Name: isolation of fidelity variants of rna viruses and characterization of virus mutation frequency
Uploaded: 2011-06-16T13:00:00
Duration: 18 min 10 s
Description: Watch this Scientific Journal Video about Isolation of Fidelity Variants of RNA Viruses and Characterization of Virus Mutation Frequency at JoVE.com

This work was supported by funding from the Medical and Health Research grant from the City of Paris, the French National grant ANR-09-JCJC-0118-1, and the ERC Starting Grant RNAvirusPopDivNVax Project no. 242719.

<ol>
	<li>Arias, A. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Determinants+of+RNA-dependent+RNA+polymerase+(in)fidelity+revealed+by+kinetic+analysis+of+the+polymerase+encoded+by+a+foot-and-mouth+disease+virus+mutant+with+reduced+sensitivity+to+ribavirin.">Determinants of RNA-dependent RNA polymerase (in)fidelity revealed by kinetic analysis of the polymerase encoded by a foot-and-mouth disease virus mutant with reduced sensitivity to ribavirin.</a> J Virol. 82, 12346-12355 (2008).</li><li>Arnold, J. J., Vignuzzi, M., Stone, J. K., Andino, R., Cameron, C. E. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Remote+site+control+of+an+active+site+fidelity+checkpoint+in+a+viral+RNA-dependent+RNA+polymerase.">Remote site control of an active site fidelity checkpoint in a viral RNA-dependent RNA polymerase.</a> J Biol Chem. 280, 25706-25716 (2005).</li><li>Korneeva, V. S., Cameron, C. E. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Structure-function+relationships+of+the+viral+RNA-dependent+RNA+polymerase:+fidelity,+replication+speed,+and+initiation+mechanism+determined+by+a+residue+in+the+ribose-binding+pocket.">Structure-function relationships of the viral RNA-dependent RNA polymerase: fidelity, replication speed, and initiation mechanism determined by a residue in the ribose-binding pocket.</a> J Biol Chem. 282, 16135-16145 (2007).</li><li>Pfeiffer, J. K., Kirkegaard, K. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=A+single+mutation+in+poliovirus+RNA-dependent+RNA+polymerase+confers+resistance+to+mutagenic+nucleotide+analogs+via+increased+fidelity.">A single mutation in poliovirus RNA-dependent RNA polymerase confers resistance to mutagenic nucleotide analogs via increased fidelity.</a> Proc Natl Acad Sci U S A. 100, 7289-7294 (2003).</li><li>Pfeiffer, J. K., Kirkegaard, K. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Increased+fidelity+reduces+poliovirus+fitness+and+virulence+under+selective+pressure+in+mice.">Increased fidelity reduces poliovirus fitness and virulence under selective pressure in mice.</a> PLoS Pathog. 1, e11-e11 (2005).</li><li>Vignuzzi, M., Stone, J. K., Arnold, J. J., Cameron, C. E., Andino, R. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Quasispecies+diversity+determines+pathogenesis+through+cooperative+interactions+in+a+viral+population.">Quasispecies diversity determines pathogenesis through cooperative interactions in a viral population.</a> Nature. 439, 344-348 (2006).</li><li>Vignuzzi, M., Wendt, E., Andino, R. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Engineering+attenuated+virus+vaccines+by+controlling+replication+fidelity.">Engineering attenuated virus vaccines by controlling replication fidelity.</a> Nat Med. 14, 154-161 (2008).</li><li>Crotty, S., Cameron, C., Andino, R. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Ribavirin's+antiviral+mechanism+of+action:+lethal+mutagenesis.">Ribavirin's antiviral mechanism of action: lethal mutagenesis.</a> J Mol Med. 80, 86-95 (2002).</li><li>Coffey, L. L., Vignuzzi, M. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Host+alternation+of+chikungunya+virus+increases+fitness+while+restricting+population+diversity+and+adaptability+to+novel+selective+pressures.">Host alternation of chikungunya virus increases fitness while restricting population diversity and adaptability to novel selective pressures.</a> J Virol. 85, 1025-1035 (2011).</li><li>Ciota, A. T. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Role+of+the+mutant+spectrum+in+adaptation+and+replication+of+West+Nile+virus.">Role of the mutant spectrum in adaptation and replication of West Nile virus.</a> J Gen Virol. 88, 865-874 (2007).</li><li>Ibarra, K. D., Pfeiffer, J. K. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Reduced+ribavirin+antiviral+efficacy+via+nucleoside+transporter-mediated+drug+resistance.">Reduced ribavirin antiviral efficacy via nucleoside transporter-mediated drug resistance.</a> J Virol. 83, 4538-4547 (2009).</li><li>Levi, L. I. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Fidelity+variants+of+RNA+dependent+RNA+polymerases+uncover+an+indirect,+mutagenic+activity+of+amiloride+compounds.">Fidelity variants of RNA dependent RNA polymerases uncover an indirect, mutagenic activity of amiloride compounds.</a> PLoS Pathog. 6, e1001163-e1001163 (2010).</li><li>Sierra, S., D&#225;vila, M., Lowenstein, P. R., Domingo, E. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Response+of+foot-and-mouth+disease+virus+to+increased+mutagenesis:+influence+of+viral+load+and+fitness+in+loss+of+infectivity.">Response of foot-and-mouth disease virus to increased mutagenesis: influence of viral load and fitness in loss of infectivity.</a> J Virol. 74, 8316-8323 (2000).</li><li>Ruiz-Jarabo, C. M., Ly, C., Domingo, E., de la Torre, J. C. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Lethal+mutagenesis+of+the+prototypic+arenavirus+lymphocytic+choriomeningitis+virus+(LCMV).">Lethal mutagenesis of the prototypic arenavirus lymphocytic choriomeningitis virus (LCMV).</a> Virology. 308, 37-47 (2003).</li><li>Sierra, M. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Foot-and-mouth+disease+virus+mutant+with+decreased+sensitivity+to+ribavirin:+implications+for+error+catastrophe.">Foot-and-mouth disease virus mutant with decreased sensitivity to ribavirin: implications for error catastrophe.</a> J Virol. 81, 2012-2024 (2007).</li></ol>

