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At least 505 records · Page 28Linked to original sources
PubMed2005

Neurofibromatosis type 1 - a model for nervous system tumour formation?

Neurofibromatosis type 1 (NF1) is a common genetic condition in which affected individuals develop benign and malignant nervous system tumours. Genetically engineered mouse (GEM) models of these NF1-associated nervous system tumours recapitulate several of the unique clinical aspects of the disease. Moreover, these Nf1 GEM models allow for a direct examination of the earliest stages of tumour evolution, including the contributions that Nf1(+/-) cellular elements and cooperating genetic changes make to facilitate the transition from the pre-neoplastic to the neoplastic state and, in some cases, to promote malignant progression.

Animals↗
PubMed2001

Sexual conflict and cooperation in butterfly reproduction: a comparative study of polyandry and female fitness.

Most butterfly species can be characterized as capital breeders, meaning that reproductive output is strongly coupled to the amount of resources they have procured during the larval stage. Accordingly, female fecundity is generally correlated with female mass, both within and across species. However, the females of some species can be partly characterized as income breeders, in the sense that their reproductive output is dependent not only on larval-derived capital but also on resources acquired during the adult stage. These adult resources can be derived from female feeding or from male-transferred nuptial gifts. Recent studies on the within-species effects of multiple matings on female fitness show that females generally gain directly from multiple matings in terms of increased lifetime offspring production. Here, we test whether the positive effects of multiple mating on female fitness also hold at a comparative level, by conducting a laboratory study of female reproductive output in eight pierid species that differ in life-time female mating frequency. Female reproductive output, measured as cumulative egg mass divided by female mass, increased significantly with polyandry (r = 0.942, p < 0.001), demonstrating that the positive effect of mating rate on female reproductive fitness also holds between species. The positive effect of male nutrient contribution is substantial, and the per capita reproductive output is more than twice as high in the most polyandrous species as in the most monandrous ones. Hence, the positive net effect of the ejaculates is highly substantial, although males and females can have sexual interests that run counter to each other, setting the stage for sexually antagonistic coevolution, so that the various component parts of the male ejaculate-sperm, nutrients, anti-aphrodisiacs, and gonadotrophic hormones-may each correspond to a separate conflict-cooperation balance between the sexes. Two scenarios for the evolution of nuptial gifts in butterflies are discussed, one arguing that variation in larval food is the underlying factor and the other arguing that sexually antagonistic coevolution is the driving force. The two views are complementary rather than mutually exclusive, although the former hypothesis predicts that variation in female mating rate depends on variation in larval food availability, whereas the latter suggests that variation in female mating rate between species results from species-specific idiosyncrasies.

Animals↗
PubMed2002

[Evolutionary aspects of a stress reaction].

Interconnections between the integrative systems, such as nervous, endocrine, and immune ones, are clearly seen during a stress response. The sources of such a cooperation should be sought at the earliest stages of evolution of multicellular organisms. The paper deals with the main points of the formation of a stress response and the development of the systems involved in this process. Based on the data available in the literature and their own findings, the authors conclude that just primitive multicellular organisms, such as coelenterates, have hemolymph cells (chemocytes) that combines the properties of all regulatory systems of more highly organized species. However, the need for such cells no longer arises afterwards. Glucocorticoids, one of the major stress hormones, show up during the development of a stress response relatively late--in fish. While in fish, the production of ACTH and glucocorticoids in the pituitary cells is under urotensin control, this function belongs to corticotropin-releasing hormone of pituitary origin in more advanced animals. The predominant value of corticotropin-releasing hormone simultaneously occurs with the development of the pituitary portal vascular system. Such transformations lead to the formation of the hierarchically arranged neuroendocrine axes that are responsible for showing a stress response, on the one hand, and to the development of qualitatively new interactions between the nervous, endocrine, and immune systems, on the other.

Animals↗
PubMed1984

Purification and characterization of Rana pipiens brain Thy-1 glycoprotein.

The occurrence of Thy-1 antigens in Rana brain has been studied by the use of heterologous anti-Rana brain antisera raised in rabbit and BALB/c mouse (Thy-1.2) and AKR/J mouse (Thy-1.1) strains and by monoclonal anti-mouse Thy-1.1 and anti-mouse Thy-1.2 antibodies with the use of quantitative absorption assays. Three antigenic determinants were defined on Rana brain and referred to as: 1) the Rana-specific xenoantigen, 2) the Rana-mouse cross-reacting xenoantigen, and 3) the Thy-1.1 antigen. Thy-1 antigenic activities were solubilized from crude brain membranes in deoxycholate and followed by measuring the Rana-specific and the Thy-1.1 antigenic determinants. After solubilization, Rana brain Thy-1 antigens were purified by lentil lectin affinity chromatography and gel filtration on Sephadex G-200. A 605-fold and 400-fold enrichment in the Rana-specific and the Thy-1.1 antigenic activities with a yield of 25% and 17%, respectively, were obtained. Both antigenic activities were associated with a single glycoprotein of molecular size 3.1 nm and m.w. estimated at 27,000 by SDS-polyacrylamide gel electrophoresis. The serologic and biochemical properties of our purified Rana brain Thy-1 glycoprotein were very similar to those of the mammalian Thy-1 molecule, suggesting the conservation of the gene coding for Thy-1 during vertebrate evolution.

