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Results for “Experimental evolution”

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PubMed1997

Organ damage is preceded by changes in protein extravasation in an experimental model of multiple organ dysfunction syndrome.

Our objective was to determine the serial evolution of vascular permeability as measured by protein extravasation in various organs during the development of zymosan-induced multiple organ dysfunction syndrome (MODS). We evaluated the biodistribution of 111Indium-labeled nonspecific polyclonal immunoglobulin G (111In-IgG). On days 2, 5, 8, and 12 after intraperitoneal challenge with 1 mg/g zymosan, mice were killed. Heart, liver, spleen, kidneys, and the mesenteric lymph node complex and tissue samples of muscle, ileum, and colon were dissected free and weighed. 24 h before death, 10 micrograms of IgG labeled with 2 MBq 111In was injected i.v. Relative organ weights (ROW), wet to dry weight ratios (WDR), and a permeability index (PI) were calculated. ROW increased gradually until day 12. WDR also increased gradually in most organs. Lung WDR, however, initially increased, with a subsequent return to normal. Splenic WDR did not change over time. Liver, spleen, ileum, and colon PI were the highest on day 2, followed by a decrease toward normal. Lung PI showed a triphasic course with peak values at days 2 and 12. Mesenteric lymph node complex-PI was continuously elevated. WDR (tissue edema) and PI (protein extravasation) have different courses in various organs. Most organs displayed an early increase in PI, followed by a late decrease, while ROW (organ damage) was still increasing. It appears that organ damage is preceded by an increased protein extravasation.

Animals↗

PubMed1990

[Morphofunctional changes in potential liver allografts in experimental conditions].

As a part of morphofunctional investigations of validations cadaveric grafts for transplantation evolution of the histomorphological changes was followed by the experiments on guinea pigs. Liver samples were immediately after sacrificing the animals and 1, 2, and 4h later and kept at body temperature, which corresponded to the conditions of "warm ischemia". Second group of samples was immerged in Saline are +4 degrees C (hibernation-preservation) and was taken for analysis in same intervals as previous ones. Evolution of morphological and enzymatic changes was evident in short interval after sacrificing the animals. First changes were observed in cytoplasm and then in nuclei and interestitum. Changes of hepatic cells from hibernation preservation group were significant damaged comparing with the corresponding samples obtained from cadaver. ("warm ischemia"). These preliminary results indicated that length of liver graft preservation is very limited. Furthermore, this results demand for the future investigations in different conditions of preservation.

Animals↗

PubMedDate not supplied

Induced corneal swelling: an experimental model for investigation of collagen and interfibrillar substance relationships.

We report on the evolution of ultrastructural modifications in bovine and rabbit corneal sections after in vitro swelling. The number of stromal fibers decreases with time during swelling. The fact that swelling occurs more rapidly in the center of a lamellae than near the interlamellar spaces indicates that there is a heterogeneous distribution of interfibrillar matrix components and that corneal inhibition mechanisms vary according to the number of lamellaes. The appearance during swelling of periodic striations of collagen fibers and of an irregular network constituted of filaments and granules in the interfibrillar spaces suggests that corneal collagen fibers are covered by a pleated proteoglycan-glycoportein substance that is unrolled during swelling. The filaments seem to be linked to collagen via dense granules located on fibers. The distance between the granules is 643 A. A definite correspondence between the distribution of these linking granules and the periodic striations of collagen cannot be determined. Other granules of undetermined chemical nature seem to link only filaments in the interfibrillar space.

Animals↗

PubMedDate not supplied

[Long-term results of biological control by predation. Experimental study of population development of several species of snails (author's transl)].

The evolution of malacological fauna, which is subject to prediation of Zonitidae snails, is studied on two types of habitats of Lymnaea truncatula: swampy meadows and banks of river maintained by a periodical grass-mowing. Two years are necessary for obtaining an entire elimination of Lymnaea truncatula. Then other species of Lymanaeidae and Succinea are affected by predation, but Succinea snails do not pass away completely. The other snails are not affected or little by predation.

Animals↗

PubMed2004

An experimental evaluation of self-interference in Narcissus assoanus: functional and evolutionary implications.

