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At least 1,621 records · Page 90Linked to original sources

PubMed2002

Modularity, individuality, and evo-devo in butterfly wings.

Modularity in animal development is thought to have facilitated morphological diversification, but independent change of those traits integrated within a module might be restricted. Correlations among traits describe potential developmental constraints on evolution. These have often been postulated to explain patterns of morphological variation and have been examined theoretically but seldom analyzed experimentally. Here, we use artificial selection to explore the modular organization of butterfly wing patterns and the extent to which their evolution is constrained by the genetic correlations among repeated pattern elements. We show that, in Bicyclus anynana butterflies, despite the evidence that all eyespots are developmentally coupled, the response to selection for increased size of one individual eyespot can proceed in a manner largely independent from selection imposed on another eyespot. We argue that among-eyespot correlations are unlikely to have constrained the evolutionary diversification of butterfly wing patterns but might be important when only limited time is available for adaptive evolution to occur. The ease with which we have been able to produce independent responses to artificial selection on different eyespots may be linked to a legacy of natural selection favoring individuality. Our results are discussed within the context of the evolution of modularity and individuality of serially repeated morphological traits.

Animals↗

PubMed2002

Altruistic punishment in humans.

Human cooperation is an evolutionary puzzle. Unlike other creatures, people frequently cooperate with genetically unrelated strangers, often in large groups, with people they will never meet again, and when reputation gains are small or absent. These patterns of cooperation cannot be explained by the nepotistic motives associated with the evolutionary theory of kin selection and the selfish motives associated with signalling theory or the theory of reciprocal altruism. Here we show experimentally that the altruistic punishment of defectors is a key motive for the explanation of cooperation. Altruistic punishment means that individuals punish, although the punishment is costly for them and yields no material gain. We show that cooperation flourishes if altruistic punishment is possible, and breaks down if it is ruled out. The evidence indicates that negative emotions towards defectors are the proximate mechanism behind altruistic punishment. These results suggest that future study of the evolution of human cooperation should include a strong focus on explaining altruistic punishment.

Altruism↗

PubMed1978

Gene regulation in adaptive evolution.

It has been suggested that gene regulation may play a critical role in adaptive evolution. However, gene regulation has proved to be most refractory to experimental investigation in multicellular organisms. Using specially constructed stocks of Drosophila melanogaster, we have demonstrated the following. (1) The existence in natural populations of ample variation in regulatory genes that modify the activity of alcohol dehydrogenase (ADH), an enzyme coded by a structural gene locus, Adh, located on the second chromosome; the regulatory genes are located on the third chromosome, and thus are not adjacent to the structural locus. (2) The regulatory genes act not by means of post-transcriptional or post-translational modification of the gene product, but rather by controlling the number of ADH molecules; this is consistent with the hypothesis of gene regulation by means of macromolecules specifically binding at control sites adjacent to the structural gene locus. (3) The variation in regulatory genes is adaptively significant; adaptation to higher levels of environmental alcohol takes place not by changes in the Adh structural locus, but by changes in regulatory genes that control the number of ADH molecules in the organisms. Our results provide direct evidence of the importance of gene regulation in eucaryotic evolution.

Alcohol Oxidoreductases↗

PubMed2004

Experimental studies on sexual reproduction in diatoms.

The diatoms are the most speciose group of algae, having global ecological significance in the carbon and silicon cycles. They are almost unique among algae in being diplontic, and sexual reproduction is an obligate stage in the life cycle of most diatom species. It is unclear which are the principal factors that have fostered the evolutionary success of diatoms, but the unique life cycle (which is correlated with a curious wall structure and cell division mechanism) and size-dependent control of sexuality must have played an important part. Progress in understanding life cycle dynamics and their interrelationships with population biology and evolution will depend on how successfully sex can be initiated and manipulated experimentally, and our review provides a foundation for such work. Relevant data are scattered in time and come mostly from non-English publications, producing a false impression of diatoms as recalcitrant with respect to sexualization. Recent advances dependent on experimental cultures include the discovery of widespread heterothallism (including some complex types of behavior) in pennate diatoms, sexual diversity among clones of centric diatoms, more flexible size restitution strategies in centric diatoms than had been suspected, and use of reproductive isolation as a criterion in diatom taxonomy. We identify unsolved problems in the life history of diatoms, including aspects of sexualization, cell-cell recognition, sexual reproduction, and the development of the special expanding cell (the auxospore), which is crucial to morphogenesis in this group. Some of these problems are being addressed using modern molecular genetic tools, and progress will be facilitated when whole-genome sequences are published (e.g., for Thalassiosira pseudonana). Problems of culture maintenance and methods for manipulating the life cycle are discussed.

