Three viruses found in the braconid parasitoid Microplitis croceipes and their implications in biological control programs

Productivity and longevity decreased in a laboratory colony of the parasitoid wasp Microplitis croceipes (Cresson) (Hymenoptera: Braconidae). Using light microscopy, it was determined that the colony was free of microsporidia. However, samples of the colony examined for pathogens by electron microscopy revealed three types of viruses: a nonpathogenic polydnavirus which is produced by all female wasps; a nonoccluded baculovirus which is pathogenic to late-stage pupae and adults; and a picorna-like virus which is present in larvae, pupae, and adults. The nonoccluded baculovirus was eliminated from the laboratory colony of M. croceipes by selection of progeny from wasps which had oviposited within 2 to 3 days after emergence from the cocoons and which had lived for at least 14 days post-emergence. Upon death, the wasps were examined by negative stain electron microscopy and only progeny from baculovirus-free wasps were retained. Parasitoid colonies should be systematically examined for pathogenic viruses that may reduce their productivity and efficacy as biological control agents. In addition, exotic parasitoids and predators should be evaluated for viruses and other pathogens while in quarantine.     

What drives interspecies graft union success? Exploring the role of phylogenetic relatedness and stem anatomy

The underlying mechanisms that determine whether two species can form a successful graft union (graft compatibility) remain obscure. Two prominent hypotheses are (1) the more closely related species are, the higher the graft success and (2) the vascular anatomy at the graft junction influences graft success. In this paper these two hypotheses are examined in a systematic way using graft combinations selected from a range of (a) phylogenetically close and more distant legume species, (b) species displaying different germination patterns and (c) scions and rootstocks possessing contrasting stem tissues and vascular patterns. Relatedness of species was not a good predictor of graft compatibility, as vascular reconnection can occur between distantly related species and can fail to occur in some more closely related species. Similarly, neither the stem tissues present at the graft junction nor the vascular anatomy correlated with the success of vascular reconnection. Relatedness and stem anatomy therefore do not appear to be the determining factors in successful vascular reconnection after grafting in legumes. These results are discussed in conjunction with other hypotheses such as the role of auxin.     

Mechanisms of outer membrane vesicle entry into host cells

Bacterial outer membrane vesicles (OMVs) are nano‐sized compartments consisting of a lipid bilayer that encapsulates periplasm‐derived, luminal content. OMVs, which pinch off of Gram‐negative bacteria, are now recognized as a generalized secretion pathway which provides a means to transfer cargo to other bacterial cells as well as eukaryotic cells. Compared with other secretion systems, OMVs can transfer a chemically extremely diverse range of cargo, including small molecules, nucleic acids, proteins, and lipids to proximal cells. Although it is well recognized that OMVs can enter and release cargo inside host cells during infection, the mechanisms of host association and uptake are not well understood. This review highlights existing studies focusing on OMV‐host cell interactions and entry mechanisms, and how these entry routes affect cargo processing within the host. It further compares the wide range of methods currently used to dissect uptake mechanisms, and discusses potential sources of discrepancy regarding the mechanism of OMV uptake across different studies.     

Tumor-Stroma Mechanics Coordinate Amino Acid Availability to Sustain Tumor Growth and Malignancy

1. Download high-res image (274KB)
2. Download full-size image

     

Elevated Prolactin during Pregnancy Drives a Phenotypic Switch in Mouse Hypothalamic Dopaminergic Neurons

1. Download high-res image (141KB)
2. Download full-size image

     

Knockdown of LRP/LR Induces Apoptosis in Breast and Oesophageal Cancer Cells

Cancer is a global burden due to high incidence and mortality rates and is ranked the second most diagnosed disease amongst non-communicable diseases in South Africa. A high expression level of the 37kDa/67kDa laminin receptor (LRP/LR) is one characteristic of cancer cells. This receptor is implicated in the pathogenesis of cancer cells by supporting tumor angiogenesis, metastasis and especially for this study, the evasion of apoptosis. In the current study, the role of LRP/LR on cellular viability of breast MCF-7, MDA-MB 231 and WHCO1 oesophageal cancer cells was investigated. Western blot analysis revealed that total LRP expression levels of MCF-7, MDA-MB 231 and WHCO1 were significantly downregulated by targeting LRP mRNA using siRNA-LAMR1. This knockdown of LRP/LR resulted in a significant decrease of viability in the breast and oesophageal cancer cells as determined by an MTT assay. Transfection of MDA-MB 231 cells with esiRNA-RPSA directed against a different region of the LRP mRNA had similar effects on LRP/LR expression and cell viability compared to siRNA-LAMR1, excluding an off-target effect of siRNA-LAMR1. This reduction in cellular viability is as a consequence of apoptosis induction as indicated by the exposure of the phosphatidylserine protein on the surface of breast MCF-7, MDA-MB 231 and oesophageal WHCO1 cancer cells, respectively, detected by an Annexin-V/FITC assay as well as nuclear morphological changes observed post-staining with Hoechst. These observations indicate that LRP/LR is crucial for the maintenance of cellular viability of breast and oesophageal cancer cells and recommend siRNA technology targeting LRP expression as a possible novel alternative technique for breast and oesophageal cancer treatment.     

