Here, we present the protocols to identify 1) virus-encoded immunomodulators that promote arbovirus replication and 2) eukaryotic host factors that restrict arbovirus replication. These fluorescence- and luminescence-based methods allow researchers to rapidly obtain quantitative readouts of arbovirus replication in simplistic assays with low signal-to-noise ratios.
RNA interference- and genome editing-based screening platforms have been widely used to identify host cell factors that restrict virus replication. However, these screens are typically conducted in cells that are naturally permissive to the viral pathogen under study. Therefore, the robust replication of viruses in control conditions may limit the dynamic range of these screens. Furthermore, these screens may be unable to easily identify cellular defense pathways that restrict virus replication if the virus is well-adapted to the host and capable of countering antiviral defenses. In this article, we describe a new paradigm for exploring virus-host interactions through the use of screens that center on naturally abortive infections by arboviruses such as vesicular stomatitis virus (VSV). Despite the ability of VSV to replicate in a wide range of dipteran insect and mammalian hosts, VSV undergoes a post-entry, abortive infection in a variety of cell lines derived from lepidopteran insects, such as the gypsy moth (Lymantria dispar). However, these abortive VSV infections can be "rescued" when host cell antiviral defenses are compromised. We describe how VSV strains encoding convenient reporter genes and restrictive L. dispar cell lines can be paired to set-up screens to identify host factors involved in arbovirus restriction. Furthermore, we also show the utility of these screening tools in the identification of virally encoded factors that rescue VSV replication during coinfection or through ectopic expression, including those encoded by mammalian viruses. The natural restriction of VSV replication in L. dispar cells provides a high signal-to-noise ratio when screening for the conditions that promote VSV rescue, thus enabling the use of simplistic luminescence- and fluorescence-based assays to monitor the changes in VSV replication. These methodologies are valuable for understanding the interplay between host antiviral responses and viral immune evasion factors.
The ability of a virus to productively replicate in a particular host is in part governed by the availability of host cell factors that support viral entry and replication1. The virus-host range can also be dictated by the capacity of a virus to counter cellular antiviral defenses that would otherwise impede viral replication2,3. It is the outcome of these complex virus-host interactions that ultimately decide whether a virus will be able to complete its life cycle in a particular host. Given the potentially pathogenic consequences for the host if viral replication ensues, it is critical to develop experimental strategies to further our understanding of the key virus-host interactions that may tip the balance between abortive and productive infections. Elucidating the molecular features of virus-host interplay will be instrumental in the development of new and alternative antiviral therapeutic strategies.
With the advent of RNA interference (RNAi)4,5 and genome-editing tools (e.g., CRISPR-Cas9, Zinc finger nucleases, TALENs)6,7, it has become experimentally feasible to alter the expression of cellular factors on genome-wide scales and explore the impact of these alterations on virus replication. Indeed, numerous RNAi and genome-editing-based screens have been conducted in invertebrate and vertebrate host cell types that have unveiled new facets of virus-host interactions8,9,10,11,12. These screens typically employ viruses encoding reporters, such as firefly luciferase (LUC) or fluorescent proteins (e.g., GFP, DsRed), that provide convenient means of quantitatively assessing viral gene expression as a readout for viral replication9,12. This strategy allows researchers to identify host factors that either promote or antagonize viral replication as evidenced by increases or decreases, respectively, in viral reporter signals9,12. However, in the vast majority of cases, these screens have been conducted using viruses that are well-adapted to the host cell type in which they are being studied. While this strategy can be important for understanding coevolutionary relationships between viral pathogens and their natural hosts, it does pose fundamental concerns regarding their use in uncovering host antiviral factors. In these cases, an enhancement in virus reporter signal upon RNAi knockdown is being looked for, or the inactivation of a cellular factor that normally impedes viral replication. First, if a virus is already able to robustly replicate in the host cell being examined under control conditions, the dynamic range of the screen (i.e., the ability to distinguish between background and enhanced viral reporter signals) may be limited. Second, this issue is further compounded by the situations in which the virus is well-adapted to the host cell and effective at countering host defense pathways that are being targeted in the screen.
