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Alternative Mechanism (alternative + mechanism)
Selected AbstractsThe influence of ant-attendance on aphid behaviour investigated with the electrical penetration graph techniqueENTOMOLOGIA EXPERIMENTALIS ET APPLICATA, Issue 1 2002Gisep Rauch Abstract For the mutualistic interaction between the aphid Metopeurum fuscoviride Stroyan (Homoptera: Aphididae) and the ant Lasius niger L. (Hymenoptera: Formicidae) it has been shown that ant-tended aphids develop faster, reproduce at a higher rate, and live longer than aphids not tended by ants. We used electrical penetration graphs (EPG) to investigate if behavioural patterns differ between ant-tended and untended M. fuscoviride during 8 h experiments. Measurements were made on adult aphids from four different ant-tended colonies that continued to be tended by L. niger during the experiments, and from four different colonies where ant workers were excluded several days before the start of the experiment and that were also not tended by ants during the experiments. Ants readily tended wired aphids and ant tending did not interfere with the EPG measurements. There were no significant differences in the duration of sieve element penetration or in any other analysed feeding-related EPG parameters between ant-tended and untended individuals. However, the quality of the EPG recordings did not allow the distinction between the EPG-waveform E1 (salivation only) and E2 (salivation and ingestion). These results suggest that the changes in life-history traits of ant-tended aphids do not result from changes in time of sieve element penetration waveforms. Alternative mechanisms may involve an increase in the rate of sap uptake or a higher effectiveness in nutrient uptake in the presence of ants. Our study demonstrates that the EPG technique is a useful tool to investigate the feeding behaviour of aphids during interactions with ants. [source] ZnO-based photodetector with internal photocurrent gainPHYSICA STATUS SOLIDI (A) APPLICATIONS AND MATERIALS SCIENCE, Issue 8 2010L. A. Kosyachenko Abstract The photoresponsive structures prepared by magnetron sputtering of ZnO on p-Si substrates followed by vacuum evaporation of semitransparent Ni film on ZnO surface are investigated. The obtained Ni/n-ZnO/p-Si structures show high sensitivity that sharply increases with increase in applied voltage. Under a bias voltage of 5,V, the responsivities at ,,=,390,nm and ,,=,850,nm were equal to 210 and 110,A/W, which correspond to quantum efficiencies of 655 and 165, respectively. It is assumed that the observed strong response is attributed to internal gain in the Ni/n-ZnO/p-Si phototransistor structure containing Ni/n-ZnO Schottky contact as the emitter junction and n-ZnO/p-Si heterostructure as the collector junction. The response time of the device is ,10,7,s. Alternative mechanisms of photocurrent multiplication in such structures are also discussed. [source] Does disturbance, competition or resource limitation underlie Hieracium lepidulum invasion in New Zealand?AUSTRAL ECOLOGY, Issue 3 2010Mechanisms of establishment, functional differentiation among invasive, native species, persistence Abstract The processes underlying plant invasions have been the subject of much ecological research. Understanding mechanisms of plant invasions are difficult to elucidate from observations, yet are crucial for ecological management of invasions. Hieracium lepidulum, an asteraceous invader in New Zealand, is a species for which several explanatory mechanisms can be raised. Alternative mechanisms, including competitive dominance, disturbance of resident vegetation allowing competitive release or nutrient resource limitation reducing competition with the invader are raised to explain invasion. We tested these hypotheses in two field experiments which manipulated competitive, disturbance and nutrient environments in pre-invasion and post-invasion vegetation. H. lepidulum and resident responses to environmental treatments were measured to allow interpretation of underlying mechanisms of establishment and persistence. We found that H. lepidulum differed in functional response profile from native species. We also found that other exotic invaders at the sites were functionally different to H. lepidulum in their responses. These data support the hypothesis that different invaders use different invasion mechanisms from one another. These data also suggest that functional differentiation between invaders and native resident vegetation may be an important contributing factor allowing invasion. H. lepidulum appeared to have little direct competitive effect on post-invasion vegetation, suggesting that competition was not a dominant mechanism maintaining its persistence. There was weak support for disturbance allowing initial establishment of H. lepidulum in pre-invasion vegetation, but disturbance did not lead to invader dominance. Strong support for nutrient limitation of resident species was provided by the rapid competitive responses with added nutrients despite presence of H. lepidulum. Rapid competitive suppression of H. lepidulum once nutrient limitation was alleviated suggests that nutrient limitation may be an important process allowing the invader to dominate. Possible roles of historical site degradation and/or invader-induced soil chemical/microbial changes in nutrient availability are discussed. [source] The Role of Myocardial KATP -Channel Blockade in the Protective Effects of Glibenclamide against Ischaemia in the Rat HeartBASIC AND CLINICAL PHARMACOLOGY & TOXICOLOGY, Issue 2 2002Roger J. Legtenberg This study addresses the possible involvement of KATP channels in this beneficial action of glibenclamide. We hypothesized that if glibenclamide improved postischaemic cardiac function by blocking of KATP channels, opening of these KATP channels should result in the opposite, namely detrimental effects on postischaemic heart function. Postischaemic functional loss and coronary blood flow were recorded during treatment with glibenclamide (4 ,mol.l,1; n=5), the KATP channel openers pinacidil (1 ,mol.l,1; n=5) and diazoxide (30 ,mol.l,1; n=5), the combination of glibenclamide with pinacidil (n=5) and glibenclamide with diazoxide (n=5), and vehicle (n=8). Both pinacidil and diazoxide significantly increased coronary blood flow 2,3 times, which was abolished by glibenclamide pre- and postischaemically. This confirms that under both flow conditions glibenclamide significantly blocks KATP channels in the coronary vasculature. The 12 min. global ischaemic incident resulted in a cardiac functional loss of 22.2±2.9% during vehicle. Glibenclamide reduced the cardiac functional loss to 4.3±1.2% (P<0.01). Interestingly, both