Reactivation of Ca2+-dependent cytoplasmic contraction in permeabilized cell models of the heliozoon Echinosphaerium akamae

Permeabilized cell models of the large heliozoon Echinosphaerium akamae were prepared by treatment with 100 mM EGTA or 1% Triton X-100. When > 10(-6) M Ca(2+) was added to the EGTA-permeabilized cells, axopodial cytoplasm became contracted and several swellings were formed along the axopodial length. Axonemal microtubules remained intact, while higher concentration of Ca(2+) (> 10(-4) M) induced microtubule disassembly and complete breakdown of the axopodia. In Triton-permeabilized cells, cytoplasmic contraction and relaxation of the cell body were induced repeatedly by successive addition and removal of Ca(2+). The contraction did not require ATP, and was not inhibited by cytochalasin B. Electron microscopy showed, in EGTA-permeabilized axopodia, contractile tubules became granulated by the addition of Ca(2+). From these observations, it is strongly suggested that Ca(2+)-dependent granulation of the contractile tubules is responsible for the axopodial contraction.     

Organization and Control of Microtubule Pattern in Centrohelidan Heliozoa*†

SYNOPSIS. Comparative studies of axopodial microtubule pattern in 10 different centrohelidan Heliozoa belonging to the genera Acanthocystis, Raphidiophrys and Heterophrys suggest that 2 basic principles govern pattern formation in centrohelidan Heliozoa. While the larger “open” arrays with unspecified number of microtubules, e.g. in A. aculeata and R. ambigua, may result from self-linkage of additional microtubules around centroplast-nucleated “starter microtubules,” the smaller “closed” arrays with specified microtubule number, e.g. in A. pectinata and H. marina, favor a template-driven linkage mechanism. The centroplast is a highly complex microtubule organizing center involved in the control of orientation, number, and diameter of the axonemes. Its shell may serve as a surface upon which the microtubule nucleating sites assemble, but how the precise positioning of these sites occurs is still open to debate. Some of the unsolved problems of microtubule pattern formation may be explained by the “linker nucleation hypothesis” which is an extension of the “gradion hypothesis” by Roth et al. It is shown how both the formation of closed arrays and the balanced lateral growth of open arrays may result from linker-induced microtubule nucleation.     

The ultrastructure of contractile tubules in the heliozoon Actinophrys sol and their possible involvement in rapid axopodial contraction

We employed an improved fixation procedure for electron microscopy using ruthenium red, and found a bundle of contractile tubules inside the axopodia of the heliozoon Actinophrys sol. Upon food uptake, the tubules shorten and transform into a mass of small granules when rapid axopodial contraction occurs, suggesting that these structures are involved in the process of axopodial contraction. The relationship between transformation of the contractile tubules and accompanying disassembly of the axonemal microtubules was studied by examining the ultrastructure of the contractile tubules after disassembly of the microtubules was artificially induced by cold or colchicine treatment. Granulation of the contractile tubules was induced by cold but not by colchicine treatment. During recovery from cold treatment, granular forms of the contractile tubules became re-elongated and their initial tubular appearance was restored. These results suggest that the contractile tubules in heliozoon axopodia play a role in repetitive cytoplasmic contraction.     

Degrading and stabilizing effects of Mg ions on microtubule-containing axopodia

Although many divalent cations are known to affect the labile microtubules as their stabilizing agents, it was found here that Mg²⁺ ions resulted in not only stabilization but also degradation of heliozoan axopodia composed mainly of the labile microtubules. The concentration range inducing the cytolysis of organisms (C), axopodial degradation (D), and axopodial stabilization (S) was 2 M C 750 mM, 2 M D 12 mM, and 10 mM S 0.07 mM, respectively. At relatively low Mg²⁺ concentration range inducing the axopodial degradation, three characteristic phenomena were observed: (1) the particles within every axopodia ceased from moving up and downwards as a first sign of axopodial degradation; (2) these particles were then accumulated around the tips of degrading axopodia; and finally (3) the distal parts of axopodia were more labile than the proximal ones. These experimental data suggested that the axopodial microtubules played two important roles not only supporting the elongated axopodial extensions but also in transporting the particles up and downwards the axopodia.     

The fine structure of the centrohelidian Heliozoan Heterophrys marina

Summary The fine structure of Heterophrys marina (Centrohelidia, Heliozoa) is described with special reference to centroplast structure, morphogenesis and behaviour of kinetocysts (= axopodial granules which perform saltatory movement), and formation of organic spicules in a new type of organelle located in the plasma membrane. A low calcium pretreatment and fixation was used to improve preservation of highly labile axopodia which near their distal end contain a single microtubule (MT) only. Two varieties of H. marina with a respective maximum of 6 and 12 MTs per axopodium, and 2 hitherto undescribed species, H. elati and H. multipoda, were found among 9 stocks collected in Europe and North America. In all species only the central 6 MTs of each axoneme originate from a scaffolding layer of electron dense material which surrounds the central granule. Evidence is presented which indicates that in Heterophrys self-linkage is not the only principle of MT pattern generation but that instead precisely localized MT nucleation and specific linkage of MTs within the cortex of the centroplast lead to the MT patterns observed. Prekinetocysts originate from vesicles found in the neighborhood of the dictyosomes. After maturation the kinetocysts become attached to the plasma membrane which seems to play an important role both in selection of particles transported in the axopodia and particle movement as well.The author thanks Anne Vees for excellent technical assistance. This study was sponsored by the Deutsche Forschungsgemeinschaft. Field trips to Naples and Woods Hole were supported by NATO Research Grant No. 657 to Dr. L. E. Roth, Kansas State University, Manhattan, Kansas, and the author.     

