The involvement of sand disturbance, cannibalism and intra-guild predation in competitive interactions among pit-building antlion larvae

Competition in trap-building predators such as antlion larvae is a complex biotic interaction, potentially involving exploitation competition, sand throwing (i.e., interference competition), cannibalism and intra-guild predation. We investigated the short-term behavioral and developmental responses of the strict sit-and-wait antlion predator Myrmeleon hyalinus to sand disturbance (i.e., quantification of the impact of severe sand throwing), and to con- and hetero-specific competition by a larger sit-and-pursue antlion species Lopezus fedtschenkoi. We found that antlions subjected to sand disturbances reduced their pit construction activity and relocated less often. Furthermore, the reduction in pit construction activity was stronger among antlions subjected to disturbances prior to feeding. Almost no death occurred during the sand disturbance experiment, but as expected, disturbances caused reductions in the relative growth rates of antlions. This negative effect was stronger in the group exposed to sand disturbances prior to feeding. The presence of the sit-and-pursue competitor led to reductions both in pit construction and in relocation activities of M. hyalinus. Although the per-capita food supply was identical in both experiments, only 48% of M. hyalinus larvae survived the competition experiment, and this pattern was consistent between the con- and hetero-specific treatments. However, in the presence of hetero-specific competitors, the relative growth rate of surviving larvae was significantly lower than that measured in the presence of con-specific competitors. Our study demonstrates that investigating the different components of complex biotic interactions can markedly improve our understanding of how these different factors interact to influence the behavior and life history of organisms.     

Levels of Selected Trace Elements, Phytohormones, and Sugars in Pseudomonas-Infected Lycopersicum esculantum Mill Plants

The present study investigated the levels of trace elements (Zn, Cu, Fe, Pb, and Cd), major elements (Ca and K), phytohormones (trans-Zeatin [t-Z] and gibberellic acid [GA]), and sugars (sucrose and glucose) following inoculation with Pseudomonas syringae pv. tomato strain. The results of the trace elements analysis showed that Fe (in the first, fourth, eighth, and tenth study days), Cd (in the fourth, eighth, and tenth study days), Cu (in the fourth and eighth study days), and Zn (in the eighth and tenth study days) increased in bacterium-infected tomato plants, compared to healthy plants. The levels of Pb, Ca, and K did not meaningfully determine a change after inoculation with pathogen. In this vein, the increase accumulation rates of Cu, Zn, and Fe in the injured plants can be an important indicator for the plant defense processes towards pathogen attack. Furthermore, in the first, fourth, eighth, and tenth study days, the glucose and sucrose contents crucially decreased in bacterium-infected plants compared to the control groups. The lowest level of sucrose in bacterium-infected plants was observed on the first day. The findings displayed that, when endogenous t-Z levels did not change after inoculation with virulent bacterium strain, there was a reduction in the first, fourth, eighth, and tenth days in the level of GA when compared with the control group levels. Therefore, there may be a link between lower GA level and enhancement in the expression of defense-related genes. The results of this study showed that there are complex relationships among levels of sugar, trace element, and endogenous phytohormone in the regulation of defense mechanisms against bacterial pathogen attacks.     

The Involvement of IL-17A in the Murine Response to Sub-Lethal Inhalational Infection with Francisella tularensis

Background

Francisella tularensis is an intercellular bacterium often causing fatal disease when inhaled. Previous reports have underlined the role of cell-mediated immunity and IFNγ in the host response to Francisella tularensis infection.

Methodology/Principal Findings

Here we provide evidence for the involvement of IL-17A in host defense to inhalational tularemia, using a mouse model of intranasal infection with the Live Vaccine Strain (LVS). We demonstrate the kinetics of IL-17A production in lavage fluids of infected lungs and identify the IL-17A-producing lymphocytes as pulmonary γδ and Th17 cells. The peak of IL-17A production appears early during sub-lethal infection, it precedes the peak of immune activation and the nadir of the disease, and then subsides subsequently. Exogenous airway administration of IL-17A or of IL-23 had a limited yet consistent effect of delaying the onset of death from a lethal dose of LVS, implying that IL-17A may be involved in restraining the infection. The protective role for IL-17A was directly demonstrated by in vivo neutralization of IL-17A. Administration of anti IL-17A antibodies concomitantly to a sub-lethal airway infection with 0.1×LD₅₀ resulted in a fatal disease.

