PA,a stress-induced short cut to switch-on ethylene signalling by switching-off CTR1?

Constitutive triple response 1 (CTR1) is a protein kinase that represses plant responses to ethylene. Recently, we have shown that CTR1 function is negatively regulated by the lipid second messenger phosphatidic acid (PA) in vitro.¹ PA was shown to inhibit (1) CTR1''s protein kinase activity, (2) the intramolecular interaction between N-terminus and kinase domain, and (3) the interaction of CTR1 with the ethylene receptor ETR1. PA typically accumulates within minutes in response to biotic or abiotic stresses, which are known to induce ethylene formation. Although long-term treatment with ethephon does stimulate PA accumulation, our results show no fast increase in PA in response to ethylene. A speculative model is presented which explains how stress-induced PA formation could switch on downstream ethylene responses via interaction of the lipid with CTR1.Key words: lipid signaling, phosphatidic acid, ethylene, constitutive triple response 1, plant stress signaling, protein kinase, phospholipase D     

Bone tissue formation from human embryonic stem cells in vivo

Although the use of embryonic stem cells in the assisted repair of musculoskeletal tissues holds promise, a direct comparison of this cell source with adult marrow-derived stem cells has not been undertaken. Here we have compared the osteogenic differentiation potential of human embryonic stem cells (hESC) with human adult-derived stem cells in vivo. hESC lines H7, H9, the HEF-1 mesenchymal-like, telomerized H1 derivative, the human embryonic kidney epithelial cell line HEK293 (negative control), and adult human mesenchymal stem cells (hMSC) were either used untreated or treated with osteogenic factors for 4 days prior to injection into diffusion chambers and implantation into nude mice. After 11 weeks in vivo chambers were removed, frozen, and analyzed for evidence of bone, cartilage, and adipose tissue formation. All hESCs, when pretreated with osteogenic (OS) factors gave rise exclusively to bone in the chambers. In contrast, untreated hESCs (H9) formed both bone and cartilage in vivo. Untreated hMSCs did not give rise to bone, cartilage, or adipose tissue in vivo, while pretreatment with OS factors engendered both bone and adipose tissue. These data demonstrate that hESCs exposed to OS factors in vitro undergo directed differentiation toward the osteogenic lineage in vivo in a similar fashion to that produced by hMSCs. These findings support the potential future use of hESC-derived cells in regenerative medicine applications.     

Assessment of the Embryonic Stem Cell Test and application and use in the pharmaceutical industry

BACKGROUND: The European Centre for the Validation of Alternative Methods (ECVAM) designed the Embryonic Stem Cell Test (EST) as a tool for classifying developmentally toxic compounds. An in vitro tool to assess developmental toxicity would be of great value to the pharmaceutical industry to help with toxicity‐associated attrition. METHODS: ECVAM's EST protocol was used, but employing a different mouse embryonic stem cell (ESC) line and an alternative differentiation medium. A subset of the compounds used to validate the EST assay along with a number of in‐house pharmaceutical compounds plus marketed pharmaceutical compounds were used to assess the EST performance with receptor‐mediated compounds. RESULTS: Our results with ECVAM compounds mirrored ECVAM's. Compounds that were developmentally toxic in vivo were classified by the EST as moderate risk. Overall, the accuracy was 75% with the current set of data and the predictivity of low‐, moderate‐, and high‐risk compounds was 90, 71, and 60% while the precision was 59, 86, and 100%, respectively. Interestingly, a number of the non‐developmentally toxic compounds had values for the 3T3 IC₅₀ values, which were lower than the ESC IC₅₀ and ID₅₀, a situation not taken into account by ECVAM when designing the EST algorithm. CONCLUSIONS: The assay as currently constructed has a significant false‐positive rate (～40%), but a very low false‐negative rate (～7%). Additional moderate‐ and high‐risk compounds need to be assessed to increase confidence, accuracy, and understanding in the EST's predictivity. Birth Defects Res (Part B), 2008. © 2008 Wiley‐Liss, Inc.     

Baseline morbidity in 2,990 adult African volunteers recruited to characterize laboratory reference intervals for future HIV vaccine clinical trials

Background

An understanding of the health of potential volunteers in Africa is essential for the safe and efficient conduct of clinical trials, particularly for trials of preventive technologies such as vaccines that enroll healthy individuals. Clinical safety laboratory values used for screening, enrolment and follow-up of African clinical trial volunteers have largely been based on values derived from industrialized countries in Europe and North America. This report describes baseline morbidity during recruitment for a multi-center, African laboratory reference intervals study.

