Effects of pre-adult and adult experience on host acceptance in choice and non-choice tests in two strains ofTrichogramma

The effect of adult learning through an oviposition experience, and pre-adult learning through development inside a host was investigated in two strains of an Australian egg parasitoid,Trichogramma nrivelae (Hymenoptera: Trichogrammatidae). Host response was measured in two types of laboratory preference tests. In single host tests, females reared on three lepidopteran hosts (Heliothis punctigera (Noctuidae),Papilio aegeus (Papilionidae), andHypolimnas bolina (Nymphalinae)) were presented host eggs individually, and allowed two ovipositions. Pre-adult experience affected host preference in only one strain, while acceptance of a host was increased in both strains when they had previously oviposited in this host species. An oviposition experience had a stronger effect on host preference than pre-adult experience. In choice tests, pairwise combinations of hosts were arranged in an alternating grid. The ratio of host acceptances to host contacts was computed for the whole test and up to the first oviposition. These indicated that effects of rearing host were weak or absent, but the host chosen initially had a strong effect on host preference. Relative size of the hosts had a strong effect on choice of the first host. The implications of learning inTrichogramma are discussed in relation to host preference testing procedures and the selection of candidate strains for mass rearing and inundative release.     

Infection with a novel gammaherpesvirus in northern elephant seals (Mirounga angustirostris)

Twenty juvenile northern elephant seals (Mirounga angustirostris) that died between 1998 and 2004 had ulcers on the tongue, palatine mucosa, and/or tonsils. Histologic examination of the lesions revealed cytoplasmic swelling, nuclear pyknosis, and eosinophilic to amphophilic intranuclear inclusions bodies suggestive of herpesviral infection. Electron microscopic examination and polymerase chain reaction analysis confirmed the presence of a herpesvirus. Subsequent DNA sequencing identified this to be a new gammaherpesvirus that was similar to Porcine lymphotropic virus 2, Alcephaline herpesvirus 1 (malignant catarrhal fever virus from wildebeest), and Chlorocebus rhadinovirus 1 from African green monkeys. Identical herpesviral DNA was also detected in blood and mucosal swabs collected from five healthy elephant seal pups.     

Cardiomyocyte Antihypertrophic Effect of Adipose Tissue Conditioned Medium from Rats and Its Abrogation by Obesity is Mediated by the Leptin to Adiponectin Ratio

White adipocytes are known to function as endocrine organs by secreting a plethora of bioactive adipokines which can regulate cardiac function including the development of hypertrophy. We determined whether adipose tissue conditioned medium (ATCM) generated from the epididymal regions of normal rats can affect the hypertrophic response of cultured rat ventricular myocytes to endothelin-1 (ET-1) administration. Myocytes were treated with ET-1 (10 nM) for 24 hours in the absence or presence of increasing ATCM concentrations. ATCM supressed the hypertrophic response to ET-1 in a concentration-dependent manner, an effect enhanced by the leptin receptor antagonist and attenuated by an antibody against the adiponectin AdipoR1 receptor. Antihypertrophic effects were also observed with ATCM generated from perirenal-derived adipose tissue. However, this effect was absent in ATCM from adipose tissue harvested from corpulent JCR:LA-cp rats. Detailed analyses of adipokine content in ATCM from normal and corpulent rats revealed no differences in the majority of products assayed, although a significant increase in leptin concentrations concomitant with decreased adiponectin levels was observed, resulting in a 11 fold increase in the leptin to adiponectin ratio in ATCM from JCR:LA-cp. The antihypertrophic effect of ATCM was associated with increased phosphorylation of AMP-activated protein kinase (AMPK), an effect abrogated by the AdipoR1 antibody. Moreover, the antihypertrophic effect of ATCM was mimicked by an AMPK activator. There was no effect of ET-1 on mitogen-activated protein kinase (MAPK) activities 24 hour after its addition either in the presence or absence of ATCM. Our study suggests that adipose tissue from healthy subjects exerts antihypertrophic effects via an adiponectin–dependent pathway which is impaired in obesity, most likely due to adipocyte remodelling resulting in enhanced leptin and reduced adiponectin levels.     

The intestinal heme transporter revealed

The iron-containing porphyrin heme provides a rich source of dietary iron for mammals. The fact that animals can derive iron from heme implies the existence of a transporter that would transport heme from the gut lumen into intestinal epithelial cells. In this issue of Cell, Shayeghi, McKie, and co-workers (Shayeghi et al., 2005) now describe a heme transporter that is expressed in the apical region of epithelial cells in the mouse duodenum. Their identification of heme carrier protein 1 (HCP1) provides a major missing piece in our understanding of iron uptake and mammalian nutrition.     

