Assessing the Impact of Disease Vectors on Animal Populations

Many studies have attempted to assess the relative effects of different vectors of a disease on animal populations. To this end, three measures have been proposed: Vectorial efficiency, Vectorial capacity and recently Vectorial effectiveness (or Vectorial impact). In this study we relate these measures to derive some of their properties emphasising in the vectorial impact for its importance in both, population performance of parasites and the proportion of the prevalence of one parasite due to a given vector. We applied the quantitative expressions advanced in this study to a simple Chilean example with one parasite (Trypanosoma cruzi), two vectors (Triatoma infestans and Mepraia spinolai) and one animal population (humans: Chagas's disease).     

Effect of d-Penicillamine on Poliovirus Replication In HeLa Cells

A series of mercaptan compounds were studied with respect to their ability to inhibit the growth of poliovirus in cultured cells. Of the compounds tested only d-penicillamine possessed antiviral activity. There was no direct effect on the virus itself, nor were the processes of adsorption, penetration and uncoating, or virus-induced "shut-off" of host cell protein synthesis inhibited. At concentrations where there was no effect on host cell RNA or protein synthesis, d-penicillamine caused a marked inhibition of virus-specific RNA and protein synthesis. Although much reduced, the relative concentrations of single-stranded and double-stranded viral RNA synthesized in the presence of d-penicillamine was unchanged. Similarly, all apparent precursor and cleavage product proteins could be synthesized in the presence of the drug. The inhibitory effect was reversible, after a lag of 1.5 to 2 h after removal of the drug, and normal yields of virus could be obtained. The structural and functional properties of d-penicillamine are discussed in relation to requirements for anti-polioviral activity.     

Interaction of Poly(rC) Binding Protein 2 with the 5′ Noncoding Region of Hepatitis A Virus RNA and Its Effects on Translation

Utilization of internal ribosome entry segment (IRES) structures in the 5′ noncoding region (5′NCR) of picornavirus RNAs for initiation of translation requires a number of host cell factors whose distribution may vary in different cells and whose requirement may vary for different picornaviruses. We have examined the requirement of the cellular protein poly(rC) binding protein 2 (PCBP2) for hepatitis A virus (HAV) RNA translation. PCBP2 has recently been identified as a factor required for translation and replication of poliovirus (PV) RNA. PCBP2 was shown to be present in FRhK-4 cells, which are permissive for growth of HAV, as it is in HeLa cells, which support translation of HAV RNA but which have not been reported to host replication of the virus. Competition RNA mobility shift assays showed that the 5′NCR of HAV RNA competed for binding of PCBP2 with a probe representing stem-loop IV of the PV 5′NCR. The binding site on HAV RNA was mapped to nucleotides 1 to 157, which includes a pyrimidine-rich sequence. HeLa cell extracts that had been depleted of PCBP2 by passage over a PV stem-loop IV RNA affinity column supported only low levels of HAV RNA translation. Translation activity was restored upon addition of recombinant PCBP2 to the depleted extract. Removal of the 5′-terminal 138 nucleotides of the HAV RNA, or removal of the entire IRES, eliminated the dependence of HAV RNA translation on PCBP2.     

Poliovirus snapback double-stranded RNA isolated from infected HeLa cells is deficient in poly(A).

A portion of poliovirus double-stranded RNA (25 to 50%) isolated from infected HeLa cells contains hairpin loops at one end of the duplex structure. These structures rapidly reformed double-stranded molecules after denaturation and appeared as molecules of up to two times genome length upon electrophoresis in denaturing agarose gels. A second form of poliovirus double-stranded RNA was readily denaturable into genome length strands. When the hairpin RNA was treated with S1 nuclease, subsequent denaturation resulted in formation of strands of up to genome length. Hairpin molecules contained very little, if any, poly(A) sequences, suggesting that the hairpin forms after nucleolytic removal of the 3' end of plus-strand templates. We conclude that the hairpin double-stranded RNA found in infected cells is likely generated by intracellular nicking and self-priming and that it does not represent an intermediate in the process of RNA replication.     

