Stocking may increase mitochondrial DNA diversity but fails to halt the decline of endangered Atlantic salmon populations

Over the last 50 years, Spanish Atlantic salmon (Salmo salar) populations have been in decline. In order to bolster these populations, rivers were stocked with fish of northern European origin during the period 1974–1996, probably also introducing the furunculosis-inducing pathogen, Aeromonas salmonicida. Here we assess the relative importance of processes influencing mitochondrial (mt)DNA variability in these populations from 1948 to 2002. Genetic material collected over this period from four rivers in northern Spain (Cantabria) was used to detect variability at the mtDNA ND1 gene. Before stocking, a single haplotype was found at high frequency (0.980). Following stocking, haplotype diversity (h) increased in all rivers (mean h before stocking was 0.041, and 0.245 afterwards). These increases were due principally to the dramatic increase in frequency of a previously very low frequency haplotype, reported at higher frequencies in northern European populations proximate to those used to stock Cantabrian rivers. Genetic structuring increased after stocking: among-river differentiation was low before stocking (1950s/1960s Φ _ST = –0.00296–0.00284), increasing considerably at the height of stocking (1980s Φ _ST = 0.18932) and decreasing post-stocking (1990s/2002 Φ _ST = 0.04934–0.03852). Gene flow from stocked fish therefore seems to have had a substantial role in increasing mtDNA variability. Additionally, we found significant differentiation between individuals that had probably died from infectious disease and apparently healthy, angled fish, suggesting a possible role for pathogen-driven selection of mtDNA variation. Our results suggest that stocking with non-native fish may increase genetic diversity in the short term, but may not reverse population declines.     

Incipient invasion of Galenia secunda Sond. (Aizoaceae) in Southern Spain

The occurrence of the carpet weed Galenia secunda (L. fil.) Sond. (Aizoaceae) has been reported in Southern Spain. G. secunda is a prostrate perennial species native to South Africa. In this paper, the current distribution of G. secunda and the main habitats invaded in Southern Spain, are reported. The distribution survey revealed an area of occupancy of 92 ha and an extent of occurrence of 14,250 ha for this species, thus suggesting an early stage of invasion. Since the first citation of this species in Spain (1965), our current data (2007) support a rapid spread and invasiveness of G. secunda as a result of an intense rate of coastal development. G. secunda was more often found near roads, because roads facilitate seed dispersal. G. secunda also appeared in other coastal natural habitats such as sand dunes, where G. secunda forms dense monospecific mats. Studies on its invasion potential and impacts in natural habitats are recommended and control measures should be developed to prevent future expansion.     

Molecular study of the rat liver NADH: Cytochrome c oxidoreductase complex during development and aging

The mechanisms involved in ageing are yet to be fully understood but it is thought that changes produced in energy transfer pathways occurring in the mitochondria may be responsible for the lack of energy typical of the later stages of life. The aim of the present investigation was to determine the enzymatic activity of the liver NADH cytochrome c oxidorectuctase complex (Complex I-III) in mitochondria isolated from the liver of rats of 3 different age groups: lactating, animals (15-17 days), adult females (3-5 months) and old animals (26-30 months). The activities of the unbound Complexes I and III were also determined.An increase in Complex I-III activity was detected during development (142 ± 10 vs. 447 ± 23 mol cyt. c/mg/min, p < 0.001) ang ageing (447 ± 23 vs. 713 ± 45 mol cyt. c/mg//min, p < 0.001). However, unbound Complex I showed a reduction in activity during the ageing period whilst Complex III activity moderately increased. Immunological studies indicated only a moderate increase in the amount of Complex I-III and studies on the purified complex suggested that the increase in activity was due to effects other than an increase in enzyme quantity. The analysis of protein bands and the quantification of prosthetic groups showed particular reductions in the relative concentrations of Complex I subunits including the 51 kDa unit, which binds FMN, confirmed by a similar reduction in levels of the nucleotide. In contrast, 4 of the 5 subunits which increased during the lifetime of the animals corresponded to those of Complex III. These subunits are responsible for the binding of catalytic groups. The results suggest that, in addition to the increase in the amount of enzyme, binding factors between Complexes I and III may also play an important role in the observed increase in Complex I-III activity.     

Two new species of Staurotheca Allman, 1888 (Cnidaria, Hydrozoa, Sertulariidae) from the Scotia Sea (Antarctica)

Two new species of the genus Staurotheca Allman, 1888 have been studied (Staurotheca cornuta sp. nov. and Staurotheca multifurcata sp. nov). The material, from the Scotia Ridge area (Antarctica), was collected in 1986/1987 by the Spanish Antarctic expedition “Antártida 8611”. Each species is described and figured, and its systematic position among allied species is noted. Data concerning autecology and geographical distribution for each species are given. A comparative table listing the main features of the known species of the genus is included. Finally, a general survey of the geographical and bathymetrical distribution of the known species of the genus is presented. Accepted: 1 September 1998     

Thermal biology of the southernmost lizards in the world: Liolaemus sarmientoi and Liolaemus magellanicus from Patagonia,Argentina

We determined the efficiency of thermoregulation by the southernmost liolaemids Liolaemus sarmientoi and L. magellanicus from Patagonia, Argentina (51°S), by measuring body (T_b), microenvironmental, and operative temperatures in the field, and preferred body temperatures in the laboratory (T_pref). L. sarmientoi was found to be a poor thermoregulator, whereas L. magellanicus was deemed to be a constrained thermoconformer. Among all known species of Liolaemus, L. sarmientoi and L. magellanicus had the lowest T_b's when tested in the field; however, their T_pref's were similar to other liolaemids. These data suggest that these southernmost liolaemid species have not evolved appropriate thermoregulatory behaviors or made adequate physiological adaptations to face the extreme thermal challenges of their environment.     

