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1.
Aggregation-dependent turnover of flagellar adhesion molecules in chlamydomonas gametes 总被引:8,自引:7,他引:1
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Previous studies on flagellar adhesion in chlamydomonas (Snell, W. and S. Roseman. 1979. J. Biol. Chem. 254:10820-10829.) have shown that as gametes adhere to flagella isolated from gametes of the opposite mating type, the adhsiveness of the added flagella but not of the gametes is lost. The studies reported here show that the addition of protein synthesis inhibitors (cycloheximide [CH] or anisomycin) to the medium of such cell- flagella mixtures causes the cells to lose their adhesiveness. This loss, however, occurs only after the cells have interacted with 4-8 flagella/cell and does not occur if the cells are kept in CH (7 h) without aggregating. The availability of an impotent (imp) mating type plus (MT(+)) mutant (provided by U.W. Goodenough), which adheres but is unable to undergo the fusion that normally follows adhesion, made it possible to determine whether a similar loss of adhesiveness occurs in mixtures of matting type minus (mt(-)) and imp mt(+) gametes. In the absence of inhibitor, mt(-) and imp mt(+) gametes adhered to each other (without fusing) for several hours; however, in the presence of CH or anisomycin, the gametes began to de-adhere 35 min after mixing, and, by 90 min, 100 percent of the cells were single again. This effect was reversible, and the rapid turnover of cells were single again. This effect was reversible, and the rapid turnover of molecules involved in adhesion occurred only during adhesion inasmuch as gametes pretreated for 4 h with CH were able to aggregate in CH for the same length of time as nonpretreated cells aggregated in CH. By the addition of CH at various times after the mt(-) and imp mt(+) gametes were mixed, measurements were made of the “pool size” of the molecules involved in adhesion. The pool reached a minimum after 25 min of aggregation, rapidly increased for the next 25 min, and then leveled off at the premixing level. These results suggest that flagellar adhesion in chlamydomonas causes modification of surface molecules (receptors, ligands), which brings about their inactivation and stimulates their replacement. 相似文献
2.
Brooke R Snyder Pei-Hsun Cheng Jinjing Yang Shang-Hsun Yang Anderson HC Huang Anthony WS Chan 《BMC cell biology》2011,12(1):1-8
Background
Activation by extracellular ligands of G protein-coupled (GPCRs) and tyrosine kinase receptors (RTKs), results in the generation of second messengers that in turn control specific cell functions. Further, modulation/amplification or inhibition of the initial signalling events, depend on the recruitment onto the plasma membrane of soluble protein effectors. High throughput methodologies to monitor quantitatively second messenger production, have been developed over the last years and are largely used to screen chemical libraries for drug development. On the contrary, no such high throughput methods are yet available for the other aspect of GPCRs regulation, i.e. protein translocation to the plasma membrane, despite the enormous interest of this phenomenon for the modulation of receptor downstream functions. Indeed, to date, the experimental procedures available are either inadequate or complex and expensive.Results
Here we describe the development of a novel conceptual approach to the study of cytosolic proteins translocation to the inner surface of the plasma membrane. The basis of the technique consists in: i) generating chimeras between the protein of interests and the calcium (Ca2+)-sensitive, luminescent photo-protein, aequorin and ii) taking advantage of the large Ca2+ concentration [Ca2+] difference between bulk cytosolic and the sub-plasma membrane rim.Conclusion
This approach, that keeps unaffected the translocation properties of the signalling protein, can in principle be applied to any protein that, upon activation, moves from the cytosol to the plasma membrane. Thus, not only the modulation of GPCRs and RTKs can be investigated in this way, but that of all other proteins that can be recruited to the plasma membrane also independently of receptor activation. Moreover, its automated version, which can provide information about the kinetics and concentration-dependence of the process, is also applicable to high throughput screening of drugs affecting the translocation process. 相似文献3.
