Página 18 dos resultados de 60878 itens digitais encontrados em 0.038 segundos

‣ Combinations of biomarkers predictive of later life mortality

Gruenewald, Tara L.; Seeman, Teresa E.; Ryff, Carol D.; Karlamangla, Arun S.; Singer, Burton H.
Fonte: National Academy of Sciences Publicador: National Academy of Sciences
Tipo: Artigo de Revista Científica
Português
Relevância na Pesquisa
451.23344%
A wide range of biomarkers, reflecting activity in a number of biological systems (e.g., neuroendocrine, immune, cardiovascular, and metabolic), have been found to prospectively predict disability, morbidity, and mortality outcomes in older adult populations. Levels of these biomarkers, singly or in combination, may serve as an early warning system of risk for future adverse health outcomes. In the current investigation, 13 biomarkers were examined as predictors of mortality occurrence over a 12-year period in a sample of men and women (n = 1,189) 70–79 years of age at enrollment into the study. Biomarkers examined in analyses included markers of neuroendocrine functioning (epinephrine, norepinephrine, cortisol, and dehydroepiandrosterone), immune activity (C-reactive protein, fibrinogen, IL-6, and albumin), cardiovascular functioning (systolic and diastolic blood pressure), and metabolic activity [high-density lipoprotein (HDL) cholesterol, total to HDL cholesterol ratio, and glycosylated hemoglobin]. Recursive partitioning techniques were used to identify a set of pathways, composed of combinations of different biomarkers, that were associated with a high-risk of mortality over the 12-year period. Of the 13 biomarkers examined...

‣ Evolution of complexity in signaling pathways

Soyer, Orkun S.; Bonhoeffer, Sebastian
Fonte: National Academy of Sciences Publicador: National Academy of Sciences
Tipo: Artigo de Revista Científica
Português
Relevância na Pesquisa
451.23344%
It is not clear how biological pathways evolve to mediate a certain physiological response and why they show a level of complexity that is generally above the minimum required to achieve such a response. One possibility is that pathway complexity increases due to the nature of evolutionary mechanisms. Here, we analyze this possibility by using mathematical models of biological pathways and evolutionary simulations. Starting with a population of small pathways of three proteins, we let the population evolve with mutations that affect pathway structure through duplication or deletion of existing proteins, deletion or creation of interactions among them, or addition of new proteins. Our simulations show that such mutational events, coupled with a selective pressure, leads to growth of pathways. These results indicate that pathways could be driven toward complexity via simple evolutionary mechanisms and that complexity can arise without any specific selective pressure for it. Furthermore, we find that the level of complexity that pathways evolve toward depends on the selection criteria. In general, we find that final pathway size tends to be lower when pathways evolve under stringent selection criteria. This leads to the counterintuitive conclusion that simple response requirements on a pathway would facilitate its evolution toward higher complexity.

‣ A tunable algorithm for collective decision-making

Pratt, Stephen C.; Sumpter, David J. T.
Fonte: National Academy of Sciences Publicador: National Academy of Sciences
Tipo: Artigo de Revista Científica
Português
Relevância na Pesquisa
451.23344%
Complex biological systems are increasingly understood in terms of the algorithms that guide the behavior of system components and the information pathways that link them. Much attention has been given to robust algorithms, or those that allow a system to maintain its functions in the face of internal or external perturbations. At the same time, environmental variation imposes a complementary need for algorithm versatility, or the ability to alter system function adaptively as external circumstances change. An important goal of systems biology is thus the identification of biological algorithms that can meet multiple challenges rather than being narrowly specified to particular problems. Here we show that emigrating colonies of the ant Temnothorax curvispinosus tune the parameters of a single decision algorithm to respond adaptively to two distinct problems: rapid abandonment of their old nest in a crisis and deliberative selection of the best available new home when their old nest is still intact. The algorithm uses a stepwise commitment scheme and a quorum rule to integrate information gathered by numerous individual ants visiting several candidate homes. By varying the rates at which they search for and accept these candidates, the ants yield a colony-level response that adaptively emphasizes either speed or accuracy. We propose such general but tunable algorithms as a design feature of complex systems...

