Fire frequency and time‐since‐fire effects on the open‐forest and woodland flora of Girraween National Park,south‐east Queensland,Australia

Abstract The effects of recent fire frequency and time‐since‐fire on plant community composition and species abundance in open‐forest and woodland vegetation in Girraween National Park, south‐east Queensland, Australia, were examined. Cover‐abundance data were collected for shrub and vine species in at least 10 400‐m² plots in each of four study areas. Study areas were within one community type and had burnt most recently either 4 or 9 years previously. Variations in fire frequency allowed us to compare areas that had burnt at least three times in the previous 25 years with less frequently burnt areas, and also woodlands that had experienced a 28‐year interfire interval with more frequently burnt areas. Although species richness did not differ significantly with either time‐since‐fire or fire frequency, both these factors affected community composition, fire frequency being the more powerful. Moisture availability also influenced floristics. Of the 67 species found in five or more plots, six were significantly associated with time‐since‐fire, whereas 11 showed a significant difference between more and less frequently burnt plots in each of the two fire‐frequency variables. Most species, however, did not vary in cover‐abundance with the fire regime parameters examined. Even those species that showed a marked drop in cover‐abundance when exposed to a particular fire regime generally maintained some presence in the community. Five species with the capacity to resprout after fire were considered potentially at risk of local extinction under regimes of frequent fire, whereas two species were relatively uncommon in long‐unburnt areas. Variable fire regimes, which include interfire intervals of at least 15 years, could be necessary for the continuity of all species in the community.     

The crystal structure and mutational binding analysis of the extracellular domain of the platelet-activating receptor CLEC-2

The human C-type lectin-like molecule CLEC-2 is expressed on the surface of platelets and signaling through CLEC-2 causes platelet activation and aggregation. CLEC-2 is a receptor for the platelet-aggregating snake venom protein rhodocytin. It is also a newly identified co-receptor for human immunodeficiency virus type 1 (HIV-1). An endogenous ligand has not yet been identified. We have solved the crystal structure of the extracellular domain of CLEC-2 to 1.6-A resolution, and identified the key structural features involved in ligand binding. A semi-helical loop region and flanking residues dominate the surface that is available for ligand binding. The precise distribution of hydrophobic and electrostatic features in this loop will determine the nature of any endogenous ligand with which it can interact. Major ligand-induced conformational change in CLEC-2 is unlikely as its overall fold is compact and robust. However, ligand binding could induce a tilt of a 3-10 helical portion of the long loop region. Mutational analysis and surface plasmon resonance binding studies support these observations. This study provides a framework for understanding the effects of rhodocytin venom binding on CLEC-2 and for understanding the nature of likely endogenous ligands and will provide a basis for rational design of drugs to block ligand binding.     

The restricted seed rain of a mistletoe specialist

Specialist frugivores are the dominant consumers of mistletoe fruit in many regions and have been shown to intensify infections of host plants as a result of their rapid gut passage rates and dependence on existing infections. The role of specialist frugivores in long distance dispersal of mistletoe and establishment of new infections is unclear, and has not been explicitly evaluated previously. Here we critically examine the premise that specialists are the dominant dispersers by examining the role of an Australian mistletoe specialist (mistletoebird Dicaeum hirundinaceum Dicaeidae) in dispersing mistletoe (Amyema preissii Santalales: Loranthaceae) seeds beyond infected host stands. We use two primary lines of evidence – presence of birds using remote call recorders, and presence of dispersed seeds via surveys for defecated seeds on host branches. The observed and inferred movements of the mistletoebird were wholly restricted to habitat patches containing mistletoe, and this bird was not observed to transport seeds to nearby uninfected host stands within the study system. While mistletoe specialists may provide much of the within‐stand dispersal service for mistletoes, this serves only to aggregate and intensify existing infections. We suggest that long distance dispersal of mistletoe seeds beyond existing hosts and infection centres is not performed by these dietary specialists, these services more likely to be provided by generalist frugivores and other occasional mistletoe fruit consumers.     

A CDK-independent function of mammalian Cks1: targeting of SCF(Skp2) to the CDK inhibitor p27Kip1.

