A mixed strategy in the annual endemic Aster laurentianus (Asteraceae)--a stress-tolerant, yet opportunistic species

Several environmental factors influence the distribution of plants in coastal salt marshes. Substrate salinity is among the major factors preventing several species from establishing near the water line. However, interspecific competition for light and nutrients is often significant in determining the upper limit of plants along the salt marsh gradient. In this study, we tested the effects of substrate salinity and light and nutrient availability on the performance of the annual Aster laurentianus (Asteraceae), an endangered species of eastern Canadian salt marshes. This species is typically found in a narrow band along the shores of shallow lagoons, cornered between the high water line and the dense, herbaceous community of the upper marsh. Low light availability was the most significant factor limiting plant performance. Salinity had little effect on A. laurentianus as, unexpectedly, did nutrient availability. Yet plants were able to absorb nutrients when these were made more available. Luxury consumption, the uptake of excess nutrients, may make sense for this annual plant because the habitat in which it grows is subject to frequent disturbances (e.g., sand accretion and salinity pulses) that may kill canopy species and release suppressed A. laurentianus individuals. These results suggest that interspecific competition for light may play a significant role in restraining A. laurentianus from the upper part of salt marshes. Luxury consumption may help the species to opportunistically take advantage of release from taller species, particularly towards the upper edge of the salt marsh gradient.     

Transgene expression of green fluorescent protein and germ line transmission in cloned calves derived from in vitro-transfected somatic cells

In vitro transfection of cultured cells combined with nuclear transfer currently is the most effective procedure to produce transgenic livestock. In the present study, bovine primary fetal fibroblasts were transfected with a green fluorescent protein (GFP)-reporter transgene and used as nuclear donor cells in oocyte reconstructions. Because cell synchronization protocols are less effective after transfection, activated oocytes may be more suitable as hosts for nuclear transfer. To examine the role of host cytoplasm on transgene expression and developmental outcome, GFP-expressing fibroblasts were fused to oocytes reconstructed either before (metaphase) or after (telophase) activation. Expression of GFP was examined during early embryogenesis, in tissues of cloned calves, and again during embryogenesis, after passage through germ line using semen from the transgenic cloned offspring. Regardless of the kind of host cytoplasm used, GFP became detectable at the 8- to 16-cell stage, approximately 80 h after reconstruction, and remained positive at all later stages. After birth, although cloned calves obtained through both procedures expressed GFP in all tissues examined, expression levels varied both between tissues and between cells within the same tissue, indicating a partial shutdown of GFP expression during cellular differentiation. Moreover, nonexpressing fibroblasts derived from transgenic offspring were unable to direct GFP expression after nuclear transfer and development to the blastocyst stage, suggesting an irreversible silencing of transgenes. Nonetheless, GFP was expressed in approximately half the blastocysts obtained with sperm from a transgenic clone, confirming transmission of the transgene through the germ line.     

Structure of a highly phosphorylated lipopolysaccharide core in the Delta algC mutants derived from Pseudomonas aeruginosa wild-type strains PAO1 (serogroup O5) and PAC1R (serogroup O3)

Lipopolysaccharides (LPS) were isolated from rough-type mutant strains of Pseudomonas aeruginosa (Delta algC) derived from wild-type strains PAO1 (serogroup O5) and PAC1R (serogroup O3). Structural studies of the LPS core region with a special focus on the phosphorylation pattern were performed by 2D NMR spectroscopy, including a 1H,(31)P HMQC-TOCSY experiment, MALDI-TOF MS, and Fourier-transform ion cyclotron resonance ESIMS using the capillary skimmer dissociation technique. Both LPS were found to contain two residues each of 3-deoxy-D-manno-oct-2-ulosonic acid (Kdo) and L-glycero-D-manno-heptose (Hep), one residue of N-(L-alanyl)-D-galactosamine and one O-carbamoyl group (Cm) on the distal Hep residue. The following structures of a tetrasaccharide trisphosphate from strain PAC1R Delta algC and that carrying an additional ethanolamine phosphate group (PEtN) from strain PAO1 Delta algC were elucidated: [carbohydrate structre: see text] where R=P in PAC1R Delta algC and PPEtN in PAO1 Delta algC. To our knowledge, in this work the presence of ethanolamine diphosphate is unambiguously confirmed and its position established for the first time in the LPS core of a rough-type strain of P. aeruginosa. In addition, the structure of the complete LPS core of wild-type strain P. aeruginosa PAO1 was reinvestigated and the position of the phosphorylation sites was revised.     