Due to the above concerns regarding traditional virus-host interaction screening methods, we developed a new paradigm for studying virus-host interactions that exploit naturally abortive arbovirus infections in lepidopteran insect cells. This strategy derives from an observation that the well-studied human arbovirus, VSV, undergoes an abortive infection in cells derived from the gypsy moth (L. dispar)13. VSV is naturally transmitted by dipteran insects (i.e., sand flies) to mammalian hosts, and has been shown experimentally to infect a wide range of invertebrate and vertebrate hosts both in cell culture and in vivo14. The 11-kb negative-sense single-stranded RNA genome of VSV encodes five subgenomic mRNAs that are each translated into the proteins that make up the enveloped virion. However, VSV reverse genetic systems have allowed for the creation of replication-competent strains encoding LUC or fluorescent proteins, in addition to the five natural VSV gene products15,16,17. Because these reporter proteins are not incorporated into the VSV virion, they provide a convenient readout for VSV gene expression that occurs post-entry. Using VSV strains encoding GFP or LUC, we have previously shown that VSV gene expression is severely restricted upon the entry of LD652 cells and that VSV titers do not increase by 72 hours post-infection (hpi). In contrast, the coinfection of LD652 cells with VSV and the mammalian poxvirus, vaccinia virus (VACV), leads to logarithmic increases in both VSV gene expression and titers by this time point. VACV undergoes early gene expression, DNA replication, and late gene expression in LD652 cell infections, but the VACV replication cycle is ultimately abortive due to incomplete virion morphogenesis18. The large ~192-kb DNA genome of VACV encodes > 200 proteins, many of which display immunomodulatory properties that promote viral replication through the suppression of host immune responses19. Therefore, we hypothesized that the "rescue" of VSV replication in LD652 cells by VACV coinfection was likely mediated by VACV immunomodulators that inhibited L. dispar responses normally restricting VSV replication. In support of this, the treatment of LD652 cells with the host RNA polymerase II inhibitor actinomycin D also rescues VSV replication in LD652 cells, indicating that the transcription-dependent host responses block VSV replication post-entry13.
The above observations suggest that the naturally restrictive nature of LD652 cells to VSV infection may provide a relatively low background when screening for the conditions that enhance VSV-encoded reporter signals (i.e., those that inhibit host antiviral defenses). Here, we provide the methods for using fluorescence or LUC-based assays to screen for conditions that relieve VSV restriction in lepidopteran cells. First, we show how these assays can be used to identify virally encoded immunomodulatory factors that break VSV restriction during either coinfection experiments or through ectopic expression of candidate viral factors. As an example, we illustrate how we used these screening techniques to identify poxvirus-encoded A51R proteins as a new family of immunomodulatory factors that rescue VSV replication in the absence of other poxvirus factors13. Second, we illustrate how RNAi screening in restrictive VSV-LD652 cell infections can be used to directly identify eukaryotic host factors involved in arbovirus restriction13.
1. General Lymantria dispar (LD652) Cell and Virus Culture
2. Fluorescence-based VSV Rescue Assay Using Co-infection and Live-cell Imaging
3. General Viral Infection Protocol for Luminescence-based VSV Rescue Assays in LD652 Cells
4. Luciferase Assay
5. Immunoblot
6. Titer of VSV from LD652 Cell Cultures
7. Variations of Luminescence-based VSV Rescue Assays in LD652 Cells: RNAi and Plasmid Transfection Experiments
As an example of live-cell imaging applications to monitor VSV rescue upon VACV coinfection, LD652 cells were plated in an 8-well chambered dish and then mock-infected or infected with VSV-DsRed (MOI = 1) in the presence or absence of VACV-FL-GFP (MOI = 25). Because VSV-DsRed expresses DsRed as a free protein and is not fused to structural VSV proteins (Figure 1A), it is only detected after VSV entry and gene expression initiates. All cells were then labeled with cell viability dye that freely passes through the plasma membrane of cells, where it is converted into a membrane-impermeant product, which promotes the retention of the fluorescent signal in labeled cells. Images were acquired every 5 h up to 65 hpi, using the 405 nm, 488 nm, 568 nm, and white light filters to capture cell viability dye, VACV-FL-GFP, VSV-DsRed, and phase contrast (PC) channels, respectively. Under single infection conditions, LD652 cells restrict VSV-DsRed replication; therefore, only a small number of cells exhibit a DsRed signal. However, coinfection of VSV-DsRed with VACV-FL-GFP results in most cells displaying DsRed signals by the end of the time course (Figure 1B). Images captured at each time point were subjected to image analysis software, where 405 nm and 568 nm channel images were used to automatically determine total and DsRed-positive cell numbers, respectively. The percentage of cells displaying a DsRed signal for each treatment is calculated by dividing objects (cells) with a positive signal in the 568-nm channel by the number of objects identified in the 405 nm channel for each time point, followed by multiplication by 100%. As shown in Figure 1C, ~2% of the cells from VSV-DsRed single infections were DsRed-positive by 65 hpi. In contrast, ~77% of the cells in VSV-DsRed + VACV-FL-GFP coinfections were DsRed-positive at this time point. Movies S1 and S2 show the progression of VSV-DsRed infection over the entire 65-h time course in single infection and coinfection conditions, respectively. It is important to note that the GFP expression by VACV-FL-GFP became detectable by 10 hpi, prior to the DsRed signal, indicating that sufficient VACV gene expression is required prior to VSV-DsRed rescue (not shown). Collectively, these results clearly indicate a rescue of VSV-DsRed replication by VACV coinfection. If a coinfecting virus was unable to rescue VSV-DsRed, we would expect equal percentages of DsRed-positive cells between single infection and coinfection treatments.
