共查询到20条相似文献，搜索用时 31 毫秒
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Human recombinant granulocyte-macrophage colony-stimulating factor: a multilineage hematopoietin 总被引：33，自引：0，他引：33
C A Sieff S G Emerson R E Donahue D G Nathan E A Wang G G Wong S C Clark 《Science (New York, N.Y.)》1985,230(4730):1171-1173
Human recombinant granulocyte-macrophage colony-stimulating factor (GM-CSF) was tested for its ability to induce colony formation in human bone marrow that had been enriched for progenitor cells. In addition to its expected granulocyte-monocyte colony-stimulating activity, the recombinant GM-CSF had burst-promoting activity for erythroid burst-forming units and also stimulated colonies derived from multipotent (mixed) progenitors. In contrast, recombinant erythroid-potentiating activity did not stimulate erythroid progenitors. The experiments prove that human GM-CSF has multilineage colony-stimulating activity. 相似文献
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Isolating "uncultivable" microorganisms in pure culture in a simulated natural environment 总被引：3，自引：0，他引：3
The majority (>99%) of microorganisms from the environment resist cultivation in the laboratory. Ribosomal RNA analysis suggests that uncultivated organisms are found in nearly every prokaryotic group, and several divisions have no known cultivable representatives. We designed a diffusion chamber that allowed the growth of previously uncultivated microorganisms in a simulated natural environment. Colonies of representative marine organisms were isolated in pure culture. These isolates did not grow on artificial media alone but formed colonies in the presence of other microorganisms. This observation may help explain the nature of microbial uncultivability. 相似文献
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Human IL-3 and GM-CSF act synergistically in stimulating hematopoiesis in primates 总被引：10，自引：0，他引：10
R E Donahue J Seehra M Metzger D Lefebvre B Rock S Carbone D G Nathan M Garnick P K Sehgal D Laston 《Science (New York, N.Y.)》1988,241(4874):1820-1823
Interleukin-3 (IL-3) is a member of a family of growth factors, each of which supports the proliferation and development of hematopoietic precursors in culture. Although the biologic effects of the different hematopoietic growth factors have been well documented in different culture systems, it has only recently become possible to study the activities of these molecules in vivo. In comparison with the later acting hematopoietic growth factors granulocyte-macrophage colony-stimulating factor (GM-CSF) and granulocyte colony-stimulating factor, IL-3 elicited a delayed and relatively modest leukocytosis when continuously infused intravenously in primates. The IL-3 infusion, however, greatly potentiated the responsiveness of the animal to subsequent administration of a low dose of GM-CSF. These results suggest that IL-3 expands an early cell population in vivo that subsequently requires the action of a later acting factor such as GM-CSF to complete its development. Optimal stimulation of hematopoiesis may be achieved with combinations of hematopoietic growth factors. 相似文献
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During Drosophila metamorphosis, most larval cells die. Pupal and adult tissues form from imaginal cells, tissue-specific progenitors allocated in embryogenesis that remain quiescent during embryonic and larval life. Clonal analysis and fate mapping of single, identified cells show that tracheal system remodeling at metamorphosis involves a classical imaginal cell population and a population of differentiated, functional larval tracheal cells that reenter the cell cycle and regain developmental potency. In late larvae, both populations are activated and proliferate, spread over and replace old branches, and diversify into various stalk and coiled tracheolar cells under control of fibroblast growth factor signaling. Thus, Drosophila pupal/adult tissue progenitors can arise both by early allocation of multipotent cells and late return of differentiated cells to a multipotent state, even within a single tissue. 相似文献