No conflicts of interest declared.

Choice of cell line. The efficacy of base analogs as RNA mutagens correlates with their relative uptake by different cell types 11. If the cell line that is normally used for virus passage proves to be refractory to mutagen uptake or too sensitive (high cell toxicity), it may be necessary to use another cell line that meets these requirements and is still permissive to viral replication. Once the mutagen resistance variant is isolated, the remainder of the characterization can be performed in the original, preferred cell line. In our experience, HeLa cells readily take up mutagen; BHK cells require up to 10-fold higher concentrations and Vero cells are refractory to mutagen uptake.
Choice of mutagen. In trying to isolate fidelity variants by mutagen treatment, the likelihood of success is increased if more than one type of mutagen is used. Base analog mutagens of different structure, that are erroneously incorporated into genomes during replication will predominantly induce result in a specific subset of mutations in subsequent replication cycles: ribavirin treatment favors GtoA and CtoU transition mutations 12; 5-azacytidine has a similar bias, with the addition of CtoG and GtoC transversions 13; 5-fluorouracil preferentially induces AtoG and UtoC transitions 14. Alternatively, higher concentrations of Mg2+ or Mn2+ can be supplemented to the medium to increase the overall mutation frequency of RNA viruses without the bias described above 12. Depending on the virus' codon sequences, and the codon changes required to generate a fidelity variant, some of these conditions will favor the emergence of this variant over others. For the higher fidelity poliovirus G64S and Coxsackie virus A372V, ribavirin treatment most readily selected for the variants because the required AtoG transition at the codon site corresponded to the mutations predominantly generated by this ribavirin.
MOI vs. population size. In virology, protocols for tissue culture infection pay particular attention to the multiplicity of infection (MOI), to avoid the accumulation of defective interfering particles (low MOI) or to promote recombination between viruses (high MOI), for example. To select for emergence events over serial passaging, it is also important to consider virus population size. Since the resistant mutant initially exists at low frequency, it is best to transfer as large a population size as possible from one passage to the next (105-106 viruses, e.g.) to avoid losing these emerging variants at each passage. Scaling up the size of well or flask (number of cells infected) may help to minimize the increase in MOI if this is of concern. On the other hand, for experiments in which the sensitivity of a virus to mutagen is being tested, low MOI infection is performed in order to increase the number of replication cycles occurring in the experiment and to avoid rescue of mutagenized genomes by higher fitness genomes through complementation in co-infected cells. This is important since the mutations generated on progeny genomes during the first round of replication will not be immediately detected. Most of these mutagenized RNAs will still be packaged into virion. It is in the next round of infection that lethal mutations present in these genomes will result in an aborted replication cycle, and reduction in virus titer. It may be necessary to allow for several rounds of accumulation of mutations before a significant effect of lethal mutagenesis is observed. Finally, if over the passage series in the presence of mutagen, the virus titers continue to drop until extinction, then the researcher should try passaging virus in gradually increasing amounts of mutagen (starting from a very low concentration).
Isolation and generation of the RNA mutagen resistant clone from the RNA mutagen-resistant population. RNA mutagens introduce multiple random mutations to each genome, but selection for resistance will only enrich (and fix to consensus sequence) the resistance mutation. To identify this mutation, we sequence the mutagen resistant population (consensus of the population) and not individual viruses. Hence, the single, random mutations created by the mutagen are not detected in the sequence; only the mutations that result in consensus changes following selection, are found. In our experience we only identify one or two such consensus sequence changes. Once the mutagen resistant population is obtained and the resistance mutation is identified, it is necessary to generate a more pure stock of this variant. Above, we described a plaque purification procedure. Alternatively, if the virus of interest does not produce easily identifiable plaques, the desired variant may be purified by limiting dilution. This approach is essentially a TCID50 in 96-well format, where the virus stock is diluted such that less than 50% of wells are infected. Using this dilution, the same approach as above is taken, in isolating up to 10 individual variants and confirming their sequences. As mentioned, in the best cases, an infectious cDNA clone of the virus strain is available. Isolation of the variant would thus not be necessary. In our experience, fidelity variants are the result of single amino acid substitutions and can thus be generated using simple, commercialized mutagenesis kits such as Quikchange (Agilent). A secondary option is to use a cDNA clone of a closely related strain. However, if a related strain is used, we strongly suggest using both this approach and virus isolation (e.g. plaque purification) because we have found that the same fidelity altering mutation on two closely related viruses will not necessarily have the same effect.
