Compositional differentiation,vegetation‐environment relationships and classification of willow‐characterised vegetation in the western Eurasian Arctic

Question: How does willow‐characterised tundra vegetation of western Eurasia vary, and what are the main vegetation types? What are the ecological gradients and climatic regimes underlying vegetation differentiation? Location: The dataset was collected across a wide spectrum of tundra habitats at 12 sites in subarctic and arctic areas spanning from NW Fennoscandia to West Siberia. Methods: The dataset, including 758 vegetation sample plots (relevés), was analysed using a TWINSPAN classification and NMDS ordination that also included analyses of vegetation‐environment correlations. Results: Based on the TWINSPAN classification, eight vegetation types characterised by willow (cover of upright willows >10%) were discerned: (1) Salix glauca‐Carex aquatilis type, (2) Aulacomnium‐Tomentypnum type, (3) Salix‐Betula‐Hylocomium type, (4) Salix lanata‐Brachythecium mildeanum type, (5) Salix‐Pachypleurum type, (6) S. lanata‐Myosotis nemorosa type, (7) Salix‐Trollius‐Geranium type and (8) Salix‐Comarum palustre‐Filipendula ulmaria type. Willow‐characterised vegetation types were compositionally differentiated from other tundra vegetation and were confined to relatively moist valley and sloping tundra sites, from mire to mineral soils. These vegetation types were encountered across a broad latitudinal zone in which July mean temperature ranged from 6 to 10°C. Conclusions: Willow‐characterised tundra vegetation forms a broad category of ecologically and geographically differentiated vegetation types that are linked to dwarf shrub tundra, shrub tundra or mire. Because of complex ecological gradients underlying compositional differentiation, predicting the responses of willow‐characterised tundra vegetation to a warming climate may be complicated.     

Ability to assess nest predation risk in secondary hole-nesting birds: an experimental study

Because nest predation is the major source of nesting mortality in birds, site-specific predation risk may play an important role in determining birds' ability to select nest sites that reduce predation risk. This possibility has not been adequately tested. Here we report on 5-year experiments by which we studied, independently from birds' earlier experience with specific nest boxes, both the selection and predation risk of nest sites in the common goldeneye (Bucephala clangula). New, previously unoccupied nest boxes were erected in two habitat types on three study areas. Experimentally measured predation risk in the nest boxes varied between 0 and 1.0, i.e. goldeneye females could select a nest site along a wide gradient of possible predation-risk values. We did not find a difference in predation risk between occupied and unoccupied nest boxes, nor was the order of nest box occupation associated with predation risk. A power analysis revealed that our test had reasonably high power to reject a false null hypothesis. Our results suggest that common goldeneye females likely have not evolved an ability to assess predation risk of new, previously unoccupied nest sites.     

Phospholipase A2 assay using an intramolecularly quenched pyrene-labeled phospholipid analog as a substrate

A phospholipid analog 1-palmitoyl-2-6(pyren-1-yl)hexanoyl-sn-glycero-3-phospho-N- (trinitrophenyl)aminoethanol (PPHTE) in which pyrene fluorescence is intramolecularly quenched by the trinitrophenyl group was used as a substrate for pancreatic phospholipase A2. Upon phospholipase A2 catalyzed hydrolysis of this molecule pyrene monomer fluorescence emission intensity increased as a result of the transfer of the pyrene fatty acid to the aqueous phase. Optimal conditions for phospholipase A2 hydrolysis of PPHTE were similar to those observed earlier for other pyrenephospholipids (T. Thuren, J. A. Virtanen, R. Verger, and P. K. J. Kinnunen (1987) Biochim. Biophys. Acta 917, 411-417). Although differential scanning calorimetry revealed no thermal phase transitions for PPHTE between +5 and +60 degrees C the Arrhenius plot of the enzymatic hydrolysis of the lipid showed a discontinuity at 30 degrees C. The molecular origin of this discontinuity remains at present unknown. To study the effects of dimyristoylphosphatidylcholine (DMPC) phase transition at 23.9 degrees C on phospholipase A2 reaction PPHTE was mixed with DMPC in a molar ratio of 1:200 in small unilamellar vesicles. The hydrolysis of DMPC-PPHTE vesicles was measured by following the increase in pyrene monomer fluorescence emission due to phospholipase A2 action on PPHTE. Below the phase transition of DMPC the enzymatic reaction exhibited a hyperbolic behavior. At the transition as well as at slightly higher temperatures a lag period was observed. The longest lag period was approximately 20 min. Above 26 degrees C no lag time could be observed. However, the reaction rates were slower than below the phase transition temperature.(ABSTRACT TRUNCATED AT 250 WORDS)     

Immunohistochemical localization of laminin and fibronectin isoforms in human placental villi.

