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At least 811 records · Page 45Linked to original sources

PubMed2005

Avian vacuolar myelinopathy linked to exotic aquatic plants and a novel cyanobacterial species.

Invasions of exotic species have created environmental havoc through competition and displacement of native plants and animals. The introduction of hydrilla (Hydrilla verticillata) into the United States in the 1960s has been detrimental to navigation, power generation, water intake, and water quality (McCann et al., 1996). Our field surveys and feeding studies have now implicated exotic hydrilla and associated epiphytic cyanobacterial species as a link to avian vacuolar myelinopathy (AVM), an emerging avian disease affecting herbivorous waterbirds and their avian predators. AVM, first reported in 1994, has caused the death of at least 100 bald eagles (Haliaeetus leucocephalus) and thousands of American coots (Fulica americana) at 11 sites from Texas to North Carolina (Thomas et al., 1998; Rocke et al., 2002). Our working hypothesis is that the agent of this disease is an uncharacterized neurotoxin produced by a novel cyanobacterial epiphyte of the order Stigonematales. This undescribed species covers up to 95% of the surface area of leaves in reservoirs where bird deaths have occurred from the disease. In addition, this species is rare or not found on hydrilla collected at sites where AVM disease has not been diagnosed. Laboratory feeding trials and a sentinel bird study using naturally occurring blooms of cyanobacteria on hydrilla leaves and farm-raised mallard ducks (Anas platyrhynchos) induced the disease experimentally. Since 1994 AVM has been diagnosed in additional sites from Texas to North Carolina. Specific site characteristics that produce the disjunct distribution of AVM are unknown, but it is probable that the incidence of this disease will increase with the introduction of hydrilla and associated cyanobacterial species into additional ponds, lakes, and reservoirs.

Animals↗

PubMed1994

Genetic and molecular analysis of hybrids in the genus Saccharomyces involving S. cerevisiae, S. uvarum and a new species, S. douglasii.

We have studied the phenomenon of infertility of yeast hybrids obtained with physiological conditions under the control of compatible mating systems. The yeasts investigated are three Saccharomyces species: S. cerevisiae, S. uvarum and a new species, S. douglasii. The diploid hybrids from crosses between these species sporulate well but are essentially infertile. The rare viable spores, one per 10(4) to 10(5) asci, that have been examined carry a complete genome comprised of chromosomes contributed by both parents but invariably have extra chromosomes, i.e. they are generally disomic for at least two or three chromosomes. This observation is consistent with a failure, in meiosis I, of the pairing and disjunction of homologous chromosomes which in most cases results in spores with an incomplete set of chromosomes. This apparent lack of pairing of 'homeologous' chromosomes in meiosis I was analysed in most detail with S. cerevisiae/S. douglasii hybrids. As a genetic tool we studied frequencies of recombination, taking advantage of an S. douglasii breeding stock of some 50 identified mutations in non-switching haploids. Recombination, although markedly reduced, could be observed at both the chromosomal and allelic levels, implying a sporadic pairing in meiosis to allow genetic exchange. Meiotic recombination frequencies were studied for 14 gene pairs and generally found to be reduced ten-fold. Heteroallelic recombination (gene conversion) frequencies were measured at 22 loci and were judged to be reduced at least two- to 100-fold. DNA hybridization experiments with S. cerevisiae gene probes gave results consistent with low DNA sequence homologies between S. cerevisiae and S. douglasii. Moreover, by change, our experiments disclosed another Saccharomyces strain (CBS2908, originally classified as S. cerevisiae) with hybridization patterns identical to S. douglasii except for the hybridization with the Ty transposon probes. Crosses between CBS2908 and S. douglasii yielded diploid hybrids with 80-90% spore viability, thus establishing a second member of the S. douglasii species.

Chromosomes, Fungal↗

PubMed1999

The Ncd tail domain promotes microtubule assembly and stability.

Non-claret disjunctional (Ncd) is a Drosophila kinesin-like motor required for spindle assembly and maintenance in oocytes and early embryos. Ncd has an ATP-independent microtubule binding site in the N-terminal tail domain as well as an ATP-dependent microtubule binding site in the C-terminal motor domain. The Ncd tail domain shares many properties with the microtubule-associated proteins that regulate microtubule assembly, including microtubule binding and bundling activity and an abundance of basic and proline residues. Given these similarities, we examined the ability of Ncd tail domain proteins to promote MT assembly and stability. The results indicate that the Ncd tail domain can promote MT assembly and stabilize MTs against conditions that induce MT disassembly, and suggest that Ncd may influence MT dynamics within the spindle.

Animals↗

PubMed2000

Escherichia coli genome is composed of two distinct types of nucleotide sequences.

