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At least 1,261 records · Page 70Linked to original sources
PubMed2002

Fin development in a cartilaginous fish and the origin of vertebrate limbs.

Recent fossil finds and experimental analysis of chick and mouse embryos highlighted the lateral fin fold theory, which suggests that two pairs of limbs in tetrapods evolved by subdivision of an elongated single fin. Here we examine fin development in embryos of the primitive cartilaginous fish, Scyliorhinus canicula (dogfish) using scanning electron microscopy and investigate expression of genes known to be involved in limb positioning, identity and patterning in higher vertebrates. Although we did not detect lateral fin folds in dogfish embryos, Engrailed-1 expression suggests that the body is compartmentalized dorso-ventrally. Furthermore, specification of limb identity occurs through the Tbx4 and Tbx5 genes, as in higher vertebrates. In contrast, unlike higher vertebrates, we did not detect Shh transcripts in dogfish fin-buds, although dHand (a gene involved in establishing Shh) is expressed. In S. canicula, the main fin axis seems to lie parallel to the body axis. 'Freeing' fins from the body axis and establishing a separate 'limb' axis has been proposed to be a crucial step in evolution of tetrapod limbs. We suggest that Shh plays a critical role in this process.

Animals↗
PubMed2002

Infection polymorphism and cytoplasmic incompatibility in Hymenoptera-Wolbachia associations.

Most cases of Wolbachia infection so far documented in haplodiploid Hymenoptera are associated with parthenogenesis induction. Only three examples of Wolbachia-mediated cytoplasmic incompatibility (CI) have been reported, resulting either in haploidisation of fertilised eggs, which develop into viable males, or in their death. To better document this variability, we studied two new Wolbachia-wasp associations involving Drosophila parasitoids. In Trichopria cf. drosophilae, individuals are infected by two different Wolbachia variants, populations are nearly totally infected, and Wolbachia induces incomplete CI resulting in death of the fertilised eggs. On the other hand, Pachycrepoideus dubius harbours only one bacterial variant, populations are polymorphic for infection, and Wolbachia has no detectable effect. These two cases show that the range of variation in Wolbachia's effects in Hymenoptera is as wide as in diploids, extending from complete CI to an undetectable effect. Cases so far studied show some parallel between the strength of incompatibility, the number of Wolbachia variants infecting each wasp, and the natural infection frequency. These empirical data support theoretical models predicting evolution of CI towards lower levels, resulting in the decline and ultimate loss of infection, and place multiple infections as being an important factor in the evolution of host-Wolbachia associations.

Animals↗
PubMed2003

An asymptotic model of unsteady airway reopening.

We consider a simple physical model for the reopening of a collapsed lung airway involving the unsteady propagation of a long bubble of air, driven at a prescribed flow-rate, into a liquid-filled channel formed by two flexible membranes that are held under large longitudinal tension and are confined between two parallel rigid plates. This system is described theoretically using an asymptotic approximation, valid for uniformly small membrane slopes, which reduces to a fourth-order nonlinear evolution equation for the channel width ahead of the bubble tip, from which the time-evolution of the bubble pressure pb* and bubble speed may be determined. The model shows that there can be a substantial delay between the time at which the bubble starts to grow in volume and the time at which its tip starts to move. Under certain conditions, the start of the bubble's motion is accompanied by a transient overshoot in pb*, as seen previously in experiment; the model predicts that the overshoot is greatest in narrow channels when the bubble is driven with a large volume flux. It is also shown how the threshold pressure for steady bubble propagation in wide channels has distinct contributions from the capillary pressure drop across the bubble tip and viscous dissipation in the channel ahead of the bubble.

Air Pressure↗
PubMedDate not supplied

Osteocalcin. A biochemical marker of bone turnover during puberty.