pinacidil and diazoxide reduced the cardiac functional loss to 4.0±1.5% (P<0.01) and 2.9±1.4% (P<0.001), respectively. The combination pinacidil+glibenclamide resulted in additional protection compared with the individual components (0.6±0.1 versus 4.0±1.5%, P<0.05). Thus, in contrast to its effect on coronary vascular tone, the glibenclamide-induced improvement of postischaemic cardiac function may not be mediated through blockade of the KATP channel. Alternative mechanisms may be operative, such as uncoupling of the mitochondrial respiratory chain, thereby preconditioning the hearts against stunning. [source] Activated NKT cells increase dendritic cell migration and enhance CD8+ T cell responses in the skinEUROPEAN JOURNAL OF IMMUNOLOGY, Issue 9 2006Anton Abstract Activated NKT cells produce cytokines such as IL-4 and IFN-, that function locally to influence the strength and functional development of antigen-specific T cells. Here we identify an alternative mechanism by which NKT cells influence the strength of T cell responses: through modulation of peripheral dendritic cell (DC) trafficking. NKT cell activation with ,-galactosylceramide induced high systemic levels of TNF-, that mediated increased DC migration from skin to draining lymph nodes. This increased DC trafficking led to a threefold increase in effector T cell priming and in the immune response elicited to antigen challenge when ,-galactosylceramide was given at the time of immunization of the skin. These studies provide important implications for the use of NKT cell activation strategies to manipulate T cell-mediated responses including responses to cutaneous tumors and graft vs. host disease. [source] DOES LARGE BODY SIZE IN MALES EVOLVE TO FACILITATE FORCIBLE INSEMINATION?EVOLUTION, Issue 11 2005A STUDY ON GARTER SNAKES Abstract A trend for larger males to obtain a disproportionately high number of matings, as occurs in many animal populations, typically is attributed either to female choice or success in male-male rivalry; an alternative mechanism, that larger males are better able to coercively inseminate females, has received much less attention. For example, previous studies on garter snakes (Thamnophis sirtalis parietalis) at communal dens in Manitoba have shown that the mating benefit to larger body size in males is due to size-dependent advantages in male-male rivalry. However, this previous work ignored the possibility that larger males may obtain more matings because of male-female interactions. In staged trials within outdoor arenas, larger body size enhanced male mating success regardless of whether a rival male was present. The mechanism involved was coercion rather than female choice, because mating occurred most often (and soonest) in females that were least able to resist courtship-induced hypoxic stress. Males do physically displace rivals from optimal positions in the mating ball, and larger males are better able to resist such displacement. Nonetheless, larger body size enhances male mating success even in the absence of such malemale interactions. Thus, even in mating systems where males compete physically and where larger body size confers a significant advantage in male-male competition, the actual selective force for larger body size in males may relate to forcible insemination of unreceptive females. Experimental studies are needed to determine whether the same situation occurs in other organisms in which body-size advantages have been attributed to male-male rather than male-female interactions. [source] CO2 and nitrogen, but not population density, alter the size and C/N ratio of Phytolacca americana seedsFUNCTIONAL ECOLOGY, Issue 3 2005J.-S. HE Summary 1Plants can provision seeds by optimizing seed size, number and nutrient content to maximize parental fitness. According to the McGinley,Charnov hypothesis, seed size should be determined by the ratio of carbon to nitrogen (C/N) available to the plant, with larger seed size correlating with larger C/N ratios and smaller absolute N content. 2This hypothesis was tested by establishing monocultures of Phytolacca americana L. (Phytolaccaceae) at three population densities under ambient and elevated CO2 environments, with two availabilities of soil N. 3Elevated CO2 reduced both seed size and N concentration while increasing the C/N ratio; high soil N availability produced the opposite result for N concentration and C/N ratio. Higher planting densities reduced plant biomass, but did not alter seed size. 4In accordance with the McGinley,Charnov hypothesis, larger seeds had both larger C/N ratios and smaller N content. However, the increase in C/N ratio caused by elevated CO2 corresponded with smaller seeds overall: elevated CO2 reduced seed size, although the seed size,C/N relationship remained positive. 5These results suggest an alternative mechanism to explain variation in seed size, and suggest that future climate conditions may alter seed quality and plant reproductive behaviour. [source] TCL1 is activated by chromosomal rearrangement or by hypomethylationGENES, CHROMOSOMES AND CANCER, Issue 4 2001Martin R. Yuille TCL1 is an oncogene activated by recurrent reciprocal translocations at chromosome segment 14q32.1 in the most common of the mature T-cell malignancies, T-cell prolymphocytic leukemia. It acts to transport Akt1 to the nucleus and enhance Akt1's serine-threonine kinase activity. TCL1 is also expressed in the B-cell malignancy, Burkitt's lymphoma (BL). However, 14q32.1 breakpoints have not been detected in BL, and we therefore investigated in more detail how expression was activated. No evidence for rearrangement near TCL1 was found in BL. Instead, a NotI site adjacent to the TATA box in the TCL1 promoter was found to be unmethylated. By contrast, tumor cell lines not expressing TCL1 were fully methylated at this NotI site, while normal somatic cells were hemimethylated. We also found that TCL1 was expressed in B-cell chronic lymphocytic leukemia (CLL) and the related disorder splenic lymphoma with villous lymphocytes (unlike in normal mature B-cells), and that the NotI site was unmethylated on both alleles. This correlation of repression and methylation was tested in vitro. When cells with both alleles methylated at the NotI site were demethylated, TCL1 expression was induced. These data provide evidence that in mature B-cell malignancies there is an alternative mechanism of TCL1 activation that apparently involves loss of methylation of one promoter allele. We discuss the significance of this for CLL tumorigenesis and for genomewide hypomethylation in CLL. © 2001 Wiley-Liss, Inc. [source] Mechanisms Controlling Crystal Habits of Gold and Silver ColloidsADVANCED FUNCTIONAL MATERIALS, Issue 7 