Cell Communication↗

PubMed1986

Have deoxyribonucleotides and DNA been among the earliest biomolecules?

Unlike ribose chemistry, the chemistry of 2-deoxyribose precludes its formation or at least its incorporation into nucleotides under accepted "primordial soup" conditions; therefore RNA and DNA could not develop in parallel during the evolution of protocells. However, deoxyribonucleotides might have been formed abiotically by direct reduction of ribonucleotides in a primitive version of the biochemical pathway. This sequence of events, in which DNA lagged behind RNA in the assembly of genetic information for an unknown--probably short--period of time is suggested by the primitive traits (i.e., nucleotide binding, thiol redox chemistry, and metal ion catalysis) of present-day enzyme systems of deoxyribonucleotide biosynthesis. The reaction should be amenable to experimental study.

Carbohydrates↗

PubMed1986

Rat apolipoprotein A-IV: application of computational methods for studying the structure, function, and evolution of a protein.

There are a great variety of computational methods available to study protein and nucleic acid sequences. The choice of a computer program appropriate to a particular problem and the critical interpretation of the results can lead to specific, and experimentally testable, predictions of a protein's structure and function and may yield insights into its evolution and the location of its gene. We have shown that rat apoA-IV bears a striking structural similarity to human apoA-I (summarized in Fig. 7). Statistical analyses of homologies between apolipoproteins A-I, A-IV, and E demonstrate conclusively that all three sequences diverged from a common ancestral gene. That apoA-IV largely composed of 22 amino acid amphipathic segments with alpha-helical potential suggests that it possesses the structural requirements for LCAT activation. Analysis of the apoB, E receptor-binding domain of human apoE3 has demonstrated that it evolved from an ancestral repeated sequence. Assuming that the genes for these proteins evolved as a result of a series of intra- and intergenic unequal crossovers, it is likely that their genetic loci were at one time linked. The repeated sequences of which these genes are composed have propagated themselves in an expansionary manner. Given this fact, the existence of other genes or pseudogenes based upon this repeated sequence motif is a distinct possibility.

Amino Acid Sequence↗

PubMed1992

Hepatic mitochondrial glutathione depletion and progression of experimental alcoholic liver disease in rats.

Long-term ethanol feeding has been shown to selectively reduce hepatic mitochondrial glutathione content by impairing mitochondrial uptake of this thiol. In this study, we assessed the role of this defect in evolution of alcoholic liver disease by examining the mitochondrial glutathione pool and lipid peroxidation during progression of experimental alcoholic liver disease to centrilobular liver necrosis and fibrosis. Male Wistar rats were intragastrically infused with a high-fat diet plus ethanol for 3, 6 or 16 wk (the duration that resulted in induction of liver steatosis, necrosis and fibrosis, respectively). During this feeding period, the cytosolic pool of glutathione remained unchanged in the ethanol-fed animals compared with that in pair-fed controls. In contrast, the mitochondrial pool of glutathione selectively and progressively decreased in rats infused with ethanol for 3, 6 or 16 wk, by 39%, 61% and 85%, respectively. Renal mitochondrial glutathione level remained unaffected throughout the experiment. Serum ALT levels increased significantly in the ethanol-fed rats at 6 wk and remained elevated at 16 wk. In the mitochondria with severely depleted glutathione levels at 16 wk, enhanced lipid peroxidation was evidenced by increased malondialdehyde levels. Thus a progressive and selective depletion of mitochondrial glutathione is demonstrated in the liver in this experimental model of alcoholic liver disease and associated with mitochondrial lipid peroxidation and progression of liver damage.

Alanine Transaminase↗

PubMed2004

Self-similar evolution of parabolic pulses in a laser.

Self-similar propagation of ultrashort, parabolic pulses in a laser resonator is observed theoretically and experimentally. This constitutes a new type of pulse shaping in mode-locked lasers: in contrast to the well-known static (solitonlike) and breathing (dispersion-managed soliton) pulse evolutions, asymptotic solutions to the nonlinear wave equation that governs pulse propagation in most of the laser cavity are observed. Stable self-similar pulses exist with energies much greater than can be tolerated in solitonlike pulse shaping, and this has implications for practical lasers.

