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1.
Rhodopsin is essential for photoreceptor morphogenesis; photoreceptors lacking rhodopsin degenerate in humans, mice, and Drosophila. Here we report that transgenic expression of a dominant-active Drosophila Rho guanosine triphosphatase, Drac1, rescued photoreceptor morphogenesis in rhodopsin-null mutants; expression of dominant-negative Drac1 resulted in a phenotype similar to that seen in rhodopsin-null mutants. Drac1 was localized in a specialization of the photoreceptor cortical actin cytoskeleton, which was lost in rhodopsin-null mutants. Thus, rhodopsin appears to organize the actin cytoskeleton through Drac1, contributing a structural support essential for photoreceptor morphogenesis. 相似文献
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Reymann AC Boujemaa-Paterski R Martiel JL Guérin C Cao W Chin HF De La Cruz EM Théry M Blanchoin L 《Science (New York, N.Y.)》2012,336(6086):1310-1314
The organization of actin filaments into higher-ordered structures governs eukaryotic cell shape and movement. Global actin network size and architecture are maintained in a dynamic steady state through regulated assembly and disassembly. Here, we used experimentally defined actin structures in vitro to investigate how the activity of myosin motors depends on network architecture. Direct visualization of filaments revealed myosin-induced actin network deformation. During this reorganization, myosins selectively contracted and disassembled antiparallel actin structures, while parallel actin bundles remained unaffected. The local distribution of nucleation sites and the resulting orientation of actin filaments appeared to regulate the scalability of the contraction process. This "orientation selection" mechanism for selective contraction and disassembly suggests how the dynamics of the cellular actin cytoskeleton can be spatially controlled by actomyosin contractility. 相似文献
3.
Organization of ion channels in the myelinated nerve fiber 总被引：8，自引：0，他引：8
The functional organization of the mammalian myelinated nerve fiber is complex and elegant. In contrast to nonmyelinated axons, whose membranes have a relatively uniform structure, the mammalian myelinated axon exhibits a high degree of regional specialization that extends to the location of voltage-dependent ion channels within the axon membrane. Sodium and potassium channels are segregated into complementary membrane domains, with a distribution reflecting that of the overlying Schwann or glial cells. This complexity of organization has important implications for physiology and pathophysiology, particularly with respect to the development of myelinated fibers. 相似文献
4.
Medalia O Weber I Frangakis AS Nicastro D Gerisch G Baumeister W 《Science (New York, N.Y.)》2002,298(5596):1209-1213
Electron tomography of vitrified cells is a noninvasive three-dimensional imaging technique that opens up new vistas for exploring the supramolecular organization of the cytoplasm. We applied this technique to Dictyostelium cells, focusing on the actin cytoskeleton. In actin networks reconstructed without prior removal of membranes or extraction of soluble proteins, the cross-linking of individual microfilaments, their branching angles, and membrane attachment sites can be analyzed. At a resolution of 5 to 6 nanometers, single macromolecules with distinct shapes, such as the 26S proteasome, can be identified in an unperturbed cellular environment. 相似文献
