Leonard Foster

 
Prospective Graduate Students / Postdocs

This faculty member is currently not actively recruiting graduate students or Postdoctoral Fellows, but might consider co-supervision together with another faculty member.

Professor

Research Classification

Biotechnology
Bioinformatics
Biological and Biochemical Mechanisms
Microbiology
Cell Signaling and Infectious and Immune Diseases
Immune System
Agriculture
Proteomics

Research Interests

Honey bees
host-pathogen interactions
antigen presentation
Systems Biology

Relevant Degree Programs

 

Research Methodology

Mass Spectrometry
biochemistry
LC-MS/MS

Postdoctoral Fellows

Graduate Student Supervision

Doctoral Student Supervision (Jan 2008 - May 2019)
Towards defining the molecular mechanism of hygienic behaviour in honey bees (Apis mellifera) (2019)

Honey bees (Apis mellifera) are integral components of the agricultural industry, but diseases and parasites like the Varroa destructor mite threaten their health and longevity. Some honey bee colonies harbor natural disease-resistance traits, and proteomics has been a fruitful tool to investigate mechanisms of disease resistance; however, Varroa proteomics is a budding field. One troubling trend is that both honey bee and Varroa proteomics samples consistently result in lower peptide identifications compared to conventional model species, which is hindering research on not only social disease-resistance mechanisms and honey bee-mite interactions, but countless other biological topics. We begin by conducting a proteogenomics interrogation to suggest improvements for both the Varroa and the honey bee genome annotations, and to help alleviate the limitations of proteomics technology. The resulting protein databases and web-based protein atlas will serve as resources for future Varroa and honey bee proteomics experiments. Next, we investigate the chemical ecological aspects underpinning hygienic behaviour in honey bees (one form of social immunity against parasites like Varroa). We use gas chromatography-mass spectrometry to analyze abundances of volatile and non-volatile odorants in freeze-killed and age-matched healthy brood, as well as Varroa-infested and non-infested brood. We identified 10 differentially emitted compounds, 2 of which (β-ocimene and oleic acid) are intriguing candidates as hygienic behaviour-inducers based on their previously known functions in honey bees and other social insects. Next, we investigate these two compounds’ abilities to induce hygienic behaviour using a series of behavioural assays. We found that, depending on the context, both odorants can induce hygienic behavior, and they may be acting synergistically. Finally, we begin to investigate physical and biochemical interactions between these odorants and two odorant binding proteins – OBP16 and OBP18 – which are thought to aid in disease odorant detection. We find that β-ocimene is a ligand of OBP16 and oleic acid is a ligand of both OBPs. We conclude by beginning to develop RNAi and transgenic methods for investigating the roles of these proteins in vivo. Overall, these studies are starting to reveal the simple molecular mechanisms underlying a complex social immunity trait in honey bees.

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ABCF1 is a novel E2 ubiquitin-conjugating enzyme that controls Toll-like receptor-mediated innate immune responses and cytokine storm during sepsis (2018)

No abstract available.

Anatomy of an RNA virus : dissecting the host-virus interactions that govern dicistrovirus gene expression and transmission (2018)

Viruses exist as obligate intracellular parasites, with one of the largest classifications of viruses being the positive single stranded RNA viruses ((+)ssRNA). Viral families in this group are incredibly diverse in their replication schemes and host tropisms. Despite this, there exist fundamental principles between them. Unravelling these common mechanisms can give rise to a greater understanding of virus biology and lead to the development of novel antiviral therapies and biotechnology. Members of the Dicistroviridae contain monopartite, (+)ssRNA genomes, between 8 to 10 kilobases in size. Infectious to agriculturally and economically important arthropods, these viruses have served as model systems to study fundamental cellular processes such as translation and innate immunity. Dicistroviruses contain two open reading frames (ORFs), which are translated by two distinct internal ribosome entry sites (IRESs). The 5’ untranslated region IRES drives translation of the viral non-structural proteins encoded in ORF1, whereas the intergenic region (IGR) IRES directs translation of the viral structural proteins of ORF2. The scheme by which these viruses replicate is poorly described. Here, we develop the first infectious clones of the dicistrovirus type species, Cricket paralysis virus (CrPV), termed CrPV-2 and -3. We demonstrate that this clone is fully infectious in Drosophila S2 cells and causes mortality when injected into adult flies. Utilizing this clone, we examined how specific mutations in the IGR IRES affect viral gene expression in vivo. Moreover, we demonstrate that the CrPV IGR IRES uses an unusual mechanism for +1-frame translation of a hidden overlapping ORF, which is important for viral pathogenesis. Finally, using a combination of biochemical and mass spectrometry based approaches we show that CrPV may usurp cellular pathways to obtain an envelope. This thesis offers insights into the complex replication scheme of dicistroviruses and provides a foundation for future studies into the life cycle of these viruses.