Risk assessment for engineered bacteria used in biocontrol of fungal disease in agricultural crops

A plant growth promoting rhizobacterium (PGPR)Pseudomonas fluorescens SBW25 (WT) protects a number of crop plant species from damping-off caused by Pythium ultimum. A genetically modified, phenazine-1-carboxylic acid (PCA) producing variant, 23.10, carries on its chromosome a single copy of phzABCDEFG, under the control of the P tac constitutive promoter. The genetically modified biological control agent (GM-BCA), 23.10, has improved biocontrol activity when compared to wild type SBW25, and can effectively suppress Pythium spp. present at up to 100 times normal field infestations. GM-BCA inocula establish high population densities which persist well in the phytosphere of several crop plants including pea, wheat and sugar beet, effectively suppressed infection and promoted increase in total plant biomass. It also has an improved spectrum of activity over other plant phytopathogens such as Fusarium spp. Gaeumannomyces graminis var. tritici, Phytophtora cinnamomi and Rhizoctonia solani. However in developing BCAs and in particular GMBCAs it is important to determine whether their use has any adverse effect in the environment. Any observed changes following inoculation with wild type BCA or GM BCA in microbial diversity (bacteria and fungi) were negligible when assessed by either quantitive selective plate count methods (CFU/g) or culture independent molecular assays (SSU rRNA based PCR-DGGE). Rhizosphere community diversity profiles (DGGE) in infected plants in the presence of inocula were highly similar to disease free systems. Histological assessment of the impact of inocula on established functional mycorrhizae associations were conducted on cores collected from an established field margin grassland pasture. No adverse impact on mycorrhizal colonization and root infection were recorded after addition of WT or GM-BCA bacterial inocula as a soil drench. This approach and the related culturable and culture independent methods have recorded only a minor, transient perturbation to microbial communities, but as far as we are aware this is the first direct demonstration that a functional, AFC producing GMM also has only a transient impact on mycorrhizal associations in established plant communities. In all instances studied the plant species, plant stage of development and disease, damping-off, had a greater impact on changes in rhizosphere diversity than the presence of an introduced GM bacterial inocula.     

The contribution of Plasmodium chabaudi to our understanding of malaria

Malaria kills close to a million people every year, mostly children under the age of five. In the drive towards the development of an effective vaccine and new chemotherapeutic targets for malaria, field-based studies on human malaria infection and laboratory-based studies using animal models of malaria offer complementary opportunities to further our understanding of the mechanisms behind malaria infection and pathology. We outline here the parallels between the Plasmodium chabaudi mouse model of malaria and human malaria. We will highlight the contribution of P. chabaudi to our understanding of malaria in particular, how the immune response in malaria infection is initiated and regulated, its role in pathology, and how immunological memory is maintained. We will also discuss areas where new tools have opened up potential areas of exploration using this invaluable model system.     

Induction of autophagy by drug-resistant esophageal cancer cells promotes their survival and recovery following treatment with chemotherapeutics

We investigated the cell-death mechanisms induced in esophageal cancer cells in response to the chemotherapeutic drugs, 5-fluorouracil (5-FU) and cisplatin. Chemosensitive cell lines exhibited apoptosis whereas chemoresistant populations exhibited autophagy and a morphology resembling type II programmed cell death (PCD). Cell populations that respond with autophagy are more resistant and will recover following withdrawal of the chemotherapeutic agents. Specific inhibition of early autophagy induction with siRNA targeted to Beclin 1 and ATG7 significantly enhanced the effect of 5-FU and reduced the recovery of drug-treated cells. Pharmacological inhibitors of autophagy were evaluated for their ability to improve chemotherapeutic effect. The PtdIns 3-kinase inhibitor 3-methyladenine did not enhance the cytotoxicity of 5-FU. Disruption of lysosomal activity with bafilomycin A 1 or chloroquine caused extensive vesicular accumulation but did not improve chemotherapeutic effect. These observations suggest that an autophagic response to chemotherapy is a survival mechanism that promotes chemoresistance and recovery and that selective inhibition of autophagy regulators has the potential to improve chemotherapeutic regimes. Currently available indirect inhibitors of autophagy are, however, ineffective at modulating chemosensitivity in these esophageal cancer cell lines.