Conclusion

In summary, these data characterize the involvement and underline the protective key role of the IL-17A axis in the lungs from inhalational tularemia.     

Infusion of a Lipid Emulsion Modulates AMPK and Related Proteins in Rat Liver,Muscle, and Adipose Tissues

The primary objective of this study was to investigate the impact of lipid oversupply on the AMPK pathway in skeletal muscle, liver, and adipose tissue. Male Wistar rats were infused with lipid emulsion (LE) or phosphate‐buffered saline for 5 h/day for 6 days. Muscles exposed to LE for 6 days exhibited increased AMPK and acetyl‐CoA carboxylase (ACC) phosphorylation, along with a greater association between AMPK and Ca²⁺/calmodulin‐dependent protein kinase kinase (CaMKK). No differences in muscle protein phosphatase 2C (PP2C) activity, LKB1 phosphorylation or AMPK and LKB1 association were observed. Muscle ACCβ, and adiponectin receptor 1 (AdipoR1) mRNA levels and PPARγ‐co‐activator 1α (PGC1α) protein levels were also increased in LE‐treated rats. In contrast, AMPK and ACC phosphorylation decreased and PP2C activity increased in rat livers exposed to LE. Hepatic mRNA levels of ACCα, PPARα, AdipoR1, AdipoR2, and sterol regulatory element–binding protein‐1c (SREBP1c) were also reduced after LE infusion. In adipose tissue, there was no significant alteration in AMPK or ACC phosphorylation. These results demonstrate that following lipid oversupply the AMPK pathway was enhanced in rat skeletal muscle while diminished in the liver and was unchanged in adipose tissue. CaMKK in skeletal muscle and PP2C in the liver, at least in part, appear to mediate these alterations. Alterations in AMPK pathway in the liver induced metabolic defects associated with lipid oversupply.     

Migration of zebrafish primordial germ cells: a role for myosin contraction and cytoplasmic flow

The molecular and cellular mechanisms governing cell motility and directed migration in response to the chemokine SDF-1 are largely unknown. Here, we demonstrate that zebrafish primordial germ cells whose migration is guided by SDF-1 generate bleb-like protrusions that are powered by cytoplasmic flow. Protrusions are formed at sites of higher levels of free calcium where activation of myosin contraction occurs. Separation of the acto-myosin cortex from the plasma membrane at these sites is followed by a flow of cytoplasm into the forming bleb. We propose that polarized activation of the receptor CXCR4 leads to a rise in free calcium that in turn activates myosin contraction in the part of the cell responding to higher levels of the ligand SDF-1. The biased formation of new protrusions in a particular region of the cell in response to SDF-1 defines the leading edge and the direction of cell migration.     

Induction of apoptosis in cultured endothelial cells by a cadherin antagonist peptide: involvement of fibroblast growth factor receptor-mediated signalling

Cadherins are a family of transmembrane glycoproteins mediating calcium-dependent, homophilic cell-cell adhesion. In addition, these molecules are involved in signaling events, regulating such processes as cell motility, proliferation, and apoptosis. Members of the cadherin subfamily, called either classical or type I cadherins, contain a highly conserved sequence at their homophilic binding site consisting of the three amino acids--histidine-alanine-valine (HAV). Previous studies have shown that peptides containing the HAV motif inhibit cadherin-dependent events such as cell aggregation, compaction, and neurite outgrowth. We report here that a cyclic peptide, N-Ac-CHAVC-NH2 can perturb cadherin-mediated endothelial cell interactions, resulting in a progressive apoptotic cell death. This effect depends on cell density, as it is only observed when dense cultures are treated with the peptide. Adherens junction (AJ)-associated cadherin and catenins are differentially affected by the N-Ac-CHAVC-NH2 treatment, as judged by double immunofluorescence labeling followed by immunofluorescence-ratio imaging. However, cell-cell adhesions are largely retained during the first few hours after addition of the peptide. It was also observed that following treatment, actin filaments partially lose their plasma membrane anchorage at AJs and translocate towards the cell center. Interestingly, addition of basic fibroblast growth factor to confluent, peptide-treated, endothelial cell cultures, completely blocks apoptosis and the inhibitory peptide reduce the phosphorylation of the FGF receptor target protein FRS2, suggesting that the peptide exerts its effect by inhibiting cadherin-mediated activation of fibroblast growth factor receptor signaling. We propose that cadherin-mediated signaling is essential for maintaining viability of confluent endothelial cells, and that its perturbation by N-Ac-CHAVC-NH2 drives these cells to apoptosis.     