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Phosphorylation of MYB75 transcription factor by MAP kinases in Arabidopsis thaliana (2018)

The Arabidopsis transcription factor MYB75 has been described in the literature as a positive transcriptional regulator of anthocyanin biosynthetic genes. More recently, MYB75 was shown to also negatively regulate lignin and other secondary cell wall biosynthetic genes. MYB75 has two canonical MAP kinase phosphorylation sites, at threonines 126 and 131; we wanted to explore the possibility that MYB75 is regulated post translationally through phosphorylation by MPKs. In our lab, Dr. Yonge found that MYB75 could be phosphorylated in vitro by MPK3, MPK4, MPK6 and MPK11, almost exclusively at threonine 131. Subsequently, I demonstrated that MYB75 interacts in vitro with a large number of Arabidopsis MAP kinases, suggesting that it could be a target for multiple MPKs. We decided to explore how phosphorylation affects MYB75 function, in terms of protein-protein interaction, protein turnover and localization, and describe the impact of this putative phosphorylation event on the ability of MYB75 to drive transcription of target genes. For this purpose we used point mutants, MYB75T131A and MYB75T131E to mimic permanently non-phosphorylated and phosphorylated versions of MYB75, respectively. While protein localization and protein-protein interactions of MYB75 were not strongly impacted in the point mutants, several in vivo experiments indicated that MYB75T131E is more labile than either MYB75WT or MYB75T131A, suggesting that phosphorylation at T-131 negatively affects protein stability. Over-expressor lines, 35Spr:3xHA:MYB75 gene, as well as inducible DEXpr:3xHA:MYB75 gene lines were used, to analyze MYB75 protein dynamics in vivo and to assess the ability of each phosphovariant to drive anthocyanin production. Arabidopsis plants over-expressing MYB75WT, MYB75T131A or MYB75T131E displayed increased anthocyanin production, compared to Col-0 WT, suggesting that phosphorylation status at T-131 does not affect this aspect of MYB75 function. However, HPLC analysis revealed quantitative differences between the biochemical species of anthocyanins and flavonols that accumulate in different phosphovariant over-expressing plants. Transcriptome analysis revealed that MYB75T131E is a more potent regulator of gene expression. This finding, along with distinct developmental differences between MYB75 phosphovariants, suggest that phosphorylation at T-131 could affect the ability of MYB75 to drive the expression of a broader spectrum of genes than previously described in the literature. Supplementary materials available at: http://hdl.handle.net/2429/66660

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A novel platform for creating digital PCR assays to detect genetic translocations and its application to the initial diagnosis of cancer. (2016)