Cleo Robinson Marinella Callow Sandra Stevenson Bruce WS Robinson Richard A Lake 《Respiratory research》2001,2(2):119-6
Background
The pathogenetic mechanisms that underlie the interstitial lung disease cryptogenic fibrosing alveolitis (CFA) may involve an immunological reaction to unidentified antigens in the lung, resulting in tissue damage. 相似文献4.
Molecular evolution of mitochondrial 12S RNA and cytochrome b sequences in the pantherine lineage of Felidae 总被引:4,自引:2,他引:2
DNA sequence comparisons of two mitochondrial DNA genes were used to infer
phylogenetic relationships among 17 Felidae species, notably 15 in the
previously described pantherine lineage. The polymerase chain reaction
(PCR) was used to generate sequences of 358 base pairs of the mitochondrial
12S RNA gene and 289 base pairs of the cytochrome b protein coding gene.
DNA sequences were compared within and between 17 felid and five nonfelid
carnivore species. Evolutionary trees were constructed using phenetic,
cladistic, and maximum likelihood algorithms. The combined results
suggested several phylogenetic relationships including (1) the recognition
of a recently evolved monophyletic genus Panthera consisting of Panthera
leo, P. pardus, P. onca, P. uncia, P. tigris, and Neofelis nebulosa; (2)
the recent common ancestry of Acinonyx jubatus, the African cheetah, and
Puma concolor, the American puma; and (3) two golden cat species, Profelis
temmincki and Profelis aurata, are not sister species, and the latter is
strongly associated with Caracal caracal. These data add to the growing
database of vertebrate mtDNA sequences and, given the relatively recent
divergence among the felids represented here (1-10 Myr), allow 12S and
cytochrome b sequence evolution to be addressed over a time scale different
from those addressed in most work on vertebrate mtDNA.
相似文献
5.
The liver is a target for toxic chemicals such as cadmium (Cd). When the liver is damaged, hepatic stellate cells (HSC) are activated and transformed into myofibroblast-like cells, which are responsible for liver fibrosis. Curcuma longa has been reported to exert a hepato-protective effect under various pathological conditions. We investigated the effects of C. longa administration on HSC activation in response to Cd induced hepatotoxicity. Forty adult male albino rats were divided into: group 1 (control), group 2 (Cd treated), group 3 (C. longa treated) and group 4 (Cd and C. longa treated). After 6 weeks, liver specimens were prepared for light and electron microscopy examination of histological changes and immunohistochemical localization of alpha smooth muscle actin (αSMA) as a specific marker for activated HSC. Activated HSC with a positive αSMA immune reaction were not detected in groups 1 and 3. Large numbers of activated HSC with αSMA immune reactions were observed in group 2 in addition to Cd induced hepatotoxic changes including excess collagen deposition in thickened portal triads, interlobular septa with hepatic lobulation, inflammatory cell infiltration, a significant increase in Kupffer cells and degenerated hepatocytes. In group 4, we observed a significant decrease in HSC that expressed αSMA with amelioration of the hepatotoxic changes. C. longa administration decreased HSC activation and ameliorated hepatotoxic changes caused by Cd in adult rats. 相似文献
6.
Odor identification: perceptual and semantic dimensions 总被引:8,自引:8,他引:0
7.
Wingfield BD; Grant WS; Wolfaardt JF; Wingfield MJ 《Molecular biology and evolution》1994,11(3):376-383
The genus Ceratocystis sensu stricto includes important fungal pathogens of
woody and herbaceous plants. This genus is distinguished from species in
Ceratocystis sensu lato by the presence of Chalara anamorphs. Ascospore
shape has been used extensively in delineating Ceratocystis taxa, which
show a large variety of ascospore shapes. Sequence analysis of one region
of he 18S ribosomal RNA subunit and two regions of the 28S ribosomal RNA
subunit showed that there was a majority of multiple substitutions at
nucleotide sites and that there was a low transition/transversion ratio, T
= 0.72. Both of these results suggest that these are well established, old
species. Ascospore morphology, for the most part, was not congruent with
the molecular phylogeny, and the use of morphological characters may be
misleading in the taxonomy of these species.
相似文献
8.
9.
