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Mechanistic Basis (mechanistic + basis)
Selected AbstractsIdentification of AF Drivers: Toward a Mechanistic Basis of AF AblationPACING AND CLINICAL ELECTROPHYSIOLOGY, Issue 11 2009KENTARO YOSHIDA M.D. No abstract is available for this article. [source] Modelling species distributions without using species distributions: the cane toad in Australia under current and future climatesECOGRAPHY, Issue 4 2008Michael Kearney Accurate predictions of the potential distribution of range-shifting species are required for effective management of invasive species, and for assessments of the impact of climate change on native species. Range-shifting species pose a challenge for traditional correlative approaches to range prediction, often requiring the extrapolation of complex statistical associations into novel environmental space. Here we take an alternative approach that does not use species occurrence data, but instead captures the fundamental niche of a species by mechanistically linking key organismal traits with spatial data using biophysical models. We demonstrate this approach with a major invasive species, the cane toad Bufo marinus in Australia, assessing the direct climatic constraints on its ability to move, survive, and reproduce. We show that the current range can be explained by thermal constraints on the locomotor potential of the adult stage together with limitations on the availability of water for the larval stage. Our analysis provides a framework for biologically grounded predictions of the potential for cane toads to expand their range under current and future climate scenarios. More generally, by quantifying spatial variation in physiological constraints on an organism, trait-based approaches can be used to investigate the range-limits of any species. Assessments of spatial variation in the physiological constraints on an organism may also provide a mechanistic basis for forecasting the rate of range expansion and for understanding a species' potential to evolve at range-edges. Mechanistic approaches thus have broad application to process-based ecological and evolutionary models of range-shift. [source] Bias in the introduction of variation as an orienting factor in evolutionEVOLUTION AND DEVELOPMENT, Issue 2 2001Lev Y. Yampolsky SUMMARY According to New Synthesis doctrine, the direction of evolution is determined by selection and not by "internal causes" that act by way of propensities of variation. This doctrine rests on the theoretical claim that because mutation rates are small in comparison to selection coefficients, mutation is powerless to overcome opposing selection. Using a simple population-genetic model, this claim is shown to depend on assuming the prior availability of variation, so that mutation may act only as a "pressure" on the frequencies of existing alleles, and not as the evolutionary process that introduces novelty. As shown here, mutational bias in the introduction of novelty can strongly influence the course of evolution, even when mutation rates are small in comparison to selection coefficients. Recognizing this mode of causation provides a distinct mechanistic basis for an "internalist" approach to determining the contribution of mutational and developmental factors to evolutionary phenomena such as homoplasy, parallelism, and directionality. [source] Reciprocal insights into adaptation from agricultural and evolutionary studies in tomatoEVOLUTIONARY APPLICATIONS (ELECTRONIC), Issue 5-6 2010Leonie C. Moyle Abstract Although traditionally separated by different aims and methodologies, research on agricultural and evolutionary problems shares a common goal of understanding the mechanisms underlying functionally important traits. As such, research in both fields offers potential complementary and reciprocal insights. Here, we discuss adaptive stress responses (specifically to water stress) as an example of potentially fruitful research reciprocity, where agricultural research has clearly produced advances that could benefit evolutionary studies, while evolutionary studies offer approaches and insights underexplored in crop studies. We focus on research on Solanum species that include the domesticated tomato and its wild relatives. Integrated approaches to understanding ecological adaptation are particularly attractive in tomato and its wild relatives: many presumptively adaptive phenotypic differences characterize wild species, and the physiological and mechanistic basis of many relevant traits and environmental responses has already been examined in the context of cultivated tomato and some wild species. We highlight four specific instances where these reciprocal insights can be combined to better address questions that are fundamental both to agriculture and evolution. [source] Comparative analysis of MLL partial tandem duplication and FLT3 internal tandem duplication mutations in 956 adult patients with acute myeloid leukemiaGENES, CHROMOSOMES AND CANCER, Issue 3 2003Christine Steudel Partial tandem duplication (PTD) of the MLL gene and internal tandem duplication (ITD) of the juxtamembrane region of the FLT3 receptor tyrosine kinase gene have been described in acute myeloid leukemia (AML) patients, preferentially in those with normal cytogenetics. These alterations have been associated with a poor prognosis. In our study, we analyzed the prevalence and the potential prognostic impact of these aberrations in a large unselected and well-defined cohort of 956 patients with AML. Results were correlated with cytogenetic data and clinical outcome. MLL PTD was detected by RT-PCR, subsequent nucleotide