Chromosomal translocations can cause cancer, often through the formation of fusion genes that code for an unnatural tyrosine kinase that promotes constitutive activation of a signaling pathway controlling cell proliferation and differentiation. For example, the diagnostic hallmark of chronic myelogenous leukemia (CML) is an oncogene fusion formed from a reciprocal translocation (t(9;22)(q34.1;q11.2)) between chromosomes 9 and 22 that results in an altered chromosome 22q known as the Philadelphia chromosome. Approximately 95% of all CML patients harbor the gene fusion, BCR-ABL, which is formed via a double stranded break (DSB) within both the Abelson oncogene 1 (ABL) on chromosome 9q, which codes for a non-receptor tyrosine kinase (ABL), and the breakpoint cluster region gene (BCR) on chromosome 22q. BCR-ABL encodes a constitutively active tyrosine kinase BCR-ABL responsible for the uncontrolled proliferation associated with chronic myelogenous leukemia. The identification of these translocation events and/or associated fusion genes in clinical samples is critical to ensure the appropriate treatment for patients where the drug and related course of therapy target an activated fusion kinase. Clinical detection of complex chromosomal rearrangements is often conducted using fluorescence in situ hybridization (FISH). The FISH analysis, though effective, offers relatively poor sensitivity while being expensive, time-consuming and technically challenging to perform. Here we have developed and validated a new general platform for creating assays against complex chromosomal rearrangements, including both reciprocal and non-reciprocal translocations. It utilizes droplet digital PCR (ddPCR) technology in lieu of FISH to quantify the rearrangement of proto-oncogenes that undergo rearrangement as part of the translocation event. The platform is applied to the creation of two new assays of potential clinical use in cancer diagnostics or theranostics. The first provides a reliable and sensitive measure of DSBs within the major breakpoint region of BCR (M-BCR), permitting initial diagnosis of CML through unequivocal detection of the BCR-ABL fusion gene to a frequency of 0.25%. The second provides for the highly sensitive detection of DSBs in the anaplastic lymphoma kinase (ALK) gene that result in a non-reciprocal (inversion) translocation (inv(2)(p21;p23)) associated with an ALK-positive non-small cell lung cancer (NSCLC).

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Analysis of the regulation of biological networks using quantitative proteomics (2013)

A protein network can be thought of as a graph with nodes and edges, where nodes represent proteins and edges represent protein-protein interactions. Neither proteins nor their interactions are stable constituents in the cell; they are constantly changing in response to external stimulation or internal programming. Changes in protein expression are regulated by transcription, translation and protein degradation, whereas protein interaction changes have been shown in focused studies to be regulated by post translational modification. To investigate the processes influencing the regulation of protein expression and interaction changes, mass spectrometry based proteomics was applied because it has two key advantages for the study of protein networks: 1) it directly detects peptides from the proteins, and so does not rely on antibodies or the generation of fusion proteins; 2) by combining mass spectrometry based proteomics with quantitative techniques, such as stable isotope labeling by amino acids in cell culture (SILAC), it is possible to quantify thousands of proteins in a single experiment. Here a systems biology approach was applied to investigate protein expression change, synthesis and degradation of proteins during cellular differentiation in two different cell lines. This allowed observing that protein expression during cellular differentiation is largely controlled by changes in the relative synthesis rate, whereas the relative degradation rate of the majority of proteins changed little. By comparing the data with previously published data of mRNA levels, there could be provide strong evidence that the generally poor correlation observed between transcript and protein levels can be explained once the protein synthesis and degradation rates are taken into account. To study how protein interactions change in response to perturbation, a novel approach was developed combining size exclusion chromatography (SEC) and protein correlation profiling (PCP)-SILAC. Stimulation with epidermal growth factor (EGF) caused 351 proteins to alter their interactions with other proteins and, interestingly, when compared to previously published phosphorylation data, these proteins tended to also have altered phosphorylation under similar experimental conditions. This approach allowed identification of protein interactions in numbers comparable to other high throughput techniques, but also enabled quantification of protein stoichiometry between proteins participating in multiple complexes.

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Dynamic composition of membrane microdomains (2012)

Lipid rafts are cholesterol enriched membrane microdomains involved in many cellular functions. Caveolae are a sub-type of lipid rafts that are smooth invaginations of the plasma membrane (PM) whose formation requires caveolin-1 (Cav1). Here, we determined the lipid rafts and caveolae proteome from various cells in an unbiased manner and examined the dynamic raft proteome change during Salmonella infection using quantitative proteomics. In chapter 2, we approach the status of mitochondrial proteins in detergent-resistant membrane (DRM) preparations by employing Stable Isotope Labeling by Amino acids in Cell culture (SILAC) to evaluate the composition of differentially purified subcellular fractions. Our data demonstrate that mitochondrial proteins that were previously identified as raft components are partially co-purifying contaminants of raft preparations. In tumor cells deficient for Golgi β-1,6N-acetylglucosaminyltransferase V (Mgat5), reduced Cav1 expression is associated not with caveolae but with oligomerized Cav1 domains, or scaffolds. These cell lines displaying differing Cav1/caveolae phenotypes are effective tools for probing the composition of caveolae. Using SILAC in chapter 3, we are able to quantitatively distinguish the composition of caveolae from the background of DRM proteins and show that the presence of caveolae enriches protein composition of DRM, including the recruitment of multiple heterotrimeric G-protein subunits. Furthermore in chapter 4, we explored the dynamic change of membrane protein composition according to an external signal. Salmonella are Gram-negative intracellular bacteria believed to attack lipid rafts as the site of entry. We applied SILAC examined the change of host raft proteome at a couple of time points during Salmonella infection. Dozens of proteins have shown to be highly regulated, one of them – Cav1 is shown to be required by Salmonella entrance. We also developed a high-content screening assay that is able to estimate the number of bacteria entered or survived inside the host for future functional studies of the novel proteins identified. This research gives us a better understanding of the raft proteome and how rafts are localized, as well as it can be changed. The Salmonella infection work leads to a global raft proteome dynamic analysis and identifies several proteins that may be novel bacterial host targets.