Fidelity and replication. Selection of RNA mutagen resistant variants have resulted in the isolation of both higher and lower fidelity variants with growth characteristics that are similar to their wild type counterparts 4,12,15. Currently, the link between polymerase activity rates and fidelity is not fully understood. In vitro biochemical studies using purified RNA polymerase have shown that higher fidelity variants have slower processing rates, while lower fidelity variants tend to have faster processing 1-3,12. In tissue culture, these differences are not usually evident, suggesting that availability of resources, rather than intrinsic polymerase activity kinetics, is the rate-limiting step. If the fidelity variant replicates with kinetics that are not significantly different from wild type, then a comparison of their mutation frequencies can be directly made. If a very significant change in replication kinetics exists, then the data should be normalized to account for kinetic differences, for example by comparing viruses that have undergone the same number of replication cycles. In our experience, although no significant differences in one-step growth kinetics were observed between wild type and high fidelity variants, we observed that higher fidelity variants consistently titer higher (within 1 log) compared to wild type but they make slightly less RNA (within the same order of magnitude), further suggesting that the genomes they produce contain fewer mutations and are thus, more infectious.
Sample preparation and sequencing. For all steps in these protocols, it is imperative that high-fidelity, proof-reading enzymes are used for PCR and RT-PCR to limit introducing additional mutations since they cannot be distinguished from biologically relevant mutations. It is critical that the virus populations to be compared have been prepared in the same conditions (passage history, tissue culture medium, temperature, RNA extraction method, RT-PCR protocols, etc.) It is also important to ensure that enough starting material was obtained from the RNA extraction such that a strong band is generated by RT-PCR. A 1/100 dilution of the RNA sample should also give a detectable RT-PCR band, indicating that the sample contains sufficient numbers of RNA molecules to avoid representation bias (amplifying the same genome repeatedly). Since mutation frequency is a distribution, one would expect that similar values will be obtained regardless of population size, provided the aforementioned bias is not occurring. As Figure 6 shows, a 105-fold dilution of a virus stock gives a mutation frequency that is not significantly different from the parental stock.
Until the optimal conditions for TopoTA cloning are found, confirm the presence of inserts after blue/white screening, by colony PCR before sequencing. As a control for mutational noise (mutations introduced by RT-PCR and sequencing), clone a PCR product from a plasmid bearing the same viral sequence and/or clone and sequence RT-PCR products of in vitro transcribed RNA corresponding to virus genome (be aware that different in vitro transcription enzymes have different error rates and may not give useful information as to the real background error in your procedure). Some virus sequences may be toxic to bacteria, so it is important to verify this before deciding on the region of viral genome to be sequenced for mutation frequency. In analyzing sequences obtained by TopoTA, note that each clone should contain only one insert/sequence. If a double peak is observed, suggesting a mixed population, it is possible that two neighboring bacterial colonies were selected. It is also possible, although highly unlikely given the low mutation frequencies in bacterial replication, that the mutation was introduced during amplification of plasmid in the bacterial culture. In plaque purified populations, a double peak may represent overlapping plaques, or a virus that is acquiring a new mutation or reverting a mutation during plaque development. Be consistent and decide on whether to count or not count these mutations.
Finally, keep in mind that the mutation frequencies used here are relative values. They are valid only in comparing virus populations grown under the same condition, and sequenced over the same region! They should not be taken as absolute values of mutation rate, or the mutation frequency of the genome as a whole. However, when conditions are controlled, they do permit reproducible, quantitative comparisons of differences in mutation distribution and frequency.

