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991.
核仁前体存在于卵母细胞及早期胚胎中,由于核仁前体在卵母细胞中的含量较少且结构致密,目前,只有少数核仁前体组分得到了鉴定.核仁前体结构的完整组成尚未被详细解析,明确核仁前体在胚胎早期发育过程中发挥的作用及其机制尚存挑战.早期的观点认为:核仁前体虽不具备加工rRNA及生成核糖体的功能,但该结构为纤维颗粒状核仁的生成提供了物质基础,从而使发育后期胚胎重获核糖体生成能力.近期,这一观点逐步得到了修正.基于显微操作技术的核仁前体转移实验证实:母源核仁前体在胚胎早期发育过程中发挥关键作用,且发挥作用的时间窗口限定在受精至原核期之间.核仁前体可参与染色质重塑过程并维持着丝粒稳定,进而影响胚胎早期发育.本文主要综述了核仁前体的结构功能特点及发挥作用的潜在机制,从核仁前体的角度为拯救早期胚胎的发育潜能提供新思路. 相似文献
992.
Maintenance of genomic stability is of crucial importance for all living organisms. It is no surprise that during evolution,
a series of highly selective and efficient systems to detect DNA damage and control its repair have evolved. To this end,
signal transduction pathways are involved in pausing the cell division cycle to provide time for repair, and ultimately releasing
the cell cycle from arrest. Genetic components of the damage and replication checkpoints have been identified and a working
model is beginning to emerge. This area of biological inquiry has received a great deal of attention in the past decade with
the realization that the underlying regulatory mechanisms controlling the cell cycle are conserved throughout eukaryotic evolution.
Many of the key players in this response have structural and functional counterparts in species as diverse as yeast and human.
In recent years attention has also been paid to the plant kingdom suggesting that checkpoint controls have been highly conserved
during evolution. The unicellular green alga Chlamydomonas reinhardtii is a suitable model organism for the study of basic cellular processes including cell cycle regulation and DNA repair. To
investigate how algal cells accomplish these tasks, we have isolated mutants in the recognition and repair of DNA damage or
in the response to DNA damage.
Presented at the International Symposium Biology and Taxonomy of Green Algae V, Smolenice, June 26–29, 2007, Slovakia. 相似文献
993.
Comparative study of a new composite biomaterial fluor-hydroxyapatite on fibroblast cell line NIH-3T3 by direct test 总被引:1,自引:0,他引:1
Marica Theiszová Soňa Jantová Silvia Letašiová Ľuboš Valík Martin T. Palou 《Biologia》2008,63(2):273-281
The number of biomaterials used in biomedical applications has rapidly increased in the past two decades. Fluorapatite (FA)
is one of the inorganic constituents of bone or teeth used for hard tissue repairs and replacements. Fluor-hydroxyapatite
(FHA) is a new synthetically prepared composite that in its structure contains the same molecular concentration of OH− groups and F− ions. The aim of this experimental investigation was to use the embryonal mouse fibroblast cell line NIH-3T3 for comparative
study of basal cytotoxicity of fluoridated biomaterials FHA and FA discs. Hydroxyapatite (HA) disc, high-density polyethylene
as negative control and polyvinyl chloride (PVC) containing organotin stabilizer as positive control were used as standard
biomaterials. The appropriateness of the use of NIH-3T3 cells and their sensitivity for tested biomaterials were evaluated
on the basis of five cytotoxic end points: cell proliferation, cell morphology, lactate dehydrogenase (LDH) released, protein
and DNA cell content. The basal cytotoxicity of FHA, FA and HA discs was measured by direct contact method. FHA composite,
FA and HA demonstrated in cell line NIH-3T3 nearly similar basal cytotoxicity increasing with the time of treatment. After
72 h of biomaterials treatment, about 25% inhibition of cell number, unchanged morphology of dividing cells, 6.31–0.16% increase
of released LDH, about 10% inhibition of cell protein content and about 20% inhibition of DNA content was found. On the other
hand, from the growth rates it resulted that NIH-3T3 cells, affected by tested biomaterials, divided about 20% slowlier than
the control (untreated cells). Using the linear regression analysis we found out that deviations in measurements of cytotoxicity
by four methods were as follows: less than 10% for cell number, protein and DNA content methods and 12.4% for released LDH
method. Based on a good correlation of the cytotoxicity of biomaterials obtained from all end points we could conclude that
fibroblast NIH-3T3 cell line was appropriate for measuring the basal cytoxicity of tested biomaterials. 相似文献
994.