‣ Modern proteomes contain putative imprints of ancient shifts in trace metal geochemistry

Dupont, Christopher L.; Yang, Song; Palenik, Brian; Bourne, Philip E.
Fonte: National Academy of Sciences Publicador: National Academy of Sciences
Tipo: Artigo de Revista Científica
Português
Relevância na Pesquisa
451.23344%
Because of the rise in atmospheric oxygen 2.3 billion years ago (Gya) and the subsequent changes in oceanic redox state over the last 2.3–1 Gya, trace metal bioavailability in marine environments has changed dramatically. Although theorized to have influenced the biological usage of metals leaving discernable genomic signals, a thorough and quantitative test of this hypothesis has been lacking. Using structural bioinformatics and whole-genome sequences, the Fe-, Zn-, Mn-, and Co-binding metallomes of 23 Archaea, 233 Bacteria, and 57 Eukarya were constructed. These metallomes reveal that the overall abundances of these metal-binding structures scale to proteome size as power laws with a unique set of slopes for each Superkingdom of Life. The differences in the power describing the abundances of Fe-, Mn-, Zn-, and Co-binding proteins in the proteomes of Prokaryotes and Eukaryotes are similar to the theorized changes in the abundances of these metals after the oxygenation of oceanic deep waters. This phenomenon suggests that Prokarya and Eukarya evolved in anoxic and oxic environments, respectively, a hypothesis further supported by structures and functions of Fe-binding proteins in each Superkingdom. Also observed is a proliferation in the diversity of Zn-binding protein structures involved in protein–DNA and protein–protein interactions within Eukarya...

‣ A fully integrated microfluidic genetic analysis system with sample-in–answer-out capability

Easley, Christopher J.; Karlinsey, James M.; Bienvenue, Joan M.; Legendre, Lindsay A.; Roper, Michael G.; Feldman, Sanford H.; Hughes, Molly A.; Hewlett, Erik L.; Merkel, Tod J.; Ferrance, Jerome P.; Landers, James P.
Fonte: National Academy of Sciences Publicador: National Academy of Sciences
Tipo: Artigo de Revista Científica
Português
Relevância na Pesquisa
451.23344%
We describe a microfluidic genetic analysis system that represents a previously undescribed integrated microfluidic device capable of accepting whole blood as a crude biological sample with the endpoint generation of a genetic profile. Upon loading the sample, the glass microfluidic genetic analysis system device carries out on-chip DNA purification and PCR-based amplification, followed by separation and detection in a manner that allows for microliter samples to be screened for infectious pathogens with sample-in–answer-out results in <30 min. A single syringe pump delivers sample/reagents to the chip for nucleic acid purification from a biological sample. Elastomeric membrane valving isolates each distinct functional region of the device and, together with resistive flow, directs purified DNA and PCR reagents from the extraction domain into a 550-nl chamber for rapid target sequence PCR amplification. Repeated pressure-based injections of nanoliter aliquots of amplicon (along with the DNA sizing standard) allow electrophoretic separation and detection to provide DNA fragment size information. The presence of Bacillus anthracis (anthrax) in 750 nl of whole blood from living asymptomatic infected mice and of Bordetella pertussis in 1 μl of nasal aspirate from a patient suspected of having whooping cough are confirmed by the resultant genetic profile.

‣ Fusicoccins are biosynthesized by an unusual chimera diterpene synthase in fungi

