Intra- and interspecific variation in trophic ecology of ‘predatory’ ants in the subfamily Ponerinae

1. The characterisation of energy flow through communities is a primary goal of ecology. Furthermore, predator–prey interactions can influence both species abundance and community composition. The ant subfamily Ponerinae includes many predatory species that range from generalist insectivores to highly specialised hunters that target a single prey type. Given their high diversity and ubiquity in tropical ecosystems, measuring intra- and interspecific variation in their trophic ecology is essential for understanding the role of ants as predators of insect communities. 2. The stable isotopic composition of nitrogen of 22 species from the ant subfamily Ponerinae was measured, relative to plants and other predatory and herbivorous insects at two Atlantic Forest sites in Argentina. The study tested the general assumption that ponerine ants are all predatory, and examined intra- and interspecific variation in trophic ecology relative to habitat, body size and cytochrome c oxidase subunit 1 sequences (DNA barcoding). 3. Stable isotope analysis revealed that most ponerines occupy high trophic levels (primary and secondary predators), but some species overlapped with known insect herbivores. Species residing at low trophic levels were primarily arboreal and may rely heavily on nectar or other plant-based resources in their diet. In addition, larger species tend to occupy lower trophic positions than smaller species. 4. Although some of the species were divided into two or more genetic clusters by DNA barcoding analysis, these clusters did not correspond to intraspecific variation in trophic position; therefore, colony dietary flexibility most probably explains species that inhabit more than one trophic level.     

Wild‐type p53 enhances endothelial barrier function by mediating RAC1 signalling and RhoA inhibition

Inflammation is the major cause of endothelial barrier hyper‐permeability, associated with acute lung injury and acute respiratory distress syndrome. This study reports that p53 “orchestrates” the defence of vascular endothelium against LPS, by mediating the opposing actions of Rac1 and RhoA in pulmonary tissues. Human lung microvascular endothelial cells treated with HSP90 inhibitors activated both Rac1‐ and P21‐activated kinase, which is an essential element of vascular barrier function. 17AAG increased the phosphorylation of both LIMK and cofilin, in contrast to LPS which counteracted those effects. Mouse lung microvascular endothelial cells exposed to LPS exhibited decreased expression of phospho‐cofilin. 17AAG treatment resulted in reduced levels of active cofilin. Silencing of cofilin pyridoxal phosphate phosphatase (PDXP) blocked the LPS‐induced hyper‐permeability, and P53 inhibition reversed the 17AAG‐induced PDXP down‐regulation. P190RHOGAP suppression enhanced the LPS‐triggered barrier dysfunction in endothelial monolayers. 17AAG treatment resulted in P190RHOGAP induction and blocked the LPS‐induced pMLC2 up‐regulation in wild‐type mice. Pulmonary endothelial cells from “super p53” mice, which carry additional p53‐tg alleles, exhibited a lower response to LPS than the controls. Collectively, our findings help elucidate the mechanisms by which p53 operates to enhance barrier function.     

Periplakin, a Novel Component of Cornified Envelopes and Desmosomes That Belongs to the Plakin Family and Forms Complexes with Envoplakin

The cornified envelope is a layer of transglutaminase cross-linked protein that is assembled under the plasma membrane of keratinocytes in the outermost layers of the epidermis. We have determined the cDNA sequence of one of the proteins that becomes incorporated into the cornified envelope of cultured epidermal keratinocytes, a protein with an apparent molecular mass of 195 kD that is encoded by a mRNA with an estimated size of 6.3 kb. The protein is expressed in keratinizing and nonkeratinizing stratified squamous epithelia and in a number of other epithelia. Expression of the protein is upregulated during the terminal differentiation of epidermal keratinocytes in vivo and in culture. Immunogold electron microscopy was used to demonstrate an association of the 195-kD protein with the desmosomal plaque and with keratin filaments in the differentiated layers of the epidermis. Sequence analysis showed that the 195-kD protein is a member of the plakin family of proteins, to which envoplakin, desmoplakin, bullous pemphigoid antigen 1, and plectin belong. Envoplakin and the 195-kD protein coimmunoprecipitate. Analysis of their rod domain sequences suggests that the formation of both homodimers and heterodimers would be energetically favorable. Confocal immunofluorescent microscopy of cultured epidermal keratinocytes revealed that envoplakin and the 195-kD protein form a network radiating from desmosomes, and we speculate that the two proteins may provide a scaffolding onto which the cornified envelope is assembled. We propose to name the 195-kD protein periplakin.     

Patterns of DNA and chromosome variation during in vitro growth in various genotypes of potato

Patterns of variation in nuclear DNA content and chromosome number were analysed in a temporal sequence, during in vitro growth of calli and cell suspensions in two monohaploids, a dihaploid and a tetraploid of potato (Solanum tuberosum). The results showed that both polyploidization and aneuploidy occurred during the initial stages of callus induction in all the genotypes. With further growth of callus, the frequency and extent of polyploidy and aneuploidy increased. In addition, the patterns of DNA and chromosome variation in cell suspension cultures revealed continued mitotic activity and transmission of cells with higher ploidy levels and aneuploidy. The results suggest that endoreduplication as well as endomitosis are important mechanisms of polyploidization, and that chromosome lagging and non-disjunction contribute to the production of aneuploidy.The various genotypes cultured under the same in vitro growth conditions differed in genetic instability, as assessed from the rate and degree of polyploidization and aneuploidy. Monohaploids showed more rapid rate of polyploidization than the dihaploid and tetraploid potatoes. It was concluded that the differences in genetic stability were due to different ploidy levels and genetic make-up of the genotypes.     

