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PubMed1979

Different concepts of univentricular heart. Experimental embryological approach.

A brief historical review of the main descriptions, definitions, classifications and nomenclatures of the univentricular heart within the historical context of the evolution of the technical and scientific knowledge, is made. The development of the ventricles and particularly the posterior interventricular septum (posterior smooth plus posterior trabeculated septa), were studied experimentally in the chick embryo, by the vivo labelling technics, since they are very important for the definition of the univentricular heart. It was demonstrated: 1. In the apical region of the embryonic heart only a primitive interventricular septum develops and this gives origin to the posterior interventricular septum. 2. The walls of the bulbus cordis and the primitive ventricle adjacent to the primitive interventricular septum contribute to the development of this septum. 3. Cell division and cell movement are the basic processes of development which seem to take part in the development of the posterior interventricular septum.

Animals↗
PubMed2004

Evolution of the innate immune system: the worm perspective.

Simple model organisms that are amenable to comprehensive experimental analysis can be used to elucidate the molecular genetic architecture of complex traits. They can thereby enhance our understanding of these traits in other organisms, including humans. Here, we describe the use of the nematode Caenorhabditis elegans as a tractable model system to study innate immunity. We detail our current understanding of the worm's immune system, which seems to be characterized by four main signaling cascades: a p38 mitogen-activated protein kinase, a transforming growth factor-beta-like, a programed cell death, and an insulin-like receptor pathway. Many details, especially regarding pathogen recognition and immune effectors, are only poorly characterized and clearly warrant further investigation. We additionally speculate on the evolution of the C. elegans immune system, taking into special consideration the relationship between immunity, stress responses and digestion, the diversification of the different parts of the immune system in response to multiple and/or coevolving pathogens, and the trade-off between immunity and host life history traits. Using C. elegans to address these different facets of host-pathogen interactions provides a fresh perspective on our understanding of the structure and complexity of innate immune systems in animals and plants.

Amino Acid Sequence↗
PubMed2007

Insights into the mechanism of electrocatalytic hydrogen evolution mediated by Fe2(S2C3H6)(CO)6: the simplest functional model of the Fe-hydrogenase active site.

The di-iron complex Fe2(S2C3H6)(CO)6 (a), one of the simplest functional models of the Fe-hydrogenases active site, is able to electrocatalyze proton reduction. In the present study, the H2 evolving path catalyzed by a has been characterized using density functional theory. It is showed that, in the early stages of the catalytic cycle, a neutral mu-H adduct is formed; monoelectron reduction and subsequent protonation can give rise to a diprotonated neutral species (a-muH-SH), which is characterized by a mu-H group, a protonated sulfur atom, and a CO group bridging the two iron centers, in agreement with experimental IR data indicating the formation of a long-lived mu7-CO species. H2 release from a-muH-SH, and its less stable isomer a-H2 is kinetically unfavorable, while the corresponding monoanionic compounds (a-muH-SH- and a-H2-) are more reactive in terms of dihydrogen evolution, in agreement with experimental data. The key species involved in electrocatalysis have structural features different from the hypothetical intermediates recently proposed to be involved in the enzymatic process, an observation that is possibly correlated with the reduced catalytic efficiency of the biomimetic di-iron assembly.

Binding Sites↗
PubMed2002

Evolution of ultracold neutral plasmas.

We present the first large-scale simulations of an ultracold neutral plasma, produced by photoionization of laser-cooled xenon atoms, from creation to initial expansion, using classical molecular-dynamics methods with open boundary conditions. We reproduce many of the experimental findings such as the trapping efficiency of electrons with increased ion number, a minimum electron temperature achieved on approach to the photoionization threshold, and recombination into Rydberg states of an anomalously low principal quantum number. In addition, many of these effects establish themselves very early in the plasma evolution ( similar ns) before the present experimental observations begin.

Journal Article↗
PubMed1994

Sex determination in the fly Megaselia scalaris, a model system for primary steps of sex chromosome evolution.

