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81.
South African savanna grasslands are often characterised by indigestible tufted grass species whereas lawn grasses are far more desirable in terms of herbivore sustenance. We aimed to investigate the role of nutrients and/or the disturbance (grazing, trampling) by herbivores on the formation of grazing lawns. We conducted a series of common garden experiments to test the effect of nutrients on interspecific competition between a typical lawn-forming grass species (Cynodon dactylon) and a species that is frequently found outside grazing lawns (Hyparrhenia hirta), and tested for the effect of herbivore disturbance in the form of trampling and clipping. We also performed a vegetation and herbivore survey to apply experimentally derived insights to field observations. Our results showed that interspecific competition was not affected by soil nutrient concentrations. C. dactylon did show much more resilience to disturbance than H. hirta, presumably due to the regenerative capacity of its rhizomes. Results from the field survey were in line with these findings, describing a correlation between herbivore pressure and C. dactylon abundance. We conclude that herbivore disturbance, and not soil nutrients, provide C. dactylon with a competitive advantage over H. hirta, due to vegetative regeneration from its rhizomes. This provides evidence for the importance of concentrated, high herbivore densities for the creation and maintenance of grazing lawns.  相似文献   
82.
DIABLO promotes apoptosis by removing MIHA/XIAP from processed caspase 9   总被引:8,自引:0,他引:8  
MIHA is an inhibitor of apoptosis protein (IAP) that can inhibit cell death by direct interaction with caspases, the effector proteases of apoptosis. DIABLO is a mammalian protein that can bind to IAPs and antagonize their antiapoptotic effect, a function analogous to that of the proapoptotic Drosophila molecules, Grim, Reaper, and HID. Here, we show that after UV radiation, MIHA prevented apoptosis by inhibiting caspase 9 and caspase 3 activation. Unlike Bcl-2, MIHA functioned after release of cytochrome c and DIABLO from the mitochondria and was able to bind to both processed caspase 9 and processed caspase 3 to prevent feedback activation of their zymogen forms. Once released into the cytosol, DIABLO bound to MIHA and disrupted its association with processed caspase 9, thereby allowing caspase 9 to activate caspase 3, resulting in apoptosis.  相似文献   
83.
Verhagen AM  Lock P 《Genome biology》2002,3(6):reports4015.1-reports40155
A report on the 14th Lorne Cancer Conference, Lorne, Victoria, Australia, 14-17 February 2002.  相似文献   
84.
Migratory and resident hosts have been hypothesized to fulfil distinct roles in infectious disease dynamics. However, the contribution of resident and migratory hosts to wildlife infectious disease epidemiology, including that of low pathogenic avian influenza virus (LPAIV) in wild birds, has largely remained unstudied. During an autumn H3 LPAIV epizootic in free-living mallards (Anas platyrhynchos) — a partially migratory species — we identified resident and migratory host populations using stable hydrogen isotope analysis of flight feathers. We investigated the role of migratory and resident hosts separately in the introduction and maintenance of H3 LPAIV during the epizootic. To test this we analysed (i) H3 virus kinship, (ii) temporal patterns in H3 virus prevalence and shedding and (iii) H3-specific antibody prevalence in relation to host migratory strategy. We demonstrate that the H3 LPAIV strain causing the epizootic most likely originated from a single introduction, followed by local clonal expansion. The H3 LPAIV strain was genetically unrelated to H3 LPAIV detected both before and after the epizootic at the study site. During the LPAIV epizootic, migratory mallards were more often infected with H3 LPAIV than residents. Low titres of H3-specific antibodies were detected in only a few residents and migrants. Our results suggest that in this LPAIV epizootic, a single H3 virus was present in resident mallards prior to arrival of migratory mallards followed by a period of virus amplification, importantly associated with the influx of migratory mallards. Thus migrants are suggested to act as local amplifiers rather than the often suggested role as vectors importing novel strains from afar. Our study exemplifies that a multifaceted interdisciplinary approach offers promising opportunities to elucidate the role of migratory and resident hosts in infectious disease dynamics in wildlife.  相似文献   
85.
Lectin galactoside-binding soluble 3 binding protein (LGALS3BP, also called Mac-2 binding protein) is a heavily glycosylated secreted molecule that has been shown previously to be up-regulated in many cancers and has been implicated in tumor metastatic processes, as well as in other cell adhesion and immune functions. The CD33-related subset of sialic acid-binding immunoglobulin-like lectins (Siglecs) consists of immunomodulatory molecules that have recently been associated with the modulation of immune responses to cancer. Because up-regulation of Siglec ligands in cancer tissue has been observed, the characterization of these cancer-associated ligands that bind to inhibitory CD33-related Siglecs could provide novel targets for cancer immunomodulatory therapy. Here we used affinity chromatography of tumor cell extracts to identify LGALS3BP as a novel sialic acid-dependent ligand for human Siglec-9 and for other immunomodulatory Siglecs, such as Siglec-5 and Siglec-10. In contrast, the mouse homolog Siglec-E binds to murine LGALS3BP with lower affinity. LGALS3BP has been observed to be up-regulated in human colorectal and prostate cancer specimens, particularly in the extracellular matrix. Finally, LGALS3BP was able to inhibit neutrophil activation in a sialic acid- and Siglec-dependent manner. These findings suggest a novel immunoinhibitory function for LGALS3BP that might be important for immune evasion of tumor cells during cancer progression.  相似文献   
86.
