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931.
Niels M. Schmidt Rolf A. Ims Toke T. H?ye Olivier Gilg Lars H. Hansen Jannik Hansen Magnus Lund Eva Fuglei Mads C. Forchhammer Benoit Sittler 《Proceedings. Biological sciences / The Royal Society》2012,279(1746):4417-4422
Alpine and arctic lemming populations appear to be highly sensitive to climate change, and when faced with warmer and shorter winters, their well-known high-amplitude population cycles may collapse. Being keystone species in tundra ecosystems, changed lemming dynamics may convey significant knock-on effects on trophically linked species. Here, we analyse long-term (1988–2010), community-wide monitoring data from two sites in high-arctic Greenland and document how a collapse in collared lemming cyclicity affects the population dynamics of the predator guild. Dramatic changes were observed in two highly specialized lemming predators: snowy owl and stoat. Following the lemming cycle collapse, snowy owl fledgling production declined by 98 per cent, and there was indication of a severe population decline of stoats at one site. The less specialized long-tailed skua and the generalist arctic fox were more loosely coupled to the lemming dynamics. Still, the lemming collapse had noticeable effects on their reproductive performance. Predator responses differed somewhat between sites in all species and could arise from site-specific differences in lemming dynamics, intra-guild interactions or subsidies from other resources. Nevertheless, population extinctions and community restructuring of this arctic endemic predator guild are likely if the lemming dynamics are maintained at the current non-cyclic, low-density state. 相似文献
932.
Christe P Glaizot O Strepparava N Devevey G Fumagalli L 《Proceedings. Biological sciences / The Royal Society》2012,279(1731):1142-1149
Parental effort is usually associated with high metabolism that could lead to an increase in the production of reactive oxidative species giving rise to oxidative stress. Since many antioxidants involved in the resistance to oxidative stress can also enhance immune function, an increase in parental effort may diminish the level of antioxidants otherwise involved in parasite resistance. In the present study, we performed brood size manipulation in a population of great tits (Parus major) to create different levels of parental effort. We measured resistance to oxidative stress and used a newly developed quantitative PCR assay to quantify malarial parasitaemia. We found that males with an enlarged brood had significantly higher level of malarial parasites and lower red blood cell resistance to free radicals than males rearing control and reduced broods. Brood size manipulation did not affect female parasitaemia, although females with an enlarged brood had lower red blood cell resistance than females with control and reduced broods. However, for both sexes, there was no relationship between the level of parasitaemia and resistance to oxidative stress, suggesting a twofold cost of reproduction. Our results thus suggest the presence of two proximate and independent mechanisms for the well-documented trade-off between current reproductive effort and parental survival. 相似文献
933.
Dendritic cells (DCs) are well known as professional antigen-presenting cells (APC) able to initiate specific T-cell responses to pathogens in lymph nodes (LN) draining the site of infection. However, the respective contribution of migratory and LN-resident DCs in this process remains unclear. As DC subsets represent important targets for vaccination strategies, more precise knowledge of DC subsets able to present vaccine antigens to T cells efficiently is required. To investigate the capacities of DCs migrating in the lymph (L-DCs) to initiate a specific T-cell response, we used physiologically generated DCs collected from a pseudoafferent lymphatic cannulation model in sheep. The CD1b+ L-DCs were assessed for presenting antigens from the vaccine attenuated strain of Salmonella enterica serovar Abortusovis. CD1b+ L-DCs were able to phagocytose, process and to present efficiently Salmonella antigens to effector/memory T cells in vitro. They were shown to be efficient APC for the priming of allogeneic naive T cells associated with inducing both IFN-γ and IL-4 responses. They were also efficient in presenting Salmonella antigens to autologous naive T cells associated with inducing both IFN-γ and IL-10 responses. The capacities of L-DCs to process and present Salmonella antigens to T cells were investigated in vivo after conjunctival inoculation of Salmonella. The CD1b+ L-DCs collected after inoculation were able to induce the proliferative response of CD4+ T cells suggesting the in vivo capture of Salmonella antigens by the CD1b+ L-DCs, and their potential to present them directly to CD4+ T cells. In this study, CD1b+ L-DCs present potential characteristics of APC to initiate by themselves T cell priming in the LN. They could be used as target cells for driving immune activation in vaccinal strategies. 相似文献
934.
Contassot E Jankovic D Schuler P Preynat-Seauve O Gehrke S Kerl K Beermann F French LE 《Pigment cell & melanoma research》2012,25(2):275-278
The incidence of melanoma has significantly increased, and a better understanding of its pathogenesis and development of new therapeutic strategies are urgently needed. Here, we describe a murine model of metastatic cutaneous melanoma using C57BL/6 mice expressing a mutated human N-Ras gene under the control of a tyrosinase promoter (TyrRas). These mice were topically exposed to 7,12- dimethylbenzanthracene (DMBA) for brief exposure periods. Cutaneous melanoma developed at the site of exposure on average by 19 weeks of age and in 80% of mice. Importantly, as in humans, melanoma development was associated with subsequent metastasis to tumor-draining lymph nodes. Critically, such metastatic behavior is transplantable, as intradermal inoculation of melanoma cells from TyrRas-DMBA mice into non-transgenic mice led to the growth of melanoma and, again, metastasis to skin-draining lymph nodes. This metastatic melanoma model closely mimics human pathology and should be a useful tool for studying melanoma pathogenesis and developing new therapies. 相似文献
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938.
Jacob F Ukegjini K Nixdorf S Ford CE Olivier J Caduff R Scurry JP Guertler R Hornung D Mueller R Fink DA Hacker NF Heinzelmann-Schwarz VA 《PloS one》2012,7(2):e31885
Background
Activation of the Wnt signaling pathway is implicated in aberrant cellular proliferation in various cancers. In 40% of endometrioid ovarian cancers, constitutive activation of the pathway is due to oncogenic mutations in β-catenin or other inactivating mutations in key negative regulators. Secreted frizzled-related protein 4 (SFRP4) has been proposed to have inhibitory activity through binding and sequestering Wnt ligands.Methodology/Principal Findings
We performed RT-qPCR and Western-blotting in primary cultures and ovarian cell lines for SFRP4 and its key downstream regulators activated β-catenin, β-catenin and GSK3β. SFRP4 was then examined by immunohistochemistry in a cohort of 721 patients and due to its proposed secretory function, in plasma, presenting the first ELISA for SFRP4. SFRP4 was most highly expressed in tubal epithelium and decreased with malignant transformation, both on RNA and on protein level, where it was even more profound in the membrane fraction (p<0.0001). SFRP4 was expressed on the protein level in all histotypes of ovarian cancer but was decreased from borderline tumors to cancers and with loss of cellular differentiation. Loss of membrane expression was an independent predictor of poor survival in ovarian cancer patients (p = 0.02 unadjusted; p = 0.089 adjusted), which increased the risk of a patient to die from this disease by the factor 1.8.Conclusions/Significance
Our results support a role for SFRP4 as a tumor suppressor gene in ovarian cancers via inhibition of the Wnt signaling pathway. This has not only predictive implications but could also facilitate a therapeutic role using epigenetic targets. 相似文献939.
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