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991.
Vascular morphogenesis by adult bone marrow progenitor cells in three-dimensional fibrin matrices 总被引:1,自引:0,他引:1
Rüger BM Breuss J Hollemann D Yanagida G Fischer MB Mosberger I Chott A Lang I Davis PF Höcker P Dettke M 《Differentiation; research in biological diversity》2008,76(7):772-783
The neovascularization of tissues is accomplished by two distinct processes: de novo formation of blood vessels through the assembly of progenitor cells during early prenatal development (vasculogenesis), and expansion of a pre-existing vascular network by endothelial cell sprouting (angiogenesis), the main mechanism of blood vessel growth in postnatal life. Evidence exists that adult bone marrow (BM)-derived progenitor cells can contribute to the formation of new vessels by their incorporation into sites of active angiogenesis. Aim of this study was to investigate the in vitro self-organizing capacity of human BM mononuclear cells (BMMNC) to induce vascular morphogenesis in a three-dimensional (3D) matrix environment in the absence of pre-existing vessels. Whole BMMNC as well as the adherent and non-adherent fractions of BMMNC were embedded in fibrin gels and cultured for 3-4 weeks without additional growth factors. The expression of hematopoietic-, endothelial-, smooth muscle lineage, and stem cell markers was analyzed by immunohistochemistry and confocal laser-scanning microscopy. The culture of unselected BMMNC in 3D fibrin matrices led to the formation of cell clusters expressing the endothelial progenitor cell (EPC) markers CD133, CD34, vascular endothelial growth factor receptor (VEGFR)-2, and c-kit, with stellar shaped spreading of peripheral elongated cells forming tube-like structures with increasing complexity over time. Cluster formation was dependent on the presence of both adherent and non-adherent BMMNC without the requirement of external growth factors. Developed vascular structures expressed the endothelial markers CD34, VEGFR-2, CD31, von Willebrand Factor (vWF), and podocalyxin, showed basement-membrane-lined lumina containing CD45+ cells and were surrounded by alpha-smooth muscle actin (SMA) expressing mural cells. Our data demonstrate that adult human BM progenitor cells can induce a dynamic self organization process to create vascular structures within avascular 3D fibrin matrices suggesting a possible alternative mechanism of adult vascular development without involvement of pre-existing vascular structures. 相似文献
992.
Peroxisome proliferator-activated receptor-gamma agonist 15-deoxy-Delta(12,14)-prostaglandin J(2) ameliorates experimental autoimmune encephalomyelitis 总被引:12,自引:0,他引:12
Diab A Deng C Smith JD Hussain RZ Phanavanh B Lovett-Racke AE Drew PD Racke MK 《Journal of immunology (Baltimore, Md. : 1950)》2002,168(5):2508-2515
Peroxisome proliferator-activated receptors (PPAR) are members of a nuclear hormone receptor superfamily that includes receptors for steroids, retinoids, and thyroid hormone, all of which are known to affect the immune response. Previous studies dealing with PPAR-gamma expression in the immune system have been limited. Recently, PPAR-gamma was identified in monocyte/macrophage cells. In this study we examined the role of PPAR-gamma in experimental autoimmune encephalomyelitis (EAE), an animal model for the human disease multiple sclerosis. The hypothesis we are testing is whether PPAR-gamma plays an important role in EAE pathogenesis and whether PPAR-gamma ligands can inhibit the clinical expression of EAE. Initial studies have shown that the presence of the PPAR-gamma ligand 15-deoxy-Delta(12,14)-PGJ(2) (15d-PGJ2) inhibits the proliferation of Ag-specific T cells from the spleen of myelin basic protein Ac(1-11) TCR-transgenic mice. 15d-PGJ2 suppressed IFN-gamma, IL-10, and IL-4 production by both Con A- and myelin basic protein Ac(1-11) peptide-stimulated lymphocytes as determined by ELISA and ELISPOT assay. Culture of encephalitogenic T cells with 15d-PGJ2 in the presence of Ag reduced the ability of these cells to adoptively transfer EAE. Examination of the target organ, the CNS, during the course of EAE revealed expression of PPAR-gamma in the spinal cord inflammatory infiltrate. Administration of 15d-PGJ2 before and at the onset of clinical signs of EAE significantly reduced the severity of disease. These results suggest that PPAR-gamma ligands may be a novel therapeutic agent for diseases such as multiple sclerosis. 相似文献
993.