Toyomasu, Tomonobu; Tsukahara, Mai; Kaneko, Akane; Niida, Rie; Mitsuhashi, Wataru; Dairi, Tohru; Kato, Nobuo; Sassa, Takeshi
Fonte: National Academy of Sciences Publicador: National Academy of Sciences
Tipo: Artigo de Revista Científica
Português
Relevância na Pesquisa
451.23344%
Fusicoccins are a class of diterpene glucosides produced by the plant-pathogenic fungus Phomopsis amygdali. As modulators of 14-3-3 proteins, fusicoccins function as potent activators of plasma membrane H+-ATPase in plants and also exhibit unique biological activity in animal cells. Despite their well studied biological activities, no genes encoding fusicoccin biosynthetic enzymes have been identified. Cyclic diterpenes are commonly synthesized via cyclization of a C20 precursor, geranylgeranyl diphosphate (GGDP), which is produced through condensation of the universal C5 isoprene units dimethylallyl diphosphate and isopentenyl diphosphate by prenyltransferases. We found that (+)-fusicocca-2,10 (14)-diene, a tricyclic hydrocarbon precursor for fusicoccins, is biosynthesized from the C5 isoprene units by an unusual multifunctional enzyme, P. amygdali fusicoccadiene synthase (PaFS), which shows both prenyltransferase and terpene cyclase activities. The functional analysis of truncated mutants and site-directed mutagenesis demonstrated that PaFS consists of two domains: a terpene cyclase domain at the N terminus and a prenyltransferase domain at the C terminus. These findings suggest that fusicoccadiene can be produced efficiently in the fungus by using the C5 precursors...

‣ HIV-1 Vpr function is mediated by interaction with the damage-specific DNA-binding protein DDB1

Schröfelbauer, Bärbel; Hakata, Yoshiyuki; Landau, Nathaniel R.
Fonte: National Academy of Sciences Publicador: National Academy of Sciences
Tipo: Artigo de Revista Científica
Português
Relevância na Pesquisa
451.23344%
The Vpr accessory protein of HIV-1 induces a response similar to that of DNA damage. In cells expressing Vpr, the DNA damage sensing kinase, ATR, is activated, resulting in G2 arrest and apoptosis. In addition, Vpr causes rapid degradation of the uracil-DNA glycosylases UNG2 and SMUG1. Although several cellular proteins have been reported to bind to Vpr, the mechanism by which Vpr mediates its biological effects is unknown. Using tandem affinity purification and mass spectrometry, we identified a predominant cellular protein that binds to Vpr as the damage-specific DNA-binding protein 1 (DDB1). In addition to its role in the repair of damaged DNA, DDB1 is a component of an E3 ubiquitin ligase that degrades numerous cellular substrates. Interestingly, DDB1 is targeted by specific regulatory proteins of other viruses, including simian virus 5 and hepatitis B. We show that the interaction with DDB1 mediates Vpr-induced apoptosis and UNG2/SMUG1 degradation and impairs the repair of UV-damaged DNA, which could account for G2 arrest and apoptosis. The interaction with DDB1 may explain several of the diverse biological functions of Vpr and suggests potential roles for Vpr in HIV-1 replication.

‣ Accurate, conformation-dependent predictions of solvent effects on protein ionization constants

Barth, P.; Alber, T.; Harbury, P. B.
Fonte: National Academy of Sciences Publicador: National Academy of Sciences
Tipo: Artigo de Revista Científica
Português
Relevância na Pesquisa
451.23344%
Predicting how aqueous solvent modulates the conformational transitions and influences the pKa values that regulate the biological functions of biomolecules remains an unsolved challenge. To address this problem, we developed FDPB_MF, a rotamer repacking method that exhaustively samples side chain conformational space and rigorously calculates multibody protein–solvent interactions. FDPB_MF predicts the effects on pKa values of various solvent exposures, large ionic strength variations, strong energetic couplings, structural reorganizations and sequence mutations. The method achieves high accuracy, with root mean square deviations within 0.3 pH unit of the experimental values measured for turkey ovomucoid third domain, hen lysozyme, Bacillus circulans xylanase, and human and Escherichia coli thioredoxins. FDPB_MF provides a faithful, quantitative assessment of electrostatic interactions in biological macromolecules.