Methods

Asymptomatic persons, aged 18–60 years, were invited to participate in a cross-sectional study at seven sites (Kigali, Rwanda; Masaka and Entebbe, Uganda; Kangemi, Kenyatta National Hospital and Kilifi, Kenya; and Lusaka, Zambia). Gender equivalency was by design. Individuals who were acutely ill, pregnant, menstruating, or had significant clinical findings were not enrolled. Each volunteer provided blood for hematology, immunology, and biochemistry parameters and urine for urinalysis. Enrolled volunteers were excluded if found to be positive for HIV, syphilis or Hepatitis B and C. Laboratory assays were conducted under Good Clinical Laboratory Practices (GCLP).

Results and Conclusions

Of the 2990 volunteers who were screened, 2387 (80%) were enrolled, and 2107 (71%) were included in the analysis (52% men, 48% women). Major reasons for screening out volunteers included abnormal findings on physical examination (228/603, 38%), significant medical history (76, 13%) and inability to complete the informed consent process (73, 13%). Once enrolled, principle reasons for exclusion from analysis included detection of Hepatitis B surface antigen (106/280, 38%) and antibodies against Hepatitis C (95, 34%). This is the first large scale, multi-site study conducted to the standards of GCLP to describe African laboratory reference intervals applicable to potential volunteers in clinical trials. Approximately one-third of all potential volunteers screened were not eligible for analysis; the majority were excluded for medical reasons.     

Does Pathogen Spillover from Commercially Reared Bumble Bees Threaten Wild Pollinators?

The conservation of insect pollinators is drawing attention because of reported declines in bee species and the 'ecosystem services' they provide. This issue has been brought to a head by recent devastating losses of honey bees throughout North America (so called, 'Colony Collapse Disorder'); yet, we still have little understanding of the cause(s) of bee declines. Wild bumble bees (Bombus spp.) have also suffered serious declines and circumstantial evidence suggests that pathogen 'spillover' from commercially reared bumble bees, which are used extensively to pollinate greenhouse crops, is a possible cause. We constructed a spatially explicit model of pathogen spillover in bumble bees and, using laboratory experiments and the literature, estimated parameter values for the spillover of Crithidia bombi, a destructive pathogen commonly found in commercial Bombus. We also monitored wild bumble bee populations near greenhouses for evidence of pathogen spillover, and compared the fit of our model to patterns of C. bombi infection observed in the field. Our model predicts that, during the first three months of spillover, transmission from commercial hives would infect up to 20% of wild bumble bees within 2 km of the greenhouse. However, a travelling wave of disease is predicted to form suddenly, infecting up to 35-100% of wild Bombus, and spread away from the greenhouse at a rate of 2 km/wk. In the field, although we did not observe a large epizootic wave of infection, the prevalences of C. bombi near greenhouses were consistent with our model. Indeed, we found that spillover has allowed C. bombi to invade several wild bumble bee species near greenhouses. Given the available evidence, it is likely that pathogen spillover from commercial bees is contributing to the ongoing decline of wild Bombus in North America. Improved management of domestic bees, for example by reducing their parasite loads and their overlap with wild congeners, could diminish or even eliminate pathogen spillover.     

Generalization mediates sensitivity to complex odor features in the honeybee

Animals use odors as signals for mate, kin, and food recognition, a strategy which appears ubiquitous and successful despite the high intrinsic variability of naturally-occurring odor quantities. Stimulus generalization, or the ability to decide that two objects, though readily distinguishable, are similar enough to afford the same consequence, could help animals adjust to variation in odor signals without losing sensitivity to key inter-stimulus differences. The present study was designed to investigate whether an animal's ability to generalize learned associations to novel odors can be influenced by the nature of the associated outcome. We use a classical conditioning paradigm for studying olfactory learning in honeybees to show that honeybees conditioned on either a fixed- or variable-proportion binary odor mixture generalize learned responses to novel proportions of the same mixture even when inter-odor differences are substantial. We also show that the resulting olfactory generalization gradients depend critically on both the nature of the stimulus-reward paradigm and the intrinsic variability of the conditioned stimulus. The reward dependency we observe must be cognitive rather than perceptual in nature, and we argue that outcome-dependent generalization is necessary for maintaining sensitivity to inter-odor differences in complex olfactory scenes.     

