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51.
Schaefer AL Greenberg EP Oliver CM Oda Y Huang JJ Bittan-Banin G Peres CM Schmidt S Juhaszova K Sufrin JR Harwood CS 《Nature》2008,454(7204):595-599
Quorum sensing is a term used to describe cell-to-cell communication that allows cell-density-dependent gene expression. Many bacteria use acyl-homoserine lactone (acyl-HSL) synthases to generate fatty acyl-HSL quorum-sensing signals, which function with signal receptors to control expression of specific genes. The fatty acyl group is derived from fatty acid biosynthesis and provides signal specificity, but the variety of signals is limited. Here we show that the photosynthetic bacterium Rhodopseudomonas palustris uses an acyl-HSL synthase to produce p-coumaroyl-HSL by using environmental p-coumaric acid rather than fatty acids from cellular pools. The bacterium has a signal receptor with homology to fatty acyl-HSL receptors that responds to p-coumaroyl-HSL to regulate global gene expression. We also found that p-coumaroyl-HSL is made by other bacteria including Bradyrhizobium sp. and Silicibacter pomeroyi. This discovery extends the range of possibilities for acyl-HSL quorum sensing and raises fundamental questions about quorum sensing within the context of environmental signalling. 相似文献
52.
Deletion of vascular endothelial growth factor in myeloid cells accelerates tumorigenesis 总被引:1,自引:0,他引:1
Stockmann C Doedens A Weidemann A Zhang N Takeda N Greenberg JI Cheresh DA Johnson RS 《Nature》2008,456(7223):814-818
Angiogenesis and the development of a vascular network are required for tumour progression, and they involve the release of angiogenic factors, including vascular endothelial growth factor (VEGF-A), from both malignant and stromal cell types. Infiltration by cells of the myeloid lineage is a hallmark of many tumours, and in many cases the macrophages in these infiltrates express VEGF-A. Here we show that the deletion of inflammatory-cell-derived VEGF-A attenuates the formation of a typical high-density vessel network, thus blocking the angiogenic switch in solid tumours in mice. Vasculature in tumours lacking myeloid-cell-derived VEGF-A was less tortuous, with increased pericyte coverage and decreased vessel length, indicating vascular normalization. In addition, loss of myeloid-derived VEGF-A decreases the phosphorylation of VEGF receptor 2 (VEGFR2) in tumours, even though overall VEGF-A levels in the tumours are unaffected. However, deletion of myeloid-cell VEGF-A resulted in an accelerated tumour progression in multiple subcutaneous isograft models and an autochthonous transgenic model of mammary tumorigenesis, with less overall tumour cell death and decreased tumour hypoxia. Furthermore, loss of myeloid-cell VEGF-A increased the susceptibility of tumours to chemotherapeutic cytotoxicity. This shows that myeloid-derived VEGF-A is essential for the tumorigenic alteration of vasculature and signalling to VEGFR2, and that these changes act to retard, not promote, tumour progression. 相似文献
53.
Mutations in the gene encoding lamin A/C cause autosomal dominant Emery-Dreifuss muscular dystrophy 总被引:15,自引:0,他引:15
Bonne G Di Barletta MR Varnous S Bécane HM Hammouda EH Merlini L Muntoni F Greenberg CR Gary F Urtizberea JA Duboc D Fardeau M Toniolo D Schwartz K 《Nature genetics》1999,21(3):285-288
Emery-Dreifuss muscular dystrophy (EDMD) is characterized by early contractures of elbows and Achilles tendons, slowly progressive muscle wasting and weakness, and a cardiomyopathy with conduction blocks which is life-threatening. Two modes of inheritance exist, X-linked (OMIM 310300) and autosomal dominant (EDMD-AD; OMIM 181350). EDMD-AD is clinically identical to the X-linked forms of the disease. Mutations in EMD, the gene encoding emerin, are responsible for the X-linked form. We have mapped the locus for EDMD-AD to an 8-cM interval on chromosome 1q11-q23 in a large French pedigree, and found that the EMD phenotype in four other small families was potentially linked to this locus. This region contains the lamin A/C gene (LMNA), a candidate gene encoding two proteins of the nuclear lamina, lamins A and C, produced by alternative splicing. We identified four mutations in LMNA that co-segregate with the disease phenotype in the five families: one nonsense mutation and three missense mutations. These results are the first identification of mutations in a component of the nuclear lamina as a cause of inherited muscle disorder. Together with mutations in EMD (refs 5,6), they underscore the potential importance of the nuclear envelope components in the pathogenesis of neuromuscular disorders. 相似文献
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55.
Degrees of longitude and the earth's shape: The diffusion of a scientific idea in Paris in the 1730s
John L. Greenberg 《Annals of science》2013,70(2):151-158
The paper deals with the confusion that has arisen in studying the revival of geodesy in Paris in the 1730s. The episode highlights the vast qualitative differences in science-reporting to be found in periodicals of the early eighteenth century, and the actual roles that certain better-known journals played in the genesis of what became a trademark for eighteenth-century Parisian science. 相似文献
56.
Kimberly A. Dodds Karen M. Clancy Kathryn J. Leyva David Greenberg Peter W. Price 《西北部美国博物学家》2011,56(2)
The western spruce budworm ( Choristoneura occidentalis Freeman) prefers to feed on flushing buds and current-year needles of Douglas-fir ( Pseudotsuga menziesii [Mirb.] Franco). Budworm larvae will not typically consume older age classes of needles unless all current-year foliage is depleted. We tested the following null hypotheses: (1) budworm larvae can feed on foliage with a wide range of qualities (i.e., current 1-, 2-, or 3-year-old needles) without measurable effects on fitness; and (2) budworm adults do not show any oviposition preference linked to the age of the foliage they fed on as larvae. We used both laboratory and field experiments. There was strong evidence to support rejection of hypothesis 1. Budworm larvae had greater survival from the 4th instar to pupal stage when they fed on current-year foliage (43%-52% survival) versus older age classes of foliage (0-25% survival). Pupae from current-year foliage were also heavier than pupae from ≥ 1-year-old foliage. There was weak evidence to support rejecting hypothesis 2; budworm adults that fed had fed on current-year or 3-year-old foliage as larvae preferred to oviposit on current-year foliage. Similar conclusions were drawn from the laboratory and field experiments. 相似文献
57.
Information analysts today face new challenges from increasingly sophisticated endusers as well as increasingly complex managerial demands. For nonspecifiable problems that require creativity and innovation, the process of information requirements analysis (INRA) seems to require different forms of implementation and control than for the problems that apply to traditional operational and supervisory computer-based applications. This paper examines the processes of INRA and creativity in the context of problem type. It develops a model in which it is argued that user and developer collaboration and project management can be manipulated to provide the conditions for the level of creativity required by a specific problem type. 相似文献
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L Wu C Timmers B Maiti H I Saavedra L Sang G T Chong F Nuckolls P Giangrande F A Wright S J Field M E Greenberg S Orkin J R Nevins M L Robinson G Leone 《Nature》2001,414(6862):457-462
60.