Efficient synthesis of 5-thio-D-arabinopyranose and 5-thio-D-xylopyranose from the corresponding D-pentono-1,4-lactones

5-Thio-D-arabinopyranose (5) and 5-thio-D-xylopyranose (10) were synthesized from the corresponding D-pentono-1,4-lactones. After regioselective bromination at C-5, transformation into 5-S-acetyl-5-thio derivatives, reduction into lactols and deprotection afforded the title compounds in 49 and 42% overall yield, respectively.     

Intracellular maturation and transport of tumor necrosis factor alpha converting enzyme

The tumor necrosis factor alpha converting enzyme (TACE) activity is required for the shedding of a variety of biologically active membrane bound precursors. The activation of TACE necessitates the proteolytic cleavage of its prodomain, a process that was suggested to be catalyzed by the proprotein convertase furin. However, the involvement of furin in this activation process has never been experimentally demonstrated. We have shown that the furinlike cleavage site (R-V-K-R(214)) localized between the prodomain and the metalloprotease domain of TACE is the sole site that can be in vitro cleaved by furin. In Cos7 cells, the release of TACE-processed substrates was reduced by the overexpression of the furin-specific proprotein convertase inhibitor Portland alpha1-antitrypsin inhibitor, but the release of TACE-processed substrates was increased by overexpression of furin in LoVo cells (deficient in furin activity) in which a mature form of TACE was identified. The immature form of TACE was detected at the surface of LoVo cells and at the surface of Cos7 and HT29 cells upon proprotein convertase inhibition. These results suggest that furin is the major proprotein convertase involved in the maturation/activation of TACE which is not a prerequisite for its cell-surface expression.     

Allosteric interactions among pyrethroid,brevetoxin, and scorpion toxin receptors on insect sodium channels raise an alternative approach for insect control

Intensive pyrethroid use in insect control has led to resistance buildup among various pests. One alternative to battle this problem envisions the combined use of synergistically acting insecticidal compounds. Pyrethroids, scorpion - and β-toxins, and brevetoxins bind to distinct receptor sites on voltage-gated sodium channels (NaChs) and modify their function. The binding affinity of scorpion -toxins to locust, but not rat-brain NaChs, is allosterically increased by pyrethroids and by brevetoxin-1. Brevetoxin-1 also increases the binding of an excitatory β-toxin to insect NaChs. These results reveal differences between insect and mammalian NaChs and may be exploited in new strategies of insect control.     

Human nongastric H+-K+-ATPase: transport properties of ATP1al1 assembled with different beta-subunits

To investigate whether nongastric H+-K+-ATPases transport Na+ in exchange for K+ and whether different beta-isoforms influence their transport properties, we compared the functional properties of the catalytic subunit of human nongastric H+-K+-ATPase, ATP1al1 (AL1), and of the Na+-K+-ATPase alpha1-subunit (alpha1) expressed in Xenopus oocytes, with different beta-subunits. Our results show that betaHK and beta1-NK can produce functional AL1/beta complexes at the oocyte cell surface that, in contrast to alpha1/beta1 NK and alpha1/betaHK complexes, exhibit a similar apparent K+ affinity. Similar to Na+-K+-ATPase, AL1/beta complexes are able to decrease intracellular Na+ concentrations in Na+-loaded oocytes, and their K+ transport depends on intra- and extracellular Na+ concentrations. Finally, controlled trypsinolysis reveals that beta-isoforms influence the protease sensitivity of AL1 and alpha1 and that AL1/beta complexes, similar to the Na+-K+-ATPase, can undergo distinct K+-Na+- and ouabain-dependent conformational changes. These results provide new evidence that the human nongastric H+-K+-ATPase interacts with and transports Na+ in exchange for K+ and that beta-isoforms have a distinct effect on the overall structural integrity of AL1 but influence its transport properties less than those of the Na+-K+-ATPase alpha-subunit.