artifacts in muscle requires specific precautions when freezing skeletal muscle for histological examination that are not commonly used when freezing other tissues. This manuscript describes a protocol for rapid freezing of skeletal muscle using isopentane (2-methylbutane) cooled with liquid nitrogen to preserve optimal skeletal muscle morphology. This procedure is also effective for freezing tissue intended for genetic or protein expression studies. Furthermore, we have integrated our freezing protocol into a broader procedure that also describes preferred methods for the short term triage of tissue for (1) single fiber functional studies and (2) myoblast cell culture, with a focus on the minimum effort necessary to collect tissue and transport it to specialized research or reference labs to complete these studies. Overall, this manuscript provides an outline of how fresh tissue can be effectively distributed for a variety of phenotypic studies and thereby provides standard operating procedures (SOPs) for pathological studies related to congenital muscle disease.
Basic Protocol, Issue 89, Tissue, Freezing, Muscle, Isopentane, Pathology, Functional Testing, Cell Culture
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Measuring Frailty in HIV-infected Individuals. Identification of Frail Patients is the First Step to Amelioration and Reversal of Frailty
Authors: Hilary C. Rees, Voichita Ianas, Patricia McCracken, Shannon Smith, Anca Georgescu, Tirdad Zangeneh, Jane Mohler, Stephen A. Klotz.
Institutions: University of Arizona, University of Arizona.
A simple, validated protocol consisting of a battery of tests is available to identify elderly patients with frailty syndrome. This syndrome of decreased reserve and resistance to stressors increases in incidence with increasing age. In the elderly, frailty may pursue a step-wise loss of function from non-frail to pre-frail to frail. We studied frailty in HIV-infected patients and found that ~20% are frail using the Fried phenotype using stringent criteria developed for the elderly1,2. In HIV infection the syndrome occurs at a younger age. HIV patients were checked for 1) unintentional weight loss; 2) slowness as determined by walking speed; 3) weakness as measured by a grip dynamometer; 4) exhaustion by responses to a depression scale; and 5) low physical activity was determined by assessing kilocalories expended in a week's time. Pre-frailty was present with any two of five criteria and frailty was present if any three of the five criteria were abnormal. The tests take approximately 10-15 min to complete and they can be performed by medical assistants during routine clinic visits. Test results are scored by referring to standard tables. Understanding which of the five components contribute to frailty in an individual patient can allow the clinician to address relevant underlying problems, many of which are not evident in routine HIV clinic visits.
Medicine, Issue 77, Infection, Virology, Infectious Diseases, Anatomy, Physiology, Molecular Biology, Biomedical Engineering, Retroviridae Infections, Body Weight Changes, Diagnostic Techniques and Procedures, Physical Examination, Muscle Strength, Behavior, Virus Diseases, Pathological Conditions, Signs and Symptoms, Diagnosis, Musculoskeletal and Neural Physiological Phenomena, HIV, HIV-1, AIDS, Frailty, Depression, Weight Loss, Weakness, Slowness, Exhaustion, Aging, clinical techniques
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Environmentally Induced Heritable Changes in Flax
Authors: Cory Johnson, Tiffanie Moss, Christopher Cullis.
Institutions: Case Western Reserve University.
Some flax varieties respond to nutrient stress by modifying their genome and these modifications can be inherited through many generations. Also associated with these genomic changes are heritable phenotypic variations 1,2. The flax variety Stormont Cirrus (Pl) when grown under three different nutrient conditions can either remain inducible (under the control conditions), or become stably modified to either the large or small genotroph by growth under high or low nutrient conditions respectively. The lines resulting from the initial growth under each of these conditions appear to grow better when grown under the same conditions in subsequent generations, notably the Pl line grows best under the control treatment indicating that the plants growing under both the high and low nutrients are under stress. One of the genomic changes that are associated with the induction of heritable changes is the appearance of an insertion element (LIS-1) 3, 4 while the plants are growing under the nutrient stress. With respect to this insertion event, the flax variety Stormont Cirrus (Pl) when grown under three different nutrient conditions can either remain unchanged (under the control conditions), have the insertion appear in all the plants (under low nutrients) and have this transmitted to the next generation, or have the insertion (or parts of it) appear but not be transmitted through generations (under high nutrients) 4. The frequency of the appearance of this insertion indicates that it is under positive selection, which is also consistent with the growth response in subsequent generations. Leaves or meristems harvested at various stages of growth are used for DNA and RNA isolation. The RNA is used to identify variation in expression associated with the various growth environments and/or t he presence/absence of LIS-1. The isolated DNA is used to identify those plants in which the insertion has occurred.
