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  • 1
    Electronic Resource
    Electronic Resource
    Springer
    Biological cybernetics 74 (1996), S. 557-567 
    ISSN: 1432-0770
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Computer Science , Physics
    Notes: Abstract.  In various organisms loss-of-function mutations of individual genes with unexpectedly weak or no phenotypic effects in the homozygous state have been observed. In several of these cases, independent evidence shows that the respective gene products do have essential biological functions. An explanation emerging from detailed biochemical and genetic studies on such genes is that two or more genetically redundant genes contribute to that function, i.e., a group of genes that is able to substitute partially for a loss of function in one member of that group. The often-observed sequence similarity among redundant genes suggests gene duplications as a frequent source of genetic redundancy. Aside from this observation, the evolution of genetic redundancy is poorly understood. Genetic redundancy is potentially of great relevance to organismal evolution, since it may (i) ‘protect’ organisms from potentially harmful mutations, and (ii) maintain pools of functionally similar, yet diverse gene products, and thus represent a source of evolutionary novelty at the biochemical level. The question of how genetic redundancy evolves should ideally be answered by experimentation. However, the large time scales involved and insufficient quantitative understanding of the underlying regulatory pathways are likely to preclude such an approach in the foreseeable future. Preliminary answers are sought here by using a biochemically motivated model of a small but central part of a developmental pathway. Sets of transcription regulators are modeled that mutually regulate each other’s expression and thereby form stable gene expression patterns. It is then studied how genetic redundancy caused by gene duplications might evolve in such networks. The results obtained suggest that redundancy may, at least in some cases, be a global property of gene interactions within a regulatory pathway, rather than a local property of genes in that pathway. They also raise the possibility that duplications of a whole regulatory gene network, as may have taken place during the evolution of HOM/Hox genes in chordates, are less likely to be reversible (by gene deletions) than duplications of individual network genes. These findings are discussed with reference to experimental evidence on the evolution of HOM/Hox genes.
    Type of Medium: Electronic Resource
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  • 2
    Electronic Resource
    Electronic Resource
    Springer
    Biological cybernetics 74 (1996), S. 557-567 
    ISSN: 1432-0770
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Computer Science , Physics
    Notes: Abstract In various organisms loss-of-function mutations of individual genes with unexpectedly weak or no phenotypic effects in the homozygous state have been observed. In several of these cases, independent evidence shows that the respective gene products do have essential biological functions. An explanation emerging from detailed biochemical and genetic studies on such genes is that two or more genetically redundant genes contribute to that function, i.e., a group of genes that is able to substitute partially for a loss of function in one member of that group. The often-observed sequence similarity among redundant genes suggests gene duplications as a frequent source of genetic redundancy. Aside from this observation, the evolution of genetic redundancy is poorly understood. Genetic redundancy is potentially of great relevance to organismal evolution, since it may (i) ‘protect’ organisms from potentially harmful mutations, and (ii) maintain pools of functionally similar, yet diverse gene products, and thus represent a source of evolutionary novelty at the biochemical level. The question of how genetic redundancy evolves should ideally be answered by experimentation. However, the large time scales involved and insufficient quantitative understanding of the underlying regulatory pathways are likely to preclude such an approach in the foreseeable future. Preliminary answers are sought here by using a biochemically motivated model of a small but central part of a developmental pathway. Sets of transcription regulators are modeled that mutually regulate each other's expression and thereby form stable gene expression patterns. It is then studied how genetic redundancy caused by gene duplications might evolve in such networks. The results obtained suggest that redundancy may, at least in some cases, be a global property of gene interactions within a regulatory pathway, rather than a local property of genes in that pathway. They also raise the possibility that duplications of a whole regulatory gene network, as may have taken place during the evolution of HOM/Hox genes in chordates, are less likely to be reversible (by gene deletions) than duplications of individual network genes. These findings are discussed with reference to experimental evidence on the evolution of HOM/Hox genes.
    Type of Medium: Electronic Resource
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  • 3
    ISSN: 1524-475X
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Medicine
    Notes: Highly reactive metabolites, such as oxygen free radicals, initiate a cascade of inflammatory processes in thermally damaged skin, leading to enhanced tissue loss and delayed wound healing. The extent of tissue necrosis in the zone of stasis is of prognostic significance in the wound healing process. In this study, the effect of oxygen free radical removal by recombinant human-Cu/Zn-superoxide dismutase, given in three different formulations during the inflammatory postburn phase and wound repair, was examined. Recombinant human superoxide dismutase was either injected directly into the lesions, spread as enzyme-containing gel onto the burned tissue, or encapsulated into liposomes consisting of 1,2 dipalmitoy-sn-glycero-3-phosphocholine, cholesterol and stearylamine, suspended into a hydrophilic gel and administered to burned animals immediately after trauma. Controls were treated with plain gel or kept untreated. Edema formation, size of lesions, deepening of necrosis, and reepithelialization were examined. Results indicate that superoxide dismutase treatment resulted in reduced and faster recruitment of edema formation, smaller wound sizes, and minor tissue necrosis compared to the controls, thus resulting in significantly faster reepithelialization after 3 weeks. These animal studies on the efficacy of liposomal oxygen free radical scavenger showed accelerated wound healing in all parameters tested. (WOUND REP REG 2002;10:366–371)
    Type of Medium: Electronic Resource
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  • 4
    Electronic Resource
    Electronic Resource
    [s.l.] : Nature America Inc.
