Next Article in Journal
Hygienic Behavior of Africanized Honey Bees Apis mellifera Directed towards Brood in Old and New Combs during Diurnal and Nocturnal Periods
Next Article in Special Issue
Grooming Behavior as a Mechanism of Insect Disease Defense
Previous Article in Journal
Microgastrinae (Hymenoptera: Braconidae) in the Forest State of Artikutza (Navarra: Spain): Diversity and Community Structure
Previous Article in Special Issue
Brevibacillus laterosporus, a Pathogen of Invertebrates and a Broad-Spectrum Antimicrobial Species
 
 
Search for Articles:
Title / Keyword
Author / Affiliation / Email
Journal
Article Type
 
 
Advanced Search
 
Section
Special Issue
Volume
Issue
Number
Page
 
Journals
Insects
Volume 4
Issue 3
10.3390/insects4030506
insects-logo
Submit to this Journal Review for this Journal Propose a Special Issue
► Article Menu

Article Menu

share Share announcement Help format_quote Cite question_answer Discuss in SciProfiles
first_page
settings
Order Article Reprints
Font Type:
Arial Georgia Verdana
Font Size:
Aa Aa Aa
Line Spacing:
Column Width:
Background:
Article

Gut Transcription in Helicoverpa zea is Dynamically Altered in Response to Baculovirus Infection

by
Jeffrey E. Noland
1,
Jonathan E. Breitenbach
2,
Holly J. R. Popham
3,
Sue M. Hum-Musser
1,
Heiko Vogel
4 and
Richard O. Musser
1,*
1
Department of Biological Sciences, Western Illinois University, Waggoner Hall 358, Macomb, IL 61455, USA
2
USDA Agricultural Research Service, Arthropod-Borne Animal Diseases Research Unit, 1515 College Avenue, Manhattan, KS 66502, USA
3
USDA Agricultural Research Service, Biological Control of Insects Research Laboratory, 1503 S. Providence, Columbia, MO 65203, USA
4
Department of Entomology, Max Planck Institute for Chemical Ecology, Beutenberg Campus, Jena 07745, Germany
*
Author to whom correspondence should be addressed.
Insects 2013, 4(3), 506-520; https://doi.org/10.3390/insects4030506
Submission received: 15 July 2013 / Revised: 4 September 2013 / Accepted: 16 September 2013 / Published: 23 September 2013
(This article belongs to the Special Issue Insect Pathology)
Browse Figures
Versions Notes

Abstract

:
The Helicoverpa zea transcriptome was analyzed 24 h after H. zea larvae fed on artificial diet laced with Helicoverpa zea single nucleopolyhedrovirus (HzSNPV). Significant differential regulation of 1,139 putative genes (p < 0.05 T-test with Benjamini and Hochberg False Discovery Rate) was detected in the gut epithelial tissue; where 63% of these genes were down-regulated and 37% of genes were up-regulated compared to the mock-infected control. Genes that play important roles in digestive physiology were noted as being generally down-regulated. Among these were aminopeptidases, trypsin-like serine proteases, lipases, esterases and serine proteases. Genes related to the immune response reacted in a complex nature having peptidoglycan binding and viral antigen recognition proteins and antiviral pathway systems down-regulated, whereas antimicrobial peptides and prophenoloxidase were up-regulated. In general, detoxification genes, specifically cytochrome P450 and glutathione S-transferase were down-regulated as a result of infection. This report offers the first comparative transcriptomic study of H. zea compared to HzSNPV infected H. zea and provides further groundwork that will lead to a larger understanding of transcriptional perturbations associated with viral infection and the host response to the viral insult in what is likely the most heavily infected tissue in the insect.

1. Introduction

Interactions between insects and the viruses that exploit them as part of their replicative cycle offer us among the oldest examples of infectious outcomes in the animal kingdom. Baculoviruses are thought to have diverged from nudiviruses approximately 350 MYA, and baculovirus-infected insects can be found all over the globe [1,2,3]. The study of baculoviruses has both offered us information regarding the insect response to infection, and an exploitable means of controlling populations of susceptible pest insects [4,5,6,7,8]. Indeed, commercialized baculovirus compositions have been labeled for use as bio-insecticides since the late 1970s, and are seeing resurgence in many parts of the world [9,10].
Baculoviridae are divided into alphabaculoviruses, betabaculoviruses, gammabaculoviruses, and deltabaculoviruses [11]. Alphabaculoviruses, the topic of this study, either incorporate one (single nucleopolyhedrovirus) or more (multiple nucleopolyhedrovirus) nucleocapsids within a viral envelope, embedded within electron-dense crystal structures termed polyhedra [12,13]. Following ingestion, polyhedra are exposed to the alkaline pH of the larval gut resulting in its dissolution and release of baculovirus virions [14]. Contact between the viral envelope glycoprotein and the apical surface of gut cells is thought to promote viral entry and establishment of primary infection. The baculovirus replication cycle proceeds in a coordinated and temporal fashion, with transcription of immediate early genes, followed by early genes that promote and facilitate DNA replication, followed by late genes that give rise to proteins responsible for packaging daughter genomes in capsids, and those responsible for complete assembly, maturation and egress of the virus [14,15,16]. Dissemination of the virus results in secondary and subsequent rounds of infection, leading to polyhedra formation, liquefaction of host tissues, enzymatic digestion of the exoskeleton chitin, and release of the viral polyhedra into the surrounding environment, thus driving spread of the virus to other host insects [14,15,16].
Much effort by numerous groups has gone into identifying, defining, and extending our knowledge regarding the function of individual baculovirus genes and groups of host genes that are specifically responsive to baculovirus infection [17,18,19,20]. However, microarray analysis, and more recently high-throughput RNA-seq approaches, offer us new means to examine the transcriptional responses of both the virus and host in non-model species, on a far more broad basis [20,21,22,23,24,25,26,27]. In this report, we examine by microarray technology the transcriptional profile of the gut of Helicoverpa zea larvae (Lepidoptera: Noctuidae) either mock-infected or experimentally challenged with a lethal dose of the alphabaculovirus Helicoverpa zea single nucleopolyhedrovirus (HzSNPV). We validate the DNA microarray results with quantitative real-time PCR (qRT-PCR) to confirm the observed up-regulation/down-regulation of specific genes, and finally, we offer ontological analysis of groups of differentially regulated genes.