2005C. Lofton Abstract Examples of gold and silver anisotropic colloids, such as prisms and rods, have appeared in the literature for many years. In most cases, the morphologies of these thermodynamically unfavorable particles have been explained by the particular reaction environment in which they were synthesized. The mechanisms used to explain the growth generally fall into two categories, one in which chemically adsorbed molecules regulate the growth of specific crystal faces kinetically, and the other where micelle-forming surfactants physically direct the shape of the particle. This paper raises questions about the growth of anisotropic metal colloids that the current mechanisms cannot adequately address, specifically, the formation of multiple shapes in a single homogeneous reaction and the appearance of similar structures in very different synthesis schemes. These observations suggest that any growth mechanism should primarily take into consideration nucleation and kinetics, and not only thermodynamics or physical constrictions. The authors suggest an alternative mechanism where the presence and orientation of twin planes in these face-centered cubic (fcc) metals direct the shape of the growing particles. This explanation follows that used for silver halide crystals, and has the advantage of explaining particle growth in many synthesis methods. In this mechanism, twin planes generate reentrant grooves, favorable sites for the attachment of adatoms. Shape and structural data are presented for gold and silver particles synthesized using several different techniques to support this new model. Triangular prisms are suggested to contain a single twin plane which directs that growth of the initial seed in two dimensions, but limits the final size of the prism. Hexagonal platelets are suggested to contain two parallel twin planes that allow the fast growing edges to regenerate one another, allowing large sizes and aspect ratios to form. Rods and wires were found to have a fivefold symmetry, which may only allow growth in one dimension. It is expected that a superior mechanistic understanding will permit shape-selective synthesis schemes to be developed. [source] Laminin-5 stimulates hepatocellular carcinoma growth through a different function of ,6,4 and ,3,1 integrins,HEPATOLOGY, Issue 6 2007Carlo Bergamini Hepatocellular carcinoma (HCC) growth severely affects prognosis. Ki-67, a known marker of cell proliferation, is a negative prognostic factor in HCC. Growth factors such as the epidermal growth factor (EGF) induce HCC cell proliferation but do not explain the great heterogeneity of HCC growth. Laminin-5 (Ln-5) is an extracellular matrix protein (ECM) present in the tissue microenvironment of HCC. The two main receptors for Ln-5, integrins ,3,1 and ,6,4, are expressed on the cell surface of HCC cells. The aim of this study is to investigate an alternative mechanism of HCC growth whereby Ln-5 promotes HCC cell proliferation through ,3,1 and ,6,4. HCC tissues containing Ln-5 display a larger diameter and higher number of positive cells for Ki-67, a well known proliferative index, as determined by double immunofluorescence staining and real-time PCR on microdissected tissues. In vitro, Ln-5, but not collagen I, collagen IV or fibronectin, induces proliferation as much as EGF does, via Erk phosphorylation as a consequence of ,4 integrin phosphorylation. However, the two HCC cell lines do not proliferate in presence of Ln-5 despite ,4 integrin and Erk1/2 activation. After transfection with ,3 integrin, in the presence of Ln-5 one of these HCC cell lines acquires a proliferative activity whereas one of the proliferative HCC cell lines, knocked-down for ,3 integrin, loses its proliferative activity. Conclusions: Our study suggests a new mechanism of HCC growth whereby Ln-5 stimulates proliferation via a different function of ,6,4 and ,3,1. (HEPATOLOGY 2007.) [source] Fas and TNFR1, but not cytolytic granule-dependent mechanisms, mediate clearance of murine liver adenoviral infection,HEPATOLOGY, Issue 1 2005Marwan S. Abougergi After intravenous injection of replication-deficient adenovirus, hepatocytes are transduced and express high levels of adenovirus-encoded genes. However, adenovirally encoded gene expression is ablated rapidly by CD8+ T-cell,dependent mechanisms. Thus, this model is suitable for examining intrahepatic cytotoxic T lymphocyte (CTL) effector mechanisms. In the present studies, recombinant adenoviruses encoding secreted (human apolipoprotein A-I) or intracellular (,-galactosidase) gene products were infused into mice with genetic deficiencies affecting the granule exocytosis-, Fas-, or tumor necrosis factor receptor 1 (TNFR1)-mediated pathways of CTL and natural killer cell effector function; the rates of clearance of adenovirus-encoded gene products were assessed. Clearance of secreted or intracellular adenoviral gene products was not delayed in perforin-deficient mice or dipeptidyl peptidase I-deficient mice, which fail to process and activate granzyme A or granzyme B. TNFR1-deficient mice also exhibited no delay in clearance of adenoviral gene products. However, adenoviral clearance from Fas-deficient mice was delayed, and such delays were much greater in mice deficient in both TNFR1 and Fas. In contrast, chimeric mice lacking both hepatic Fas and lymphocyte perforin function exhibited no greater delay in adenoviral clearance than chimeras deficient only in hepatic Fas expression. In conclusion, Fas-dependent mechanisms are required for efficient clearance of virally infected hepatocytes and, in Fas-deficient animals, TNFR1-dependent mechanisms provide an alternative mechanism for hepatic adenovirus clearance. In contrast, perforin- and granule protease,dependent cytotoxicity mechanisms play no apparent role in clearance of adenovirus from the liver. (HEPATOLOGY 2005;41:97,105.) [source] The Global Marketplace and the Privatisation of SecurityIDS BULLETIN, Issue 2 2009Jeffrey Isima The privatisation of security in the age of globalisation raises crucial concerns for global governance and development. Key among these are the impacts on the structures of poverty and inequality, and how these twin development issues shape global security privatisation. Equally important are the structural limits on public policy imposed by the promotion of the market as a powerful alternative mechanism for security provisioning. These concerns have become more urgent as the dominant neoliberal security governance paradigm has tended to avoid questions relating to poverty, social inequality and the dire condition of those who live on the margins of state protection. This calls for innovative policy changes for transforming security institutions and