<table border="1">
 <tbody>
 <tr>
 <th>Name of the reagent</th>
 <th>Company</th>
 <th>Catalogue number</th>
 <th>Comments</th>
 </tr>
 <tr>
 <td>ribavirin</td>
 <td>Sigma</td>
 <td>R9644-10MG</td>
 <td>&nbsp;</td>
 </tr>
 <tr>
 <td>5-fluorouracil</td>
 <td>Sigma</td>
 <td>F6627-1G</td>
 <td>&nbsp;</td>
 </tr>
 <tr>
 <td>5-azacytidine</td>
 <td>Sigma</td>
 <td>A2385-100MG</td>
 <td>&nbsp;</td>
 </tr>
 <tr>
 <td>MgCl2</td>
 <td>Sigma</td>
 <td>M1028-100ML</td>
 <td>&nbsp;</td>
 </tr>
 <tr>
 <td>MnCl2</td>
 <td>Sigma</td>
 <td>M1787</td>
 <td>&nbsp;</td>
 </tr>
 <tr>
 <td>Trypan blue</td>
 <td>Sigma</td>
 <td>T8154-20ML</td>
 <td>&nbsp;</td>
 </tr>
 <tr>
 <td>TopoTA cloning kit</td>
 <td>Invitrogen</td>
 <td>10351021</td>
 <td>&nbsp;</td>
 </tr>
 <tr>
 <td>Quikchange mutagenesis kit</td>
 <td>Agilent</td>
 <td>200516</td>
 <td>If a cDNA infectious clone is available</td>
 </tr>
 <tr>
 <td>96-well miniprep kit</td>
 <td>Macherey-nagel</td>
 <td>740625</td>
 <td>&nbsp;</td>
 </tr>
 <tr>
 <td>Lasergene, Sequencher</td>
 <td>DNAstar, Gene Codes Corporation</td>
 <td><a href="http://www.dnastar.com">www.dnastar.com</a> 
 <a href="http://www.genecodes.com">www.genecodes.com</a></td>
 <td>Or other alignment software</td>
 </tr>
 </tbody>
</table>

isolation of fidelity variants of rna viruses and characterization of virus mutation frequency

RNA viruses use RNA dependent RNA polymerases to replicate their genomes. The intrinsically high error rate of these enzymes is a large contributor to the generation of extreme population diversity that facilitates virus adaptation and evolution. Increasing evidence shows that the intrinsic error rates, and the resulting mutation frequencies, of RNA viruses can be modulated by subtle amino acid changes to the viral polymerase. Although biochemical assays exist for some viral RNA polymerases that permit quantitative measure of incorporation fidelity, here we describe a simple method of measuring mutation frequencies of RNA viruses that has proven to be as accurate as biochemical approaches in identifying fidelity altering mutations. The approach uses conventional virological and sequencing techniques that can be performed in most biology laboratories. Based on our experience with a number of different viruses, we have identified the key steps that must be optimized to increase the likelihood of isolating fidelity variants and generating data of statistical significance. The isolation and characterization of fidelity altering mutations can provide new insights into polymerase structure and function1-3. Furthermore, these fidelity variants can be useful tools in characterizing mechanisms of virus adaptation and evolution4-7.