VSV replication in LD652 cells can alternatively be quantified using luminescence-based assays when using VSV-LUC strains (Figure 2A). As an example, Figure 2B shows the results of a LUC assay using lysates prepared over a 72 h time course from mock-infected cells or cells infected with VSV-LUC (MOI =10) in the presence or absence of VACV-WR (MOI = 25). A positive rescue of VSV-LUC replication is indicated by the logarithmic increase in arbitrary LU detected with lysates prepared from coinfected cells, compared to lysates from single VSV-LUC infections. A negative result would be indicated in this assay by the failure of a coinfection to alter LU readings from those observed in single VSV-LUC infection treatments. If desired, prepared lysates can also be used for immunoblotting, to confirm enhanced VSV gene expression in coinfection treatments. For example, Figure 2C shows a typical immunoblot result for VSV-encoded LUC and matrix (M) proteins in lysates prepared from mock-, VSV-LUC, and VSV-LUC + VACV-WR treatments 72 hpi. Immunoblotting for VACV I3L protein served as a marker of VACV infection, and immunoblotting for cellular actin was used as a loading control. The clear enhancement of VSV-encoded LUC and M proteins in the coinfection lysates further confirm VSV rescue by VACV. Finally, productive VSV replication can be confirmed by collecting supernatants from these LD652 cell cultures and titrating an infectious virus on BSC-40 monolayers (Figure 2D). This result illustrates that only during VACV coinfection does VSV productively replicate.
Once a coinfecting virus is shown capable of rescuing VSV replication in LD652 cells, RNAi screening can be used to identify factors encoded by the coinfecting virus that contribute to VSV rescue. In this experiment, screen for an RNAi condition that leads to a "loss of rescue" phenotype during VSV-LUC coinfection with a rescuing virus. We previously identified the VACV A51R protein as a VSV rescue factor through an RNAi screening of dozens of VACV-encoded transcripts13. As an example, we have recapitulated a smaller scale version of this screen (Figure 3). RNAi is mediated by transfection of in vitro transcribed dsRNAs that target transcripts encoded by the coinfecting virus. In the data shown here, viral transcripts encoding VACV A50R, A51R, and A52R proteins were targeted for RNAi knockdown. As a negative control for loss of rescue, cells were also transfected with dsRNAs targeting GFP-encoding transcripts. As a positive control for a loss of rescue phenotype, cells were transfected with dsRNAs against LUC-encoding transcripts. This treatment produces a strong loss of LU signal during coinfection and helps researchers confirm that transfection/RNAi protocols are working. After 5 h of dsRNA transfection, cells were coinfected with VSV-LUC (MOI = 10) and VACV-WR (MOI = 25). Separate infections with only VSV-LUC were also performed to establish a background level of LU signal. Lysates were then harvested 72 hpi and used in a LUC assay. Comparing the level of VSV rescue across dsRNA treatments to the GFP dsRNA control treatment, the results indicate that the knockdown of VACV A51R produces a strong loss of rescue phenotype, whereas the knockdown of A50R and A52R produces a negative result (no loss of rescue compared to GFP dsRNA).