sequencing, and Southern blotting. The overall incidence was found to be 5.0% (48/956), whereas FLT3 ITD was detected in 19.2% (184/956). Sixteen cases were positive for both alterations. The rate of MLL PTD in FLT3 ITD positive patients was significantly higher than that in FLT3 ITD negative patients [16/184 (8.7%); 32/772 (4.1%); P = 0.025]. However, both aberrations were highly increased in patients with normal karyotype (MLL PTD 35/431, P = 0.004; FLT3 ITD 132/334, P < 0.001). When restricted to this subgroup, the rate of MLL PTD in patients with FLT3 mutations was not significantly increased. No statistically significant differences were detected between patients positive for MLL PTD and patients negative for MLL PTD in the rate of complete remissions or the overall survival, although we did see a significantly shorter disease-free survival in patients age 60 or younger. In conclusion, although there is an overlap in the mutational spectrum in AML with FLT3 ITD and MLL PTD mutations, our data do not support a common mechanistic basis. Although associated with inferior disease-free survival, the results of this study do not unequivocally support the notion that MLL PTD mutations represent an independent prognostic factor. © 2003 Wiley-Liss, Inc. [source] Transcriptional regulatory cascades controlling plasma cell differentiationIMMUNOLOGICAL REVIEWS, Issue 1 2003Kuo-I Lin Summary:, Plasma cells are the terminally differentiated effector cells of the B lymphocyte lineage. Recently, studies using genetically altered mice and analyses of global gene expression programs have significantly expanded our understanding of the molecular mechanisms regulating plasmacytic differentiation. Specific molecular components of a multistep cascade of transcriptional regulators have been identified. Furthermore, two transcriptional regulators, X box binding protein-1 (XBP-1) and B lymphocyte induced maturation protein-1 (Blimp-1), have been shown to be necessary for plasmacytic differentiation. In addition to providing a mechanistic basis for the induction of genes necessary for immunoglobulin secretion, cessation of cell cycle and other phenotypic changes characteristic of terminally differentiated plasma cells, these studies have led to the important concept that plasmacytic differentiation involves repression of regulators, such as Bcl-6 and Pax5, that are necessary to maintain the earlier developmental phenotype of activated, germinal center B cells. This review describes our current understanding of the transcriptional cascades regulating terminal differentiation of B cells. [source] In Vitro Selection of Self-Interacting Transmembrane Segments--Membrane Proteins Approached from a Different PerspectiveIUBMB LIFE, Issue 3 2002Dieter Langosch Abstract The principles underlying the folding of integral membrane proteins are uncovered in an increasingly detailed way. Experimental determination of high-resolution structures followed by analysis of packing reveal structural similarities as well as differences to soluble globular proteins. At the same time, protein/protein interactions at the level of membrane-embedded domains have been investigated for different model proteins. More recently, self-interacting transmembrane helices have been selected from combinatorial libraries in vitro to study the mechanistic basis of protein/protein interaction in membranes in a systematic way. With an emphasis on the latter approach, this review discusses insights emerging from an integrated view on the recent advances. [source] TCDD suppresses insulin-responsive glucose transporter (GLUT-4) gene expression through C/EBP nuclear transcription factors in 3T3-L1 adipocytesJOURNAL OF BIOCHEMICAL AND MOLECULAR TOXICOLOGY, Issue 2 2006Phillip Chin-Chen Liu Abstract TCDD is known to reduce significantly the level of the functionally active form of glucose transporter type 4 (GLUT4) in vivo in adipose tissue and muscles. To study the mechanistic basis of this phenomenon, we conducted transient transfection and DNA deletion analysis in 3T3-L1 cells using chloramphenicol acetyltransferase (CAT) reporter plasmids containing the GLUT4 promoter joined to the bacterial CAT. It was found that in transfected control samples, CAT activity was significantly higher in cells transfected with p469CAT and p273CAT than those with p78CAT, indicating that the region between ,78 and ,273 contained elements that play major roles in transactivation of this gene. Treatment with TCDD decreased CAT activity with p469CAT and p273CAT, but not with p78CAT, indicating the same region to contain the element(s) affected by TCDD. A gel-shift (EMSA) analysis result indicated that TCDD shows the profound effect only on the nuclear proteins binding to the [32P]-labeled probe containing C/EBP response element equivalent of the ,265 to ,242 stretch of the GLUT4 promoter. The results of supershift analysis showed that TCDD caused a decrease in the tier of C/EBP, and an increase in that of C/EBP, among the proteins bound to this C/EBP response element. We studied the effect of TCDD in cells overexpressing either C/EBP,, C/EBP,, or C/EBP, through transient transfection of p273CAT or p469CAT. The results clearly showed that the effect of TCDD to suppress the CAT activity of p273 or p469 disappeared in those cells overexpressing C/EBP, or C/EBP,. These results implicate the C/EBP proteins to be the main mediator of suppressive action of TCDD on GLUT4 gene expression in 3T3-L1 cells. © 2006 Wiley Periodicals, Inc. J Biochem Mol Toxicol 20:79,87, 2006; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/jbt.20120 [source] Endocardial Noncontact