Sea-ice algae in Arctic pack ice during late winter

Pack ice around Svalbard was sampled during the expedition ARK XIX/1 of RV “Polarstern” (March–April 2003) in order to determine environmental conditions, species composition and abundances of sea-ice algae and heterotrophic protists during late winter. As compared to other seasons, species diversity of algae (total 40 taxa) was not low, but abundances (5,000–448,000 cells l⁻¹) were lower by one to two orders of magnitude. Layers of high algal abundances were observed both at the bottom and in the ice interior. Inorganic nutrient concentrations (NO₂, NO₃, PO₄, Si(OH)₄) within the ice were mostly higher than during other seasons, and enriched compared to seawater by enrichment indices of 1.6–24.6 (corrected for losses through the desalination process). Thus, the survival of algae in Arctic pack ice was not limited by nutrients at the beginning of the productive season. Based on less-detailed physical data, light was considered as the most probable factor controlling the onset of the spring ice-algal bloom in the lower part of the ice, while low temperatures and salinities inhibit algal growth in the upper part of the ice at the end of the winter. Incorporation of ice algae probably took place during the entire freezing period. Possible overwintering strategies during the dark period, such as facultative heterotrophy, energy reserves, and resting spores are discussed.     

Hatching late in the season requires flexibility in the timing of song learning

Most songbirds learn their songs from adult tutors, who can be their father or other male conspecifics. However, the variables that control song learning in a natural social context are largely unknown. We investigated whether the time of hatching of male domesticated canaries has an impact on their song development and on the neuroendocrine parameters of the song control system. Average age difference between early- and late-hatched males was 50 days with a maximum of 90 days. Song activity of adult tutor males decreased significantly during the breeding season. While early-hatched males were exposed to tutor songs for on average the first 99 days, late-hatched peers heard adult song only during the first 48 days of life. Remarkably, although hatching late in the season negatively affected body condition, no differences between both groups of males were found in song characteristics either in autumn or in the following spring. Similarly, hatching date had no effect on song nucleus size and circulating testosterone levels. Our data suggest that late-hatched males must have undergone accelerated song development. Furthermore, the limited tutor song exposure did not affect adult song organization and song performance.     

Baseline,diurnal variations,and stress-induced changes of stress hormones in three captive beluga whales,Delphinapterus leucas

Concentrations of plasma adrenocorticotropic hormone (ACTH), cortisol, and aldosterone were investigated in three adult beluga whales (Delphinapterus leucas), held in a large outdoor public aquarium exhibit. The purpose of this study was to evaluate resting concentrations of these hormones and associated diurnal variations with routine interactions and medical procedures. Resting blood samples were collected voluntarily from the ventral fluke veins at predetermined times of the day to evaluate diurnal changes in analyte concentrations. In addition, hematology and serum chemistry analyses were performed to monitor health status and evaluate changes related to physical exam procedures. Analogous sampling was conducted during out-of-water physical examinations and before and after wading-contact sessions (WCS). Baseline stress hormone concentrations (± SD) were as follows: plasma ACTH (8.41 ± 5.8 pg/mL), serum cortisol (1.80 ± 0.71 g/dL), and serum aldosterone (11.42 ± 5.5 pg/mL). Plasma ACTH and cortisol concentrations were consistently higher in early morning than evening, while aldosterone was higher in the evening. All stress-related hormones were significantly elevated during physical examination. Plasma ACTH concentrations were most increased, 5–10-fold, during physical examination, whereas cortisol and aldosterone showed 2–4-fold elevations. Stress response analytes measured during the WCS did not differ significantly from baseline concentrations.     

Filopodia and adhesion in cancer cell motility

Slender bundled actin containing plasma membrane protrusions, called filopodia, are important for many essential cellular processes like cell adhesion, migration, angiogenesis and the formation of cell-cell contacts. In migrating cells, filopodia are the pioneers at the leading edge which probe the environment for cues. Integrins are cell surface adhesion receptors critically implicated in cell migration and they are transported actively to filopodia tips by an unconventional myosin, myosin-X. Integrin mediated adhesion stabilizes filopodia and promotes cell migration even though integrins are not essential for filopodia initiation. Myosin-X binds also PtdIns(3,4,5)P₃ and this regulates its activation and localization to filopodia. Filopodia stimulate cell migration in many cell types and increased filopodia density has been described in cancer. Furthermore, several proteins implicated in filopodia formation, like fascin, are also relevant for cancer progression. To investigate this further, we performed a meta-analysis of the expression profiles of 10 filopodia-linked genes in human breast cancer. These data implicated that several different filopodia-inducing genes may contribute in a collective manner to cancer progression and the high metastasis rates associated with basal-type breast carcinomas.Key words: filopodia, integrins, migration, cancer     

Proton motive force generation by citrolactic fermentation in Leuconostoc mesenteroides.