Watch this Scientific Journal Video about Isolation of Fidelity Variants of RNA Viruses and Characterization of Virus Mutation Frequency at JoVE.com

Isolation of Fidelity Variants of RNA Viruses and Characterization of Virus Mutation Frequency

The present article describes the steps required to isolate and characterize RNA polymerase fidelity variants of RNA viruses and how to use mutation frequency data to confirm fidelity changes in tissue culture.

RNA viruses use RNA dependent RNA polymerases to replicate their genomes. The intrinsically high error rate of these enzymes is a large contributor to the ...

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Research

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Immunology and Infection

RNA Isolation of Pseudomonas aeruginosa Colonizing the Murine Gastrointestinal Tract

Pseudomonas aeruginosa (PA) infections result in significant morbidity and mortality in hosts with compromised immune systems, such as patients with leukemia, severe burn wounds, or organ transplants1. In patients at high-risk for developing PA bloodstream infections, the gastrointestinal (GI) tract is the main reservoir for colonization2, but the mechanisms by which PA transitions from an asymptomatic colonizing microbe to an invasive, and often deadly, pathogen are unclear. Previously, we performed in vivo transcription profiling experiments by recovering PA mRNA from bacterial cells residing in the cecums of colonized mice 3 in order to identify changes in bacterial gene expression during alterations to the host&#x2019;s immune status.
As with any transcription profiling experiment, the rate-limiting step is in the isolation of sufficient amounts of high quality mRNA. Given the abundance of enzymes, debris, food residues, and particulate matter in the GI tract, the challenge of RNA isolation is daunting. Here, we present a method for reliable and reproducible isolation of bacterial RNA recovered from the murine GI tract. This method utilizes a well-established murine model of PA GI colonization and neutropenia-induced dissemination4. Once GI colonization with PA is confirmed, mice are euthanized and cecal contents are recovered and flash frozen. RNA is then extracted using a combination of mechanical disruption, boiling, phenol/chloroform extractions, DNase treatment, and affinity chromatography. Quantity and purity are confirmed by spectrophotometry (Nanodrop Technologies) and bioanalyzer (Agilent Technologies) (Fig 1). This method of GI microbial RNA isolation can easily be adapted to other bacteria and fungi as well.

RNA Isolation of Pseudomonas aeruginosa Colonizing the Murine Gastrointestinal Tract

A reliable method for the RNA isolation of Pseudomonas aeruginosa recovered from murine cecums is described. The RNA recovered is of sufficient quantity and quality for subsequent qPCR, transcription profiling, and RNA Seq experiments. This technique can be adapted for RNA isolation of other intestinal microbes.

Pseudomonas aeruginosa (PA) infections result in significant morbidity and mortality in hosts with compromised immune systems, such as patients with ...

High-throughput Screening for Broad-spectrum Chemical Inhibitors of RNA Viruses

RNA viruses are responsible for major human diseases such as flu, bronchitis, dengue, Hepatitis C or measles. They also represent an emerging threat because of increased worldwide exchanges and human populations penetrating more and more natural ecosystems. A good example of such an emerging situation is chikungunya virus epidemics of 2005-2006 in the Indian Ocean. Recent progresses in our understanding of cellular pathways controlling viral replication suggest that compounds targeting host cell functions, rather than the virus itself, could inhibit a large panel of RNA viruses. Some broad-spectrum antiviral compounds have been identified with host target-oriented assays. However, measuring the inhibition of viral replication in cell cultures using reduction of cytopathic effects as a readout still represents a paramount screening strategy. Such functional screens have been greatly improved by the development of recombinant viruses expressing reporter enzymes capable of bioluminescence such as luciferase. In the present report, we detail a high-throughput screening pipeline, which combines recombinant measles and chikungunya viruses with cellular viability assays, to identify compounds with a broad-spectrum antiviral profile.

In vitro assays to measure virus replication have been greatly improved by the development of recombinant RNA viruses expressing luciferase or other enzymes capable of bioluminescence. Here we detail a high-throughput screening pipeline that combines such recombinant strains of measles and chikungunya viruses to isolate broad-spectrum antivirals from chemical libraries.

RNA viruses are responsible for major human diseases such as flu, bronchitis, dengue, Hepatitis C or measles. They also represent an emerging threat ...

