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At least 1,621 records · Page 90Linked to original sources
PubMed2000

Do proteins learn to evolve? The Hopfield network as a basis for the understanding of protein evolution.

Correlations between amino-acid residues can be observed in sets of aligned protein sequences, and the analysis of their statistical and evolutionary significance and distribution has been thoroughly investigated. In this paper, we present a model based on such covariations in protein sequences in which the pairs of residues that have mutual influence combine to produce a system analogous to a Hopfield neural network. The emergent properties of such a network, such as soft failure and the connection between network architecture and stored memory, have close parallels in known proteins. This model suggests that an explanation for observed characters of proteins such as the diminution of function by substitutions distant from the active site, the existence of protein folds (superfolds) that can perform several functions based on one architecture, and structural and functional resilience to destabilizing substitutions might derive from their inherent network-like structure. This model may also provide a basis for mapping the relationship between structure, function and evolutionary history of a protein family, and thus be a powerful tool for rational engineering.

Animals↗
PubMed1989

Immunoproteins in evolution.

All vertebrates respond to antigenic challenge by specific cellular reactions and by producing circulating antibodies, and they also contain recognition molecules that are evolutionary relics of primitive non-immune recognition. One such ancient recognition molecule is C-reactive protein (CRP), a member of the pentraxin family, that has homologs occurring in species as diverse as vertebrates, tunicates and the horseshoe crab (an ancient arachnoid). This molecule has lectin-like properties, can act as an opsonin and interact with complement and cells in a manner paralleling immunoglobulins (Igs). The horseshoe crab lectin and CRP, although unrelated to Igs, share functional idiotopes with classical antibodies. This finding reflects either an evolutionary convergence or a mechanism of "mini gene insertion" that allows molecules of distinct evolutionary histories to react to the same ligands. Serum antibodies of all vertebrates are polydisperse in charge and are composed of polypeptide chains comparable in mass to those of mammalian light and heavy chains. Molecular genetic studies of placoderm derived vertebrates are incomplete but are sufficient to allow the conclusion that Igs of these species are specified by variable (V), joining (J) and constant (C) gene segments and that rearrangement are an essential feature for the generation of antibody diversity. Here we present new evidence following from the use of antibodies directed against synthetic joining region peptides as probes in the study of rearranging Igs in evolution, the use of recombinant DNA technology to study T cell receptor V beta genes in a goldfish genomic library and the isolation and characterization of a gene fragment specifying sandbar shark light chain C region. We reached the following conclusions: (1) J region segments are the most conserved in evolution, and this most probably reflects the essential requirements for these gene segments in the formation of intact Ig genes by rearrangement; (2) the framework segments of V regions are highly conserved in vertebrate evolution for both T cell receptors and classical Igs; and (3) although C region segments of light chains of lower vertebrates are homologous to their mammalian counterparts, the degree of conservation of C region structure in phylogeny is apparently less than that for V regions. Essentially, phylogenetic trees can be built using C regions but not V regions. We have identified a molecule of approximate mass of 26 kDa in the hemolymph of the tunicate, Boltenia ovipera, that is serologically cross-reactive with shark heavy chain and with J region peptides.(ABSTRACT TRUNCATED AT 400 WORDS)

Amino Acid Sequence↗
PubMedDate not supplied

TSRH instrumentation: evolution of a new system. Part 1. Texas Scottish Rite Hospital.

The TSRH System was designed at Texas Scottish Rite Hospital for Crippled Children in Dallas, Texas, to correct spinal deformities in a three-dimensional plane. The system's greatest advantage is its application in spinal revisions. The other advantage to the TSRH system is the crosslink system used in linking paralleling rods for spinal fusion. The TSRH spinal system is paralleled to the Cotrel-Dubousset (CD) system. Advantages of both systems are discussed in this article.

Child↗
PubMedDate not supplied

Evolution of carotid atheromatous lesions in endarterectomized patients.

A noninvasive follow-up using duplex ultrasonography was conducted in 128 patients who had undergone carotid endarterectomy from January 1987 to December 1988. Repeated scans of the operated area revealed a distinct increase in thickened ultrasonographic features (32% vs 8%), and a stenosing lesion was detected in 8 patients. There was also a parallel increase in the number of subjects with thicknesses of the intima adjacent to the endarterectomy area exceeding 2.5 mm. In 7% of cases, dilatation was detected in the operated area and in 27% the margin of the area was raised. The study also dealt with the contralateral carotid artery, where a progression of atheromatous involvement was observed with an increased number of cases of hemodynamically significant stenosis and 3 cases of occlusion. Periodic duplex ultrasonography in endarterectomized patients proves useful for the early detection of hemodynamically significant stenoses or of structural features potentially capable of generating emboli.