Lasers↗

PubMed1999

On the origin of sex chromosomes.

In all living forms, the organization of the genetic material must enable two universally fundamental functions: the elaboration of biological properties and their transmission. In spite of these inexorable commonalties, genomes have a bewildering variety of forms, with differences occurring not only among distant taxa but also, in many instances, between members of the opposite sex within species. The rapidly growing field of comparative genomics offers a powerful tool for unraveling the evolutionary pathways that led to these karyotypic differences. This new method of genetic analysis [Fridolfsson et al, Proc Nat Acad Sci USA 1998; 95: 8147-8152. (Ref. 1)] complements still valuable, traditional experimental approaches.

Animals↗

PubMed1996

Structure and experimental uses of arthropod venom proteins.

In summary, the initial studies conducted thus far into the components of venoms of parasitic wasps and other arthropods have already yielded a number of interesting properties of the proteins therein. These properties have already offered the possibilities of additional principles operating in the evolution of venoms. That so many unexpected rewards have already surfaced with the relatively little experimental digging conducted thus far generates great anticipation that indeed there remains a pharmacological gold mine awaiting to be discovered in components of the other insect venoms as yet unmined by science.

Amino Acid Sequence↗

PubMed1994

Drug-metabolizing enzymes in ligand-modulated transcription.

Genes encoding many of the so-called drug-metabolizing enzymes (DMEs) are present in both prokaryotes and eukaryotes, suggesting that these genes arose on this planet more than 3.5 billion years ago--long before animal-plant divergence (estimated to be about 1.2 billion years ago) and long before the use and commercial development of drugs. What, therefore, are the real functions of DMEs? Several years ago I proposed that DMEs are upstream in the regulatory cascade of numerous signal transduction pathways, i.e. necessary for maintaining physiologically "safe", or "acceptable", steady-state levels of all small non-protein endogenous ligands (M(r) = 250 +/- 200) in each cell. Innumerable foreign chemicals and drugs mimic these small endogenous ligands, thus binding to a particular receptor and acting either as an agonist or antagonist in activating or inhibiting genes effecting growth, differentiation, apoptosis, homeostasis and neuroendocrine functions. Discussed in this review are additional examples consistent with this theory and not described in previous reviews, including: (i) insect-plant symbiosis; (ii) "cross-talk" amongst genes in the aromatic hydrocarbon-responsive [Ah] battery; (iii) signal transduction pathways involving the arachidonic acid cascade; and (iv) the explanation in carcinogen-screening studies as to why a maximum, or half maximum, tolerated dose (MTD, MTD50) of many test compounds might cause cell division and tumorigenesis in experimental animals.

Animals↗

PubMed2006

Exogenously triggered, enzymatic degradation of photopolymerized hydrogels with polycaprolactone subunits: experimental observation and modeling of mass loss behavior.

Degradation plays an important role in the evolution of the extracellular matrix secreted by chondrocytes encapsulated in PEG-based hydrogels. For this study, macromonomers were synthesized by methacrylating both ends of polycaprolactone-b-poly(ethylene glycol)-b-polycaprolactone (PEG-CAP) tri-block copolymers. These divinyl molecules were photopolymerized to form hydrogels with PEG-CAP crosslinks that were subsequently degraded upon exogenous addition of a lipase enzyme. The rate of degradation and subsequent mass loss depends on both the length of the polycaprolactone units and the concentration of enzyme. Control gels that did not receive lipase did not significantly degrade on the time scale of these experiments. A model was developed to predict mass loss using enzyme kinetics and a previously described statistical treatment of bulk network degradation. The model was used to predict mass loss profiles at the specific conditions used, and also to demonstrate the importance of potential changes in reaction rate and enzyme stability on temporal mass loss.

Hydrogels↗

PubMed2004

Simulated evolution of emergent chiral structures in polyalanine.

The relationship between monomer chirality and polymer structure has been studied using both theoretical and experimental methods. Atomistic models, such as the ones employed in computational protein folding and design, can be used to study the relationship between monomer chirality and the properties of polypeptides. Using a simulated evolution approach that combines side-chain epimerization with backbone flexibility, we recapitulate the relationship between basic forces that drive secondary structure formation and sequence homochirality. Additionally, we find heterochiral motifs including a C-terminal helix capping interaction and stable helix-reversals that result in bent helix structures. Our studies show that simulated evolution of chirality with backbone flexibility can be a powerful tool in the design of novel heteropolymers with tuned stereochemical properties.