Floral traits that reduce self-pollination in hermaphroditic plants have usually been interpreted as mechanisms that limit the genetic consequences of self-fertilization. However, the avoidance of sexual conflict between female and male function (self-interference) may also represent an important selection pressure for the evolution of floral traits, particularly in self-incompatible species. Here, we use experimental manipulations to investigate self-interference in Narcissus assoanus, a self-incompatible species with a stigma-height dimorphism in which the degree of spatial separation between sex organs (herkogamy) differs strikingly between the long- and short-styled morphs (hereafter L- and S-morphs). We predicted that weak herkogamy in the L-morph would cause greater self-pollination and hence self-interference. Experimental self-pollination reduced seed set when it occurred prior to, or simultaneously with, cross-pollination in the L-morph, but only if it occurred prior to cross-pollination in the S-morph. In the field, autonomous self-pollination was greater in the L-morph than the S-morph, but we found no evidence that self-interference reduced maternal or paternal fitness in either morph. One-day-old flowers of the L-morph have reduced stigma receptivity and hence exhibit protandry, whereas stigma receptivity and anther dehiscence are concurrent in the S-morph. This suggests that the two style morphs have alternative strategies for reducing self-interference: dichogamy in the L-morph and herkogamy in the S-morph. These results provide insight into the mechanisms that reduce sexual conflict in hermaphrodite plants and are of significance for understanding the evolution and maintenance of sexual polymorphisms.

Analysis of Variance↗

PubMed2004

Evo-devo aspects of classical and molecular data in a historical perspective.

We discuss the interplay between evolution and development as reflected in data and concepts since about 1800. Darwin and his "continental apostle" Haeckel put the striking similarity between early vertebrate embryos in an evolutionary context. Haeckel's partly illicit generalizations discredited evolutionary thinking among early experimental embryologists who moreover noted riddles incompatible with contemporary concepts of homology and evolution. Relevant solutions were suggested by the more recent concept of ontogenetic networks that embody complex regulatory properties and genes with partly overlapping functions. Molecular data on development increasingly reveal evolutionary opportunism, for instance when a widespread signaling chain involved in primitive immune defense was apparently recruited later on for dorso-ventral axis determination in some evolutionarily advanced insect groups. Recently, Rickettsia-related bacteria colonizing many arthropod species were found to "manipulate" the first steps of host development to the advantage of their own propagation, but by ways that could also promote host speciation. Molecular genetics can now document evolutionary steps in ontogenetic networks. In the fruit fly for instance, the novel bicoid gene has superseded a crucial patterning function within a pre-existing network--a case of "molecular caenogenesis." The expression patterns of conserved genes that antagonistically determine dorso-ventral polarity support a literal revolution envisioned almost 200 years ago. This is the dorso-ventral inversion of the body plan in some metazoans--ascribed then to the Articulata, now to the Chordata. The final section posits that the opportunistic character of evolutionary innovations is detrimental to parsimony in development.

Animals↗

PubMed1999

Diminishing returns from mutation supply rate in asexual populations.

Mutator genotypes with increased mutation rates may be especially important in microbial evolution if genetic adaptation is generally limited by the supply of mutations. In experimental populations of the bacterium Escherichia coli, the rate of evolutionary adaptation was proportional to the mutation supply rate only in particular circumstances of small or initially well-adapted populations. These experiments also demonstrate a "speed limit" on adaptive evolution in asexual populations, one that is independent of the mutation supply rate.

Adaptation, Physiological↗

PubMed1985

Comparative Amperometric Study of Uptake Hydrogenase and Hydrogen Photoproduction Activities between Heterocystous Cyanobacterium Anabaena cylindrica B629 and Nonheterocystous Cyanobacterium Oscillatoria sp. Strain Miami BG7.

Heterocystous filamentous cyanobacterium Anabaena cylindrica B629 and nonheterocystous filamentous cyanobacterium Oscillatoria sp. strain Miami BG7 were cultured in media with N(2) as the sole nitrogen source; and activities of oxygen-dependent hydrogen uptake, photohydrogen production, photooxygen evolution, and respiration were compared amperometrically under the same or similar experimental conditions for both strains. Distinct differences in these activities were observed in both strains. The rates of hydrogen photoproduction and hydrogen accumulation were significantly higher in Oscillatoria sp. strain BG7 than in A. cylindrica B629 at every light intensity tested. The major reason for the difference was attributable to the fact that the heterocystous cyanobacterium had a high rate of oxygen-dependent hydrogen consumption activity and the nonheterocystous cyanobacterium did not. The activity of oxygen photoevolution and respiration also contributed to the difference. Oscillatoria sp. strain BG7 had lower O(2) evolution and higher respiration than did A. cylindrica B629. Thus, the effect of O(2) on hydrogen photoproduction was minimized in Oscillatoria sp. strain BG7.

Journal Article↗

PubMed2005

Comparative interactomics.