‣ Predicting protein–protein interactions based only on sequences information

Shen, Juwen; Zhang, Jian; Luo, Xiaomin; Zhu, Weiliang; Yu, Kunqian; Chen, Kaixian; Li, Yixue; Jiang, Hualiang
Fonte: National Academy of Sciences Publicador: National Academy of Sciences
Tipo: Artigo de Revista Científica
Português
Relevância na Pesquisa
451.23344%
Protein–protein interactions (PPIs) are central to most biological processes. Although efforts have been devoted to the development of methodology for predicting PPIs and protein interaction networks, the application of most existing methods is limited because they need information about protein homology or the interaction marks of the protein partners. In the present work, we propose a method for PPI prediction using only the information of protein sequences. This method was developed based on a learning algorithm-support vector machine combined with a kernel function and a conjoint triad feature for describing amino acids. More than 16,000 diverse PPI pairs were used to construct the universal model. The prediction ability of our approach is better than that of other sequence-based PPI prediction methods because it is able to predict PPI networks. Different types of PPI networks have been effectively mapped with our method, suggesting that, even with only sequence information, this method could be applied to the exploration of networks for any newly discovered protein with unknown biological relativity. In addition, such supplementary experimental information can enhance the prediction ability of the method.

‣ Directing macromolecular conformation through halogen bonds

Voth, Andrea Regier; Hays, Franklin A.; Ho, P. Shing
Fonte: National Academy of Sciences Publicador: National Academy of Sciences
Tipo: Artigo de Revista Científica
Português
Relevância na Pesquisa
451.23344%
The halogen bond, a noncovalent interaction involving polarizable chlorine, bromine, or iodine molecular substituents, is now being exploited to control the assembly of small molecules in the design of supramolecular complexes and new materials. We demonstrate that a halogen bond formed between a brominated uracil and phosphate oxygen can be engineered to direct the conformation of a biological molecule, in this case to define the conformational isomer of a four-stranded DNA junction when placed in direct competition against a classic hydrogen bond. As a result, this bromine interaction is estimated to be ≈2–5 kcal/mol stronger than the analogous hydrogen bond in this environment, depending on the geometry of the halogen bond. This study helps to establish halogen bonding as a potential tool for the rational design and construction of molecular materials with DNA and other biological macromolecules.

‣ Multiple reaction monitoring for robust quantitative proteomic analysis of cellular signaling networks

Wolf-Yadlin, Alejandro; Hautaniemi, Sampsa; Lauffenburger, Douglas A.; White, Forest M.
Fonte: National Academy of Sciences Publicador: National Academy of Sciences
Tipo: Artigo de Revista Científica
Português
Relevância na Pesquisa
451.23344%
Although recent developments in MS have enabled the identification and quantification of hundreds of phosphorylation sites from a given biological sample, phosphoproteome analysis by MS has been plagued by inconsistent reproducibility arising from automated selection of precursor ions for fragmentation, identification, and quantification. To address this challenge, we have developed a new MS-based strategy, based on multiple reaction monitoring of stable isotope-labeled peptides, that enables highly reproducible quantification of hundreds of nodes (phosphorylation sites) within a signaling network and across multiple conditions simultaneously. We have applied this strategy to quantify temporal phosphorylation profiles of 222 tyrosine phosphorylated peptides across seven time points following EGF treatment, including 31 tyrosine phosphorylation sites not previously known to be regulated by EGF stimulation. With this approach, 88% of the signaling nodes were reproducibly quantified in four analyses, as compared with only 34% by typical information-dependent analysis. As a result of the improved reproducibility, full temporal phosphorylation profiles were generated for an additional 104 signaling nodes with the multiple reaction monitoring strategy...

‣ Oncogenic inhibition by a deleted in liver cancer gene requires cooperation between tensin binding and Rho-specific GTPase-activating protein activities