The volatile constituents of the essential oils of 23 taxa belonging to the Apioideae subfamily were studied in detail. The investigated taxa were Pimpinella serbica (Vis.) Bentham & Hooker, Libanotis montana Cr., Cnidium silaifolium (Jacq.) Simk. ssp. orientale (Boiss.) Tutin, Bupleurum praealtum L., B. sibthorpianum S. S. var. diversifolium (Roch.) Hay, Aegopodium podagraria L., Torilis anthriscus (L.) Gmel., Orlaya grandiflora (L.) Hoffm., Laserpitium siler L., Laser trilobum (L.) Brokh., Chaerophyllum aureum L., C. hirsutum L., C. temulum L., Pastinaca sativa L., P. hirsuta Pancic., Tordylium maximum L., Physospermum cornubiense (L.) DC., Peucedanum alsaticum L., P. oreoselinum (L.) Moench, P. cervaria (L.) Cuss., P. austriacum (Jacq.) Koch, P. longifolium W. et K., and P. officinale L. All of these species grow wild in the central part of the Balkan Peninsula. The essential oils were found to be complex mixtures of various compounds, more than 100 constituents being in each taxon, with contributions of main products never exceeding 25% of the total content. Sesquiterpene hydrocarbons were found to be the main group of constituents of all taxa, except for Peucedanum species, where monoterpene hydrocarbons were identified as the main components. The chemotaxonomic value of the essential-oil composition is discussed according to results of principal-component analysis (PCA). The essential-oil composition mainly reflects current taxonomic relationships between the investigated taxa. 相似文献
995.
Curcumin (1,7-bis(4-hydroxy-3-methoxyphenyl)-1,6-heptadiene-3,5-dione, 1) is a yellow ingredient isolated from turmeric (Curcumin longa). It has been shown to exhibit a variety of biological activities including antioxidative activity. In order to find more active antioxidants with 1 as the lead compound we synthesized curcumin analogues, i.e., 1,7-bis(3,4-dihydroxyphenyl)-1,6-heptadiene-3,5-dione (2), 1-(3,4-dihydroxyphenyl)-7-(4-hydroxy-3-methoxyphenyl)-1,6-heptadiene-3,5-dione (3), 1-(4-hydroxy-3-methoxyphenyl)-7-(4-hydroxyphenyl)-1,6-heptadiene-3,5-dione (4), 1,7-bis (4-hydroxyphenyl)-1,6-heptadiene-3,5-dione (5), 1-(3,4-dimethoxyphenyl)-7-(4-hydroxy-3-methoxyphenyl)-1,6-heptadiene-3,5-dione (6), 1,7-bis(3,4-dimethoxyphenyl)-1,6- heptadiene-3,5-dione (7), 1,7-bis(4-methoxyphenyl)-1,6-heptadiene-3,5-dione (8), and 1,7-diphenyl-1,6-heptadiene-3,5-dione (9). Antioxidative effects of curcumin and its analogues against free radical initiated peroxidation of human low density lipoprotein (LDL) were studied. The peroxidation was initiated either by a water-soluble initiator 2,2'-azobis(2-amidinopropane hydrochloride) (AAPH), or by cupric ion (Cu2+). The reaction kinetics were monitored either by the uptake of oxygen and the depletion of alpha-tocopherol present in the native LDL, or by the formation of thiobarbituric acid reactive substances. Kinetic analysis of the antioxidation process demonstrates that these compounds, except 7, 8, and 9, are effective antioxidants against AAPH- and Cu2+ -initiated LDL peroxidation by H-atom abstraction from the phenolic groups. Compounds 2 and 3 which bear ortho-diphenoxyl functionality possess significantly higher antioxidant activity than curcumin and other analogues, and the 4-hydroxy-3-methoxyphenyl group also play an important role in the antioxidative activity. 相似文献
996.
Summary
Azotobacter chroococcum was grown in continuous culture at two temperatures (30 °C and 20 °C) and different dissolved oxygen tensions (DOT) (30 % to 40 % and 70 % to 80 % of air saturation), respectively. At the temperature of 30 °C and low DOT a relatively high volumetric productivity and efficiency of nitrogen fixation were obtained. After lowering the temperature to 20 °C, an intensive formation of cysts was observed associated with a drastic decrease of the bacterial growth. Bacteria in the form of cysts kept their physiological activity for a long period of time depending on temperature and preparation. 相似文献
997.
In contrast to the epidermal growth factor (EGF) receptor, ErbB2 is known to remain at the plasma membrane after ligand binding and dimerization. However, why ErbB2 is not efficiently down-regulated has remained elusive. Basically, two possibilities exist: ErbB2 is internalization resistant or it is efficiently recycled after internalization. By a combination of confocal microscopy, immunogold labeling electron microscopy, and biochemical techniques we show that ErbB2 is preferentially associated with membrane protrusions. Moreover, it is efficiently excluded from clathrin-coated pits and is not seen in transferrin receptor-containing endosomes. This pattern is not changed after binding of EGF, heregulin, or herceptin. The exclusion from coated pits is so pronounced that it cannot just be explained by lack of an internalization signal. Although ErbB2 is a raft-associated protein, the localization of ErbB2 to protrusions is not a result of raft binding. Also, an intact actin cytoskeleton is not required for keeping ErbB2 away from coated pits. However, after efficient cross-linking, ErbB2 is removed from protrusions to occur on the bulk membrane, in coated pits, and in endosomes. These data show that ErbB2 is a remarkably internalization-resistant receptor and suggest that the mechanism underlying the firm association of ErbB2 with protrusions also is the reason for this resistance. 相似文献
998.