In Leuconostoc mesenteroides subsp. mesenteroides 19D, citrate is transported by a secondary citrate carrier (CitP). Previous studies of the kinetics and mechanism of CitP performed in membrane vesicles of L. mesenteroides showed that CitP catalyzes divalent citrate HCit2-/H+ symport, indicative of metabolic energy generation by citrate metabolism via a secondary mechanism (C. Marty-Teysset, J. S. Lolkema, P. Schmitt, C. Divies, and W. N. Konings, J. Biol. Chem. 270:25370-25376, 1995). This study also revealed an efficient exchange of citrate and D-lactate, a product of citrate/carbohydrate cometabolism, suggesting that under physiological conditions, CitP may function as a precursor/product exchanger rather than a symporter. In this paper, the energetic consequences of citrate metabolism were investigated in resting cells of L. mesenteroides. The generation of metabolic energy in the form of a pH gradient (delta pH) and a membrane potential (delta psi) by citrate metabolism was found to be largely dependent on cometabolism with glucose. Furthermore, in the presence of glucose, the rates of citrate utilization and of pyruvate and lactate production were strongly increased, indicating an enhancement of citrate metabolism by glucose metabolism. The rate of citrate metabolism under these conditions was slowed down by the presence of a membrane potential across the cytoplasmic membrane. The production of D-lactate inside the cell during cometabolism was shown to be responsible for the enhancement of the electrogenic uptake of citrate. Cells loaded with D-lactate generated a delta psi upon dilution in buffer containing citrate, and cells incubated with citrate built up a pH gradient upon addition of D-lactate. The results are consistent with an electrogenic citrate/D-lactate exchange generating in vivo metabolic energy in the form of a proton electrochemical gradient across the membrane. The generation of metabolic energy from citrate metabolism in L. mesenteroides may contribute significantly to the growth advantage observed during cometabolism of citrate and glucose.     

Integrin trafficking regulated by Rab21 is necessary for cytokinesis

Adherent cells undergo remarkable changes in shape during cell division. However, the functional interplay between cell adhesion turnover and the mitotic machinery is poorly understood. The endo/exocytic trafficking of integrins is regulated by the small GTPase Rab21, which associates with several integrin alpha subunits. Here, we show that targeted trafficking of integrins to and from the cleavage furrow is required for successful cytokinesis, and that this is regulated by Rab21. Rab21 activity, integrin-Rab21 association, and integrin endocytosis are all necessary for normal cytokinesis, which becomes impaired when integrin-mediated adhesion at the cleavage furrow fails. We also describe a chromosomal deletion and loss of Rab21 gene expression in human cancer, which leads to the accumulation of multinucleate cells. Importantly, reintroduction of Rab21 rescued this phenotype. In conclusion, Rab21-regulated integrin trafficking is essential for normal cell division, and its defects may contribute to multinucleation and genomic instability, which are hallmarks of cancer.     

Post-translational import of the prion protein into the endoplasmic reticulum interferes with cell viability: a critical role for the putative transmembrane domain

Aberrant folding of the mammalian prion protein (PrP) is linked to prion diseases in humans and animals. We show that during post-translational targeting of PrP to the endoplasmic reticulum (ER) the putative transmembrane domain induces misfolding of PrP in the cytosol and interferes with its import into the ER. Unglycosylated and misfolded PrP with an uncleaved N-terminal signal sequence associates with ER membranes, and, moreover, decreases cell viability. PrP expressed in the cytosol, lacking the N-terminal ER targeting sequence, also adopts a misfolded conformation; however, this has no adverse effect on cell growth. PrP processing, productive ER import, and cellular viability can be restored either by deleting the putative transmembrane domain or by using a N-terminal signal sequence specific for co-translational ER import. Our study reveals that the putative transmembrane domain features in the formation of misfolded PrP conformers and indicates that post-translational targeting of PrP to the ER can decrease cell viability.     

Effects of biocides on gene expression in the sulfate-reducing bacterium Desulfovibrio vulgaris Hildenborough

Although sulfate-reducing bacteria (SRB), such as Desulfovibrio vulgaris Hildenborough (DvH) are often eradicated in oil and gas operations with biocides, such as glutaraldehyde (Glut), tetrakis (hydroxymethyl) phosphonium sulfate (THPS), and benzalkonium chloride (BAC), their response to these agents is not well known. Whole genome microarrays of D. vulgaris treated with biocides well below the minimum inhibitory concentration showed that 256, 96, and 198 genes were responsive to Glut, THPS, and BAC, respectively, and that these three commonly used biocides affect the physiology of the cell quite differently. Glut induces expression of genes required to degrade or refold proteins inactivated by either chemical modification or heat shock, whereas BAC appears to target ribosomal structure. THPS appears to primarily affect energy metabolism of SRB. Mutants constructed for genes strongly up-regulated by Glut, were killed by Glut to a similar degree as the wild type. Hence, it is difficult to achieve increased sensitivity to this biocide by single gene mutations, because Glut affects so many targets. Our results increase understanding of the biocide's mode of action, allowing a more intelligent combination of mechanistically different agents. This can reduce stress on budgets for chemicals and on the environment.