Animals↗
PubMedDate not supplied

[Ketoacidosis with false hyponatremia and important hyperchylomicronemia (author's transl)].

The ketoacidosis coma is described with plasma lipids at 270 g/l and hyperchylomicronemia. That is completed by a xanthomatosis rash and false hyponatremia (91 mEq/L). This fact is important because the prognosis is better than hyponatremia of ketoacidosis, after treatment evolution is good. Nevertheless because of the non-cooperation of the patient, sucrose level and HBA are high, and triglycerides are still elevated, but of type IV henceforth.

Adolescent↗
PubMed1981

U.S. centralized cancer patient data system for uniform communication among cancer centers.

The evolution of the Centralized Cancer Patient Data System, a cooperative venture of the 21 comprehensive cancer centers in the United States, and its structure at the end of 3 years of data collection are described. Functions of the data system are detailed in terms of input and output. It is concluded that the short-run objective of establishing a data system to provide high-quality patient data that ae 21 comprehensive cancer centers in the United States, and its structure at the end of 3 years of data collection are described. Functions of the data system are detailed in terms of input and output. It is concluded that the short-run objective of establishing a data system to provide high-quality patient data that ae 21 comprehensive cancer centers in the United States, and its structure at the end of 3 years of data collection are described. Functions of the data system are detailed in terms of input and output. It is concluded that the short-run objective of establishing a data system to provide high-quality patient data that are comparable among cancer centers has been largely accomplished. Moreover, the very process of setting up the national data system has benefited the participating centers by upgrading their individual cancer registries. For the future, the goal is to realize the research potential of this new cooperative data collection mechanism, as well as the accumulating data themselves. Progress toward the long-term goal is just beginning.

Cancer Care Facilities↗
PubMed1998

Testing the Cambrian explosion hypothesis by using a molecular dating technique.

Molecular studies have the potential to shed light on the origin of the animal phyla by providing independent estimates of the divergence times, but have been criticized for failing to account adequately for variation in rate of evolution. A method of dating divergence times from molecular data addresses the criticisms of earlier studies and provides more realistic, but wider, confidence intervals. The data are not compatible with the Cambrian explosion hypothesis as an explanation for the origin of metazoan phyla, and provide additional support for an extended period of Precambrian metazoan diversification.

Animals↗
PubMed2001

Evolution of thermal dependence of growth rate of Escherichia coli populations during 20,000 generations in a constant environment.

Twelve experimental populations of the bacterium Escherichia coli evolved for 20,000 generations in a defined medium at 37 degrees C. We measured their maximum growth rates across a broad range of temperatures and at several evolutionary time points to quantify the extent to which they became thermal specialists with diminished performance at other temperatures. We also sought to determine whether antagonistic pleiotropy (genetic trade-offs) or mutation accumulation (drift decay) was primarily responsible for any thermal specialization. Populations showed consistent improvement in growth rate at moderate temperatures (27-39 degrees C), but tended to have decreased growth rate at both low (20 degrees C) and high (41-42 degrees C) temperatures. Most loss occurred early in the experiment, when adaptation was most rapid. This dynamic is predicted by antagonistic pleiotropy but not by mutation accumulation. Several populations evolved high mutation rates due to defects in their DNA repair, but they did not subsequently undergo a greater decrease in growth rate at thermal extremes than populations that retained low mutation rates, contrary to the acceleration of decay predicted by mutation accumulation. Antagonistic pleiotropy therefore is more likely to be responsible for the evolution of thermal specialization observed in maximum growth rate.

Adaptation, Physiological↗
PubMed1997

Transitions in individuality.

The evolution of multicellular organisms is the premier example of the integration of lower levels into a single, higher-level individual. Explaining the evolutionary transition from single cells to multicellular organisms is a major challenge for evolutionary theory. We provide an explicit two locus genetic framework for understanding this transition in terms of the increase of cooperation among cells and the regulation of conflict within the emerging organism. Heritability of fitness and individuality at the new level emerge as a result of the evolution of organismal functions that restrict the opportunity for conflict within and ensure cooperation among cells. Conflict leads, through the evolution of adaptations that reduce it, to greater individuality and harmony for the organism.