The fly Megaselia scalaris Loew possesses three homomorphic chromosome pairs; 2 is the sex chromosome pair in two wild-type laboratory stocks of different geographic origin (designated "original" sex chromosome pair in this paper). The primary male-determining function moves at a very low rate to other chromosomes, thereby creating new Y chromosomes. Random amplified polymorphic DNA markers obtained by polymerase chain reaction with single decamer primers and a few available phenotypic markers were used in testcrosses to localize the sex-determining loci and to define the new sex chromosomes. Four cases are presented in which the primary male-determining function had been transferred from the original Y chromosome to a new locus either on one of the autosomes or on the original X chromosome, presumably by transposition. In these cases, the sex-determining function had moved to a different locus without an obvious cotransfer of other Y chromosome markers. Thus, with Megaselia we are afforded an experimental system to study the otherwise hypothetical primary stages of sex chromosome evolution. An initial molecular differentiation is apparent even in the new sex chromosomes. Molecular differences between the original X and Y chromosomes illustrate a slightly more advanced stage of sex chromosome evolution.

Animals↗
PubMed2005

[How should potential selection for bacterial antibiotic resistance be defined?].

Evolution of bacterial resistance to antibiotics could be better controlled if we knew how to define the potential of evolution of bacterial resistance towards a given antibiotic, prospectively. No unique method allows to do it. Pieces of answers can be obtained by using diverse methods using bacteriological, ecological pharmaco-epidemiological techniques and experimental models. Association of the results obtained with these various techniques is mandatory to understand the evolution potential of resistance towards a given antibiotic when it is used in the clinical setting.

Anti-Bacterial Agents↗
PubMed2005

Comment définir le potentiel de sélection de la résistance bactérienne aux antibiotiques ?

Evolution of bacterial resistance to antibiotics could be better controlled if we knew how to define the potential of evolution of bacterial resistance towards a given antibiotic, prospectively. No unique method allows to do it. Pieces of answers can be obtained by using diverse methods using bacteriological, ecological pharmaco-epidemiological techniques and experimental models. Association of the results obtained with these various techniques is mandatory to understand the evolution potential of resistance towards a given antibiotic when it is used in the clinical setting.

Journal Article↗
PubMed2006

How to reach linguistic consensus: a proof of convergence for the naming game.

In this paper we introduce a mathematical model of naming games. Naming games have been widely used within research on the origins and evolution of language. Despite the many interesting empirical results these studies have produced, most of this research lacks a formal elucidating theory. In this paper we show how a population of agents can reach linguistic consensus, i.e. learn to use one common language to communicate with one another. Our approach differs from existing formal work in two important ways: one, we relax the too strong assumption that an agent samples infinitely often during each time interval. This assumption is usually made to guarantee convergence of an empirical learning process to a deterministic dynamical system. Two, we provide a proof that under these new realistic conditions, our model converges to a common language for the entire population of agents. Finally the model is experimentally validated.

Biological Evolution↗
PubMedDate not supplied

Cell fusion by simulated atmospheric discharges: further support for the hypothesis of involvement of electrofusion in evolution.

Electrofusion of mesophyll cell protoplasts of Avena sativa was induced by simulated atmospheric discharges. It is shown both experimentally and theoretically that the potential differences which occur at quite long distances from the point of lightning stroke are large enough to induce fusion. Besides electromagnetic waves which are emitted during lightning (G. Küppers and U. Zimmermann, FEBS Lett. 164, 323 (1983] cell fusion may have also occurred directly by means of the voltage built-up on the earth during evolution in response to a lightning stroke.

Biological Evolution↗
PubMed1993

Pathogen evolution within host individuals as a primary cause of senescence.

This paper discusses a novel theory of senescence: the community of pathogens within each host individual evolves during the life-time of the host, and in doing so progressively reduces host vigour. I marshal evidence that asymptomatic host individuals maintain persistent populations of viral pathogens; that these pathogens replicate; that they are often extremely variable; that selection within hosts causes the evolution of pathogens better able to exploit the host; that selection is host-specific; and that such evolving infections cause appreciable and progressive deterioration. Experimental approaches to testing the theory are discussed.

Aging↗
PubMedDate not supplied

Consciousness and biological order: toward a quantum theory of life and its evolution.

Biological order is discussed within the context of the idealist interpretation of quantum mechanics. A quantum mechanism is proposed for quantum speciation and for quantum evolution, in general. It is shown that an extension of neo-Darwinism to include quantum evolution via a quantum mechanism can resolve some of the recent controversies that have rattled evolution theory. It is pointed out that the quantum approach has the further benefit of giving a straightforward insight into the nature of life itself. Experimental support for some aspects of the theory is discussed.

Biological Evolution↗
PubMed2004

Adaptive evolution of transcription factor binding sites.

