Within-host Competition Does Not Select for Virulence in Malaria Parasites; Studies with Plasmodium yoelii

In endemic areas with high transmission intensities, malaria infections are very often composed of multiple genetically distinct strains of malaria parasites. It has been hypothesised that this leads to intra-host competition, in which parasite strains compete for resources such as space and nutrients. This competition may have repercussions for the host, the parasite, and the vector in terms of disease severity, vector fitness, and parasite transmission potential and fitness. It has also been argued that within-host competition could lead to selection for more virulent parasites. Here we use the rodent malaria parasite Plasmodium yoelii to assess the consequences of mixed strain infections on disease severity and parasite fitness. Three isogenic strains with dramatically different growth rates (and hence virulence) were maintained in mice in single infections or in mixed strain infections with a genetically distinct strain. We compared the virulence (defined as harm to the mammalian host) of mixed strain infections with that of single infections, and assessed whether competition impacted on parasite fitness, assessed by transmission potential. We found that mixed infections were associated with a higher degree of disease severity and a prolonged infection time. In the mixed infections, the strain with the slower growth rate was often responsible for the competitive exclusion of the faster growing strain, presumably through host immune-mediated mechanisms. Importantly, and in contrast to previous work conducted with Plasmodium chabaudi, we found no correlation between parasite virulence and transmission potential to mosquitoes, suggesting that within-host competition would not drive the evolution of parasite virulence in P. yoelii.     

The Human-Baited Double Net Trap: An Alternative to Human Landing Catches for Collecting Outdoor Biting Mosquitoes in Lao PDR

Estimating the exposure of individuals to mosquito-borne diseases is a key measure used to evaluate the success of vector control operations. The gold standard is to use human landing catches where mosquitoes are collected off the exposed limbs of human collectors. This is however an unsatisfactory method since it potentially exposes individuals to a range of mosquito-borne diseases. In this study several sampling methods were compared to find a method that is representative of the human-biting rate outdoors, but which does not expose collectors to mosquito-borne infections. The sampling efficiency of four odour-baited traps were compared outdoors in rural Lao PDR; the human-baited double net (HDN) trap, CDC light trap, BG sentinel trap and Suna trap. Subsequently the HDN, the best performing trap, was compared directly with human landing catches (HLC), the ‘gold standard’, for estimating human-biting rates. HDNs collected 11–44 times more mosquitoes than the other traps, with the exception of the HLC. The HDN collected similar numbers of Anopheles (Rate Ratio, RR = 1.16, 95% Confidence Intervals, 95% CI = 0.61–2.20) and Culex mosquitoes (RR = 1.26, 95% CI = 0.74–2.17) as HLC, but under-estimated the numbers of Aedes albopictus (RR = 0.45, 95% CI = 0.27–0.77). Simpson’s index of diversity was 0.845 (95% CI 0.836–0.854) for the HDN trap and 0.778 (95% CI 0.769–0.787) for HLC, indicating that the HDN collected a greater diversity of mosquito species than HLC. Both HLC and HDN can distinguish between low and high biting rates and are crude ways to measure human-biting rate. The HDN is a simple and cheap method to estimate the human-biting rate outdoors without exposing collectors to mosquito bites.     

Glucocorticoid-induced androgen inactivation by aldo-keto reductase 1C2 promotes adipogenesis in human preadipocytes

