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71.
72.
REL Paul T Lafond CDM Müller-Graf S Nithiuthai PT Brey JC Koella 《BMC evolutionary biology》2004,4(1):30
Background
Evolutionary theory suggests that the selection pressure on parasites to maximize their transmission determines their optimal host exploitation strategies and thus their virulence. Establishing the adaptive basis to parasite life history traits has important consequences for predicting parasite responses to public health interventions. In this study we examine the extent to which malaria parasites conform to the predicted adaptive trade-off between transmission and virulence, as defined by mortality. The majority of natural infections, however, result in sub-lethal virulent effects (e.g. anaemia) and are often composed of many strains. Both sub-lethal effects and pathogen population structure have been theoretically shown to have important consequences for virulence evolution. Thus, we additionally examine the relationship between anaemia and transmission in single and mixed clone infections. 相似文献73.
González Romero MA Villaescusa Castillo L Díaz Lanza AM Arribas Bricio JM Soria Monzón CA Sanz Perucha J 《Zeitschrift für Naturforschung. C, Journal of biosciences》2003,58(11-12):804-806
Using GC-MS the volatile composition of Jasonia glutinosa D. C., was studied by comparing two different methods for the isolation of a volatile fraction: distillation from the fresh plant in order to obtain the essential oil, and direct thermal desorption (DTD). Compared with essential oil extraction the main advantages of the DTD technique are the smaller sample amount required, and the increased range of volatile compounds which can be subsequently analysed by GC-MS. 相似文献
74.
S S Metkar M Marchioretto V Antonini L Lunelli B Wang R JC Gilbert G Anderluh R Roth M Pooga J Pardo J E Heuser M D Serra C J Froelich 《Cell death and differentiation》2015,22(1):74-85
Perforin-mediated cytotoxicity is an essential host defense, in which defects contribute to tumor development and pathogenic disorders including autoimmunity and autoinflammation. How perforin (PFN) facilitates intracellular delivery of pro-apoptotic and inflammatory granzymes across the bilayer of targets remains unresolved. Here we show that cellular susceptibility to granzyme B (GzmB) correlates with rapid PFN-induced phosphatidylserine externalization, suggesting that pores are formed at a protein-lipid interface by incomplete membrane oligomers (or arcs). Supporting a role for these oligomers in protease delivery, an anti-PFN antibody (pf-80) suppresses necrosis but increases phosphatidylserine flip-flop and GzmB-induced apoptosis. As shown by atomic force microscopy on planar bilayers and deep-etch electron microscopy on mammalian cells, pf-80 increases the proportion of arcs which correlates with the presence of smaller electrical conductances, while large cylindrical pores decline. PFN appears to form arc structures on target membranes that serve as minimally disrupting conduits for GzmB translocation. The role of these arcs in PFN-mediated pathology warrants evaluation where they may serve as novel therapeutic targets.The cytotoxic cell granule-secretory pathway depends on perforin (PFN) to deliver granzyme (Gzm) proteases to the cytosol of target cells where they induce apoptosis and other biological effects, such as inflammation.1 Ring-shaped transmembrane PFN pores hereafter called ‘cylindrical pores'', are presumed to act as the gateway for cytosolic entry, either at the plasma membrane or after endocytosis.2, 3, 4 In either case the highly cationic Gzms are thought to diffuse through these cylindrical pores formed by poly-PFN. Nevertheless, a mechanistic understanding of the phenomenon (how the cationic globular protein exchanges from its carrier proteoglycan, serglycin, to the pore and crosses the plasma and/or vesicular membranes) has been lacking due to limitations in imaging technology and in our detailed understanding of the molecular forms that PFN may adopt following interaction with a target cell plasma membrane.Here we show under conditions where cylindrical pore formation is minimal,5 that granzyme B (GzmB) translocation readily occurs. We previously demonstrated that a prelude to granzyme translocation is PFN-mediated, Ca-independent phosphatidylserine (PS) externalization (flip-flop) measured by annexin-V and lactadherin binding.6 This rapid PS flip-flop also occurs when mouse CD8 cells contact antigen-pulsed target cells. Inasmuch as the proteinaceous cylinders offer a formidable barrier to lipid