Qian, Xiaolan; Li, Guorong; Asmussen, Holly K.; Asnaghi, Laura; Vass, William C.; Braverman, Richard; Yamada, Kenneth M.; Popescu, Nicholas C.; Papageorge, Alex G.; Lowy, Douglas R.
Fonte: National Academy of Sciences Publicador: National Academy of Sciences
Tipo: Artigo de Revista Científica
Português
Relevância na Pesquisa
451.23344%
The three deleted in liver cancer genes (DLC1–3) encode Rho-GTPase-activating proteins (RhoGAPs) whose expression is frequently down-regulated or silenced in a variety of human malignancies. The RhoGAP activity is required for full DLC-dependent tumor suppressor activity. Here we report that DLC1 and DLC3 bind to human tensin1 and its chicken homolog. The binding has been mapped to the tensin Src homology 2 (SH2) and phosphotyrosine binding (PTB) domains at the C terminus of tensin proteins. Distinct DLC1 sequences are required for SH2 and PTB binding. DCL binding to both domains is constitutive under basal conditions. The SH2 binding depends on a tyrosine in DCL1 (Y442) but is phosphotyrosine-independent, a highly unusual feature for SH2 binding. DLC1 competed with the binding of other proteins to the tensin C terminus, including β3-integrin binding to the PTB domain. Point mutation of a critical tyrosine residue (Y442F) in DLC1 rendered the protein deficient for binding the tensin SH2 domain and binding full-length tensin. The Y442F protein was diffusely cytoplasmic, in contrast to the localization of wild-type DLC1 to focal adhesions, but it retained the ability to reduce the intracellular levels of Rho-GTP. The Y442F mutant displayed markedly reduced biological activity...

‣ Protein structure determination from NMR chemical shifts

Cavalli, Andrea; Salvatella, Xavier; Dobson, Christopher M.; Vendruscolo, Michele
Fonte: National Academy of Sciences Publicador: National Academy of Sciences
Tipo: Artigo de Revista Científica
Português
Relevância na Pesquisa
451.23344%
NMR spectroscopy plays a major role in the determination of the structures and dynamics of proteins and other biological macromolecules. Chemical shifts are the most readily and accurately measurable NMR parameters, and they reflect with great specificity the conformations of native and nonnative states of proteins. We show, using 11 examples of proteins representative of the major structural classes and containing up to 123 residues, that it is possible to use chemical shifts as structural restraints in combination with a conventional molecular mechanics force field to determine the conformations of proteins at a resolution of 2 Å or better. This strategy should be widely applicable and, subject to further development, will enable quantitative structural analysis to be carried out to address a range of complex biological problems not accessible to current structural techniques.

‣ X-ray fluorescence microscopy reveals large-scale relocalization and extracellular translocation of cellular copper during angiogenesis

Finney, Lydia; Mandava, Suneeta; Ursos, Lyann; Zhang, Wen; Rodi, Diane; Vogt, Stefan; Legnini, Daniel; Maser, Jorg; Ikpatt, Francis; Olopade, Olufunmilayo I.; Glesne, David
Fonte: National Academy of Sciences Publicador: National Academy of Sciences
Tipo: Artigo de Revista Científica
Português
Relevância na Pesquisa
451.23344%
Although copper has been reported to influence numerous proteins known to be important for angiogenesis, the enhanced sensitivity of this developmental process to copper bioavailability has remained an enigma, because copper metalloproteins are prevalent and essential throughout all cells. Recent developments in x-ray optics at third-generation synchrotron sources have provided a resource for highly sensitive visualization and quantitation of metalloproteins in biological samples. Here, we report the application of x-ray fluorescence microscopy (XFM) toin vitro models of angiogenesis and neurogenesis, revealing a surprisingly dramatic spatial relocalization specific to capillary formation of 80–90% of endogenous cellular copper stores from intracellular compartments to the tips of nascent endothelial cell filopodia and across the cell membrane. Although copper chelation had no effect on process formation, an almost complete ablation of network formation was observed. XFM of highly vascularized ductal carcinomas showed copper clustering in putative neoangiogenic areas. This use of XFM for the study of a dynamic developmental process not only sheds light on the copper requirement for endothelial tube formation but highlights the value of synchrotron-based facilities in biological research.