2. Experimental Section

2.1. Insect Rearing, Infection, and Gut Isolation

H. zea larvae were grown from neonates on a corn based artificial diet (BioServ, Frenchtown, NJ, USA) in separate medicine cups (Solo Cup Company, Lake Forest, IL, USA) at 33 °C until the first day of the 6th instar. The larvae were starved for two hours and then fed a 2.0 cm3 cube of artificial diet coated with either 7.5 µL of double-distilled water (mock) or an HzSNPV Elcar inoculum (Thermo Trilogy Corp, Columbia, MD, USA) containing ~1,500 occlusion bodies (OBs) in 7.5 µL of double-distilled water. The larvae were allowed to feed for 24 h after which the gut from each larva was excised and the peritrophic matrix was removed, thus isolating the gut epithelium. Four biological replicates were collected each consisting of eight larval gut epithelial tissues.

2.2. Total RNA Isolation

Gut epithelial tissues were immediately placed in 1.0 mL of TRIzol (Life Technologies, Carlsbad, CA, USA), ground until the tissue was homogenized, and total RNA was purified and recovered in 100 µL of nuclease free water according to the manufacturer’s protocol. The purity and concentration of the RNA was measured with a Nanodrop 2000 UV-VIS Spectrophotometer (Agilent Technologies, Santa Clara, CA, USA) using samples with a A260/280 purity ratio of 2.0 ± 0.1. RNA was stored at −80 °C pending further processing.

2.3. Amplification and Labeling of mRNA

Amplification and labeling of the mRNA was completed using the Agilent two-color Low Input Quick Amp Labeling Kit (Agilent Technologies, Inc., Santa Clara, CA, USA). To summarize, 200–400 ng of total RNA was added with a T7 Promoter Primer for cDNA synthesis, then the labeled cRNA was synthesized and purified. cRNA and dye concentrations were determined by spectrophotometry. Specific activity of labeled cRNA was determined according to the manufacturer’s protocol and a specific activity of at least 8 OD was used for microarray analysis.

2.4. Hybridization and Scanning of the Microarray Chip

Helicoverpa armigera microarray slides (Agilent Technologies) used for transcriptome profiling were developed by Dr. Heiko Vogel (Max Plank Institute for Chemical Ecology, Jena, Germany) [28]. Each microarray had four arrays per chip, each containing 44,000 oligonucleotides with approximately 27,000 putative gene targets. Following Agilent protocols, samples were added with fragmentation and hybridization buffers and pipetted onto a gasket slide covering each Agilent array. The chip and cRNA samples were incubated together at 65 °C for 17 h. Following hybridization, the microarray chips were treated twice with Gene Expression (GE) wash buffer and once with GE Wash Buffer 2 containing 0.01% wash buffer additive according to the manufacturer’s protocol. The slides were then dipped in an acetonitrile dip and Agilent Drying Solution to prevent oxidation by ozone.
The arrays were then immediately scanned with a GenePix Personal 4100 Microarray Scanner (Axon Instruments Inc., Forster City, CA, USA) following the protocol described by Musser et al. (2012) [29]. The arrays were scanned at 5.0 µm to elucidate the best image with photomultiplier tube (PMT) gain adjusted to maximize the total number of features to measure and was normalized on a genomic scale for the dyes to have a 1:1 ratio and further normalized using GeneSifter software (Geospiza, PerkinElmer, Inc.) [30].

2.5. Microarray Experimental Design and Analysis

To detect and quantify gene expression, samples were arranged as four biological replicates on microarrays and dyes were reversed using a replicated loop design (6) as follows: array one—Virus 4 (Cy-5) vs. Control 2 (Cy-3), array two—Virus 3 (Cy-5) vs. Control 1 (Cy-3), array three—Virus 2 (Cy-3) vs. Control 4 (Cy-5), and array four—Virus 1 (Cy-3) vs. Control 3 (Cy-5). Data collected from each experiment was uploaded to the GeneSifterTM software. The data was log-transformed and scaled across all microarrays. A Benjamini-Hochberg corrected two-sample t-test (p < 0.05) was used as a statistical correction that controls the familywise error rate in multiple hypotheses testing for microarray studies [31]. Genes that were found to be significantly up- or down-regulated were sorted into functional groups and gene groups based on literature searches.

2.6. Primer Design and qRT-PCR

Quantitative real-time polymerase chain reaction was performed on selected genes in four biological replicates using the Verso cDNA Synthesis Kit and Fast SYBR Green Master Mix following the manufacturer’s protocol and described by Musser et al. (2012) [29] to validate and expand the microarray data set using the same RNA sample previously isolated as described. Selected template cDNA primers were targeted at the 3' end of each gene. qRT-PCR data was analyzed by the ΔΔCt method to determine the magnitude of up- or down-regulation for each gene tested between mock and experimentally infected larvae [32]. Genes of interest were also compared against an endogenous control gene, eukaryotic initiation factor 5c (EIF5c), using the Applied Biosystems Step-One Plus qPCR system (Applied Biosystems by Life Technologies). EIF5c was selected as the endogenous control gene based on the stability of its expression from the microarray and qRT-PCR results. The primers used can be found in Table 1.
Table
Table 1. Primers designed to verify gene regulation in the gut epithelium.
Table 1. Primers designed to verify gene regulation in the gut epithelium.
Gene Identifier 1Gene NameForward PrimerReverse Primer
AAL34109.1Alpha-amylase5'-accgttggcgtcaaatctac-3'5'-ggagctgctgtagtggtcgt-3'
AAT08964.1Cytochrome P450 (CYP)5'-gttggatcccattcagtgct-3'5'-ctggctcttgagatgctggt-3'
EEB16964.1Glucose Dehydrogenase (GDH)5'-tgactgtccaagactggtg-3'5'-atcgctccgctctttctccta-3'
AAZ52554.1Prophenoloxidase Subunit 2 (PROPO)5'-gcctaccagttgttcgttat-3'5'-agggtactttctgtccttcag-3'
AAO16241.1Effector Caspase (ECAS)5'-caagccagagaacctgtggt-3'5'-gaagcagaaggtgagccatc-3'
ACL51928.1Lysozyme (LYZ)5'-atgagttgaggaggcaagga-3'5'-gcccactttgtctgtcttcc-3'
ACD74811.1Eukaryotic Initiation Factor 5c5'-agaggttcgtcgagtggcta-3'5'-agcctcactggctgctctta-3'
1 Gene identifiers correspond to the reference numbers specified by microarray analysis.