Isolation and Characterization of Neutrophils with Anti-Tumor Properties

Neutrophils, the most abundant of all white blood cells in the human circulation, play an important role in the host defense against invading microorganisms. In addition, neutrophils play a central role in the immune surveillance of tumor cells. They have the ability to recognize tumor cells and induce tumor cell death either through a cell contact-dependent mechanism involving hydrogen peroxide or through antibody-dependent cell-mediated cytotoxicity (ADCC). Neutrophils with anti-tumor activity can be isolated from peripheral blood of cancer patients and of tumor-bearing mice. These neutrophils are termed tumor-entrained neutrophils (TEN) to distinguish them from neutrophils of healthy subjects or na&#239;ve mice that show no significant tumor cytotoxic activity. Compared with other white blood cells, neutrophils show different buoyancy making it feasible to obtain a &#62; 98% pure neutrophil population when subjected to a density gradient. However, in addition to the normal high-density neutrophil population (HDN), in cancer patients, in tumor-bearing mice, as well as under chronic inflammatory conditions, distinct low-density neutrophil populations (LDN) appear in the circulation. LDN co-purify with the mononuclear fraction and can be separated from mononuclear cells using either positive or negative selection strategies. Once the purity of the isolated neutrophils is determined by flow cytometry, they can be used for in vitro and in vivo functional assays. We describe techniques for monitoring the anti-tumor activity of neutrophils, their ability to migrate and to produce reactive oxygen species, as well as monitoring their phagocytic capacity ex vivo. We further describe techniques to label the neutrophils for in vivo tracking, and to determine their anti-metastatic capacity in vivo. All these techniques are essential for understanding how to obtain and characterize neutrophils with anti-tumor function.

Neutrophils play an important role not only in host defense against invading microorganisms, but are also involved in the immune surveillance of tumor cells. Here, we describe techniques related to the isolation of neutrophils with anti-tumor properties and methods for monitoring anti-tumor neutrophil function in vitro and in vivo.

Neutrophils, the most abundant of all white blood cells in the human circulation, play an important role in the host defense against invading ...

Bacterial Artificial Chromosomes: A Functional Genomics Tool for the Study of Positive-strand RNA Viruses

Reverse genetics, an approach to rescue infectious virus entirely from a cloned cDNA, has revolutionized the field of positive-strand RNA viruses, whose genomes have the same polarity as cellular mRNA. The cDNA-based reverse genetics system is a seminal method that enables direct manipulation of the viral genomic RNA, thereby generating recombinant viruses for molecular and genetic studies of both viral RNA elements and gene products in viral replication and pathogenesis. It also provides a valuable platform that allows the development of genetically defined vaccines and viral vectors for the delivery of foreign genes. For many positive-strand RNA viruses such as Japanese encephalitis virus (JEV), however, the cloned cDNAs are unstable, posing a major obstacle to the construction and propagation of the functional cDNA. Here, the present report describes the strategic considerations in creating and amplifying a genetically stable full-length infectious JEV cDNA as a bacterial artificial chromosome (BAC) using the following general experimental procedures: viral RNA isolation, cDNA synthesis, cDNA subcloning and modification, assembly of a full-length cDNA, cDNA linearization, in vitro RNA synthesis, and virus recovery. This protocol provides a general methodology applicable to cloning full-length cDNA for a range of positive-strand RNA viruses, particularly those with a genome of &gt;10 kb in length, into a BAC vector, from which infectious RNAs can be transcribed in vitro with a bacteriophage RNA polymerase.

Here, a protocol is presented for creating an infectious bacterial artificial chromosome containing a full-length cDNA of the positive-strand genomic RNA of Japanese encephalitis virus. This protocol can be used to construct a functional cDNA of other positive-strand RNA viruses, making it a powerful genomic tool for studying virus biology.

Reverse genetics, an approach to rescue infectious virus entirely from a cloned cDNA, has revolutionized the field of positive-strand RNA viruses, whose ...

