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761.
Raihana Zaka David Stokes Arnold S Dion Anna Kusnierz Fei Han Charlene J Williams 《Arthritis research & therapy》2007,8(6):R164
Ank is a multipass transmembrane protein that regulates the cellular transport of inorganic pyrophosphate. In the progressive
ankylosis (ank) mouse, a premature termination mutation at glutamic acid 440 results in a phenotype characterized by inappropriate deposition
of basic calcium phosphate crystals in skeletal tissues. Mutations in the amino terminus of ANKH, the human homolog of Ank,
result in familial calcium pyrophosphate dihydrate deposition disease. It has been hypothesized that these mutations result
in a gain-of-function with respect to the elaboration of extracellular inorganic pyrophosphate. To explore this issue in a
mineralization-competent system, we stably transduced ATDC5 cells with wild-type Ank as well as with familial chondrocalcinosis-causing
Ank mutations. We evaluated the elaboration of inorganic pyrophosphate, the activity of pyrophosphate-modulating enzymes,
and the mineralization in the transduced cells. Expression of transduced protein was confirmed by quantitative real-time PCR
and by ELISA. Levels of inorganic pyrophosphate were measured, as were the activities of nucleotide pyrophosphatase phosphodiesterase
and alkaline phosphatase. We also evaluated the expression of markers of chondrocyte maturation and the nature of the mineralization
phase elaborated by transduced cells. The cell line expressing the proline to leucine mutation at position 5 (P5L) consistently
displayed higher levels of extracellular inorganic pyrophosphate and higher phosphodiesterase activity than the other transduced
lines. During hypertrophy, however, extracellular inorganic pyrophosphate levels were modulated by alkaline phosphatase activity
in this cell system, resulting in the deposition of basic calcium phosphate crystals only in all transduced cell lines. Cells
overexpressing wild-type Ank displayed a higher level of expression of type X collagen than cells transduced with mutant Ank.
Other markers of hypertrophy and terminal differentiation, such as alkaline phosphatase, osteopontin, and runx2, were not significantly different in cells expressing wild-type or mutant Ank in comparison with cells transduced with an
empty vector or with untransduced cells. These results suggest that the P5L Ank mutant is capable of demonstrating a gain-of-function
with respect to extracellular inorganic pyrophosphate elaboration, but this effect is modified by high levels of expression
of alkaline phosphatase in ATDC5 cells during hypertrophy and terminal differentiation, resulting in the deposition of basic
calcium phosphate crystals. 相似文献
762.
763.
Discordant 16S and 23S rRNA gene phylogenies for the genus Helicobacter: implications for phylogenetic inference and systematics 下载免费PDF全文
Dewhirst FE Shen Z Scimeca MS Stokes LN Boumenna T Chen T Paster BJ Fox JG 《Journal of bacteriology》2005,187(17):6106-6118
Analysis of 16S rRNA gene sequences has become the primary method for determining prokaryotic phylogeny. Phylogeny is currently the basis for prokaryotic systematics. Therefore, the validity of 16S rRNA gene-based phylogenetic analyses is of fundamental importance for prokaryotic systematics. Discrepancies between 16S rRNA gene analyses and DNA-DNA hybridization and phenotypic analyses have been noted in the genus Helicobacter. To clarify these discrepancies, we sequenced the 23S rRNA genes for 55 helicobacter strains representing 41 taxa (>2,700 bases per sequence). Phylogenetic-tree construction using neighbor-joining, parsimony, and maximum likelihood methods for 23S rRNA gene sequence data yielded stable trees which were consistent with other phenotypic and genotypic methods. The 16S rRNA gene sequence-derived trees were discordant with the 23S rRNA gene trees and other data. Discrepant 16S rRNA gene sequence data for the helicobacters are consistent with the horizontal transfer of 16S rRNA gene fragments and the creation of mosaic molecules with loss of phylogenetic information. These results suggest that taxonomic decisions must be supported by other phylogenetically informative macromolecules, such as the 23S rRNA gene, when 16S rRNA gene-derived phylogeny is discordant with other credible phenotypic and genotypic methods. This study found Wolinella succinogenes to branch with the unsheathed-flagellum cluster of helicobacters by 23S rRNA gene analyses and whole-genome comparisons. This study also found intervening sequences (IVSs) in the 23S rRNA genes of strains of 12 Helicobacter species. IVSs were found in helices 10, 25, and 45, as well as between helices 31' and 27'. Simultaneous insertion of IVSs at three sites was found in H. mesocricetorum. 相似文献
764.