3. Results and Discussion

3.1. Ontology of Differentially-Regulated Genes in Response to Baculovirus Infection

The transcriptome of the gut epithelial tissue of H. zea infected per os with HzSNPV was analyzed by microarray 24 h post infection. 1,138 genes were significantly altered (p < 0.05) by baculovirus infection. Of the 1,138 genes, 748 genes were annotated and sorted (Figure 1 and Figure 2, Table 2 and Supplementary Table S1). Figure 1 and Figure 2 offer a survey of differentially regulated genes that were sorted based on ontology among those with defined function.
Insects 04 00506 g001 1024
Figure 1. Global gene expression profile of the gut epithelium of Helicoverpa zea infected with HzSNPV. Percentages shown in the pie chart represent the percent of genes altered in each group out of the 1,138 genes altered in this study.
Figure 1. Global gene expression profile of the gut epithelium of Helicoverpa zea infected with HzSNPV. Percentages shown in the pie chart represent the percent of genes altered in each group out of the 1,138 genes altered in this study.
Insects 04 00506 g001
Insects 04 00506 g002 1024
Figure 2. Number of genes stimulated or repressed due to viral infection associated with specific gene groups. Groups shown were most affected 24 h post infection in the gut epithelium.
Figure 2. Number of genes stimulated or repressed due to viral infection associated with specific gene groups. Groups shown were most affected 24 h post infection in the gut epithelium.
Insects 04 00506 g002
Table
Table 2. Identified genes from the gut epithelium infected with HzSNPV pertaining to apoptosis, detoxification, and immunity with fold change and NCBI reference sequence indicated. The data listed represents the significant (Benjamini-Hochberg corrected t-test, p < 0.05) fold change in gene expression.
Table 2. Identified genes from the gut epithelium infected with HzSNPV pertaining to apoptosis, detoxification, and immunity with fold change and NCBI reference sequence indicated. The data listed represents the significant (Benjamini-Hochberg corrected t-test, p < 0.05) fold change in gene expression.
Gene classification/nameFold changeGene Identifier
Apoptosis
 Caspase short class−1.97XP_320581.3
 CG10641-PA2.41XP_624640.1
 Daxx-like protein2.67XP_973237.1
 Death related ced-3/Nedd2-like protein; Initiator caspase−1.92NP_001108337.1
 Death related ced-3/Nedd2-like protein; Initiator caspase−1.65NP_001108337.1
 Death related ced-3/Nedd2-like protein; Initiator caspase−1.35NP_001108337.1
 Death related ced-3/Nedd2-like protein; Initiator caspase−1.24NP_001108337.1
 Effector caspase; SI-caspase-1−2.57AAO16241.1
 Survivin−1.86XP_001662572.1
Detoxification
 Cytochrome P450−8.26XP_0010604810.1
 Cytochrome P450−6.82XP_0010604810.1
 Cytochrome P450−3.59XP_0010604810.1
 Cytochrome P450−16.09NP_001104007.1
 Cytochrome P450−11.02NP_001104007.1
 Cytochrome P450 CYP4S1−6.88ABU88427.1
 Cytochrome P450 monooxygenase −5.41NP_001104007.1
 GA10313-PA3.22XP_001601512.1
 Glutathione S-transferase3.39AAL23839.1
 Glutathione S-transferase−9.38ABU88426.1
 Glutathione S-transferase GSTX01−11.14ABK29516.1
 Glutathione S-transferase 1−8.69P46430.1
Insect Immunity
 Adhesion-like transmembrane protein2.61CAB65413.1
 H. armigera cecropin-D (HacD)2.49AAX51193.1
 Hemolymph proteinase 184.41AAZ52554.1
 M-like protein5.07YP_313517.1
 Prophenoloxidase subunit 25.46ABF18489.1
 Toll-interacting protein1.66XP_975168.1

3.2. Apoptosis

Apoptosis-related transcripts in the gut epithelium represented <1% (11 genes) (Table 2 and Table S1). HzSNPV infection altered these groups by down-regulating more than half (7) of those identified as differentially regulated.

3.3. Cellular Maintenance and Signaling

10% (115) of the genes shown to be differentially regulated in response to baculovirus infection related to cellular function, and of these, approximately 2/3 were down-regulated (Figure 2, Table 2 and Table S1). These included genes such as cyclin and cyclin-activating kinases, transporters and cell membrane constituents, as well as those with defined roles in signal transduction such as chemosensory proteins. Genes responsible for cell maintenance and signaling constituted 69% (67) of the genes. The remaining genes related to energy metabolism were almost universally down-regulated (25 genes or 96%).

3.4. Chitin Binding

Following infection, 16 genes (100%) associated with chitin binding were found to be substantially repressed following baculovirus infection (Table S1). Chitin deacetylase, chitin binding domains, cuticle proteins, and peritrophic membrane genes were repressed due to viral infection. The peritrophic matrix is present, particularly in Lepidopterans, to serve as a barrier to crystalline toxins, various anti-nutritive enzymes, and pathogenic infections. However, through a long evolutionary history with their hosts, baculoviruses including, but not limited to HzSNPV, have successfully acquired genes through horizontal gene transfer [33]. Baculoviruses were able to obtain genes like chitinase, which is an enzyme that breaks down chitin and is a main constituent of the peritrophic matrix [33]. Two genes (Table S1) coding for insect intestinal mucin 3, responsible for gut chitin binding and the regeneration of damaged areas of the peritrophic compartment, were found to be down-regulated approximately 4 and 6 fold, respectively, during infection. Poor membrane integrity may allow the virus to translocate more efficiently from the gut within the host.

