Phenoloxidase activity acts as a mosquito innate immune response against infection with semliki forest virus

Several components of the mosquito immune system including the RNA interference (RNAi), JAK/STAT, Toll and IMD pathways have previously been implicated in controlling arbovirus infections. In contrast, the role of the phenoloxidase (PO) cascade in mosquito antiviral immunity is unknown. Here we show that conditioned medium from the Aedes albopictus-derived U4.4 cell line contains a functional PO cascade, which is activated by the bacterium Escherichia coli and the arbovirus Semliki Forest virus (SFV) (Togaviridae; Alphavirus). Production of recombinant SFV expressing the PO cascade inhibitor Egf1.0 blocked PO activity in U4.4 cell- conditioned medium, which resulted in enhanced spread of SFV. Infection of adult female Aedes aegypti by feeding mosquitoes a bloodmeal containing Egf1.0-expressing SFV increased virus replication and mosquito mortality. Collectively, these results suggest the PO cascade of mosquitoes plays an important role in immune defence against arboviruses

SNAP-tagged Chikungunya Virus Replicons Improve Visualisation of Non-Structural Protein 3 by Fluorescence Microscopy

Chikungunya virus (CHIKV), a mosquito-borne alphavirus, causes febrile disease, muscle and joint pain, which can become chronic in some individuals. The non-structural protein 3 (nsP3) plays essential roles during infection, but a complete understanding of its function is lacking. Here we used a microscopy-based approach to image CHIKV nsP3 inside human cells. The SNAP system consists of a self-labelling enzyme tag, which catalyses the covalent linking of exogenously supplemented synthetic ligands. Genetic insertion of this tag resulted in viable replicons and specific labelling while preserving the effect of nsP3 on stress granule responses and co-localisation with GTPase Activating Protein (SH3 domain) Binding Proteins (G3BPs). With sub-diffraction, three-dimensional, optical imaging, we visualised nsP3-positive structures with variable density and morphology, including high-density rod-like structures, large spherical granules, and small, low-density structures. Next, we confirmed the utility of the SNAP tag for studying protein turnover by pulse-chase labelling. We also revealed an association of nsP3 with cellular lipid droplets and examined the spatial relationships between nsP3 and the non-structural protein 1 (nsP1). Together, our study provides a sensitive, specific, and versatile system for fundamental research into the individual functions of a viral non-structural protein during infection with a medically important arthropod-borne virus (arbovirus)

Erratum to: 36th International Symposium on Intensive Care and Emergency Medicine

[This corrects the article DOI: 10.1186/s13054-016-1208-6.]

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PostkaartTrükitud: Foto E. Tamber

Geometric properties of Gabor frames with a random window

In this paper we address various geometric properties of frames, such as spark, coherence, restricted isometry property, and frame order statistics. These properties play crucial role in various signal processing problems, including compressive sensing, phase retrieval, and quantization. We focus on a particular case of structured frames, namely on Gabor frames, where frame vectors are time and frequency shifts of a random window, and show that geometric properties of Gabor frames are close to optimum, which is usually demonstrated by Gaussian frames with independent vectors

Geometric properties of Gabor frames with a random window

In this paper we address various geometric properties of frames, such as spark, coherence, restricted isometry property, and frame order statistics. These properties play crucial role in various signal processing problems, including compressive sensing, phase retrieval, and quantization. We focus on a particular case of structured frames, namely on Gabor frames, where frame vectors are time and frequency shifts of a random window, and show that geometric properties of Gabor frames are close to optimum, which is usually demonstrated by Gaussian frames with independent vectors

Magnetic Fractionation and Proteomic Dissection of Cellular Organelles Occupied by the Late Replication Complexes of Semliki Forest Virus

Alphavirus replicase complexes are initially formed at the plasma membrane and are subsequently internalized by endocytosis. During the late stages of infection, viral replication organelles are represented by large cytopathic vacuoles, where replicase complexes bind to membranes of endolysosomal origin. In addition to viral components, these organelles harbor an unknown number of host proteins. In this study, a fraction of modified lysosomes carrying functionally intact replicase complexes was obtained by feeding Semliki Forest virus (SFV)-infected HeLa cells with dextran-covered magnetic nanoparticles and later magnetically isolating the nanoparticle-containing lysosomes. Stable isotope labeling with amino acids in cell culture combined with quantitative proteomics was used to reveal 78 distinct cellular proteins that were at least 2.5-fold more abundant in replicase complex-carrying vesicles than in vesicles obtained from noninfected cells. These host components included the RNA-binding proteins PCBP1, hnRNP M, hnRNP C, and hnRNP K, which were shown to colocalize with the viral replicase. Silencing of hnRNP M and hnRNP C expression enhanced the replication of SFV, Chikungunya virus (CHIKV), and Sindbis virus (SINV). PCBP1 silencing decreased SFV-mediated protein synthesis, whereas hnRNP K silencing increased this synthesis. Notably, the effect of hnRNP K silencing on CHIKV- and SINV-mediated protein synthesis was opposite to that observed for SFV. This study provides a new approach for analyzing the proteome of the virus replication organelle of positive-strand RNA viruses and helps to elucidate how host RNA-binding proteins exert important but diverse functions during positive-strand RNA viral infection