Adaptation, Physiological↗
PubMed2005

Molecular phylogeny of coleoid cephalopods (Mollusca: Cephalopoda) using a multigene approach; the effect of data partitioning on resolving phylogenies in a Bayesian framework.

The resolution of higher level phylogeny of the coleoid cephalopods (octopuses, squids, and cuttlefishes) has been hindered by homoplasy among morphological characters in conjunction with a very poor fossil record. Initial molecular studies, based primarily on small fragments of single mitochondrial genes, have produced little resolution of the deep relationships amongst coleoid cephalopod families. The present study investigated this issue using 3415 base pairs (bp) from three nuclear genes (octopine dehydrogenase, pax-6, and rhodopsin) and three mitochondrial genes (12S rDNA, 16S rDNA, and cytochrome oxidase I) from a total of 35 species (including representatives of each of the higher level taxa). Bayesian analyses were conducted on mitochondrial and nuclear genes separately and also all six genes together. Separate analyses were conducted with the data partitioned by gene, codon/rDNA, gene+codon/rDNA or not partitioned at all. In the majority of analyses partitioning the data by gene+codon was the appropriate model with partitioning by codon the second most selected model. In some instances the topology varied according to the model used. Relatively high posterior probabilities and high levels of congruence were present between the topologies resulting from the analysis of all Octopodiform (octopuses and vampire "squid") taxa for all six genes, and independently for the datasets of mitochondrial and nuclear genes. In contrast, the highest levels of resolution within the Decapodiformes (squids and cuttlefishes) resulted from analysis of nuclear genes alone. Different higher level Decapodiform topologies were obtained through the analysis of only the 1st+2nd codon positions of nuclear genes and of all three codon positions. It is notable that there is strong evidence of saturation among the 3rd codon positions within the Decapodiformes and this may contribute spurious signal. The results suggest that the Decapodiformes may have radiated earlier and/or had faster rates of evolution than the Octopodiformes. The following taxonomic conclusions are drawn from our analyses: (1) the order Octopoda and suborders Cirrata, Incirrata, and Oegopsida are monophyletic groups; (2) the family Spirulidae (Ram's horn squids) are the sister taxon to the family Sepiidae (cuttlefishes); (3) the family Octopodidae, as currently defined, is paraphyletic; (4) the superfamily Argonautoidea are basal within the suborder Incirrata; and (5) the benthic octopus genera Benthoctopus and Enteroctopus are sister taxa.

Animals↗
PubMed2006

Genome increase as a clock for the origin and evolution of life.

BACKGROUND: The size of non-redundant functional genome can be an indicator of biological complexity of living organisms. Several positive feedback mechanisms including gene cooperation and duplication with subsequent specialization may result in the exponential growth of biological complexity in macro-evolution. RESULTS: I propose a hypothesis that biological complexity increased exponentially during evolution. Regression of the logarithm of functional non-redundant genome size versus time of origin in major groups of organisms showed a 7.8-fold increase per 1 billion years, and hence the increase of complexity can be viewed as a clock of macro-evolution. A strong version of the exponential hypothesis is that the rate of complexity increase in early (pre-prokaryotic) evolution of life was at most the same (or even slower) than observed in the evolution of prokaryotes and eukaryotes. CONCLUSION: The increase of functional non-redundant genome size in macro-evolution was consistent with the exponential hypothesis. If the strong exponential hypothesis is true, then the origin of life should be dated 10 billion years ago. Thus, the possibility of panspermia as a source of life on earth should be discussed on equal basis with alternative hypotheses of de-novo life origin. Panspermia may be proven if bacteria similar to terrestrial ones are found on other planets or satellites in the solar system. REVIEWERS: This article was reviewed by Eugene V. Koonin, Chris Adami and Arcady Mushegian.

Journal Article↗
PubMed1984

An evolutionary model of a neural network.

A very general model of an idealized neural network is proposed, in which the system is governed by an evolution equation. The equation determines the state of the network at time t greater than 0, if its state at time t = 0 and the kernel (in the equation) are known. It is shown that, by making specific assumptions about the kernal and the initial state, the evolution equation describes a distributed memory having the properties of recognition and association. In this case the model of the distributed memory is identical to that of Anderson and Cooper. Further, it is shown that by a different choice of the kernel, the evolution equation goes beyond the earlier model and is able to describe learning as a dynamic process.

Biological Evolution↗
PubMed2002

Distribution and evolution of the Anopheles punctulatus group (Diptera: Culicidae) in Australia and Papua New Guinea.