Activation Mapping of Idiopathic Left Ventricular TachycardiaJOURNAL OF CARDIOVASCULAR ELECTROPHYSIOLOGY, Issue 12 2000JASBIR SRA M.D. Mapping of Idiopathic Ventricular Tachycardia. Idiopathic left ventricular tachycardia with a right bundle, left-axis deviation is thought to originate from posterior fascicles. Recently, there has been considerable interest in the anatomic and mechanistic basis of this arrhythmia. We report our experience with a 26-year-old man in whom new noncontact mapping technology was used to acquire detailed data from the left ventricle, identify the mid-diastolic potential and part of the ventricular tachycardia circuit, and perform successful ablation. This information helped define the physiologic aspects of this unique tachycardia. [source] Cellular stress triggers TEL nuclear export via two genetically separable pathwaysJOURNAL OF CELLULAR BIOCHEMISTRY, Issue 2 2008Caroline A. Hanson Abstract TEL (translocation ets leukemia, also known as ETV6) is a repressor of transcription that is disrupted by the t(12;21), which is the most frequent chromosomal translocation in pediatric acute lymphocytic leukemia. TEL is modified by SUMOylation, and the lysine (Lys 99) that is conjugated to SUMO is required for TEL nuclear export. In addition, TEL is phosphorylated by p38 kinase, which is activated by cellular stress. Induction of cellular stress reduced the ability of TEL to repress transcription in vitro, but the mechanistic basis of this phenomenon was unclear. In this study, we show that osmotic stress causes re-localization of TEL to the cytoplasm and that p38-mediated phosphorylation of TEL is sufficient for this re-localization. However, impairment of both SUMOylation of Lys 99 and p38-dependent phosphorylation of Ser 257 of TEL were required to impair the re-localization of TEL in response to cellular stress induced by high salt, identifying two separate nuclear export pathways. Thus, alteration of the cellular localization of TEL may be a part of the cellular stress response and re-localization of TEL to the cytoplasm is an important step in the regulation of TEL. J. Cell. Biochem. 104: 488,498, 2008. © 2007 Wiley-Liss, Inc. [source] Regulation of lipopolysaccharide-induced inflammatory response and endotoxemia by ,-arrestins,JOURNAL OF CELLULAR PHYSIOLOGY, Issue 2 2010Katie J. Porter ,-Arrestins are scaffolding proteins implicated as negative regulators of TLR4 signaling in macrophages and fibroblasts. Unexpectedly, we found that ,-arrestin-1 (,-arr-1) and -2 knockout (KO) mice are protected from TLR4-mediated endotoxic shock and lethality. To identify the potential mechanisms involved, we examined the plasma levels of inflammatory cytokines/chemokines in the wild-type (WT) and ,-arr-1 and -2 KO mice after lipopolysaccharide (LPS, a TLR4 ligand) injection. Consistent with lethality, LPS-induced inflammatory cytokine levels in the plasma were markedly decreased in both ,-arr-1 and -2 KO, compared to WT mice. To further explore the cellular mechanisms, we obtained splenocytes (separated into CD11b+ and CD11b, populations) from WT, ,-arr-1, and -2 KO mice and examined the effect of LPS on cytokine production. Similar to the in vivo observations, LPS-induced inflammatory cytokines were significantly blocked in both splenocyte populations from the ,-arr-2 KO compared to the WT mice. This effect in the ,-arr-1 KO mice, however, was restricted to the CD11b, splenocytes. Our studies further indicate that regulation of cytokine production by ,-arrestins is likely independent of MAPK and I,B,-NF,B pathways. Our results, however, suggest that LPS-induced chromatin modification is dependent on ,-arrestin levels and may be the underlying mechanistic basis for regulation of cytokine levels by ,-arrestins in vivo. Taken together, these results indicate that ,-arr-1 and -2 mediate LPS-induced cytokine secretion in a cell-type specific manner and that both ,-arrestins have overlapping but non-redundant roles in regulating inflammatory cytokine production and endotoxic shock in mice. J. Cell. Physiol. 225: 406,416, 2010. © 2010 Wiley-Liss, Inc. [source] Diuretic-Related Side Effects: Development and TreatmentJOURNAL OF CLINICAL HYPERTENSION, Issue 9 2004Domenic A. Sica MD Diuretics are important therapeutic tools. First, they effectively reduce blood pressure and have been shown in numerous hypertension clinical trials to reduce both cardiovascular and cerebrovascular morbidity and mortality. In addition, their use has been equally effective in controlling cardiovascular events as angiotensin-converting enzyme inhibitors or calcium channel blockers. Diuretics are currently recommended by the Seventh Report of the Joint National Commission on Prevention, Detection, Evaluation, and Treatment of High Blood Pressure report as first-line therapy for the treatment of hypertension. In addition, they remain an important aspect of congestive heart failure treatment in that they improve the congestive symptomatology, which typifies the more advanced stages of congestive heart failure. This article reviews the commonly encountered side effects with the various diuretic classes. Where indicated, the mechanistic basis and treatment of such side effects is further discussed. [source] An ecologist's guide to ecogenomicsJOURNAL OF ECOLOGY, Issue 1 2007N. J. OUBORG Summary 1Currently, plant ecologists are increasingly adopting approaches and techniques from molecular biology. The new field of ecogenomics aims at understanding the mechanistic basis for adaptation and phenotypic variation by using genomic techniques to investigate the mechanistic and evolutionary basis of species interactions, and focuses on identifying the genes affected by evolution. 