Frank JH Gijsen Francesco Migliavacca Silvia Schievano Laura Socci Lorenza Petrini Attila Thury Jolanda J Wentzel Anton FW van der Steen Patrick WS Serruys Gabriele Dubini 《Biomedical engineering online》2008,7(1):23
Background
The process of restenosis after a stenting procedure is related to local biomechanical environment. Arterial wall stresses caused by the interaction of the stent with the vascular wall and possibly stress induced stent strut fracture are two important parameters. The knowledge of these parameters after stent deployment in a patient derived 3D reconstruction of a diseased coronary artery might give insights in the understanding of the process of restenosis. 相似文献10.
The orientation of plant root growth is modulated by developmental as well as environmental cues. Among the environmental factors, gravity has been extensively studied because of its overpowering effects in modulating root growth direction. However, our knowledge of the effects of other abiotic signals that influence root growth direction is largely unknown. Recently, we have shown that high salinity can modify root growth direction by inducing rapid amyloplast degradation in root columella cells of Arabidopsis thaliana. By exploiting salt overly sensitive (sos) mutants and PIN2 expression analyses, we have shown that the altered root growth direction in response to salt is mediated by ion disequilibrium and is correlated with PIN2 mRNA abundance and expression and localization of the protein. Our study demonstrates that the SOS pathway may mediate this process. Here we discuss our data from broader perspectives. We propose that salt-induced modification of root growth direction is a salt-avoidance behavior, which is an active adaptive mechanism for plants grown under saline conditions. Furthermore, high salinity also stimulates alteration of gravitropic growth of shoots. These findings illustrate that plants have a fine and sophisticated sensory and communication system that enable plants to dynamically and efficiently cope with rapidly changing environment.Key words: abidopsis, adaptation, avoidance, root, salt stress, tropic growthOwing to their sessile nature, plant roots are constantly bombarded with various environmental stimuli from the soil, such as gravity, physical obstacles and imbalanced distribution of water and/or nutrients and high salinity. Where to grow is an important developmental decision in the life cycle of a plant that is crucial for its adaptation and the subsequent reproductive success. The proper orientation of root growth is shaped by both the developmental inputs and external signals.1,2 The overwhelming environmental factor that modulates root growth direction is gravity, and plant primary roots grow downward toward the gravity vector. This directed growth of root in response to gravity is named as tropic growth to gravity or gravitropism. Studies of gravity perception and signaling pathway of the root cap at the primary root of Arabidopsis strongly support the starch statolith hypothesis.3 In this hypothesis, the columella cells in the root cap, which contain sedimentable amyloplasts, are the gravity-perceptive site in roots. The inner columella cells of the second tier have been proposed as making the greatest contribution to root gravitropism.4 Upon gravity stimulation, cytosolic ions such as Ca2+ and rapid cytoplasmic alkalization may be involved in gravity signal transduction.5–7 Asymmetric distribution of auxin in roots caused by basipetal transport mainly through the auxin efflux carrier PIN-FORMED2 (PIN2), which is distributed asymmetrically within the cells, results in gravitropic root response of the root elongation zone.8,9In contrast to our understanding of gravitropism of root, our knowledge of tropistic responses of root to other major environmental stimuli, such as water availability, imbalanced nutrient distribution and high salinity, and the interplay between these stimuli in determining the directional growth of root remains enigmatic. Recent studies have confirmed the existence of hydrotropism and the molecular genetic basis of the tropistic growth of root to water in determining the final direction of root growth starts to be deciphered.10–12 Hydrotropic growth of roots is an important trait for plants to actively find water and to optimize their fitness under drought condition. Salinity is another major constraint to root system development, and limits the productivity of agricultural crops and the distribution of plant species.13–15 It is known that salt stress-induced disturbed balance of ions is the primary cause for inhibition of plant growth and subsequent yield reduction. How does root minimize entrance of harmful ions and subsequently avoid salt injury? Does plant have capacity to sense salt signal, and prevent potentially harmful ions reaching root and shoot?Previous