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41.
Mónica B. Mazzola Jeanne C. Chambers Robert R. Blank David A. Pyke Eugene W. Schupp Kimberly G. Allcock Paul S. Doescher Robert S. Nowak 《Biological invasions》2011,13(2):513-526
Resource availability and propagule supply are major factors influencing establishment and persistence of both native and
invasive species. Increased soil nitrogen (N) availability and high propagule inputs contribute to the ability of annual invasive
grasses to dominate disturbed ecosystems. Nitrogen reduction through carbon (C) additions can potentially immobilize soil
N and reduce the competitiveness of annual invasive grasses. Native perennial species are more tolerant of resource limiting
conditions and may benefit if N reduction decreases the competitive advantage of annual invaders and if sufficient propagules
are available for their establishment. Bromus tectorum, an exotic annual grass in the sagebrush steppe of western North America, is rapidly displacing native plant species and
causing widespread changes in ecosystem processes. We tested whether nitrogen reduction would negatively affect B. tectorum while creating an opportunity for establishment of native perennial species. A C source, sucrose, was added to the soil,
and then plots were seeded with different densities of both B. tectorum (0, 150, 300, 600, and 1,200 viable seeds m−2) and native species (0, 150, 300, and 600 viable seeds m−2). Adding sucrose had short-term (1 year) negative effects on available nitrogen and B. tectorum density, biomass and seed numbers, but did not increase establishment of native species. Increasing propagule availability
increased both B. tectorum and native species establishment. Effects of B. tectorum on native species were density dependent and native establishment increased as B. tectorum propagule availability decreased. Survival of native seedlings was low indicating that recruitment is governed by the seedling
stage. 相似文献
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44.
Electromechanical integration of cardiomyocytes derived from human embryonic stem cells 总被引:1,自引:0,他引:1
Kehat I Khimovich L Caspi O Gepstein A Shofti R Arbel G Huber I Satin J Itskovitz-Eldor J Gepstein L 《Nature biotechnology》2004,22(10):1282-1289
Cell therapy is emerging as a promising strategy for myocardial repair. This approach is hampered, however, by the lack of sources for human cardiac tissue and by the absence of direct evidence for functional integration of donor cells into host tissues. Here we investigate whether cells derived from human embryonic stem (hES) cells can restore myocardial electromechanical properties. Cardiomyocyte cell grafts were generated from hES cells in vitro using the embryoid body differentiating system. This tissue formed structural and electromechanical connections with cultured rat cardiomyocytes. In vivo integration was shown in a large-animal model of slow heart rate. The transplanted hES cell-derived cardiomyocytes paced the hearts of swine with complete atrioventricular block, as assessed by detailed three-dimensional electrophysiological mapping and histopathological examination. These results demonstrate the potential of hES-cell cardiomyocytes to act as a rate-responsive biological pacemaker and for future myocardial regeneration strategies. 相似文献
45.
Jossi Hillel Martien AM Groenen Michèle Tixier-Boichard Abraham B Korol Lior David Valery M Kirzhner Terry Burke Asili Barre-Dirie Richard PMA Crooijmans Kari Elo Marcus W Feldman Paul J Freidlin Asko M?ki-Tanila Marian Oortwijn Pippa Thomson Alain Vignal Klaus Wimmers Steffen Weigend 《遗传、选种与进化》2003,35(6):533-557
In a project on the biodiversity of chickens funded by the European Commission (EC), eight laboratories collaborated to assess the genetic variation within and between 52 populations from a wide range of chicken types. Twenty-two di-nucleotide microsatellite markers were used to genotype DNA pools of 50 birds from each population. The polymorphism measures for the average, the least polymorphic population (inbred C line) and the most polymorphic population (Gallus gallus spadiceus) were, respectively, as follows: number of alleles per locus, per population: 3.5, 1.3 and 5.2; average gene diversity across markers: 0.47, 0.05 and 0.64; and proportion of polymorphic markers: 0.91, 0.25 and 1.0. These were in good agreement with the breeding history of the populations. For instance, unselected populations were found to be more polymorphic than selected breeds such as layers. Thus DNA pools are effective in the preliminary assessment of genetic variation of populations and markers. Mean genetic distance indicates the extent to which a given population shares its genetic diversity with that of the whole tested gene pool and is a useful criterion for conservation of diversity. The distribution of population-specific (private) alleles and the amount of genetic variation shared among populations supports the hypothesis that the red jungle fowl is the main progenitor of the domesticated chicken. 相似文献
46.