Adipogenesis and lipid storage in human adipose tissue are inhibited by androgens such as DHT. Inactivation of DHT to 3α-diol is stimulated by glucocorticoids in human preadipocytes. We sought to characterize glucocorticoid-induced androgen inactivation in human preadipocytes and to establish its role in the antiadipogenic action of DHT. Subcutaneous and omental primary preadipocyte cultures were established from fat samples obtained in subjects undergoing abdominal surgeries. Inactivation of DHT to 3α/β-diol for 24 h was measured in dexamethasone- or vehicle-treated cells. Specific downregulation of aldo-keto reductase 1C (AKR1C) enzymes in human preadipocytes was achieved using RNA interference. In whole adipose tissue sample, cortisol production was positively correlated with androgen inactivation in both subcutaneous and omental adipose tissue (P < 0.05). Maximal dexamethasone (1 μM) stimulation of DHT inactivation was higher in omental compared with subcutaneous fat from men as well as subcutaneous and omental fat from women (P < 0.05). A significant positive correlation was observed between BMI and maximal dexamethasone-induced DHT inactivation rates in subcutaneous and omental adipose tissue of men and women (r = 0.24, n = 26, P < 0.01). siRNA-induced downregulation of AKR1C2, but not AKR1C1 or AKR1C3, significantly reduced basal and glucocorticoid-induced androgen inactivation rates (P < 0.05). The inhibitory action of DHT on preadipocyte differentiation was potentiated following AKR1C2 but not AKR1C1 or AKR1C3 downregulation. Specifically, lipid accumulation, G3PDH activity, and FABP4 mRNA expression in differentiated preadipocytes exposed to DHT were reduced further upon AKR1C2 siRNA transfection. We conclude that glucocorticoid-induced androgen inactivation is mediated by AKR1C2 and is particularly effective in omental preadipocytes of obese men. The interplay between glucocorticoids and AKR1C2-dependent androgen inactivation may locally modulate adipogenesis and lipid accumulation in a depot-specific manner.     

Parameters for using mannan-MUC1 fusion protein to induce cellular immunity

 We have previously reported preclinical studies in mice of the human mucin 1 (MUC1) antigen covalently linked to the yeast cell-wall mannan polysaccharide (MFP), and shown strong cellular responses of the T1 type using mice. We now describe the optimum parameters for administration of MFP to obtain cellular immunity [as measured by the cytotoxic T cell precursor (CTLp) frequency]. In dose/response studies, in which 1 μg–150 μg was given by the i.p. route, it was clear that doses of 1–7 μg led to cellular and not humoral immunity; at doses above 7 μg humoral immunity prevailed with little cellular immunity - increasing doses giving greater amounts of antibody. The most favoured routes of administration were intraperitoneal or intradermal immunisation, which were substantially better than i.m., i.v.; s.c. administration was the worst. Three immunisations were necessary for a maximum cellular response, further immunisation decreasing the CTLp frequency. Six different adjuvants were used with MFP [complete and incomplete Freund’s adjuvant (CFA, IFA) Alum, Adjuprime, muramyl dipeptide (MDP) and glutaminyl-muramyl dipeptide (GMDP)]; Alum, GMDP, MDP and IFA moderately increased the CTLp frequency, IFA being the best. Even though preclinical studies of the immunogen in mice may not necessarily mirror the behaviour of the immunogen in humans, these studies demonstrate the factors to be taken into account for phase I/II clinical trials. Received: 8 July 1997 / Accepted: 4 September 1997     

Human Adipose Stromal Cells (ASC) for the Regeneration of Injured Cartilage Display Genetic Stability after In Vitro Culture Expansion

Mesenchymal stromal cells are emerging as an extremely promising therapeutic agent for tissue regeneration due to their multi-potency, immune-modulation and secretome activities, but safety remains one of the main concerns, particularly when in vitro manipulation, such as cell expansion, is performed before clinical application. Indeed, it is well documented that in vitro expansion reduces replicative potential and some multi-potency and promotes cell senescence. Furthermore, during in vitro aging there is a decrease in DNA synthesis and repair efficiency thus leading to DNA damage accumulation and possibly inducing genomic instability. The European Research Project ADIPOA aims at validating an innovative cell-based therapy where autologous adipose stromal cells (ASCs) are injected in the diseased articulation to activate regeneration of the cartilage. The primary objective of this paper was to assess the safety of cultured ASCs. The maintenance of genetic integrity was evaluated during in vitro culture by karyotype and microsatellite instability analysis. In addition, RT-PCR array-based evaluation of the expression of genes related to DNA damage signaling pathways was performed. Finally, the senescence and replicative potential of cultured cells was evaluated by telomere length and telomerase activity assessment, whereas anchorage-independent clone development was tested in vitro by soft agar growth. We found that cultured ASCs do not show genetic alterations and replicative senescence during the period of observation, nor anchorage-independent growth, supporting an argument for the safety of ASCs for clinical use.     