2While the entire toolbox of genomics is only available for model species such as Arabidopsis thaliana, we describe the options open to ecologists interested in pursuing an ecogenomics research program on ecologically relevant traits or phenomena in non-model species, for which part of the genomic toolbox may be currently unavailable. In these non-model species, a viable ecogenomics research program is possible with relatively modest effort. 3Four challenges to further development of ecogenomics are described and discussed: (i) the ecogenomic study of non-model species; (ii) reconciliation of experimental languages of ecology and evolutionary biology with molecular biology; (iii) development of specific ecogenomic data analysis tool; and (iv) adoption of a multidisciplinary cooperative research culture. 4An important task for ecologists is to provide the necessary ecological input (the ,eco' part) to ecogenomics. [source] Trade-offs between longevity and pathogen resistance in Drosophila melanogaster are mediated by NF,B signalingAGING CELL, Issue 6 2006Sergiy Libert Summary The innate immune response protects numerous organisms, including humans, from the universe of pathogenic molecules, viruses and micro-organisms. Despite its role in promoting pathogen resistance, inappropriate activation and expression of NF,B and other immunity-related effector molecules can lead to cancer, inflammation, and other diseases of aging. Understanding the mechanisms leading to immune system activation as well as the short- and long-term consequences of such activation on health and lifespan is therefore critical for the development of beneficial immuno-modulating and longevity-promoting interventions. Mechanisms of innate immunity are highly conserved across species, and we take advantage of genetic tools in the model organism, Drosophila melanogaster, to study the effects of acute and chronic activation of immunity pathways on pathogen resistance and general fitness of adult flies. Our findings indicate that fat body specific overexpression of a putative pathogen recognition molecule, peptidoglycan recognition protein (PGRP-LE), is sufficient for constitutive up-regulation of the immune response and for enhanced pathogen resistance. Primary components of fitness are unaffected by acute activation, but chronic activation leads to an inflammatory state and reduced lifespan. These phenotypes are dependent on the NF,B-related transcriptional factor, Relish, and they establish a mechanistic basis for a link between immunity, inflammation, and longevity. [source] Musculoskeletal underpinnings to differences in killing behavior between North American accipiters (Falconiformes: Accipitridae) and falcons (Falconidae)JOURNAL OF MORPHOLOGY, Issue 3 2008Diego Sustaita Abstract Accipiters (Accipiter spp.) and falcons (Falco spp.) both use their feet to seize prey, but falcons kill primarily with their beaks, whereas accipiters kill with their feet. This study examines the mechanistic basis to differences in their modes of dispatching prey, by focusing on the myology and biomechanics of the jaws, digits, and distal hindlimb. Bite, grip, and distal hindlimb flexion forces were estimated from measurements of physiological cross-sectional area (PCSA) and indices of mechanical advantage (MA) for the major jaw adductors, and digit and tarsometatarsal flexors. Estimated bite force, total jaw adductor PCSA, and jaw MA (averaged over adductors) tended to be relatively and absolutely greater in falcons, reflecting their emphasis on biting for dispatching their prey. Differences between genera in estimated grip force, total digit flexor PCSA, and digit MA (averaged over inter-phalangeal joints and digits) were not as clear-cut; each of these parameters scaled positively allometric in accipiters, which may reflect the scaling of both prey size, and the proportion of mammalian prey consumed by this lineage with increasing body size. Estimated tarsometatarsal force was greater in falcons than in accipiters, due to their greater MA, which may reflect selection for incurring greater forces during prey strikes. Conversely, the comparatively lower tarsometatarsal MA in accipiters reflects their capacity for greater foot speed potentially necessary for grasping elusive prey. Thus, this study elucidates how differences in jaw and hindlimb musculoskeletal morphology of accipiters and falcons are reflected in differences in their killing modes, and through differences in their force-generating capacities. J. Morphol., 2008. © 2007 Wiley-Liss, Inc. [source] SEQUENCE ANALYSIS AND TRANSCRIPTIONAL REGULATION OF IRON ACQUISITION GENES IN TWO MARINE DIATOMS,JOURNAL OF PHYCOLOGY, Issue 4 2007Adam B. Kustka The centric diatom Thalassiosira pseudonana Hasle et Heimdal and the pennate diatom Phaeodactylum tricornutum Bohlin possess genes with translated sequences homologous to high-affinity ferric reductases present in model organisms. Thalassiosira pseudonana also possesses putative genes for membrane-bound ferroxidase (TpFET3) and two highly similar iron (Fe) permeases (TpFTR1 and TpFTR2), as well as a divalent metal (M2+) transporter belonging to the NRAMP superfamily (TpNRAMP). In baker's yeast, the ferroxidase,permease complex transports Fe(II) produced by reductases. We investigated transcript abundances of these genes as a function of Fe quota (QFe). Ferric reductase transcripts are abundant in both species (15%,60% of actin) under low QFe and are down-regulated by 5- to 35-fold at high QFe, suggesting Fe(III) reduction is a common, inducible strategy for Fe acquisition