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191.
Siliceous sinters that precipitate around modern hot spring systems are able to fossilize the indigenous microbial communities, forming molds that accurately outline the shape of the microorganisms. Over time, the biomass decays, and only silica molds or their infill may remain as evidence of the former living cells. However, little is known regarding the fidelity of such silica molds in terms of size and morphology, and the preservation of critical parameters for the identification of ancient silicified microorganisms by silica molds remains untested. Here we report experiments examining the formation of microbial molds of the cyanobacterium Synechococcus elongatus in silica gel. We demonstrate that post-depositional processes, primarily desiccation, are crucial for obtaining accurate and robust molds, and that initial desiccation acts to strengthen cell molds against further alteration. However, all silica gel treatments systematically created preservational biases (changes in size, additional structures) that may be misleading and may complicate the identification of fossil microorganisms. 相似文献
192.
Acquisition of scientific reasoning is one of the big challenges in education. A popular educational strategy advocated for acquiring deep knowledge is inquiry-based learning, which is driven by emerging ‘good questions’. This study will address the question: ‘Which design features allow learners to refine questions while preserving student ownership of the inquiry process?’ This design-based research has been conducted over several years with advanced high-school biology classes. The results confirm the central role of question elaboration as an interactive process that leads from vague to complex and adequate. To make this happen, the inquiry process must extend over a long time, learners and teachers should share a knowledge improvement goal, and text produced by students should be structured by question–answer pairs addressing a single concept using authentic resources. Further features are discussion with peers, teacher feedback with respect to answer elaboration and conceptual differentiation, and finally, teacher guidance that should fade out in successive inquiry cycles to ensure student responsibility. 相似文献
193.
Jean‐François Bourzac Karine L'Ériger Jean‐François Larrivée Guillaume Arguin Maude S. Bilodeau Jana Stankova Fernand‐Pierre Gendron 《Journal of cellular physiology》2013,228(1):120-129
With the diabetes epidemic affecting the world population, there is an increasing demand for means to regulate glycemia. Dietary glucose is first absorbed by the intestine before entering the blood stream. Thus, the regulation of glucose absorption by intestinal epithelial cells (IECs) could represent a way to regulate glycemia. Among the molecules involved in glycemia homeostasis, extracellular ATP, a paracrine signaling molecule, was reported to induce insulin secretion from pancreatic β cells by activating P2Y and P2X receptors. In rat's jejunum, P2X7 expression was previously immunolocalized to the apex of villi, where it has been suspected to play a role in apoptosis. However, using an antibody recognizing the receptor extracellular domain and thus most of the P2X7 isoforms, we showed that expression of this receptor is apparent in the top two‐thirds of villi. These data suggest a different role for this receptor in IECs. Using the non‐cancerous IEC‐6 cells and differentiated Caco‐2 cells, glucose transport was reduced by more than 30% following P2X7 stimulation. This effect on glucose transport was not due to P2X7‐induced cell apoptosis, but rather was the consequence of glucose transporter 2 (Glut2)'s internalization. The signaling pathway leading to P2X7‐dependent Glut2 internalization involved the calcium‐independent activation of phospholipase Cγ1 (PLCγ1), PKCδ, and PKD1. Although the complete mechanism regulating Glut2 internalization following P2X7 activation is not fully understood, modulation of P2X7 receptor activation could represent an interesting approach to regulate intestinal glucose absorption. J. Cell. Physiol. 228: 120–129, 2013. © 2012 Wiley Periodicals, Inc. 相似文献
194.
Juliana L. França Marcelo R. Pinto Malson N. Lucena Daniela P. Garçon Wagner C. Valenti John C. McNamara Francisco A. Leone 《The Journal of membrane biology》2013,246(7):529-543
The stimulation by Mg2+, Na+, K+, NH4 +, and ATP of (Na+, K+)-ATPase activity in a gill microsomal fraction from the freshwater prawn Macrobrachium rosenbergii was examined. Immunofluorescence labeling revealed that the (Na+, K+)-ATPase α-subunit is distributed predominantly within the intralamellar septum, while Western blotting revealed a single α-subunit isoform of about 108 kDa M r. Under saturating Mg2+, Na+, and K+ concentrations, the enzyme hydrolyzed ATP, obeying cooperative kinetics with V M = 115.0 ± 2.3 U mg?1, K 0.5 = 0.10 ± 0.01 mmol L?1. Stimulation by Na+ (V M = 110.0 ± 3.3 U mg?1, K 0.5 = 1.30 ± 0.03 mmol L?1), Mg2+ (V M = 115.0 ± 4.6 U mg?1, K 0.5 = 0.96 ± 0.03 mmol L?1), NH4 + (V M = 141.0 ± 5.6 U mg?1, K 0.5 = 1.90 ± 0.04 mmol L?1), and K+ (V M = 120.0 ± 2.4 U mg?1, K M = 2.74 ± 0.08 mmol L?1) followed single saturation curves and, except for K+, exhibited site–site interaction kinetics. Ouabain inhibited ATPase activity by around 73 % with K I = 12.4 ± 1.3 mol L?1. Complementary inhibition studies suggest the presence of F0F1–, Na+-, or K+-ATPases, but not V(H+)- or Ca2+-ATPases, in the gill microsomal preparation. K+ and NH4 + synergistically stimulated enzyme activity (≈25 %), suggesting that these ions bind to different sites on the molecule. We propose a mechanism for the stimulation by both NH4 +, and K+ of the gill enzyme. 相似文献
195.