Karrikins Discovered in Smoke Trigger Arabidopsis Seed Germination by a Mechanism Requiring Gibberellic Acid Synthesis and Light

Discovery of the primary seed germination stimulant in smoke, 3-methyl-2H-furo[2,3-c]pyran-2-one (KAR₁), has resulted in identification of a family of structurally related plant growth regulators, karrikins. KAR₁ acts as a key germination trigger for many species from fire-prone, Mediterranean climates, but a molecular mechanism for this response remains unknown. We demonstrate that Arabidopsis (Arabidopsis thaliana), an ephemeral of the temperate northern hemisphere that has never, to our knowledge, been reported to be responsive to fire or smoke, rapidly and sensitively perceives karrikins. Thus, these signaling molecules may have greater significance among angiosperms than previously realized. Karrikins can trigger germination of primary dormant Arabidopsis seeds far more effectively than known phytohormones or the structurally related strigolactone GR-24. Natural variation and depth of seed dormancy affect the degree of KAR₁ stimulation. Analysis of phytohormone mutant germination reveals suppression of KAR₁ responses by abscisic acid and a requirement for gibberellin (GA) synthesis. The reduced germination of sleepy1 mutants is partially recovered by KAR₁, which suggests that germination enhancement by karrikin is only partly DELLA dependent. While KAR₁ has little effect on sensitivity to exogenous GA, it enhances expression of the GA biosynthetic genes GA3ox1 and GA3ox2 during seed imbibition. Neither abscisic acid nor GA levels in seed are appreciably affected by KAR₁ treatment prior to radicle emergence, despite marked differences in germination outcome. KAR₁ stimulation of Arabidopsis germination is light-dependent and reversible by far-red exposure, although limited induction of GA3ox1 still occurs in the dark. The observed requirements for light and GA biosynthesis provide the first insights into the karrikin mode of action.Germination is a critical event in the plant life cycle, as the timing of emergence from the protective seed coat is crucial for survival and reproductive success. A variety of abiotic stimuli, including light, temperature, and nitrates, provide information about the external environment that affects germination. Seed dormancy gates responses to these factors. Upon maturation, physiologically dormant seeds are in a primary dormant (PD) state, which is lost during afterripening. The transition between a PD and nondormant state is both gradual and reversible and results in relaxation of the set of environmental conditions under which a seed will germinate (Baskin and Baskin, 2004; Finch-Savage and Leubner-Metzger, 2006).Despite decades of research, seed dormancy remains a complex physiological state that is not well understood. The plant hormones abscisic acid (ABA) and GA are mutually antagonistic central players in the germination decision (Finch-Savage and Leubner-Metzger, 2006; Finkelstein et al., 2008). The role of dormancy establishment and maintenance has been attributed to ABA, while GA has been implicated in the initiation and completion of germination. The ratio of ABA to GA signaling, rather than absolute amounts of the hormones, appears to be critical to dormancy breaking (Finch-Savage and Leubner-Metzger, 2006). Environmental stimuli and phytohormones influence the ABA/GA balance, although the mechanisms of signal integration and hormone cross talk are still largely unknown.In many biodiverse regions, fire events provide an irregular but important opportunity for seedling establishment by freeing up key resources such as light, space, and nutrients (Van Staden et al., 2000; Dixon et al., 2009). A clear example of this is seen in the flush of new growth in the immediate postfire environment, indicating potent activation of the soil seed bank. Heat is not required for the germination response, as cold smoke application induced an up to 48-fold increase in the number of germinating seedlings and approximately 3-fold enrichment in species abundance in field trials (Roche et al., 1997; Rokich et al., 2002). It has now been well established that smoke is a broadly effective stimulant that enhances germination of approximately 1,200 species in more than 80 genera worldwide (Dixon et al., 2009). Attempts to study smoke effects on plant physiology have been confounded by the complex mixture of components within smoke, some of which confer toxicity at high concentrations. Bioassay-guided fractionation of smoke water culminated in the discovery and synthesis of the primary germination stimulant 3-methyl-2H-furo[2,3-c]pyran-2-one (KAR₁; Flematti et al., 2004). With the recent identification of three analogous active compounds in smoke water fractions (Fig. 1A; G. Flematti, unpublished data), this family of butenolide molecules have been designated karrikins, after “karrik,” the first recorded Aboriginal Nyungar word for smoke (Dixon et al., 2009).Open in a separate windowFigure 1.Partial structural similarity between the karrikin family of plant growth regulators and strigolactones. A, Molecular structures of KAR₁ (3-methyl-2H-furo[2,3-c]pyran-2-one), KAR₂ (2H-furo[2,3-c]pyran-2-one), KAR₃ (3,5-dimethyl-2H-furo[2,3-c]pyran-2-one), and KAR₄ (3,7-dimethyl-2H-furo[2,3-c]pyran-2-one). B, Molecular structures of a natural (strigol) and a synthetic (GR-24) strigolactone.The parent molecule, KAR_1, is a potent stimulant that enhances germination in some species at subnanomolar concentrations (Flematti et al., 2004; Stevens et al., 2007). In field trials, KAR₁ is effective at less than 5 g ha⁻¹ compared with 10 ton ha⁻¹ smoke water and thus may have practical value in agriculture, conservation, and restoration (Stevens et al., 2007). Smoke water fractions containing KAR₁ have been reported to enhance seedling vigor of several weed and crop species, indicating potential use for KAR₁ as a seed priming agent to improve germination and seedling establishment (Jain et al., 2006; Jain and Van Staden, 2006; Kulkarni et al., 2006; van Staden et al., 2006; Daws et al., 2007a). Since its discovery, a widespread capacity for KAR₁ germination response among angiosperms has been demonstrated (Flematti et al., 2004; van Staden et al., 2004, 2006; Merritt et al., 2006; Daws et al., 2007a; Stevens et al., 2007). Thus, karrikins may be considered a novel class of plant growth regulators with broad impact. To gain a better understanding of the mechanism by which karrikins trigger seed germination and explore their interaction with ABA and GA, we examined KAR₁ responses in Arabidopsis (Arabidopsis thaliana).     