As an alternative to RNAi screening to identify viral factors that contribute to VSV rescue, overexpress candidate viral factors in LD652 cells and then assay for VSV-LUC rescue. This can be accomplished by cloning candidate genes of interest into appropriate expression vectors such as p16629 and transfecting these plasmids into LD652 cells prior to the VSV-LUC challenge. As an example, Figure 4A shows a rescue experiment in which FLAG-tagged GFP (FGFP) or FLAG-tagged A51R (FA51R) p166 vectors were transfected into LD652 cells at various concentrations, followed by VSV-LUC infection (MO = 10) 24 h later. As a negative control for VSV rescue, additional cultures were mock-transfected and did not receive plasmid DNA. Lysates were collected from cultures 72 hpi and were subjected to LUC assays. FA51R treatments produced a positive VSV rescue result as demonstrated by enhanced LU signals over mock-transfected treatments at multiple doses. In contrast, FGFP treatments were negative for VSV rescue at any dose tested. Immunoblotting of the lysates from Figure 4A confirmed a similar expression of FGFP and FA51R proteins (Figure 4B).
Using an RNAi screening of candidate L. dispar factors, we have shown that the restriction of VSV in LD652 cells is mediated by various cellular factors belonging to antiviral RNAi pathways (e.g., AGO2 and Dicer-2), the Nuclear Factor kappa B (NF-κB)-related IMD pathway (e.g., Relish), and the ubiquitin-proteasome system (e.g., polyubiquitin)13. As an example, we have repeated a smaller scale version of these RNAi experiments with dsRNAs targeting L. dispar transcripts that enhanced VSV-LUC replication upon knockdown (e.g., AGO2, Dicer-2, Relish, polyubiquitin) or had no effect (AGO1)13. After 24 h of dsRNA transfection, cells were challenged with VSV-LUC for 72 h to determine if RNAi treatments enhanced LU signals over negative control GFP dsRNA treatments. RNAi treatments that enhance LU signals indicate that the factor encoded by the targeted transcript restricts VSV replication. As a positive control for RNAi knockdown, dsRNAs targeting LUC-encoding transcripts were also transfected in parallel treatments. Due to the low background LU signals detected in GFP dsRNA control treatments, it was relatively straightforward to identify host-encoded restriction factors using RNAi screening because their knockdown produces ~10- to 1,000-fold increases in LU signals (Figure 5). Thus, it is possible to take advantage of the relatively low background level of VSV gene expression in LD652 cells to screen for host RNAi knockdown conditions that relieve VSV restriction.
Figure 1: Identification of VSV rescue by virus coinfection of LD652 cells using fluorescence-based live-cell imaging. (A) This panel shows a schematic of a VSV-DsRed genome indicating the DsRed (dR) gene location. (B) These representative 10X confocal microscopy images are captured 60 hpi. The 405 nm channel indicates a stain for viable cells, the 488-nm channel indicates VACV-FL-GFP infection, and the 568 nm channel indicates VSV-DsRed infection. Phase contrast (PC) images are also shown. Scale bars = 100 µm. (C) This panel shows the percentage of DsRed-positive LD652 cells over the entire 65 h infection time course. The mean (SD) percentage of the cells showing a DsRed signal for each time point is shown. Please click here to view a larger version of this figure.
Figure 2: Assessment of VSV rescue in LD652 cells using LUC assays. (A) This panel shows a schematic of a VSV-LUC genome. (B) This panel shows arbitrary light units (LUC) assays of lysates from mock-infected cells or cells infected with VSV-LUC, in the absence or presence of VACV-WR. (C) This panel shows an immunoblot of LUC, VSV M, VACV I3L, and cellular actin proteins in the lysates from panel A collected 72 hpi. (D) This panel shows VSV-LUC titers in culture supernatants obtained from panel B. The quantitative data in panels B and D represent the means (± SD) from experiments performed in triplicate. Please click here to view a larger version of this figure.
Figure 3: Identification of a virally-encoded VSV rescue factor through RNAi screening during the coinfection of LD652 cells. This panel shows fold changes in LU detected in lysates from cells 72 hpi with VSV-LUC and VACV-WR after the indicated RNAi treatment, relative to LU detected in lysates from cells singly infected with VSV-LUC. The data represent the means (± SD) from experiments performed in triplicate. Please click here to view a larger version of this figure.
Figure 4: Rescue of VSV by the overexpression of a viral immunomodulator in LD652 cells. (A) This panel shows a LUC assay from VSV-LUC-infected cells 72 hpi that were mock-transfected (mock) or transfected with either FGFP or FA51R p166 expression plasmids. LU signals from each treatment were normalized to signals detected in mock-transfected control treatments. The data represent the means (± SD) from experiments performed in triplicate. (B) This panel shows lysates from panel A, immunoblotted with FLAG and actin antibodies. Please click here to view a larger version of this figure.