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【目的】研究生理型雄性不育小麦花粉细胞内微丝和胼胝质的结构及其相关基因的表达,并揭示其与生理型雄性不育的关系,为进一步研究化学杂交剂SQ-1诱导小麦生理型雄性不育的机理提供一定的理论依据。【方法】以化学杂交剂SQ-1诱导的生理型雄性不育系ms(A)-西农1376及对应正常可育系(A)-西农1376为试材,用TRITC-phalloidin标记细胞内微丝,苯胺蓝标记胼胝质,qRT-PCR技术分别对肌动蛋白解聚因子TaADF（Actin depolymerizing factor）、类葡聚糖合成酶TaGSL（Glucan synthase-like）进行差异表达分析。【结果】(1)在减数分裂前期Ⅰ、中期Ⅰ、后期Ⅰ这三个时期,生理型雄性不育系花粉细胞的微丝结构与可育系没有显著差异：前期Ⅰ,微丝分布于整个细胞质中,细胞核区域也可见少量微丝环绕细胞核;中期Ⅰ,微丝分布在细胞质中,在形成纺锤体部位染色更深,形成纺锤体微丝,由细胞两极发出的纺锤体微丝伸向赤道板;后期Ⅰ,在向两极移动的染色体的中间部位染色较深,微丝分布较多。(2)在早末期Ⅰ,与可育系相比,不育系花粉细胞没有形成清晰且明显可见的中国灯笼状成膜体微丝结构,且在细胞中线部位亦没有清晰可见的微丝累积。(3)晚末期Ⅰ,可育系花粉细胞在形成细胞板的部位是线性的、平滑的,成膜体微丝消失,而不育系花粉细胞在形成细胞板的部位形成了很大的缝隙,同时,可育系胼胝质在细胞板处的沉积比较平滑,而不育系胼胝质在细胞板处的沉积较可育系相比缺乏,并且是褶皱的、有裂纹的。(4)四分体时期,可育系花粉可见围绕细胞核的辐射状微丝,不育系花粉细胞中微丝呈模糊状态,并且不育系中胼胝质染色的整体荧光强度较可育系减弱。利用实时荧光定量PCR技术分析肌动蛋白解聚因子TaADF和类葡聚糖合成酶TaGSL在减数分裂期的相对表达量,结果发现,不育系中TaADF的相对表达量是可育系的4.28倍,由于TaADF表达量上调,加剧了细胞内微丝解聚,微丝结构受到破坏,同时不育系中TaGSL表达量下降,只有可育系的0.83倍,胼胝质的沉积也受到影响。【结论】TaADF在不育系中上调表达,破坏了细胞内微丝的正常结构,使微丝不能正常行使其功能,进而可能导致花药发育中与育性相关的某些代谢通路等受到影响。与此同时,微丝结构的破坏导致细胞板形成出现异常也可能是引起胼胝质在细胞板处沉积受到影响的一个重要原因。因此,微丝和胼胝质的异常变化与化学杂交剂SQ-1诱导的生理型雄性不育密切相关。 相似文献
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Mechanics of stimulated neutrophils: cell stiffening induces retention in capillaries 总被引：30，自引：0，他引：30
The effect of peptide chemoattractants on neutrophil mechanical properties was studied to test the hypothesis that stimulated neutrophils (diameter, 8 micrometers) are retained in pulmonary capillaries (5.5 micrometers) as a result of a decreased ability of the cell to deform within the capillary in response to the hydrodynamic forces of the bloodstream. Increased neutrophil stiffness, actin assembly, and retention in both 5-micrometer pores and the pulmonary vasculature were seen in response to N-formyl-methionyl-leucyl-phenylalanine. These changes were abolished in cells that had been incubated with 2 micromolar cytochalasin D, an agent that disrupts cellular actin organization. A monoclonal antibody directed at the CD11-CD18 adhesive glycoprotein complex did not inhibit the increase in stiffness or retention in pores. These data suggest that neutrophil stiffening may be both necessary and sufficient for the retention that is observed. Hence, neutrophil sequestration in lung and other capillaries in the acute inflammatory process may be the result of increased stiffness stimulated by chemoattractants. 相似文献
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20世纪中国文学的雅与俗 总被引：1，自引：0，他引：1
曹银灵 《信阳农业高等专科学校学报》2006,16(1):69-72
在20世纪中国文学中,雅文学曾因其对社会、人生的影响而成为大众精神文化生活的一个重要组成部分。但进入80年代后,随着社会经济的发展,经济全球化导致了文化的全球化,通俗文学迅猛膨胀,高雅文学急剧萎缩,俗文化压倒了雅文化,居于中国文学的主流地位。本文通过分析这一现象及变化,揭示雅与俗的关系,倡导雅俗共享、依存互动的文学观。 相似文献
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Arendt D Tessmar-Raible K Snyman H Dorresteijn AW Wittbrodt J 《Science (New York, N.Y.)》2004,306(5697):869-871
For vision, insect and vertebrate eyes use rhabdomeric and ciliary photoreceptor cells, respectively. These cells show distinct architecture and transduce the light signal by different phototransductory cascades. In the marine rag-worm Platynereis, we find both cell types: rhabdomeric photoreceptor cells in the eyes and ciliary photoreceptor cells in the brain. The latter use a photopigment closely related to vertebrate rod and cone opsins. Comparative analysis indicates that both types of photoreceptors, with distinct opsins, coexisted in Urbilateria, the last common ancestor of insects and vertebrates, and sheds new light on vertebrate eye evolution. 相似文献
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Cyclic guanosine monophosphate: elevation in degenerating photoreceptor cells of the C3H mouse retina 总被引：17，自引：0，他引：17
