An electron microscopic study on the mating tube formation in the heterobasidiomycete Tremella mesenterica

Ultrastructure of the mating tube formed in yeast haplont of the heterobasidiomycete Tremella mesenterica was studied by electron microscopy. Cell wall of the mating tube emerged as evagination of the inner layers, rupturing outer layers of the mother cell wall. Comparison with budding cells suggested that the tube emergence place at bud scar and the process of tube emergence was the same as that of bud emergence. Electron transparent vesicles of 0.1 m diameter were scattered in the cytoplasm of the mating tube. Nucleus-associated organelle was located at one side of the nuclear envelope which extended towards the mating tube. A few microtubules were detected in the mating tube, but their association with a nucleus was not clear. The cytoplasmic structure of the mating tube was discussed in comparison with that of hyphae of the filamentous fungi.     

The changes of nuclear position and distribution of circumferentially aligned cortical microtubules during the progression of cell cycle inAdiantum protonemata

The intracellular positions of the nucleus and of cortical, circumferentially aligned microtubules (CCAM) in filamentous, single-celled protonemata ofAdiantum capillus-veneris were determined throughout the cell cycle in the dark. When apical growth continued at G₁ phase, the nucleus migrated keeping a constant distance from the tip. When the apical growth stopped at late S or G₂ phase, the nucleus stopped moving forward and then slightly moved backward to the site of cytokinesis. The CCAM were found only in the dome of protonemal tip when growing under continuous red light; they increased in number after dark incubation for 12 hr and then decreased after 20th hr in the dark. The CCAM were usually observed in the region between the nucleus and the tip at 28 hr in the dark. They were located around the nuclear region at pre-prophase and prophase, but then totally disappeared at metaphase and thereafter.     

Association of centrioles with clusters of apical vesicles in mitotic thyroid epithelial cells. Are centrioles involved in directing secretion?

Summary The ultrastructure of thyroid epithelial cells in mitosis has been investigated. A spatial association is described between clusters of apical vesicles (believed to contain thyroglobulin destined for secretion into the follicular lumen) and centrioles, in late prophase and late telophase cells. Quantitative techniques demonstrate the statistical significance of this association and suggest that it is not related to proximity of the Golgi apparatus or to the location of the centriole in the cell, which changes considerably during these phases of mitosis. The physical basis for this association remains uncertain, but microtubules emanating from the pericentriolar area may be involved.In interphase cells, centrioles are located very close to the follicular lumen, where the majority of apical vesicles are also found. The association of centrioles with clusters of apical vesicles also in mitotic cells suggests that in interphase cells the apically located centrioles may serve as a focus for apical vesicles, helping to direct these secretory vesicles toward the follicular lumen and to maintain cellular polarization. Previous studies demonstrating that centrioles can act as microtubule organizing centers in interphase cells and studies linking microtubules and secretion also tend to support this hypothesis.The author is grateful to Drs. Jan Wolff, Lars E. Ericson, and Seymour H. Wollman for useful discussions and to Mr. Franklin E. Reed for expert technical assistance.     

激素引起伊贝母愈伤组织微管蛋白变化的免疫细胞化学研究(简报)

微管蛋白聚合形成微管。微管在维持细胞结构、物质运输、分裂及植物细胞壁的建成等过程中起着重要的作用。70年代后期,在微管生物化学研究取得很大进展的基础上,免疫细胞化学技术与微管研究结合起来,使人们能够从整体水平观察以微管蛋白为主要成份的细胞骨架的动态变化。我们采用免疫酶标技术,对生长在含不同激素培养基上的伊贝母愈伤组织的微管及微管蛋白变化进行了观察和分析,结果表明,激素种类和微管的存在形式是相关的。     

Effects of ligand binding on the stability of aldo–keto reductases: Implications for stabilizer or destabilizer chaperones

Ligands such as enzyme inhibitors stabilize the native conformation of a protein upon binding to the native state, but some compounds destabilize the native conformation upon binding to the non‐native state. The former ligands are termed “stabilizer chaperones” and the latter ones “destabilizer chaperones.” Because the stabilization effects are essential for the medical chaperone (MC) hypothesis, here we have formulated a thermodynamic system consisting of a ligand and a protein in its native‐ and non‐native state. Using the differential scanning fluorimetry and the circular dichroism varying the urea concentration and temperature, we found that when the coenzyme NADP⁺ was absent, inhibitors such as isolithocholic acid stabilized the aldo–keto reductase AKR1A1 upon binding, which showed actually the three‐state folding, but destabilized AKR1B10. In contrast, in the presence of NADP⁺, they destabilized AKR1A1 and stabilized AKR1B10. To explain these phenomena, we decomposed the free energy of stabilization (ΔΔG) into its enthalpy (ΔΔH) and entropy (ΔΔS) components. Then we found that in a relatively unstable protein showing the three‐state folding, native conformation was stabilized by the negative ΔΔH in association with the negative ΔΔS, suggesting that the stabilizer chaperon decreases the conformational fluctuation of the target protein or increase its hydration. However, in other cases, ΔΔG was essentially determined by the delicate balance between ΔΔH and ΔΔS. The proposed thermodynamic formalism is applicable to the system including multiple ligands with allosteric interactions. These findings would promote the development of screening strategies for MCs to regulate the target conformations.     

