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The genus Alphavirus consists of a group of enveloped, single-stranded RNA viruses, many of which are transmitted by arthropods to a wide range of vertebrate host species. Here we report that Sindbis virus (SINV) produced from a representative mammalian cell line consists of at least two unique particle subpopulations, separable on the basis of virion density. In contrast, mosquito-derived SINV consists of a homogeneous population of particles. Our findings indicate that the denser particle subpopulation, SINV(Heavy), is more infectious on a per-particle basis than SINV(Light). SINV produced in mosquito cell lines (SINV(C6/36)) exhibited particle-to-PFU ratios similar to those observed for SINV(Heavy). In mammalian cells, viral RNA was synthesized and accumulated more rapidly following infection with SINV(Heavy) or SINV(C6/36) than following infection with SINV(Light), due partly to enhanced translation of viral genomic RNA early in infection. Analysis of the individual particle subpopulations indicated that SINV(Heavy) and SINV(C6/36) contain host-derived factors whose presence correlates with the enhanced translation, RNA synthesis, and infectivity observed for these particles.

Alphaviruses are enveloped, single-stranded positive sense RNA viruses that are transmitted by an arthropod vector to a wide host range, including avian and mammalian species. Arthropods and vertebrates have different cellular environments and this may cause the different cellular pathologies that are observed between the invertebrate vector and vertebrate hosts in both whole organisms and cultured cell lines. In this report, we used Sindbis virus and examined mosquito and mammalian cell lines for their ability to produce progeny virus particles. Total particles produced, viral titers, and overall infectivity (or the ratio of total particles-to-infectious particles) was investigated. Our results show (1) Sindbis infectivity is more a function of the host cell used in titering the virus rather than the cell line used to produce the virus, (2) the number of total and infectious particles produced is cell line dependent, and (3) the infectivity of released virus particles improves during the course of infection in both cells that have cytolytic infections and persistent infections., (Copyright © 2012 Elsevier B.V. All rights reserved.)

The rate of mRNA turnover is an important determinant of levels of gene expression. Although this process has been studied extensively in mammalian cells and yeast, relatively little is known about the mRNA decay pathways in insects. Our analysis found that the vast majority of components of the mRNA decay machinery are conserved between humans and mosquitoes. Moreover, the half-lives of Aedes albopictus mRNAs are within a similar range to those of mammalian mRNAs. In order to investigate mechanistic aspects of mRNA decay in mosquitoes, we developed an in vitro system using cytoplasmic S100 extracts from A. albopictus C6/36 cells. Using this decay assay, we show here that all the pathways of mRNA turnover that have been observed in mammalian cells (deadenylation, decapping, 3'-to-5' exonucleolytic decay and 5'-to-3' exonucleolytic decay) are active in C6/36 extracts. Finally, we present compelling evidence that the major deadenylase in C6/36 extracts is likely to be a homolog of the human poly(A) specific ribonuclease, PARN. Our results suggest a high level of conservation in the factors and pathways of mRNA decay between mosquitoes and humans.