Class 1 integrons potentially predating the association with tn402-like transposition genes are present in a sediment microbial community 总被引:5,自引:0,他引:5 下载免费PDF全文
Stokes HW Nesbø CL Holley M Bahl MI Gillings MR Boucher Y 《Journal of bacteriology》2006,188(16):5722-5730
Integrons are genetic elements that contribute to lateral gene transfer in bacteria as a consequence of possessing a site-specific recombination system. This system facilitates the spread of genes when they are part of mobile cassettes. Most integrons are contained within chromosomes and are confined to specific bacterial lineages. However, this is not the case for class 1 integrons, which were the first to be identified and are one of the single biggest contributors to multidrug-resistant nosocomial infections, carrying resistance to many antibiotics in diverse pathogens on a global scale. The rapid spread of class 1 integrons in the last 60 years is partly a result of their association with a specific suite of transposition functions, which has facilitated their recruitment by plasmids and other transposons. The widespread use of antibiotics has acted as a positive selection pressure for bacteria, especially pathogens, which harbor class 1 integrons and their associated antibiotic resistance genes. Here, we have isolated bacteria from soil and sediment in the absence of antibiotic selection. Class 1 integrons were recovered from four different bacterial species not known to be human pathogens or commensals. All four integrons lacked the transposition genes previously considered to be a characteristic of this class. At least two of these integrons were located on a chromosome, and none of them possessed antibiotic resistance genes. We conclude that novel class 1 integrons are present in a sediment environment in various bacteria of the beta-proteobacterial class. These data suggest that the dispersal of this class may have begun before the "antibiotic era." 相似文献
765.
Superoxide anion is produced during normal cellular respiration and plays key roles in cellular physiology with its dysregulation being associated with a variety of diseases. Superoxide anion is a short-lived molecule and, therefore, its homeostatic regulation and role in biology and disease requires dynamic quantification with fine temporal resolution. Here we validated coelenterazine as a reporter of intracellular superoxide anion concentration and used it as a dynamic measure both in vitro and in vivo. Chemiluminescence was dependent upon superoxide anion levels, including those produced during cellular respiration, and concentrations varied both kinetically and temporally in response to physiologically relevant fluctuations in glucose levels. In vivo imaging with coelenterazine revealed that beta cells of the pancreas have increased levels of superoxide anion, which acted as a measure of beta-cell function and mass and could predict the susceptibility of mice to diabetes mellitus. Glucose response and regulation are key elements of cellular physiology and organismal biology, and superoxide anion appears to play a fundamental and dynamic role in both of these processes. 相似文献
766.
Linking carbon supply to root cell-wall chemistry and mechanics at high altitudes in Abies georgei 总被引:3,自引:0,他引:3
Background and Aims
The mobile carbon supply to different compartments of a tree is affected by climate, but its impact on cell-wall chemistry and mechanics remains unknown. To understand better the variability in root growth and biomechanics in mountain forests subjected to substrate mass movement, we investigated root chemical and mechanical properties of mature Abies georgei var. smithii (Smith fir) growing at different elevations on the Tibet–Qinghai Plateau.Methods
Thin and fine roots (0·1–4·0 mm in diameter) were sampled at three different elevations (3480, 3900 and 4330 m, the last corresponding to the treeline). Tensile resistance of roots of different diameter classes was measured along with holocellulose and non-structural carbon (NSC) content.Key Results
The mean force necessary to break roots in tension decreased significantly with increasing altitude and was attributed to a decrease in holocellulose content. Holocellulose was significantly lower in roots at the treeline (29·5 ± 1·3 %) compared with those at 3480 m (39·1 ± 1·0 %). Roots also differed significantly in NSC, with 35·6 ± 4·1 mg g−1 dry mass of mean total soluble sugars in roots at 3480 m and 18·8 ± 2·1 mg g−1 dry mass in roots at the treeline.Conclusions
Root mechanical resistance, holocellulose and NSC content all decreased with increasing altitude. Holocellulose is made up principally of cellulose, the biosynthesis of which depends largely on NSC supply. Plants synthesize cellulose when conditions are optimal and NSC is not limiting. Thus, cellulose synthesis in the thin and fine roots measured in our study is probably not a priority in mature trees growing at very high altitudes, where climatic factors will be limiting for growth. Root NSC stocks at the treeline may be depleted through over-demand for carbon supply due to increased fine root production or winter root growth. 相似文献767.