Assembly of cortical microtubules during cold treatment of the coenocytic green alga,Chaetomorpha moniligera

The effects of cold treatment on the cortical microtubules (MTs) of Chaetomorpha moniligera Kjellman were investigated by immunofluorescence microscopy. Cortical MTs in Chaetomorpha thallus are arranged longitudinally. In this study, 70–75% of MTs disassembled within 4 h on ice while the others remained stable under these conditions. Reticulate background immunofluorescence, assumed to indicate the presence of a tubulin monomer, was distributed about the stable MTs. Immunofluorescence was prominent in only 50% of the cells. Tubulin polymerization was noted where the background and MT immunofluorescence was strong. New MTs grew transversely as single strings or clusters from the sides of MTs after cold treatment for 4 h and elongated with time to take on a reticulate form at 24 h. The significance of this tubulin polymerization under cold treatment is discussed.Abbreviations MT microtubule - MTOC microtubule-organizing center     

萱草花粉中微管蛋白生物化学性质

微管（microtubule）是细胞骨架的重要成份,参与囊泡运输、信息传递等多种生命活动。我们从萱草花粉中纯化了植物微管蛋白,对其生物化学及生物物理学部分性质研究表明,纯化的微管蛋白经超离心法测定沉降系数为6．2S,SDS-PAGE分析α,β微管蛋白分子量为56kD、58kD,凝胶扫描分析纯度为93．7％。等电聚焦电泳测定等电点为pI=5．35。光谱学性质研究结果表明,最大紫外吸收峰为280．8nm,荧光光谱研究表明最大激发波长为282nm;此时的最大发射峰为338nm,圆二色光谱分析二级结构表明小螺旋占27．24％,β-折叠占24．48％,无规卷曲为48．28％,呈典型球蛋白特征。     

Ca regulates the subcellular localization of adenomatous polyposis coli tumor suppressor protein

Microtubule (MT) plus-end tracking proteins (+TIPs) are involved in the regulation of MT plus-end dynamics and stabilization. It was reported previously that an increase in intracellular Ca²⁺ concentration ([Ca²⁺]_i) induced by disruption of the plasma membrane stimulates rearrangement of MTs [T. Togo, Disruption of the plasma membrane stimulates rearrangement of microtubules and lipid traffic toward the wound site, J. Cell Sci. 119 (2006) 2780-2786], suggesting that some +TIPs are regulated by Ca²⁺. In the present study, the behavior of adenomatous polyposis coli (APC) following an increase in [Ca²⁺]_i was observed using Xenopus A6 epithelial cell expressing GFP-tagged APC. An increase in [Ca²⁺]_i by cell membrane disruption or by ionomycin treatment induced dissociation of APC without depolymerizing MTs. Inhibition of a tyrosine kinase and GSK-3β suppressed APC dissociation upon an increase in [Ca²⁺]_i. Western blotting analysis showed that Ca²⁺ transients activated GSK-3β through a tyrosine kinase. These results suggest that Ca²⁺ stimulates redistribution of APC through a tyrosine kinase- and GSK-3β-dependent pathway.     

包囊游仆虫皮层和营养核的超微结构研究

为研究纤毛虫在不同生理条件下结构的分化及其调节机理,本文应用透射电镜术显示,营养期包囊游仆虫背、腹面皮层表膜下含３种方式排列组成的纵微管层以及深部微管;口区皮层内含高电子密度的杆状小体;口围带小腹基部含电子致密带和小腹托架,棘毛基体基部及基体下微管束形成围棘纤维篮;背纤毛基体下方也含微管结构;大核染色质附着在核膜上,核膜其他区域有规则排列的核孔。     

钙调素抑制剂——三氟拉嗪对肿瘤细胞增殖和微管组装的影响

本文用钙调素抑制剂——三氟拉嗪处理人胃癌MGC-803细胞,用免疫荧光细胞化学方法,放射免疫法和速流荧光分析等方法研究了钙调素对细胞增殖,环核苷酸代谢及微管组装,有丝分裂等细胞功能的调节作用。实验结果表明,TFP明显地抑制了人胃癌细胞的增殖,这种抑制增殖的作用,具有剂量和时间依赖关系,细胞群体中G_1期细胞增多,S期细胞下降,DNA合成明显地受到抑制。TFP处理的胃癌细胞仅在短时间内(5'-30')cAMP含量升高,cGMP浓度降低,cAMP/ ??cGMP比值比对照组高4.4倍,但此后环核苷酸含量又很快恢复到对照组水平。本实验还观察到TFP处理后的MGC-803细胞胞质铺展,细胞形态的改变与胞质微管的分布有密切联系,实验结果表明TFP加强了人胃癌细胞MTOC对微管的组装能力,使微管分布得到恢复,微管纤维呈放射状延伸到细胞边缘,充满胞浆,使细胞呈现出展平的多边形,趋向于正常上皮细胞形态的变化,本实验结果表明TFP抑制癌细胞增殖及使微管组装加强可能是通过对CaM活性的抑制作用。此结果有助于说明转化细胞内钙调素的变化,可能是与转化细胞增殖失控和胞质微管消退有关。