Co‐occurrence patterns of trees along macro‐climatic gradients and their potential influence on the present and future distribution of Fagus sylvatica L.

Aim During recent and future climate change, shifts in large‐scale species ranges are expected due to the hypothesized major role of climatic factors in regulating species distributions. The stress‐gradient hypothesis suggests that biotic interactions may act as major constraints on species distributions under more favourable growing conditions, while climatic constraints may dominate under unfavourable conditions. We tested this hypothesis for one focal tree species having three major competitors using broad‐scale environmental data. We evaluated the variation of species co‐occurrence patterns in climate space and estimated the influence of these patterns on the distribution of the focal species for current and projected future climates. Location Europe. Methods We used ICP Forest Level 1 data as well as climatic, topographic and edaphic variables. First, correlations between the relative abundance of European beech (Fagus sylvatica) and three major competitor species (Picea abies, Pinus sylvestris and Quercus robur) were analysed in environmental space, and then projected to geographic space. Second, a sensitivity analysis was performed using generalized additive models (GAM) to evaluate where and how much the predicted F. sylvatica distribution varied under current and future climates if potential competitor species were included or excluded. We evaluated if these areas coincide with current species co‐occurrence patterns. Results Correlation analyses supported the stress‐gradient hypothesis: towards favourable growing conditions of F. sylvatica, its abundance was strongly linked to the abundance of its competitors, while this link weakened towards unfavourable growing conditions, with stronger correlations in the south and at low elevations than in the north and at high elevations. The sensitivity analysis showed a potential spatial segregation of species with changing climate and a pronounced shift of zones where co‐occurrence patterns may play a major role. Main conclusions Our results demonstrate the importance of species co‐occurrence patterns for calibrating improved species distribution models for use in projections of climate effects. The correlation approach is able to localize European areas where inclusion of biotic predictors is effective. The climate‐induced spatial segregation of the major tree species could have ecological and economic consequences.     

The exosome of Trypanosoma brucei.

The yeast exosome is a complex of at least 10 essential 3'-5' riboexonucleases which is involved in 3'-processing of many RNA species. An exosome-like complex has been found or predicted to exist in other eukaryotes but not in Escherichia coli. The unicellular parasite Trypanosoma brucei diverged very early in eukaryotic evolution. We show here that T.brucei contains at least eight exosome subunit homologs, but only a subset of these associate in a complex. Accordingly, the T.brucei exosome is smaller than that of yeast. Both free and complex-associated homologs are essential for cell viability and are involved in 5.8S rRNA maturation. We suggest that the exosome was present in primitive eukaryotes, and became increasingly complex during subsequent evolution.     

Synthesis of sulfated proteoglycans throughout the cell cycle in smooth muscle cells from pig aorta

Cultured smooth muscle cells from pig aorta arrested in G0 phase by serum deprivation were stimulated to proliferate by replacing the medium with one containing 10% serum. Studies in DNA replication and proliferation of cells showed a relatively good synchrony: 90% of the cells were in G1 phase for 16 h after addition of serum; they entered S phase between 18 and 24 h, completed S phase and traversed G2 phase between 24 and 30–32 h; 75% of these cells multiplied after 30–32 h and the remainder were blocked at the end of G2 phase. The synthesis and secretion of sulfated proteoglycans were examined throughout a full cell cycle using metabolic labelling with [³⁵S]sulfate. Smooth muscle cells in G1 or G2 phase synthesized and secreted sulfated proteoglycans with a possible pause at the end of the G2 phase but at the beginning of the S phase and during mitosis the incorporation of [³⁵S]sulfate into these macromolecules stopped entirely. Structural characteristics of sulfated proteoglycans secreted into the medium during G1 phase and an entire cell cycle were investigated. The proportion of proteoglycan complexes and the relative hydrodynamic size of monomers and of constituent subunits of complexes were determined after chromatography on Sepharose CL-2B and CL-6B columns run under both associative and dissociative conditions. No significant differences were observed for the periods of the cell cycle that were studied:

1. 1. [³⁵S]Proteoglycan complexes represented at the end of G1 phase and of the cell cycle respectively 19 and 16% of the total [³⁵S]proteoglycans secreted into the medium.

2. 2. More than 90% of the subunits, obtained after dissociation of complexes, were characterized by a similar k_av after chromatography on Sepharose CL-2B columns eluted under dissociative conditions (k_av 0.68 at the end of G1 phase and 0.65 at the end of full cell cycle).

3. 3. About 95% of monomers synthesized at the two stages of the cell cycle were eluted at k_av 0.25 after chromatography on Sepharose CL-6B column run under associative conditions and were characterized by a similar glycosaminoglycan distribution. These results suggest that smooth muscle cells in culture liberate similar populations of proteoglycans into the medium during the G1 and G2 phases.

     

Endogenous activation by indirect muta-carcinogens and DNA-repair synthesis in mouse-lung fibroblast cultures

Cultures of adult mouse-lung fibroblasts have been treated by series of strong and weak muta-carcinogens. Unscheduled DNA synthesis has been measured by quantitative autoradiography using automatic image analysis. Some of the muta-carcinogens (AFB1, DMN, B(a)P, DMBA, MNNG, 4-NQO) yielded a measurable UDS response, whereas others (2-AA, AFB2, B(e)P, ICR-191) usually known as weak carcinogens, gave no response. The response was not improved by addition of liver S9. This shows that mouse-lung fibroblasts possess their own but limited metabolic activation systems.     

The folding of ovalbumin. Renaturation in vitro versus biosynthesis in vitro.

