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A cell ensures that its genome is replicated only once during its division cycle through a process called licensing. In an enlightening Perspective, Lygerou and Nurse explain how binding of the Geminin protein to Cdt1 blocks the binding of licensing factors to chromatin, inhibiting the onset of S phase (Wohlschlegel et al.). 相似文献
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[目的]为了解决栝楼悬浮细胞系在继代培养中容易退化,生长速度减慢的问题。[方法]以栝楼的茎为外植体诱导出愈伤组织,筛选出质地疏松、生长迅速、易于分散、可以长期进行继代培养的淡黄色半透明状愈伤组织系,将该愈伤组织接种在液体培养基中进行振荡悬浮培养,建立起分散程度好的栝楼悬浮细胞系。同时对影响愈伤组织的诱导及细胞悬浮培养的条件进行研究,确定适合愈伤组织生长的条件及影响细胞悬浮培养的主要因素。[结果]看护培养可以使栝楼悬浮培养细胞长势良好,并在低密度下获得由单细胞形成的细胞系。[结论]该悬浮系的建立为栝楼细胞大规模培养,进而实现有效药物成分的工业化生产奠定了理论基础。 相似文献
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Minegishi Y Rohrer J Coustan-Smith E Lederman HM Pappu R Campana D Chan AC Conley ME 《Science (New York, N.Y.)》1999,286(5446):1954-1957
The signal transduction events that control the progenitor B cell (pro-B cell) to precursor B cell (pre-B cell) transition have not been well delineated. In evaluating patients with absent B cells, a male with a homozygous splice defect in the cytoplasmic adapter protein BLNK (B cell linker protein) was identified. Although this patient had normal numbers of pro-B cells, he had no pre-B cells or mature B cells, indicating that BLNK plays a critical role in orchestrating the pro-B cell to pre-B cell transition. The immune system and overall growth and development were otherwise normal in this patient, suggesting that BLNK function is highly specific. 相似文献
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[目的]为机插水稻培育矮化壮秧提供科学依据。[方法]选用拌种剂、多效唑和旱育保姆3种化学调控剂对水稻机插秧苗进行矮化壮秧处理,并以不使用化学调控剂作对照,研究不同化学调控剂在水稻机插育秧中的作用。[结果]拌种剂、多效唑和旱育保姆均有矮化壮秧作用,在秧龄小于20 d时,采用3种化学调控剂育秧均可;当培育的机插秧秧龄达到25 d时,以旱育保姆育秧效果最好。28 d时,旱育保姆处理的秧苗出苗率达80.31%,成苗率达71.94%,出苗率和成苗率均最高;拌种剂处理的成苗率最低。机插后旱育保姆处理的秧苗综合质量最好。[结论]旱育保姆对水稻机插育秧秧苗矮化壮秧作用明显,是值得推广应用的机插水稻化学调控剂。 相似文献
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Matsuo T Yamaguchi S Mitsui S Emi A Shimoda F Okamura H 《Science (New York, N.Y.)》2003,302(5643):255-259
Cell division in many mammalian tissues is associated with specific times of day, but just how the circadian clock controls this timing has not been clear. Here, we show in the regenerating liver (of mice) that the circadian clock controls the expression of cell cycle-related genes that in turn modulate the expression of active Cyclin B1-Cdc2 kinase, a key regulator of mitosis. Among these genes, expression of wee1 was directly regulated by the molecular components of the circadian clockwork. In contrast, the circadian clockwork oscillated independently of the cell cycle in single cells. Thus, the intracellular circadian clockwork can control the cell-division cycle directly and unidirectionally in proliferating cells. 相似文献
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Serological visualization of interleukin 2 总被引：5，自引：0，他引：5