Aged↗
PubMed2006

Energetic efficiency under stress underlies positive genetic correlations between longevity and other fitness traits in natural populations.

Evolutionary relationships among fitness traits are considered in terms of the near-to-universal scenario of stressful environments leading to a resource-deficient and hence energy-deficient world. Fitness approximates to energetic (and metabolic) efficiency under this environmental model. When fitness is high, stress resistance (reducible to oxidative-stress resistance) and metabolic stability are maximal, and energy expenditure is minimal. Rapid development should then be favored followed by a long lifespan and high adult survival. Positive associations among diverse fitness or life-history traits are expected, controlled by stress-resistant 'good genotypes'. Heterozygotes tend to show higher energetic efficiency and hence higher fitness than do corresponding homozygotes under extreme environments, and to give parallel associations among life-history traits. Energy budgets under abiotic environments are pivotal for integrative evolutionary studies of life histories in natural populations.

Animals↗
PubMed2003

Bimodal run distribution in a northern population of sockeye salmon (Oncorhynchus nerka): life history and genetic analysis on a temporal scale.

Life history variation and genetic differentiation were analysed in sockeye salmon in Klukshu River, Yukon Canada over 7 years (1994-2000). Sockeye salmon return to the Klukshu River in two distinct runs, with a small 'early run' in June-August, and a larger 'late run' in August-September. A maximum likelihood test for clusters indicated that the return frequency distribution was bimodal in all the years analysed. Life history differences (fork length, sex ratio, age at maturity, fresh- and saltwater residency times) were found between the early and late runs; however, inconsistent patterns suggest that environmental effects outweigh, or strongly interact with, genetic effects for the life history characters evaluated. Analysis of variation at eight microsatellite loci showed that the early and late runs are genetically differentiated in all years examined (exact test). FST estimates between runs within years were significantly greater than zero (range: 0.018-0.041) for all years except one (0.004). The genetic variance explained by early vs. late runs (2.27%) was twice the variance among years (1.16%) based on analysis of molecular variance. Our neighbour-joining tree showed early and late runs generally clustering separately, indicating higher gene flow among the early or late run fish across years relative to between-run gene flow. Two years did not fit the general clustering pattern; although the early and late runs in 1995 and 2000 were genetically differentiated, they clustered separately from the rest of the groups. We cannot offer a definitive explanation for these anomalies; however, an analysis of possible cryptic population structure in early and late runs indicated that at least a few fish strayed between the runs in each year, and the highest rate of mixing was in 1995 and 2000. Our data indicate that the runs are at least partially reproductively isolated as a result of temporal and/or spatial isolating mechanisms. Such reproductive isolation has important implications for conservation and management of the Klukshu sockeye salmon, and make them an evolutionarily interesting group because of parallels with incipient speciation.

Alleles↗
PubMed2006

Crab scars reveal survival advantage of left-handed snails.

Biological asymmetries are important elements of the structure and function of many living organisms. Using the Plio-Pleistocene fossil record of crab predation on morphologically similar pairs of right- and left-handed snail species, we show here for the first time, contrary to traditional wisdom, that rare left-handed coiling promotes survival from attacks by right-handed crabs. This frequency-dependent result influences the balance of selection processes that maintain left-handedness at the species level and parallels some social interactions in human cultures, such as sports that involve dual contests between opponents of opposite handedness.

Adaptation, Physiological↗
PubMed2004

Evolutionary dynamics of complex biomechanical systems: an example using the four-bar mechanism.

Like many phenotypic traits, biomechanical systems are defined by both an underlying morphology and an emergent functional property. The relationship between these levels may have a profound impact on how selection for functional performance is translated into morphological evolution. In particular, complex mechanical systems are likely to be highly redundant, because many alternative morphologies yield equivalent functions. We suggest that this redundancy weakens the relationship between morphological and functional diversity, and we illustrate this effect using an evolutionary model of the four-bar lever system of labrid fishes. Our results demonstrate that, when traits are complex, the morphological diversity of a clade may only weakly predict its mechanical diversity. Furthermore, parallel or convergent selection on function does not necessarily produce convergence in morphology. Empirical observations suggest that this weak form-function relationship has contributed to the morphological diversity of labrid fishes, as functionally equivalent species may nevertheless possess morphologically distinct jaws. We suggest that partial decoupling of morphology and mechanics due to redundancy is a major factor in morphological diversification.