Hen ovalbumin, the major secretory product of oviduct cells, is a 43 000-dalton glycoprotein. Many studies have led to controversy over the question of whether ovalbumin (OA) can be fully renatured after chemical denaturation. We have studied the renaturation of OA after denaturation with guanidinium chloride, urea or alkaline pH. Denatured OA displays an intrinsic viscosity consistent with nearly complete unfolding of the protein. Removal of the denaturant results in a complete reversal of the changes in intrinsic viscosity. However, closer examination of the renatured protein reveals major differences from the native form. Renatured OA (OAR) can be completely separated from the native form (OAN) by affinity chromatography on phenyl-Sepharose. OAR displays altered tryptophan fluorescence, u.v.-absorption and c.d. spectra. Only OAR binds anilinonaphthalenesulphonate (as measured by fluorescence enhancement). OAR, but not OAN, binds about 2 mol of the covalent hydrophobic affinity probe phenyl isothiocyanate/mol. Renaturation, and the production of OAR, occurs regardless of the oxidation state of the disulphide bonds, of phosphorylation of the protein, and of the presence or the absence of the single carbohydrate chain. OAR may be either monomeric or an irreversible aggregate. Which of these two states is formed depends on the protein concentration during renaturation. Monomeric and aggregated OAR can be distinguished on the basis of some spectroscopic characteristics, but they share the essential hydrophobic characteristics that distinguish them from OAN. OAN and OAR do not spontaneously interconvert. Antibodies raised to each can be made monospecific by immunoabsorption. Thus two stable forms of OA can be obtained, one of which, OAR, displays hydrophobic characteristics. OAN, but not OAR, is formed when OA is synthesized in vitro in a translation system.     

Etude des premiers stades de développement de la Coccidie Coelotropha durchoni

Summary This study considers the earlier growth stages of Coccidium Coelotropha durchoni in its host, Nereis diversicolor. Before evolving into free trophozoites and gamontes in coeliac fluid, the parasites remain in muscular and coeliac cells in microscopic intracellular form. Electron microscope reveals that these stages show an intermediary fine structure between that of a sporozoite — from which they keep some typical characteristics such as the conoid, the fibers and the involuted tubuli — and that of the future free trophozoites. The wall consisting in two clear membrans is provided with one or several micropores. The classical cytoplasmic organites clearly stand out: dictyosomes show constant relationship with ergastoplasm, the mitochondria contain short inner tubuli. Besides the paraglycogen granules and lipoid vacuoles, at least three types of vacuoles may be observed. Peculiar topographic relationship connects mitochondria and paraglycogen granules probably in formation. In the nucleus with classical membrane and heterogeneous structure, a rather voluminous nucleolus may be seen.     

The osmoprotectant proline betaine is a major substrate for the binding-protein-dependent transport system ProU of Escherichia coli K-12

The ProP and ProU transport systems of Escherichia coli mediate the uptake of several osmoprotectants including glycine betaine. Here we report that both ProP and ProU are involved in the transport of the potent osmoprotectant proline betaine. A set of isogenic E. coli strains carrying deletions in either the proP or proU loci was constructed. The growth properties of these mutants in high osmolarity minimal media containing 1 mM proline betaine demonstrated that the osmoprotective effect of this compound was dependent on either an intact ProP or ProU uptake system. Proline betaine competes with glycine betaine for binding to the proU-encoded periplasmic substrate binding protein (ProX) and we estimate a K_D of 5.2 μM for proline betaine binding. This value is similar to the binding constant of the ProX protein determined previously for the binding of glycine betaine (K_D of 1.4 μM). Our results thus demonstrate that the binding-protein-dependent ProU transport system of E. coli mediates the efficient uptake of the osmoprotectants glycine betaine and proline betaine.     

The 85-kilodalton phosphoprotein (pp85) of human herpesvirus 7 is encoded by open reading frame U14 and localizes to a tegument substructure in virion particles.

A family of antigenically related proteins present in cells infected with human herpesvirus 7 (HHV-7), designated phosphoprotein 85 (pp85), comprises a complex of proteins, of which the 85-kDa species is phosphorylated. pp85 is a major determinant of human response to HHV-7 infection (L. Foà-Tomasi, E. Avitabile, L. Ke, and G. Campadelli-Fiume, J. Gen. Virol. 75:2719-2727, 1994; L. Foà-Tomasi, M. P. Fiorilli, E. Avitabile, and G. Campadelli-Fiume, J. Gen. Virol. 77:511-518, 1996; J. B. Black et al., Clin. Diagn. Lab. Immunol. 3:79-83, 1996). By immunoscreening of a cDNA library from HHV-7-infected cells with monoclonal antibody (MAb) 5E1, directed to the proteins of the pp85 complex, we mapped the gene encoding pp85 to the U14 open reading frame of the HHV-7 genome. A prokaryotically expressed fusion protein containing the U14 open reading frame reacted with MAb 5E1 in an immunoblot assay. A functional role for pp85 was defined by immunoelectron microscopy studies. Immunogold labeling of cryosections of HHV-7-infected cord blood mononuclear cells at high resolution localized the reactivity of MAb 5E1 to the outer surface of the virion tegument. This finding demonstrates that pp85, the product of the U14 gene, is a component of the HHV-7 tegument and suggests that the HHV-7 tegument is not a homogeneous structure but rather is composed of substructures, including an outermost layer containing pp85. The present findings, together with previously reported properties of MAb 5E1, including its ability to react with formalin-fixed paraffin-embedded samples, make this antibody a specific tool useful for etiopathogenetic studies of HHV-7 infection in humans and provide the basis for further development of pp85 into a specific recombinant diagnostic reagent.