‣ Assessment of nitric oxide signals by triiodide chemiluminescence

Hausladen, Alfred; Rafikov, Ruslan; Angelo, Michael; Singel, David J.; Nudler, Evgeny; Stamler, Jonathan S.
Fonte: National Academy of Sciences Publicador: National Academy of Sciences
Tipo: Artigo de Revista Científica
Português
Relevância na Pesquisa
451.23344%
Nitric oxide (NO) bioactivity is mainly conveyed through reactions with iron and thiols, furnishing iron nitrosyls and S-nitrosothiols with wide-ranging stabilities and reactivities. Triiodide chemiluminescence methodology has been popularized as uniquely capable of quantifying these species together with NO byproducts, such as nitrite and nitrosamines. Studies with triiodide, however, have challenged basic ideas of NO biochemistry. The assay, which involves addition of multiple reagents whose chemistry is not fully understood, thus requires extensive validation: Few protein standards have in fact been characterized; NO mass balance in biological mixtures has not been verified; and recovery of species that span the range of NO-group reactivities has not been assessed. Here we report on the performance of the triiodide assay vs. photolysis chemiluminescence in side-by-side assays of multiple nitrosylated standards of varied reactivities and in assays of endogenous Fe- and S-nitrosylated hemoglobin. Although the photolysis method consistently gives quantitative recoveries, the yields by triiodide are variable and generally low (approaching zero with some standards and endogenous samples). Moreover, in triiodide, added chemical reagents...

‣ Ultradian oscillations of Stat, Smad, and Hes1 expression in response to serum

Yoshiura, Shigeki; Ohtsuka, Toshiyuki; Takenaka, Yoshiko; Nagahara, Hiroki; Yoshikawa, Kenichi; Kageyama, Ryoichiro
Fonte: National Academy of Sciences Publicador: National Academy of Sciences
Tipo: Artigo de Revista Científica
Português
Relevância na Pesquisa
451.23344%
Serum response has been used as a model for studying signaling transduction for many biological events such as cell proliferation and survival. Although expression of many genes is up- or down-regulated after serum stimulation, the Notch effector Hes1 displays oscillatory response. However, the precise mechanism and biological significance of this oscillation remain to be determined. Here, we identified serum-induced ultradian oscillators, including molecules in Stat and Smad signaling. Stat and Smad oscillations involve activation of Stat3 and Smad1 and delayed negative feedback by their inhibitors Socs3 and Smad6, respectively. Moreover, Stat oscillations induce oscillatory expression of Hes1 by regulating its half-life, and loss of Hes1 oscillations leads to G1 phase retardation of the cell cycle. These results indicate that coupled Stat and Hes1 oscillations are important for efficient cell proliferation and provide evidence that expression modes of signaling molecules affect downstream cellular events.

‣ A general model for allometric covariation in botanical form and function

Price, Charles A.; Enquist, Brian J.; Savage, Van M.
Fonte: National Academy of Sciences Publicador: National Academy of Sciences
Tipo: Artigo de Revista Científica
Português
Relevância na Pesquisa
451.23344%
The West, Brown, and Enquist (WBE) theory for the origin of allometric scaling laws is centered on the idea that the geometry of the vascular network governs how a suite of organismal traits covary with each other and, ultimately, how they scale with organism size. This core assumption has been combined with other secondary assumptions based on physiological constraints, such as minimizing the scaling of transport and biomechanical costs while maximally filling a volume. Together, these assumptions give predictions for specific “quarter-power” scaling exponents in biology. Here we provide a strong test of the core assumption of WBE by examining how well it holds when the secondary assumptions have been relaxed. Our relaxed version of WBE predicts that allometric exponents are highly constrained and covary according to specific quantitative functions. To test this core prediction, we assembled several botanical data sets with measures of the allometry of morphological traits. A wide variety of plant taxa appear to obey the predictions of the model. Our results (i) underscore the importance of network geometry in governing the variability and central tendency of biological exponents, (ii) support the hypothesis that selection has primarily acted to minimize the scaling of hydrodynamic resistance...