3.5. Detoxification

Two major classes of detoxification enzymes (Table 2 and Table S1) were altered following infection, specifically cytochrome p450’s (CYP) and glutathione S-transferases (GST). 90.9% (40 genes) in the gut epithelium were down-regulated. 28 CYP genes ranged from a 3.9 fold increase to a down-regulation of 23.2. Infection also led to the suppression of 3 GST-related genes between 8 and 11 fold, and the induction of one by approximately 3-fold. Other genes broadly relating to detoxification were down-regulated including alkaline phosphatase 1 and 2, and one gene for hemolysin-type calcium-binding protein (Table S1).
Our array results further argue for the production or presence of cytotoxic compounds by 24 h post infection. Some baculoviruses produce conotoxin-like compounds, which are disulfide-rich ion channel antagonists [34,35,36]. These are toxin homologs that act on ion channels and inhibit proper function of the various sodium, potassium, calcium, and/or voltage-dependent ion channels, which are supported by the noted up-regulation of various ion transporters described in the cellular function section. Another possible explanation for the presence of detoxification-related compounds such as cytochrome p450 and GST is viral-mediated breakdown of cellular components, such as the endocytic vesicles, or other cytolytic activities prompting such a response from either affected or neighboring cells.
It has been suggested that cytochrome P450’s are responsible for toxin degradation and general detoxification, whereas glutathione S-transferase genes are responsible for intracellular detoxification and aid in the resistance of insecticides [37,38]. Cytochrome P450’s, in generalist polyphagous insects like H. zea, are speculated to have very broad ranges of specificity for environmental and microbial resistance. Not only can these insects feed on many plants, but the series of cytochrome P450’s allows them to resist microbial toxins, which include conotoxins and conotoxin-like homologs. The class of glutathione S-transferase genes is associated with the degradation of insecticides and is efficient at detoxifying pyrethroids [38]. The gut epithelium has several genes that function in intracellular detoxification such as glutathione S-transferase; broad down-regulation among these could potentially be attributed to the virus antagonizing various cell transporters during infection.

3.6. Digestive Function

A large number of genes relating to insect metabolism and digestion were significantly altered in response to viral infection. Of the 289 differentially regulated genes in the digestive category (Table S1), the vast majority (93%) were down-regulated. 128 genes that code for proteases and protein-turnover-related proteins were among those significantly different, whereas 52 play known roles in carbohydrate utilization. Ten percent of those genes identified as differentially regulated were related to insect metabolism; these exhibited a similar trend of down-regulation in response to baculovirus infection. Among these metabolism related genes were those including various dehydrogenases, lyases, and lipases associated with sugar, amino acid, and fatty acid synthesis. Overall digestive and metabolic function of the gut epithelium was considerably affected by viral infection (Figure 1), which showed a combined 90% down-regulation among those genes that were differentially regulated in response to viral infection. The large number of genes altered in the gut is likely indicative of this tissue as a site of primary infection. These results, demonstrating a breadth of the digestion-related genes, differ from those of Breitenbach et al., which may reflect the different tissue (hemocytes versus gut epithelium) used in that study, differences in timing (12 versus 24 h), or a combination thereof [20].

3.7. Immunity

Of the identified differentially-regulated genes, 4% (39 genes) of these have been implicated in insect immunity (Table 2 and Table S1). The majority (69%) of these immunity-related transcripts were shown to be repressed in response to baculovirus infection. Important genes for humoral immunity were both up- and down-regulated. Innate and humoral immunity, specifically antibacterial protein and antimicrobial peptide binding genes, were repressed while antiviral genes prophenoloxidase and Helicoverpa armigera cecropin-D (HacD) were up-regulated. Toll pathway genes, surface antigen ariel1 genes, and hemolymph protease genes, all of which are immune reactive genes, were stimulated over 2.2 fold in the gut. Genes for encapsulation were found to be alternatively up- or down-regulated, depending on the specified transcript.
Insects mount an immune response to pathogens that shares limited similarities with that of mammals. We observed a pronounced down-regulation of genes in the gut associated with immunity and the host response to pathogens. Again, this is due to the site of infection in synergy with the time point. In insects, the largest portion of the immunity-related genes that target viruses is located in the gut epithelium, where an insect can rid itself of a virus by activating pro-apoptotic signaling, thus passing apoptotic cells and vesicles through the digestive tract [39]. The gut acts as the center for signaling cascades that can induce further immune response throughout the organism in order to ensure stability of the gut for digestion, as well as ensure survival of the organism [39]. These findings broadly agree with those of Nguyen, et al. who documented alterations of those genes involved in the TOLL signaling pathway, caspases, and adhesion-related genes [27]. Additionally, studies by Shelby and Popham in 2008 showed the alteration of gram negative bacteria recognition proteins, as well as, the alteration in macrophage migration inhibitory factors, both of which are seen here [40].

3.8. Virus Related Replication/Physiology Alteration/Endogenous Retroviral Intrusions

Differentially expressed transcripts associated with endogenous retroviral intrusions (errantiviruses) or retro-transposon-like elements were detected in the microarray analysis, as was a selection of host genes that are thought to be exploited by the virus to facilitate its replication cycle (Table S1). A number of genes involved in insect development and life cycle changes were differentially transcribed, as has been well documented in prior reports [20,27]. Half of these genes (54%, or 14 genes) were up-regulated following infection. Among the host genes associated with viral replication that were differentially regulated were DEAD H- and X-Box helicases, ribonucleoside-diphosphate reductase large chain, and retroelement polyproteins. Several genes responsible for baculovirus-mediated suppression of ecdysteroids and encoding baculovirus-specific chitin-binding proteins represented 10 of these genes, or 1.3%.