昆虫普通气味结合蛋白研究进展

昆虫气味结合蛋白(OBPs)参与昆虫识别环境中气味信息的第一步反应,在调控昆虫生命活动中起着重要的作用。普通气味结合蛋白(GOBPs)主要参与昆虫对寄主植物挥发物或信息素的识别。本文总结了GOBPs基因的分子特征和生理功能,以及GOBPs基因在不同组织、性别和发育阶段的表达特性;针对GOBPs与性信息素结合蛋白(PBPs)在染色体上串联形成的GOBPs/PBPs亚家族基因簇,阐述了GOBPs基因的进化起源、扩增与丢失现象;梳理了昆虫GOBPs基因在虫情监测和害虫防治等方面的应用前景,提出GOBPs基因是未来害虫生物防治的重要靶点。     

Axopodial contraction in the heliozoon Raphidiophrys contractilis requires extracellular Ca2+

Axopodial contraction of the centrohelid heliozoon Raphidiophrys contractilis was induced by mechanical or electrical stimulation. For inducing contraction, extracellular Ca(2+) was required. The threshold level of extracellular Ca(2+) was between 10(-6)-10(-7) M. The speed of axopodial contraction was faster than 3.0 mm/sec. Re-elongation of axopodia started just after contraction, and its initial velocity was approximately 0.30 microm/sec. Electron microscopic observations were carried out using an improved fixative that contained 1 mg/ml ruthenium red and 15 microM Taxol. This fixative prevented artificial retraction of axopodia and resulted in better fixation. A bundle of hexagonally-arranged microtubules was observed in each axopodium, but no other filamentous structures were detected, suggesting that the contractile machinery of axopodia in R. contractilis may be different from that in actinophryid heliozoons in which Ca(2+)-dependent contractile filaments are employed for contraction.     

STUDIES ON THE MICROTUBULES IN HELIOZOA : III. A Pressure Analysis of the Role of These Structures in the Formation and Maintenance of the Axopodia of Actinosphaerium nucleofilum (Barrett)

Electron microscope preparations were made of specimens of Actinosphaerium nucleofilum fixed in glutaraldehyde before, during, and after exposure to high pressures (4,000 to 8,000 psi). A study of this material showed that, although other organelles were relatively stable, the microtubular elements of the axopodia and cytosome became unstable under pressure. Their rapid disintegration under pressure was correlated with beading and retraction of the axopodia. Moreover, after the release of pressure, microtubules reappeared as soon as, or sooner than the reextension of the axopodia. The rate of disintegration increased as the pressure was raised. At 4,000 psi, few if any tubules remained after 10 min, whereas at 6,000 and 8,000 psi the disintegration was much more rapid. Some adaptational reorganization of the microtubules and axopodia occurred while relatively low pressures were maintained. This was accompanied by an actual elongation of the axopodia in specimens maintained for 20 min at 4,000 psi, but was confined to knoblike axopodial remnants in animals kept at 6,000 psi. No regeneration of tubules or axopodia occurred at 8,000 psi. The presence of fibers and a finely fibrillar material in pressurized animals suggests that these may be derivatives of microtubular disintegration. This evidence, though purely morphological, is consistent with the hypothesis that microtubules play an important role not only in maintaining the formstability of the axopodia, but also in the active process by which the axopodia reextend themselves after retraction.     

基于转录组的冬虫夏草菌微循环产孢研究

为研究冬虫夏草菌（Ophiocordyceps sinensis）微循环产孢过程中的分子机理,采用高通量测序技术,对微循环产孢前后冬虫夏草菌的转录组进行研究。筛选获得差异表达基因6 902个。Gene Ontology（GO）功能聚类分析表明,差异表达基因主要参与分子功能、胞内运输、核糖核蛋白复合体等生物学通路。京都基因与基因组百科全书（Kyoto Encyclopedia of Genes and Genomes,KEGG)功能富集分析结果表明,差异表达基因参与了核糖体、嘧啶代谢、蛋白酶体、嘌呤代谢、甘氨酸代谢等过程。Mmc、Mcb、MaH1、MaPP5、MaAGA、Pyk等候选基因不同程度的参与了冬虫夏草菌微循环产孢过程,其中Mcb家族基因可能起到关键作用。通过qRT PCR验证差异表达基因,定量结果与转录组测序结果一致。本研究为进一步揭示冬虫夏草菌微循环产孢分子机制以及关键基因的调控提供了重要信息。     

多刺绿绒蒿WD40基因家族的鉴定及生物信息学分析

WD40转录因子家族广泛参与调节植物生长、发育、次生代谢物积累和环境适应等过程。为了探究WD40家族在多刺绿绒蒿生长、发育和次生代谢物积累以及抗逆方面的作用,该研究基于全长转录组测序数据,鉴定了多刺绿绒蒿WD40基因家族成员,并对这些基因及其编码的蛋白进行了生物信息学分析。结果表明:(1)共鉴定到19个WD40基因,编码的蛋白均具有WD40结构域,氨基酸数目为109～758 aa,分子量介于11 830～84 130 Da之间,预测大多数蛋白定位在细胞核中且都为亲水性蛋白;(2)系统进化树分析表明多刺绿绒蒿与罂粟、博落回亲缘关系较近;(3)WD40基因启动子区域均存在数量不等的激素或逆境响应元件,表明该家族基因可能参与植物生长、发育和次生代谢物积累等多种生物学进程的调节;(4)蛋白三级结构显示这些蛋白在进化过程中发生了不同程度的进化。这些结果可为深入研究多刺绿绒蒿WD40基因家族在其响应逆境胁迫和次生代谢物积累等方面的具体机制提供前期基础。