Recognition of Smac-mimetic compounds by the BIR domain of cIAP1

Inhibitor of apoptosis proteins (IAPs) are negative regulators of apoptosis. As IAPs are overexpressed in many tumors, where they confer chemoresistance, small molecules inactivating IAPs have been proposed as anticancer agents. Accordingly, a number of IAP-binding pro-apoptotic compounds that mimic the sequence corresponding to the N-terminal tetrapeptide of Smac/DIABLO, the natural endogenous IAPs inhibitor, have been developed. Here, we report the crystal structures of the BIR3 domain of cIAP1 in complex with Smac037, a Smac-mimetic known to bind potently to the XIAP-BIR3 domain and to induce degradation of cIAP1, and in complex with the novel Smac-mimetic compound Smac066. Thermal stability and fluorescence polarization assays show the stabilizing effect and the high affinity of both Smac037 and Smac066 for cIAP1- and cIAP2-BIR3 domains.     

Acute effects of wortmannin on insulin's hemodynamic and metabolic actions in vivo

Wortmannin, an inhibitor of phosphatidylinositol 3-kinase, was systemically infused during a hyperinsulinemic euglycemic clamp to investigate its effects in vivo. Rats were infused under anesthesia with saline, 10 or 20 mU.min-1.kg-1 insulin, wortmannin (1 microg.min-1.kg-1)+saline, or wortmannin+insulin (10 mU.min-1.kg-1); wortmannin was present for 1 h before and throughout the 2-h clamp. Femoral blood flow (FBF), glucose infusion rate to maintain euglycemia (GIR), glucose appearance (Ra), glucose disappearance (Rd), capillary recruitment by 1-methylxanthine metabolism (MXD), hindleg glucose uptake (HLGU), liver, muscle, and aorta Akt phosphorylation (P-Akt/Akt), and plasma insulin concentrations were determined. Plasma insulin increased from 410+/-49 to 1,680+/-430 and 5,060+/-230 pM with 10 and 20 mU.min-1.kg-1 insulin, respectively. Insulin (10 and 20 mU.min-1.kg-1) increased FBF, MXD, GIR, Rd, and HLGU as well as liver, muscle, and aorta P-Akt/Akt and decreased Ra (all P<0.05). Wortmannin alone increased plasma insulin to 5,450+/-770 pM and increased Ra, Rd, HLGU, and muscle P-Akt/Akt without effect on blood glucose, FBF, MXD liver, or aorta P-Akt/Akt. Wortmannin blocked FBF, MXD, and liver P-Akt/Akt increases from 10 mU.min-1.kg-1 insulin. Comparison of wortmannin+10 mU.min-1.kg-1 insulin and 20 mU.min-1.kg-1 insulin alone (both at approximately 5,000 pM PI) showed that wortmannin fully blocked the changes in FBF and Ra and partly those of GIR, Ra, Rd, HLGU, and muscle P-AKT/Akt. In summary, wortmannin in vivo increases plasma insulin and fully inhibits insulin-mediated effects in liver and aorta and partially those of muscle, where the latter may result from inhibition of insulin-mediated increases in blood flow and capillary recruitment.     

The Activator of Apoptosis Smac-DIABLO Acts as a Tetramer in Solution

Smac-DIABLO in its mature form (20.8 kDa) binds to baculoviral IAP repeat (BIR) domains of inhibitor of apoptosis proteins (IAPs) releasing their inhibitory effects on caspases, thus promoting cell death. Despite its apparent molecular mass (∼100 kDa), Smac-DIABLO was held to be a dimer in solution, simultaneously targeting two distinct BIR domains. We report an extensive biophysical characterization of the protein alone and in complex with the X-linked IAP (XIAP)-BIR2-BIR3 domains. Our data show that Smac-DIABLO adopts a tetrameric assembly in solution and that the tetramer is able to bind two BIR2-BIR3 pairs of domains. Our small-angle x-ray scattering-based tetrameric model of Smac-DIABLO/BIR2-BIR3 highlights some conformational freedom of the complex that may be related to optimization of IAPs binding.