3.9. Quantitative Real Time-Polymerase Chain Reaction

Several genes of interest were analyzed by qRT-PCR in order to validate and extend response in gut epithelium to viral infection (Figure 3). The data confirm transcriptional repression of alpha amylase, cytochrome P450, effector caspase, and glucose dehydrogenase, while prophenoloxidase was stimulated, also in agreement with the DNA microarray data (p < 0.05, Benjamini-Hochberg).
Insects 04 00506 g003 1024
Figure 3. Relative fold changes (y-axis) in expression of alpha-amylase (AAM), cytochrome P450 (CYP), effector caspase (ECAS), glucose dehydrogenase (GDH), lysozyme (LYZ), and prophenoloxidase (PROPO). These data indicate the relationship between these genes and the fold change expressed between mock and virus infected treatments.
Figure 3. Relative fold changes (y-axis) in expression of alpha-amylase (AAM), cytochrome P450 (CYP), effector caspase (ECAS), glucose dehydrogenase (GDH), lysozyme (LYZ), and prophenoloxidase (PROPO). These data indicate the relationship between these genes and the fold change expressed between mock and virus infected treatments.
Insects 04 00506 g003

4. Conclusions

The transcriptional profile of H. zea gut epithelial tissue was analyzed by DNA microarray 24 h following viral infection and compared to that of uninfected tissues. The gut epithelium is a tissue that, by virtue of its function, undergoes dynamic changes in transcription during different life stages, diet and feeding conditions, and exposure to environmental hazards such as pathogens or toxins [41,42,43]. It is generally accepted that the gut is the site of primary baculovirus infection, and our analyses reveal a rapidly evolving reaction by the host to respond offensively to the virus, as well as virus manipulation of the host defense and cellular machinery to propagate itself at the expense of the insect [44,45,46]. These findings are supported by those seen by Breitenbach et al. [20] and Nguyen et al. [27], where both analyzed Heliothis virescens or H. zea transcriptional responses to similar baculoviruses, HzSNPV or Helicoverpa armigera nucleopolyhedrovirus (HearNPV), respectively. Importantly, as well as being the first report on H. zea gut global transcription in response to baculovirus infection, these data complement those of the other groups, who focused on hemocytes in H. virescens or cell line cultures of H. zea, and careful comparison may provide insights into how these vastly different tissues both respond to, and are exploited by, the replicating virus.
In agreement with extensive research in baculovirus-mediated suppression of the insect’s apoptotic pathway(s), our results likewise demonstrate the extent and magnitude of the effect of baculovirus inhibitors of apoptosis [19,47,48,49,50]. Over half of the apoptotic genes analyzed were suppressed; some genes related to apoptosis, however, were up-regulated. Most notably, in the gut epithelium (Table 2) short class caspase, initiator caspase (DREDD), and effector caspase were all repressed in response to viral infection. Baculoviruses, including HzSNPV, inhibit the efficacy of the caspase, which are enzymes that promote the apoptotic program of planned cell death. Survivin (Table 2) works in tandem with viral-encoded apoptotic inhibitors as it acts as an inhibitor of apoptosis proteins (iaps) [51,52]. While the vast majority of the genes in this group for the gut epithelium were repressed, we detected a number that were up-regulated, such as DAXX-like protein. While it remains incompletely characterized, this protein is thought to play a crucial role in cell survival signaling [53,54,55]. Therefore, the higher expression levels of DAXX-like protein observed in this study suggests the stimulation of the anti-apoptosis regulation, which in turn, prolongs the infectivity of HzSNPV throughout its infection cycles. The observation of a number of up-regulated genes related to apoptosis likely points to the relatively early 24 h time point at which these tissues were harvested; the general outcome and hallmark of lethal infection is a global suppression of the apoptotic response, allowing the virus to disseminate within and without the hemoceol by later times post infection. Our work also reinforces the extent to which the virus modulates the life cycle and development of the insect during its natural history of infection, demonstrating hormone suppression, specifically found in phenol UDP-glucosyltransferase (Table 2 and Table S1), that functions to suppress ecdysteroids [56,57]. This functionally slows, or stops the progression of molting/pupating, thus allowing the virus to prolong infection and produce more environmentally stable polyhedra. Other notable genes involved in viral exploitation of host function include DEAD Box RNA helicase genes, which aid in viral replication [58,59]. HzSNPV, as well as other baculoviruses, alter eukaryotic initiation factors in the cells they manipulate [60,61]. Also of significance was the observation of a generalized inhibition of several key metabolic pathways that function in energy storage and utilization. Whereas healthy larvae move metabolites and digestive products efficiently from the midgut into the hemocel for storage in the fat body, the nearly global inhibition of these processes, including glucose and other sugar utilization, fatty acid metabolism, and amino acid trafficking offer additional insights as to the degree to which baculoviruses alter host behavior at the molecular level to promote their replication and spread at the expense of the host.
Endogenous retrotransposon and retrovirus-like genes were detected in this microarray study. These genes are related to the evolutionary histories of insects and retroviral elements that have been assimilated into the host genome [62,63]. These genes generally code for gag-pol repeat proteins, as well those identified as retroelement polypeptides and reverse transcriptase, findings that agree with previous analysis of other tissues in infected HzSNPV [20]. It remains poorly understood how baculovirus infection stimulates retroviral reactivation and/or retrotransposon activity; given the large number of transposable elements found in these and other insects, it is quite likely that a combination of direct stimulation by baculovirus transcriptional transactivators and cellular transactivators in the infected cells both play a role in mobilizing these otherwise quiescent elements [64].
Taken together, these results demonstrate the degree to which lethal HzSNPV infection modulates the gut epithelium of its natural host, and adds to an evolving picture of virus-mediated transcriptional regulation during the natural history of infection by baculoviruses. Our real-time qRT-PCR results confirm the validity of a sampling of those genes that were identified in our microarray, and further analysis of baculovirus transcriptional targets may provide new insights as to how this and closely related baculoviruses have evolved to exploit host machinery, as well as identify cellular pathways and effector molecules that may suppress replication and allow for host escape from mortal infection.

Supplementary Files

Supplementary File 1

Acknowledgments

This work was supported by the USDA Agricultural Research Service. Mention of trade names or commercial products in this article is solely for the purpose of providing specific information and does not imply recommendation or endorsement by the U.S. Department of Agriculture. All programs and services of the U.S. Department of Agriculture are offered on a nondiscriminatory basis without regard to race, color, national origin, religion, sex, age, marital status, or handicap. Funding was provided in part for this project by the National Science Foundation Plant Genome Research Initiative (No. 0820367 to ROM and SMH).

Conflicts of Interest

The authors declare no conflict of interest.

