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Saunders JW 《Cell》2002,110(5):541-543
The prevailing view has long been that mesenchymal cells at the apex of the vertebrate limb bud proliferate in a progress zone (PZ) under the influence of the apical ectodermal ridge (AER). According to the PZ model, proximodistal cell fates are specified according to the time spent in the PZ. New results, considered along with some earlier findings, fail to support this model.  相似文献   

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《Biomass》1987,12(1):27-36
The use of wood for energy — including the burning of solid wood and black liquor from pulping — has been growing at a rate significantly greater than that for all other uses such as lumber, pulp, or particleboard. In the United States, the end of most wood is not lumber or pulp and paper but feed for energy. In 1983, 155·5 M Mg of wood were used for energy. This could threaten to increase the price of wood for those other uses, or it can stimulate us to seek more creative ways of using untapped wood resources for fuel.On the basis of estimates of heavy wood energy use relative to other uses for wood, and estimates of continuing high costs for fossil fuels, we suggest here the feasibility of meeting the demand for fuelwood through small-scale cooperatives. Such an approach can improve forestry practices and can avoid unduly increasing the cost of wood for other end uses.  相似文献   

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Cytokine and activation of lymphocytes are critical for tumor growth. We investigated whether interleukin (IL)-32β overexpression changes other cytokine levels and activates cytotoxic lymphocyte, and thus modify tumor growth. Herein, IL-32β inhibited B16 melanoma growth in IL-32β-overexpressing transgenic mice (IL-32β mice), and downregulated the expressions of anti-apoptotic proteins (bcl-2, IAP, and XIAP) and cell growth regulatory proteins (Ki-67 antigen (Ki-67) and proliferating cell nuclear antigen (PCNA)), but upregulated the expressions of pro-apoptotic proteins (bax, cleaved caspase-3, and cleaved caspase-9). IL-32β also inhibited colon and prostate tumor growth in athymic nude mice inoculated with IL-32β-transfected SW620 colon or PC3 prostate cancer cells. The forced expression of IL-32β also inhibited cell growth in cultured colon and prostate cancer cells, and these inhibitory effects were abolished by IL-32 small interfering RNA (siRNA). IL-10 levels were elevated, but IL-1β, IL-6, and tumor necrosis factor-alpha (TNF-α) levels were reduced in the tumor tissues and spleens of IL-32β mice, and athymic nude mice. The number of cytotoxic T (CD8+) and natural killer (NK) cells in tumor tissues, spleen, and blood was significantly elevated in IL-32β mice and athymic nude mice inoculated with IL-32β-transfected cancer cells. Constituted activated NF-κB and STAT3 levels were reduced in the tumor tissues of IL-32β mice and athymic nude mice, as well as in IL-32β-transfected cultured cancer cells. These findings suggest that IL-32β inhibits tumor growth by increasing cytotoxic lymphocyte numbers, and by inactivating the NF-κB and STAT3 pathways through changing of cytokine levels in tumor tissues.  相似文献   

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Chemotactic properties of amino acids (L-alanine, glycine and L-lysine) and their oligopeptides (10–6M) and binding sites to these ligands were investigated in two unicellular models, the heterotrophicTetrahymena pyriformis and the auxotrophicDunaliella salina. Chemotaxis ofDunaliella induced by simple amino acids and their derivatives demonstrated that binding sites (receptors) for food molecules are not only present in the membrane but are also able to induce their basic physiological response. InTetrahymena, substances with special molecular structure and properties (polar, hydrophilic character of the signal peptide chain)-5-L-Lys, 5-Glywere required for chemoattraction, other peptides tested, lacking the required structure, were repellent. Divergences in chemotaxis and binding assays of both species suggest that trends of functional and binding parameters do not run parallel at this level of evolution.  相似文献   

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The chairbound, handicapped person often requires a cushion to distribute the supportive forces over the largest area possible in order to reduce the risk of the development of a pressure sore. The paraplegic, or someone with a pelvic obliquity, may require a specially contoured cushion to redistribute seating pressures. Additionally, postural support can be provided by a relatively simple harness or by lateral support pads, either fitted as extras to standard wheelchairs or included as part of some wheelchair designs. The severely handicapped person may require padded inserts in his wheelchair or an intimately moulded seat which helps to control some spasms as well as to provide a functional, comfortable posture. Each of the commonly used methods of solving the seating problems of the chairbound person is discussed and different production processes used for the manufacture of personalized seats are presented.  相似文献   

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Kang W  Reid KB 《FEBS letters》2003,540(1-3):21-25
DMBT1 (deleted in malignant brain tumor 1), which encodes a large scavenger receptor cysteine rich (SRCR) B protein, has been proposed to be a tumor suppressor gene, due to the high frequency of its homozygous deletion and the lack of expression in a variety of cancers. However, studies on its physiological functions and its relationship with tumorigenesis are still at an initial stage. Two mucosal defense-related molecules, gp-340 and salivary agglutinin, have been identified to be alternatively spliced products of DMBT1, which suggests that DMBT1 is a pattern recognition receptor in innate immunity. Meanwhile, results from immunohistochemical staining and studies at the cellular level, began to associate DMBT1 with a proliferation to differentiation switching process in gastrointestinal epithelial cells. Together with its up-regulation in inflammation, these findings suggest that DMBT1 might be a local regulator of homeostasis, possibly through linking mucosal inflammation to the modulation of epithelial regeneration, and whose abnormality is a frequent cause of malignancy.  相似文献   