During bone remodelling, osteocalcin is produced by osteoblasts and its level increases during the events characterized by rapid bone turnover. Osteocalcin is a bone matrix protein, which is specific for bone metabolism and it is not influenced by metabolic bone disorders. Osteocalcin is an important marker of bone turnover in physiological and pathological conditions. Physiologically, serum osteocalcin was increased in children, particularly during the first year of life and during puberty, when evolution of the concentration was related to rapidity of physical growth. Evidence of a correlation with growth rates comes from the observation that serum osteocalcin levels parallel the height velocity curve, with higher values in childhood and during adolescence, that later fall to adult values. There are previous studies reporting that there is age- and sex-dependent change in serum osteocalcin levels in children and adolescents with a pattern resembling height velocity curves for children and serum osteocalcin elevation coincides with the pubertal growth spurt. These findings demonstrate that pubertal development and sex should be taken into account rather than chronological age when serum levels of osteocalcin are evaluated. In most of the studies relationships among osteocalcin and chronological age and bone age, but not pubertal developmental stage (sexual maturation stage) were investigated. The aim of our study was to determine whether osteocalcin is a useful marker for the pubertal growth spurt period. In this study, osteocalcin levels in male adolescents were examined in relation to their sexual maturation stage and age. According to our findings, the follow up of osteocalcin levels in relation to sexual maturation stages could be a new method to determine the phase of the pubertal growth spurt. An increase or decrease in osteocalcin levels on consecutive measurements may indicate the child's entering accelerated or decelerated stages of the growth spurt, respectively. We emphasize that the follow up of adolescent growth is made by determination of the sexual maturation stage, and not by age. Osteocalcin is a highly specific, reliable and useful marker for evaluation of the growth spurt and is not influenced by nonosseous disorders.

Adolescent↗
PubMed1990

[Severe cervical spinal cord injuries without traumatic osteo-disco-ligamentous lesion].

The existence of cervical spinal cord injury without bony nor disco-ligamentous lesion rises pathogenic, prognostic and therapeutic challenges. The extent and localisation of cord injury, which depends on intensity and direction of the applied force, can explain the different clinical patterns: incomplete quadriplegia: 8 cases, incomplete Brown-Sequard-like quadriplegia: 2 cases, diplegia brachialis: 5 cases. We have not observed any complete quadriplegia. The presence of arthritic or congenital spinal canal stenosis has been found in 12 cases. We have used a coupled myelographic-CT Scan study. MRI has been employed more recently. This X-ray study has never found any major cord compression. Improvement of neurologic troubles, under medical treatment, was constant, but sequelae were always present, hands being most concerned; their importance was paralleled to the initial clinical feature. The Brown-Sequard-like quadriplegia were more pejorative. 3 patients, after an initial improvement, have presented a cervical myelopathic evolution and have been successfully operated on. On the other hand, the only initially operated on patient has been immediately worsened. Operation is indicated by the third week, when coexist: a spinal stenosis and a poor clinical evolution.

Adult↗
PubMed1990

[Have lupus characteristics changed?].

The features of lupus have been changing for 30 years. The aim of this study was to determine the main modifications and to search for the possible causes. Lupus epidemiology, the clinical symptoms and the prognostic subsets were investigated. The rising incidence of lupus closely paralleled improvements in diagnostic techniques (LE cell testing, anti-nuclear antibodies) but has since remained stable. The prevalence progressively increased over this time, but this evolution is associated with better detection of benign subsets and improvement in the management of the disease and its complications. More sensitive serological methods have attributed new symptoms to lupus, revealing that some forms are benign. Survival has been improving and infection has become the primary cause of death. Opportunistic infections in lupus are increasing, however the majority of them remain undiagnosed until the autopsy.

Humans↗
PubMed1989

Drug use trends in a nuclear power company: cumulative data from an ongoing testing program.

This article has traced the evolution of Southern California Edison's San Onofre Nuclear Generating Station (SONGS) from fledgling nuclear facility to one of the largest nuclear power installations in America. Paralleling this growth has been an increasing sophistication and commitment to preserving the public trust through efforts to eliminate substance abuse in the workplace. Southern California Edison's substance abuse program has grown and changed in many ways. The results of this change were presented through data gathered at SONGS. These efforts continue to be directed toward an ultimate goal--the creation of a truly drug-free workplace. Work continues.

California↗
PubMedDate not supplied

[Direct relation between the significantly increased IgG specific antibody titer and the clinico-evolutive form in respiratory infections in infants and children. IgA and IgD levels in the evolution].