Paul R. Lintott Nils Bunnefeld Elisa Fuentes-Montemayor Jeroen Minderman Lorna M. Blackmore Dave Goulson Kirsty J. Park 《Biodiversity and Conservation》2014,23(11):2875-2901
Urban expansion threatens global biodiversity through the destruction of natural and semi-natural habitats and increased levels of disturbance. Whilst woodlands in urban areas may reduce the impact of urbanisation on biodiversity, they are often subject to under or over-management and consist of small, fragmented patches which may be isolated. Effective management strategies for urban woodland require an understanding of the ecology and habitat requirements of all relevant taxa. Yet, little is known of how invertebrate, and in particular moth, assemblages utilise urban woodland despite being commonly found within the urban landscape. Here we show that the abundance, species richness, and species diversity of moth assemblages found within urban woodlands are determined by woodland vegetation character, patch configuration and the surrounding landscape. In general, mature broadleaved woodlands supported the highest abundance and diversity of moths. Large compact woodlands with proportionally less edge exposed to the surrounding matrix were associated with higher moth abundance than small complex woodlands. Woodland vegetation characteristics were more important than the surrounding landscape, suggesting that management at a local scale to ensure provision of good quality habitat may be relatively more important for moth populations than improving habitat connectivity across the urban matrix. Our results show that the planting of broadleaved woodlands, retaining mature trees and minimising woodland fragmentation will be beneficial for moth assemblages. 相似文献
994.
Karola Stotz Paul E. Griffiths Rob Knight 《Studies in History and Philosophy of Science Part C: Studies in History and Philosophy of Biological and Biomedical Sciences》2004,35(4):444
Philosophers and historians of biology have argued that genes are conceptualized differently in different fields of biology and that these differences influence both the conduct of research and the interpretation of research by audiences outside the field in which the research was conducted. In this paper we report the results of a questionnaire study of how genes are conceptualized by biological scientists at the University of Sydney, Australia. The results provide tentative support for some hypotheses about conceptual differences between different fields of biological research. 相似文献
995.
The proteins of bacteriophage T7 DNA replication mediate coordinated leading and lagging strand synthesis on a minicircle template. A distinguishing feature of the coordinated synthesis is the presence of a replication loop containing double and single-stranded DNA with a combined average length of 2600 nucleotides. Lagging strands consist of multiple Okazaki fragments, with an average length of 3000 nucleotides, suggesting that the replication loop dictates the frequency of initiation of Okazaki fragments. The size of Okazaki fragments is not affected by varying the components (T7 DNA polymerase, gene 4 helicase-primase, gene 2.5 single-stranded DNA binding protein, and rNTPs) of the reaction over a relatively wide range. Changes in the size of Okazaki fragments occurs only when leading and lagging strand synthesis is no longer coordinated. The synthesis of each Okazaki fragment is initiated by the synthesis of an RNA primer by the gene 4 primase at specific recognition sites. In the absence of a primase recognition site on the minicircle template no lagging strand synthesis occurs. The size of the Okazaki fragments is not affected by the number of recognition sites on the template. 相似文献
996.
Hydrologic Regime Controls Soil Phosphorus Fluxes in Restoration and Undisturbed Wetlands 总被引:4,自引:0,他引:4
Allison Aldous Paul McCormick Chad Ferguson Sean Graham Chris Craft 《Restoration Ecology》2005,13(2):341-347
Many wetland restoration projects occur on former agricultural soils that have a history of disturbance and fertilization, making them prone to phosphorus (P) release upon flooding. To study the relationship between P release and hydrologic regime, we collected soil cores from three restoration wetlands and three undisturbed wetlands around Upper Klamath Lake in southern Oregon, U.S.A. Soil cores were subjected to one of three hydrologic regimes—flooded, moist, and dry—for 7.5 weeks, and P fluxes were measured upon reflooding. Soils from restoration wetlands released P upon reflooding regardless of the hydrologic regime, with the greatest releases coming from soils that had been flooded or dried. Undisturbed wetland soils released P only after drying. Patterns in P release can be explained by a combination of physical and biological processes, including the release of iron‐bound P due to anoxia in the flooded treatment and the mineralization of organic P under aerobic conditions in the dry treatment. Higher rates of soil P release from restoration wetland soils, particularly under flooded conditions, were associated with higher total P concentrations compared with undisturbed wetland soils. We conclude that maintaining moist soil is the means to minimize P release from recently flooded wetland soils. Alternatively, prolonged flooding provides a means of liberating excess labile P from former agricultural soils while minimizing continued organic P mineralization and soil subsidence. 相似文献
997.
