Behaviourally and genetically distinct populations of an invasive ant provide insight into invasion history and impacts on a tropical ant community

Populations of invasive species often exhibit a high degree of spatial and temporal variability in abundance and hence their effects on resident communities. Here, we examine behavioural, genetic and environmental factors that influence variation in populations of the yellow crazy ant, Anoplolepis gracilipes, on the remote Nukunonu Atoll of Tokelau, Pacific Ocean. Behavioural assays revealed high levels of aggression between two groups of yellow crazy ants from different islands, and genetic analysis confirmed the presence of two distinct populations with unique mitochondrial (mt)DNA haplotypes, designated A and D. The two populations likely resulted from two separate invasion events. The populations exhibited significant differences in abundance of A. gracilipes, with a mean sevenfold difference in relative abundance between the two main haplotypes. The higher density haplotype D population coexisted with 50% fewer other ant species and altered ant community composition. Vegetation composition was also significantly different on islands harbouring the two populations. The results suggest genetic differences could play a role in the spatial and temporal variation in the effect of the yellow crazy ant on a small oceanic atoll. We could not differentiate between genetic effects and effects of vegetation. However, our results indicate that spatial variability in behaviour and impacts within populations of invasive species could be in part due to genetic differences, and play a substantial role in influencing the outcome of biological invasions.     

Membrane-bound CC chemokine inhibitor 35K provides localized inhibition of CC chemokine activity in vitro and in vivo

CC chemokines mediate mononuclear cell recruitment and activation in chronic inflammation. We have shown previously that gene transfer using recombinant adenoviruses, encoding a soluble CC chemokine-binding protein of vaccinia virus 35K, can dramatically reduce atherosclerosis and vein graft remodeling in apolipoprotein E knockout mice. In this study, we report the development of a membrane-bound form of 35K (m35K), tagged with GFP, which allows for localized, broad-spectrum CC chemokine blockade. In vitro experiments indicate that m35K-expressing cells no longer undergo CC chemokine-induced chemotaxis, and m35K-expressing cells can locally deplete the CC chemokines RANTES (CCL5) and MIP-1alpha (CCL3) from supernatant medium. This sequestration of CC chemokines can prevent chemotaxis of bystander cells to CC, but not CX(3)C chemokines. Intraperitoneal injection of mice with an adenovirus-encoding m35K leads to a significant (44%) decrease in leukocyte recruitment into the peritoneal cavity in a sterile peritonitis model. Intravenous adenovirus-encoding m35K delivery leads to m35K expression in hepatocytes, which confers significant protection against liver damage (75% reduction in liver enzymes) in a Con A-induced hepatitis model. In summary, we have generated a membrane-bound CC chemokine-binding protein (m35K) that provides localized broad-spectrum CC chemokine inhibition in vitro and in vivo. m35K may be a useful tool to study the role of CC chemokines in leukocyte trafficking and block the recruitment of monocytes in chronic inflammation.     

Palmitoylation of the SNAP25 Protein Family: SPECIFICITY AND REGULATION BY DHHC PALMITOYL TRANSFERASES*

SNAP25 plays an essential role in neuronal exocytosis pathways. SNAP25a and SNAP25b are alternatively spliced isoforms differing by only nine amino acids, three of which occur within the palmitoylated cysteine-rich domain. SNAP23 is 60% identical to SNAP25 and has a distinct cysteine-rich domain to both SNAP25a and SNAP25b. Despite the conspicuous differences within the palmitoylated domains of these secretory proteins, there is no information on their comparative interactions with palmitoyl transferases. We report that membrane association of all SNAP25/23 proteins is enhanced by Golgi-localized DHHC3, DHHC7, and DHHC17. In contrast, DHHC15 promoted a statistically significant increase in membrane association of only SNAP25b. To investigate the underlying cause of this differential specificity, we examined a SNAP23 point mutant (C79F) designed to mimic the cysteine-rich domain of SNAP25b. DHHC15 promoted a marked increase in membrane binding and palmitoylation of this SNAP23 mutant, demonstrating that the distinct cysteine-rich domains of SNAP25/23 contribute to differential interactions with DHHC15. The lack of activity of DHHC15 toward wild-type SNAP23 was not overcome by replacing its DHHC domain with that from DHHC3, suggesting that substrate specificity is not determined by the DHHC domain alone. Interestingly, DHHC2, which is closely related to DHHC15, associates with the plasma membrane in PC12 cells and can palmitoylate all SNAP25 isoforms. DHHC2 is, thus, a candidate enzyme to regulate SNAP25/23 palmitoylation dynamics at the plasma membrane. Finally, we demonstrate that overexpression of specific Golgi-localized DHHC proteins active against SNAP25/23 proteins perturbs the normal secretion of human growth hormone from PC12 cells.     

