Arbuscular mycorrhizal colonization of tomato by Gigaspora and Glomus species in the presence of root flavonoids

The effect of flavonoids isolated from arbuscular mycorrhizal (AM) colonized and noncolonized clover roots on the number of entry points and percentage of root colonization of tomato (Lycopersicum esculentum L.) by Gigaspora rosea, Gi margarita, Glomus mosseae and G. intrarradices symbionts was determined. With fungi of both genera, a correlation between the number of entry points and the percentage of root colonization was found in the presence of some of the tested flavonoids. The flavonoids acacetin and rhamnetin, present in AM clover roots, inhibited the formation of AM penetration structures and the AM colonization of tomato roots, whereas the flavonoid 5,6,7,8,9-hydroxy chalcone, which could not be detected in AM clover root, inhibited both parameters. The flavonoid quercetin, which was present in AM clover roots, stimulated the penetration and root colonization of tomato by Gigaspora. However, the flavonoids 5,6,7,8-hydroxy-4'-methoxy flavone and 3,5,6,7,4'-hydroxy flavone, which was not found in AM clover root, increased the number of entry points and the AM colonization of tomato roots by Gigaspora. These results indicated that flavonoids could be imnplicated in the process of regulation of AM colonization in plant root, but its role is highly complex and depend not only on flavonoids, but also on AM fungal genus or even species.     

Reciprocal regulation of nuclear import of the yeast MutSα DNA mismatch repair proteins Msh2 and Msh6

DNA mismatch recognition is performed in eukaryotes by two heterodimers known as MutSα (Msh2/Msh6) and MutSβ (Msh2/Msh3) that must reside in the nucleus to function. Two putative Msh2 nuclear localization sequences (NLS) were characterized by fusion to green fluorescent protein (GFP) and site-directed mutagenesis in the context of Msh2. One NLS functioned in GFP targeting assays and both acted redundantly within Msh2. We examined nuclear localization of each of the MutS monomers in the presence and absence of their partners. Msh2 translocated to the nucleus in cells lacking Msh3 and Msh6; however, cells lacking Msh6 showed significantly decreased levels of nuclear Msh2. Furthermore, the overall protein levels of Msh2 were significantly diminished in the absence of Msh6, particularly if Msh2 lacked a functional NLS. Msh3 localized in the absence of Msh2, but Msh6 localization depended on Msh2 expressing functional NLSs. Overall, the nuclear levels of Msh2 and Msh6 decline when the other partner is absent. The data suggest a stabilization mechanism to prevent free monomer accumulation in the cytoplasm.     

Functional role of bacterial multidrug efflux pumps in microbial natural ecosystems

Multidrug efflux pumps have emerged as relevant elements in the intrinsic and acquired antibiotic resistance of bacterial pathogens. In contrast with other antibiotic resistance genes that have been obtained by virulent bacteria through horizontal gene transfer, genes coding for multidrug efflux pumps are present in the chromosomes of all living organisms. In addition, these genes are highly conserved (all members of the same species contain the same efflux pumps) and their expression is tightly regulated. Together, these characteristics suggest that the main function of these systems is not resisting the antibiotics used in therapy and that they should have other roles relevant to the behavior of bacteria in their natural ecosystems. Among the potential roles, it has been demonstrated that efflux pumps are important for processes of detoxification of intracellular metabolites, bacterial virulence in both animal and plant hosts, cell homeostasis and intercellular signal trafficking.     

The Significance of Genetic Polymorphisms within and between Founder Populations of Ceratitis capitata (Wied.) from Argentina

Background

The Mediterranean fruit fly Ceratitis Capitata (DIPTERA: Tephritidae) is a major agricultural pest in Argentina. One main cause for the success of non-contaminant control programs based on genetic strategies is compatibility between natural and laboratory germplasms.A comprehensive characterization of the fruit fly based on genetic studies and compatibility analysis was undertaken on two founder populations from the provinces of Buenos Aires and Mendoza, used in pioneering sterile male technique control programmes in our country. The locations are 1,000 km apart from each other.