flow, we have speculated that the observed movement of anionic phospholipids to the external leaflet is due to the formation of proteo-lipidic structures, which consists of oligomerized PFN monomers bearing an arc morphology and plasma membrane lipids.6, 7, 8In the work reported here, the topology of PFN embedded into homogeneous planar bilayers and tumor cell plasma membranes was imaged by atomic force microscopy (AFM) and deep etch electron microscopy (DEEM), respectively. Further, the influence of an anti-human PFN mAb (pf-80) that rescues target cells from necrosis,9 was examined. The AFM data show that PFN forms arcs as well as rings in planar bilayers, while conductance measurements across equivalent membranes in parallel experiments measured functional pore sizes consistent with these varied structures. The pf-80 mAb increased the frequency of arc formation and reduced conductance values. Interestingly, PS flip-flop and granzyme delivery were both increased in target cells after PFN oligomerization was interrupted by the pf-80 mAb. A similar effect was seen in T24 bladder carcinoma cells imaged by DEEM. Treatment with PFN leads to deposition of rings (barrel stave pores) and arcs and the pf-80 mAb increased the ratio of arcs to rings on the surface of these cells. We suggest that the observed protein arcs function as toroidal pores in whole cells, explaining PS flip-flop, and act as focal points for granzyme translocation across lipid bilayer. 相似文献
75.
JC Barbero-Alvarez JV Subiela J Granda-Vera C Castagna M Gómez J Del Coso 《Biology of sport / Institute of Sport》2015,32(4):339-344
Despite its growing popularity, few studies have investigated specific physiological demands for elite female futsal. The aim of this study was to determine aerobic fitness in elite female futsal players using laboratory and field testing. Fourteen female futsal players from the Venezuelan National team (age =21.2±4.0 years; body mass =58.6±5.6 kg; height =161±5.0 cm) performed a progressive maximal treadmill test under laboratory conditions. Players also performed a progressive intermittent futsal-specific field test for endurance, the Futsal Intermittent Endurance Test (FIET), until volitional fatigue. Outcome variables were exercise heart rate (HR), VO2, post-exercise blood lactate concentrations ([La]b) and running speeds (km · h-1). During the treadmill test, VO2max, maximal aerobic speed (MAS), HR and peak [La]b were 45.3±5.6 ml · kg-1 · min-1, 12.5±1.77 km · h-1, 197±8 beats · min-1 and 11.3±1.4 mmol · l-1, respectively. The FIET total distance, peak running velocity, peak HR and [La]b were 1125.0±121.0 m, 15.2±0.5 km · h-1, 199±8 beats · min-1 and 12.5±2.2 mmol · l-1, respectively. The FIET distance and peak speed were strongly associated (r= 0.85-87, p < 0.0001) with VO2max and MAS, respectively. Peak HR and [La]b were not significantly different between tests. Elite female futsal players possess moderate aerobic fitness. Furthermore, the FIET can be considered as a valid field test to determine aerobic fitness in elite level female futsal players. 相似文献
76.
Rodríguez P Montoro A Barquinero JF Caballín MR Villaescusa I Barrios L 《Radiation research》2004,162(1):31-38
The aim of the present study was to evaluate the influence of the exclusion of cells with unstable aberrations in the elaboration of dose-effect curves for translocations and their implications in biological dosimetry of past exposures. To establish dose-effect curves, peripheral blood samples were irradiated with 60Co gamma rays at ten different doses and the yield of translocations analyzed by FISH was considered in all cells and in stable cells (those without dicentrics, acentrics or rings). To discriminate transmissible translocations, the dose- effect curve for total apparently simple translocations in stable cells was chosen as the reference. In stable cells, dose- effect curves for apparently simple translocations without pseudosimple and complex-derived one-way patterns, tAbtBa and total translocations were obtained. None of these curves differed from the reference curve. When all cells were considered, only the curve for total translocations was significantly different from the reference curve. From the results obtained it can be concluded that the use of dose-effect curves for apparently simple translocations in stable cells and in all cells will give similar dose estimates in retrospective biological dosimetry studies. However, the use of dose-effect curves for total translocations in all cells will lead to underestimations of the dose mainly at high doses. 相似文献
77.
