Engineered anti-viral shRNAs are more effective than lhRNAs in transgenic Aedes aegypti

The Aedes aegypti mosquito is a major vector of chikungunya virus (CHIKV), which has no licensed vaccine. Engineered mosquitoes expressing long RNA hairpins (lhRNA) or small RNAs against selected arboviruses have been developed to limit virus replication, but their silencing efficiency has not been compared.

We developed lhRNA and short hairpin RNA (shRNA) arrays against CHIKV non-structural protein nsP2. We used a Tet-response element (TRE) and a tTA transactivator to control expression of lhRNAs (TRE-lhRNA) and shRNAs (TRE-shRNA). Constitutive expression in Aag2 cells was assessed with a PUb-tTA driverand midgut specific expression in transgenic mosquitoes was assessed using Carboxypeptidase A (AeCPA)-tTA as driver. In vitrointerference ability was determined with a CHIKV split replication system, and a synthetic luciferase reporter with mRNA containing the targeted CHIKV sequence (CHIK-FF). In vivo interference was tested by inserting the TRE-lhRNA and TRE-shRNA constructs into a AeCPA-tTA line so both constructs expressed from the same locus, and a TRE reporter line that expressed an AmCyan reporter with an N terminal CHIKV fusion (CHIK-AmC).

In Aag2 cells, shRNAs were more effective than lhRNA in silencing both the CHIKV split replication system (99.7%, S. D. ± 0.47 and 72.8%, S. D. ± 9.50, respectively, P<0.001) and CHIK-FF (98.8%, S. D. ± 0.71 and 50.9%, S. D. ± 7.92, respectively, P<0.05). Similar results were observed in transgenic mosquitoes when comparing AmC expression in the midgut.

This study demonstrates that, in mosquitoes, effectively chosen shRNAs can induce greater interference of the desired viral target than the corresponding lhRNA.

Dengue virus seroprevalence among febrile patients in Bamako, Mali: results of a 2006 surveillance study

BACKGROUND

Dengue viruses (DENV) are endemic in over 100 countries worldwide, and annually 50 to 100 million people are infected by one of the four DENV serotypes, whereas over 2.5 billion people are at risk for infection. West African countries lack the surveillance to determine the true incidence of dengue; hence, this disease is likely significantly underestimated. In Mali, ?14 million people are potentially at risk of acquiring a dengue infection.

METHODS AND FINDINGS

A serosurvey for DENV was conducted on 95 human serum samples obtained from the Institute National de Recherche en Sante Publique in 2006. DENV-specific IgM and IgG enzyme-linked immunosorbent assays were performed on all samples, and a subset was tested using the plaque-reduction neutralization test against the DENV and yellow fever virus (YFV). Samples collected during the acute infection (0-5 days postonset of symptoms) were tested for dengue NS1 antigen and reverse-transcriptase polymerase chain reaction for Flaviviruses, Alphaviruses, and Bunyaviruses RNA. A total of 87 (93%) of samples were positive for anti-DENV IgG antibodies. Of a subset of 13 IgG positive samples, 2 samples neutralized monotypically against DENV-1 and -2, whereas 3 others neutralized broadly against YFV and multiple DENV. Although no polymerase chain reaction positives were found, DENV NS1 was detected in 1 of the 20 acute samples tested.

CONCLUSIONS

Of the 93 human serum samples tested, the dengue prevalence based on dengue IgG enzyme-linked immunosorbent assay results was 93%. Three DENV specific positive samples and two YFV positives were identified by plaque-reduction neutralization test. Finally, one sample tested positive for dengue NS1, thus suggestive of an acute infection within 14 days of obtaining the sample from the patient. Based on these serological data from this study, YFV and DENV appear to be co-circulating in Mali.

Effect of prophenoloxidase expression knockout on the melanization of microfilariae in the mosquito Armigeres subalbatus

Melanization is an effective defence reaction used by mosquito hosts to kill malarial and filarial worm parasites. Although phenoloxidase (PO) has long been considered to be the key enzyme in the biosynthesis of melanotic material in insects, there is no direct evidence verifying its role in parasite melanization. To elucidate the role of PO in the melanization of microfilariae (mf) by mosquitoes, a double subgenomic Sindbis (dsSIN) recombinant virus was used to transduce Armigeres subalbatus mosquitoes with a 600 base antisense RNA targeted to the highly conserved copper-binding region of an Ar. subalbatus PO gene. Compared with controls, haemolymph PO activity in mosquitoes transduced with antisense RNA was significantly reduced. When these mosquitoes were challenged with Dirofilaria immitis mf, the melanization of mf was almost completely inhibited. These data verify that PO is an essential component of the biochemical pathway required for the melanization of parasites, and that the dsSIN expression system represents a useful tool in the functional analysis of endogenous gene expression in mosquitoes.

Evolutionarily conserved and divergent expression of members of the FGF receptor family among vertebrate embryos, as revealed by FGFR expression patterns in Xenopus

Fibroblast growth factors (FGFs) mediate many cell-cell signaling events during early development. While the actions of FGFs have been well-studied, the roles played by specific members of the FGF receptor (FGFR) family are poorly understood. To characterize the roles played by individual FGFRs we compared the regulation and expression of the three Xenopus FGFRs described to date (XFGFR-1, XFGFR-2, and XFGFR-4). First, we describe the expression of Xenopus FGFR-4; XFGFR-4 is present as a maternal mRNA and is found in the embryo through at least the tadpole stage. XFGFR-4 and XFGFR-1 mRNAs are present at comparable levels, arguing that both mediate FGF signaling during early development. Second, the expression of XFGFR-4 in animal caps differs from the expression of XFGFR-1 and XFGFR-2, suggesting that the FGFRs are independently regulated in ectoderm. Third, using whole-mount in situ hybridization, we show that XFGFR-1, XFGFR-2, and XFGFR-4 are expressed in dramatically different patterns, arguing that specific FGF signaling events are mediated by different members of the FGFR family. Among these, FGF signaling during the induction of neural crest cells is likely to be mediated by XFGFR-4. Comparison of our results with previously reported FGFR expression patterns reveals that FGFR-1 expression is highly conserved among vertebrate embryos, and FGFR-2 expression shows many features that are conserved and some that are divergent. In contrast, the expression pattern of FGFR-4 is highly divergent among vertebrate embryos.