The Cks/Suc1 proteins associate with CDK/cyclin complexes, but their precise function(s) is not well defined. Here we demonstrate that Cks1 directs the ubiquitin-mediated proteolysis of the CDK-bound substrate p27Kip1 by the protein ubiquitin ligase (E3) SCF(Skp2). Cks1 associates with the F box protein Skp2 and is essential for recognition of the p27Kip1 substrate for ubiquitination in vivo and in vitro. Using purified recombinant proteins, we reconstituted p27Kip1 ubiquitination activity and show that it is dependent on Cks1. CKS1-/- mice are abnormally small, and cells derived from them proliferate poorly, particularly under limiting mitogen conditions, possibly due to elevated levels of p27Kip1.     

Receptor expression and oxidase activity in human neutrophils: Regulation by granulocyte-macrophage colony-stimulating factor and dependence upon protein biosynthesis

Incubation of human bloodstream neutrophils with 50 u/ml recombinant granulocyte-macrophage colony-stimulating factor (rGM-CSF) primed the respiratory burst (as assessed by fMet-Leu-Phe stimulated luminol-dependent chemiluminescence) and resulted in a rapid (within 15 min) upregulation of expression of CD11b and CD18 (as measured by FACS analysis). This rapid priming and modulation of receptor expression was not inhibited by cycloheximide and hence appeared to be independent ofde novo protein biosynthesis. When neutrophils were incubated for up to 5 h in culture, the fluorescence distributions of CD11b and CD18 declined indicating the loss of expression of these receptors as the neutrophils aged, but in rGM-CSF treated suspensions receptor expression was maintained. When neutrophils were incubated in the presence of cycloheximide, they progressively lost their ability to generate reactive oxidants in response to fMet-Leu-Phe so that by 5 h incubation with this inhibitor they could only generate about 25% of the oxidative response stimulated in untreated cells, and the expression of CD16 and CD18 was grossly impaired. Similar effects were observed in rGM-CSF treated suspensions except that cycloheximide required longer incubation times (typically 4–5 h) before impairment of function or receptor expression occurred. These data show thatde novo protein biosynthesis is required for both the maintenance of neutrophil function and also for the continued expression of some plasma membrane receptors.Abbreviations fMet-Leu-Phe N-formylmethionyl-Leucyl-Phenylalanine - rGM-CSF recombinant granulocyte-macrophage colony-stimulating factor - FITC fluorescein isothiocyanate conjugate - Luminol 5-amino-2,3-dihydrophthalazine-1,4-dione     

A biomechanical analysis of prognathous and orthognathous insect head capsules: evidence for a many‐to‐one mapping of form to function

Insect head shapes are remarkably variable, but the influences of these changes on biomechanical performance are unclear. Among ‘basal’ winged insects, such as dragonflies, mayflies, earwigs and stoneflies, some of the most prominent anatomical changes are the general mouthpart orientation, eye size and the connection of the endoskeleton to the head. Here, we assess these variations as well as differing ridge and sclerite configurations using modern engineering methods including multibody dynamics modelling and finite element analysis in order to quantify and compare the influence of anatomical changes on strain in particular head regions and the whole head. We show that a range of peculiar structures such as the genal/subgenal, epistomal and circumocular areas are consistently highly loaded in all species, despite drastically differing morphologies in species with forward‐projecting (prognathous) and downward‐projecting (orthognathous) mouthparts. Sensitivity analyses show that the presence of eyes has a negligible influence on head capsule strain if a circumocular ridge is present. In contrast, the connection of the dorsal endoskeletal arms to the head capsule especially affects overall head loading in species with downward‐projecting mouthparts. Analysis of the relative strains between species for each head region reveals that concerted changes in head substructures such as the subgenal area, the endoskeleton and the epistomal area lead to a consistent relative loading for the whole head capsule and vulnerable structures such as the eyes. It appears that biting‐chewing loads are managed by a system of strengthening ridges on the head capsule irrespective of the general mouthpart and head orientation. Concerted changes in ridge and endoskeleton configuration might allow for more radical anatomical changes such as the general mouthpart orientation, which could be an explanation for the variability of this trait among insects. In an evolutionary context, many‐to‐one mapping of strain patterns onto a relatively similar overall head loading indeed could have fostered the dynamic diversification processes seen in insects.     