Genetic ablation of caveolin-2 sensitizes mice to bleomycin-induced injury

Caveolar domains act as platforms for the organization of molecular complexes involved in signal transduction. Caveolin proteins, the principal structural components of caveolae, have been involved in many cellular processes. Caveolin-1 (Cav-1) and caveolin-2 (Cav-2) are highly expressed in the lung. Cav-1-deficient mice (Cav-1^−/−) and Cav-2-deficient mice (Cav-2^−/−) exhibit severe lung dysfunction attributed to a lack of Cav-2 expression. Recently, Cav-1 has been shown to regulate lung fibrosis in different models. Here, we show that Cav-2 is also involved in modulation of the fibrotic response, but through distinct mechanisms. Treatment of wild-type mice with the pulmonary fibrosis-inducer bleomycin reduced the expression of Cav-2 and its phosphorylation at tyrosine 19. Importantly, Cav-2^−/− mice, but not Cav-1^−/− mice, were more sensitive to bleomycin-induced lung injury in comparison to wild-type mice. Bleomycin-induced lung injury was characterized by alveolar thickening, increase in cell density, and extracellular matrix deposition. The lung injury observed in bleomycin-treated Cav-2^−/− mice was not associated with alterations in the TGF-β signaling pathway and/or in the ability to produce collagen. However, apoptosis and proliferation were more prominent in lungs of bleomycin-treated Cav-2^−/− mice. Since Cav-1^−/− mice also lack Cav-2 expression and show a different outcome after bleomycin treatment, we conclude that Cav-1 and Cav-2 have distinct roles in bleomycin induced-lung fibrosis, and that the balance of both proteins determines the development of the fibrotic process.     

REPRODUCTIVE BIOLOGY OF THREE SPECIES OF EUPHORBIA SUBGENUS CHAMAESYCE (EUPHORBIACEAE)

The breeding system, pollen tube development, and floral biology of three species of Euphorbia subgenus Chamaesyce from southeastern Arizona have been examined in field and greenhouse studies. E. albomarginata is entirely dependent on insect vectors for pollination and seed production, E. capitellata requires insect visitors for maximum seed set but is capable of limited self-pollination, and E. hyssopifolia is self-pollinating and entirely independent of insect vectors. All three species are self-compatible. The differences in reliance on insect vectors, diversity of insects and probable amount of outcrossing are related to differences in cyathial size and arrangement. The reproductive biology of the three species is similar to that described for other weedy plant taxa.     

Replicase mediated resistance against potato leafroll virus in potato Desirée plants

Potato leafroll virus (PLRV) is a major menace for the potato production all over the world. PLRV is transmitted by aphids, and until now, the only strategy available to control this pest has been to use large amounts of insecticides. Transgenic approaches involving the expression of viral replicases are being developed to provide protection for plants against viral diseases. The purpose of this study was to compare the protection afforded by the differential expression of PLRV replicate transgene in potato plants cv. Desirée, Plants were genetically modified to express the complete sense PLRV replicase gene. Two constructions were used, one containing the constitutive 35SCaMV promoter and the other the phloem-specific RolA promoter from Agrobacterium rhizogenes. Transgenic plants were infected with PLRV in vitro, using infested aphids. In plants in which 35SCaMV controlled the expression of the PLRV replicase gene, signs of infection were initially detected, although most plants later developed a recovery phenotype showing undetectable virus levels 40 days after infection. In turn, those plants with the RolA promoter displayed an initial resistance that was later overcome. Different molecular mechanisms are likely to participate in the response to PLRV infection of these two types of transgenic plants.     

Apical membrane sodium and chloride entry during osmotic swelling of renal (A6) epithelial cells

To assess the role of chloride in cell volume and sodium transport regulation, we measured cell height changes (CH), transepithelial chloride and sodium fluxes, and intracellular chloride content during challenge with hyposmotic solutions under open circuit (OC) conditions. CH maximally increased following hyposmotic challenge within 5 minutes. The change in CH was smaller under short circuit (SC) conditions or following replacement of chloride in the mucosal solution by gluconate or cyclamate (Cl^–-free _m ). When corrected for the osmotically inactive cell volume (30 ± 2%), CH for controls (OC) were greater than predicted for an ideal osmometer. In contrast, ACH for Cl^–-free _m or SC conditions were similar to that predicted for an ideal osmometer.Na⁺ and Cl^– mucosa-to-serosa fluxes increased following hyposmotic challenge. Chloride fluxes increased maximally within 5 min, then decreased. In contrast, the Na⁺ flux increased slowly and reached a steady state after 25 min. Under isosmotic conditions, exposure to Cl^–-free _m solutions led to decreases in the transepithelial conductance, Na⁺ flux, and CH. Chloride permeabilities in the apical and basolateral membranes were detected using the fluorescent intracellular chloride indicator MQAE.