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Kim J Wu HH Lander AD Lyons KM Matzuk MM Calof AL 《Science (New York, N.Y.)》2005,308(5730):1927-1930
The orderly generation of cell types in the developing retina is thought to be regulated by changes in the competence of multipotent progenitors. Here, we show that a secreted factor, growth and differentiation factor 11 (GDF11), controls the numbers of retinal ganglion cells (RGCs), as well as amacrine and photoreceptor cells, that form during development. GDF11 does not affect proliferation of progenitors-a major mode of GDF11 action in other tissues-but instead controls duration of expression of Math5, a gene that confers competence for RGC genesis, in progenitor cells. Thus, GDF11 governs the temporal windows during which multipotent progenitors retain competence to produce distinct neural progeny. 相似文献
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Receptor-associated resistance to growth hormone-releasing factor in dwarf "little" mice 总被引：5，自引：0，他引：5
Anterior pituitaries from the dwarf mouse strain "little" did not release growth hormone or accumulate adenosine 3',5'-monophosphate (cyclic AMP) in response to human and rat growth hormone-releasing factor (GRF). Dibutyryl cyclic AMP, as well as the adenylate cyclase stimulators forskolin and cholera toxin, markedly stimulated growth hormone (GH) release. The basis of the GH deficiency in the little mouse may therefore be a defect in an early stage of GRF-stimulated GH release related either to receptor binding or to the function of the hormone-receptor complex. 相似文献
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张述银 《安徽农业大学学报》1987,(3)
研究辽东栎的生长速度及生长轮年龄对密度的影响。结果表明,生长轮年龄是决定木材性质的主要因子,生长速度对木材密度的影响较小。而生长速度对密度的影响又随年轮宽度、生长轮年龄及取样部位(早材,晚材或整个年轮)而异。 相似文献
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应用灰色关联分析方法,分析了会宁县1996～2009年粮食产量与粮食单产、粮食作物播种面积、农村劳动力、农用化肥施用折纯量等要素之间的关联程度,揭示了影响粮食产量的驱动因素。结果表明1,996～2009年,会宁县粮食产量表现为阶段性波动增长的特征。从驱动力看,单产是影响粮食产量的首要因素,农用化肥施用折纯量是影响粮食产量的重要因素,农用地膜、节水灌溉等技术的投入是影响粮食产量的关键因素,且表现出很大的潜力,干旱黄土沟壑区特定的资源禀赋是影响粮食产量的基础性因素。 相似文献
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Lhx2 maintains stem cell character in hair follicles 总被引：1，自引：0，他引：1
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龙栖山黄山松种群优势度增长规律研究 总被引：16，自引：2，他引：16
本文应用有限空间种群增长的逻辑斯谛模型研究了龙栖山自然保护区黄山松种群基面积增长规律，指出黄山松在不同林型下和同一林型不同密度下的基面积最大增长速度的径级范围． 相似文献
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李小食心虫幼虫在美国杏李上的空间分布格局 总被引：1，自引：2，他引：1
初步调查研究了河南驻马店蚁封林场7年生美国杂交杏李李小食心虫幼虫的种群动态,结果显示,李小食心虫幼虫在美国杏李上的空间格局为聚集型,而每个果实中李小食心虫幼虫分布均匀,分布的基本成分是个体群,个体间相互吸引.不同调查时间同一枝条上李小食心虫的幼虫密度不相同.李小食心虫幼虫存在明显的扩散性和空间移动性. 相似文献
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Purified human granulocyte-macrophage colony-stimulating factor: direct action on neutrophils 总被引：57，自引：0，他引：57
J C Gasson R H Weisbart S E Kaufman S C Clark R M Hewick G G Wong D W Golde 《Science (New York, N.Y.)》1984,226(4680):1339-1342
Neutrophil migration inhibition factor from T lymphocytes (NIF-T) is a lymphokine that acts to localize granulocytes. Medium conditioned by the Mo human T-lymphoblast cell line was used to purify NIF-T, a glycoprotein with a molecular weight of 22,000. The NIF-T was found to potently stimulate the growth of granulocyte and macrophage colonies from human bone marrow and colony formation by the KG-1 myeloid leukemia cell line. Thus a human lymphokine (NIF-T) that modulates the activities of mature neutrophilic granulocytes is also a colony-stimulating factor acting on precursors to induce growth and differentiation of new effector cells. 相似文献