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This review traces the heretofore unsung hero role of engineering in the evolution of today's healthcare and the growing bond between physics, engineering, and medicine. It recognizes the debt owed to the various specialties of healthcare engineering, especially the bioengineers who contribute not only to a better understanding of basic physiologic and pathologic processes but also to the development and application of technology and the adaptation of new engineering discoveries to medicine. In the past half-millennium, the fields of physics, engineering, and medicine have made a large number of seminal contributions to each other, resulting in ever-advancing healthcare methodologies, although only a precious few remain identified by the originators' names. In this review, 3 engineers are cited in detail for their milestone contributions to medical progress: Roentgen in radiology, Bovie in electrosurgery, and, more recently, Greatbatch in implantable cardiac pacemakers. Future horizons in medicine appear to be ever more attainable because of the synergism between the physical and biological sciences.  相似文献   

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Sepsis is a leading cause of morbidity and mortality worldwide, and the magnitude of the problem seems higher in developing countries. In the last two decades the accepted standard treatment has resulted in only a slight decrease in mortality, and that decrease has been overshadowed by an almost 300% increase in incidence. Recently has been documented the close relationship between infection, inflammation and coagulation in sepsis has been documented; and although clinically overt disseminated intravascular coagulation may occur in only 30% to 50% of septic patients, the activation of the coagulation cascade is an early and common response to the infectious challenge. Moreover most of the molecules involved in the pro-coagulant state that characterizes sepsis are also powerful generators or amplifiers of the inflammatory response. These findings have fostered a comprehensive body of research regarding biological products with anticoagulant activity, as additional therapies for patients with the most severe states of the sepsis syndrome. This review explains the biological and molecular aspects that support the potential use of anticoagulant treatments in sepsis. Furthermore, we analyze the evidence provided by experimental and pre-clinical studies, which suggest the usefulness of heparin as an effective complementary treatment throughout the clinical stages of the disease.  相似文献   

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Object recognition and classification by sensory pathways is rooted in spike trains provided by sensory neurons. Nervous systems had to evolve mechanisms to extract information about relevant object properties, and to separate these from spurious features. In this review, problems caused by spike train variability and counterstrategies are exemplified for the processing of acoustic signals in orthopteran insects. Due to size limitations of their nervous system we expect to find solutions that are stripped to the computational basics. A key feature of auditory systems is temporal resolution, which is likely limited by spike train variability. Basic strategies to reduce such variability are to integrate over time, or to average across several neurons. The first strategy is constrained by its possible interference with temporal resolution. Grasshoppers do not seem to explore temporal integration much, in spite of the repetitive structure of their songs, which invites for multiple looks at the signal. The benefits of averaging across neurons depend on uncorrelated responses, a factor that may be crucial for the performance and evolution of small nervous systems. In spite of spike train variability the temporal information necessary for the recognition of conspecifics is preserved to a remarkable degree in the auditory pathway.Abbreviations dB decibel - CV coefficient of variation - SNR signal to noise ratio  相似文献   

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《Seminars in Virology》1994,5(2):133-145
The incidence of the mosquito-borne flavivirus diseases, yellow fever, dengue and dengue hemorrhagic fever has increased dramatically in recent years. Both diseases are characterized by the emergence of explosive epidemics. Yellow fever outbreaks appear to have a periodicity dependent upon fluctuations in sylvatic (enzootic) transmission cycles and the ecological factors that influence these cycles. Spread of the virus from the sylvatic cycle to human settlements, ultimately with interhuman transmission by domestic Aedes aegypti is a repeating event in Africa, and presents a renewed threat in the Americas, where effective Ae. aegypti control collapsed in the 1970s. The incidence of dengue has also increased dramatically in recent years, with up to 80 million persons living in tropical regions of the world now affected annually—an attack rate of 4%. The severe form, dengue hemorrhagic fever (DHF) has become a leading health problem throughout Asia in the last 20 years and is emerging as an epidemic disease in the Americas. Unlike yellow fever, sylvatic dengue transmission cycles are not responsible for disease emergence. The major factors underlying dengue epidemics are changes in human ecology, increasing contact with Ae. aegypti, the co-circulation of multiple dengue serotypes, and a rising prevalence of immunity and immunopathological events that underlie the pathogenesis of DHF. In this review, the complex interplay of virus, host, vector, environment and weather in the ecology of yellow fever and dengue are explored.  相似文献   

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In September 2012, a video entitled ‘Innocence of Muslims’ was uploaded to YouTube. The fourteen-minute clip featured actors playing the Prophet Muhammad, his companions and wives, and while production values were amateurish, aided by airings on Egyptian national television and others elsewhere, the video went viral. Recalling the Rushdie affair two decades beforehand, angry protests took place across the world. In the UK, the response from Muslims was markedly different. This article traces the ‘Innocence of Muslims’ affair from the eyes of those involved in formal Muslim-governmental relations. It explores what the new controversy tells us about the representation of Muslim communities in the process of political engagement since the Rushdie affair. It considers the experiential disconnect that exists between Muslim and political actors in contemporary Britain before exploring three important political factors – the cultural, representational and geopolitical – that influence and impact upon Muslim–governmental relations.  相似文献   

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