practices in a way that promotes security, not just for state officials and the wealthy, but most importantly, for the poor. This article attempts to explore these core development concerns in relation to the increasing outsourcing of security to non-state actors and how state actors, as leading agents of development, can protect and promote the wellbeing of vulnerable populations within the global market order. [source] Functional characterization of human natural killer cells responding to Mycobacterium bovis bacille Calmette-GuérinIMMUNOLOGY, Issue 1 2004Semih Esin Summary The kinetics of activation and induction of several effector functions of human natural killer (NK) cells in response to Mycobacterium bovis bacille Calmette-Guérin (BCG) were investigated. Owing to the central role of monocytes/macrophages (MM) in the initiation and maintenance of the immune response to pathogens, two different experimental culture conditions were analysed. In the first, monocyte-depleted nylon wool non-adherent (NW) cells from healthy donors were stimulated with autologous MM preinfected with BCG (intracellular BCG). In the second, the NW cells were directly incubated with BCG, which was therefore extracellular. In the presence of MM, CD4+ T lymphocytes were the cell subset mainly expressing the activation marker, CD25, and proliferating with a peak after 7 days of culture. In contrast, in response to extracellular BCG, the peak of the proliferative response was observed after 6 days of stimulation, and CD56+ CD3, cells (NK cells) were the cell subset preferentially involved. Such proliferation of NK cells did not require a prior sensitization to mycobacterial antigens, and appeared to be dependent upon contact between cell populations and bacteria. Following stimulation with extracellular BCG, the majority of interferon-, (IFN-,)-producing cells were NK cells, with a peak IFN-, production at 24,30 hr. Interleukin (IL)-2 and IL-4 were not detectable in NK cells or in CD3+ T lymphocytes at any time tested. IL-12 was not detectable in the culture supernatant of NW cells stimulated with extracellular BCG. Compared to the non-stimulated NW cells, the NW cells incubated for 16,20 hr with BCG induced the highest levels of expression of apoptotic/death marker on the NK-sensitive K562 cell line. BCG also induced expression of the activation marker, CD25, and proliferation, IFN-, production and cytotoxic activity, on negatively selected CD56+ CD3, cells. Altogether, the results of this study demonstrate that extracellular mycobacteria activate several NK-cell functions and suggest a possible alternative mechanism of NK-cell activation as the first line of defence against mycobacterial infections. [source] The mechanisms underlying MMR deficiency in immunodeficiency-related non-Hodgkin lymphomas are different from those in other sporadic microsatellite instable neoplasmsINTERNATIONAL JOURNAL OF CANCER, Issue 10 2009Claire Borie Abstract The spectrum of tumors showing microsatellite instability (MSI) has recently been enlarged to sporadic neoplasms whose incidence is favored in the context of chronic immunosuppression. We investigated the biological, therapeutic and clinical features associated with MSI in immunodeficiency-related non-Hodgkin lymphomas (ID-RL). MSI screening was performed in 275 ID-RL. MSI ID-RL were further analyzed for MMR gene expression and for BRAF/KRAS mutations since these genes are frequently altered in MSI cancers. We also assessed the expression of O6 -methylguanine-DNA methyltransferase (MGMT), an enzyme whose inactivation has been reported in lymphomas and may help in the selection of MMR deficient clones. Unlike other sporadic MSI neoplasms, MSI ID-RL (N = 17) presented with heterogeneous MMR defects and no MLH1 promoter methylation. About one third of these tumors presented with normal expression of MLH1, MSH2, MSH6 and PMS2. They accumulated BRAF activating mutations (33%). Unlike other ID-RL, MSI ID-RL were primarily EBV-negative NHL of T-cell origin, and arose after long-term immunosuppression in patients who received azathioprine as part of their immunosuppressive regimen (p = 0.05) and/or who exhibited methylation-induced loss of expression of MGMT in tumor cells (p= 0.02). Overall, these results highlight that, in the context of deficient immune status, some MSI neoplasms arise through alternative mechanism when compared to other sporadic MSI neoplasms. They give the exact way how to make the diagnosis of MSI in these tumors and may help to define biological and clinicalrisk factors associated with their emergence in such a clinicalcontext. © 2009 UICC [source] Upregulation of miR-23a,27a,24 decreases transforming growth factor-beta-induced tumor-suppressive activities in human hepatocellular carcinoma cellsINTERNATIONAL JOURNAL OF CANCER, Issue 4 2008Shenglin Huang Abstract Transforming growth factor-beta (TGF-beta) plays a dual and complex role in human cancer. In this report, we observe a specific set of MicroRNAs (miRNAs) changed in response to TGF-beta in human hepatocellular carcinoma (HCC) cells by miRNA microarray screening. A cluster of miRNA, miR-23a,27a,24, is induced in an early stage by TGF-beta in Huh-7 cells. Knockdown of Smad4, Smad2 or Smad3 expression by RNA interference can attenuate the response of miR-23a,27a,24 to TGF-beta addition, indicating that this induction is dependent on Smad pathway. We also explore that miR-23a,27a,24 can function as an antiapoptotic and proliferation-promoting factor in liver cancer cells. In addition, expression of this miRNA cluster is found to be remarkably upregulated in HCC tissues versus normal liver tissues. These findings suggest a novel, alternative mechanism through which TGF-beta could induce specific miRNA expression to escape from tumor-suppressive response in HCC cells. © 2008 Wiley-Liss, Inc. [source] Habitat heterogeneity affects population growth in goshawk Accipiter gentilisJOURNAL OF ANIMAL ECOLOGY, Issue 2 2001Oliver Krüger Summary 1The concept of site-dependent population regulation combines the ideas of Ideal Free Distribution-type of habitat settlement and density dependence in a vital rate mediated by habitat heterogeneity. The latter is also known as habitat heterogeneity hypothesis. Site-dependent population regulation hypothesis predicts that increasing population density should lead to inhabitation of increasingly poor territories and decreasing per capita population growth rate. An alternative mechanism for population regulation in a territorial breeding system is interference competition. However, this would be expected to cause a more even decrease in individual success with increasing density than site-dependent regulation. 