Louisa V. Forbes Tove Sj?gren Fran?oise Auchère David W. Jenkins Bob Thong David Laughton Paul Hemsley Garry Pairaudeau Rufus Turner H?kan Eriksson John F. Unitt Anthony J. Kettle 《The Journal of biological chemistry》2013,288(51):36636-36647
The neutrophil enzyme myeloperoxidase (MPO) promotes oxidative stress in numerous inflammatory pathologies by producing hypohalous acids. Its inadvertent activity is a prime target for pharmacological control. Previously, salicylhydroxamic acid was reported to be a weak reversible inhibitor of MPO. We aimed to identify related hydroxamates that are good inhibitors of the enzyme. We report on three hydroxamates as the first potent reversible inhibitors of MPO. The chlorination activity of purified MPO was inhibited by 50% by a 5 nm concentration of a trifluoromethyl-substituted aromatic hydroxamate, HX1. The hydroxamates were specific for MPO in neutrophils and more potent toward MPO compared with a broad range of redox enzymes and alternative targets. Surface plasmon resonance measurements showed that the strength of binding of hydroxamates to MPO correlated with the degree of enzyme inhibition. The crystal structure of MPO-HX1 revealed that the inhibitor was bound within the active site cavity above the heme and blocked the substrate channel. HX1 was a mixed-type inhibitor of the halogenation activity of MPO with respect to both hydrogen peroxide and halide. Spectral analyses demonstrated that hydroxamates can act variably as substrates for MPO and convert the enzyme to a nitrosyl ferrous intermediate. This property was unrelated to their ability to inhibit MPO. We propose that aromatic hydroxamates bind tightly to the active site of MPO and prevent it from producing hypohalous acids. This mode of reversible inhibition has potential for blocking the activity of MPO and limiting oxidative stress during inflammation. 相似文献
196.
Jimmy Stalin Karim Harhouri Lucas Hubert Caroline Subrini Daniel Lafitte Jean-Claude Lissitzky Nadia Elganfoud Stéphane Robert Alexandrine Foucault-Bertaud Elise Kaspi Florence Sabatier Michel Aurrand-Lions Nathalie Bardin Lars Holmgren Fran?oise Dignat-George Marcel Blot-Chabaud 《The Journal of biological chemistry》2013,288(13):8991-9000
The melanoma cell adhesion molecule (CD146) contains a circulating proteolytic variant (sCD146), which is involved in inflammation and angiogenesis. Its circulating level is modulated in different pathologies, but its intracellular transduction pathways are still largely unknown. Using peptide pulldown and mass spectrometry, we identified angiomotin as a sCD146-associated protein in endothelial progenitor cells (EPC). Interaction between angiomotin and sCD146 was confirmed by enzyme-linked immunosorbent assay (ELISA), homogeneous time-resolved fluorescence, and binding of sCD146 on both immobilized recombinant angiomotin and angiomotin-transfected cells. Silencing angiomotin in EPC inhibited sCD146 angiogenic effects, i.e. EPC migration, proliferation, and capacity to form capillary-like structures in Matrigel. In addition, sCD146 effects were inhibited by the angiomotin inhibitor angiostatin and competition with recombinant angiomotin. Finally, binding of sCD146 on angiomotin triggered the activation of several transduction pathways that were identified by antibody array. These results delineate a novel signaling pathway where sCD146 binds to angiomotin to stimulate a proangiogenic response. This result is important to find novel target cells of sCD146 and for the development of therapeutic strategies based on EPC in the treatment of ischemic diseases. 相似文献
197.