Interleukin-4 induction of the CC chemokine TARC (CCL17) in murine macrophages is mediated by multiple STAT6 sites in the TARC gene promoter

Background  

Macrophages (Mθ) play a central role in the innate immune response and in the pathology of chronic inflammatory diseases. Macrophages treated with Th2-type cytokines such as Interleukin-4 (IL-4) and Interleukin-13 (IL-13) exhibit an altered phenotype and such alternatively activated macrophages are important in the pathology of diseases characterised by allergic inflammation including asthma and atopic dermatitis. The CC chemokine Thymus and Activation-Regulated Chemokine (TARC/CCL17) and its murine homologue (mTARC/ABCD-2) bind to the chemokine receptor CCR4, and direct T-cell and macrophage recruitment into areas of allergic inflammation. Delineating the molecular mechanisms responsible for the IL-4 induction of TARC expression will be important for a better understanding of the role of Th2 cytokines in allergic disease.     

Dual role of the cysteine-string domain in membrane binding and palmitoylation-dependent sorting of the molecular chaperone cysteine-string protein

S-palmitoylation occurs on intracellular membranes and, therefore, membrane anchoring of proteins must precede palmitate transfer. However, a number of palmitoylated proteins lack any obvious membrane targeting motifs and it is unclear how this class of proteins become membrane associated before palmitoylation. Cysteine-string protein (CSP), which is extensively palmitoylated on a "string" of 14 cysteine residues, is an example of such a protein. In this study, we have investigated the mechanisms that govern initial membrane targeting, palmitoylation, and membrane trafficking of CSP. We identified a hydrophobic 31 amino acid domain, which includes the cysteine-string, as a membrane-targeting motif that associates predominantly with endoplasmic reticulum (ER) membranes. Cysteine residues in this domain are not merely sites for the addition of palmitate groups, but play an essential role in membrane recognition before palmitoylation. Membrane association of the cysteine-string domain is not sufficient to trigger palmitoylation, which requires additional downstream residues that may regulate the membrane orientation of the cysteine-string domain. CSP palmitoylation-deficient mutants remain "trapped" in the ER, suggesting that palmitoylation may regulate ER exit and correct intracellular sorting of CSP. These results reveal a dual function of the cysteine-string domain: initial membrane binding and palmitoylation-dependent sorting.     

Delayed chromosome changes in gamma-irradiated normal and Li-Fraumeni fibroblasts

Knockout mice with only one Trp53 allele (+/- genotype) are highly susceptible to radiation-induced cancers, possibly through numerical chromosome changes. Patients with the Li-Fraumeni syndrome, having heterozygous TP53 germline mutations (+/mut genotype), are also susceptible to spontaneous and radiogenic cancers. We have investigated the susceptibility of six Li-Fraumeni syndrome +/mut and six normal fibroblast strains to induced numerical and unstable structural aberrations at six population doublings after exposure to 3 or 6 Gy gamma rays. Four of the irradiated Li-Fraumeni syndrome strains showed small increases in both aberration types, similar to those seen in the normal strains. In two irradiated Li-Fraumeni syndrome strains, there were high levels of induced structural changes, and one of these showed a modest increase in hyperploidy. We suggest that enhanced sensitivity to delayed radiation-induced chromosome changes in Li-Fraumeni syndrome cells requires other genetic alterations in addition to TP53 heterozygosity, apparently in contrast to the situation in Trp53 heterozygous null mice. If such additional alterations occur in vivo in Li-Fraumeni syndrome patients, they may predispose them to radiogenic cancers, mainly through enhanced structural rather than numerical chromosome changes. Our findings raise questions about the validity of quantitative extrapolation of cytogenetic data from Trp53-defective mice to radiogenic cancer risk in humans.