Interleukin 2, a lymphokine that acts as a second signal of cellular immune response by way of its action as a T-cell growth factor, was morphologically identified by immunoperoxidase staining. With the use of a monoclonal antibody to interleukin 2 and several complex-forming antisera, the lymphokine was readily distinguished in cytocentrifuge preparations of peripheral blood leukocytes stimulated with a T-cell mitogen. When preparations of cloned interleukin 2 producer and responder cells were stained by the same procedures, discrete patterns of both responder and producer cell phenotypes were revealed. Interleukin 2 producer T cells exhibited a characteristic intense, ringlike cytoplasmic staining, whereas the responder cells (as exemplified by interleukin 2-dependent cell lines) exhibited a less intensive, spotlike membrane staining. In addition, intense membrane localization of interleukin 2, reminiscent of potential capping phenomena, could be observed in stained preparations of cloned responder cells. 相似文献
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用水牛9头,黄牛、猪、狗各3头,顺序取消化道12个部位,切片观察结果,水牛消化道嗜银性内分泌细胞比其他动物多,草食动物的胃和直肠细胞数比杂食动物和肉食动物都多。草食动物从胃和小肠这两个部位开始,嗜银性内分泌细胞都多,向后逐渐减少。胃肠道内分泌细胞多为单个,分散的夹杂在腺上皮细胞之间。此项内分泌细胞分布于每个腺管的中部或基部,向腺管顶端渐少,胃的内分泌细胞多为圆形,嗜银颗粒均匀分布于核周围;而肠的内分泌细胞多为锥形,颗粒集中于细胞基部,顶端逐渐稀疏。 相似文献
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本文首次对番茄大孢子的发生和胚羹发育的细胞学过程进行了较系统的研究。结果表明，番茄为弯生胚珠，同一子房内数以百计的胚珠着生于同一中轴胎座上。大孢子和胚囊发育的类型为单孢子胚羹，薯型。其主要特点在于，由大孢子母细胞经过减数分裂形成的单倍体的四分孢子呈直线排列，然而只有靠近合点端一个最后发育成大孢子，其余三个相继退化。大孢子经过３次连续的有丝分裂，形成一个含有８个单倍体细胞核的胚囊。即雌配子体，经过进一步发育，番茄的成熟的雌配子体包括：１个卵细胞，２个助细胞，３个反足细胞和一个具有２个极核的中心细胞。 相似文献
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甘蔗宿根矮化病(Ratoon stunting disease,RSD)病原细菌一般集中在甘蔗基部2～3节间处.利用透射电镜对感染RSD的甘蔗茎组织细胞进行超微结构观察,结果显示细胞内和细胞壁都发生了明显的病理变化.甘蔗茎细胞被RSD病原细菌侵染后,细胞内积累有大量分布不均的电子致密物质,这种物质可能与甘蔗茎细胞抵抗、减少或延迟RSD病原菌入侵的抗性机制相关.这些电子致密物质在感病细胞内均有出现,而正常细胞内没有.维管束导管细胞壁增厚,表面附着一层胶黏物质;有的细胞壁厚薄不均,局部变形断裂,成为细胞壁碎屑和纤维丝. 相似文献
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Application of the quail-chick chimera system to the study of brain development and behavior 总被引：4，自引：0，他引：4
Hatched chicks with chimeric brains containing cells from both the domestic chicken (Gallus gallus domesticus) and the Japanese quail (Coturnix coturnix japonica) have been produced by transplantation of various regions of the neural tube at the 8- to 15- somite stage. The positions of host and donor cells relative to graft boundaries observed throughout embryonic development and after hatching implicated both radial and tangential cell movements in brain morphogenesis. In addition, transplants containing the entire quail mesencephalon and diencephalon resulted in the transfer of certain aspects of species-typical crowing behavior. 相似文献