The fatty acid compositions of the hyperthermophilic microorganisms Thermotoga maritima and Pyrococcus furiosus were studied and compared. A total of 37 different fatty acids were identified in T. maritima, including the novel 13,14-dimethyloctacosanedioic acid. In contrast, a total of 18 different fatty acids were characterized, as minor components, in P. furiosus, and these included saturated, monounsaturated, and dicarboxylic acids. This is the first report of fatty acids from an archaeon.  相似文献   
87.
Family-wide molecular diagnostic assays are valuable tools for initial identification of viruses during outbreaks and to limit costs of surveillance studies. Recent discoveries of paramyxoviruses have called for such assay that is able to detect all known and unknown paramyxoviruses in one round of PCR amplification. We have developed a RT-PCR assay consisting of a single degenerate primer set, able to detect all members of the Paramyxoviridae family including all virus genera within the subfamilies Paramyxovirinae and Pneumovirinae. Primers anneal to domain III of the polymerase gene, with the 3' end of the reverse primer annealing to the conserved motif GDNQ, which is proposed to be the active site for nucleotide polymerization. The assay was fully optimized and was shown to indeed detect all available paramyxoviruses tested. Clinical specimens from hospitalized patients that tested positive for known paramyxoviruses in conventional assays were also detected with the novel family-wide test. A high-throughput fluorescence-based RT-PCR version of the assay was developed for screening large numbers of specimens. A large number of samples collected from wild birds was tested, resulting in the detection of avian paramyxoviruses type 1 in both barnacle and white-fronted geese, and type 8 in barnacle geese. Avian metapneumovirus type C was found for the first time in Europe in mallards, greylag geese and common gulls. The single round family-wide RT-PCR assay described here is a useful tool for the detection of known and unknown paramyxoviruses, and screening of large sample collections from humans and animals.  相似文献   
88.
Pyridine-type nucleotides were identified in cell-free extracts of the hyperthermophilic archaeon Pyrococcus furiosus by their ability to replace authentic nicotinamide adenine dinucleotide (phosphate) [NAD(P)] in assays using pure P. furiosus enzymes. The nucleotides were purified using a combination of ion-exchange and reverse-phase chromatography. They were identified as NAD and NADP by analyses using liquid chromatography-mass spectrometry and high performance liquid chromatography. Their intracellular concentrations were measured in P. furiosus grown using maltose and peptides as the carbon sources. The concentrations decreased during the lag phase but remained constant during the exponential phase at approximately 0.17 and 0.13 mM, respectively. The amount of NAD was significantly lower (more than four-fold lower) than that in mesophilic bacteria, although the NADP concentration was comparable. The internal concentrations of NADH and NADPH in P. furiosus were determined to be 0.14 mM and 0.04 mM, respectively. The overall cellular concentration of NAD(P)(H) in P. furiosus (0.48 mM) is about half the value in the mesophiles. The NAD(H)/NADP(H) ratio in P. furiosus is consistent with the preferred use of NADP by several catabolic enzymes that have been purified from this organism. The mechanisms by which hyperthermophiles stabilize these thermally labile nicotinamide nucleotides are not known.  相似文献   
89.
The effects of X irradiation on oligodendrocyte-type-2-astrocyte (O-2A) progenitor cells derived from different regions of the perinatal central nervous system (CNS) of rats were investigated in vitro. The O-2A progenitor cells can differentiate into either oligodendrocytes or type-2 astrocytes. The depletion of these cells could lead to demyelination, seen as a delayed reaction after irradiation of the CNS in vivo. To quantify cell survival, O-2A progenitor cells were grown on monolayers of type-1 astrocytes. Monolayers of type-1 astrocytes stimulate O-2A progenitor cells to divide. O-2A progenitor cells were irradiated in vitro and clonogenic cell survival was measured. The O-2A progenitor cells derived from perinatal optic nerve were quite radiosensitive in contrast to O-2A progenitor cells derived from perinatal spinal cord and perinatal corpus callosum. Furthermore, O-2A progenitor cells derived from the optic nerve formed smaller colonies, with most colonies showing early differentiation into oligodendrocytes. In contrast, more than half of the colonies derived from corpus callosum did not show any differentiation after 2 weeks in vitro and kept growing. These differences support the view that perinatal O-2A progenitor cells derived from the optic nerve are committed progenitor cells while the O-2A progenitor cells derived from the perinatal corpus callosum and the perinatal spinal cord have more stem cell properties.  相似文献   
90.
De Wolf  H.  Backeljau  T.  Verhagen  R. 《Hydrobiologia》1998,378(1-3):27-32
The relationship between gene flow and the maintenance of geographic or morphology-related variation in the polymorphic Macaronesian periwinkle, Littorina striata, was investigated by means of isoelectric focusing of esterases (EST) and myoglobin (Mb). This revealed that: (1) individual EST variation is very high, (2) there is no EST differentiation between sexes, shell morphotypes or wave-exposure regimes, (3) there is no clear macrogeographic patterning of EST variability, although both Cape Verde Islands have the highest, with exception of Flores, mean number of EST bands, and (4) there is no Mb variation, not even between islands separated by more than 2000 km. These results indicate that L. striata shows a high degree of genetic homogeneity among geographic populations and that the morphological patterning in this species persists in the presence of intense gene flow.  相似文献   
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