As a result of an early deficiency in cyclic nucleotide phosphodiesterase activity, guanosine 3',5'-monophosphate accumulates in retinal photoreceptor cells before they begin to degenerate. It is suggested that degeneration of the photoreceptor cells is related to an imbalance in their metabolism or function which is caused by the elevated levels of cyclic guanosine monophosphate. 相似文献
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Cyclic adenosine monophosphate: function in photoreceptors 总被引：2，自引：0，他引：2
Inactivation of adenylate cyclase in outer segments of retinal photoreceptor cells is proportional to the bleaching of rhodopsin. Membranes of the outer segments also contain a particulate, light-insensitive phosphodiesterase of high specific activity. In electrophysiological experiments, application of cyclic adenosine monophosphate along with a methylxanthine mimics the effects of illumination on the photoreceptor cell of the compound eye of Limulus. 相似文献
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Both flavins and carotenoids have some of the attributes expected for a photoreceptor mediating blue light-induced phototropism in plants. Besides the classical photoreceptor candidate, beta-carotene, coleoptiles contain many other carotenoids, including the main components of the xanthophyll cycle, violaxanthin and zeaxanthin. Here, dark-grown coleoptiles accumulated violaxanthin, but lacked zeaxanthin. Coleoptiles devoid of zeaxanthin did not bend in response to a blue light pulse. Coleoptile tips converted violaxanthin into zeaxanthin in the light. Manipulation of coleoptile zeaxanthin content by red light, red light plus darkness, or incubation with the inhibitor of zeaxanthin formation, dithiothreitol, resulted in a blue light-induced bending that was proportional to zeaxanthin content. These data indicate that zeaxanthin may be a blue light photoreceptor in corn coleoptiles. 相似文献
14.
Christie JM Arvai AS Baxter KJ Heilmann M Pratt AJ O'Hara A Kelly SM Hothorn M Smith BO Hitomi K Jenkins GI Getzoff ED 《Science (New York, N.Y.)》2012,335(6075):1492-1496
The recently identified plant photoreceptor UVR8 (UV RESISTANCE LOCUS 8) triggers regulatory changes in gene expression in response to ultraviolet-B (UV-B) light through an unknown mechanism. Here, crystallographic and solution structures of the UVR8 homodimer, together with mutagenesis and far-UV circular dichroism spectroscopy, reveal its mechanisms for UV-B perception and signal transduction. β-propeller subunits form a remarkable, tryptophan-dominated, dimer interface stitched together by a complex salt-bridge network. Salt-bridging arginines flank the excitonically coupled cross-dimer tryptophan "pyramid" responsible for UV-B sensing. Photoreception reversibly disrupts salt bridges, triggering dimer dissociation and signal initiation. Mutation of a single tryptophan to phenylalanine retunes the photoreceptor to detect UV-C wavelengths. Our analyses establish how UVR8 functions as a photoreceptor without a prosthetic chromophore to promote plant development and survival in sunlight. 相似文献
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采用免疫胶体金电镜技术研究光暗适应条件下不同Ca2+浓度对罗氏沼虾(Macrobrachium rosenbergi)感光细胞中Gq蛋白α亚基亚细胞定位的影响.结果表明,对于光适应组,在高Ca2+溶液、生理溶液和低Ca2+溶液中细胞质与感杆束中胶体金密度的比值是3.51、2.13和0.93.对于暗适应组,在高Ca2+溶液、生理溶液和低Ca2+溶液中细胞质与感杆束中胶体金密度的比值是3.01、1.08和0.47.这些表明了罗氏沼虾感光细胞中Gq蛋白α亚基在暗适应条件下同时分配在感杆束和细胞质中.在光照和细胞质内Ca2+浓度适度升高的条件下,膜结合的Gq蛋白α亚基进而转化为可溶性的Gq蛋白α亚基. 相似文献
