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排序方式: 共有186条查询结果,搜索用时 24 毫秒
91.
Ho QT Verboven P Verlinden BE Herremans E Wevers M Carmeliet J Nicolaï BM 《Plant physiology》2011,155(3):1158-1168
Respiration of bulky plant organs such as roots, tubers, stems, seeds, and fruit depends very much on oxygen (O2) availability and often follows a Michaelis-Menten-like response. A multiscale model is presented to calculate gas exchange in plants using the microscale geometry of the tissue, or vice versa, local concentrations in the cells from macroscopic gas concentration profiles. This approach provides a computationally feasible and accurate analysis of cell metabolism in any plant organ during hypoxia and anoxia. The predicted O2 and carbon dioxide (CO2) partial pressure profiles compared very well with experimental data, thereby validating the multiscale model. The important microscale geometrical features are the shape, size, and three-dimensional connectivity of cells and air spaces. It was demonstrated that the gas-exchange properties of the cell wall and cell membrane have little effect on the cellular gas exchange of apple (Malus×domestica) parenchyma tissue. The analysis clearly confirmed that cells are an additional route for CO2 transport, while for O2 the intercellular spaces are the main diffusion route. The simulation results also showed that the local gas concentration gradients were steeper in the cells than in the surrounding air spaces. Therefore, to analyze the cellular metabolism under hypoxic and anoxic conditions, the microscale model is required to calculate the correct intracellular concentrations. Understanding the O2 response of plants and plant organs thus not only requires knowledge of external conditions, dimensions, gas-exchange properties of the tissues, and cellular respiration kinetics but also of microstructure. 相似文献
92.
The menopause transition is a dynamic process that begins with the first appearance of menstrual irregularity and ends with a woman's final menstrual period. As ovarian follicle numbers dwindle, the hypothalamic-pituitary-ovarian axis enters a state of compensated failure. In this state, elevated FSH is capable of maintaining relatively regular folliculogenesis and ovulation, but fertility is reduced. Eventually, this state of compensated failure cannot be sustained, and the ovary becomes unable to produce functioning follicles. Recent multicenter studies from several countries have addressed the pattern of change in hormones and a model form reproductive aging has been developed that helps explain the changes in hormone patterns and fertility that accompany menopause. Perhaps more important, the hormonal changes of the menopausal transition may be predictive of future disease risk. This review will undertake an explanation of the current literature on this topic. 相似文献
93.
Renfree MB Papenfuss AT Deakin JE Lindsay J Heider T Belov K Rens W Waters PD Pharo EA Shaw G Wong ES Lefèvre CM Nicholas KR Kuroki Y Wakefield MJ Zenger KR Wang C Ferguson-Smith M Nicholas FW Hickford D Yu H Short KR Siddle HV Frankenberg SR Chew KY Menzies BR Stringer JM Suzuki S Hore TA Delbridge ML Patel HR Mohammadi A Schneider NY Hu Y O'Hara W Al Nadaf S Wu C Feng ZP Cocks BG Wang J Flicek P Searle SM Fairley S Beal K Herrero J Carone DM Suzuki Y Sugano S Toyoda A Sakaki Y Kondo S 《Genome biology》2011,12(8):R81
94.
Rodrigues CO Shehadeh LA Hoosien M Otero V Chopra I Tsinoremas NF Bishopric NH 《PloS one》2011,6(8):e24013
Rationale
The adult myocardium has been reported to harbor several classes of multipotent progenitor cells (CPCs) with tri-lineage differentiation potential. It is not clear whether c-kit+CPCs represent a uniform precursor population or a more complex mixture of cell types.Objective
To characterize and understand vasculogenic heterogeneity within c-kit+presumptive cardiac progenitor cell populations.Methods and Results
c-kit+, sca-1+ CPCs obtained from adult mouse left ventricle expressed stem cell-associated genes, including Oct-4 and Myc, and were self-renewing, pluripotent and clonogenic. Detailed single cell clonal analysis of 17 clones revealed that most (14/17) exhibited trilineage differentiation potential. However, striking morphological differences were observed among clones that were heritable and stable in long-term culture. 3 major groups were identified: round (7/17), flat or spindle-shaped (5/17) and stellate (5/17). Stellate morphology was predictive of vasculogenic differentiation in Matrigel. Genome-wide expression studies and bioinformatic analysis revealed clonally stable, heritable differences in stromal cell-derived factor-1 (SDF-1) expression that correlated strongly with stellate morphology and vasculogenic capacity. Endogenous SDF-1 production contributed directly to vasculogenic differentiation: both shRNA-mediated knockdown of SDF-1 and AMD3100, an antagonist of the SDF-1 receptor CXC chemokine Receptor-4 (CXCR4), reduced tube-forming capacity, while exogenous SDF-1 induced tube formation by 2 non-vasculogenic clones. CPCs producing SDF-1 were able to vascularize Matrigel dermal implants in vivo, while CPCs with low SDF-1 production were not.Conclusions
Clonogenic c-kit+, sca-1+ CPCs are heterogeneous in morphology, gene expression patterns and differentiation potential. Clone-specific levels of SDF-1 expression both predict and promote development of a vasculogenic phenotype via a previously unreported autocrine mechanism. 相似文献95.