Role of cytokinin in the regulation of root gravitropism

The models explaining root gravitropism propose that the growth response of plants to gravity is regulated by asymmetric distribution of auxin (indole-3-acetic acid, IAA). Since cytokinin has a negative regulatory role in root growth, we suspected that it might function as an inhibitor of tropic root elongation during gravity response. Therefore, we examined the free-bioactive-cytokinin-dependent ARR5::GUS expression pattern in root tips of transformants of Arabidopsis thaliana (L.) Heynh., visualized high cytokinin concentrations in the root cap with specific monoclonal antibodies, and complemented the analyses by external application of cytokinin. Our findings show that mainly the statocytes of the cap produce cytokinin, which may contribute to the regulation of root gravitropism. The homogenous symmetric expression of the cytokinin-responsive promoter in vertical root caps rapidly changed within less than 30 min of gravistimulation into an asymmetrical activation pattern, visualized as a lateral, distinctly stained, concentrated spot on the new lower root side of the cap cells. This asymmetric cytokinin distribution obviously caused initiation of a downward curvature near the root apex during the early rapid phase of gravity response, by inhibiting elongation at the lower side and promoting growth at the upper side of the distal elongation zone closely behind the root cap. Exogenous cytokinin applied to vertical roots induced root bending towards the application site, confirming the suspected inhibitory effect of cytokinin in root gravitropism. Our results suggest that the early root graviresponse is controlled by cytokinin. We conclude that both cytokinin and auxin are key hormones that regulate root gravitropism.Electronic Supplementary Material Supplementary material is available in the online version of this article at http://dx.doi.org/10.1007/s00425-004-1381-8     

Primordial germ-cell development: the zebrafish perspective

Primordial germ cells follow a characteristic developmental path that is manifested in the specialized regulation of basic cell functions and behaviour. Recent studies in zebrafish have greatly enhanced our understanding of the mode of specification of primordial germ cells, cell-fate maintenance and the migration of these cells towards their target, the gonad, where they differentiate into gametes.     

Putrescine activates oxidative stress dependent apoptotic death in ornithine decarboxylase overproducing mouse myeloma cells

Accumulation of putrescine in ornithine decarboxylase overproducing cells provokes apoptotic death that is inhibited by 2-difluoromethylornithine, a specific inhibitor of ODC. The apoptotic process provoked by putrescine involves the release of cytochrome c from the mitochondria and activation of caspases cascades demonstrated by the cleavage of caspase-2, polyA-ribose polymerase (PARP), and proteolytic cleavage of the translation initiation factor 4G (eIF4G). The general caspases inhibitor BD-fmk inhibits PARP cleavage but not cell death. Aminoguanidine, an inhibitor of amine oxidases, inhibits the cleavage of PARP and cell death, whereas the antioxidant BHA inhibits PARP cleavage but not cell death. The intracellular Ca2+ chelator 1,2-bis(o-aminophenoxy)ethane-N,N,N',N'-tetraacetic acid tetra(acetoxymethyl) ester (BAPTA/AM) inhibits both PARP cleavage and cell death. Although the ability of BAPTA/AM to inhibit the induction of apoptosis may suggest that the accumulating putrescine stimulates the release of Ca2+, such a Ca2+ elevation was not observed. We suggest that the accumulation of putrescine leads to oxidative stress that causes cell death.