2We tested these ideas using long-term (1975,99) population data from a goshawk Accipiter gentilis population in Eastern Westphalia, Germany. 3Goshawk territory occupancy patterns and reproduction parameters support predictions of site-dependent population regulation: territories that were occupied more often and earlier had a higher mean brood size. Fecundity did not decrease with increasing density in best territories. 4Using time-series modelling, we also showed that the most parsimonious model explaining per capita population growth rate included annual mean habitat quality, weather during the chick rearing and autumn period and density as variables. This model explained 63% of the variation in per capita growth rate. The need for including habitat quality in the time-series model provides further support for the idea of site-dependent population regulation in goshawk. [source] Inhibition of neuronal migration by JONES antibody is independent of 9-O-acetyl GD3 in GD3-synthase knockout miceJOURNAL OF NEUROSCIENCE RESEARCH, Issue 7 2007Chia-Ron Yang Abstract It has been shown previously that the migration of granule neurons in neonatal cerebellum can be inhibited by a monoclonal antibody (Mab) JONES. Because the inhibition is presumed to be mediated through binding of the JONES antibody to 9-O-acetyl GD3, we used GD3-synthase knockout (GD3S,/,) mice that do not express 9-O-acetyl GD3 and also have no detectable defect in brain development, to examine the mechanism of the inhibitory effect. We found no difference between the migration of granule neurons in the neonatal cerebellar explant culture in GD3S,/, mice and in wild-type mice. Addition of the Mab JONES, but not Mab R24 or A2B5, in the culture medium blocked the neuronal migration in the explant culture of the wild-type mice. The inhibitory effect of Mab JONES was also observed, however, in the explant culture of GD3S,/, mice. Immuno-HPTLC analysis showed at least two JONES-positive glycolipids bands in the lipid extract of GD3S+/+ mice, and none was detected in that of GD3S,/, mice. Western blot analysis of the cerebellum homogenate of wild-type and GD3S,/, mice identified at least 3 JONES-positive protein bands, one of which is ,1-integrin. Because the JONES antibody also blocked neuronal migration in the cerebellar explant culture of GD3S,/, mice that do not express 9-O-acetyl-GD3, it suggested an alternative mechanism for the inhibitory effect of the antibody, at least in the GD3S knockout mice, and the inhibitory effect of the JONES antibody on neuronal migration could be mediated through its binding to ,1-integrin. © 2007 Wiley-Liss, Inc. [source] PRESENCE OF SPOROPHYLLS IN FLOATING KELP RAFTS OF MACROCYSTIS SPP. (PHAEOPHYCEAE) ALONG THE CHILEAN PACIFIC COAST,JOURNAL OF PHYCOLOGY, Issue 5 2005Erasmo C. Macaya Some species of macroalgae continue to live for extended periods of time after detachment and may even maintain reproductive structures, yet very little is known about this process. Here, we describe the presence of sporophylls (with sporogenous tissues) on floating kelp rafts of Macrocystis spp. along the coast of Chile. Surveys were conducted at nine sites (18,50° S) during austral summer 2002, and floating kelp rafts were seen and collected at seven of these nine sites (between 22 and 50° S). Fifteen (26.8%) of the 56 samples had sporophylls, indicating maintenance of sporophylls after detachment. Some of the kelp sporophytes with reproductive blades showed signs of having been afloat for long periods (indicated by the large size of attached stalked barnacles). Additionally, experiments showed that floating kelps released viable zoospores. To understand the reproductive dynamics of floating kelps, we compared these results with information from attached populations of Macrocystis spp. at nearby coastal sites. In general, attached kelp had higher proportions of sporophylls than floating rafts, suggesting that detachment may negatively affect reproductive status. Nevertheless, floating kelps remained functionally reproductive, suggesting that zoospores may be dispersed via floating rafts. Published reports on other macroalgae indicate that some species (Lessoniaceae, Fucaceae, and Sargassaceae) are fertile and probably release zoospores or zygotes while floating or drifting in ocean currents. Because dispersal distances achieved by spores of most macroalgae are relatively short, release of spores from floating algae may be an alternative mechanism of long-distance dispersal. [source] Nuclear magnetic resonance water relaxation time changes in bananas during ripening: a new mechanismJOURNAL OF THE SCIENCE OF FOOD AND AGRICULTURE, Issue 12 2010Fayene Zeferino Ribeiro Abstract BACKGROUND: Nuclear magnetic resonance studies of banana fragments during ripening show an increase on the water transverse relaxation time (T2) and a decrease in water self-diffusion coefficient (D). As T2 and D are normally directly correlated, we studied these two properties in intact bananas during ripening, in an attempt to rule out the effect of injury on the apparent discrepancies in the behavior of T2 and D. RESULTS: The results show that injury in bananas causes a decrease in T2 of the water in vacuoles (T2vac). They also show that T2vac increased and D decreased during ripening, ruling out the injury effect. To explain the apparent discrepancies, we propose a new hypothesis for the increase in T2 values, based on the reduction of Fe3+ ions to Fe2+ by galacturonic acid, produced by the hydrolysis of pectin and a decrease in internal oxygen concentration during ripening. CONCLUSION: As injury alters T2 values it is necessary to use intact bananas to study relaxation times during ripening. The novel interpretation for the increase in T2vac based on reduction of Fe+3 and O2 concentration is an alternative mechanism to that based on the hydrolysis of starch in amyloplasts. Copyright © 2010 Society of Chemical Industry [source] Pituitary luteinizing hormone responses to single doses of exogenous GnRH in female social Cape ground squirrels exhibiting low reproductive skewJOURNAL OF ZOOLOGY, Issue 1 2007T. P. Jackson Abstract The Cape ground squirrel Xerus inauris is unusual among social mammals as it exhibits a low reproductive skew, being a facultative plural breeder with not all females breeding within a group. We investigated pituitary function to assess whether there was reproductive inhibition at the level of the pituitary and potentially the hypothalamus in breeding and non-breeding female Cape ground squirrels. We did so during the summer and winter periods by measuring luteinizing hormone (LH) responses to single doses of 2 g exogenous gonadotropin-releasing hormone (GnRH) and physiological saline administered to 42 females from 11 