Animals↗
PubMed2002

Higher brain functions of PACAP and a homologous Drosophila memory gene amnesiac: insights from knockouts and mutants.

Neuropeptides usually exert a long-lived modulatory effect on the small-molecule neurotransmitters with which they colocalize via regulation of the response times of second messenger systems. Pituitary adenylate cyclase-activating polypeptide (PACAP) functions as a neuromodulator and neurotransmitter and regulates a variety of physiological processes. PACAP is structurally highly conserved during evolution, implying its vital importance. In Drosophila, loss-of-function mutations in a PACAP-like neuropeptide gene, amnesiac (amn), affect both memory retention and ethanol sensitivity. The amnesiac gene is expressed in neurons innervating the mushroom body lobes, the olfactory associative learning center. Conditional genetic ablation of neurotransmitter release from these neurons mimics the amnesiac memory phenotypes, suggesting an acute role for amnesiac in memory. However, genetic rescue experiments also suggest developmental defects in amnesiac mutants, implying a role in neuronal development. There is a parallel between memory formation in Drosophila and mammals. PACAP-specific (PAC(1)) receptor-deficient mice show a deficit in hippocampus-dependent associative learning and mossy fiber long-term potentiation (LTP). Meanwhile, PACAP-deficient mice display a high early mortality rate and additional CNS phenotypes including behavioral and psychological phenotypes (e.g., hyperlocomotion, intense novelty-seeking behavior, and explosive jumping). A functional comparison between PACAP and amnesiac underlines phylogenetically conserved functions across phyla and may provide insights into the possible mechanisms of action and evolution of this neuropeptidergic system.

Amino Acid Sequence↗
PubMed2006

Wnt3a gradient converts radial to bilateral feather symmetry via topological arrangement of epithelia.

The evolution of bilaterally symmetric feathers is a fundamental process leading toward flight. One major unsolved mystery is how the feathers of a single bird can form radially symmetric downy feathers and bilaterally symmetric flight feathers. In developing downy feather follicles, barb ridges are organized parallel to the long axis of the feather follicle. In developing flight-feather follicles, the barb ridges are organized helically toward the anterior region, leading to the fusion and creation of a rachis. Here we discover an anterior-posterior molecular gradient of wingless int (Wnt3)a in flight but not downy feathers. Global inhibition of the Wnt gradient transforms bilaterally symmetric feathers into radially symmetric feathers. Production of an ectopic local Wnt3a gradient reoriented barb ridges toward the source and created an ectopic rachis. We further show that the orientation of the Wnt3a gradient is dictated by the dermal papilla (DP). Swapping DPs between wing covert and breast downy feathers demonstrates that both feather symmetry and molecular gradients are in accord with the origin of the DP. Thus the fates of feather epidermal cells are not predetermined through some molecular codes but can be modulated. Together, our data suggest feathers are shaped by a DP--> Wnt gradient-->helical barb ridge organization-->creation of rachis-->bilateral symmetry sequence. We speculate diverse feather forms can be achieved by adjusting the orientation and slope of molecular gradients, which then shape the topological arrangements of feather epithelia, thus linking molecular activities to organ forms and novel functions.

Animals↗
PubMed2002

Extreme genome reduction in Buchnera spp.: toward the minimal genome needed for symbiotic life.

Buchnera is a mutualistic intracellular symbiont of aphids. Their association began about 200 million years ago, with host and symbiont lineages evolving in parallel since that time. During this coevolutionary process, Buchnera has experienced a dramatic decrease of genome size, retaining only essential genes for its specialized lifestyle. Previous studies reported that genome size in Buchnera spp. is very uniform, suggesting that genome shrinkage occurred early in evolution, and that modern lineages retain the genome size of a common ancestor. Our physical mapping of Buchnera genomes obtained from five aphid lineages shows that the genome size is not conserved among them, but has been reduced down to 450 kb in some species. Here we show evidence of six species with a genome size smaller than Mycoplasma genitalium, the smallest bacterial genome reported thus far (580 kb). Our findings strongly suggest that the Buchnera genome is still experiencing a reductive process toward a minimum set of genes necessary for its symbiotic lifestyle.

Animals↗
PubMed1996

Na-K-ATPase along rat nephron after subtotal nephrectomy: effect of enalapril.

