Signs of stabilisation and stable coexistence

Many empirical studies motivated by an interest in stable coexistence have quantified negative density dependence, negative frequency dependence, or negative plant–soil feedback, but the links between these empirical results and ecological theory are not straightforward. Here, we relate these analyses to theoretical conditions for stabilisation and stable coexistence in classical competition models. By stabilisation, we mean an excess of intraspecific competition relative to interspecific competition that inherently slows or even prevents competitive exclusion. We show that most, though not all, tests demonstrating negative density dependence, negative frequency dependence, and negative plant–soil feedback constitute sufficient conditions for stabilisation of two‐species interactions if applied to data for per capita population growth rates of pairs of species, but none are necessary or sufficient conditions for stable coexistence of two species. Potential inferences are even more limited when communities involve more than two species, and when performance is measured at a single life stage or vital rate. We then discuss two approaches that enable stronger tests for stable coexistence‐invasibility experiments and model parameterisation. The model parameterisation approach can be applied to typical density‐dependence, frequency‐dependence, and plant–soil feedback data sets, and generally enables better links with mechanisms and greater insights, as demonstrated by recent studies.     

Scavenging of extracellular H2O2 by catalase inhibits the proliferation of HER-2/Neu-transformed rat-1 fibroblasts through the induction of a stress response

High levels of reactive oxygen species (ROS) are associated with cytotoxicity. Alternatively, nontoxic levels of ROS like hydrogen peroxide (H(2)O(2)) can mediate the transmission of many intracellular signals, including those involved in growth and transformation. To identify pathways downstream of endogenous cellular H(2)O(2) production, the response of Rat-1 fibroblasts exhibiting differential HER-2/Neu receptor tyrosine kinase activity to removal of physiological H(2)O(2) concentrations was investigated. The proliferation of all cells was abolished by addition of the H(2)O(2) scavenger catalase to the culture medium. HER-2/Neu activity was not significantly affected by catalase treatment, suggesting that the target(s) of the H(2)O(2) signal lie downstream of the receptor in our model. ERK1/2 phosphorylation was blocked by catalase in fibroblasts expressing wild type Neu, however such a response did not occur in cells possessing activated mutant Neu. This indicates that the ERK1/2 response contributes little to the growth inhibition observed. By contrast, JNK1 activity increased following the addition of catalase or H(2)O(2), regardless of Neu activity or level of cell transformation. Phosphorylation of p38 MAPK was induced by H(2)O(2) but not by catalase. These observations suggest that scavenging of H(2)O(2) from the cellular environment blocks Rat-1 proliferation primarily through the activation of stress pathways.     

Molecular cloning and characterization of the human protein kinase D2. A novel member of the protein kinase D family of serine threonine kinases

We have isolated the full-length cDNA of a novel human serine threonine protein kinase gene. The deduced protein sequence contains two cysteine-rich motifs at the N terminus, a pleckstrin homology domain, and a catalytic domain containing all the characteristic sequence motifs of serine protein kinases. It exhibits the strongest homology to the serine threonine protein kinases PKD/PKCmicro and PKCnu, particularly in the duplex zinc finger-like cysteine-rich motif, in the pleckstrin homology domain and in the protein kinase domain. In contrast, it shows only a low degree of sequence similarity to other members of the PKC family. Therefore, the new protein has been termed protein kinase D2 (PKD2). The mRNA of PKD2 is widely expressed in human and murine tissues. It encodes a protein with a molecular mass of 105 kDa in SDS-polyacrylamide gel electrophoresis, which is expressed in various human cell lines, including HL60 cells, which do not express PKCmicro. In vivo phorbol ester binding studies demonstrated a concentration-dependent binding of [(3)H]phorbol 12,13-dibutyrate to PKD2. The addition of phorbol 12,13-dibutyrate in the presence of dioleoylphosphatidylserine stimulated the autophosphorylation of PKD2 in a synergistic fashion. Phorbol esters also stimulated autophosphorylation of PKD2 in intact cells. PKD2 activated by phorbol esters efficiently phosphorylated the exogenous substrate histone H1. In addition, we could identify the C-terminal Ser(876) residue as an in vivo phosphorylation site within PKD2. Phosphorylation of Ser(876) of PKD2 correlated with the activation status of the kinase. Finally, gastrin was found to be a physiological activator of PKD2 in human AGS-B cells stably transfected with the CCK(B)/gastrin receptor. Thus, PKD2 is a novel phorbol ester- and growth factor-stimulated protein kinase.     