We calculated correlations of the nucleotide distributions along the E. coli genome. Subsequent cluster analysis of the correlation distributions showed that the genome was composed of two qualitatively different types of nucleotide sequences. The first type exhibited strong correlations of the genomic distributions of A with T and G with C, and high anticorrelations of A with C and G with T. In contrast, the second type was characterized by weak or negligible correlations typical of randomized sequences. Both types of sequences were almost equally abundant in the E. coli genome and their length varied from several hundred nucleotides to about 70 kilobases. They were not disjunct with respect to their (G + C) content but the high correlations and anticorrelations were rather characteristic for (A + T)-rich genomic segments. We offer possible explanations of the mosaic structure of the E. coli genome.

Base Composition↗

PubMed1993

Lead and behavioral development in young herring gulls: effects of timing of exposure on individual recognition.

Lead exposure early in life affects behavioral, physiological, and intellectual development in humans and other animals. Recognition of parents or other caregivers and eventual bonding are essential aspects of behavioral development. In this paper young herring gulls, Larus argentatus, were used to examine the effect of timing of lead exposure on individual recognition behavior and development. Each of 60 1-day-old herring gull chicks was randomly assigned to a control group or to one of three treatment groups that received a single dose of lead nitrate solution (100 mg/kg) at Day 2 or 6 of age or the same total dose divided in thirds on Day 2, 4, and 6. Matched controls were injected with isotonic saline on the same schedules. Variations in individual recognition of human attendants were largely explained by age and status (lead versus control), and some variation was explained by day of injection (exposure regime). Using a feeding paradigm, the percentage responding to their caretaker compared to another person was higher (70% versus 38%), and occurred earlier in controls compared to lead-injected birds. Lead-injected birds required longer to respond initially, took longer to choose, moved less distance per time, and took longer to eventually reach the food. These results were all significant by GLM models and Kruskal-Wallis tests. Among lead-injected birds there was a disjunction of effect related to dosing schedule: birds injected on Day 6 chose more correctly but were slower to respond, indicating that these behavioral traits were differentially affected by timing of exposure.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗

PubMed1993

Feature-based versus exemplar-based strategies in preschoolers' category learning.

Five experiments examined whether preschool children learn categories by formulating a categorization rule based on attention to one or two features, or by memorizing the category assignment for whole exemplars. Using fictitious animals as stimuli, children were taught a two-category discrimination at the basic level and were tested for their category learning using a procedure that required them to categorize from memory, rather than perform perceptual matching. Transfer stimuli manipulated the retention of features encountered in the training instances, and children were instructed to classify only the items about whose category membership they were certain. By measuring the extent of generalization, in addition to categorization accuracy, it was possible to assess whether children were applying a feature-based rule in making their categorization decisions. The studies found little evidence that children were employing rules. Analyses of the individual response patterns identified few children who categorized by attending to a single attribute such as shape, or else who used a two-feature disjunctive rule. In addition, a recognition memory test given after category gaining produced strong evidence that children had encoded the training examples as wholes, rather than focusing on individual features. Despite clear evidence that children had encoded the training examples, however, examplar information was not used successfully in categorization when subjects were trained on only a single instance per category. The implication of these results for theories of early categorization are discussed.

Attention↗

PubMed2001

A comparison of sustainability theory with UK and European airports policy and practice.

There are three main theoretical difficulties involved in relating sustainability to aviation, and which a research agenda for sustainable aviation needs to address. The first is uncertainty regarding the critical thresholds of global environmental systems. The second is a lack of protocols for allocating permissible environmental consumption shares to, and hence targets for, individual enterprises or sectors. The third is differing value judgements of what natural features should be sustained. For the time being, these difficulties preclude determination of the degree of sustainability or unsustainability of any individual airport with respect to global environmental systems. Nevertheless, at this stage it can at least be said that since most economic activity has an adverse environmental impact, airports with higher throughputs of material and people will tend to be less sustainable than smaller-scale airports given similar technologies and regulatory compliance. This is theoretically supported and illustrated with waste arising as an indicator at reviewed airports. Despite governmental policies of sustainable mobility, there is a disjunction between EU and UK policy on airports and individual airport practice, and environmental sustainability theory. In the UK and EU, airport practice and governmental policy is to mitigate the impacts of aviation, but not at the expense of its aviation growth. This mitigation practice is summarised for the reviewed airports and presented in a framework that accounts for the suggested, interim approach to sustainability assessment.

Aviation↗

PubMed1996

Weak and strong states of kinesin and ncd.