‣ Metabolite essentiality elucidates robustness of Escherichia coli metabolism

Kim, Pan-Jun; Lee, Dong-Yup; Kim, Tae Yong; Lee, Kwang Ho; Jeong, Hawoong; Lee, Sang Yup; Park, Sunwon
Fonte: National Academy of Sciences Publicador: National Academy of Sciences
Tipo: Artigo de Revista Científica
Português
Relevância na Pesquisa
451.23344%
Complex biological systems are very robust to genetic and environmental changes at all levels of organization. Many biological functions of Escherichia coli metabolism can be sustained against single-gene or even multiple-gene mutations by using redundant or alternative pathways. Thus, only a limited number of genes have been identified to be lethal to the cell. In this regard, the reaction-centric gene deletion study has a limitation in understanding the metabolic robustness. Here, we report the use of flux-sum, which is the summation of all incoming or outgoing fluxes around a particular metabolite under pseudo-steady state conditions, as a good conserved property for elucidating such robustness of E. coli from the metabolite point of view. The functional behavior, as well as the structural and evolutionary properties of metabolites essential to the cell survival, was investigated by means of a constraints-based flux analysis under perturbed conditions. The essential metabolites are capable of maintaining a steady flux-sum even against severe perturbation by actively redistributing the relevant fluxes. Disrupting the flux-sum maintenance was found to suppress cell growth. This approach of analyzing metabolite essentiality provides insight into cellular robustness and concomitant fragility...

‣ Searching for species in haloarchaea

Papke, R. Thane; Zhaxybayeva, Olga; Feil, Edward J.; Sommerfeld, Katrin; Muise, Denise; Doolittle, W. Ford
Fonte: National Academy of Sciences Publicador: National Academy of Sciences
Tipo: Artigo de Revista Científica
Português
Relevância na Pesquisa
451.23344%
Prokaryotic (bacterial and archaeal) species definitions and the biological concepts that underpin them entail clustering (cohesion) among individuals, in terms of genome content and gene sequence similarity. Homologous recombination can maintain gene sequence similarity within, while permitting divergence between, clusters and is thus the basis for recent efforts to apply the Biological Species Concept in prokaryote systematics and ecology. In this study, we examine isolates of the haloarchaeal genus Halorubrum from two adjacent ponds of different salinities at a Spanish saltern and a natural saline lake in Algeria by using multilocus sequence analysis. We show that, although clusters can be defined by concatenation of multiple marker sequences, barriers to exchange between them are leaky. We suggest that no nonarbitrary way to circumscribe “species” is likely to emerge for this group, or by extension, to apply generally across prokaryotes. Arbitrary criteria might have limited practical use, but still must be agreed upon by the community.

‣ The circadian clock stops ticking during deep hibernation in the European hamster

Revel, Florent G.; Herwig, Annika; Garidou, Marie-Laure; Dardente, Hugues; Menet, Jérôme S.; Masson-Pévet, Mireille; Simonneaux, Valérie; Saboureau, Michel; Pévet, Paul
Fonte: National Academy of Sciences Publicador: National Academy of Sciences
Tipo: Artigo de Revista Científica
Publicado em 21/08/2007 Português
Relevância na Pesquisa
451.23344%
Hibernation is a fascinating, yet enigmatic, physiological phenomenon during which body temperature and metabolism are reduced to save energy. During the harsh season, this strategy allows substantial energy saving by reducing body temperature and metabolism. Accordingly, biological processes are considerably slowed down and reduced to a minimum. However, the persistence of a temperature-compensated, functional biological clock in hibernating mammals has long been debated. Here, we show that the master circadian clock no longer displays 24-h molecular oscillations in hibernating European hamsters. The clock genes Per1, Per2, and Bmal1 and the clock-controlled gene arginine vasopressin were constantly expressed in the suprachiasmatic nucleus during deep torpor, as assessed by radioactive in situ hybridization. Finally, the melatonin rhythm-generating enzyme, arylalkylamine N-acetyltransferase, whose rhythmic expression in the pineal gland is controlled by the master circadian clock, no longer exhibits day/night changes of expression but constantly elevated mRNA levels over 24 h. Overall, these data provide strong evidence that in the European hamster the molecular circadian clock is arrested during hibernation and stops delivering rhythmic output signals.