Glucocorticoid‐inducible expression of a bacterial avirulence gene in transgenic Arabidopsis induces hypersensitive cell death

Pathogenic strains of Pseudomonas syringae pv. tomato carrying the avrRpt2 avirulence gene specifically induce a hypersensitive cell death response in Arabidopsis plants that contain the complementary RPS2 disease resistance gene. Transient expression of avrRpt2 in Arabidopsis plants having the RPS2 gene has been shown to induce hypersensitive cell death. In order to analyze the effects of conditional expression of avrRpt2 in Arabidopsis plants, transgenic lines were constructed that contained the avrRpt2 gene under the control of a tightly regulated, glucocorticoid-inducible promoter. Dexamethasone-induced expression of avrRpt2 in transgenic lines having the RPS2 gene resulted in a specific hypersensitive cell death response that resembled a Pseudomonas syringae-induced hypersensitive response and also induced the expression of a pathogenesis-related gene (PR1). Interestingly, high level expression of avrRpt2 in a mutant rps2–101C background resulted in plant stress and ultimately cell death, suggesting a possible role for avrRpt2 in Pseudomonas syringae virulence. Transgenic RPS2 and rps2 plants that contain the glucocorticoid-inducible avrRpt2 gene will provide a powerful new tool for the genetic, physiological, biochemical, and molecular dissection of an avirulence gene-specified cell death response in both resistant and susceptible plants.     

The Discovery of orally available thrombin inhibitors : Studies towards the optimisation of CGH1668

The chemical optimisation of CGH1668 1 is described employing an in vivo model of absorption to determine the influence on bioavailability of single point modifications to five key molecular templates. The discovery of an orally bioavailable and selective thrombin inhibitor, 24, highlights the utility of this approach.     

Organometallic flavonoid derivatives as spectroscopic probes

Derivatives of naringenin have been synthesized with organometalcarbonyl reporting groups for IR spectroscopy attached at C-2, C-3′, or C-6, and the products have been tested for the induction of nod gene expression using a Rhizobium leguminosarum strain which contains the Escherichia coli lacZ (β-galactosidase) gene fused to nodABC. Derivatives with an OMe substituent within the reporting group moiety showed residual gene induction activity.     

Intraspecific brood mixing and reduced polyandry in a maternal mouth-brooding cichlid

Microsatellite loci were used to evaluate the level of polyandryand intraspecific brood mixing in Protomelas c.f. spilopterus,a paedophagous, maternal mouth-brooding cichlid from Lake MakaiAfrica. We found that broods were fertilized by one to threemales, which was a reduced level of multiple paternity comparedto other mouth-brooding cichlids. Low density of breeding malesand the risk of intraspecific predation are likely explanationsfor reduced polyandry. Intraspecific brood-mixing was foundin four out of the six broods examined, with the proportionsof foreign fry ranging from 6% to 65%. The potential originsof brood mixing are discussed, although no firm conclusionscan be drawn given the limited behavioral observations for thisspecies.     

Desensitization of the Neurokinin-1 Receptor (NK1-R) in Neurons: Effects of Substance P on the Distribution of NK1-R, Gαq/11, G-Protein Receptor Kinase-2/3, and β-Arrestin-1/2

Observations in reconstituted systems and transfected cells indicate that G-protein receptor kinases (GRKs) and β-arrestins mediate desensitization and endocytosis of G-protein–coupled receptors. Little is known about receptor regulation in neurons. Therefore, we examined the effects of the neurotransmitter substance P (SP) on desensitization of the neurokinin-1 receptor (NK1-R) and on the subcellular distribution of NK1-R, G_αq/11, GRK-2 and -3, and β-arrestin-1 and -2 in cultured myenteric neurons. NK1-R was coexpressed with immunoreactive G_αq/11, GRK-2 and -3, and β-arrestin-1 and -2 in a subpopulation of neurons. SP caused 1) rapid NK1-R–mediated increase in [Ca²⁺]_i, which was transient and desensitized to repeated stimulation; 2) internalization of the NK1-R into early endosomes containing SP; and 3) rapid and transient redistribution of β-arrestin-1 and -2 from the cytosol to the plasma membrane, followed by a striking redistribution of β-arrestin-1 and -2 to endosomes containing the NK1-R and SP. In SP-treated neurons G_αq/11 remained at the plasma membrane, and GRK-2 and -3 remained in centrally located and superficial vesicles. Thus, SP induces desensitization and endocytosis of the NK1-R in neurons that may be mediated by GRK-2 and -3 and β-arrestin-1 and -2. This regulation will determine whether NK1-R–expressing neurons participate in functionally important reflexes.     

Do Bird Perching Structures Elevate Seed Rain and Seedling Establishment in Abandoned Tropical Pasture?

Lack of seed dispersal has been shown to be a major factor limiting tropical forest recovery in abandoned pasture land. The goal of this work was to determine whether bird perching structures serve to enhance seed dispersal and seedling establishment in an abandoned pasture in Costa Rica. Two types of perching structures (crossbar and branch) were tested. Bird visitation rates were significantly higher on branch than on crossbar perches. The number of animal-dispersed seeds was significantly higher below branch perches than below crossbar perches or in open pasture. Despite differences in seed rain, percent cover of animal-dispersed plants and the number of seedlings of animal-dispersed plant species were similar below both perch types and in open pasture. Baiting perches with bananas did not increase either bird visitation rates or seed rain. These results suggest that, although bird perching structures increase seed dispersal, they do not overcome other barriers to tropical forest recovery such as seed predation and low seed germination.     

Cytokine inducible matrix metalloproteinase expression in immortalized rat chondrocytes is independent of nitric oxide stimulation

Summary The objective of this study was to determine if an immortalized mammalian chondrocyte cell line had a profile of matrix metalloproteinase (MMP) expression that was consistent with what has been reported for primary chondrocytes in vitro and in vivo. A combination of zymography, Western, and Northern analysis was used to examine the expression of MMPs that are relevant to cartilage degradation. Both interleukin-1β and tumor necrosis factor α induced a 4- to 9-fold increase in the level of MMP-9 expression in conditioned media, and a 17- to 24-fold increase in MMP-3 mRNA. Other compounds such as basic fibroblast growth factor and staurosporine each increased MMP-9 expression individually and potentiated the effects of the two cytokines. Transforming growth factor β had no positive or inhibitory effects. N-methyl arginine blocked the increase in nitric oxide observed following treatment with the cytokines but did not prevent the increased expression of MMPs. The pattern of metalloproteinase expression observed in IRC cells and the response to cytokines is very similar to what has been reported during the pathogenesis of osteoarthritis. The IRC cells should be useful as a model system to study basic mechanisms controlling chondrocyte MMP expression and to identify pharmacological modulators of this process.