in marine diatoms. Permease transcript abundance was regulated by Fe status in T. pseudonana, but we did not detect significant differences in expression of the copper (Cu)-containing ferroxidase. TpNRAMP showed the most dramatic regulation by QFe, suggesting a role in cellular Fe transport in either cell-surface uptake or vacuolar mobilization. We could not identify ferroxidase or permease homologues in the P. tricornutum genome. The up-regulation of genes in T. pseudonana that appear to be missing altogether from P. tricornutum as well as the finding that P. tricornutum seems to have an efficient system to acquire Fe,, suggest that diverse (and uncharacterized) Fe-uptake systems may be at play within diatom assemblages. Different uptake systems among diatoms may provide a mechanistic basis for niche differentiation with respect to Fe availability in the ocean. [source] Variations in body melanization impact desiccation resistance in Drosophila immigrans from Western HimalayasJOURNAL OF ZOOLOGY, Issue 2 2008R. Parkash Abstract Ectothermic species face problems of water balance under colder and drier climatic conditions in montane localities. We investigated five ecophysiological traits (body melanization, desiccation resistance, rate of water loss or gain and body size) in eight populations of Drosophila immigrans from an altitudinal gradient (600,2226 m) in the Western Himalayas. The traits showed bell-shaped variability patterns characteristic of quantitative traits. For body melanization, we observed high heritability (0.65) on the basis of parent,offspring regression. A comparison of highland versus foothill populations showed significant divergence for all the traits except body size. Darker flies from the highlands exhibited higher desiccation resistance but reduced rate of water loss or gain as compared with lighter flies from the foothills, which showed lower desiccation resistance and higher rates of water loss as well as gain. Lack of differences in the amount of epicuticular lipids cannot account for differential reduction in cuticular water loss in altitudinal populations. However, within- as well as between-population differences in body melanization can account for changes in desiccation resistance and reduction in cuticular water loss. Analyses of highland versus lowland populations as well as in assorted darker and lighter flies from a highland population have shown differences in haemolymph and dehydration tolerance. For the mechanistic basis of desiccation resistance, our results on wild populations of Drosophila immigrans are not in agreement with those reported for laboratory-selected desiccation-resistant strains in Drosophila melanogaster. Thus, ecophysiological mechanisms could be different under laboratory versus field selection. [source] Systematic review: the application of molecular pathogenesis to prevention and treatment of oesophageal adenocarcinomaALIMENTARY PHARMACOLOGY & THERAPEUTICS, Issue 11 2007C. J. PETERS Summary Background Oesophageal adenocarcinoma is an increasingly common cancer with a poor prognosis. It develops in a stepwise progression from Barrett's metaplasia to dysplasia, and then adenocarcinoma followed by metastasis. Aim To outline the key molecular changes in oesophageal adenocarcinoma and to summarize the chemopreventative and therapeutic strategies proposed. Methods A literature search was performed to identify appropriate research papers in the field. Search terms included: Barrett's (o)esophagus, intestinal metaplasia, (o)esophageal adenocarcinoma, molecular changes, genetic changes, pathogenesis, chemoprevention, therapeutic strategies and treatment. The search was restricted to English language articles. Results A large number of molecular changes have been identified in the progression from Barrett's oesophagus to oesophageal adenocarcinoma although there does not appear to be an obligate order of events. Potential chemoprevention strategies include acid suppression, anti-inflammatory agents and antioxidants. In established adenocarcinoma, targeted treatments under evaluation include receptor tyrosine kinase inhibitors of EGFR and cyclin-dependent kinase inhibitors, which may benefit a subgroup of patients. Conclusions Advances in molecular methodology have led to a greater understanding of the oesophageal adenocarcinoma pathways, which provides opportunities for chemoprevention and therapeutic strategies with a mechanistic basis. More work is required to assess both the safety and efficacy of these new treatments. [source] Thyrocyte integration, and thyroid folliculogenesis and tissue regeneration: Perspective for thyroid tissue engineeringPATHOLOGY INTERNATIONAL, Issue 6 2001Shuji Toda The thyroid gland is composed of many ball-like structures called thyroid follicles, which are supported by the interfollicular extracellular matrix (ECM) and a capillary network. The component thyrocytes are highly integrated in their specific structural and functional polarization. In conventional monolayer and floating culture systems, thyrocytes cannot organize themselves into follicles with normal polarity. In contrast, in 3-D collagen gel culture, thyrocytes easily form stable follicles with physiological polarity. Integration of thyrocyte growth and differentiation results ultimately in thyroid folliculogenesis. This culture method and subacute thyroiditis are two promising models for addressing mechanisms of folliculogenesis, because thyroid-follicle formation actively occurs both in the culture system and at the regenerative phase of the disorder. The understanding of the mechanistic basis of folliculogenesis is prerequisite