Figure 5: Identification of host factors restricting VSV replication in LD652 cells through RNAi screening. This panel shows the fold change in LU signals in indicated RNAi treatments relative to the GFP dsRNA control treatments 72 hpi with VSV-LUC. The data represent the means (± SD) from experiments performed in triplicate. Please click here to view a larger version of this figure.
Movie S1: Representative 405-nm (cell viability dye) and 568 nm (DsRed) channel images captured over a 65 h time course (each frame = 5 h interval) after VSV-DsRed infection of LD652 cells. Please click here to download this file.
Movie S2: Representative 405-nm (cell viability dye) and 568 nm (DsRed) channel images captured over a 65 h time course (each frame = 5 h interval) after coinfection of LD652 cells with VSV-DsRed and VACV-FL-GFP. Please click here to download this file.
Here we have described simple fluorescence- and luminescence-based assays to screen for conditions that rescue VSV replication in restrictive lepidopteran cell cultures. The abortive infection of VSV in lepidopteran cells creates an excellent signal-to-noise ratio when assaying for VSV gene expression. For example, the LU signals detected in lysates from single VSV-LUC infections were ~1,000-fold higher than in mock-infected lysates, yet these signals only changed approximately twofold over a 72-h time course. In contrast, coinfection of VSV-LUC with VACV enhanced LU signals ~300-fold over single VSV-LUC infections by 72 hpi. Thus, VSV rescue assays display an excellent dynamic range, encompassing several orders of magnitude.
One of the critical steps in setting up these assays involves the decision to assay for VSV rescue using fluorescence- or luminescence-based approaches. We have shown examples of how VSV-encoded DsRed signals can be assayed quantitatively using live-cell imaging techniques and software packages that facilitate the automated quantification of DsRed-positive cells in the absence or presence of a rescuing coinfection. If researchers have access to live-cell imaging capabilities, these assays are inexpensive to set up and allow them to capture a wide range of time points that may aid in the detection of differences in VSV replication kinetics that are only observable in narrow time windows. In contrast, luminescence-based approaches are essentially end-point assays that require the preparation of cell lysates at predetermined time points, and lysate preparation can be time-consuming. On the other hand, the luminescence-based assays do not require sophisticated microscopy equipment—only a plate reader capable of reading luminescence signals. Furthermore, luminescence-based assays have a greater dynamic range than microscopy-based assays that calculate the percentage of cells infected. For example, in microscopy assays, DsRed-positive cells (indicating VSV-DsRed infection) can only range from 0–100% of analyzed cells in a field of view. In contrast, LU signals between single VSV-LUC and coinfection conditions (or other rescue conditions) can range over several orders of magnitude.
A key advantage of using the VSV-L. dispar cell system presented here to screen for mammalian virus-encoded immunomodulators is that it inherently selects for the identification of viral factors that suppress what are likely to be conserved and ancient antiviral responses that predate the vertebrate-specific interferon response. Indeed, preliminary observations suggest that A51R proteins inhibit conserved antiviral ubiquitin-proteasome-related cellular responses (see Gammon et al.13 and unpublished data). The discovery of VACV A51R rescue of VSV was the first example of a heterologous virus rescue by a vertebrate virus in an invertebrate host13, and it is likely that these screening systems will uncover additional vertebrate virus-encoded immunomodulators. It is important to note that the key to using VSV rescue as a readout for conditions that inhibit host immunity is that VSV replication must be heavily restricted (or abortive) in the cell type that VSV replication is being examined in. Therefore, most mammalian cell types would likely be unsuitable for these types of assays, given that VSV replicates well in mammalian cells. This is why L. dispar cells were used here as a naturally restrictive host cell type for VSV.
A prior study in Drosophila cells showed that viral suppressors of antiviral RNAi responses could be identified by cotransfection of expression plasmids encoding candidate RNAi suppressors and a self-replicating Flock House virus genomic RNA that encodes GFP in place of B2, its natural RNAi suppressor30. The replication of the Flock House genomic RNA and production of GFP was dependent upon the suppression of RNAi by the cotransfected candidate factor and, thus, the rescue of GFP expression indicated RNAi suppression30. Our unpublished work indicates that the overexpression of virus-encoded RNAi inhibitors also rescues VSV-LUC gene expression in L. dispar cells, suggesting that this system can also be used to identify suppressors of RNAi responses in the context of infection by a bona fide viral pathogen as opposed to a replicon. Indeed, the finding that RNAi-, IMD-, and ubiquitin-proteasome-related pathways contribute to the restriction of VSV replication in L. dispar cells13 suggests that viral antagonists of several antiviral pathways may be identified by the VSV rescue assays presented here.
