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Comparative Study
, 74 (10), 3251-6

Drosophila Melanogaster Mounts a Unique Immune Response to the Rhabdovirus Sigma Virus

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Comparative Study

Drosophila Melanogaster Mounts a Unique Immune Response to the Rhabdovirus Sigma Virus

C W Tsai et al. Appl Environ Microbiol.

Abstract

Rhabdoviruses are important pathogens of humans, livestock, and plants that are often vectored by insects. Rhabdovirus particles have a characteristic bullet shape with a lipid envelope and surface-exposed transmembrane glycoproteins. Sigma virus (SIGMAV) is a member of the Rhabdoviridae and is a naturally occurring disease agent of Drosophila melanogaster. The infection is maintained in Drosophila populations through vertical transmission via germ cells. We report here the nature of the Drosophila innate immune response to SIGMAV infection as revealed by quantitative reverse transcription-PCR analysis of differentially expressed genes identified by microarray analysis. We have also compared and contrasted the immune response of the host with respect to two nonenveloped viruses, Drosophila C virus (DCV) and Drosophila X virus (DXV). We determined that SIGMAV infection upregulates expression of the peptidoglycan receptor protein genes PGRP-SB1 and PGRP-SD and the antimicrobial peptide (AMP) genes Diptericin-A, Attacin-A, Attacin-B, Cecropin-A1, and Drosocin. SIGMAV infection did not induce PGRP-SA and the AMP genes Drosomycin-B, Metchnikowin, and Defensin that are upregulated in DCV and/or DXV infections. Expression levels of the Toll and Imd signaling cascade genes are not significantly altered by SIGMAV infection. These results highlight shared and unique aspects of the Drosophila immune response to the three viruses and may shed light on the nature of the interaction with the host and the evolution of these associations.

Figures

FIG. 1.
FIG. 1.
SIGMAV infection (green fluorescence) in the compound eye (ce), brain (br), other nerve ganglia (ng), and nerves (ne) in the head of an infected Drosophila (A) compared to that of a noninfected fly (B). In each case, the head was split transversely to expose internal structures and immediately fixed and processed for iCLSM using SIGMAV antiserum as a primary antibody, Alexa Fluor 488 as a secondary antibody, the nuclear stain propidium iodide (red), and the actin stain phalloidin (blue or purple). Arrows indicate compound eye lenses. ol, optic lobe. Scale bar, 50 μm.
FIG. 2.
FIG. 2.
Relative abundance of SIGMAV (SiV) per sample based on the expression of the SIGMAV N and P genes normalized against host Actin 88F expression. Error bars represent the range from assay replicates.
FIG. 3.
FIG. 3.
Innate immune gene expression normalized against host Actin 88F by functional group. Values are mean ± standard error of the mean. SIGMAV-negative (white) and SIGMAV-positive (gray) bars represent results of five and six samples, respectively. *, P <0.05 for the difference between SIGMAV-negative and SIGMAV-positive flies.

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