Plant Biology, Issue 47, Flax, genome variation, environmental stress, small RNAs, altered gene expression
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Site-specific Bacterial Chromosome Engineering: ΦC31 Integrase Mediated Cassette Exchange (IMCE)
Authors: John R. Heil, Jiujun Cheng, Trevor C. Charles.
Institutions: University of Waterloo.
The bacterial chromosome may be used to stably maintain foreign DNA in the mega-base range1. Integration into the chromosome circumvents issues such as plasmid replication, plasmid stability, plasmid incompatibility, and plasmid copy number variance. This method uses the site-specific integrase from the Streptomyces phage (Φ) C312,3. The ΦC31 integrase catalyzes a direct recombination between two specific DNA sites: attB and attP (34 and 39 bp, respectively)4. This recombination is stable and does not revert5. A "landing pad" (LP) sequence consisting of a spectinomycin- resistance gene, aadA (SpR), and the E. coli ß-glucuronidase gene (uidA) flanked by attP sites has been integrated into the chromosomes of Sinorhizobium meliloti, Ochrobactrum anthropi, and Agrobacterium tumefaciens in an intergenic region, the ampC locus, and the tetA locus, respectively. S. meliloti is used in this protocol. Mobilizable donor vectors containing attB sites flanking a stuffer red fluorescent protein (rfp) gene and an antibiotic resistance gene have also been constructed. In this example the gentamicin resistant plasmid pJH110 is used. The rfp gene6 may be replaced with a desired construct using SphI and PstI. Alternatively a synthetic construct flanked by attB sites may be sub-cloned into a mobilizable vector such as pK19mob7. The expression of the ΦC31 integrase gene (cloned from pHS628) is driven by the lac promoter, on a mobilizable broad host range plasmid pRK78139. A tetraparental mating protocol is used to transfer the donor cassette into the LP strain thereby replacing the markers in the LP sequence with the donor cassette. These cells are trans-integrants. Trans-integrants are formed with a typical efficiency of 0.5%. Trans-integrants are typically found within the first 500-1,000 colonies screened by antibiotic sensitivity or blue-white screening using 5-bromo-4-chloro-3-indolyl-beta-D-glucuronic acid (X-gluc). This protocol contains the mating and selection procedures for creating and isolating trans-integrants.
Bioengineering, Issue 61, ΦC31 Integrase, Rhizobiales, Chromosome Engineering, bacterial genetics
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Microarray-based Identification of Individual HERV Loci Expression: Application to Biomarker Discovery in Prostate Cancer
Authors: Philippe Pérot, Valérie Cheynet, Myriam Decaussin-Petrucci, Guy Oriol, Nathalie Mugnier, Claire Rodriguez-Lafrasse, Alain Ruffion, François Mallet.
Institutions: Joint Unit Hospices de Lyon-bioMérieux, BioMérieux, Hospices Civils de Lyon, Lyon 1 University, BioMérieux, Hospices Civils de Lyon, Hospices Civils de Lyon.