BACKGROUND: The regulation of a gene depends on the binding of transcription factors to specific sites located in the regulatory region of the gene. The generation of these binding sites and of cooperativity between them are essential building blocks in the evolution of complex regulatory networks. We study a theoretical model for the sequence evolution of binding sites by point mutations. The approach is based on biophysical models for the binding of transcription factors to DNA. Hence we derive empirically grounded fitness landscapes, which enter a population genetics model including mutations, genetic drift, and selection. RESULTS: We show that the selection for factor binding generically leads to specific correlations between nucleotide frequencies at different positions of a binding site. We demonstrate the possibility of rapid adaptive evolution generating a new binding site for a given transcription factor by point mutations. The evolutionary time required is estimated in terms of the neutral (background) mutation rate, the selection coefficient, and the effective population size. CONCLUSIONS: The efficiency of binding site formation is seen to depend on two joint conditions: the binding site motif must be short enough and the promoter region must be long enough. These constraints on promoter architecture are indeed seen in eukaryotic systems. Furthermore, we analyse the adaptive evolution of genetic switches and of signal integration through binding cooperativity between different sites. Experimental tests of this picture involving the statistics of polymorphisms and phylogenies of sites are discussed.

Animals↗
PubMedDate not supplied

Exaggerated femoral anteversion and acetabular development: experimental study in growing dogs.

Femoral excessive anteversion caused by femoral osteotomy in growing dogs is an accurate dynamic model of experimental acetabular dysplasia. Radiographic and CT scan examinations were performed throughout the growing period. Evolution showed an incomplete femoral detorsion. It induced acetabular developmental modification leading to an anterior and superior acetabular dysplasia. At the end of the growing period, hips were not dislocated, but signs of femoral and acetabular osteoarthritis were obvious, which shows the importance of mechanical force modification in the creation of experimental osteoarthritis. The links between hip osteoarthritis and exaggerated femoral anteversion are discussed. Might acetabular dysplasia be secondary to femoral anteversion, which could justify a corrective osteotomy during childhood? Our experiment leads to a better comprehension of this phenomenon.

Acetabulum↗
PubMed1990

Macrophage responses in inflammatory demyelinating neuropathies.

Macrophages are prominent participants in inflammatory demyelinating neuropathies. To provide a different means of evaluating macrophage behavior, we used immunostaining of teased nerve fibers and endoneurial blood vessels. We assessed the frequency with which macrophages were seen in inflammatory demyelinating neuropathies, their relationship to normal and demyelinating fibers, and their expression of major histocompatibility Class II markers (Ia antigen). In 6 patients with chronic inflammatory neuropathy and 1 with Guillain-Barré syndrome, we found regularly that macrophages were adherent to teased blood vessels. Cells presumed to be entering the nerve were elongated, often with a polarized appearance suggesting motility, and were Ia-positive. After entry into nerve, the Ia-positive macrophages were adherent to both normal and demyelinating fibers. They often retained their Ia positivity after penetrating into the nerve fiber and removing myelin. Foamy macrophages, judged to be postphagocytic, were Ia-negative. The foamy macrophages found adhering to blood vessels were presumed to be leaving the nerve. This pattern of entry as Ia-positive prephagocytic cells and evolution to Ia-negative foamy macrophages was compared with other experimental and human neuropathies.

Demyelinating Diseases↗
PubMed1987

Animal models of exocrine pancreatic carcinogenesis.

In order to understand the evolution, histogenesis, and biological behaviour of exocrine pancreatic carcinoma, some reproducible experimental models have been developed in certain rodent species. To date, more than 16 chemicals, many of them structurally unrelated, have been shown to induce pancreatic tumors. Although some of these chemicals appear species specific in their effect on the pancreas, others have been shown to be capable of inducing pancreatic tumors in more than one species. In hamsters, the administration of diisopropylnitrosamine or its oxidized metabolites leads to the development of ductal adenocarcinomas that histologically resemble human pancreatic carcinomas. The histogenesis of the ductal type of adenocarcinoma in hamsters is complex, and appears to involve both the duct cells and dedifferentiated acinar cells. All pancreatic tumors in rats develop from acinar cells showing variable degrees of differentiation, regardless of the type of carcinogen used. The type of pancreatic lesions that develop in mice are also of acinar cell origin. In guinea pigs the tumors are adenocarcinomas of the ductal type and are shown to be derived from dedifferentiated acinar cells that have undergone duct-like transformation. Irrespective of the type of tumor that develops in these experimental animals, all of these models can be successfully used to evaluate the various modifying (risk) factors and biological behaviour of these neoplasms.

4-Hydroxyaminoquinoline-1-oxide↗