Of 69 children suffering from acute respiratory infections, with increased IgG titers 34 presented normal or high IgAs titers in the laryngotracheal exudate. All these patients had a favourable evolution. The other children with low IgAs levels or absent IgAs in the laryngotracheal exudate had a prolonged relapsing evolution, regardless of serum IgG levels. The presence of IgA 7S in the laryngotracheal exudate did not influence the course of the disease. As a conspicuous parallelism was observed between laryngotracheal exudate IgAs and serum IgA it was assumed that IgAs participates in the formation of serum IgA "mixtures". Increased IgD values were found in 34 of these patients, ten of whom presented respiratory allergy and recurrent infections.

Adolescent↗
PubMed1997

The history of the Army weight standards.

Medical officers in the U.S. Army are tasked with screening, evaluating, and processing soldiers in accordance with AR 600-9, the Army's height and weight standards regulation. This essay traces the origins of the Army's weight standards to the present day. The Army's height and weight standards have varied markedly, from the crude subjective assessment of selective service candidates at the local draft examination boards at the turn of the century to the modern, highly accurate methods currently used in anthropomorphic research. The strictness of military recruitment and retention standards closely paralleled changing military personnel requirements in any particular era. Racial integration and the influx of women into the ranks had noteworthy effects on this history. The evolution of the Army's weight-control program and screening standards reflects advancements in medical knowledge and technology, societal and political pressure, and the empirical tests of world wars.

Anthropometry↗
PubMed1998

Structured-tree topology and adaptive evolution of the simian immunodeficiency virus SIVsm envelope during serial passage in rhesus macaques according to likelihood mapping and quartet puzzling.

Species-specific strains of simian immunodeficiency virus (SIV) are nonpathogenic in African primates. The SIV strain most closely related to human immunodeficiency virus type 2 (HIV-2) is SIVsm, the strain specific to the sooty mangabey (Cercocebus atys). Infection of Asian primates with SIV causes AIDS and allows the study of the adaptive evolution of a lentivirus to replicate efficiently in a new host, providing a useful animal model of HIV infection and AIDS in humans. Serial passage of SIVsm from sooty mangabeys in rhesus macaques drastically shortened the time of disease progression from 1.5 years to 1 month as the retrovirus adapted to these Asian hosts. In the present study we analyzed the quasispecies nature of the SIVsm envelope gene (env) during serial population passage in rhesus macaques. We asked ourselves if phylogenetic evidence could be provided for the structured topology of the SIVsm env tree and subsequently for the adaptive evolution of SIVsm env. Likelihood mapping showed that phylogenetic reconstruction of the passage was possible because a high percentage of the sequence data had a "tree-like" form. Subsequently, quartet puzzling was used and produced a phylogeny with a structure parallel to the known infection history. The adaptation of SIVsm to Asian rhesus macaques appears to be an ordered process in which the env evolves in a tree-like manner, particularly in its constant regions.

Adaptation, Biological↗
PubMed2003

The co-evolution of people, plants, and parasites: biological and cultural adaptations to malaria.

The urgency generated by drug-resistant strains of malaria has accelerated anti-malarial drug research over the last two decades. While synthetic pharmaceutical agents continue to dominate research, attention increasingly has been directed to natural products. The present paper explores the larger context in which plant use occurs and considers how the selection of medicinal plants has evolved over millennia as part of the larger human effort to mediate illness. First attention is directed to indigenous medicinal plants whose anti-malarial activity is based on an oxidant mode of action, by which intracellular constituents lose electrons (become more electropositive). Next, parallels are drawn between these plant substances and a suite of malaria-protective genetic traits: glucose-6-phosphate dehydrogenase deficiency; haemoglobins S, C and E; alpha- and beta-thalassemias. These erythrocyte anomalies are classic examples of Darwinian evolution, occurring in high frequency in populations who have experienced considerable selective pressure from malaria. Characterized by discrete loci and pathophysiologies, they are united through the phenomenon of increased erythrocyte oxidation. In this model, then, oxidant anti-malarial plants are culturally constructed analogues, and molecular mimics, of these genetic adaptations. To further reinforce the scheme, it is noted that the anti-malarial action of pharmaceutical agents such as chloroquine and mefloquine duplicates both the genetic anomalies and the folk therapeutic models based in oxidant plants. This discussion coheres around a theoretical foundation that relates plant secondary metabolites (oxidants) to plasmodial biochemistry and human biological and cultural adaptations to malaria. Co-evolution provides a theoretical link that illuminates how medical cultures manage the relationships among humans, plants, herbivores and their respective pathogens.