The prostate-specific antigen (PSA) is the main diagnostic biomarker for prostate cancer in clinical use, but it lacks specificity and sensitivity, particularly in low dosage values1​​. ‘How to use PSA' remains a current issue, either for diagnosis as a gray zone corresponding to a concentration in serum of 2.5-10 ng/ml which does not allow a clear differentiation to be made between cancer and noncancer2 or for patient follow-up as analysis of post-operative PSA kinetic parameters can pose considerable challenges for their practical application3,4. Alternatively, noncoding RNAs (ncRNAs) are emerging as key molecules in human cancer, with the potential to serve as novel markers of disease, e.g. PCA3 in prostate cancer5,6 and to reveal uncharacterized aspects of tumor biology. Moreover, data from the ENCODE project published in 2012 showed that different RNA types cover about 62% of the genome. It also appears that the amount of transcriptional regulatory motifs is at least 4.5x higher than the one corresponding to protein-coding exons. Thus, long terminal repeats (LTRs) of human endogenous retroviruses (HERVs) constitute a wide range of putative/candidate transcriptional regulatory sequences, as it is their primary function in infectious retroviruses. HERVs, which are spread throughout the human genome, originate from ancestral and independent infections within the germ line, followed by copy-paste propagation processes and leading to multicopy families occupying 8% of the human genome (note that exons span 2% of our genome). Some HERV loci still express proteins that have been associated with several pathologies including cancer7-10. We have designed a high-density microarray, in Affymetrix format, aiming to optimally characterize individual HERV loci expression, in order to better understand whether they can be active, if they drive ncRNA transcription or modulate coding gene expression. This tool has been applied in the prostate cancer field (Figure 1).
Medicine, Issue 81, Cancer Biology, Genetics, Molecular Biology, Prostate, Retroviridae, Biomarkers, Pharmacological, Tumor Markers, Biological, Prostatectomy, Microarray Analysis, Gene Expression, Diagnosis, Human Endogenous Retroviruses, HERV, microarray, Transcriptome, prostate cancer, Affymetrix
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A Restriction Enzyme Based Cloning Method to Assess the In vitro Replication Capacity of HIV-1 Subtype C Gag-MJ4 Chimeric Viruses
Authors: Daniel T. Claiborne, Jessica L. Prince, Eric Hunter.
Institutions: Emory University, Emory University.
The protective effect of many HLA class I alleles on HIV-1 pathogenesis and disease progression is, in part, attributed to their ability to target conserved portions of the HIV-1 genome that escape with difficulty. Sequence changes attributed to cellular immune pressure arise across the genome during infection, and if found within conserved regions of the genome such as Gag, can affect the ability of the virus to replicate in vitro. Transmission of HLA-linked polymorphisms in Gag to HLA-mismatched recipients has been associated with reduced set point viral loads. We hypothesized this may be due to a reduced replication capacity of the virus. Here we present a novel method for assessing the in vitro replication of HIV-1 as influenced by the gag gene isolated from acute time points from subtype C infected Zambians. This method uses restriction enzyme based cloning to insert the gag gene into a common subtype C HIV-1 proviral backbone, MJ4. This makes it more appropriate to the study of subtype C sequences than previous recombination based methods that have assessed the in vitro replication of chronically derived gag-pro sequences. Nevertheless, the protocol could be readily modified for studies of viruses from other subtypes. Moreover, this protocol details a robust and reproducible method for assessing the replication capacity of the Gag-MJ4 chimeric viruses on a CEM-based T cell line. This method was utilized for the study of Gag-MJ4 chimeric viruses derived from 149 subtype C acutely infected Zambians, and has allowed for the identification of residues in Gag that affect replication. More importantly, the implementation of this technique has facilitated a deeper understanding of how viral replication defines parameters of early HIV-1 pathogenesis such as set point viral load and longitudinal CD4+ T cell decline.
Infectious Diseases, Issue 90, HIV-1, Gag, viral replication, replication capacity, viral fitness, MJ4, CEM, GXR25
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Using Coculture to Detect Chemically Mediated Interspecies Interactions
Authors: Elizabeth Anne Shank.
Institutions: University of North Carolina at Chapel Hill .