for generation of artificial thyroid tissue, which would enable a more physiological strategy to the treatment of hypothyroidism caused by various diseases and surgical processes than conventional hormone replacement therapy. We review here thyrocyte integration, and thyroid folliculogenesis and tissue regeneration. We also briefly discuss a perspective for thyroid tissue regeneration and engineering. [source] Triptan-induced latent sensitization: A possible basis for medication overuse headacheANNALS OF NEUROLOGY, Issue 3 2010Milena De Felice PhD Objective Identification of the neural mechanisms underlying medication overuse headache resulting from triptans. Methods Triptans were administered systemically to rats by repeated intermittent injections or by continuous infusion over 6 days. Periorbital and hind paw sensory thresholds were measured to detect cutaneous allodynia. Immunofluorescent histochemistry was employed to detect changes in peptidic neurotransmitter expression in identified dural afferents. Enzyme-linked immunoabsorbent assay was used to measure calcitonin gene-related peptide (CGRP) levels in blood. Results Sustained or repeated administration of triptans to rats elicited time-dependent and reversible cutaneous tactile allodynia that was maintained throughout and transiently after drug delivery. Triptan administration increased labeling for CGRP in identified trigeminal dural afferents that persisted long after discontinuation of triptan exposure. Two weeks after triptan exposure, when sensory thresholds returned to baseline levels, rats showed enhanced cutaneous allodynia and increased CGRP in the blood following challenge with a nitric oxide donor. Triptan treatment thus induces a state of latent sensitization characterized by persistent pronociceptive neural adaptations in dural afferents and enhanced responses to an established trigger of migraine headache in humans. Interpretation Triptans represent the treatment of choice for moderate and severe migraine headaches. However, triptan overuse can lead to an increased frequency of migraine headache. Overuse of these medications could induce neural adaptations that result in a state of latent sensitization, which might increase sensitivity to migraine triggers. The latent sensitization could provide a mechanistic basis for the transformation of migraine to medication overuse headache. ANN NEUROL 2010;67:325,337 [source] High cortical spreading depression susceptibility and migraine-associated symptoms in Cav2.1 S218L miceANNALS OF NEUROLOGY, Issue 1 2010Arn M. J. M. van den Maagdenberg PhD Objective The CACNA1A gene encodes the pore-forming subunit of neuronal CaV2.1 Ca2+ channels. In patients, the S218L CACNA1A mutation causes a dramatic hemiplegic migraine syndrome that is associated with ataxia, seizures, and severe, sometimes fatal, brain edema often triggered by only a mild head trauma. Methods We introduced the S218L mutation into the mouse Cacna1a gene and studied the mechanisms for the S218L syndrome by analyzing the phenotypic, molecular, and electrophysiological consequences. Results Cacna1aS218L mice faithfully mimic the associated clinical features of the human S218L syndrome. S218L neurons exhibit a gene dosage,dependent negative shift in voltage dependence of CaV2.1 channel activation, resulting in enhanced neurotransmitter release at the neuromuscular junction. Cacna1aS218L mice also display an exquisite sensitivity to cortical spreading depression (CSD), with a vastly reduced triggering threshold, an increased propagation velocity, and frequently multiple CSD events after a single stimulus. In contrast, mice bearing the R192Q CACNA1A mutation, which in humans causes a milder form of hemiplegic migraine, typically exhibit only a single CSD event after one triggering stimulus. Interpretation The particularly low CSD threshold and the strong tendency to respond with multiple CSD events make the S218L cortex highly vulnerable to weak stimuli and may provide a mechanistic basis for the dramatic phenotype seen in S218L mice and patients. Thus, the S218L mouse model may prove a valuable tool to further elucidate mechanisms underlying migraine, seizures, ataxia, and trauma-triggered cerebral edema. ANN NEUROL 2010;67:85,98 [source] Incorporating Physiological and Biochemical Mechanisms into Pharmacokinetic,Pharmacodynamic Models: A Conceptual Framework,BASIC AND CLINICAL PHARMACOLOGY & TOXICOLOGY, Issue 1 2010Svein G. Dahl In general, modelling of data has the purpose (1) to describe experimental data, (2a) to reduce the amount of data resulting from an experiment, e.g. a clinical trial and (2b) to obtain the most relevant parameters, (3) to test hypotheses and (4) to make predictions within the boundaries of experimental conditions, e.g. range of doses tested (interpolation) and out of the boundaries of the experimental conditions, e.g. to extrapolate from animal data to the situation in man. Describing the drug/xenobiotic-target interaction and the chain of biological events following the interaction is the first step to build a biologically based model. This is an approach to represent the underlying biological mechanisms in qualitative and also quantitative terms, thus being inherently connected in many aspects to systems biology. As the systems biology models may contain variables in the order of hundreds connected with differential equations, it is obvious that it is in most cases not possible to assign values to the variables resulting from experimental data. Reduction techniques may be used to create a manageable model which, however, captures the biologically meaningful events in qualitative