colonies. Basal LH concentrations of females increased in response to the GnRH challenge. Basal plasma LH concentrations were greater during winter, when most oestrus events are observed. However, we found no differences in plasma LH concentrations between breeding and non-breeding females. We showed that the anterior pituitary of non-breeding female ground squirrels is no less sensitive to exogenously administered GnRH than that of breeding females. We therefore concluded that the pituitary is no more active in breeding than non-breeding females. The lack of differentiation in response to GnRH suggests that either non-breeding females have ovaries that are less sensitive to LH or that they refrain from sexual activity with males through an alternative mechanism of self-restraint. [source] How Green Was My Valley?LAW & SOCIETY REVIEW, Issue 4 2003An Examination of Tournament Theory as a Governance Mechanism in Silicon Valley Law Firms The tournament model is a widely used mechanism to control opportunistic behavior by associates in law firms. However, this mechanism can only operate in certain economic (and social) circumstances. When those circumstances do not exist, the model breaks down, and with it the ability to control opportunism in the absence of some alternative mechanism. Prior research has not investigated whether the utilization of a tournament model prevents the opportunistic behaviors identified as grabbing, leaving, and shirking. In order to test the limits of the tournament model, it is necessary to find particular historical moments when the economic environment radically challenges assumptions/premises of the model. The dot-com bubble in Silicon Valley provides precisely such a time and place. This article demonstrates limits to the applicability of tournament theory. Those limits are to be found in the economic environment in circumstances in which: (1) exogenous reward structures offer many multiples of internal rewards; (2) demonstrably high short-term rewards outside the firm starkly contrast with the delayed long-term rewards inside the firm; (3) the managerial strata reduce their emphasis on long-term recruiting of potential partners in favor of short-term productivity by young associates; and (4) firms develop departmental leverage ratios in excess of their capacity to monitor, mentor, and train recruits. [source] Cooperative biodegradation of geosmin by a consortium comprising three gram-negative bacteria isolated from the biofilm of a sand filter columnLETTERS IN APPLIED MICROBIOLOGY, Issue 4 2006D. Hoefel Abstract Aims:, To isolate and identify bacteria from a sand filter column capable of degrading the taste and odour compound, geosmin. In doing so, to investigate if these organisms degrade geosmin either individually or if an alternative mechanism is utilized. Methods and Results:, Geosmin-degrading bacteria from a biologically active sand filter column were enriched by their growth in a minimal medium supplemented with geosmin as the sole carbon source. By day 51, 21·7 mg l,1 of geosmin had been degraded as determined by solid-phase microextraction gas chromatography/mass spectrometry, and was accompanied by a 2·12 log10 increase in active bacterial numbers as measured using the BacLightTM bacterial viability kit and flow cytometric enumeration. During the onset of geosmin degradation, the predominance of three bacteria, most similar to previously cultured species of Sphingopyxis alaskensis, Novosphingobium stygiae and Pseudomonas veronii based on 16S rRNA gene sequences was detected by denaturing gradient gel electrophoresis. Subsequent isolation of these organisms revealed that degradation of geosmin, when present as either the sole carbon source (ranging from 40 ng l,1 to 20 mg l,1) or when spiked into sterile reservoir water (37 and 131 ng l,1), occurred only when all three isolates were present. None of the isolates was shown to be capable of degrading geosmin either individually or in any combination of two. Conclusions:, This study has reported, for the first time, the cooperative degradation of geosmin by a consortium comprising three gram-negative bacteria isolated from a biologically active sand filter column. Significance and Impact of the Study:, These results are important for researchers currently employing molecular-based approaches to further understand the biodegradation of geosmin by bacteria, as such studies may be complicated by the discovery of geosmin degradation occurring by a consortium. This study also advances the knowledge surrounding the types of bacteria capable of degrading the taste and odour compound, as investigations to date regarding this are limited. [source] Characterization of Mixtures Part 1: Prediction of Infinite-Dilution Activity Coefficients Using Neural Network-Based QSPR ModelsMOLECULAR INFORMATICS, Issue 11-12 2008Subhash Ajmani Abstract The major problem in building QSAR/QSPR models for mixtures lies in their characterization. It has been shown that it is possible to construct QSPR models for the density of binary liquid mixtures using simple mole fraction weighted physicochemical descriptors. Such parameters are unsatisfactory; however, from the point of view of interpretation of the resultant models. In this paper, an alternative mechanism-based approach to the characterization of mixtures has been investigated. It has been shown that while it is not possible to build significant linear models using these descriptors, it has been possible to construct satisfactory artificial neural network models. The performance of these models and the importance of the individual descriptors are discussed. [source] Dynamics of grazing lawn formation: an experimental test of the role of scale-dependent processesOIKOS, Issue 10 2008Joris P. G. M. Cromsigt Grazing lawns are characteristic for African savanna grasslands, standing out as intensely grazed patches of stoloniferous grazing-tolerant grass species. Grazing lawn development has been associated with grazing and increased nutrient input by large migratory herds. However, we argue that in systems without mass migrations disturbances, other than direct grazing, drive lawn development. Such disturbances, e.g. termite activity or megaherbivore middens, also increase nutrient input and keep the bunch vegetation down for a prolonged time period. However, field observations show that not all such disturbances lead to grazing lawns. We hypothesize that the initial disturbance has to be of a minimal threshold spatial scale, for grazing intensity to be high enough to induce lawn formation. We experimentally tested this idea in natural tall savanna grassland. We mowed different-sized plots to simulate initial disturbances of different scales (six times during one year) and applied fertilizer to half of the plots during two years to simulate increased nutrient input by herbivores or termite activity. Allowing grazing by naturally occurring herbivores, we followed the vegetation development over more than three years. Grazing kept bunch grass short in coarser, fertilized plots, while grasses grew out toward their initial height in fine-scale and unfertilized plots. Moreover, lawn grasses strongly increased in cover in plots with an increased nutrient input but only after coarser scale disturbance. These results support our hypothesis that an increased nutrient input in combination with grazing indeed induces grazing lawn formation, but only above a threshold scale of the initial disturbance. Our results provide an alternative mechanism for the development of grazing lawns in systems that lack mass migrating herds. Moreover, it gives a new spatial dimension to the processes behind grazing lawn development, and hence help to understand how herbivores might create and maintain spatial heterogeneity in grassland systems. [source] Re-examining the role of Lys67 in class C ,-lactamase catalysisPROTEIN SCIENCE, Issue 3 2009Yu Chen Abstract Lys67 is essential for the hydrolysis reaction mediated by class C ,-lactamases. Its exact catalytic role lies at the center of several different proposed reaction mechanisms, particularly for the deacylation step, and has been intensely debated. Whereas a conjugate base hypothesis postulates that a neutral Lys67 and Tyr150 act together to deprotonate the deacylating water, previous experiments on the K67R mutants of class C ,-lactamases suggested that the role of Lys67 in deacylation is mainly electrostatic, with only a 2- to 3-fold decrease in the rate of the mutant vs the wild type enzyme. Using the Class C ,-lactamase AmpC, we have reinvestigated the activity of this K67R mutant enzyme, using biochemical and structural studies. Both the rates of acylation and deacylation were affected in the AmpC K67R mutant, with a 61-fold decrease in kcat, the deacylation rate. We have determined the structure of the K67R mutant by X-ray crystallography both in apo and transition state-analog complexed forms, and observed only minimal conformational changes in the catalytic residues relative to the wild type. These results suggest that the arginine side chain is unable to play the same catalytic role as Lys67 in either the acylation or deacylation reactions catalyzed by AmpC. Therefore, the activity of this mutant can not be used to discredit the conjugate base hypothesis as previously concluded, although the reaction catalyzed by the K67R mutant itself likely proceeds by an alternative mechanism. Indeed, a manifold of mechanisms may contribute to hydrolysis in class C ,-lactamases, depending on the enzyme (wt or mutant) and the substrate, explaining why different mutants and substrates seem to support different pathways. For the WT enzyme itself, the conjugate base mechanism may be well favored. [source] Frontal Fusion: Collapse of Another Anthropoid SynapomorphyTHE ANATOMICAL RECORD : ADVANCES IN INTEGRATIVE ANATOMY AND EVOLUTIONARY BIOLOGY, Issue 3 2008Alfred L. Rosenberger Abstract We test the hypothesis that the fused interfrontal suture of anthropoids is a uniquely distinguishing feature and a derived characteristic indicative of their monophyletic origin. Our survey of nonanthropoid primates and several archontan families indicates frontal fusion is widespread. It is most variable (fused, open or partially fused) inter- and intra-specifically among strepsirhines. The frontal bone is more commonly fused in living lemuroids and indrioids than among lorisoids. It appears to be fused regularly among Eocene adapids. Among nonanthropoid haplorhines, the interfrontal is fused in Tarsius, even in neonates and invariably in adults, probably also in all fossil tarsiiforms preserving the frontal bone, and in the late Eocene protoanthropoid Rooneyia. The plesiadapiform pattern remains uncertain, but fusion is ubiquitous among living tree shrews, colugos and bats. Distributional evidence implies that interfrontal fusion was present in the last common ancestor (LCA) of haplorhine primates and possibly in the LCA of euprimates as well. Anthropoids, therefore, cannot be defined cladistically by interfrontal fusion, not out of concern for homoplasy but because it is probably a primitive feature inherited from other taxa related to anthropoids. Fusion of the large anthropoid frontal bone, which was extended anteriorly to roof the orbits and expanded laterally in connection with a wide forebrain in the LCA of anthropoids and protoanthropoids, may have been preadaptive to the evolution of the postorbital septum. The zygomatico-frontal suture of the septum may provide an alternative mechanism for dissipating the calvarial strains of mastication formerly taken up by an open interfrontal suture. Anat Rec, 291:308,317, 2008. © 2008 Wiley-Liss, Inc. [source] Aberrant BRAF splicing as an alternative mechanism for oncogenic B-Raf activation in thyroid carcinoma,THE JOURNAL OF PATHOLOGY, Issue 5 2009Essa Y Baitei Abstract Activating BRAF mutations have recently been reported in 28,83% of papillary thyroid carcinomas (PTCs). However, it is not known whether aberrant BRAF splicing occurs in thyroid carcinoma. To investigate aberrant BRAF splicing and its association with BRAF mutation in thyroid tumours, we studied aberrant BRAF splicing and BRAF mutation from 68 thyroid tumours. BRAFV600E mutation was detected in 20 of 43 PTCs and all three anaplastic thyroid carcinomas (ATCs). There is a higher frequency of BRAF mutation in PTC patients with stage III and IV tumours compared with stage I and II. Novel BRAF splicing variants were detected in 12 PTCs, three follicular variants of PTC (FVPTCs), and one ATC, as well as in two thyroid carcinoma cell lines, ARO and NPA. These variants did not have the N-terminal auto-inhibitory domain of wild-type B-Raf, resulting in an in-frame truncated protein that contained only the C-terminal kinase domain and caused constitutive activation of B-Raf. These variants were significantly associated with advanced disease stage and BRAFV600E mutation (p < 0.001, Fisher exact test). Furthermore, expression of these variants in NIH3T3 and CHO cells could activate the MAP kinase signalling pathway, transform them in vitro, and induce tumours in nude mice. These data suggest that BRAF splicing variants may function as an alternative mechanism for oncogenic B-Raf activation. Combination of the BRAFV600E mutation and its splicing variants may contribute towards disease progression to poorly differentiated thyroid carcinoma. Copyright © 2008 Pathological Society of Great