In nature, bacteria rarely exist in isolation; they are instead surrounded by a diverse array of other microorganisms that alter the local environment by secreting metabolites. These metabolites have the potential to modulate the physiology and differentiation of their microbial neighbors and are likely important factors in the establishment and maintenance of complex microbial communities. We have developed a fluorescence-based coculture screen to identify such chemically mediated microbial interactions. The screen involves combining a fluorescent transcriptional reporter strain with environmental microbes on solid media and allowing the colonies to grow in coculture. The fluorescent transcriptional reporter is designed so that the chosen bacterial strain fluoresces when it is expressing a particular phenotype of interest (i.e. biofilm formation, sporulation, virulence factor production, etc.) Screening is performed under growth conditions where this phenotype is not expressed (and therefore the reporter strain is typically nonfluorescent). When an environmental microbe secretes a metabolite that activates this phenotype, it diffuses through the agar and activates the fluorescent reporter construct. This allows the inducing-metabolite-producing microbe to be detected: they are the nonfluorescent colonies most proximal to the fluorescent colonies. Thus, this screen allows the identification of environmental microbes that produce diffusible metabolites that activate a particular physiological response in a reporter strain. This publication discusses how to: a) select appropriate coculture screening conditions, b) prepare the reporter and environmental microbes for screening, c) perform the coculture screen, d) isolate putative inducing organisms, and e) confirm their activity in a secondary screen. We developed this method to screen for soil organisms that activate biofilm matrix-production in Bacillus subtilis; however, we also discuss considerations for applying this approach to other genetically tractable bacteria.
Microbiology, Issue 80, High-Throughput Screening Assays, Genes, Reporter, Microbial Interactions, Soil Microbiology, Coculture, microbial interactions, screen, fluorescent transcriptional reporters, Bacillus subtilis
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Creating Dynamic Images of Short-lived Dopamine Fluctuations with lp-ntPET: Dopamine Movies of Cigarette Smoking
Authors: Evan D. Morris, Su Jin Kim, Jenna M. Sullivan, Shuo Wang, Marc D. Normandin, Cristian C. Constantinescu, Kelly P. Cosgrove.
Institutions: Yale University, Yale University, Yale University, Yale University, Massachusetts General Hospital, University of California, Irvine.
We describe experimental and statistical steps for creating dopamine movies of the brain from dynamic PET data. The movies represent minute-to-minute fluctuations of dopamine induced by smoking a cigarette. The smoker is imaged during a natural smoking experience while other possible confounding effects (such as head motion, expectation, novelty, or aversion to smoking repeatedly) are minimized. We present the details of our unique analysis. Conventional methods for PET analysis estimate time-invariant kinetic model parameters which cannot capture short-term fluctuations in neurotransmitter release. Our analysis - yielding a dopamine movie - is based on our work with kinetic models and other decomposition techniques that allow for time-varying parameters 1-7. This aspect of the analysis - temporal-variation - is key to our work. Because our model is also linear in parameters, it is practical, computationally, to apply at the voxel level. The analysis technique is comprised of five main steps: pre-processing, modeling, statistical comparison, masking and visualization. Preprocessing is applied to the PET data with a unique 'HYPR' spatial filter 8 that reduces spatial noise but preserves critical temporal information. Modeling identifies the time-varying function that best describes the dopamine effect on 11C-raclopride uptake. The statistical step compares the fit of our (lp-ntPET) model 7 to a conventional model 9. Masking restricts treatment to those voxels best described by the new model. Visualization maps the dopamine function at each voxel to a color scale and produces a dopamine movie. Interim results and sample dopamine movies of cigarette smoking are presented.
Behavior, Issue 78, Neuroscience, Neurobiology, Molecular Biology, Biomedical Engineering, Medicine, Anatomy, Physiology, Image Processing, Computer-Assisted, Receptors, Dopamine, Dopamine, Functional Neuroimaging, Binding, Competitive, mathematical modeling (systems analysis), Neurotransmission, transient, dopamine release, PET, modeling, linear, time-invariant, smoking, F-test, ventral-striatum, clinical techniques
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Two Methods for Establishing Primary Human Endometrial Stromal Cells from Hysterectomy Specimens
Authors: Kasey Jividen, Mercedeh Javanbakht Movassagh, Amir Jazaeri, Hui Li.
Institutions: University of Virginia, University of Virginia.