Tubular overwork is thought to be a promoter of the tubular hypertrophy and renal failure that occur in response to renal mass reduction. Because Na-K-adenosinetriphosphatase (Na-K-ATPase) is an index of tubular work, we evaluated the effects of subtotal nephrectomy and of enalapril therapy, which delays the evolution of renal lesions, on tubular hypertrophy and Na-K-ATPase activity along the rat nephron. Within 6 wk, 70% reduction of renal mass engendered hypertrophy of the proximal convoluted tubule (PCT), thick ascending limb (TAL), and collecting duct (CD), as well as parallel increments in Na-K-ATPase activity per millimeter tubule length (Na-K-ATPase activity per unit surface area was not modified by subtotal nephrectomy). Chronic enalapril therapy prevented part of the hypertrophy (but not Na-K-ATPase stimulation) of the PCT and the whole stimulation of Na-K-ATPase (but not hypertrophy) in the CD, whereas it had no effect on the TAL. Enalapril effect on Na-K-ATPase in CD might result from reduced bradykinin metabolism, as the reduction in urinary excretion of bradykinin observed in subtotally nephrectomized rats was prevented by enalapril therapy.

Aldosterone↗
PubMed2001

Reversible aphasic disorder induced by lamotrigine in atypical benign childhood epilepsy.

PURPOSE: We studied an eleven year-old girl with atypical, benign partial epilepsy who acutely presented a severe aphasia associated with marked EEG deterioration after lamotrigine administration. A parallel monitoring of language disorders and EEG changes during the gradual withdrawal of lamotrigine was performed in order to evaluate their possible correlation with lamotrigine administration. METHODS: Detailed neuropsychological and linguistic examinations in association with awake and sleep EEG were periodically performed. RESULTS: The evolution of the aphasic disorder was closely related to the EEG abnormalities, and disappeared after the withdrawal of lamotrigine. CONCLUSIONS: We considered the hypothesis that our case could be an expression of a paradoxical reaction to lamotrigine, in which the transitory aphasic disorder was sustained by an epileptiform electric activation.

Anticonvulsants↗
PubMed2004

Evolution of somatosensory and motor cortex in primates.

Inferences about how the complex somatosensory systems of anthropoid primates evolved are based on comparative studies of such systems in extant mammals. Experimental studies of members of the major clades of extant mammals suggest that somatosensory cortex of early mammals consisted of only a few areas, including a primary area, S1, bordered by strip-like rostral and caudal somatosensory fields, SR and SC. In addition, the second somatosensory area, S2, and the parietal ventral area, PV, were probably present. S1, S2, and PV were activated independently via parallel projections from the ventroposterior nucleus, VP. Little posterior parietal cortex existed, and it was unlikely that a separate primary motor area, M1, existed until placental mammals evolved. Early primates retained this basic organization and also had a larger posterior parietal region that mediated sensorimotor functions via connections with motor and premotor areas. The frontal cortex included M1, dorsal and ventral premotor areas, supplementary motor area, and cingulate motor fields. Ventroposterior superior and ventroposterior inferior nuclei were distinct from the ventroposterior nucleus in the thalamus. In early anthropoid primates, areas S1, SR, and SC had differentiated into the fields now recognized as areas 3b, 3a, and 1. Areas 3b and 1 contained parallel mirror-image representations of cutaneous receptors and a parallel representation in area 2 was probable. Serial processing became dominant, so that neurons in areas 1, S2, and PV became dependent on area 3b for activation. Posterior parietal cortex expanded into more areas that related to frontal cortex. Less is known about changes that might have occurred with the emergence of apes and humans, but their brains were larger and posed scaling problems most likely solved by increasing the number of cortical areas and reducing the proportion of long connections.

Adaptation, Physiological↗
PubMed2000

Lipid dynamics in the embryos of Patiriella species (Asteroidea) with divergent modes of development.

Evolution of lecithotrophic development in sea stars involved a modification in maternal provisioning from the production of yolk-dominated to lipid-dominated eggs. The dynamics of lipid reserves in the embryos of four Patiriella species differing in their lipid provisions were examined. Patiriella regularis had small yolk protein-dominated eggs (150 microm in diameter) and an ancestral mode of development through planktotrophic larvae. Patiriella calcar, Patiriella exigua and Patiriella pseudoexigua had large eggs (390-440 microm in diameter) and lecithotrophic planktonic, benthic and intragonadal larvae, respectively. Patiriella exigua deposited negatively buoyant eggs containing substantial yolk protein and lipid reserves onto the substratum. In contrast, the planktonic eggs of P. calcar and the intragonadal eggs of P. pseudoexigua were dominated by lipid and were neutrally and positively buoyant, respectively. By the blastula stage there was little trace of lipid in P. regularis embryos. Blastulae of the lecithotrophic developers, by contrast, had conspicuous lipid droplets distributed through their cells. In parallel with the change from cuboidal to columnar epithelium during the blastula to gastrula transition, lipid reserves became redistributed into the basal cytoplasm. The extent of lipid transport reflected the amount of lipid reserves. In P. pseudoexigua embryos with the greatest lipid load, basal shunting was followed by secretion of lipid into the blastocoele where it was stored for the perimetamorphic period. Evolution of lecithotrophy in Patiriella appears to reflect selection to provide metamorphic stages with nutrients normally accrued by feeding larvae with the consequence that early development is burdened by voluminous, potentially inert nutritive stores. Lipid redistribution coincident with a major developmental stage transition may be required to facilitate unimpeded morphogenesis. This phenomenon may be characteristic of lecithotrophic development in echinoderms and appears pre-adaptive for extrusion of lipid in species like P. pseudoexigua with particularly extensive lipid reserves.