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Proteomic analysis of Salmonella-host interactions reveals novel host targets of SopB (2011)

Salmonella enterica is an intracellular bacterium causing gastroenteritis and typhoid fever. Virulence is achieved by two type III secretion systems (T3SS) encoded on Salmonella pathogenicity islands 1 and 2 (SPI-1 and SPI-2) that translocate effector proteins into host cells where they mimic or block host protein function. Effectors translocated by T3SS-1 facilitate internalization of the bacteria into the Salmonella-containing vacuole (SCV), actively stimulate intracellular signaling cascades, and regulate trafficking of the SCV to avoid degradation. A T3SS-1 effector, SopB has been shown to regulate a vast array of host processes important for pathogenesis, but only a few host proteins have been identified as targets of this effector. Here quantitative mass spectrometry-based proteomics and bioinformatics techniques have been employed to identify novel host targets of SopB. Quantitative immunoprecipitation experiments identified Cell division control protein 42 (Cdc42) as a direct SopB binding partner, and the binding site within SopB was localized to residues 117-168. SopB and active Cdc42 were shown to colocalize at membrane ruffles on the host cell surface, and two SopB monoubiquitylation sites were identified. To globally analyze host protein phosphorylation events regulated by SopB, a phosphoproteomics method employing heat and chaotropic denaturation for phosphatase inactivation, peptide fractionation by in-solution isoelectric focusing, and phosphopeptide enrichment by metal oxide chromatography was developed. Quantitative analysis of host protein phosphorylation during the initial 20 minutes post Salmonella infection identified >9000 phosphorylation sites, >2000 of which were dynamic. Signaling cascades downstream of T3SS-1 were compared to those induced by growth factor simulation, revealing stark differences between these signaling mechanisms. Kinase prediction upstream of dynamic phosphosites revealed protein kinases B and C as master host regulators during Salmonella infection, and phosphorylation dynamics following wild type versus ΔsopB infection were compared to identify novel host targets of SopB. This work has greatly improved our understanding of SopB’s activity within host cells. It has also provided the first global view of host protein phosphorylation dynamics during bacterial infection, and developed several techniques that can be widely applied within the field of pathogen-host interactions.

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Proteomic analysis of Apis mellifera immune response against Paenibacillus larvae (2010)

The honey bee Apis mellifera is an extremely beneficial insect due to its role in pollination and honey production. Honey bees are vulnerable to many diseases, one of which is caused by the bacterium Paenibacillus larvae. Ingestion of its spores by honey bees early in their larval stage results in death before adulthood. This disease is known as American foulbrood. Interestingly, this deadly consequence does not occur when older larvae or adults consume the spores, a phenomenon which we hypothesize to be the result of an underdeveloped immune system in young larvae. To address this issue, we mainly employed mass spectrometry-based proteomics techniques to learn about the protein effectors that are present in the host. We focused on the hemolymph (insect blood) where a significant repertoire of immunity-related proteins exists. In our comparison of adults and larvae, we saw age-correlated differences in the levels of the antimicrobial peptide hymenoptaecin, the phenoloxidase enzyme which lead to the production of cytotoxic free radicals, and several bacterial recognition proteins. This prompted a detailed study of the larval development in which many new expression trends were revealed; for example, the age-related decrease of antioxidant proteins, proteins associated with translational machinery, and enzymes related to protein turnover. Unexpectedly, most immunity-related proteins showed no significant age correlation, except the antimicrobial peptide apisimin and phenoloxidase. The latter protein was particularly intriguing, given that its increased expression and activity with respect to age agreed with the buildup of resistance against P. larvae. Furthermore, this protein was upregulated in P. larvae infected larvae compared to healthy controls. This enzyme may be an important factor of the host immune response. The decrease of nutrient storage proteins in the diseased state which we observed also implied that the defense response was mounted with an associated energetic cost. Data from the work covered in this thesis has helped explain, from a molecular point-of-view, the pathogenesis of American foulbrood. Although our focus was on honey bee immunity, the proteomics-based approach taken here has provided protein evidence and expression data that will serve as a resource for the wider scientific community.