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[目的]研究人参水提物对VERO细胞在体外培养中的氧化损伤。[方法]采用细胞体外培养技术、MTF比色法、SOD和MDA试剂盒法、原子显微镜（AFM）观察法,研究人参水提物对VERO细胞氧化损伤的机制。[结果]人参水提物对VERO细胞能够起到明显的增殖抑制作用。人参水提物对VERO细胞具有一定的的氧化损伤作用且有一定的剂量及时间依赖性。原子力显微扫描成像结果表明正常生长的VERO细胞表面光滑、细胞体积饱满,而人参水提物处理组细胞膜损坏现象明显,细胞表面的粗糙度较大。[结论]人参水提物对VERO细胞具有一定的氧化损伤作用,其作用机制可能与细胞膜的损伤有关。 相似文献
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[目的]研究软骨发育与重建,建立软骨体外培养模式,[方法]通过改良组织块细胞培养法,进行家兔耳廓弹性软骨细胞的体外培养,研究其形态与生长特性。[结果]兔耳软骨组织16 h完成贴壁,1.5 d软骨细胞迁出,144 h细胞生长达到融合;传代兔耳软骨细胞12 h贴壁,生长特性与原代相似,但第3代细胞的延滞期长,在培养48 h开始进入对数期,培养第8天细胞数量达到峰值。HE染色结果表明弹性软骨细胞形态均匀,细胞呈圆形或椭圆形,核呈椭圆形,可见双核或多核现象。软骨陷窝和核深染,胞浆着色均匀。细胞分裂旺盛。同族细胞群清晰。[结论]原代及2代耳软骨细胞体外生长特性及细胞形态一致,培养条件稳定。 相似文献
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YIGSR, a synthetic laminin pentapeptide, inhibits experimental metastasis formation 总被引：30，自引：0，他引：30
Y Iwamoto F A Robey J Graf M Sasaki H K Kleinman Y Yamada G R Martin 《Science (New York, N.Y.)》1987,238(4830):1132-1134
The invasion of tumor cells through basement membranes is a critical step in the formation of metastases. The binding of the malignant cells to laminin in the basement membranes allows their attachment and activates their invasiveness. Recently a synthetic nonapeptide from the B1 chain sequence of laminin was identified as a major site for cell binding. A pentapeptide within the nonapeptide sequence was found to reduce the formation of lung colonies in mice injected with melanoma cells and also to inhibit the invasiveness of the cells in vitro. 相似文献
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本文对一例莎能间性山羊从行为、解剖和细胞遗传学方面进行了研究。与正常莎能山羊相比较,间性的行为和生殖系统的构造有很大的差异;经细胞遗传学的研究进一步证实,确定其染色体组型为60,XX/60,XY嵌合体。随机统计了165个分裂相,结果为60,XX型细胞占40%;60,XY型细胞占60%。分析几方面的结果,认为该间性属于雌雄同体嵌合型。 相似文献
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The latent period of the light-evoked receptor potential was increased by hyperpolarizing currents injected directly into doubly impaled retinular cells. Indirect hyperpolarization of these cells by injection of hyperpolarizing current into the eccentric cell or other intraommatidial retinular cells either shortened or did not change the latent period. The modification of the latent period may depend upon the direction of current flow across some regions of the membrane system constituting the rhabdomere. The reduction in magnitude of the receptor potential obtained with strong hyperpolarizing currents may also depend upon the direction of current flow. The results support the conclusion that the receptor potential originates in retinular cells within the membrane system of the rhabdomere. 相似文献
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为从细胞学水平揭示稀土元素对动物的促生长机理,本文选择中国仓鼠肺成纤维细胞(Wg_3 1)和卵巢细胞(CHO),在含有不同浓度 STN 的1640完全培养液中培养;以及来自非免疫健康鸡群11日龄鸡胚所制成的鸡胚细胞,使之在0ppm、1.25ppm、2.5ppm、5ppm,10ppm、20ppm 和40ppm 稀土浓度的199培养液中培养.CHO 细胞的生长速率表现在10ppm浓度时细胞数最多,Wg_3 1 和 CHO 的细胞分裂指数也以10ppm 时显著高于对照组(P<0.05).96小时鸡胚细胞单层面形成状况表明:三种类型的稀土化合物均以5ppm 浓度时对鸡胚细胞的促生长作用最明显,STV-2优于 CL-1,CL-1优于 CL-3.20ppm 和40ppm 浓度使 CHO、Wg_3 1和鸡胚细胞生长受到抑制.结论认为,适量浓度的稀土可促进动物细胞生长,高浓度稀土抑制动物细胞生长. 相似文献