A potential limitation of these screening methods with regard to the identification of host antiviral proteins is that the L. dispar genome sequence is not yet available. However, there are publicly available L. dispar transcriptomes that can be used to identify candidate host targets for RNAi knockdown26,27,28. Additionally, we have shown previously that VSV is restricted in cell lines derived from other lepidopterans13 that now have a publicly available genome (e.g., Manduca sexta)31. Therefore, cell lines derived from other lepidopterans with sequenced genomes may substitute the L. dispar cells described in the protocol here.
Given the growing economic and public health threat of arboviruses32, the screening assays presented here may provide novel strategies to identify new features of arbovirus-host interactions that may have value in the design of new antiviral therapeutics. Furthermore, because of our relatively limited understanding of lepidopteran mechanisms for restricting RNA virus replication, the tools presented here provide new opportunities to probe the host defense mechanisms encoded by this economically important order of insects.
The authors have nothing to disclose.
D.G. was supported by funding from the University of Texas Southwestern Medical Center's Endowed Scholars Program. The authors thank Michael Whitt (The University of Tennessee Health Science Center) and Sean Whelan (Harvard Medical School) for the provision of VSV-DsRed and VSV-LUC. The authors also thank Gary Luker (University of Michigan Medical School) for the kind gift of the VACV-FL-GFP strain.
6-well tissue culture plates | CELLTREAT | 229106 | |
24-well tissue culture plates | CELLTREAT | 229124 | |
10 cm tissue culture dishes | Corning | C430167 | |
Grace’s Insect Medium | Sigma | G8142 | |
EX-CELL 420 | Sigma | 14420C | |
Fetal Bovine Serum – Optima | Atlanta Biologicals | S12450 | |
Growth medium | 1:1 mixture of Grace's Insect Medium and EX-Cell 420 Serum-Free Medium also containing 1 % antibiotic-antimycotic solution and 10 % Fetal bovine serum | ||
Antibiotic-Antimycotic Solution (100×) | Sigma | A5955 | |
Dulbecco’s Phosphate Buffered Saline (DPBS) | Sigma | D8662 | |
Serum Free Media (SFM) | Thermo Fisher | 10902096 | |
Cytosine arabinoside | Sigma | C1768 | |
Transfection reagent | Thermo Fisher | 10362100 | |
Corning cellgro DMSO (Dimethyl Sulfoxide) | Corning | 25950CQC | |
Reporter lysis buffer 5X | Promega | E3971 | |
Luciferase Assay Reagent | Promega | E1483 | |
96-Well Microplates | Corning | 3915 | |
Mouse anti-FLAG antibody | Wako | 014-22383 | |
Rabbit anti-firefly luciferase antibody | Abcam | ab21176 | |
Mouse anti-actin antibody | Sigma | A2066 | |
Mouse anti-VSV M | N/A | N/A | Dr. John Connor (Boston University) |
Mouse anti-VACV I3L | N/A | N/A | Dr. David Evans (University of Alberta) |
8-well Chambered dish | Lab-Tek II | 155409 | |
Cell viability dye | Thermo Fisher | C12881 | |
FLUOstar microplate reader | BMG Labtech | FLUOstar | |
Confocal microscope | Olympus | FV10i-LIV | |
Image analysis software | Olympus | v1.18 | cellSens software |
Eppendorf 5702 ventilated centrifuge | Eppendorf | 22628102 | |
Odyssey Fc Infrared Imaging System | Li-COR Biosciences | Odyssey Fc | |
LD652 cells | N/A | N/A | Dr. Basil Arif (Natural Resources Canada) |
BSC-40 cells | ATCC | CRL-2761 | |
BHK cells | ATCC | CCL-10 | |
HeLa cells | ATCC | CCL-2 | |
BSC-1 cells | ATCC | CCL-26 | |
in vitro transcription and purification kit | Thermo Fisher | AM1626 | |
PCR purification kit | Qiagen | 28104 |