Many efforts have been devoted to establish in vitro cell culture systems. These systems are designed to model a vast number of in vivo processes. Cell culture systems arising from human endometrial samples are no exception. Applications range from normal cyclic physiological processes to endometrial pathologies such as gynecological cancers, infectious diseases, and reproductive deficiencies. Here, we provide two methods for establishing primary endometrial stromal cells from surgically resected endometrial hysterectomy specimens. The first method is referred to as “the scraping method” and incorporates mechanical scraping using surgical or razor blades whereas the second method is termed “the trypsin method.” This latter method uses the enzymatic activity of trypsin to promote the separation of cells and primary cell outgrowth. We illustrate step-by-step methodology through digital images and microscopy. We also provide examples for validating endometrial stromal cell lines via quantitative real time polymerase chain reactions (qPCR) and immunofluorescence (IF).
Medicine, Issue 87, uterus, endometrium, endometrial stroma, (primary) cell culture, surgical blade, trypsin, tissue procurement, spontaneous decidualization
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A Novel Method for Localizing Reporter Fluorescent Beads Near the Cell Culture Surface for Traction Force Microscopy
Authors: Samantha G. Knoll, M. Yakut Ali, M. Taher A. Saif.
Institutions: University of Illinois at Urbana-Champaign.
PA gels have long been used as a platform to study cell traction forces due to ease of fabrication and the ability to tune their elastic properties. When the substrate is coated with an extracellular matrix protein, cells adhere to the gel and apply forces, causing the gel to deform. The deformation depends on the cell traction and the elastic properties of the gel. If the deformation field of the surface is known, surface traction can be calculated using elasticity theory. Gel deformation is commonly measured by embedding fluorescent marker beads uniformly into the gel. The probes displace as the gel deforms. The probes near the surface of the gel are tracked. The displacements reported by these probes are considered as surface displacements. Their depths from the surface are ignored. This assumption introduces error in traction force evaluations. For precise measurement of cell forces, it is critical for the location of the beads to be known. We have developed a technique that utilizes simple chemistry to confine fluorescent marker beads, 0.1 and 1 µm in diameter, in PA gels, within 1.6 μm of the surface. We coat a coverslip with poly-D-lysine (PDL) and fluorescent beads. PA gel solution is then sandwiched between the coverslip and an adherent surface. The fluorescent beads transfer to the gel solution during curing. After polymerization, the PA gel contains fluorescent beads on a plane close to the gel surface.
Bioengineering, Issue 91, cell mechanics, polyacrylamide (PA) gel, traction force microscopy, fluorescent beads, poly-D-lysine (PDL), cell culture surface
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Cell Surface Marker Mediated Purification of iPS Cell Intermediates from a Reprogrammable Mouse Model
Authors: Christian M. Nefzger, Sara Alaei, Anja S. Knaupp, Melissa L. Holmes, Jose M. Polo.
Institutions: Monash University, Monash University.
Mature cells can be reprogrammed to a pluripotent state. These so called induced pluripotent stem (iPS) cells are able to give rise to all cell types of the body and consequently have vast potential for regenerative medicine applications. Traditionally iPS cells are generated by viral introduction of transcription factors Oct-4, Klf-4, Sox-2, and c-Myc (OKSM) into fibroblasts. However, reprogramming is an inefficient process with only 0.1-1% of cells reverting towards a pluripotent state, making it difficult to study the reprogramming mechanism. A proven methodology that has allowed the study of the reprogramming process is to separate the rare intermediates of the reaction from the refractory bulk population. In the case of mouse embryonic fibroblasts (MEFs), we and others have previously shown that reprogramming cells undergo a distinct series of changes in the expression profile of cell surface markers which can be used for the separation of these cells. During the early stages of OKSM expression successfully reprogramming cells lose fibroblast identity marker Thy-1.2 and up-regulate pluripotency associated marker Ssea-1. The final transition of a subset of Ssea-1 positive cells towards the pluripotent state is marked by the expression of Epcam during the late stages of reprogramming. Here we provide a detailed description of the methodology used to isolate reprogramming intermediates from cultures of reprogramming MEFs. In order to increase experimental reproducibility we use a reprogrammable mouse strain that has been engineered to express a transcriptional transactivator (m2rtTA) under control of the Rosa26 locus and OKSM under control of a doxycycline responsive promoter. Cells isolated from these mice are isogenic and express OKSM homogenously upon addition of doxycycline. We describe in detail the establishment of the reprogrammable mice, the derivation of MEFs, and the subsequent isolation of intermediates during reprogramming into iPS cells via fluorescent activated cells sorting (FACS).