Intracerebral hemorrhages and syncytium formation induced by endothelial cell infection with a murine leukemia virus. 总被引:3,自引:8,他引:3 下载免费PDF全文
The mechanisms of endothelial cell damage that lead to cerebral hemorrhage are not completely understood. In this study, a cloned murine retrovirus, TR1.3, that uniformly induced stroke in neonatal BALB/c mice is described. Restriction digest mapping suggests that TR1.3 is part of the Friend murine leukemia virus (FMuLV) family. However, unlike mice exposed to other FMuLVs, mice infected with TR1.3 virus developed tremors and seizures within 8 to 18 days postinoculation. This was uniformly followed by paralysis and death within 1 to 2 days. Postmortem examination of TR1.3-inoculated mice revealed edematous brain tissue with large areas of intracerebral hemorrhage. Histologic analysis revealed prominent small vessel pathology including syncytium formation of endothelial cells. Immunohistochemical analysis of frozen brain sections using double fluorescence staining demonstrated that TR1.3 virus specifically infected small vessel endothelial cells. Although infection of vessel endothelial cells was detected in several organs, only brain endothelial cells displayed viral infection associated with hemorrhage. The primary determinant of TR1.3-induced neuropathogenicity was found to reside within a 3.0-kb fragment containing the 3' end of the pol gene, the env gene, and the U3 region of the long terminal repeat. The restricted tropism and acute pathogenicity of this cloned murine retrovirus provide a model for studying virus-induced stroke and for elucidating the mechanisms involved in syncytium formation by retroviruses in vivo. 相似文献
47.
48.
Conrad MD Gorman AW Schillinger JA Fiori PL Arroyo R Malla N Dubey ML Gonzalez J Blank S Secor WE Carlton JM 《PLoS neglected tropical diseases》2012,6(3):e1573
Background
Trichomonas vaginalis is the causative agent of human trichomoniasis, the most common non-viral sexually transmitted infection world-wide. Despite its prevalence, little is known about the genetic diversity and population structure of this haploid parasite due to the lack of appropriate tools. The development of a panel of microsatellite makers and SNPs from mining the parasite''s genome sequence has paved the way to a global analysis of the genetic structure of the pathogen and association with clinical phenotypes.Methodology/Principal Findings
Here we utilize a panel of T. vaginalis-specific genetic markers to genotype 235 isolates from Mexico, Chile, India, Australia, Papua New Guinea, Italy, Africa and the United States, including 19 clinical isolates recently collected from 270 women attending New York City sexually transmitted disease clinics. Using population genetic analysis, we show that T. vaginalis is a genetically diverse parasite with a unique population structure consisting of two types present in equal proportions world-wide. Parasites belonging to the two types (type 1 and type 2) differ significantly in the rate at which they harbor the T. vaginalis virus, a dsRNA virus implicated in parasite pathogenesis, and in their sensitivity to the widely-used drug, metronidazole. We also uncover evidence of genetic exchange, indicating a sexual life-cycle of the parasite despite an absence of morphologically-distinct sexual stages.Conclusions/Significance
Our study represents the first robust and comprehensive evaluation of global T. vaginalis genetic diversity and population structure. Our identification of a unique two-type structure, and the clinically relevant phenotypes associated with them, provides a new dimension for understanding T. vaginalis pathogenesis. In addition, our demonstration of the possibility of genetic exchange in the parasite has important implications for genetic research and control of the disease. 相似文献49.
Lior Almagor Orna Chomsky-Hecht Adva Ben-Mocha Doran Hendin-Barak Nathan Dascal Joel A. Hirsch 《Channels (Austin, Tex.)》2012,6(6):468-472
CaV channels are multi-subunit protein complexes that enable inward cellular Ca2+ currents in response to membrane depolarization. We recently described structure-function studies of the intracellular α1 subunit domain I-II linker, directly downstream of domain IS6. The results show the extent of the linker’s helical structure to be subfamily dependent, as dictated by highly conserved primary sequence differences. Moreover, the difference in structure confers different biophysical properties, particularly the extent and kinetics of voltage and calcium-dependent inactivation. Timothy syndrome is a human genetic disorder due to mutations in the CaV1.2 gene. Here, we explored whether perturbation of the I-II linker helical structure might provide a mechanistic explanation for a Timothy syndrome mutant’s (human CaV1.2 G406R equivalent) biophysical effects on inactivation and activation. The results are equivocal, suggesting that a full mechanistic explanation for this Timothy syndrome mutation requires further investigation. 相似文献
50.
The potential of viral contamination is a regulatory concern for continuous cell line-derived pharmaceutical proteins. Complementary and redundant safety steps, including an evaluation of the viral clearance capacity of unit operations in the purification process, are performed prior to registration and marketing of biotechnology pharmaceuticals. Because process refinement is frequently beneficial, CBER/FDA has published guidance facilitating process improvement by delineating specific instances where the bracketing and generic approaches are appropriate for virus removal validation. In this study, a generic/matrix study was performed using Q-Sepharose Fast Flow (QSFF) chromatography to determine if bracketing and generic validation can be applied to anion exchange chromatography. Key operational parameters were varied to upper and lower extreme values and the impact on viral clearance was assessed using simian virus 40 (SV40) as the model virus. Operational ranges for key chromatography parameters were identified where an SV40 log(10) reduction value (LRV) of >or=4.7 log(10) is consistently achieved. On the basis of the apparent robustness of SV40 removal by Q-anion exchange chromatography, we propose that the concept of "bracketed generic" validation can be applied to this and potentially other chromatography unit operations. 相似文献