studies have shown that plant use different strategies to avoid salt injury at various levels. After Na+ enters the root cells, the Casparian strip can restrict the movements of the harmful ion into the xylem.16 Root cells also avoid salt injury by extruding Na+ actively back to the outside solution. This energy-dependent ion efflux from cytosol across the plasma membrane is mediated by SOS1 gene, a Na+-H+ antiporter, which is regulated by at least other genes, SOS3 (calcium binding protein) and SOS2 (serine/threonine kinase). This is the well characterized SOS (Salt Overly Sensitive) signaling pathway.17,18 Another way for plant root cells to avoid ion injury is to accumulate Na+ into vacuole. Vacuolar compartmentation of Na+ is also in part regulated by Na+-H+ antiporters, such as AtNHX1.19 These findings reveal mechanisms of how plants avoid Na+ injury after passive entrance of sodium ions into root cells. We questioned whether a plant is capable of actively preventing the harmful ions from reaching root cells or escape from high salinity in the environment, and how plant roots respond to changing salt conditions, because salt distribution is unbalanced under natural saline conditions, especially after rain and irrigation. With a new assay that allows us to specifically address how plant roots respond to changing salt levels, we discovered an alternative adaptive mechanism for plant root to avoid salt injury.20We set up a two-layer medium assay in which a sodium ion gradient would be generated. A normal nutrient agar medium is at the top of the growth bottle and an agar with salt-stressed medium is in the bottom of the bottle. This simple assay allows us to monitor root growth and orientation. The roots of the wild type seedlings penetrated the interface of the layers and grew straight downwards exhibiting gravitropism, when both layers were MS media. In contrast, when the bottom medium contained NaCl, roots of seedlings grew downward first, and then curved and grew upward toward the lower levels of salt. Roots started to bend upward at an early stage even before contacting high-salt medium (250 mM NaCl) on the bottom. The results indicate that roots can sense ion gradients in the growing environment and transduce the signal, combine with internal signals to make decisions that enable roots to stay away from high salt.21,22 Here, we would like to propose this salt-induced tropic growth as a salt-avoidance tropism, which is an important adaptive behavior for plant roots to avoid salt injury and direct them toward their goal of optimal fitness.23 Because salt stress inhibits root elongation, we tested impact of salt-induced negative gravitropism on the root growth. The results showed that inhibitory effect of salt on root growth was largely alleviated with this tropic curve (Fig. 1), further verifying our hypothesis that the salt-induced developmental plasticity is a salt-avoidance behavior (Fig. 2).Open in a separate windowFigure 1Effects of salt on root elongation of Arabidopsis thaliana seedlings from different salt treatments. The inhibitory effect of salt stress on root growth was greatly alleviated in the wild type (Col-0) when root growth of the seedlings was analyzed using a two-layer medium assay (black bars). The MS nutrient medium is on the top, and NaCl concentrations in the media on the bottom are 0, 150 and 250 mM. More severe inhibition of root growth of the seedlings by various levels of NaCl in a root bending assay (white bars) was observed. Data represents means of measurements from >40 individuals from three independent experiments. Bars represent standard error.Open in a separate windowFigure 2An illustrative model of the sensing and response by the plant root when grown under different saline conditions. This model proposes two major mechanisms of salt responses by plants, where salt tolerance is the ability to function while stressed; Salt avoidance is the capacity to stay away from salt stress when growing in changing saline conditions.Another important point that we would like to bring out based on our observation in this work is that salinity also stimulated shoot positive gravitropism or negative phototropism. The observation implicates long-distance communication from root to shoot during plant salt response in the stressed plants. The exact biological function of shoot tropic growth, the signals in this long-distance communication, and underlying molecular mechanism still remains unknown.In conclusion, our study has revealed a novel complex adaptive mechanism that provides plants a capacity for avoiding injury from salt. The hypothesis we have proposed here should provide novel insights into plant stress avoidance. Further analysis using a combinatorial approach, mutant analysis and genomics, is required to decipher the molecular network underlying this salt-avoidance behavior. 相似文献