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比较了牛胚胎与小鼠胚胎在体外培养过程中的生长行为，结果表明，牛滋养层细胞与内细胞团（ｉｎｎｅｒ ｃｅｌｌｍａｓｓ，简称ＩＣＭ）连接不紧密，其迅速增殖，形成半透明囊腔结构；小鼠胚胎滋养层与ＩＣＭ密切相连，形成盘状结构，并推移原代小鼠胎儿成纤维细胞（Ｐｒｉｍａｒｙ ｍｕｒｉｎｅ ｅｍｂｒｙｏｓｆｉｂｒｏｂｌａｓｔ，ＰＭＥＦ）饲养层。牛ＩＣＭ形态呈现多样性，表现为团状、条状、网状和混合型；小鼠ＩＣＭ形态单一，多呈圆盘状。体外培养的牛胚胎发育速度比小鼠胚胎迟缓，牛ＩＣＭ初次传代时间为胚胎体外培养开始后５～６ｄ，小鼠ＩＣＭ初次传代时间为胚胎体外培养后３～４ｄ。牛ＩＣＭ分化程度由小到大依次为团状ＩＣＭ、条状ＩＣＭ、混合型正 和网状ＩＣＭ。牛和小鼠胚胎附着率及ＩＣＭ克隆率由大到小均依次为孵化胚、囊胚和桑褡胚，但桑褡胚和囊胚附着率和ＩＣＭ克隆率均无显著差异（Ｐ＞０．０５）。与全胚相比较，牛和小鼠裸胚（无透明带或透明带不完整的胚胎）贴壁时间提前，但ＩＣＭ形成率和ＩＣＭ的生长行为均无显著差异；小鼠和牛桑椹胚卵裂球（中、晚期）体外分化抑制培养，形成亚囊胚而不能获得 ＥＳ细胞；剥离牛胚胎滋胚层细胞，ＩＣＭ细胞更易分化。 相似文献
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研究以油松外生茵根真菌浅黄根须腹茵（Rhizopogonluteolus）的子实体作为分离材料,通过采用组织分离方法获得纯菌种。以菌丝体生长速度和生长状况为参照标准,将菌种接种于不同培养基,筛选出茵丝体生长最适基础培养基为PACH,在此基础上通过单因素试验对其pH值,碳源,氮源等培养条件进行研究,结果表明,菌丝体生长最佳pH值,碳源及氮源分别为6．0、葡萄糖和酒石酸铵。通过pH值、碳源及氮源3个较优水平的正交试验,确定在（pH5．0＋牛肉膏＋蔗糖）组合中茵丝体生长速度最快,而在（pH6．O＋牛肉膏＋葡萄糖）组合中茵丝体生长状况为最佳。 相似文献
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[目的]研究水田土和旱地土添加火山灰石砾比例对烟草农艺性状和生理指标的影响,为植烟土壤的改良提供参考.[方法]以盆栽烤烟云87为材料,分析不同环境条件下纯旱地土、纯水田土及与10％、20％、30％的火山灰石砾混合、纯火山灰土等9个处理对移栽后苗期烤烟农艺性状和生理指标的影响.[结果]相对于其他处理,纯火山灰土处理的烟株苗期长势较好;纯水田土和纯旱地土处理的烤烟苗期长势相对优于添加火山灰石砾处理.在一定时期内,随着火山灰石砾比例的增加,水田土添加火山灰石砾处理的烟株株高、茎围、最大叶面积均有提升,旱地土添加火山灰石砾处理的烟株株高、茎围、最大叶面积呈增加趋势.在移栽后15～36 d,随着水田土添加火山灰石砾比例的增加,大田盆栽烤烟根系活力、NR活性显著降低,但叶绿素a与叶绿素b变化不明显.[结论]纯火山灰更有利于烤烟前期生长,水田土较旱地土利于烤烟前期生长;随着时间的延长,不同土壤类型添加不同比例火山灰石砾对烟株生长的影响逐渐变弱. 相似文献
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Engineering enzyme specificity by "substrate-assisted catalysis" 总被引：8，自引：0，他引：8
A novel approach to engineering enzyme specificity is presented in which a catalytic group from an enzyme is first removed by site-directed mutagenesis causing inactivation. Activity is then partially restored by substrates containing the missing catalytic functional group. Replacement of the catalytic His with Ala in the Bacillus amyloliquefaciens subtilisin gene (the mutant is designated His64Ala) by site-directed mutagenesis reduces the catalytic efficiency (kcat/Km) by a factor of a million when assayed with N-succinyl-L-Phe-L-Ala-L-Ala-L-Phe-p-nitroanilide (sFAAF-pNA). Model building studies showed that a His side chain at the P2 position of a substrate bound at the active site of subtilisin could be virtually superimposed on the catalytic His side chain of this serine protease. Accordingly, the His64Ala mutant hydrolyzes a His P2 substrate (sFAHF-pNA) up to 400 times faster than a homologous Ala P2 or Gln P2 substrate (sFAAF-pNA or sFAQF-pNA) at pH 8.0. In contrast, the wild-type enzyme hydrolyzes these three substrates with similar catalytic efficiencies. Additional data from substrate-dependent pH profiles and hydrolysis of large polypeptides indicate that the His64Ala mutant enzyme can recover partially the function of the lost catalytic histidine from a His P2 side chain on the substrate. Such "substrate-assisted catalysis" provides a new basis for engineering enzymes with very narrow and potentially useful substrate specificities. These studies also suggest a possible functional intermediate in the evolution of the catalytic triad of serine proteases. 相似文献
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Transforming growth factor-alpha: a more potent angiogenic mediator than epidermal growth factor 总被引：54，自引：0，他引：54
Transforming growth factor-alpha (TGF-alpha) and epidermal growth factor (EGF) are structurally related peptides. Purified human TGF-alpha produced in Escherichia coli and pure natural mouse EGF were compared for their ability to bind to target cells in vitro and to promote angiogenesis in the hamster cheek pouch bioassay. Both polypeptides were found to bind in vitro to several target cells, including endothelial cells, and to stimulate their DNA synthesis in an equipotent fashion. In vivo, however, TGF-alpha was more potent than EGF in promoting angiogenesis and, because TGF-alpha is known to be secreted by a variety of human tumors, it is suggested that this growth factor may contribute to tumor-induced angiogenesis. 相似文献