    Nature genetics 24 (2000), S. 355-361 
    ISSN: 1546-1718
    Source: Nature Archives 1869 - 2009
    Topics: Biology , Medicine
    Notes: [Auszug] There are two principal mechanisms that are responsible for the ability of an organism's physiological and developmental processes to compensate for mutations. In the first, genes have overlapping functions, and loss-of-function mutations in one gene will have little phenotypic effect if there ...
    Type of Medium: Electronic Resource
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  • 5
    Electronic Resource
    Electronic Resource
    [s.l.] : Nature America Inc.
    Nature biotechnology 18 (2000), S. 1121-1122 
    ISSN: 1546-1696
    Source: Nature Archives 1869 - 2009
    Topics: Biology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: [Auszug] Genome sequencing is now advancing at a frenetic pace, which has the consequence that many organisms now being sequenced have not had their biochemistry extensively studied. Thus, the metabolic phenotype of these organisms has to be determined using annotated genome sequence data. Ideally, this ...
    Type of Medium: Electronic Resource
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  • 6
    Electronic Resource
    Electronic Resource
    [s.l.] : Nature Publishing Group
    Nature genetics 34 (2003), S. 264-266 
    ISSN: 1546-1718
    Source: Nature Archives 1869 - 2009
    Topics: Biology , Medicine
    Notes: [Auszug] Convergent evolution is a potent indicator of optimal design. We show here that convergent evolution occurs in genetic networks. Specifically, we show that multiple types of transcriptional regulation circuitry in Escherichia coli and the yeast Saccharomyces cerevisiae have evolved independently ...
    Type of Medium: Electronic Resource
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  • 7
    Electronic Resource
    Electronic Resource
    Springer
    Naturwissenschaften 85 (1998), S. 117-120 
    ISSN: 1432-1904
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Chemistry and Pharmacology , Natural Sciences in General
    Type of Medium: Electronic Resource
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  • 8
    ISSN: 1573-7241
    Keywords: congestive heart failure ; flosequinan ; cardiac performance ; neurohumoral regulation
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Summary We evaluated the responses to 90 minutes and 8 days of therapy with a new long-acting vasodilator flosequinan in ten patients with moderate chronic congestive heart failure in an open, uncontrolled study. Acute administration of 100 mg orally resulted in a decrease of preload, with a reduction of left ventricular end-diastolic volume, left ventricular end-diastolic pressure, pulmonary capillary wedge pressure, and right atrial pressure. Following the acute administration, we found no significant changes of heart rate, cardiac index, stroke volume, peripheral vascular resistance, ejection fraction, and dp/dt. Chronic application for 8 days (100 mg/day) showed persistent effects on preload, with a significant decrease of pulmonary capillary wedge pressure, right atrial pressure, and pulmonary arterial pressure. After 8 days of treatment, cardiac index was significantly increased from 2.2±0.2 l/min/m2 to 2.8±0.2 l/min/m2 (p=0.013) and stroke volume from 57±10 ml to 74±9 ml (p=0.022). Peripheral vascular resistance decreased by 28%. After 8 days, bicycle exercise capacity increased significantly from 383±44 sec to 422±43 sec (p=0.01) and the patients were able to increase their walking distance over a 6-minute exercise test from 426±46 m to 477±33 m (p=0.007), with a concomitant decrease of dyspnea (p=0.013). Plasma renin concentration showed only a rise 90 minutes after the acute administration on day 8 of the study, and atrial natriuretic peptide and 6-keto-prostaglandin F1-alpha decreased significantly. Plasma norepinephrine, epinephrine, dopamine, and prostaglandin E2 did not change. After 8 days body weight was reduced from 76.5±2.1 kg to 75.1±2.4 kg. These data indicate that flosequinan is effective in patients with heart failure during a relatively short duration of treatment, improving cardiac performance and exercise capacity and acting primarily on preload, and it may have cumulative vasodilator effects on arterial vessels during chronic therapy. We observed no substantial stimulation of neurohumoral factors and no fluid retention.
    Type of Medium: Electronic Resource
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  • 9
    Electronic Resource
    Electronic Resource
    Springer
    Biology and philosophy 14 (1999), S. 83-101 
    ISSN: 1572-8404
    Keywords: ceteris paribus ; epistasis ; nonlinear gene interactions ; polygenic diseases ; regular causes
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Philosophy
    Notes: Abstract Systems involving many interacting variables are at the heart of the natural and social sciences. Causal language is pervasive in the analysis of such systems, especially when insight into their behavior is translated into policy decisions. This is exemplified by economics, but to an increasing extent also by biology, due to the advent of sophisticated tools to identify the genetic basis of many diseases. It is argued here that a regularity notion of causality can only be meaningfully defined for systems with linear interactions among their variables. For the vastly more important class of nonlinear systems, no such notion is likely to exist. This thesis is developed with examples of dynamical systems taken mostly from mathematical biology. It is discussed with particular reference to the problem of causal inference in complex genetic systems, systems for which often only statistical characterizations exist.
    Type of Medium: Electronic Resource
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