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Master's Student Supervision (2010 - 2018)
Investigation of the effect of genetic polymorphism on the selection of antigenic peptides in major histocompatibility complexes (2015)

Major histocompatibility complexes (MHCs) play a prominent role in the human adaptive immune system by presenting peptides derived from both host and foreign sources on the cell surface to T cells and eliciting appropriate immune responses during pathogenic invasions. MHC genes are highly polymorphic and the effect of polymorphism on the phenotype, known as an individual’s immunopeptidome, is still unclear. In this thesis, two independent but complementary methods of research were conducted to better understand the interaction between MHC alleles and the identities of peptides presented. First, the antigen presentation machinery was reconstructed in vitro for class II MHCs. This was accomplished by cloning and expressing HLA-DM and HLA-DR in insect cells and purifying the proteins via affinity and size exclusion chromatography. While DM was successfully purified, DR was not. However, once established the in vitro system will offer a novel way to deduce the preferred binding residues for any MHC allele or combinations of alleles, information traditional immunoprecipitation experiments cannot obtain.Next, in an effort to achieve higher confident assignments of class II MHC binding residues, a cell surface acid elution protocol was developed and performed on consanguineous B cell lines. Extracted peptides were identified using liquid chromatography tandem mass spectrometry. To verify that most surface peptides originated from MHCs, lentiviral shRNA was used to knock down HLA-A prior to acid elution, and the identities of peptides were compared to those obtained from the same cell line transduced with a non-targeting shRNA sequence. Results followed anticipated trends and validated the technique as a means to extract MHC peptides. Furthermore, the nature of consanguineous data sets allows for intra-experimental comparisons to decipher allele-specific peptides. Ultimately, these experiments present new ways to study the immunopeptidome and possess the potential to be applied to the vaccine development research field in the future.

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Analysis of the host-pathogen proteomics of Israeli Acute Paralysis Virus in the honey bee using mass spectrometry (2013)

Recent declines in honey bee populations worldwide have spurred significant research into the impact of pathogens on colony health. The role of the Israeli Acute Paralysis Virus (IAPV) in hive mortality has become of particular concern since being correlated with colony losses, although the pathogenic mechanism used by IAPV remains largely unknown. To compound this problem, few molecular studies of the honey bee immune response exist. This lack of knowledge poses a significant barrier if we are to address the impact IAPV has on honey bee health. In this thesis, two routes of research were conducted to aid our understanding of the honey bee host-pathogen relationship. First, a cell culture system using honey bee hemocytes was established and optimized to address the lack of an available honey bee in vitro system, which has significantly delayed honey bee molecular research and especially host-pathogen studies. While hemocyte cultures were simple to create, cell division was not observed and attempts to immortalize the hemocytes through oncogene transfection were hindered by the fragility of these cells. Overall, hemocyte cultures are a useful tool for some experimental applications requiring medium numbers of cells and not involving substantial manipulation. Next, to investigate changes in host protein expression during IAPV infection, mass spectrometry-based quantitative proteomics was used to compare IAPV infected and healthy pupae. This approach applied stable isotope dimethylation labeling combined with multidimensional fractionation using strong cation exhcange to identify and quantify ~800 proteins over three time points. Proteins that were significantly changing during infection were determined and clustered into four distinct expression patterns. To infer functional roles of proteins, Drosophila homologues were obtained for each protein in the data set and the corresponding GO Terms used for functional analysis. Proteins involved in processes including translation and the ubiquitin-proteasome pathway, among others, were identified and future investigation of these pathways will be useful in identifying host proteins required for infection. This analysis represents an important first step towards understanding the honey bee host response to IAPV infection through the systems-level analysis of protein expression and demonstrates the utility of mass spectrometry-based proteomics in honey bee research.