AMPK activation attenuates S6K1, 4E-BP1, and eEF2 signaling responses to high-frequency electrically stimulated skeletal muscle contractions.

Regulation of protein translation through Akt and the downstream mammalian target of rapamycin (mTOR) pathway is an important component of the cellular response to hypertrophic stimuli. It has been proposed that 5'-AMP-activated protein kinase (AMPK) activation during muscle contraction may limit the hypertrophic response to resistance-type exercise by inhibiting translational signaling. However, experimental manipulation of AMPK activity during such a stimulus has not been attempted. Therefore, we investigated whether AMPK activation can attenuate the downstream signaling response of the Akt/mTOR pathway to electrically stimulated lengthening muscle contractions. Extensor digitorum longus muscles (n = 8/group) were subjected to a 22-min bout of lengthening contractions by high-frequency sciatic nerve electrical stimulation (STIM) in young adult (8 mo) Fischer 344 x Brown Norway male rats. Forty minutes before electrical stimulation, rats were subcutaneously injected with saline or 5-aminoimidazole-4-carboxamide-1-4-ribofuranoside (AICAR; 1 mg/g body wt), an AMPK activator. Stimulated and contralateral resting muscles were removed at 0, 20, and 40 min post-STIM, and AMPK, acetyl CoA carboxylase (ACC), Akt, eukaryotic initiation factor 4E-binding protein (4E-BP1), 70-kDa ribosomal protein S6 kinase (S6K1), and eukaryotic elongation factor 2 (eEF2) phosphorylations were assessed by Western blot. AICAR treatment increased (P < or = 0.05) post-STIM AMPK (Thr172) and ACC phosphorylation (Ser79/221), inhibited post-STIM S6K1 (Thr389) and 4E-BP1 (gel shift) phosphorylation, and elevated post-STIM eEF2 phosphorylation (Thr56). These findings suggest that translational signaling downstream of Akt/mTOR can be inhibited after lengthening contractions when preceded by AMPK activation and that energetic stress may be antagonistic to the hypertrophic translational signaling response to loaded muscle contractions.     

Influence of previous frost damage on tree growth and insect herbivory of Eucalyptus globulus globulus

The plant stress hypothesis suggests that some herbivores favour stressed plants, whereas the plant vigour hypothesis proposes that other herbivores prefer vigorous plants. The effects of a prior stress, that of frost damage, were examined on the subsequent growth of Eucalyptus globulus globulus and on the response of insect herbivores. Frost damage affected tree growth by reducing new leaf area and increasing specific leaf area (SLA). However, herbivore abundance was not affected by prior frost damage. Two feeding trials using Anoplognathus chloropyrus and Hyalarcta huebneri and a morphometric study of Ctenarytaina eucalypti were conducted to assess the performance of herbivores on trees that had suffered more or less frost damage. Consumption by A. chloropyrus and H. huebneri was unaffected by foliage origin (damaged versus healthy). Hyalarcta huebneri grew faster when fed leaves from previously damaged trees, and C. eucalypti from previously damaged trees were larger than those from healthy trees. Enhanced insect performance on frost damaged plants may have resulted from the high specific leaf area (most likely thinner) leaves. The herbivore abundance data did not support the hypothesis that previously frost damaged plants are preferred by insects. However, increased growth of H. huebneri and larger body size of C. eucalypti on damaged trees indicates that previously stressed trees may produce leaves of higher nutritional value.     

What is driving male mate preference evolution in Jamaican field crickets?

Male mating preferences are often a neglected aspect of studies on sexual selection. Male mating preferences may evolve if they provide males with direct‐fitness benefits such as increased opportunity to fertilize more eggs or indirect‐fitness benefits such as enhanced offspring survival. We tested these ideas using Jamaican field crickets, Gryllus assimilis, previously shown to exhibit male mating preferences. We randomly mated males to either their preferred or non‐preferred potential mates and then asked whether mating treatment influenced egg oviposition or offspring viability. Preferred females were not significantly more fecund and did not produce more viable eggs or offspring than non‐preferred females. Male mate preferences were therefore inconsistent with both the direct‐ and indirect‐fitness benefits hypotheses under the conditions of our experiment. Our null results leave us with an open question about what is driving the evolution of mating preferences in male crickets. Future research should explore the whether the offspring of preferred females are more attractive, have stronger immune systems, and/or experience higher adult longevity.