Alexia Stokes Franck Salin Adzo Dzifa Kokutse Stéphane Berthier Henri Jeannin Shaun Mochan Luuk Dorren Nomessi Kokutse Murad Abd.Ghani Thierry Fourcaud 《Plant and Soil》2005,278(1-2):107-117
In order to determine the mechanical resistance of several forest tree species to rockfall, an inventory of the type of damage
sustained in an active rockfall corridor was carried out in the French Alps. The diameter, spatial position and type of damage
incurred were measured in 423 trees. Only 5% of trees had sustained damage above a height of 1.3 m and in damaged trees, 66%
of broken or uprooted trees were conifers. Larger trees were more likely to be wounded or dead than smaller trees, although
the size of the wounds was relatively smaller in larger trees. The species with the least proportion of damage through stem
breakage, uprooting or wounding was European beech (Fagus sylvatica L.). Winching tests were carried out on two conifer species, Norway spruce (Picea abies L.) and Silver fir (Abies alba Mill.), as well as European beech, in order to verify the hypothesis that beech was highly resistant to rockfall and that
conifers were more susceptible to uprooting or stem breakage. Nineteen trees were winched downhill and the force necessary
to cause failure was measured. The energy (E
fail) required to break or uproot a tree was then calculated. Most Silver fir trees failed in the stem and Norway spruce usually
failed through uprooting. European beech was either uprooted or broke in the stem and was twice as resistant to failure as
Silver fir, and three times more resistant than Norway spruce. E
fail was strongly related to stem diameter in European beech only, and was significantly higher in this species compared to Norway
spruce. Results suggest that European beech would be a better species to plant with regards to protection against rockfall.
Nevertheless, all types of different abiotic stresses on any particular alpine site should be considered by the forest manager,
as planting only broadleaf species may compromise the protecting capacity of the forest e.g. in the case of snow avalanches. 相似文献
768.
769.
Class 1 integrons carried by pathogens have acquired over 100 different gene cassettes encoding resistance to antimicrobial compounds, helping to generate a crisis in the management of infectious disease. It is presumed that these cassettes originated from environmental bacteria, but exchange of gene cassettes has surprisingly never been demonstrated outside laboratory or clinical contexts. We aimed to identify a natural environment where such exchanges might occur, and determine the phylogenetic range of participating integrons. Here we examine freshwater biofilms and show that families of cassettes conferring resistance to quaternary ammonium compounds ( qac ) are found on class 1 integrons identical to those from clinical contexts, on sequence variants of class 1 integrons only known from natural environments, and on other diverse classes of integrons only known from the chromosomes of soil and freshwater Proteobacteria . We conclude that gene cassettes might be readily shared between different integron classes found in environmental, commensal and pathogenic bacteria. This suggests that class 1 integrons in pathogens have access to a vast pool of gene cassettes, any of which could confer a phenotype of clinical relevance. Exploration of this resource might allow identification of resistance or virulence genes before they become part of multi-drug-resistant human pathogens. 相似文献
770.
Four neural circuit models and their role in the organization of voluntary movement are presented here. These circuits collectively control a ballistic type biped voluntary movement. The structure of each circuit, and its function is discussed. Three of the circuits are central and contribute to the construction of two classes of inputs, analogous to the α signals and γ signals in biological systems. The fourth circuit plays a role in stabilization of the movement, and in compensation for the receptors. Digital computer simulations are undertaken to demonstrate the construction of all the intermediate signals and the response of a two link biped to these efferent signals. 相似文献