The amino acid sequence of peanut agglutinin

The amino acid sequence of peanut (Arachis hypogaea) agglutinin was determined from three major fragments obtained by mild acid cleavage at Asp-Pro peptide bonds. The sequence of 236 amino acids has residues identical to those that form the metal-binding site and the hydrophobic pocket in concanavalin A and other lectins, although the overall similarity is only 42%. In the segments of peanut agglutinin that correspond to the four loops that form the carbohydrate-binding site in concanavalin A and favin, several central residues are homologous, while others show changes to smaller side chains, such as Tyr----Gly. The carbohydrate-binding site of peanut agglutinin may therefore have a similar peptide-backbone architecture, but form a considerably more open cleft.     

Sex chromosome elimination,X chromosome inactivation and reactivation in the southern brown bandicoot Isoodon obesulus (Marsupialia: Peramelidae)

Cytogenetic studies have shown that bandicoots (family Peramelidae) eliminate one X chromosome in females and the Y chromosome in males from some somatic tissues at different stages during development. The discovery of a polymorphism for X-linked phosphoglycerate kinase (PGK-1) in a population of Isoodon obesulus from Mount Gambier, South Australia, has allowed us to answer a number of long standing questions relating to the parental source of the eliminated X chromosome, X chromosome inactivation and reactivation in somatic and germ cells of female bandicoots. We have found no evidence of paternal PGK-1 allele expression in a wide range of somatic tissues and cell types from known female heterozygotes. We conclude that paternal X chromosome inactivation occurs in bandicoots as in other marsupial groups and that it is the paternally derived X chromosome that is eliminated from some cell types of females. The absence of PGK-1 paternal activity in somatic cells allowed us to examine the state of X chromosome activity in germ cells. Electrophoresis of germ cells from different aged pouch young heterozygotes showed only maternal allele expression in oogonia whereas an additional paternally derived band was observed in pre-dictyate oocytes. We conclude that reactivation of the inactive X chromosome occurs around the onset of meiosis in female bandicoots. As in other mammals, late replication is a common feature of the Y chromosome in male and the inactive X chromosome in female bandicoots. The basis of sex chromosome loss is still not known; however later timing of DNA synthesis is involved. Our finding that the paternally derived X chromosome is eliminated in females suggests that late DNA replication may provide the imprint for paternal X inactivation and the elimination of sex chromosomes in bandicoots.     

Virological Efficacy in Cerebrospinal Fluid and Neurocognitive Status in Patients with Long-Term Monotherapy Based on Lopinavir/Ritonavir: An Exploratory Study

Background

Data on suppression of HIV replication in the CNS and on the subsequent risk of neurocognitive impairment using monotherapy with boosted protease inhibitors are limited.

Methods

Ours was an exploratory cross-sectional study in patients on lopinavir/ritonavir-based monotherapy (LPV/r-MT) or standard triple therapy (LPV/r-ART) for at least 96 weeks who maintained a plasma viral load <50 copies/mL. HIV-1 RNA in CSF was determined by HIV-1 SuperLow assay (lower limit of detection, 1 copy/mL). Neurocognitive functioning was assessed using a recommended battery of neuropsychological tests covering 7 areas. Neurocognitive impairment (NCI) was determined and also a global deficit score (GDS) for study comparisons.

Results

Seventeen patients on LPV/r-MT and 17 on LPV/r-ART were included. Fourteen (82.4%) patients on LPV/r-MT and 16 (94.1%) on LPV/r-ART had HIV-1 RNA <1 copy/mL in CSF (p = 0.601). NCI was observed in 7 patients on LPV/r-MT and in 10 on LPV/r-ART (41% vs 59%; p = 0.494). Mean (SD) GDS was 0.22 (0.20) in patients on LPV/r-MT and 0.47 (0.34) in those on LPV/r-ART (p = 0.012).

Conclusions

Suppression of HIV in CSF is similar in individuals with durable plasma HIV-1 RNA suppression who are receiving LPV/r-MT or LPV/r-ART for at least 96 weeks. Findings for HIV-1 replication in CSF and neurocognitive status indicate that this strategy seems to be safe for CNS functioning.