A mouse model for mucopolysaccharidosis type III A (Sanfilippo syndrome)

Mucopolysaccharidosis type III A (MPS III A, Sanfilippo syndrome) is a rare, autosomal recessive, lysosomal storage disease characterized by accumulation of heparan sulfate secondary to defective function of the lysosomal enzyme heparan N- sulfatase (sulfamidase). Here we describe a spontaneous mouse mutant that replicates many of the features found in MPS III A in children. Brain sections revealed neurons with distended lysosomes filled with membranous and floccular materials with some having a classical zebra body morphology. Storage materials were also present in lysosomes of cells of many other tissues, and these often stained positively with periodic-acid Schiff reagent. Affected mice usually died at 7-10 months of age exhibiting a distended bladder and hepatosplenomegaly. Heparan sulfate isolated from urine and brain had nonreducing end glucosamine- N -sulfate residues that were digested with recombinant human sulfamidase. Enzyme assays of liver and brain extracts revealed a dramatic reduction in sulfamidase activity. Other lysosomal hydrolases that degrade heparan sulfate or other glycans and glycosaminoglycans were either normal, or were somewhat increased in specific activity. The MPS III A mouse provides an excellent model for evaluating pathogenic mechanisms of disease and for testing treatment strategies, including enzyme or cell replacement and gene therapy.     

Nociceptin receptor activation inhibits tachykinergic non adrenergic non cholinergic contraction of guinea pig isolated bronchus

We studied the action of nociceptin (NC) on the atropine-resistant contractions of the guinea pig isolated bronchus evoked by the electrical field stimulation (EFS), an effect that is mediated by the activation of excitatory non adrenergic-non cholinergic (eNANC) nerves and the subsequent release of tachykinins. The functional site by which NC acts in this preparation was investigated using few different NC receptor agonists and the newly discovered NC receptor antagonist, [Phe1psi(CH2-NH)Gly2]NC(1-13)NH2 ([F/G]NC(1-13)NH2). NC inhibited in a concentration dependent manner (pEC50 7.14; Em - 87 +/- 3% of control values) EFS induced contractions. NC effect was mimicked by the NC analogues, NCNH2 and NC(1-13)NH2, but not by NC(1-9)NH2. NC (1 microM) did not affect the contractile effects of exogenously applied neurokinin A (1 microM). [F/G]NC(1-13)NH2 (10 microM) completely prevented the inhibition induced by NC (1 microM), whereas naloxone (1 microM) was found inactive. Both naloxone and ([F/G]NC(1-13)NH2 were per se inactive on basal resting tone as well as on the electrically induced contractions. The present findings show that NC inhibits the atropine-resistant EFS-induced contraction in the guinea pig bronchus by inhibiting eNANC nerves, and suggest the presence of NC receptors, distinct from opioid receptors, on the nerves of the guinea pig bronchus.     

Nickel and cobalt reagents promote selective oxidation of Z-DNA

The structural characteristics of Z-DNA were used to challenge the selectivity of guanine oxidation promoted by nickel and cobalt reagents. Base pairing and stacking within all helical structures studied previously had hindered access to guanine and limited its reaction. However, the Z-helix uniquely retains high exposure of guanine N7. This exposure was sufficient to direct oxidation specifically to a plasmid insert -(CG)(13)AATT(CG)(13)- that adopted a Z-conformation under native supercoiling. An alternative insert -(CG)(7)- retained its B-conformation and demonstrated the expected lack of reactivity. For a nickel salen complex made from a particularly bulky ligand, preferential reaction shifted to the junctions within the Z-DNA insert as is common for large reagents. Inactivation of the nickel reagents by high-salt concentrations prevented parallel investigations of Z-DNA, formed by oligonucleotides. However, the activity of Co(2+) was minimally affected by salt and consequently confirmed the high reactivity of 5'-p(CG)(4) in its Z-conformation. These reagents may now be applied to a broad array of targets, since their structural specificity remains predictable for both complex and helical assemblies of nucleic acids.     

AUX1 regulates root gravitropism in Arabidopsis by facilitating auxin uptake within root apical tissues

Plants employ a specialized transport system composed of separate influx and efflux carriers to mobilize the plant hormone auxin between its site(s) of synthesis and action. Mutations within the permease-like AUX1 protein significantly reduce the rate of carrier-mediated auxin uptake within Arabidopsis roots, conferring an agravitropic phenotype. We are able to bypass the defect within auxin uptake and restore the gravitropic root phenotype of aux1 by growing mutant seedlings in the presence of the membrane-permeable synthetic auxin, 1-naphthaleneacetic acid. We illustrate that AUX1 expression overlaps that previously described for the auxin efflux carrier, AtPIN2, using transgenic lines expressing an AUX1 promoter::uidA (GUS) gene. Finally, we demonstrate that AUX1 regulates gravitropic curvature by acting in unison with the auxin efflux carrier to co-ordinate the localized redistribution of auxin within the Arabidopsis root apex. Our results provide the first example of a developmental role for the auxin influx carrier within higher plants and supply new insight into the molecular basis of gravitropic signalling.