Stem Cell Biology, Issue 91, Induced pluripotent stem cells; reprogramming; intermediates; fluorescent activated cells sorting; cell surface marker; reprogrammable mouse model; derivation of mouse embryonic fibroblasts
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In Vivo Modeling of the Morbid Human Genome using Danio rerio
Authors: Adrienne R. Niederriter, Erica E. Davis, Christelle Golzio, Edwin C. Oh, I-Chun Tsai, Nicholas Katsanis.
Institutions: Duke University Medical Center, Duke University, Duke University Medical Center.
Here, we present methods for the development of assays to query potentially clinically significant nonsynonymous changes using in vivo complementation in zebrafish. Zebrafish (Danio rerio) are a useful animal system due to their experimental tractability; embryos are transparent to enable facile viewing, undergo rapid development ex vivo, and can be genetically manipulated.1 These aspects have allowed for significant advances in the analysis of embryogenesis, molecular processes, and morphogenetic signaling. Taken together, the advantages of this vertebrate model make zebrafish highly amenable to modeling the developmental defects in pediatric disease, and in some cases, adult-onset disorders. Because the zebrafish genome is highly conserved with that of humans (~70% orthologous), it is possible to recapitulate human disease states in zebrafish. This is accomplished either through the injection of mutant human mRNA to induce dominant negative or gain of function alleles, or utilization of morpholino (MO) antisense oligonucleotides to suppress genes to mimic loss of function variants. Through complementation of MO-induced phenotypes with capped human mRNA, our approach enables the interpretation of the deleterious effect of mutations on human protein sequence based on the ability of mutant mRNA to rescue a measurable, physiologically relevant phenotype. Modeling of the human disease alleles occurs through microinjection of zebrafish embryos with MO and/or human mRNA at the 1-4 cell stage, and phenotyping up to seven days post fertilization (dpf). This general strategy can be extended to a wide range of disease phenotypes, as demonstrated in the following protocol. We present our established models for morphogenetic signaling, craniofacial, cardiac, vascular integrity, renal function, and skeletal muscle disorder phenotypes, as well as others.
Molecular Biology, Issue 78, Genetics, Biomedical Engineering, Medicine, Developmental Biology, Biochemistry, Anatomy, Physiology, Bioengineering, Genomics, Medical, zebrafish, in vivo, morpholino, human disease modeling, transcription, PCR, mRNA, DNA, Danio rerio, animal model
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Stress-induced Antibiotic Susceptibility Testing on a Chip
Authors: Maxim Kalashnikov, Jennifer Campbell, Jean C. Lee, Andre Sharon, Alexis F. Sauer-Budge.
Institutions: Fraunhofer USA Center for Manufacturing Innovation, Harvard Medical School, Boston University, Boston University.
We have developed a rapid microfluidic method for antibiotic susceptibility testing in a stress-based environment. Fluid is passed at high speeds over bacteria immobilized on the bottom of a microfluidic channel. In the presence of stress and antibiotic, susceptible strains of bacteria die rapidly. However, resistant bacteria survive these stressful conditions. The hypothesis behind this method is new: stress activation of biochemical pathways, which are targets of antibiotics, can accelerate antibiotic susceptibility testing. As compared to standard antibiotic susceptibility testing methods, the rate-limiting step - bacterial growth - is omitted during antibiotic application. The technical implementation of the method is in a combination of standard techniques and innovative approaches. The standard parts of the method include bacterial culture protocols, defining microfluidic channels in polydimethylsiloxane (PDMS), cell viability monitoring with fluorescence, and batch image processing for bacteria counting. Innovative parts of the method are in the use of culture media flow for mechanical stress application, use of enzymes to damage but not kill the bacteria, and use of microarray substrates for bacterial attachment. The developed platform can be used in antibiotic and nonantibiotic related drug development and testing. As compared to the standard bacterial suspension experiments, the effect of the drug can be turned on and off repeatedly over controlled time periods. Repetitive observation of the same bacterial population is possible over the course of the same experiment.