Adaptation, Physiological↗
PubMed1986

Character displacement and niche shift analyzed using consumer-resource models of competition.

This paper analyzes the adaptive responses to competition (both character displacement and niche shift) in a two consumer-two resource model. The model includes density dependence that is unrelated to the resources that are explicit in the model. This could be due to another resource dimension, parasites, or interference competition. Competitors adapt by changing their relative consumption rate constants on the two resource types. This model can result in mutually divergent, parallel, or mutually convergent displacement of competitors. Parallel displacement may entail net divergence, net convergence, or no net change. Parallel change with net convergence is most likely when the competitors have similar constraints on the possible values of consumption rate constants, unequal allopatric abundances, and significant intraspecific density dependence. Numerical calculations of displacements are presented for several models and the effect of a number of different possible alterations of the model are discussed. The evolution of resource handling and processing efficiency, and displacement in the presence of additional selective pressures on the character are considered in detail. The results have implications for questions about maximization of population size, the relationship of character displacement and the competition coefficient, and "null" models in the study of competition. Differences between this and previous theoretical works are discussed. It is argued that conditions allowing parallel or convergent displacement are not biologically unlikely, and possible examples are discussed. Data on resource partitioning seem to be more consistent with the results reached here than with previous theory.

Animals↗
PubMed2005

Using parallel evolutionary development for a biologically-inspired computer vision system for mobile robots.

We describe a new approach to attacking the problem of robust computer vision for mobile robots. The overall strategy is to mimic the biological evolution of animal vision systems. Our basic imaging sensor is based upon the eye of the common house fly, Musca domestica. The computational algorithms are a mix of traditional image processing, subspace techniques, and multilayer neural networks.

Algorithms↗
PubMed2001

Fish gonadotropin and thyrotropin receptors: the evolution of glycoprotein hormone receptors in vertebrates.

We have cloned and characterized, for the first time in fish, two different gonadotropin receptors (GTHR) and a single thyrotropin receptor (TSHR) from amago salmon (Oncorhynchus rhodurus) and Nile tilapia (Oreochromis niloticus). Phylogenetic analyses and intron/exon structure suggest that the two GTHRs in fish are comparable to tetrapod follicle stimulating hormone and luteinizing hormone receptors. Temporal and spatial expression patterns, examined by Northern blot analysis and in situ hybridization, paralleled those seen in mammals and birds. Consequently, genetic and functional divergence of two GTHRs and TSHR probably occurred before the teleost and tetrapod split.

Animals↗
PubMed2026

Reframing early gastric carcinogenesis through lineage, niche, and evolution.

Early gastric cancer is still commonly conceptualized as the endpoint of a linear sequence from chronic gastritis to intestinal metaplasia, dysplasia, and invasion. Yet recent single-cell, spatial, genomic, and functional studies indicate that this model incompletely captures the biology of early gastric carcinogenesis. Malignant potential is established progressively within a precancerous gastric field already shaped by somatic evolution, chronic inflammatory injury, and epithelial lineage distortion. Within this field, progression is concentrated in a restricted set of precursor states, particularly incomplete, hybrid, and stem-like metaplastic populations that display plasticity, persistence, and increasing compatibility with a supportive microenvironment. Fibroblast niche remodeling, immune protection loss, endothelial rewiring, genomic instability, epigenetic drift, and selective retention of advantageous molecular alterations further promote malignant commitment. In parallel, diffuse gastric cancer appears to follow a distinct route that may arise independently of conventional intestinal metaplasia through E-cadherin-deficient epithelial transformation and downstream chromatin reprogramming. Here, we synthesize recent evidence to propose an updated framework for early gastric carcinogenesis based on field evolution, lineage instability, ecosystem support, and pathway divergence. Rather than replacing the classical Correa cascade, this framework seeks to refine it by shifting the unit of risk assessment from histologic stage alone to biologically defined precursor states shaped by lineage instability, clonal persistence, niche permissiveness, and pathway-specific molecular constraints. This perspective shifts the emphasis of prevention from detecting smaller cancers to identifying and intercepting biologically committed precursor states before invasion occurs.