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Intense colored light from a gas laser evokes a photoelectric potential in the photoreceptor cells of the ventral eye of Limulus. This potential has two components, both of which have the action spectrum of a rhodopsin with an absorbancy maximum at 530 nm. The evidence is consistent with the hypothesis that the photoelectric potential arises directly from the orderly array of rhodopsin molecules which are an integral part of the photoreceptor cell membrane. 相似文献
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Gu Y Filippi MD Cancelas JA Siefring JE Williams EP Jasti AC Harris CE Lee AW Prabhakar R Atkinson SJ Kwiatkowski DJ Williams DA 《Science (New York, N.Y.)》2003,302(5644):445-449
The Rho guanosine triphosphatases (GTPases) Rac1 and Rac2 are critical signaling regulators in mammalian cells. The deletion of both Rac1 and Rac2 murine alleles leads to a massive egress of hematopoietic stem/progenitor cells (HSC/Ps) into the blood from the marrow, whereas Rac1-/- but not Rac2-/- HSC/Ps fail to engraft in the bone marrow of irradiated recipient mice. In contrast, Rac2, but not Rac1, regulates superoxide production and directed migration in neutrophils, and in each cell type, the two GTPases play distinct roles in actin organization, cell survival, and proliferation. Thus, Rac1 and Rac2 regulate unique aspects of hematopoietic development and function. 相似文献
18.
Methoxyindoles and photoreceptor metabolism: activation of rod shedding 总被引：17，自引：0，他引：17
Using an in vitro eye-cup preparation, we have evaluated a potential relationship between methoxyindole metabolism and photoreceptor disk shedding. Melatonin, 6-chloromelatonin, and 5-methoxytryptophol all activate rod disk shedding in culture. The effect is compound specific since serotonin and N-acetylserotonin are without effect, and it is similar to shedding in vivo because it is evoked by light and is quantitatively comparable to a normal intact animal response. The results suggest the involvement of 5-methoxyindoles in the control of rhythmic photoreceptor metabolism. 相似文献
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窦薇 《云南农业大学学报(自然科学版)》2011,(6):108-111
通过对宋代内向型精神文化的特征与淡美风格渊源关系的分析，进一步解读了宋代山水诗的四种美学风格，即：以隐逸心态为主的平淡清远之美；以主体人格的修养为基调的高洁淡瑟之美；化奇峭为平淡的古淡之美和由雄豪归乎平淡的雅丽精绝之美；以老境为基调的萧条淡泊之美。 相似文献
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The relation between terminal mitosis and the events that determine the developmental fate of embryonic precursor cells is not well understood. This relation has now been investigated with [3H]thymidine autoradiography to determine the time of cell birth and with a culture system that allows the testing of the developmental potential of cells isolated from the chick embryo retina. Contrary to the situation in vivo, where neuronal differentiation always precedes photoreceptor differentiation, photoreceptor differentiation occurs prematurely and precedes neuronal differentiation when precursor cells are isolated from the retina at early embryonic stages. Thus, cells born by embryonic day 5 (ED-5) give rise predominantly to photoreceptors when isolated for culture on ED-6 but develop mainly as neurons when isolated on ED-8. This suggests that retinal precursor cells retain after terminal mitosis the capacity to develop either as neurons or as photoreceptors. Moreover, photoreceptor differentiation appears to represent a constitutive or "default" pathway that precursor cells follow in the absence of neuron-inducing signals. 相似文献