Bioengineering, Issue 83, antibiotic, susceptibility, resistance, microfluidics, microscopy, rapid, testing, stress, bacteria, fluorescence
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Protease- and Acid-catalyzed Labeling Workflows Employing 18O-enriched Water
Authors: Diana Klingler, Markus Hardt.
Institutions: Boston Biomedical Research Institute.
Stable isotopes are essential tools in biological mass spectrometry. Historically, 18O-stable isotopes have been extensively used to study the catalytic mechanisms of proteolytic enzymes1-3. With the advent of mass spectrometry-based proteomics, the enzymatically-catalyzed incorporation of 18O-atoms from stable isotopically enriched water has become a popular method to quantitatively compare protein expression levels (reviewed by Fenselau and Yao4, Miyagi and Rao5 and Ye et al.6). 18O-labeling constitutes a simple and low-cost alternative to chemical (e.g. iTRAQ, ICAT) and metabolic (e.g. SILAC) labeling techniques7. Depending on the protease utilized, 18O-labeling can result in the incorporation of up to two 18O-atoms in the C-terminal carboxyl group of the cleavage product3. The labeling reaction can be subdivided into two independent processes, the peptide bond cleavage and the carboxyl oxygen exchange reaction8. In our PALeO (protease-assisted labeling employing 18O-enriched water) adaptation of enzymatic 18O-labeling, we utilized 50% 18O-enriched water to yield distinctive isotope signatures. In combination with high-resolution matrix-assisted laser desorption ionization time-of-flight tandem mass spectrometry (MALDI-TOF/TOF MS/MS), the characteristic isotope envelopes can be used to identify cleavage products with a high level of specificity. We previously have used the PALeO-methodology to detect and characterize endogenous proteases9 and monitor proteolytic reactions10-11. Since PALeO encodes the very essence of the proteolytic cleavage reaction, the experimental setup is simple and biochemical enrichment steps of cleavage products can be circumvented. The PALeO-method can easily be extended to (i) time course experiments that monitor the dynamics of proteolytic cleavage reactions and (ii) the analysis of proteolysis in complex biological samples that represent physiological conditions. PALeO-TimeCourse experiments help identifying rate-limiting processing steps and reaction intermediates in complex proteolytic pathway reactions. Furthermore, the PALeO-reaction allows us to identify proteolytic enzymes such as the serine protease trypsin that is capable to rebind its cleavage products and catalyze the incorporation of a second 18O-atom. Such "double-labeling" enzymes can be used for postdigestion 18O-labeling, in which peptides are exclusively labeled by the carboxyl oxygen exchange reaction. Our third strategy extends labeling employing 18O-enriched water beyond enzymes and uses acidic pH conditions to introduce 18O-stable isotope signatures into peptides.
Biochemistry, Issue 72, Molecular Biology, Proteins, Proteomics, Chemistry, Physics, MALDI-TOF mass spectrometry, proteomics, proteolysis, quantification, stable isotope labeling, labeling, catalyst, peptides, 18-O enriched water
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A Strategy to Identify de Novo Mutations in Common Disorders such as Autism and Schizophrenia
Authors: Gauthier Julie, Fadi F. Hamdan, Guy A. Rouleau.
Institutions: Universite de Montreal, Universite de Montreal, Universite de Montreal.