Amino Acid Sequence↗

PubMed1987

Evolution of substance P immunofluorescent nerves in callus tissue during fracture healing.

Tibial fractures were experimentally produced in rats. The fractures were allowed to heal spontaneously. Samples of callus tissue were studied by a specific immunohistochemical method for substance P, the peptide which is found in sensory nerves and probably plays a role in nociceptive nerve transmission. The control periosteum contained a rich network of substance P immunofluorescent nerves. The early callus tissue also contained such sensory nerves, the peak frequency of which was at the end of the second week. It is proposed that the substance P-containing nerves play a protective nociceptive role during fracture healing.

Animals↗

PubMed2001

New method to calculate the N2 evolution from mixed venous blood during the N2 washout.

To model the normalized phase III slope (Sn) from N2 expirograms of the multibreath N2 washout is a challenge to researchers. Experimental measurements show that Sn increases with the number of breaths. Previously, we predicted Sn by setting the concentration (atm) of mixed venous blood (Fbi,N2) to a constant value of 0.3 after the fifth breath to calculate the amount of N2 transferred from the blood to the alveoli. As a consequence, the predicted curve of the Sn values showed a maximum before the quasi-steady state was reached. In this paper, we present a way of calculating the amount of N2 transferred from the blood to the alveoli by setting Fbi,N2 in the following way: In the first six breaths Fbi,N2 is kept constant at the initial value of 0.8 because circulation time needs at least 30 s to alter it. Thereafter, a single exponential function with respect the number of breaths is used: Fbi = 0.8 exp[0.112(6-n)], in which n is the breath number. The predicted Sn values were compared with experimental data from the literature. The assumption of an exponential decay in the N2 evolved from mixed venous blood is important in determining the shape of the Sn curve but new experimental data are needed to determine the validity of the model. We concluded that this new approach to calculate the N2 evolution from the blood is more meaningful physiologically.

Biomedical Engineering↗

PubMed1990

[The dynamics of the form of the extracellular potentials and of the process of depolarization wave spreading in the intramural layers of the myocardium in dogs with experimental ischemia].

The reversal of directions and local delays or accelerations of the extracellular potentials evolution occurred at arrival of the depolarization wave after coronary occlusion in dogs. General patterns of directions of the activation spread changed relatively little when compared to normal. Apparently, in spite of the ligation of the left anterior descending coronary artery, ischemia was not achieved. There was some additional blood supply to the ischemic myocardium from deep collateral arterial branches. Therefore, the observed abnormalities of electrical potentials and the reversals of the depolarization wave direction only took place in local small zones of ischemic myocardium.

Animals↗

PubMed1977

[Possible vertebrate use of a mechanism of chromatin reduction to fuse the V and C genes of immunoglobulins].

Diminution of a chromatin fragment separating V- and C-immunoglobulin genes is suggested as possible mechanism of fusion of V- and C-genes into one functionally active cisrtron. During the early stage of immunodifferentiation of lymphocytes, the chromatin fibrills unfold, and V- and C-genes bring together by DNA-DNA and DNA-protein interaction. The endonucleases excise the chromatin fragment interlocated between V- and C-genes, then the repair enzymes restore the intactness of chromating structure by fusion of V- and C-genes. A number of human pathologic syndromes, the elimination of nucleus during erythrocyte differentiation in mammals indicate the possibility of manifestation on diminution mechanism in vertebrates. Fusion of V- and C-genes by chromatin diminution fits the number of immunologic phenomena, and it may display for different paths of V-gene coding and may be experimentally verified.

Animals↗

PubMed1976

Experimental intraocular nocardiosis.

We attempted to produce intraocular nocardiosis in rabbits. The clinical features and evolution of the disease and the role of corticosteroids was observed. N. asteroides suspension when injected into the anterior chamber produced a self limited nodular iridocyclitis. Local or systemic corticosteroids produced a severe anterior uveitis and progressive endophthalmitis. The organisms could be demonstrated from aqueous smears at the time of enucleation. When the suspension was injected into the vitreous cavity, it produced endophthalmitis. Local or systemic corticosteroids administration suppressed the anterior uveal inflammation and produced a purulent subconjunctival granuloma.

Animals↗