References

  1. Kozlov, E.A.; Levitina, T.L.; Gusak, N.M. The primary structure of baculovirus inclusion body proteins. Evolution and structure-function aspects. Curr. Top. Microbiol. Immunol. 1986, 131, 135–164. [Google Scholar] [CrossRef]
  2. Rohrmann, G.F.; Pearson, M.N.; Bailey, T.J.; Becker, R.R.; Beaudreau, G.S. N-Terminal polyhedrin sequences and occluded Baculovirus evolution. J. Mol. Evol. 1981, 17, 329–333. [Google Scholar] [CrossRef]
  3. Wang, Y.; Jehle, J.A. Nudiviruses and other large, double-stranded circular DNA viruses of invertebrates: New insights on an old topic. J. Invertebr. Pathol. 2009, 101, 187–193. [Google Scholar] [CrossRef]
  4. Shim, H.J.; Choi, J.Y.; Wang, Y.; Tao, X.Y.; Liu, Q.; Roh, J.Y.; Kim, J.S.; Kim, W.J.; Woo, S.D.; Jin, B.R.; Je, Y.H. NeuroBactrus, a novel, highly effective, and environmentally friendly recombinant baculovirus insecticide. Appl. Environ. Microbiol. 2013, 79, 141–149. [Google Scholar] [CrossRef]
  5. Gramkow, A.W.; Perecmanis, S.; Sousa, R.L.; Noronha, E.F.; Felix, C.R.; Nagata, T.; Ribeiro, B.M. Insecticidal activity of two proteases against Spodoptera frugiperda larvae infected with recombinant baculoviruses. Virology J. 2010, 7. [Google Scholar] [CrossRef]
  6. Jakubowska, A.K.; Vogel, H.; Herrero, S. Increase in gut microbiota after immune suppression in baculovirus-infected larvae. PLoS Pathog. 2013, 9, e1003379. [Google Scholar] [CrossRef]
  7. Jayachandran, B.; Hussain, M.; Asgari, S. RNA interference as a cellular defense mechanism against the DNA virus baculovirus. J. Virol. 2012, 86, 13729–13734. [Google Scholar] [CrossRef]
  8. Mitchell, J.K.; Friesen, P.D. Baculoviruses modulate a proapoptotic DNA damage response to promote virus multiplication. J. Virol. 2012, 86, 13542–13553. [Google Scholar] [CrossRef]
  9. Hammock, B.D.; McCutchen, B.F.; Beetham, J.; Choudary, P.V.; Fowler, E.; Ichinose, R.; Ward, V.K.; Vickers, J.M.; Bonning, B.C.; Harshman, L.G.; et al. Development of recombinant viral insecticides by expression of an insect-specific toxin and insect-specific enzyme in nuclear polyhedrosis viruses. Arch. Insect Biochem. Physiol. 1993, 22, 315–344. [Google Scholar] [CrossRef]
  10. Menn, J.J. Current trends and new directions in crop protection. Am. J. Ind. Med. 1990, 18, 499–504. [Google Scholar] [CrossRef]
  11. Jehle, J.A.; Blissard, G.W.; Bonning, B.C.; Cory, J.S.; Herniou, E.A.; Rohrmann, G.F.; Theilmann, D.A.; Thiem, S.M.; Vlak, J.M. On the classification and nomenclature of baculoviruses: A proposal for revision. Arch. Virol. 2006, 151, 1257–1266. [Google Scholar] [CrossRef]
  12. Braunagel, S.C.; Summers, M.D. Molecular biology of the baculovirus occlusion-derived virus envelope. Curr. Drug Targets 2007, 8, 1084–1095. [Google Scholar] [CrossRef]
  13. Slack, J.; Arif, B.M. The baculoviruses occlusion-derived virus: Virion structure and function. Adv. Virus Res. 2007, 69, 99–165. [Google Scholar] [CrossRef]
  14. Volkman, L.E. Nucleopolyhedrovirus interactions with their insect hosts. Adv. Virus Res. 1997, 48, 313–348. [Google Scholar] [CrossRef]
  15. Cory, J.S.; Hails, R.S. The ecology and biosafety of baculoviruses. Curr. Opin. Biotechnol. 1997, 8, 323–327. [Google Scholar] [CrossRef]
  16. Blissard, G.W.; Rohrmann, G.F. Baculovirus diversity and molecular biology. Annu. Rev. Entomol. 1990, 35, 127–155. [Google Scholar] [CrossRef]
  17. Clem, R.J. The role of apoptosis in defense against baculovirus infection in insects. Curr. Top. Microbiol. Immunol. 2005, 289, 113–129. [Google Scholar] [CrossRef]
  18. Clarke, T.E.; Clem, R.J. Insect defenses against virus infection: The role of apoptosis. Int. Rev. Immunol. 2003, 22, 401–424. [Google Scholar] [CrossRef]
  19. Clem, R.J. Baculoviruses and apoptosis: The good, the bad, and the ugly. Cell Death Differ. 2001, 8, 137–143. [Google Scholar] [CrossRef]
  20. Breitenbach, J.E.; Shelby, K.S.; Popham, H.J.R. Baculovirus induced transcripts in hemocytes from the larvae of Heliothis virescens. Viruses 2011, 3, 2047–2064. [Google Scholar] [CrossRef]
  21. Huang, L.; Cheng, T.; Xu, P.; Fang, T.; Xia, Q. Bombyx mori transcription factors: Genome-wide identification, expression profiles and response to pathogens by microarray analysis. J. Insect Sci. 2012. [Google Scholar] [CrossRef]
  22. Yamagishi, J.; Burnett, E.D.; Harwood, S.H.; Blissard, G.W. The AcMNPV pp31 gene is not essential for productive AcMNPV replication or late gene transcription but appears to increase levels of most viral transcripts. Virology 2007, 365, 34–47. [Google Scholar] [CrossRef]
  23. Fujita, R.; Matsuyama, T.; Yamagishi, J.; Sahara, K.; Asano, S.; Bando, H. Expression of Autographa californica multiple nucleopolyhedrovirus genes in mammalian cells and upregulation of the host beta-actin gene. J. Virol. 2006, 80, 2390–2395. [Google Scholar] [CrossRef]
  24. Ote, M.; Mita, K.; Kawasaki, H.; Daimon, T.; Kobayashi, M.; Shimada, T. Identification of molting fluid carboxypeptidase A (MF-CPA) in Bombyx mori. Comp. Biochem. Physiol. B Biochem. Mol. Biol. 2005, 141, 314–322. [Google Scholar] [CrossRef]
  25. Chen, Y.R.; Zhong, S.; Fei, Z.; Hashimoto, Y.; Xiang, J.Z.; Zhang, S.; Blissard, G.W. The transcriptome of the baculovirus Autographa californica multiple nucleopolyhedrovirus in Trichoplusia ni cells. J. Virol. 2013, 87, 6391–6405. [Google Scholar] [CrossRef]
  26. Choi, J.Y.; Roh, J.Y.; Wang, Y.; Zhen, Z.; Tao, X.Y.; Lee, J.H.; Liu, Q.; Kim, J.S.; Shin, S.W.; Je, Y.H. Analysis of genes expression of Spodoptera exigua larvae upon AcMNPV infection. PLoS One 2012, 7, e42462. [Google Scholar] [CrossRef]
  27. Nguyen, Q.; Palfreyman, R.W.; Chan, L.C.; Reid, S.; Nielsen, L.K. Transcriptome sequencing of and microarray development for a Helicoverpa zea cell line to investigate in vitro insect cell-baculovirus interactions. PLoS One 2012, 7, e36324. [Google Scholar]
  28. Celorio-Mancera, M.P.; Ahn, S.-J.; Vogel, H.; Heckel, D.G. Transcriptional responses underlying the hormetic and detrimental effects of the plant secondary metabolite gossypol on the generalist herbivore Helicovepa armigera. BMC Genomics 2011, 12. [Google Scholar] [CrossRef]
  29. Musser, R.O.; Hum-Musser, S.M.; Lee, H.K.; Des Rochers, B.L.; Williams, S.A.; Vogel, H. Caterpillar labial saliva alters tomato plant gene expression. J. Chem. Ecol. 2012, 38, 1381–1401. [Google Scholar]
  30. PerkinElmer, Inc. “geospiza”. Available online: http://www.geospiza.com/index.shtml/ (accessed on 1 January 2012).
  31. Klipper-Aurbach, Y.; Wasserman, M.; Braunspiegel-Weintrob, N.; Borstein, D.; Peleg, S.; Assa, S.; Karp, M.; Benjamini, Y.; Hochberg, Y.; Laron, Z. Mathematical formulae for the prediction of the residual beta cell function during the first two years of disease in children and adolescents with insulin-dependent diabetes mellitus. Med. Hypotheses 1995, 45, 486–490. [Google Scholar] [CrossRef]