and quantitative terms. Until now, some success has been obtained by applying empirical pharmacokinetic/pharmacodynamic models which describe direct and indirect relationships between the xenobiotic molecule and the effect, including tolerance. Some of the models may have physiological components built in the structure of the model and use parameter estimates from published data. In recent years, some progress toward semi-mechanistic models has been made, examples being chemotherapy-induced myelosuppression and glucose-endogenous insulin-antidiabetic drug interactions. We see a way forward by employing approaches to bridge the gap between systems biology and physiologically based kinetic and dynamic models. To be useful for decision making, the ,bridging' model should have a well founded mechanistic basis, but being reduced to the extent that its parameters can be deduced from experimental data, however capturing the biological/clinical essential details so that meaningful predictions and extrapolations can be made. [source] Does CTCF mediate between nuclear organization and gene expression?BIOESSAYS, Issue 1 2010Rolf Ohlsson Abstract The multifunctional zinc-finger protein CCCTC-binding factor (CTCF) is a very strong candidate for the role of coordinating the expression level of coding sequences with their three-dimensional position in the nucleus, apparently responding to a "code" in the DNA itself. Dynamic interactions between chromatin fibers in the context of nuclear architecture have been implicated in various aspects of genome functions. However, the molecular basis of these interactions still remains elusive and is a subject of intense debate. Here we discuss the nature of CTCF-DNA interactions, the CTCF-binding specificity to its binding sites and the relationship between CTCF and chromatin, and we examine data linking CTCF with gene regulation in the three-dimensional nuclear space. We discuss why these features render CTCF a very strong candidate for the role and propose a unifying model, the "CTCF code," explaining the mechanistic basis of how the information encrypted in DNA may be interpreted by CTCF into diverse nuclear functions. [source] PAD: the smoking gun behind arginine methylation signaling?BIOESSAYS, Issue 3 2005Robert B. Denman Post-translational modifications (PTM) supply the proteome with functional and regulatory diversity. Modifications including phosphorylation, acetylation and methylation have been identified in eucaryotic proteins. For all but the last, corresponding "de-modifying" enzymes exist to remove the PTM tag returning the protein to its basal state. Recently, a novel mechanism in which peptidylarginine deiminase (PAD4) converts histone H3 and H4 methyl arginine residues into citrulline was proposed to regulate estrogen-responsive gene transcription.1,2 These data, the first to provide a mechanistic basis for the dynamic changes observed in a subset of protein arginine methylated substrates,3 lead to a host of questions concerning the generality of this mechanism for non-histone targets of the protein arginine methyltransferases (PRMTs). BioEssays 27:242,246, 2005. © 2005 Wiley Periodicals, Inc. [source] Role of coordinated molecular alterations in the development of androgen-independent prostate cancer: an in vitro model that corroborates clinical observationsBJU INTERNATIONAL, Issue 1 2006YAN SHI OBJECTIVE To investigate the role of potential downstream targets of HER-2/neu, including the cell-cycle regulator p27, proliferation-associated protein Ki-67, apoptosis inhibitor Bcl-2, and signal-transduction molecule Akt (which is associated with cell survival), as the development of androgen-independent prostate cancer (AIPC) in patients who are initially responsive to androgen-ablation therapy (AAT) is a significant clinical problem. PATIENTS AND METHODS Earlier studies showed that high levels of HER-2/neu tyrosine kinase receptor expression as assessed by immunohistochemistry were significantly associated with the development of AIPC, and we hypothesised that HER-2/neu overexpression provides an alternative proliferative stimulus upon androgen depletion. We established a unique clinical model system, comprising patients who received no AAT, or who had preoperative AAT, or those with advanced tumours resistant to AAT. To test our hypothesis in vitro, we stably transfected full-length HER-2/neu cDNA in androgen-responsive LNCaP cells and examined the effects of HER-2/neu overexpression on cell proliferation, apoptosis, androgen-receptor activation, and Akt phosphorylation upon androgen deprivation by using immunohistochemistry and Western blot technique. RESULTS p27 expression was initially induced on exposure to AAT, and significantly decreased in AIPC (P < 0.001). There was also a significant increase in the Ki-67 index in AIPC (P = 0.001). Elevated Bcl-2 expression was closely associated with AAT (P = 0.002), suggesting that Bcl-2 expression is induced on initial exposure to AAT. Further, Bcl-2 expression was highest in hormone-resistant cancers (P < 0.001). Using the HER-2/neu transfected cell-line model, we confirmed the mechanistic basis of the clinical observations which elucidate the pathway leading to HER-2/neu-mediated androgen independence. On androgen deprivation, the HER-2/neu transfected cells had higher proliferation rates, lower G1 arrest, inhibited p27 up-regulation, a lower apoptotic index, and higher Bcl-2, prostate-specific antigen and phosphorylated Akt expression than the mock-transfected LNCaP cells. CONCLUSION This study suggests that prostate cancer cells undergo a series of coordinated changes after exposure to