Loo YM Fornek J Crochet N Bajwa G Perwitasari O Martinez-Sobrido L Akira S Gill MA García-Sastre A Katze MG Gale M 《Journal of virology》2008,82(1):335-345
Alpha/beta interferon immune defenses are essential for resistance to viruses and can be triggered through the actions of the cytoplasmic helicases retinoic acid-inducible gene I (RIG-I) and melanoma differentiation-associated gene 5 (MDA5). Signaling by each is initiated by the recognition of viral products such as RNA and occurs through downstream interaction with the IPS-1 adaptor protein. We directly compared the innate immune signaling requirements of representative viruses of the Flaviviridae, Orthomyxoviridae, Paramyxoviridae, and Reoviridae for RIG-I, MDA5, and interferon promoter-stimulating factor 1 (IPS-1). In cultured fibroblasts, IPS-1 was essential for innate immune signaling of downstream interferon regulatory factor 3 activation and interferon-stimulated gene expression, but the requirements for RIG-I and MDA5 were variable. Each was individually dispensable for signaling triggered by reovirus and dengue virus, whereas RIG-I was essential for signaling by influenza A virus, influenza B virus, and human respiratory syncytial virus. Functional genomics analyses identified cellular genes triggered during influenza A virus infection whose expression was strictly dependent on RIG-I and which are involved in processes of innate or adaptive immunity, apoptosis, cytokine signaling, and inflammation associated with the host response to contemporary and pandemic strains of influenza virus. These results define IPS-1-dependent signaling as an essential feature of host immunity to RNA virus infection. Our observations further demonstrate differential and redundant roles for RIG-I and MDA5 in pathogen recognition and innate immune signaling that may reflect unique and shared biologic properties of RNA viruses whose differential triggering and control of gene expression may impact pathogenesis and infection. 相似文献
96.
Burkart V Germaschewski L Schloot NC Bellmann K Kolb H 《Biochemical and biophysical research communications》2008,369(2):421-425
Type 1 diabetes is caused by the immune-mediated destruction of pancreatic beta cells. Animal models of the disease demonstrate an increased susceptibility of beta cells to immunological attacks due to their defective stress-responsiveness. To investigate the stress-responsiveness in human type 1 diabetes we analyzed the heat-inducibility of the dominant stress protein heat shock protein (Hsp)70 in diabetic patients at different disease stages. At diabetes-manifestation heat-induced Hsp70 levels in peripheral blood mononuclear cells (PBMC) reached only about 25% of the levels expressed by heat-treated PBMC from non-diabetic subjects (p < 0.05). Heat-responsiveness improved with disease duration and was re-established at more than eight months after disease-manifestation. Hyperthermia-induced Hsp70 expression was decreased by the T-helper 1-associated cytokine interferon-γ and increased by the T-helper 2-associated transforming growth factor-β. We conclude that impaired cellular stress-responsiveness, aggravated by the inflammatory milieu at the onset of type 1 diabetes, contributes to disease manifestation. 相似文献
97.
Aryal Sitaram Nielsen Uffe N. Sumaya Nanette H. De Faveri Stefano Wilson Craig Riegler Markus 《BioControl》2022,67(1):63-74
BioControl - Entomopathogenic nematodes (EPNs) are used in biological control of pest insects but their potential may be limited by strain availability from different bioregions and effectiveness... 相似文献
98.
Antarctic lakes are extreme ecosystems with microbially dominated food webs, in which viruses may be important in controlling
community dynamics. A year long investigation of two Antarctic saline lakes (Ace and Pendant Lakes) revealed high concentrations
of virus like particles (VLP) (0.20–1.26 × 108 ml−1), high VLP: bacteria ratios (maximum 70.6) and a seasonal pattern of lysogeny differing from that seen at lower latitudes.
Highest rates of lysogeny (up to 32% in Pendant Lake and 71% in Ace Lake) occurred in winter and spring, with low or no lysogeny
in summer. Rates of virus production (range 0.176–0.823 × 106 viruses ml−1 h−1) were comparable to lower latitude freshwater lakes. In Ace Lake VLP did not correlate with bacterial cell concentration
or bacterial production but correlated positively with primary production, while in Pendant Lake VLP abundance correlated
positively with both bacterial cell numbers and bacterial production but not with primary production. In terms of virus and
bacterial dynamics the two saline Antarctic lakes studied appear distinct from other aquatic ecosystems investigated so far,
in having very high viral to bacterial ratios (VBR) and a very high occurrence of lysogeny in winter. 相似文献
99.
100.