Methodology/Principal Findings

We compared the genetic composition of both populations based on cytological, physiological and morphological characterization. Compatibility studies were performed in order to determine the presence of isolation barriers. Results indicate that the Buenos Aires germplasm described previously is partially different from that of the Mendoza population. Both laboratory colonies are a reservoir of mutational and cytological polymorphisms. Some sexual chromosome variants such as the XL and the YL resulting from attachment of a B-chromosome to the X-chromosome or Y-chromosome behave as a lethal sex-linked factor. Our results also show incompatibility between both germplasms and pre-zygotic isolation barriers between them. Our evidence is consistent with the fact that polymorphisms are responsible for the lack of compatibility.

Conclusions

The genetic control mechanism should be directly produced in the germplasm of the target population in order to favour mating conditions. This is an additional requirement for the biological as well as economic success of control programs based on genetic strategies such as the sterile insect technique. The analysis of representative samples also revealed natural auto-control mechanisms which could be used in modifying pest population dynamics.     

Induction of disease by a molecularly cloned highly pathogenic simian immunodeficiency virus/human immunodeficiency virus chimera is multigenic

One of three full-length infectious molecular clones of SHIV(DH12R), designated SHIV(DH12R-CL-7) and obtained from productively infected rhesus monkey peripheral blood mononuclear cells, directed rapid and irreversible loss of CD4+ T cells within 3 weeks of its inoculation into Indian rhesus monkeys. Induction of complete CD4+ T-cell depletion by SHIV(DH12R-CL-7) was found to be dependent on inoculum size. The acquisition of this pathogenic phenotype was accompanied by the introduction of 42 amino acid substitutions into multiple genes of parental nonpathogenic SHIV(DH12). Transfer of the entire SHIV(DH12R-CL-7) env gene into the genetic background of nonpathogenic SHIV(DH12) failed to confer the rapid CD4+ T-lymphocyte-depleting syndrome; similarly, the substitution of gag plus pol sequences from SIV(smE543) for analogous SIV(mac239) genes in SHIV(DH12R-CL-7) attenuated the pathogenic phenotype. Amino acid changes affecting multiple viral genes are necessary, but insufficient by themselves, to confer the prototypically rapid and irreversible CD4+ T-cell-depleting phenotype exhibited by molecularly cloned SHIV(DH12R-CL-7).     

Immune failure in the absence of profound CD4+ T-lymphocyte depletion in simian immunodeficiency virus-infected rapid progressor macaques

A fraction of simian immunodeficiency virus (SIV)-infected macaques develop rapidly progressive disease in the apparent absence of detectable SIV-specific antibody responses. To characterize the immunopathogenesis of this syndrome, we studied viral load, CD4+ T-lymphocyte numbers as well as cellular and humoral immune responses to SIV and other exogenous antigens in four SIVsm-infected rhesus macaques that progressed to AIDS 9 to 16 weeks postinoculation. Each of these animals exhibited high levels of viremia but showed relatively preserved CD4 T lymphocytes in blood and lymphoid tissues at the time of death. Transient SIV-specific antibody responses and cytotoxic T-lymphocyte responses were observed at 2 to 4 weeks postinoculation. Two of the macaques that were immunized sequentially with tetanus toxoid and hepatitis A virus failed to develop antibody to either antigen. These studies show that the SIV-infected rapid progressor macaques initially mounted an appropriate but transient cellular and humoral immune response. The subsequent immune defect in these animals appeared to be global, affecting both cellular and humoral immunity to SIV as well as immune responses against unrelated antigens. The lack of CD4 depletion and loss of humoral and cellular immune responses suggest that their immune defect may be due to an early loss in T helper function.     