The behavior, morphology and response to stimuli in biological systems are dictated by the interactions between their components. These interactions, as we observe them now, are therefore shaped by genetic variations and selective pressure. Similar to what has been achieved by comparing genome structures and protein sequences, we hope to obtain valuable information about systems' evolution by comparing the organization of interaction networks and by analyzing their variation and conservation. Equally, significantly we can learn whether and how to extend the network information obtained experimentally in well-characterized model systems to different organisms. We conclude from our analysis that, despite the recent completion of several high throughput experiments aimed at the description of complete interactomes, the available interaction information is not yet of sufficient coverage and quality to draw any biologically meaningful conclusion from the comparison of different interactomes. Thus, the transfer of network information obtained from simple organism to evolutionary distant species should be carried out and considered with caution. By using smaller higher-confidence datasets, a larger fraction of interactions is shown to be conserved; this suggests that with the development of more accurate experimental and informatic approaches, we will soon be in the position to study the network evolution.

Animals↗

PubMed1976

Precursor lesions of bronchogenic carcinoma.

Clinical investigations and experimental studies concerned with preneoplastic and early neoplastic lesions in the respiratory tract are discussed. The occurrence of preinvasive states of carcinoma in the bronchus has been recognized for over 20 years. Histopathological and cytological studies suggest that it might become possible to identify even earlier preneoplastic precursor lesions provided the proper tissue or cell markers can be found. Experimental models that could be useful in establishing a better understanding of the evolution of the neoplastic diseases in the respiratory tract are now available.

Aged↗

PubMed2006

Heterotachy in mammalian promoter evolution.

We have surveyed the evolutionary trends of mammalian promoters and upstream sequences, utilising large sets of experimentally supported transcription start sites (TSSs). With 30,969 well-defined TSSs from mouse and 26,341 from human, there are sufficient numbers to draw statistically meaningful conclusions and to consider differences between promoter types. Unlike previous smaller studies, we have considered the effects of insertions, deletions, and transposable elements as well as nucleotide substitutions. The rate of promoter evolution relative to that of control sequences has not been consistent between lineages nor within lineages over time. The most pronounced manifestation of this heterotachy is the increased rate of evolution in primate promoters. This increase is seen across different classes of mutation, including substitutions and micro-indel events. We investigated the relationship between promoter and coding sequence selective constraint and suggest that they are generally uncorrelated. This analysis also identified a small number of mouse promoters associated with the immune response that are under positive selection in rodents. We demonstrate significant differences in divergence between functional promoter categories and identify a category of promoters, not associated with conventional protein-coding genes, that has the highest rates of divergence across mammals. We find that evolutionary rates vary both on a fine scale within mammalian promoters and also between different functional classes of promoters. The discovery of heterotachy in promoter evolution, in particular the accelerated evolution of primate promoters, has important implications for our understanding of human evolution and for strategies to detect primate-specific regulatory elements.

Animals↗

PubMed1996

Genetic redundancy caused by gene duplications and its evolution in networks of transcriptional regulators.

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 case, 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.

Computer Simulation↗

PubMed2001

Applications of yeast in drug discovery.

The yeast Saccharomyces cerevisiae is perhaps the best-studied eukaryotic organism. Its experimental tractability, combined with the remarkable conservation of gene function throughout evolution, makes yeast the ideal model genetic organism. Yeast is a non-pathogenic model of fungal pathogens used to identify antifungal targets suitable for drug development and to elucidate mechanisms of action of antifungal agents. As a model of fundamental cellular processes and metabolic pathways of the human, yeast has improved our understanding and facilitated the molecular analysis of many disease genes. The completion of the Saccharomyces genome sequence helped launch the post-genomic era, focusing on functional analyses of whole genomes. Yeast paved the way for the systematic analysis of large and complex genomes by serving as a test bed for novel experimental approaches and technologies, tools that are fast becoming the standard in drug discovery research

Antifungal Agents↗

PubMed2005

Blocking of leukocyte accumulation in the cerebrospinal fluid augments bacteremia and increases lethality in experimental pneumococcal meningitis.

The role of leukocyte accumulation in the cerebrospinal fluid (CSF) in the evolution of the pathophysiological changes that occur in bacterial meningitis is unclear. Here, we investigate how leukocyte recruitment to the CSF, modulated by the leukocyte blocker fucoidin, affects the extent of brain damage and outcome in pneumococcal meningitis in rats treated with ceftriaxone from 28 h after infection. Rats treated with fucoidin from time of infection had an excess risk of a fatal outcome compared to rats not receiving fucoidin (25/63 versus 5/34, p=0.012), whereas the risk of cortical damage in surviving animals was comparable (16/44 versus 9/29, p=0.8). Pre-treatment with fucoidin attenuated CSF pleocytosis 24 h after infection (median 400 versus 800x10(6) cells/l, p=0.01) without affecting CSF bacterial counts (2.3x10(5) versus 3.6x10(5) CFU/ml, p=0.54). A significant increase in blood bacterial counts was found among rats pre-treated with fucoidin (median 9.6x10(2) versus 5.2x10(2) CFU/ml, p=0.03). Furthermore, blood bacterial count was found to be an important predictor of fatal outcome as shown by multivariate logistical regression analysis (OR 4.43, 95% CI [1.16-17.0] p=0.03). In summary, blocking leukocyte entry to the central nervous system in experimental pneumococcal meningitis compromises the survival prognosis but does not affect the risk of brain damage or level of infection in this compartment. Conversely, poorer prognosis was associated with an increase in bacterial load in blood, suggesting that leukocyte blockage affects the host's ability to control systemic infection.