Immunoreactivity of Thomsen-Friedenreich (TF) antigen in human neoplasms: the importance of carrier-specific glycotope expression on MUC1.

On the basis of their known fine specificities we evaluated the immunohistochemical marker qualities of two monoclonal antibodies (mabs) defining the tumor-associated TF disaccharide Gal beta 1-3 GalNAc. This antigen is expressed in certain tumors in correlation with prognosis and metastasis. The reactivity of one of these mabs (A78-G/A7) depends on clustered TF disaccharides (glycosylation at vicinal Ser/Thr positions) while the other--mab BW835--has been characterized to bind specifically to TF disaccharide linked to a motif within the MUC1 repeat. Therefore, mab BW835 represents an interesting tool for the identification of tumor-associated glycoforms of MUC1, which are involved in tumor progression and metastasis, but also in the recognition of tumor cells by cytotoxic T cells. As references the TF-binding lectins from peanut (PNA) and Artocarpus integrifolia (jacalin) were applied. The binding patterns of these immunoreagents were strikingly distinct. Mab BW835 showed a significantly stronger reactivity than mab A78-G/A7, especially in gastric, mammary, pancreatic, thyreoideal, renal and bladder carcinomas. PNA and jacalin receptors exhibited an expression in the majority of all cancer types, with the exception of seminoma and glioblastoma/sarcoma. These results can be explained by the broader fine specificities of the lectins. Furthermore, a strong expression of MUC1-bound TF antigen is indicated by the staining pattern of mab BW835. The marker qualities of both antigens, TF and MUC1, are combined in the binding specificity of BW835, and hence this antibody may have a high impact for the immunodetection of these tumor-associated antigens.     

Endoparasitoid wasp bracovirus-mediated inhibition of hemolin function and lepidopteran host immunosuppression

Successful embryonic development of parasitoid wasps in lepidopteran hosts is achieved through co-injection of polydna viruses whose gene products are thought to target the immune responses of the host. One gene product of the endosymbiont bracovirus of the parasitic wasp Cotesia rubecula, CrV1, has been reported to inhibit the immune responses of its endoparasitized lepidopteran host through interference with the haematocyte cytoskeletal structure. Here we establish that CcV1, the Cotesia congregata bracovirus orthologue of CrV1, is also uptaken by lepidopteran haemocytes and haemocyte-like established cell lines, but we also report on a different function of CcV1, which is highly relevant to the inhibition of the host immune responses and is based on its direct interaction with the pattern recognition molecule hemolin. Recombinant CcV1 inhibits hemolin functions, such as lipopolysaccharide binding and bacterial agglutination as well as bacterial phagocytosis by haemocytes and haemocyte-like cell lines, producing functional phenotypes equivalent to those observed to arise from RNAi-based inhibition of hemolin gene expression. Finally, we show that CcV1 and hemolin colocalize on the membrane surface of hemolin-expressing cells, a finding suggesting that CcV1 may be uptaken by haemocytes and inhibit haemocyte function as a result of its interaction with membrane-anchored hemolin.     

Thrombin-Induced Regulation of CD95(Fas) Expression in the N9 Microglial Cell Line: Evidence for Involvement of Proteinase-Activated Receptor<Subscript>1</Subscript> and Extracellular Signal-Regulated Kinase 1/2

Microglia are the immune cells of the CNS. Brain injury triggers phenotypic changes in microglia including regulation of surface antigens. The serine proteinase α-thrombin can induce profound changes in neural cell physiology via cleavage of proteinase-activated receptors (PARs). We recently demonstrated that pharmaceutical-grade recombinant human α-thrombin (rh-thr) induces a restricted set of proteolysis-dependent changes in microglia. CD95(Fas) is a cell-death receptor that is up-regulated in microglia by inflammatory stimuli. Here we characterized the effect of rh-thr on CD95(Fas) expression in the N9 microglial cell line. Dose–response and time course studies demonstrated maximal effects at 100 U/ml and 24 h, respectively. Regulation of expression was seen at both the surface protein and steady-state mRNA levels. The rh-thr-induced effects were mimicked by PAR₁ agonist peptides and blocked by pharmacologic inhibitors selective for extracellular signal-regulated kinase 1/2 (ERK 1/2). Rh-thr also induced a rapid and sustained phosphorylation of ERK 1/2. Thrombin-induced regulation of CD95(Fas) could modulate the neuroinflammatory response in a variety of neurological disorders.     

Assessing the residual effects of Carpobrotus edulis invasion, implications for restoration

We examined whether the residual effects on soil caused by the invasion of Carpobrotus edulis, common iceplant, would inhibit the reestablishment of a native plant species. Carpobrotus edulis interacts both directly by suppressing the growth and establishment of other plants and indirectly by altering soil chemistry. We tested whether the residual effects of C. edulis resulted in lowered germination, survival, growth, and reproduction of Gilia millefoliata, a rare dune annual. We compared G. millefoliata planted in plots previously occupied by C. edulis to G. millefoliata planted in plots that previously had native vegetation. Each plot received three treatments: seed, transplant, and unplanted, and were censused every three weeks until senescence. Carpobrotus edulis had strong negative effects on the germination, survival, growth, and reproduction of G. millefoliata. C. edulis lowers soil pH and increases organic content due to the recalcitrance of tissue to decomposition, which may have evolved as a mechanism to facilitate recolonization and invasion.