Lloyd Donaldson Ksenija Radotić Aleksandar Kalauzi Daniela Djikanović Milorad Jeremić 《Journal of structural biology》2010,169(1):106-115
Confocal fluorescence microscopy was used to examine the spectral characteristics of lignin autofluorescence in secondary cell walls of normal and compression wood from Pinus radiata. Using UV excitation, fluorescence spectra of normal and compression wood sections showed significant differences, especially in the outer secondary cell wall of tracheids, with a shift in maxima from violet to blue wavelengths between normal and compression wood. A comparison of normal wood, mild and severe compression wood, showed that the wavelength shift was intermediate in the mild compression wood compared to the severe compression wood, thus offering the possibility of quantifying the severity by measuring ratios of fluorescence at violet and blue wavelengths. Fluorescence induced by blue light, rather than UV, was less well differentiated amongst wood types. Spectral deconvolution indicated the presence of a minimum of five discrete lignin fluorophores in the cell walls of both normal and compression wood tracheids. Comparison with lignin model compounds suggest that the wavelength shift may correspond in part to increased levels of p-hydroxy type lignin in the compression wood samples. The combination of confocal fluorescence imaging and related spectral deconvolution therefore offers a novel technique for characterising cell wall lignin in situ. 相似文献
999.
Background
The evolutionary origin of cooperation among unrelated individuals remains a key unsolved issue across several disciplines. Prominent among the several mechanisms proposed to explain how cooperation can emerge is the existence of a population structure that determines the interactions among individuals. Many models have explored analytically and by simulation the effects of such a structure, particularly in the framework of the Prisoner''s Dilemma, but the results of these models largely depend on details such as the type of spatial structure or the evolutionary dynamics. Therefore, experimental work suitably designed to address this question is needed to probe these issues.Methods and Findings
We have designed an experiment to test the emergence of cooperation when humans play Prisoner''s Dilemma on a network whose size is comparable to that of simulations. We find that the cooperation level declines to an asymptotic state with low but nonzero cooperation. Regarding players'' behavior, we observe that the population is heterogeneous, consisting of a high percentage of defectors, a smaller one of cooperators, and a large group that shares features of the conditional cooperators of public goods games. We propose an agent-based model based on the coexistence of these different strategies that is in good agreement with all the experimental observations.Conclusions
In our large experimental setup, cooperation was not promoted by the existence of a lattice beyond a residual level (around 20%) typical of public goods experiments. Our findings also indicate that both heterogeneity and a “moody” conditional cooperation strategy, in which the probability of cooperating also depends on the player''s previous action, are required to understand the outcome of the experiment. These results could impact the way game theory on graphs is used to model human interactions in structured groups. 相似文献1000.
Alien plant invasions in tropical and sub-tropical savannas: patterns,processes and prospects 总被引:1,自引:0,他引:1
Llewellyn C. Foxcroft David M. Richardson Marcel Rejmánek Petr Pyšek 《Biological invasions》2010,12(12):3913-3933
Biological invasions affect virtually all ecosystems on earth, but the degree to which different regions and biomes are invaded,
and the quality of information from different regions, varies greatly. A large body of literature exists on the invasion of
savannas in the Neotropics and northern Australia where invasive plants, especially African grasses, have had major impacts.
Less has been published on plant invasions in African savannas, except for those in South Africa. Negative impacts due to
plant invasions in African savannas appear to be less severe than in other regions at present. As savannas cover about 60%
of the continent, with tens of millions of people relying on the services they provide, it is timely to assess the current
status of invasions as a threat to these ecosystems. We reviewed the literature, contrasting the African situation with that
of Neotropical and Australian savannas. A number of drivers and explanatory factors of plant invasions in savannas have been
described, mostly from the Neotropics and Australia. These include herbivore presence, residence time, intentional introductions
for pasture improvements, fire regimes, the physiology of the introduced species, and anthropogenic disturbance. After comparing
these drivers across the three regions, we suggest that the lower extent of alien plant invasions in African savannas is largely
attributable to: (1) significantly lower rates of intentional plant introductions and widespread plantings (until recently);
(2) the role of large mammalian herbivores in these ecosystems; (3) historical and biogeographical issues relating to the
regions of origin of introduced species; and (4) the adaptation of African systems to fire. We discuss how changing conditions
in the three regions are likely to affect plant invasions in the future. 相似文献