Adeline Arini Fabien Durant Michel Coste François Delmas Agnès Feurtet‐Mazel 《Journal of phycology》2013,49(2):361-370
While the induction of teratology by cadmium (Cd) on diatoms is already known, reversal kinetics are not well documented. This study aims to understand the viability of diatoms exhibiting teratological frustules and their reproduction capacities within a Cd‐impacted population to predict their return to normal diatom forms. We worked on a frequently encountered species in French hydrosystems: Planothidium frequentissimum (Lange‐Bertalot) Round & L. Bukhtiyarova. First, a 21‐d contamination phase highlighted increasing inductionof different teratological types in response to two levels of Cd contamination: 20 and 100 μg · L?1. The deformity counting indicated that Cd firstly generated striae and mixed teratologies, then affected the central area and the valves. Second, a 28‐d decontamination phase demonstrated the Cd depuration capacity of Planothidium frequentissimum. Cd half‐lives appeared relatively low, ~6 d for the 100 μg · L?1 condition. Moreover, the decontamination phase showed a decrease in teratology abundances, but a still incomplete recovery after 28 d. Deformations of the striae appeared to be the most sustainable phenotype since they were still significantly higher than in reference cultures at the end of the decontamination phase for both Cd cultures. 相似文献
198.
Hugues Clivot Michael Danger Christophe Pagnout Philippe Wagner Philippe Rousselle Pascal Poupin François Guérold 《Microbial ecology》2013,65(1):1-11
Anthropogenic acidification in headwater streams is known to affect microbial assemblages involved in leaf litter breakdown. Far less is known about its potential effects on microbial enzyme activities. To assess the effects of acidification on microbial activities associated with decaying leaves, a 70-day litter bag experiment was conducted in headwater streams at six sites across an acidification gradient. The results revealed that microbial leaf decomposition was strongly and negatively correlated with total Al concentrations (r?=??0.99, p?<?0.001) and positively correlated with Ca2+ concentrations (r?=?0.94, p?=?0.005) and pH (r?=?0.93, p?=?0.008). Denaturing gradient gel electrophoresis analyses showed that microbial assemblages differed between non-impacted and impacted sites, whereas fungal biomass associated with decaying leaves was unaffected. The nutrient content of leaf detritus and ecoenzymatic activities of carbon (C), nitrogen (N) and phosphorus (P) acquisition revealed that N acquisition was unaltered, while P acquisition was significantly reduced across the acidification gradient. The P content of leaf litter was negatively correlated with total Al concentrations (r?=??0.94, p?<?0.01) and positively correlated with decomposition rates (r?=?0.95, p?<?0.01). This potential P limitation of microbial decomposers in impacted sites was confirmed by the particularly high turnover activity for phosphatase and imbalanced ratios between the ecoenzymatic activities of C and P acquisition. The toxic form of Al has well-known direct effects on aquatic biota under acidic conditions, but in this study, Al was found to also potentially affect microbially mediated leaf processing by interfering with the P cycle. These effects may in turn have repercussions on higher trophic levels and whole ecosystem functioning. 相似文献
199.
200.
Alexis Dereeper Romain Guyot Christine Tranchant-Dubreuil François Anthony Xavier Argout Fabien de Bellis Marie-Christine Combes Frederick Gavory Alexandre de Kochko Dave Kudrna Thierry Leroy Julie Poulain Myriam Rondeau Xiang Song Rod Wing Philippe Lashermes 《Plant molecular biology》2013,83(3):177-189
Coffee is one of the world’s most important agricultural commodities. Coffee belongs to the Rubiaceae family in the euasterid I clade of dicotyledonous plants, to which the Solanaceae family also belongs. Two bacterial artificial chromosome (BAC) libraries of a homozygous doubled haploid plant of Coffea canephora were constructed using two enzymes, HindIII and BstYI. A total of 134,827 high quality BAC-end sequences (BESs) were generated from the 73,728 clones of the two libraries, and 131,412 BESs were conserved for further analysis after elimination of chloroplast and mitochondrial sequences. This corresponded to almost 13 % of the estimated size of the C. canephora genome. 6.7 % of BESs contained simple sequence repeats, the most abundant (47.8 %) being mononucleotide motifs. These sequences allow the development of numerous useful marker sites. Potential transposable elements (TEs) represented 11.9 % of the full length BESs. A difference was observed between the BstYI and HindIII libraries (14.9 vs. 8.8 %). Analysis of BESs against known coding sequences of TEs indicated that 11.9 % of the genome corresponded to known repeat sequences, like for other flowering plants. The number of genes in the coffee genome was estimated at 41,973 which is probably overestimated. Comparative genome mapping revealed that microsynteny was higher between coffee and grapevine than between coffee and tomato or Arabidopsis. BESs constitute valuable resources for the first genome wide survey of coffee and provide new insights into the composition and evolution of the coffee genome. 相似文献