  32. Bustin, S.A.; Benes, V.; Garson, J.A.; Hellemans, J.; Huggett, J.; Kubista, M.; Mueller, R.; Nolan, T.; Pfaffl, M.W.; Shipley, G.L.; Vandesompele, J.; Wittwer, C.T. The MIQE guidelines: Minimum information for publication of quantitative real-time PCR experiments. Clin. Chem. 2009, 55, 611–622. [Google Scholar] [CrossRef]
  33. Hughes, A.L.; Friedman, R. Genome-wide survey for genes horizontally transferred from cellular organisms to baculoviruses. Mol. Biol. Evol. 2003, 20, 979–987. [Google Scholar] [CrossRef]
  34. McIntosh, J.M.; Hasson, A.; Spira, M.E.; Gray, W.R.; Li, W.; Marsh, M.; Hillyard, D.R.; Olivera, B.M. A new family of conotoxins that blocks voltage-gated sodium channels. J. Biol. Chem. 1995, 270, 16796–16802. [Google Scholar] [CrossRef]
  35. Nie, Z.M.; Zhang, Z.F.; Wang, D.; He, P.A.; Jiang, C.Y.; Song, L.; Chen, F.; Xu, J.; Yang, L.; Yu, L.L.; et al. Complete sequence and organization of Antheraea pernyi nucleopolyhedrovirus, a dr-rich baculovirus. BMC Genomics 2007. [Google Scholar] [CrossRef]
  36. Faulkner, P.; Kuzio, J.; Williams, G.V.; Wilson, J.A. Analysis of p74, a PDV envelope protein of Autographa californica nucleopolyhedrovirus required for occlusion body infectivity in vivo. J. Gen. Virol. 1997, 78, 3091–3100. [Google Scholar]
  37. Zeng, R.S.; Wen, Z.; Niu, G.; Schuler, M.A.; Berenbaum, M.R. Enhanced toxicity and induction of cytochrome P450s suggest a cost of “eavesdropping” in a multitrophic interaction. J. Chem. Ecol. 2009, 35, 526–532. [Google Scholar] [CrossRef]
  38. Kostaropoulos, I.; Kalmanti, D.; Theodoropoulou, B.; Loumbourdis, N.S. Effects of exposure to a mixture of cadmium and chromium on detoxification enzyme (GST, P450-MO) activities in the frog Rana ridibunda. Ecotoxicology 2005, 14, 439–447. [Google Scholar] [CrossRef]
  39. Schmid-Hempel, P. Evolutionary ecology of insect immune defenses. Annu. Rev. Entomol. 2005, 50, 529–551. [Google Scholar] [CrossRef]
  40. Shelby, K.S.; Popham, H.J.R. Cloning and characterization of the secreted hemocytic prophenoloxidases of Heliothis virescens. Arch. Insect Biochem. Physiol. 2008, 69, 127–142. [Google Scholar]
  41. Chamberlin, M.E. Changes in mitochondrial electron transport chain activity during insect metamorphosis. Am. J. Physiol. Regul. Integr. Comp. Physiol. 2007, 292, R1016–R1022. [Google Scholar] [CrossRef]
  42. Micchelli, C.A.; Perrimon, N. Evidence that stem cells reside in the adult Drosophila midgut epithelium. Nature 2006, 439, 475–479. [Google Scholar] [CrossRef]
  43. Braun, L.; Keddie, B.A. A new tissue technique for evaluating effects of Bacillus thuringiensis toxins on insect midgut epithelium. J. Invert. Pathol. 1997, 69, 92–104. [Google Scholar] [CrossRef]
  44. Rahman, M.M.; Gopinathan, K.P. Systemic and in vitro infection process of Bombyx mori nucleopolyhedrovirus. Virus Res. 2004, 101, 109–118. [Google Scholar] [CrossRef]
  45. Haas-Stapleton, E.J.; Washburn, J.O.; Volkman, L.E. Pathogenesis of Autographa californica M nucleopolyhedrovirus in fifth instar Spodoptera frugiperda. J. Gen. Virol. 2003, 84, 2033–2040. [Google Scholar] [CrossRef]
  46. Granados, R.R.; Lawler, K.A. In vivo pathway of Autographa californica baculovirus invasion and infection. Virology 1981, 108, 297–308. [Google Scholar] [CrossRef]
  47. Clem, R.J. Baculoviruses and apoptosis: A diversity of genes and responses. Curr. Drug Targets 2007, 8, 1069–1074. [Google Scholar] [CrossRef]
  48. Bushell, M.; McKendrick, L.; Janicke, R.U.; Clemens, M.J.; Morley, S.J. Caspase-3 is necessary and sufficient for cleavage of protein synthesis eukaryotic initiation factor 4G during apoptosis. FEBS Lett. 1999, 451, 332–336. [Google Scholar] [CrossRef]
  49. Clem, R.J.; Miller, L.K. Apoptosis reduces both the in vitro replication and the in vivo infectivity of a baculovirus. J. Virol. 1993, 67, 3730–3738. [Google Scholar]
  50. Miller, L.K. Baculovirus interaction with host apoptotic pathways. J. Cell. Physiol. 1997, 173, 178–182. [Google Scholar] [CrossRef]
  51. Chiou, S.K.; Jones, M.K.; Tarnawski, A.S. Survivin—An anti-apoptosis protein: Its biological roles and implications for cancer and beyond. Med. Sci. Mon. Int. Med. J. Exp. Clin. Res. 2003, 9, PI25–PI29. [Google Scholar]
  52. O'Driscoll, L.; Linehan, R.; Clynes, M. Survivin: Role in normal cells and in pathological conditions. Curr. Cancer Drug Targets 2003, 3, 131–152. [Google Scholar] [CrossRef]
  53. Dionne, K.R.; Zhuang, Y.; Leser, J.S.; Tyler, K.L.; Clarke, P. Daxx upregulation within the cytoplasm of reovirus-infected cells is mediated by interferon and contributes to apoptosis. J. Virol. 2013, 87, 3447–3460. [Google Scholar] [CrossRef]
  54. Yang, X.; Khosravi-Far, R.; Chang, H.Y.; Baltimore, D. Daxx, a novel Fas-binding protein that activates JNK and apoptosis. Cell 1997, 89, 1067–1076. [Google Scholar] [CrossRef]
  55. Zobalova, R.; Swettenham, E.; Chladova, J.; Dong, L.F.; Neuzil, J. Daxx inhibits stress-induced apoptosis in cardiac myocytes. Redox Rep. Commun. Free Radic. Res. 2008, 13, 263–270. [Google Scholar] [CrossRef]
  56. Miller, J.E.; Levine, R.B. Steroid hormone activation of wandering in the isolated nervous system of Manduca sexta. J. Comp. Physiol. A Neuro. Sens. Neur. Behav. Physiol. 2006, 192, 1049–1062. [Google Scholar] [CrossRef]
  57. O'Reilly, D.R.; Miller, L.K. A baculovirus blocks insect molting by producing ecdysteroid UDP-glucosyl transferase. Science 1989, 245, 1110–1112. [Google Scholar]
  58. Cordin, O.; Banroques, J.; Tanner, N.K.; Linder, P. The DEAD-box protein family of RNA helicases. Gene 2006, 367, 17–37. [Google Scholar] [CrossRef]
  59. Cordin, O.; Beggs, J.D. RNA helicases in splicing. RNA Biol. 2013, 10, 83–95. [Google Scholar] [CrossRef]
  60. Berretta, M.F.; Deshpande, M.; Crouch, E.A.; Passarelli, A.L. Functional characterization of Bombyx mori nucleopolyhedrovirus late gene transcription and genome replication factors in the non-permissive insect cell line SF-21. Virology 2006, 348, 175–189. [Google Scholar] [CrossRef]
  61. Du, X.; Thiem, S.M. Responses of insect cells to baculovirus infection: Protein synthesis shutdown and apoptosis. J. Virol. 1997, 71, 7866–7872. [Google Scholar]
  62. Ludwig, A.; Valente, V.L.; Loreto, E.L. Multiple invasions of Errantivirus in the genus Drosophila. Insect Mol. Biol. 2008, 17, 113–124. [Google Scholar] [CrossRef]
  63. Terzian, C.; Pelisson, A.; Bucheton, A. Evolution and phylogeny of insect endogenous retroviruses. BMC Evolut. Biol. 2001. [Google Scholar] [CrossRef]
  64. Menzel, T.; Rohrmann, G.F. Diversity of errantivirus (retrovirus) sequences in two cell lines used for baculovirus expression, Spodoptera frugiperda and Trichoplusia ni. Virus Genes 2008, 36, 583–586. [Google Scholar] [CrossRef]

