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Induction of reaper ortholog mx in mosquito midgut cells following baculovirus infection.

ABSTRACT: Many vertebrate and insect viruses possess antiapoptotic genes that are required for their infectivity. This led to the hypothesis that apoptosis is an innate immunoresponse important for limiting virus infections. The role of apoptosis may be especially important in insect antiviral defense because of the lack of adaptive immunity. However, the cellular mechanism that elicits apoptosis in response to viral infection in insects has not been determined. Using an in vivo infection system with the mosquito baculovirus CuniNPV (Culex nigripalpus nucleopolyhedrovirus), we demonstrated that michelob_x (mx), the mosquito ortholog of Drosophila proapoptotic gene reaper, is specifically induced in larval midgut cells following viral infection. Interestingly, the dynamics of mx induction corresponds with the outcome of the infection. In the permissive mosquito C. quinquefasciatus, a slow induction of mx failed to induce prompt apoptosis, and the infected cells eventually undergo necrosis with heavy loads of encapsulated viruses. In contrast, in the refractory mosquito Aedes aegypti, a rapid induction of mx within 30? min p.i. is followed by apoptosis within 2-6? h p.i., suggesting a possible role for apoptosis in limiting viral infection. When the execution of apoptosis was delayed by caspase inhibitors, viral gene expression became detectable in the A. aegypti larvae.

SUBMITTER: Liu B

PROVIDER: S-EPMC3172108 | biostudies-literature | 2011 Aug

REPOSITORIES: biostudies-literature

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Induction of reaper ortholog mx in mosquito midgut cells following baculovirus infection.

Liu B B Becnel J J JJ Zhang Y Y Zhou L L

Cell death and differentiation 20110218 8

Many vertebrate and insect viruses possess antiapoptotic genes that are required for their infectivity. This led to the hypothesis that apoptosis is an innate immunoresponse important for limiting virus infections. The role of apoptosis may be especially important in insect antiviral defense because of the lack of adaptive immunity. However, the cellular mechanism that elicits apoptosis in response to viral infection in insects has not been determined. Using an in vivo infection system with the ...[more]

PMID: 21331076

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Project description:Infection of lepidopterans by baculoviruses has been traditionally studied using in vitro systems which enable efficient and highly synchronous infection. Many studies using varied virus-host combinations have yielded great insight into the molecular processes by which these large double-stranded DNA viruses achieve infection of host cells. However, a key difference in the virus strategy for infection between individual hosts, and within an individual host, lies with the production of two different forms of the virus; occlusion derived virus, which enables primary infection of insect gut tissues and budded virus, which efficiently infects a variety of different insect tissues throughout the host. To examine the primary infection of midgut cells specifically, we used MacoNPV infection of Mamestra configurata fourth instar larvae as our model and measured the expression of viral genes over a time course of infection. Both digital PCR and RNA sequencing methods showed the profile of transcription to be different from those typically seen with in vitro methods, having unique collections of genes expressed early, as well as much greater expression of p6.9 and much reduced expression of polh and p10 late, in comparison with in vitro studies. These differences likely reflect unique characteristics of midgut cell infection, and provide clues as to the processes these viruses use to regulate expression of different viral forms used to access different host tissues. Baculoviruses are versatile DNA viruses with great potential both as gene therapy vehicles and as biological control tools. Extensive study of their transcriptome in vitro has yielded valuable tools for use in protein expression systems, however it is critical that we obtain a fuller understanding of their in vivo activities before their full medical and agricultural potential can be realized. In these studies we have assessed the gene expression program from a group II alphabaculovirus in the midgut of its complementary larval host and confirmed that the in vivo activities of baculoviruses are unique from what is known of their in vitro transcriptome. These studies provide a first foray with next-generation molecular tools into the characterization of baculovirus biology in vivo.

Project description:Baculoviruses are large double-stranded DNA viruses that are virulent pathogens of certain insect species. In a natural host, Trichoplusia ni, infection by the model baculovirus Autographa californica multiple nucleopolyhedrovirus (AcMNPV) begins when the occluded form of the virus disassembles in the midgut and virions infect midgut epithelial cells to establish the primary phase of the infection. To better understand the primary phase of the AcMNPV infection cycle, newly molted 5th-instar T. ni larvae were orally infected with AcMNPV occlusion bodies and the transcriptional responses of the T. ni midgut were analyzed at various times from 0 to 72 h postinfection, using transcriptome sequencing analysis and a T. ni reference genome. The numbers of differentially expressed host genes increased as the infection progressed, and we identified a total of 3,372 differentially expressed T. ni transcripts in the AcMNPV-infected midgut. Genes encoding orthologs of HMG176, atlastin, and CPH43 were among the most dramatically upregulated in response to AcMNPV infection. A number of cytochrome P450 genes were downregulated in response to infection. We also identified the effects of AcMNPV infection on a large variety of genes associated with innate immunity. This analysis provides an abundance of new and detailed information on host responses to baculovirus infection during the primary phase of the infection in the midgut and will be important for understanding how baculoviruses establish productive infections in the organism.IMPORTANCE Baculoviruses are virulent pathogens of a number of important insect pest species. In the host Trichoplusia ni, infection begins in the midgut when infectious virions of the occlusion-derived virus (ODV) phenotype enter and subsequently replicate in cells of the midgut epithelium. A second virion phenotype (budded virus [BV]) is produced there, and BV mediates systemic infection of the animal. Most prior detailed studies of baculovirus infections have focused on BV infections of cultured cells. In this study, we examined the transcriptional responses of the T. ni midgut to infection by ODV of the baculovirus AcMNPV and identified a variety of host genes that respond dramatically to viral infection. Understanding the transcriptional responses of the host midgut to viral infection is critically important for understanding the biphasic infection in the animal as a whole.

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Induction of reaper ortholog mx in mosquito midgut cells following baculovirus infection.

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Induction of reaper ortholog mx in mosquito midgut cells following baculovirus infection.

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