Visceral and not subcutaneous abdominal adiposity reduction drives the benefits of a 1-year lifestyle modification program

Excess visceral adipose tissue (VAT) is associated with an increased cardiometabolic risk. The study examined whether changes in cardiometabolic risk markers after a 1-year lifestyle intervention in viscerally obese men were associated with changes in VAT or with changes in subcutaneous abdominal adipose tissue (SAT). The relative contributions of changes in global adiposity vs. changes in cardiorespiratory fitness to changes in VAT were also quantified. One hundred and forty four men were selected on the basis of an increased waist circumference (≥ 90 cm) associated with dyslipidemia (triglycerides ≥ 1.69 and/or high-density lipoprotein (HDL)-cholesterol <1.03 mmol/l); 117 men completed the 1-year intervention which consisted in a healthy eating, physical activity/exercise program. Body weight, body composition, and fat distribution were assessed by anthropometry and dual-energy X-ray absorptiometry (DEXA)/computed tomography. Cardiorespiratory fitness, plasma adipokine/inflammatory markers, fasting lipoprotein-lipid profile, and oral glucose tolerance test (OGTT) were assessed. VAT volume decreased by 26%, cardiorespiratory fitness improved by 20% (P < 0.0001) after 1 year. Plasma adipokine/inflammatory markers, lipids/lipoproteins, and glucose homeostasis were improved. One-year changes in triglyceride (r = 0.29), apolipoprotein B (r = 0.21), 120-min OGTT-glucose (r = 0.27), and fasting insulin (r = 0.27) levels correlated with changes in VAT (all P < 0.05) after adjustment for changes in SAT. Using a multilinear regression model, VAT reduction was independently associated with SAT reduction and with improvement in cardiorespiratory fitness (R(2) = 0.58, P < 0.0001). Therefore, this healthy eating-physical activity/exercise program improved the cardiometabolic risk profile of viscerally obese men in relation to the reduction of VAT. Furthermore, the reduction in VAT was independently related to the reduction in global adiposity and to the improvement in cardiorespiratory fitness.     

Eight polymorphic microsatellite loci for the Australian plague locust, Chortoicetes terminifera

Few population genetics studies have been carried out on major locust species. In particular, an understanding of the population genetic structure of the Australian plague locust, Chortoicetes terminifera, is lacking. We isolated and characterized eight polymorphic microsatellite loci in C. terminifera, and described experimental conditions for polymerase chain reaction multiplexing and genotyping these loci. The number of alleles per locus ranged from 11 to 29 and the expected heterozygosity ranged from 0.797 to 0.977. One locus was found to be X-linked. Results of cross-taxon amplification tests are reported in four species of the Oedipodinae subfamily.     

Faculty and employee ownership of inventions in Australia

A recent Australian legal decision means that, unless faculty members are bound by an assignment or intellectual property policy, they may own inventions resulting from their research.