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A novel pathway to sequester ASC at mitochondria-associated membranes dampens inflammasome activation during early Salmonella infection (2012)

Salmonella enterica is an intracellular bacterial pathogen that injects effector proteins into host cells and induces rapid cell death. Mitochondria associated membranes (MAMs) are important contact sites between mitochondria and ER and selectively facilitate Ca²⁺ uptake from ER lumen into mitochondria. In the context of early Salmonella infection of THP-1 cells, a discontinuous sucrose gradient was used in combination with Stable Isotope Labeling by Amino acids in Cell culture (SILAC) to profile organelle proteomes. Protein profiles were generated for >800 mitochondria and ER proteins. I observed unique protein recruitments to MAMs during early Salmonella infection. The inflammasome adaptor protein, ASC is co-purified with MAM markers. SILAC immunoprecipitation (IP) experiments showed that ASC interacts directly with the VDAC/Stress-70 complex at MAMs, suggesting that ASC is specifically recruited to MAMs during Salmonella infection. SILAC IP experiments identified an interaction between Flightless-I and ASC. Flightless-I is an actin binding protein and also interacts with Salmonella flagellin (FliC). siRNA knockdown of Flightless-I and mitofusin 2 (a structural protein of MAMs) both leads to significant increase of IL-1β during Salmonella infection. Simultaneous knockdown of Flightless-I and mitofusin 2 does not have additive effect, suggesting that they are in the same pathway to dampen inflammasome activation. Actin isolation experiments showed that ASC is enriched at actin filaments during Salmonella infection. Therefore, I proposed a model that during early Salmonella infection, FliC interacts with Flightless-I that then interacts with and transports ASC to MAMs via actin filaments. This process specifically sequesters ASC at MAMs to dampen inflammasome activation in the cytosol. Experimental data from ΔfliCΔfljB Salmonella infection of THP-1 cells and inflammasome reconstitution in 293T cells supported this model. This study was the first characterization of MAM protein composition during bacterial infection. Furthermore, enrichment of ASC at MAMs was identified during early Salmonella infection, with Flightless-I interacting with and transporting ASC to MAMs via actin filaments at the presence of Salmonella flagellin. This novel pathway dampened the inflammasome activation during early Salmonella infection. This is the first report of the negative regulation of pyroptosis by Salmonella flagellin.

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Development and application of honey bee in vitro systems (2012)

The honey bee, Apis mellifera, has become tightly linked to human agriculture as one of the most important pollinators. The recent honey bee population decline has raised global concerns of a pollination crisis, yet honey bee research lags far behind in available research tools compared to other model organisms, limiting the pace we can hope to advance our knowledge of honey bee biology and improve bee health. Therefore, the major goal of this thesis was to establish new tools and to improve some of the existing tools for honey bee research and then to demonstrate that these tools can be combined with other genetic and proteomic techniques to help us address questions on honey bee biology. First of all, honey bee primary cell cultures from various tissues could be established and maintained for at least four months. Embryonic cultures could be cryopreserved and also transduced with lentivirus to express EGFP. Proteomic analysis revealed biological pathways related to glucose metabolism and oxidative stress were significantly altered in primary cells during two weeks of cultivation. In addition to cell culture, in vitro larval rearing was also established and the use of various artificial diets was compared for ability to sustain growth. Basic larval diet was by far the most efficient formulation and it was applied to study honey bees’ response to American foulbrood (AFB) infection. RNA interference (RNAi) was used to silence prophenoloxidase, a gene implicated in bees’ resistance to AFB and a multiple reaction monitoring mass (MRM) spectrometry assay was developed to assess degree of knockdown. Although dosage response was observed in in vitro rearing for AFB infection, significant gene silencing could not be achieved. Overall, we established several in vitro systems, including cell cultures and in vitro larval rearing, for honey bee research and these systems in combination with lentiviral transduction, RNA interference, proteome analysis, and MRM assay could form a thorough analysis platform for future studies to improve our knowledge of honey bee biology.

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