Animals↗

PubMed2005

The natural history of group I introns.

There are four major classes of introns: self-splicing group I and group II introns, tRNA and/or archaeal introns and spliceosomal introns in nuclear pre-mRNA. Group I introns are widely distributed in protists, bacteria and bacteriophages. Group II introns are found in fungal and land plant mitochondria, algal plastids, bacteria and Archaea. Group II and spliceosomal introns share a common splicing pathway and might be related to each other. The tRNA and/or archaeal introns are found in the nuclear tRNA of eukaryotes and in archaeal tRNA, rRNA and mRNA. The mechanisms underlying the self-splicing and mobility of a few model group I introns are well understood. By contrast, the role of these highly distinct processes in the evolution of the 1500 group I introns found thus far in nature (e.g. in algae and fungi) has only recently been clarified. The explosion of new sequence data has facilitated the use of comparative methods to understand group I intron evolution in a broader context and to generate hypotheses about intron insertion, splicing and spread that can be tested experimentally.

Alternative Splicing↗

PubMed2003

Granular dynamics of density profiles in a suspension interface.

The temporal evolution of the density profiles at the interface of a Rayleigh-Taylor instability in a sedimenting suspension is experimentally investigated. It is found that the sand-glycerin density gradients within the interface change with time, and that the evolution of the gradients differs significantly, depending on the location: The density profiles become steeper in the regions where the suspension flows downwards, whereas the profiles become flatter in the regions where the fluid flows upwards. This observation shows that there is a motion of the sand grains relative to the carrier fluid and hence reveals the prevailing granular dynamics in the suspension interface. It shows a behavior of the suspension which is different from the behavior of a homogeneous Newtonian one-component fluid whose density profiles do not change in time. Another interesting result is that the slopes of the profiles differ already at the very beginning (t=0) of the evolution of the instability, indicating that the suspension might have self-structured prior to instability onset.

Journal Article↗

PubMed2005

Solitons in nonlinear media with an infinite range of nonlocality: first observation of coherent elliptic solitons and of vortex-ring solitons.

We present an experimental study on wave propagation in highly nonlocal optically nonlinear media, for which far-away boundary conditions significantly affect the evolution of localized beams. As an example, we set the boundary conditions to be anisotropic and demonstrate the first experimental observation of coherent elliptic solitons. Furthermore, exploiting the natural ability of such nonlinearities to eliminate azimuthal instabilities, we perform the first observation of stable vortex-ring solitons. These features of highly nonlocal nonlinearities affected by far-away boundary conditions open new directions in nonlinear science by facilitating remote control over soliton propagation.

Journal Article↗

PubMed2003

Leishmania (Viannia) braziliensis-induced chronic granulomatous cutaneous lesions affecting the nasal mucosa in the rhesus monkey (Macaca mulatta) model.

The present studies on infections with Leishmania (Viannia) braziliensis in rhesus macaques were made to characterize the evolution of different parasite strains and the immune responses they elicited in this experimental host. A standardized inoculum of promastigotes was injected intradermally either above the eyelid or on the forearm of each monkey. Sixteen infected monkeys developed longstanding infections which lasted until the end of the observation period (33 months). The time required for lesion development was very variable, not only for the isolates showing molecular differences but also for individual animals in groups infected with the same parasite strain. The inocula produced lesions of variable severity, ranging from localized cutaneous leishmaniasis (CL) with a tendency to spontaneous healing to non-healing disease. One infected animal developed persistent metastatic skin and mucosal lesions. Anti-Leishmania antibodies and parasite-specific T-cell responses were induced by the experimental infections. As the granulomatous inflammatory response found at the lesions in L. (V.) braziliensis-infected M. mulatta was similar to that in patients with CL, this primate model could be useful for studying the pathophysiology and immunoregulatory events associated with disease evolution, as well as for the evaluation of new drugs or candidate vaccines.

Animals↗