Holly Croft Jing M. Chen Xiangzhong Luo Paul Bartlett Bin Chen Ralf M. Staebler 《Global Change Biology》2017,23(9):3513-3524
Improving the accuracy of estimates of forest carbon exchange is a central priority for understanding ecosystem response to increased atmospheric CO2 levels and improving carbon cycle modelling. However, the spatially continuous parameterization of photosynthetic capacity (Vcmax) at global scales and appropriate temporal intervals within terrestrial biosphere models (TBMs) remains unresolved. This research investigates the use of biochemical parameters for modelling leaf photosynthetic capacity within a deciduous forest. Particular attention is given to the impacts of seasonality on both leaf biophysical variables and physiological processes, and their interdependent relationships. Four deciduous tree species were sampled across three growing seasons (2013–2015), approximately every 10 days for leaf chlorophyll content (ChlLeaf) and canopy structure. Leaf nitrogen (NArea) was also measured during 2014. Leaf photosynthesis was measured during 2014–2015 using a Li‐6400 gas‐exchange system, with A‐Ci curves to model Vcmax. Results showed that seasonality and variations between species resulted in weak relationships between Vcmax normalized to 25°C () and NArea (R2 = 0.62, P < 0.001), whereas ChlLeaf demonstrated a much stronger correlation with (R2 = 0.78, P < 0.001). The relationship between ChlLeaf and NArea was also weak (R2 = 0.47, P < 0.001), possibly due to the dynamic partitioning of nitrogen, between and within photosynthetic and nonphotosynthetic fractions. The spatial and temporal variability of was mapped using Landsat TM/ETM satellite data across the forest site, using physical models to derive ChlLeaf. TBMs largely treat photosynthetic parameters as either fixed constants or varying according to leaf nitrogen content. This research challenges assumptions that simple NArea– relationships can reliably be used to constrain photosynthetic capacity in TBMs, even within the same plant functional type. It is suggested that ChlLeaf provides a more accurate, direct proxy for and is also more easily retrievable from satellite data. These results have important implications for carbon modelling within deciduous ecosystems. 相似文献
998.
Worldwide genetic relationships among Francisella tularensis isolates determined by multiple-locus variable-number tandem repeat analysis 下载免费PDF全文
Johansson A Farlow J Larsson P Dukerich M Chambers E Byström M Fox J Chu M Forsman M Sjöstedt A Keim P 《Journal of bacteriology》2004,186(17):5808-5818
The intracellular bacterium Francisella tularensis is the causative agent of tularemia and poses a serious threat as an agent of bioterrorism. We have developed a highly effective molecular subtyping system from 25 variable-number tandem repeat (VNTR) loci. In our study, multiple-locus VNTR analysis (MLVA) was used to analyze genetic relationships and potential population structure within a global collection of 192 F. tularensis isolates, including representatives from each of the four subspecies. The VNTR loci displayed between 2 and 31 alleles with Nei's diversity values between 0.05 and 0.95. Neighbor-joining cluster analysis of VNTR data revealed 120 genotypes among the 192 F. tularensis isolates, including accurate subspecies identification. F. tularensis subsp. tularensis (type A) isolates showed great diversity at VNTR loci, while F. tularensis subsp. holarctica (type B) isolates showed much lower levels despite a much broader geographical prevalence. The resolution of two distinct clades within F. tularensis subsp. tularensis (designated A.I and A.II) revealed a previously unrecognized genetic division within this highly virulent subspecies. F. tularensis subsp. holarctica appears to have recently spread globally across continents from a single origin, while F. tularensis subsp. tularensis has a long and complex evolutionary history almost exclusively in North America. The sole non-North American type A isolates (Slovakian) were closely related to the SCHU S4 strain. Significant linkage disequilibrium was detected among VNTR loci of F. tularensis consistent with a clonal population structure. Overall, this work greatly augments the study of tularemia ecology and epidemiology, while providing a framework for future forensic analysis of F. tularensis isolates. 相似文献
999.
In cellular environments, coupled hydrolytic reactions are used to force efficient product formation in enzyme-catalyzed reactions. In the first step of protein synthesis, aminoacyl-tRNA synthetases react with amino acid and ATP to form an enzyme-bound adenylate that, in the next step, reacts with tRNA to form aminoacyl-tRNA. The reaction liberates pyrophosphate (PP(i)) which, in turn, can be hydrolyzed by pyrophosphatase to drive efficient aminoacylation. A potential polymorphic variant of human tryptophanyl-tRNA synthetase is shown here to sequester tryptophanyl adenylate. The bound adenylate does not react efficiently with the liberated PP(i) that normally competes with tRNA to resynthesize ATP and free amino acid. Structural analysis of this variant showed that residues needed for binding ATP phosphates and thus PP(i) were reoriented from their conformations in the structure of the more common sequence variant. Significantly, the reorientation does not affect reaction with tRNA, so that efficient aminoacylation is achieved. 相似文献
1000.
Hybridization can drive the convergence of territorial and sexual signals. However, non-genetic processes such as competition,
environment matching, or cultural transmission, also generate this pattern. We investigated the effect of hybridization on
song convergence between two interspecifically territorial warblers in a moving hybrid zone. We confirmed song convergence
in each species. Using an AFLP-based genetic index, we detected an effect of genetics on song convergence in Hippolais polyglotta, the expanding species. Evidence was weaker for H. icterina, the receding species. In moving zones, introgression is expected to be larger in the expanding species than in the receding.
Thus, the asymmetric contribution of the genetic index to convergence was consistent with expectations for genetically determined
traits in moving hybrid zones, and the observed introgression pattern of AFLP markers. However, the geographical location
of individuals had an effect on song variation too when genetics was accounted for, suggesting that convergence also has non-genetic
explanations. We examine the possible role of alternative processes to that of hybridization and discuss their conflicting
effects on reinforcement and hybrid zone dynamics. 相似文献