Britain and Ireland. Published by John Wiley & Sons, Ltd. [source] The high affinity inositol transport system , implications for the pathophysiology and treatment of bipolar disorderBIPOLAR DISORDERS, Issue 2 2000Dietrich van Calker The ,inositol-depletion hypothesis' postulates that the therapeutic effects of lithium are due to inhibition of inositol monophosphatase, which leads to depletion of brain cells of myo-inositol and consequently to dampening of phosphoinositide (PI) signaling. This article examines the potential relevance of an alternative mechanism for inositol depletion: inhibition of myo-inositol uptake that proceeds via the sodium/myo-inositol cotransport (SMIT). We discuss recent in vitro experiments that show a pronounced downregulation of SMIT after chronic treatment with lithium, carbamazepine, and valproate at therapeutically relevant concentrations. It is concluded that downregulation of SMIT could represent a common mechanism of action of mood stabilizers. [source] Assessing the Risk of Introducing Exotic Species via the Live Marine Species TradeCONSERVATION BIOLOGY, Issue 1 2005SHANNON M. WEIGLE especies estuarinas; introducción de especies; mecanismos de transferencia de especies invasoras; prevención de especies invasoras; riesgo de invasiones Abstract:,Although the shipping industry has received considerable attention as a dispersal mechanism for aquatic nuisance species, many invasions have been linked to other mechanisms of transfer. The threat posed to coastal ecosystems by these alternative mechanisms, however, remains largely unquantified. We assessed the potential risks of introducing marine and estuarine species associated with seven mechanisms of transfer: seafood companies, aquaculture operations, bait shops, stores that sell marine ornamental species, research and educational organizations, public aquariums, and coastal restoration projects. For each, we compiled a comprehensive database of organizations in coastal Massachusetts. We then designed and administered a survey to a subset of organizations that inquired about (1) their proximity to saltwater and methods of handling live imports; (2) the type and quantity of marine species being imported; and (3) the organization's familiarity with marine invasions. Respondents in five of the seven categories acknowledged importing nonlocal live marine species to the area. Seafood companies handled the majority of individuals but relatively few taxa. This mechanism of transfer also had the most complex trade patterns and the greatest number of operations located near saltwater. In contrast, the other transfer mechanisms each had simpler trade pathways and fewer operations but varied in the quantity and taxonomic diversity of their imports. Significantly, no single mechanism of transfer stood out as presenting a primary risk. Rather, each had characteristics or used handling practices at different points in the importation process that could facilitate introductions. To prevent future marine invasions, better reporting requirements for live species imports are needed, and best-management practices and outreach strategies specific to the transfer mechanism should be developed and implemented. Resumen:,Aunque la industria de transportación marítima ha recibido considerable atención como un mecanismo de dispersión de especies acuáticas molestas, muchas invasiones han sido relacionadas con otros mecanismos de transferencia. Sin embargo, la amenaza de estos mecanismos alternativos a los ecosistemas costeros permanece en gran parte sin cuantificar. Evaluamos los potenciales riesgos para especies marinas y estuarinas asociados con siete mecanismos de transferencia: compañías de mariscos, operaciones acuaculturales, tiendas de especies marinas ornamentales, organizaciones de investigación y educativas, acuarios públicos y proyectos de restauración costera. Para cada uno, compilamos una amplia base de datos de organizaciones en la costa de Massachussetts. Luego diseñamos y aplicamos una encuesta a un subconjunto de organizaciones para obtener información sobre (1) su proximidad al agua marina y sus métodos para el manejo de importaciones vivas, (2) el tipo y cantidad de especies marinas importadas y (3) la familiaridad de la organización con invasiones marinas. Evaluamos los potenciales riesgos de introducciones de especies marinas y estuarinas. Los encuestados en cinco de siete categorías reconocieron importar especies marinas vivas no locales al área. Las compañías de mariscos manejaron a la mayoría de los individuos pero relativamente pocos taxa. Este mecanismo de transferencia también tuvo los patrones comerciales más complejos y el mayor número de operaciones localizadas cerca de agua marina. En contraste, cada uno de los demás mecanismos de transferencia tuvo canales de comercialización más simples y menos operaciones, pero variaron en la cantidad y diversidad taxonómica de sus importaciones. Significativamente, ningún mecanismo individual resaltó como un riesgo primario. Más bien, cada uno tenía características o utilizaba prácticas de manejo en diferentes etapas del proceso de importación que podían facilitar las introducciones. Para prevenir futuras invasiones marinas, se necesitan mejores requerimientos para reportar la importación de especies vivas, y se deben desarrollar e implementar prácticas de manejo óptimo y estrategias de extensión específicas para el mecanismo de transferencia. [source] Atypical molecular profile for joint development in the avian costal jointDEVELOPMENTAL DYNAMICS, Issue 10 2010B.B. Winslow Abstract Development of synovial joints involves generation of cartilaginous anlagen, formation of interzones between cartilage anlagen, and cavitation of interzones to produce fluid filled cavities. Interzone development is not fully understood, but interzones are thought to develop from skeletogenic cells that are inhibited from further chondrogenic development by a cascade of gene expression including Wnt and Bmp family members. We examined the development of the rarely studied avian costal joint to better understand mechanisms of joint development. The costal joint is found within ribs, is morphologically similar to the metatarsophalangeal joint, and undergoes cavitation in a similar manner. In contrast to other interzones, Wnt14/9a, Gdf5, Chordin, Barx1, and Bapx1 are absent from the costal joint interzone, consistent with the absence of active ,-catenin and phosphorylated Smad 1/5/8. However Autotaxin and Noggin are expressed. The molecular profile of the costal joint suggests there are alternative mechanisms of interzone development. Developmental Dynamics 239:2547,2557, 2010. © 2010 Wiley-Liss, Inc. [source] | |||||||||||||||||||||||||||||||||||||||||||