Neutrophil Isolation and Analysis to Determine their Role in Lymphoma Cell Sensitivity to Therapeutic Agents

Neutrophils are the most abundant (40% to 75%) type of white blood cells and among the first inflammatory cells to migrate towards the site of inflammation. They are key players in the innate immune system and play major roles in cancer biology. Neutrophils have been proposed as key mediators of malignant transformation, tumor progression, angiogenesis and in the modulation of the antitumor immunity; through their release of soluble factors or their interaction with tumor cells. To characterize the specific functions of neutrophils, a fast and reliable method is coveted for in vitro isolation of neutrophils from human blood. Here, a density gradient separation method is demonstrated to isolate neutrophils as well as mononuclear cells from the blood. The procedure consists of layering the density gradient solution such as Ficoll carefully above the diluted blood obtained from patients diagnosed with chronic lymphocytic leukemia (CLL), followed by centrifugation, isolation of mononuclear layer, separation of neutrophils from RBCsby dextran then lysis of residual erythrocytes. This method has been shown to isolate neutrophils &#8805; 90 % pure. To mimic the tumor microenvironment, 3-dimensional (3D) experiments were performed using basement membrane matrix such as Matrigel. Given the short half-life of neutrophils in vitro, 3D experiments with fresh human neutrophils cannot be performed. For this reason promyelocytic HL60 cells are differentiated along the granulocytic pathway using the differentiation inducers dimethyl sulfoxide (DMSO) and retinoic acid (RA). The aim of our experiments is to study the role of neutrophils on the sensitivity of lymphoma cells to anti-lymphoma agents. However these methods can be generalized to study the interactions of neutrophils or neutrophil-like cells with a large range of cell types in different situations.

Neutrophils are the most abundant type of white blood cells. The isolation of neutrophils from human blood by density gradient separation method and the differentiation of human promyelocytic (HL60) cells along the granulocytic pathway are described here; to test their role on sensitivity of lymphoma cells to anti-lymphoma agents.

Neutrophils are the most abundant (40% to 75%) type of white blood cells and among the first inflammatory cells to migrate towards the site of ...

Rescue and Characterization of Recombinant Virus from a New World Zika Virus Infectious Clone

Infectious cDNA clones allow for genetic manipulation of a virus, thus facilitating work on vaccines, pathogenesis, replication, transmission and viral evolution. Here we describe the construction of an infectious clone for Zika virus (ZIKV), which is currently causing an explosive outbreak in the Americas. To prevent toxicity to bacteria that is commonly observed with flavivirus-derived plasmids, we generated a two-plasmid system which separates the genome at the NS1 gene and is more stable than full-length constructs that could not be successfully recovered without mutations. After digestion and ligation to join the two fragments, full-length viral RNA can be generated by in vitro transcription with T7 RNA polymerase. Following electroporation of transcribed RNA into cells, virus was recovered that exhibited similar in vitro growth kinetics and in vivo virulence and infection phenotypes in mice and mosquitoes, respectively.

This protocol describes the recovery of infectious Zika virus from a two-plasmid infectious cDNA clone.

Infectious cDNA clones allow for genetic manipulation of a virus, thus facilitating work on vaccines, pathogenesis, replication, transmission and viral ...

Generation of Escape Variants of Neutralizing Influenza Virus Monoclonal Antibodies

Influenza viruses exhibit a remarkable ability to adapt and evade the host immune response. One way is through antigenic changes that occur on the surface glycoproteins of the virus. The generation of escape variants is a powerful method in elucidating how viruses escape immune detection and in identifying critical residues required for antibody binding. Here, we describe a protocol on how to generate influenza A virus escape variants by utilizing human or murine monoclonal antibodies (mAbs) directed against the viral hemagglutinin (HA). With the use of our technique, we previously characterized critical residues required for the binding of antibodies targeting either the head or stalk of the novel avian H7N9 HA. The protocol can be easily adapted for other virus systems. Analyses of escape variants are important for modeling antigenic drift, determining single nucleotide polymorphisms (SNPs) conferring resistance and virus fitness, and in the designing of vaccines and/or therapeutics.

We describe a method by which we identify critical residues required for the binding of human or murine monoclonal antibodies that target the viral hemagglutinin of influenza A viruses. The protocol can be adapted to other virus surface glycoproteins and their corresponding neutralizing antibodies.

Influenza viruses exhibit a remarkable ability to adapt and evade the host immune response. One way is through antigenic changes that occur on the surface ...