We studied the localization of laminin alpha1, alpha2, alpha3, alpha5, beta1, beta2, and gamma1 chains and extradomain A- (EDA), EDB-, and oncofetal fibronectin by immunohistochemistry in human placental villi during placental development. The laminin alpha2, alpha5, beta1, beta2, and gamma1 chains were detected in the trophoblastic basement membrane (BM) at all stages of gestation, suggesting the presence of laminin-2, -4, -10, and -11 trimers. The laminin alpha1 chain was selectively found at sites where the villous BM was in contact with proliferating cells in trophoblastic islands or columns. EDA-Fn, but not other Fn isoforms, was found in the trophoblastic BM during the first trimester. The laminin alpha2, beta1, beta2, and gamma1 chains were detected in the villous stroma and capillaries throughout placental development, while the laminin alpha5 chain emerged distinctly during development. Extensive EDA-Fn immunoreactivity was found in first-trimester villous stroma, but distinctly fewer Fn isoforms were seen in the villous stroma during the later stages of gestation. Our results also suggest that, during the formation of new villi, laminins are not found in trophoblastic sprouts before the ingrowth of the villous mesenchyme. Rather, laminins may be deposited at the villous epithelial-mesenchymal interface. Furthermore, the results show that distinct changes occur in the localization of various laminin and Fn isoforms during the maturation of villous trophoblastic and capillary BMs.     

Aminothiazoles inhibit osteoclastogenesis and PGE2 production in LPS‐stimulated co‐cultures of periodontal ligament and RAW 264.7 cells,and RANKL‐mediated osteoclastogenesis and bone resorption in PBMCs

Inflammatory mediator prostaglandin E₂ (PGE₂) contributes to bone resorption in several inflammatory conditions including periodontitis. The terminal enzyme, microsomal prostaglandin E synthase‐1 (mPGES‐1) regulating PGE₂ synthesis is a promising therapeutic target to reduce inflammatory bone loss. The aim of this study was to investigate effects of mPGES‐1 inhibitors, aminothiazoles TH‐848 and TH‐644, on PGE₂ production and osteoclastogenesis in co‐cultures of periodontal ligament (PDL) and osteoclast progenitor cells RAW 264.7, stimulated by lipopolysaccharide (LPS), and bone resorption in RANKL‐mediated peripheral blood mononuclear cells (PBMCs). PDL and RAW 264.7 cells were cultured separately or co‐cultured and treated with LPS alone or in combination with aminothiazoles. Multinucleated cells stained positively for tartrate‐resistant acid phosphatase (TRAP) were scored as osteoclast‐like cells. Levels of PGE₂, osteoprotegerin (OPG) and interleukin‐6, as well as mRNA expression of mPGES‐1, OPG and RANKL were analysed in PDL cells. PBMCs were treated with RANKL alone or in combination with aminothiazoles. TRAP‐positive multinucleated cells were analysed and bone resorption was measured by the CTX‐I assay. Aminothiazoles reduced LPS‐stimulated osteoclast‐like cell formation both in co‐cultures and in RAW 264.7 cells. Additionally, aminothiazoles inhibited PGE₂ production in LPS‐stimulated cultures, but did not affect LPS‐induced mPGES‐1, OPG or RANKL mRNA expression in PDL cells. In PBMCs, inhibitors decreased both osteoclast differentiation and bone resorption. In conclusion, aminothiazoles reduced the formation of osteoclast‐like cells and decreased the production of PGE₂ in co‐cultures as well as single‐cell cultures. Furthermore, these compounds inhibited RANKL‐induced bone resorption and differentiation of PBMCs, suggesting these inhibitors for future treatment of inflammatory bone loss such as periodontitis.     

Two new variants of the lipocalin allergen Bos d 2

Allergens from various sources have been shown to comprise several isoforms. In the present study, a series of chromatographic steps was carried out to separate the lipocalin allergen Bos d 2 isoforms present in cow dander. Subsequent HPLC-MS–MS analyses revealed two new Bos d 2 variants. In one of the proteins, tyrosine (Y83) was substituted by aspartic acid, and in the other protein valine (V102) was replaced by alanine. We propose the three Bos d 2 variants be named as Bos d 2.0101 (previously sequenced Bos d 2), Bos d 2.0102 and Bos d 2.0103. Our results suggest that molecular polymorphism is a common property among lipocalin allergens. Since allergen isoforms may show variation in their IgE binding and/or T-cell reactivity, all of the many allergen forms should be taken into account when planning preparations for immunotherapy.     