AAT, which eventually result in the development of androgen independence. Further, in support of previous results, it appears that a major factor in this process is the induction of HER-2/neu overexpression, which occurs after initial exposure to AAT. HER-2/neu may contribute to the development of androgen independence through: (i) maintaining cell proliferation; (ii) inhibiting apoptosis; and/or (iii) inducing AR activation in a ligand-independent fashion. These effects may be mediated, at least in part, through activation of the PI3K/Akt pathway. [source] Danofloxacin-mesylate is a substrate for ATP-dependent efflux transportersBRITISH JOURNAL OF PHARMACOLOGY, Issue 4 2007J A Schrickx Background and purpose: Next to its broad antimicrobial spectrum, the therapeutic advantages of the fluoroquinolone antimicrobial drug Danofloxacin-Mesylate (DM) are attributed to its rapid distribution to the major target tissues such as lungs, intestines and the mammary gland in animals. Previous analyses revealed that effective drug concentrations are achieved also in luminal compartments of these organs, suggesting that active transport proteins facilitate excretion into the luminal space. Members of the ATP-Binding Cassette (ABC) superfamily, including P-gp, BCRP and MRP2 are known to be expressed in many tissue barriers and in cell-membranes facing luminal compartments. Hence we hypothesized that DM is a substrate for one of these efflux-transporters. Experimental approach: Confluent monolayers of Caco-2 cells, grown on microporous membranes in two-chamber devices were used. DM concentrations were measured by fluorimetric assay after HPLC of the culture media. Key results: DM transport across Caco-2 cells was asymmetric, with a rate of secretion exceeding that of absorption. The P-gp inhibitors PSC833 and GF120918 and the MRP-inhibitor MK571 partially decreased the secretion of DM and increased its absorption rate. The BCRP inhibitor, Ko143, decreased secretion only at a concentration of 1 ,M. When DM was applied together with ciprofloxacin, secretion as well as absorption of DM decreased. Conclusions and Implications: DM is a substrate for the efflux transporters P-gp and MRP2, whereas the specific role of BCRP in DM transport needs further evaluation. These findings provide a mechanistic basis for the understanding of the pharmacokinetics of DM in healthy and diseased individuals. British Journal of Pharmacology (2007) 150, 463,469. doi:10.1038/sj.bjp.0706974 [source] Do studies in caveolin-knockouts teach us about physiology and pharmacology or instead, the ways mice compensate for ,lost proteins'?BRITISH JOURNAL OF PHARMACOLOGY, Issue 3 2007P A Insel A wide array of phenotypic changes have been reported in mice with knockout of expression of caveolin-1. Neidhold et al. (2007) describe results in this issue that continue this trend by showing that saphenous arteries from adult caveolin-1 knockout mice lack caveolae, lose ,1 -adrenoceptor-promoted relaxation, gain ,3 -adrenoceptor-promoted relaxation but show no change in vasomotor response to ,2 -adrenoceptor activation. Neither the physiological importance for wild-type animals nor the mechanistic basis for these changes is clear. Although the caveolin-1 knockout and wild-type mice express similar levels of the receptor mRNAs, the protein expression of the receptors is not specified and represents, in our view, an important limitation of the study. We also question the physiological relevance of the findings and ask: Do studies in total body/lifespan caveolin-knockout mice further understanding of physiology and pharmacology or do they primarily characterize secondary consequences? We propose that alternative approaches that decrease caveolin expression in a temporally and spatially discrete manner are more likely to facilitate definitive conclusions regarding caveolin-1 and its role in regulation of , -adrenoceptors and other pharmacological targets. British Journal of Pharmacology (2007) 150, 251,254. doi:10.1038/sj.bjp.0706981 [source] The Large-Scale Structure of Semantic Networks: Statistical Analyses and a Model of Semantic GrowthCOGNITIVE SCIENCE - A MULTIDISCIPLINARY JOURNAL, Issue 1 2005Mark Steyvers Abstract We present statistical analyses of the large-scale structure of 3 types of semantic networks: word associations, WordNet, and Roget's Thesaurus. We show that they have a small-world structure, characterized by sparse connectivity, short average path lengths between words, and strong local clustering. In addition, the distributions of the number of connections follow power laws that indicate a scale-free pattern of connectivity, with most nodes having relatively few connections joined together through a small number of hubs with many connections. These regularities have also been found in certain other complex natural networks, such as the World Wide Web, but they are not consistent with many conventional models of semantic organization, based on inheritance hierarchies, arbitrarily structured networks, or high-dimensional vector spaces. We propose that these structures reflect the mechanisms by which semantic networks grow. We describe a simple model for semantic growth, in which each new word or concept is connected to an existing network by differentiating the connectivity pattern of an existing node. This model generates appropriate small-world statistics and power-law connectivity distributions, and it also suggests one possible mechanistic basis for the effects of learning history variables (age of acquisition, usage frequency) on behavioral performance in semantic processing tasks. [source] | |||||||||||||||||||||||||