The members of the Anopheles punctulatus group are major vectors of malaria and Bancroftian filariasis in the southwest Pacific region. The group is comprised of 12 cryptic species that require DNA-based tools for species identification. From 1984 to 1998 surveys were carried out in northern Australia, Papua New Guinea and on islands in the southwest Pacific to determine the distribution of the A. punctulatus group. The results of these surveys have now been completed and have generated distribution data from more than 1500 localities through this region. Within this region several climatic and geographical barriers were identified that restricted species distribution and gene flow between geographic populations. This information was further assessed in light of a molecular phylogeny derived from the ssrDNA (18S). Subsequently, hypotheses have been generated on the evolution and distribution of the group so that future field and laboratory studies may be approached more systematically. This study suggested that the ability for widespread dispersal was found to have appeared independently in species that show niche-specific habitat preference (Anopheles farauti s.s. and A. punctulatus) and conversely in species that showed diversity in their larval habitat (Anopheles farauti 2). Adaptation to the monsoonal climate of northern Australia and southwest Papua New Guinea was found to have appeared independently in A. farauti s.s., A. farauti 2 and Anopheles farauti 3. Shared or synapomorphic characters were identified as saltwater tolerance (A. farauti s.s. and Anopheles farauti 7) and elevational affinities above 1500 m (Anopheles farauti 5, Anopheles farauti 6 and A. farauti 2).

Animals↗
PubMed2006

The evolution of adaptive immunity.

Approximately 500 mya two types of recombinatorial adaptive immune systems appeared in vertebrates. Jawed vertebrates generate a diverse repertoire of B and T cell antigen receptors through the rearrangement of immunoglobulin V, D, and J gene fragments, whereas jawless fish assemble their variable lymphocyte receptors through recombinatorial usage of leucine-rich repeat (LRR) modular units. Invariant germ line-encoded, LRR-containing proteins are pivotal mediators of microbial recognition throughout the plant and animal kingdoms. Whereas the genomes of plants and deuterostome and chordate invertebrates harbor large arsenals of recognition receptors primarily encoding LRR-containing proteins, relatively few innate pattern recognition receptors suffice for survival of pathogen-infected nematodes, insects, and vertebrates. The appearance of a lymphocyte-based recombinatorial system of anticipatory immunity in the vertebrates may have been driven by a need to facilitate developmental and morphological plasticity in addition to the advantage conferred by the ability to recognize a larger portion of the antigenic world.

Adaptation, Physiological↗
PubMed1997

Homology modelling of the catalytic domain of early mammalian protein C: evolution of structural features.

By means of a novel cDNA-based strategy employing the maximum parsimony principle, we have previously deduced probable amino acid sequences for the catalytic domains of the early mammalian ancestors of each of the five extant vitamin K-dependent serine proteases of coagulation, and for their common ancestor from a still earlier stage of vertebrate evolution. In the present study, we employed one of these sequences to construct a molecular model of the catalytic domain of early mammalian protein C and to explore its functional architecture. Following the domain's progression from the common ancestor of the vitamin K-dependent serine proteases toward extant human protein C, this novel application of homology modelling to a reconstructed amino acid sequence has allowed us to trace the evolution of structural features in a vital coagulation protein.

Amino Acid Sequence↗
PubMed2003

Foraging mode and evolution of strike-induced chemosensory searching in lizards.

Strike-induced chemosensory searching (SICS) in lizards and snakes is a means of relocating prey by scent-trailing. The two main components of SICS are an elevated tongue-flick rate for vomerolfactory sampling after biting prey (PETF) and searching movements. In combination, these behaviors permit scent-trailing. Prey chemical discrimination, which is a prerequisite for SICS, is present in active foragers, but not in ambush foragers. Using comparative data. I show that searching movements and SICS have undergone correlated evolution with foraging mode and with prey chemical discrimination in lizards. This suggests that active foraging selects for prey chemical discrimination, which is then employed to search for escaped prey using the typical movements and tongue-flicking behaviors of active foragers. SICS in lizards is simply heightened active foraging after biting prey. In nonvenomous snakes, SICS is similar to that in lizards but is not restricted to active foragers. Only highly venomous snakes voluntarily release dangerous prey upon envenomation, pause to let the venom incapacitate the prey, and then relocate the prey by scent-trailing. PETF was observed in two ambush foragers and is not evolutionarily correlated with foraging mode or searching movements. Because it occurs in species lacking prey chemical discrimination, such PETF may be a response to gustatory cues or to internal chemicals not encountered on surfaces or trails of uninjured prey.

Adaptation, Physiological↗