Mouse Macrophage Galactose-type Lectin (mMGL) is Critical for Host Resistance against Trypanosoma cruzi Infection

The C-type lectin receptor mMGL is expressed exclusively by myeloid antigen presenting cells (APC) such as dendritic cells (DC) and macrophages (Mφ), and it mediates binding to glycoproteins carrying terminal galactose and α- or β-N-acetylgalactosamine (Gal/GalNAc) residues. Trypanosoma cruzi (T. cruzi) expresses large amounts of mucin (TcMUC)-like glycoproteins. Here, we show by lectin-blot that galactose moieties are also expressed on the surface of T. cruzi. Male mMGL knockout (-/-) and wild-type (WT) C57BL/6 mice were infected intraperitoneally with 10⁴ T. cruzi trypomastigotes (Queretaro strain). Following T. cruzi infection, mMGL-/- mice developed higher parasitemia and higher mortality rates compared with WT mice. Although hearts from T. cruzi-infected WT mice presented few amastigote nests, mMGL-/- mice displayed higher numbers of amastigote nests. Compared with WT, Mφ from mMGL-/- mice had low production of nitric oxide (NO), interleukin (IL)-12 and tumor necrosis factor (TNF)-α in response to soluble T. cruzi antigens (TcAg). Interestingly, upon in vitro T. cruzi infection, mMGL-/- Mφ expressed lower levels of MHC-II and TLR-4 and harbored higher numbers of parasites, even when mMGL-/- Mφ were previously primed with IFN-γ or LPS/IFN-γ. These data suggest that mMGL plays an important role during T. cruzi infection, is required for optimal Mφ activation, and may synergize with TLR-4-induced pathways to produce TNF-α, IL-1β and NO during the early phase of infection.     

The epithelial-mesenchymal transition generates cells with properties of stem cells

The epithelial-mesenchymal transition (EMT) is a key developmental program that is often activated during cancer invasion and metastasis. We here report that the induction of an EMT in immortalized human mammary epithelial cells (HMLEs) results in the acquisition of mesenchymal traits and in the expression of stem-cell markers. Furthermore, we show that those cells have an increased ability to form mammospheres, a property associated with mammary epithelial stem cells. Independent of this, stem cell-like cells isolated from HMLE cultures form mammospheres and express markers similar to those of HMLEs that have undergone an EMT. Moreover, stem-like cells isolated either from mouse or human mammary glands or mammary carcinomas express EMT markers. Finally, transformed human mammary epithelial cells that have undergone an EMT form mammospheres, soft agar colonies, and tumors more efficiently. These findings illustrate a direct link between the EMT and the gain of epithelial stem cell properties.     

The locus encoding an oligomorphic family of <Emphasis Type="Italic">MHC-A</Emphasis> alleles (<Emphasis Type="Italic">Mane-A</Emphasis>*06/<Emphasis Type="Italic">Mamu-A</Emphasis>*05) is present at high frequency in several macaque species

Several macaques species are used for HIV pathogenesis and vaccine studies, and the characterization of their major histocompatibility complex (MHC) class I genes is required to rigorously evaluate the cellular immune responses induced after immunization and/or infection. In this study, we demonstrate that the gene expressing the Mane-A*06 allele of pig-tailed macaques is an orthologue of the locus encoding the Mamu-A*05 allele family in rhesus macaques. Analysis of the distribution of this locus in a cohort of 63 pig-tailed macaques revealed that it encodes an oligomorphic family of alleles, highly prevalent (90%) in the pig-tailed macaque population. Similarly, this locus was very frequently found (62%) in a cohort of 80 Indian rhesus macaques. An orthologous gene was also detected in cynomolgus monkeys originating from four different geographical locations, but was absent in two African monkey species. Expression analysis in pig-tailed macaques revealed that the Mane-A*06 alleles encoded by this locus are transcribed at 10- to 20-fold lower levels than other MHC-A alleles (Mane-A*03 or Mane-A*10). Despite their conservation and high prevalence among Asian macaque species, the alleles of the Mane-A*06 family and, by extension their orthologues in rhesus and cynomolgus monkeys, may only modestly contribute to cellular immune responses in macaques because of their low level of expression.