A simple procedure for isolation of eukaryotic mRNA polyadenylation factors.

We have devised a simple chromatographic procedure which isolates five polyadenylation factors that are required for polyadenylation of eukaryotic mRNA. The factors were separated from each other by fractionation of HeLa cell nuclear extract in two consecutive chromatographic steps. RNA cleavage at the L3 polyadenylation site of human adenovirus 2 required at least four factors. Addition of adenosine residues required only two of these factors. The fractionation procedure separates two components that are both likely to be poly(A) polymerases. The candidate poly(A) polymerases were interchangeable and participated during both RNA cleavage and adenosine addition. They were discriminated from each other by chromatographic properties, heat sensitivity and divalent cation requirement. We have compared our data with published information and have been able to correlate the activities that we have isolated to previously identified polyadenylation factors. However, we have not been able to assign one of the candidate poly(A) polymerases to a previously identified poly(A) polymerase. This simple fractionation procedure can be used for generating an in vitro reconstituted system for polyadenylation within a short period of time.     

Triggering of the activity of phospholipase A2 by an electric field

In this paper we show that the action of phospholipase A2 can be triggered by applying an electric field across a 1,2-didodecanoyl-sn-3-phosphoglycerol monolayer residing between an alkylated silicon surface and water. When the silicon wafer served as a cathode, rapid activation of porcine pancreatic phospholipase was observed and did depend on the magnitude of the applied potential. The degree of activation was different for the pancreatic phospholipase A2 and snake and bee venom enzymes. Maximally, a 7-fold activation of pancreatic phospholipase A2 was observed when the applied potential was 75 V. The effective field over the lipid film could be estimated to be approximately 25-175 mV, i.e., in the range of membrane potentials found in cells. On the basis of these results, we suggest that changes in membrane potential might be an important factor in the regulation of the action of intracellular phospholipases A2 in vivo.     

Influence of thioacetamide-provoked liver injury on female rat blood and alveolar bone under stress

Experimental liver injury with different stages was induced to adult female test rats with daily injection of thioacetamide (ThAA). The doses administered intraperitoneally were 50 mg/kg body weight. In the liver sections progressive changes of damage, regeneration and fat substitution were noticed. Kidney sections revealed enhanced glomerular atrophy, particularly in the cortical tubules, provoked in the 3-week traumatization period. The influence of ThAA on female rat blood was assayed using standard biochemical methods. The analyses done were: the percentage of blood obtainable and the serum/blood ratio; the serum alanine transferase; serum alkaline phosphatase; serum creatinine; serum hydroxyproline and serum beta-glucuronidase activity in the acute, subacute, chronic and highly chronic stage of liver injury. The biochemical findings show continuously progressing damages when traumatization proceeds. In the 3-week test period the histological findings processed showed an increase in osteoclastic resorption in the alveolar bone around the occlusally stressed tooth simultaneously with a horizontal bone loss. Some indications of recovering incidents were seen, too. Only in the histological findings was no difference seen in the deterioration between both sexes, contrarily to the biochemical results also discussed in this study.     

Ca2+-induced lateral phase separation in phosphatidic acid/phosphatidylcholine monolayers as revealed by fluorescence microscopy

Phase separation in mixed monolayers of phosphatidylcholine (PC) and pyrene-labeled phosphatidic acid (PA) was observed by fluorescence microscopy on an air/water interface as a function of subphase Ca2+ concentration and lateral packing pressure of the film. Below 45 mN m-1 and in the absence of Ca2+ no indications of phase immiscibility were observed. Addition of 1 mM Ca2+ caused extensive phase separation, which was evident immediately after spreading of the film. Further increase in Ca2+ concentration up to 30 mM increased the pyrene excimer intensity of the separated phosphatidic acid enriched domains. In the presence of Ca2+ (1-30 mM) and at surface pressures below 10 mN m-1 phase separation was always evident. However, as surface pressure exceeded 10 mN m-1, mixing of PC and PA occurred. Upon decompression of the film, phase separation reappeared at surface pressures close to 10 mN m-1. The surface textures of the film before and after the compression and subsequent relaxation were different. Inclusion of 30 mol% cholesterol increased the number and decreased the size of the PA domains. In films containing 50 mol% cholesterol no phase separation could be detected at the resolution available.