Methylation-independent DNA Binding Modulates Specificity of Repressor of Silencing 1 (ROS1) and Facilitates Demethylation in Long Substrates

DNA cytosine methylation is an epigenetic mark that promotes gene silencing and performs critical roles during reproduction and development in both plants and animals. The genomic distribution of DNA methylation is the dynamic outcome of opposing methylation and demethylation processes. In plants, active demethylation occurs through a base excision repair pathway initiated by 5-methycytosine (5-meC) DNA glycosylases of the REPRESSOR OF SILENCING 1 (ROS1)/DEMETER (DME) family. To gain insight into the mechanism by which Arabidopsis ROS1 recognizes and excises 5-meC, we have identified those protein regions that are required for efficient DNA binding and catalysis. We have found that a short N-terminal lysine-rich domain conserved in members of the ROS1/DME family mediates strong methylation-independent binding of ROS1 to DNA and is required for efficient activity on 5-meC·G, but not for T·G processing. Removal of this domain does not significantly affect 5-meC excision from short molecules, but strongly decreases ROS1 activity on long DNA substrates. This region is not required for product binding and is not involved in the distributive behavior of the enzyme on substrates containing multiple 5-meC residues. Altogether, our results suggest that methylation-independent DNA binding allows ROS1 to perform a highly redundant search for efficient excision of a nondamaged, correctly paired base such as 5-meC in long stretches of DNA. These findings may have implications for understanding the evolution of structure and target specificity in DNA glycosylases.     

Arabidopsis irregular xylem8 and irregular xylem9: implications for the complexity of glucuronoxylan biosynthesis

Mutations of Arabidopsis thaliana IRREGULAR XYLEM8 (IRX8) and IRX9 were previously shown to cause a collapsed xylem phenotype and decreases in xylose and cellulose in cell walls. In this study, we characterized IRX8 and IRX9 and performed chemical and structural analyses of glucuronoxylan (GX) from irx8 and irx9 plants. IRX8 and IRX9 are expressed specifically in cells undergoing secondary wall thickening, and their encoded proteins are targeted to the Golgi, where GX is synthesized. 1H-NMR spectroscopy showed that the reducing end of Arabidopsis GX contains the glycosyl sequence 4-beta-D-Xylp-(1-->4)-beta-D-Xylp-(1-->3)-alpha-L-Rhap-(1-->2)-alpha-D-GalpA-(1-->4)-D-Xylp, which was previously identified in birch (Betula verrucosa) and spruce (Picea abies) GX. This indicates that the reducing end structure of GXs is evolutionarily conserved in woody and herbaceous plants. This sequence is more abundant in irx9 GX than in the wild type, whereas irx8 and fragile fiber8 (fra8) plants are nearly devoid of it. The number of GX chains increased and the GX chain length decreased in irx9 plants. Conversely, the number of GX chains decreased and the chain length heterodispersity increased in irx8 and fra8 plants. Our results suggest that IRX9 is required for normal GX elongation and indicate roles for IRX8 and FRA8 in the synthesis of the glycosyl sequence at the GX reducing end.     

Glutamate Activates Protein Kinase B (PKB/Akt) through AMPA Receptors in Cultured Bergmann Glia Cells

Glutamate is involved in gene expression regulation in neurons and glial cells through the activation of a diverse array of signaling cascades. In Bergmann glia, Ca²⁺-permeable α-hydroxy-5-methyl-4-isoazole-propionic acid (AMPA) receptors become tyrosine phosphorylated after ligand binding and by these means form multiprotein signaling complexes. Of the various proteins that associate to these receptors, the phosphatidylinositol 3-kinase (PI-3K) deserves special attention since D3-phosphorylated phosphoinositides are docking molecules for signaling proteins with a pleckstrin homology domain. In order to characterize the role of PI-3K in AMPA receptors signaling, in the present report we analyze the involvement of the serine/threonine protein kinase B in this process. Our results demonstrate an augmentation in protein kinase B phosphorylation and activity after glutamate exposure. Interestingly, the effect is independent of Ca²⁺ influx, but sensitive to Src blockers. Our present findings broaden our current knowledge of glial glutamate receptors signaling and their involvement glutamatergic neurotransmission.Special issue dedicated to Miklós Palkovits.     

Membrane-transferring sequences of the HIV-1 Gp41 ectodomain assemble into an immunogenic complex

The membrane-proximal stem region of gp41 has been postulated to host the two conserved membrane-transferring domains that promote HIV-1 fusion: the amino-terminal fusion peptide (FP) and the highly aromatic pre-transmembrane sequence. Our results confirm that the hydrophobic FP and membrane-proximal sequences come into contact and form structurally defined complexes. These complexes are immunogenic and evoke responses in rabbits that compete with the recognition of native functional gp41 by the 2F5 monoclonal antibody. We conclude that co-assembly of the FP and the pre-transmembrane sequences might exert a constraint that helps maintain a gp41 stem region pre-fusion structure.