Humans↗
PubMed2000

Experimental evolution recapitulates natural evolution.

Genomes of the closely related bacteriophages phiX174 and S13 are 5386 bases long and differ at 114 nucleotides, affecting 28 amino acids. Both parental phages were adapted to laboratory culture conditions in replicate lineages and analysed for nucleotide changes that accumulated experimentally Of the 126 experimental substitutions, 90% encoded amino-acid changes, and 62% of the substitutions occurred in parallel in more than one experimental line. Furthermore, missense changes at 12 of the experimental sites were at residues differing between the parental phages; in ten cases the phiX174 experimental lineages were convergent with the S13 parent, or vice versa, at both the nucleotide and amino-acid levels. Convergence at a site was even obtained in both directions in three cases. These results point to a limited number of pathways taken during evolution in these viruses, and also raise the possibility that much of the amino-acid variation in the natural evolution of these viruses has been selected.

Bacteriophage phi X 174↗
PubMed1994

Combined transsylvian-subtemporal exposure of cerebral aneurysms involving the basilar apex.

The surgical repair of cerebral aneurysms involving the apex of the basilar artery continues to undergo refinement and evolution. The inherent difficulty in accessing the basilar apex as well as the complexities of the microanatomy render this area a notoriously hazardous and technically challenging region in which to perform microsurgical clipping of cerebral aneurysms. Several operative approaches have been described and are constantly undergoing a state of evolution in the hopes of optimizing the exposure of the distal basilar artery and minimizing the inherent risks of surgery. The consistent decline in operative morbidity has paralleled improved understanding of the microvascular anatomy, both in this region and along the various corridors of approach. No single operative approach is universally superior, considering the wide variability of individual patient anatomy and vascular configurations. Each approach has strengths, weaknesses, and potential complications that must be considered in the though process of planning an operative attack on a basilar apex aneurysm. Intimate familiarity with the microvasculature and the microsurgical anatomy of the region is an imperative prerequisite for the application of any surgical approach to this region. This paper outlines a detailed review of the microsurgical anatomy that is pertinent to microsurgery of aneurysms in this region, and describes an approach referred to as the combined transsylvian-subtemporal approach. We have found this operative approach particularly useful in aneurysm surgery of the basilar apex but do not mean to imply that this single approach is suitable for all surgeons or all patients.(ABSTRACT TRUNCATED AT 250 WORDS)

Basilar Artery↗
PubMed2004

Amyloid fibrillogenesis of silkmoth chorion protein peptide-analogues via a liquid-crystalline intermediate phase.

Chorion, the major component of silkmoth eggshell, consists of the A and B classes of low-molecular weight structural proteins. Chorion protects the oocyte and the developing embryo from environmental hazards and this is due to the extraordinary physical and chemical properties of its constituent proteins. We have shown previously [FEBS Lett. 479 (2000) 141; 499 (2001) 268] that peptide-analogues of the A and B classes of chorion proteins form amyloid fibrils under a variety of conditions, which led us to propose that silkmoth chorion is a natural, protective amyloid. In this work, we present data showing conclusively that, the first main step of amyloid-like fibrillogenesis of chorion peptides is the formation of nuclei of liquid crystalline nature, which is reminiscent of spider-silk formation. We show that these liquid-crystalline nuclei (spherulites) 'collapse'/deteriorate to form amyloid fibrils in a spectacular manner, important, it seems, for chorion morphogenesis and amyloid fibrillogenesis in general. The molecular 'switch' causing this spectacular transformation is, most probably, a conformational transition to the structure of chorion peptides, from a left-handed parallel beta-helix to an antiparallel beta-pleated sheet. Apparently, these peptides were suitably designed to play this role, after millions of years of molecular evolution.

Amino Acid Sequence↗