Share and Cite

MDPI and ACS Style

Noland, J.E.; Breitenbach, J.E.; Popham, H.J.R.; Hum-Musser, S.M.; Vogel, H.; Musser, R.O. Gut Transcription in Helicoverpa zea is Dynamically Altered in Response to Baculovirus Infection. Insects 2013, 4, 506-520. https://doi.org/10.3390/insects4030506

AMA Style

Noland JE, Breitenbach JE, Popham HJR, Hum-Musser SM, Vogel H, Musser RO. Gut Transcription in Helicoverpa zea is Dynamically Altered in Response to Baculovirus Infection. Insects. 2013; 4(3):506-520. https://doi.org/10.3390/insects4030506

Chicago/Turabian Style

Noland, Jeffrey E., Jonathan E. Breitenbach, Holly J. R. Popham, Sue M. Hum-Musser, Heiko Vogel, and Richard O. Musser. 2013. "Gut Transcription in Helicoverpa zea is Dynamically Altered in Response to Baculovirus Infection" Insects 4, no. 3: 506-520. https://doi.org/10.3390/insects4030506

APA Style

Noland, J. E., Breitenbach, J. E., Popham, H. J. R., Hum-Musser, S. M., Vogel, H., & Musser, R. O. (2013). Gut Transcription in Helicoverpa zea is Dynamically Altered in Response to Baculovirus Infection. Insects, 4(3), 506-520. https://doi.org/10.3390/insects4030506

Article Metrics

Back to TopTop