Identification of Coding and Non-coding RNA Classes Expressed in Swine Whole Blood

The advent of innovative and increasingly powerful next generation sequencing techniques has opened new avenues into the ability to examine the underlying gene expression related to biological processes of interest. These innovations not only allow researchers to observe expression from the mRNA sequences that code for genes that effect cellular function, but also the non-coding RNA (ncRNA) molecules that remain untranslated, but still have regulatory functions. Although researchers have the ability to observe both mRNA and ncRNA expression, it has been customary for a study to focus on one or the other. However, when studies are interested in both mRNA and ncRNA expression, many times they use separate samples to examine either coding or non-coding RNAs due to the difference in library preparations. This can lead to the need for more samples which can increase time, consumables, and animal stress. Additionally, it may cause researchers to decide to prepare samples for only one analysis, usually the mRNA, limiting the number of biological questions that can be investigated. However, ncRNAs span multiple classes with regulatory roles that effect mRNA expression. Because ncRNA are important to fundamental biologic processes and disorder of these processes in during infection, they may, therefore, make attractive targets for therapeutics. This manuscript demonstrates a modified protocol for the generation mRNA and non-coding RNA expression libraries, including viral RNA, from a single sample of whole blood. Optimization of this protocol, improved RNA purity, increased ligation for recovery of methylated RNAs, and omitted&#160;size selection, to allow capture of more RNA species.

Here, we present a protocol optimized for the processing of coding (mRNA) and non-coding&#160;(ncRNA) globin reduced RNA-seq libraries from a single whole blood sample.

The advent of innovative and increasingly powerful next generation sequencing techniques has opened new avenues into the ability to examine the underlying ...

Confocal Imaging of Double-Stranded RNA and Pattern Recognition Receptors in Negative-Sense RNA Virus Infection

Double-stranded (ds) RNA is produced as a replicative intermediate during RNA virus infection. Recognition of dsRNA by host pattern recognition receptors (PRRs) such as the retinoic acid (RIG-I) like receptors (RLRs) RIG-I and melanoma differentiation-associated protein 5 (MDA-5) leads to the induction of the innate immune response. The formation and intracellular distribution of dsRNA in positive-sense RNA virus infection has been well characterized by microscopy. Many negative-sense RNA viruses, including some arenaviruses, trigger the innate immune response during infection. However, negative-sense RNA viruses were thought to produce low levels of dsRNA, which hinders the imaging study of PRR recognition of viral dsRNA. Additionally, infection experiments with highly pathogenic arenaviruses must be performed in high containment biosafety level facilities (BSL-4). The interaction between viral RNA and PRRs for highly pathogenic RNA virus is largely unknown due to the additional technical challenges that researchers need to face in the BSL-4 facilities. Recently, a monoclonal antibody (Mab) (clone 9D5) originally used for pan-enterovirus detection has been found to specifically detect dsRNA with a higher sensitivity than the traditional J2 or K1 anti-dsRNA antibodies. Herein, by utilizing the 9D5 antibody, we describe a confocal microscopy protocol that has been used successfully to visualize dsRNA, viral protein and PRR simultaneously in individual cells infected by arenavirus. The protocol is also suitable for imaging studies of dsRNA and PRR distribution in pathogenic arenavirus infected cells in BSL4 facilities.

Double-stranded RNA produced during RNA virus replication can be recognized by pattern recognition receptors to induce an innate immune response. For negative-sense RNA viruses, the interaction between the low-level dsRNA and PRRs remains unclear. We have developed a confocal microscopy method to visualize arenavirus dsRNA and PRR in individual cells.

Double-stranded (ds) RNA is produced as a replicative intermediate during RNA virus infection. Recognition of dsRNA by host pattern recognition receptors ...

Vector Competence Analyses on Aedes aegypti Mosquitoes using Zika Virus

The procedures presented describe a generalized methodology to infect Aedes aegypti mosquitoes with Zika virus under laboratory conditions to determine the rate of infection, disseminated infection, and potential transmission of the virus in the mosquito population in question. These procedures are widely utilized with various modifications in vector competence evaluations globally. They are important in determining the potential role that a given mosquito (i.e., species, population, individual) may play in the transmission of a given agent.

Vector Competence Analyses on Aedes aegypti Mosquitoes using Zika Virus

The presented protocol can determine the vector competence of Aedes aegypti mosquito populations for a given virus, such as Zika, in a containment setting.

The procedures presented describe a generalized methodology to infect Aedes aegypti mosquitoes with Zika virus under laboratory conditions to determine ...