There are several lines of evidence supporting the role of de novo mutations as a mechanism for common disorders, such as autism and schizophrenia. First, the de novo mutation rate in humans is relatively high, so new mutations are generated at a high frequency in the population. However, de novo mutations have not been reported in most common diseases. Mutations in genes leading to severe diseases where there is a strong negative selection against the phenotype, such as lethality in embryonic stages or reduced reproductive fitness, will not be transmitted to multiple family members, and therefore will not be detected by linkage gene mapping or association studies. The observation of very high concordance in monozygotic twins and very low concordance in dizygotic twins also strongly supports the hypothesis that a significant fraction of cases may result from new mutations. Such is the case for diseases such as autism and schizophrenia. Second, despite reduced reproductive fitness1 and extremely variable environmental factors, the incidence of some diseases is maintained worldwide at a relatively high and constant rate. This is the case for autism and schizophrenia, with an incidence of approximately 1% worldwide. Mutational load can be thought of as a balance between selection for or against a deleterious mutation and its production by de novo mutation. Lower rates of reproduction constitute a negative selection factor that should reduce the number of mutant alleles in the population, ultimately leading to decreased disease prevalence. These selective pressures tend to be of different intensity in different environments. Nonetheless, these severe mental disorders have been maintained at a constant relatively high prevalence in the worldwide population across a wide range of cultures and countries despite a strong negative selection against them2. This is not what one would predict in diseases with reduced reproductive fitness, unless there was a high new mutation rate. Finally, the effects of paternal age: there is a significantly increased risk of the disease with increasing paternal age, which could result from the age related increase in paternal de novo mutations. This is the case for autism and schizophrenia3. The male-to-female ratio of mutation rate is estimated at about 4–6:1, presumably due to a higher number of germ-cell divisions with age in males. Therefore, one would predict that de novo mutations would more frequently come from males, particularly older males4. A high rate of new mutations may in part explain why genetic studies have so far failed to identify many genes predisposing to complexes diseases genes, such as autism and schizophrenia, and why diseases have been identified for a mere 3% of genes in the human genome. Identification for de novo mutations as a cause of a disease requires a targeted molecular approach, which includes studying parents and affected subjects. The process for determining if the genetic basis of a disease may result in part from de novo mutations and the molecular approach to establish this link will be illustrated, using autism and schizophrenia as examples.
Medicine, Issue 52, de novo mutation, complex diseases, schizophrenia, autism, rare variations, DNA sequencing
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Molecular Evolution of the Tre Recombinase
Authors: Frank Buchholz.
Institutions: Max Plank Institute for Molecular Cell Biology and Genetics, Dresden.
Here we report the generation of Tre recombinase through directed, molecular evolution. Tre recombinase recognizes a pre-defined target sequence within the LTR sequences of the HIV-1 provirus, resulting in the excision and eradication of the provirus from infected human cells. We started with Cre, a 38-kDa recombinase, that recognizes a 34-bp double-stranded DNA sequence known as loxP. Because Cre can effectively eliminate genomic sequences, we set out to tailor a recombinase that could remove the sequence between the 5'-LTR and 3'-LTR of an integrated HIV-1 provirus. As a first step we identified sequences within the LTR sites that were similar to loxP and tested for recombination activity. Initially Cre and mutagenized Cre libraries failed to recombine the chosen loxLTR sites of the HIV-1 provirus. As the start of any directed molecular evolution process requires at least residual activity, the original asymmetric loxLTR sequences were split into subsets and tested again for recombination activity. Acting as intermediates, recombination activity was shown with the subsets. Next, recombinase libraries were enriched through reiterative evolution cycles. Subsequently, enriched libraries were shuffled and recombined. The combination of different mutations proved synergistic and recombinases were created that were able to recombine loxLTR1 and loxLTR2. This was evidence that an evolutionary strategy through intermediates can be successful. After a total of 126 evolution cycles individual recombinases were functionally and structurally analyzed. The most active recombinase -- Tre -- had 19 amino acid changes as compared to Cre. Tre recombinase was able to excise the HIV-1 provirus from the genome HIV-1 infected HeLa cells (see "HIV-1 Proviral DNA Excision Using an Evolved Recombinase", Hauber J., Heinrich-Pette-Institute for Experimental Virology and Immunology, Hamburg, Germany). While still in its infancy, directed molecular evolution will allow the creation of custom enzymes that will serve as tools of "molecular surgery" and molecular medicine.
Cell Biology, Issue 15, HIV-1, Tre recombinase, Site-specific recombination, molecular evolution
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