DNA hybridization evidence for the principal lineages of hummingbirds (Aves:Trochilidae) 总被引:3,自引:0,他引:3
The spectacular evolutionary radiation of hummingbirds (Trochilidae) has
served as a model system for many biological studies. To begin to provide a
historical context for these investigations, we generated a complete matrix
of DNA hybridization distances among 26 hummingbirds and an outgroup swift
(Chaetura pelagica) to determine the principal hummingbird lineages. FITCH
topologies estimated from symmetrized delta TmH-C values and subjected to
various validation methods (bootstrapping, weighted jackknifing, branch
length significance) indicated a fundamental split between hermit
(Eutoxeres aquila, Threnetes ruckeri; Phaethornithinae) and nonhermit
(Trochilinae) hummingbirds, and provided strong support for six principal
nonhermit clades with the following branching order: (1) a predominantly
lowland group comprising caribs (Eulampis holosericeus) and relatives
(Androdon aequatorialis and Heliothryx barroti) with violet-ears (Colibri
coruscans) and relatives (Doryfera ludovicae); (2) an Andean-associated
clade of highly polytypic taxa (Eriocnemis, Heliodoxa, and Coeligena); (3)
a second endemic Andean clade (Oreotrochilus chimborazo, Aglaiocercus
coelestis, and Lesbia victoriae) paired with thorntails (Popelairia
conversii); (4) emeralds and relatives (Chlorostilbon mellisugus, Amazilia
tzacatl, Thalurania colombica, Orthorhyncus cristatus and Campylopterus
villaviscensio); (5) mountain-gems (Lampornis clemenciae and Eugenes
fulgens); and (6) tiny bee-like forms (Archilochus colubris, Myrtis fanny,
Acestrura mulsant, and Philodice mitchellii). Corresponding analyses on a
matrix of unsymmetrized delta values gave similar support for these
relationships except that the branching order of the two Andean clades (2,
3 above) was unresolved. In general, subsidiary relationships were
consistent and well supported by both matrices, sometimes revealing
surprising associations between forms that differ dramatically in plumage
and bill morphology. Our results also reveal some basic aspects of
hummingbird ecologic and morphologic evolution. For example, most of the
diverse endemic Andean assemblage apparently comprises two genetically
divergent clades, whereas the majority of North American hummingbirds
belong a single third clade. Genetic distances separating some
morphologically distinct genera (Oreotrochilus, Aglaiocercus, Lesbia;
Myrtis, Acestrura, Philodice) were no greater than among congeneric
(Coeligena) species, indicating that, in hummingbirds, morphological
divergence does not necessarily reflect level of genetic divergence.
相似文献
78.
79.
Loss of phylogenetic information in chorion gene families of Bombyx mori gene conversion 总被引:1,自引:0,他引:1
Regier JC; Weigmann BM; Leclerc RF; Friedlander TP 《Molecular biology and evolution》1994,11(1):72-87
The silkmoth chorion has provided a stimulating model for the study of
evolution and developmental regulation of gene families. Previous attempts
at inferring relationships among chorion sequences have been based on
pairwise comparisons of overall similarity, a potentially problematic
approach. To remedy this, we identified the alignable regions of low
sequence variability and then analyzed this restricted database by
parsimony and neighbor-joining methods. At the deepest level, the chorion
sequence tree is split into two branches, called "alpha" and "beta." Within
each branch, early- and late-expressing genes each constitute monophyletic
groups, while the situation with middle-expressing genes remains uncertain.
The HcB gene family appears to be the most basal beta-branch group, but
this conclusion is qualified because the effect of gene conversion on
branching order is unknown. Previous studies by Eickbush and colleagues
have strongly suggested that ErA, HcA, and HcB families undergo gene
conversion within a gene family, whereas the ErB family does not. The
occurrence of conversion correlates with a particular tree structure;
namely, branch lengths are much greater at the base of the family than at
higher internodes and terminal branches. These observations raise the
possibility that chorion gene families are defined by gene conversion
events (reticulate evolution) rather than by descent with modification
(synapomorphy).
相似文献
80.