Animals↗
PubMed1975

Non-mendelian segregation in hybrids between chinese hamster cells.

Mechanisms of segregation have been examined in hybrids between Chinese hamster cells, where chromosome loss in comparison to other systems is minimal. Hybrid cells were grown in HAT medium and subjected to back selection with bromodeoxyuridine (BUDR) or azaguanine (AZG). In AZG or BUDR at 30 mug/ml, segregation began with a random high frequency event that gave rise to cells capable of growth in both HAT and back selection medium, unlike the precursor hybrid or original parental cell types. BUDR-resistant segregants were propagated serially in the presence of BUDR, and were examined by clonal analysis for changes in plating properties during long term culture. Over a period of 300 days the HAT/BUDR plating ratio for sergregant cells declined continuously. A parallel decrease was observed in the rate of H3-thymidine incorporation, along with a drop in thymidine kinase activity. These shifts took place only in the presence of BUDR, and could be reversed by altered selection in HAT medium. Clonal studies showed that the evolution of segregant properties occurred in most if not all cells of the population, and did not arise from variation and selection of minority cell types. These properties of the segregating system are not consistent with models based on gene mutation, chromosome rearrangements, or chromosome loss. The evolution of segregants resembles more closely a sorting-out progress, taking place by intracellular selection over many generations. The segregating units may conceivably be cytoplasmic determinants linked functionally to nuclear genes, and which serve to modulate the events of phenotypic expression. Several lines of evidence which bear on this concept are discussed.

Azaguanine↗
PubMed2003

Vocal learning in birds and humans.

Vocal learning is the modification of vocal output by reference to auditory information. It allows for the imitation and improvisation of sounds that otherwise would not occur. The emergence of this skill may have been a primary step in the evolution of human language, but vocal learning is not unique to humans. It also occurs in songbirds, where its biology can be studied with greater ease. What follows is a review of some of the salient anatomical, developmental, and behavioral features of vocal learning, alongside parallels and differences between vocal learning in songbirds and humans.

Age Factors↗
PubMed1984

The isthmus-tegmentum complex in the turtle and rat: a comparative analysis of its interconnections with the optic tectum.

Injections of horseradish peroxidase, wheat germ agglutinin and various amino acids into the optic tectum in both the turtle and rat, and into the nucleus isthmi magnocellularis (IsM) in the turtle were used to analyse the connections of the isthmus-tegmentum complex. The connectivities and the selective retrograde transport properties in certain tectal pathways were taken as a basis to define more accurately isthmus-tegmentum complex subdivisions. There were several main findings. In the turtle the projection from the tectum to the IsM originated in the stratum griseum periventriculare, whereas the projection from the IsM to the tectum terminated in the superficial tectal layers (both projections homolateral). The terminations of the pathway from IsM to tectum were not uniformly distributed throughout the tectal surface; rather, alternating zones of high and low termination density along the lateral dimension were observed. The turtle nucleus isthmi parvocellularis, receiving a few tectal fibers and afferents from the ipsilateral IsM, gave rise to a bilateral tectal projection. Evidence was obtained for a crossed collicular projection to the rat parabigeminal nucleus (Pbg) in addition to the established uncrossed one. GABA was retrogradely transported from the optic tectum to the Pbg in the rat, and to the dorsolateral mesencephalic tegmentum and the IsM in the turtle. After glycine injections into the optic tectum, the dorsomedial peri-parabigeminal tegmentum was retrogradely labeled in the rat, and the IsM in the turtle. An attempt was made to outline the parallelism between the organizations of the isthmus-tegmentum complexes in the turtle, pigeon and rat. It was concluded that some basic features in the inter-connectivity of the isthmus-tegmentum complex and other parts of the visual system have been preserved in evolution, despite the apparent loss of the isthmo-retinal projection in mammals.

Animals↗