Kinesin superfamily molecular motors step along microtubules (MTs) via a cycle of conformational changes which is coupled to ATP turnover. To probe the coupling mechanism, we titrated the effects of various nucleotides on MT binding by two superfamily members; MT plus-end-directed kinesin and MT minus-end-directed non claret disjunctional (ncd). For both motors, the nucleotide-free state induced by apyrase was the strongest binding (K(kin)d approximately 0.003 micro M, K(ncd)d approximately 0.24 micro M), whilst the ADp state was the weakest binding (K(kin)d approximately 11.32 micro M, K(ncd)d approximately 12.02 micro M). In ATP, the motor. ADP state dominates and the binding is accordingly ADP-like, but in the presence of the slowly hydrolysed analogue adenosine 5'-O-(3-thiotriphosphate) there is a shift towards tighter binding (K(kin)d approximately 4.23 micro M, K(ncd)d approximately 2.34 micro M), consistent with a tight-binding motor. ATP-like state being enriched. In the presence of non-hydrolysable analogue beta,gamma-imidoadenosine 5'-triphosphate the binding is still tighter (K(kin)d approximately <0.27 micro M, K(ncd)d approximately 0.21 micro M), close to the values obtained with apyrase. For both kinesin and ncd, ADP has the unique quality that it traps the motor in a weak binding state. MT tight binding catalyses escape from this state, changing the active site conformation such that both ADP release and ADP binding are accelerated. The data are consistent with a simple two-state scheme in which both kinesis and ncd switch from weak to strong binding via ADP release, and back again via ADP trapping. In a two-state model, the transition from weak to strong binding is force-generating.

Animals↗

PubMed1997

Motor domains of kinesin and ncd interact with microtubule protofilaments with the same binding geometry.

Kinesin and ncd (non-claret disjunctional) are microtubule associated motor proteins which share several structural features: both motors are dimers; each monomer is composed of a stalk region, a cargo binding domain and a motor domain; the motor domains have approximately 41% sequence identity. Despite these similarities the two motors have strikingly different movement properties: kinesin is a plus-end directed molecular motor, while ncd is minus-end directed. Here we compare the structure and the microtubule-binding properties of these oppositely directed molecular motors. We determined the three-dimensional structure of tubulin sheets decorated with the motor domains of either kinesin or ncd to a resolution of < 20 A by negative stain electron microscopy and tilt series reconstruction. Comparisons with a control structure of tubulin alone revealed that in both cases the motor domain binds to the outer crest of a single protofilament making contacts with both alpha and beta tubulin. Despite their opposite directionality, the geometry of attachment of the motor domain to the protofilament in the presence of AMP-PNP is very similar for both motors. These data rule out models for directionality which have the motors binding in an opposite orientation to the microtubules. Binding of the ncd as well as the kinesin motor domain appears to induce conformational changes in tubulin. This observation suggests an active role of tubulin in motor movement and/or in the determination of directionality.

Animals↗

PubMed1997

Molecular cloning and expression of the Caenorhabditis elegans klp-3, an ortholog of C terminus motor kinesins Kar3 and ncd.

Common to all eukaryotes, kinesins are cytoskeletal motor proteins that mediate intracellular transport on microtubule tracks, using ATP hydrolysis. A Caenorhabditis elegans cDNA clone corresponding to the klp-3 gene, encoding a novel kinesin, was isolated, and mapped on LGII. Northern blot analysis using the klp-3 cDNA probe reveals a 1.9 kb mRNA that is transcribed at a low level during development. Temporal and spatial expression of the klp-3::lacZ fusion gene is limited to the marginal cells in the pharynx, and a group of muscle cells in the posterior gut region. The nucleotide sequence of klp-3 has been deduced from the cDNA and nematode genome sequencing consortium data. Conceptual translation of the klp-3 gene reveals a kinesin-like protein with its conserved motor domain containing the ATP binding and microtubule binding sites located in the C terminus. KLP-3 shares extensive homology with the yeast Kar3 and Drosophila ncd kinesins, which have previously been shown to mediate chromosomal movement and segregation during meiosis and mitosis. Overexpression of the klp-3 gene partially rescues the lethal phenotype of the maternal lethal him-14 ts(it44) mutants at non-permissive temperatures, and reduces the incidence of males caused by non-disjunction of the X-chromosome. Similarly, expression of a klp-3 antisense RNA, under the control of a heat shock promoter, causes embryonic arrest, dead eggs and polyploid cells in transgenic lines, suggesting a critical role for the klp-3 function in chromosome segregation. Further analysis of the klp-3 gene in C. elegans may elucidate diverse functions of the C terminus mitotic motor proteins during development.

Amino Acid Sequence↗

PubMed2000

Regulation of ncd by the oligomeric state of tubulin.

We have compared the interaction of ncd (non-claret disjunctional), a kinesin related protein, with microtubules and tubulin heterodimer. Ultracentrifugation experiments revealed that the ncd motor domain, residues 335-700 (ncd335), does not induce tubulin polymerization but stabilizes pre-formed microtubules with a maximum effect at a 1:1 ncd335:tubulin ratio. Ncd335 binding to tubulin or microtubules was estimated by following the change in fluorescence polarization of an exogenous dye attached to Cys670 of ncd335. Ncd335 binding to tubulin (containing GTP or GDP-bound) is characterized by a 2:1 stoichiometry, a higher affinity and an increased sensitivity towards salt, ADP, ATP and AMPPNP, as compared with ncd335 binding to microtubules. Maximum ATPases were 0.06-0.08 sec(-1) and 1.8-2.0 sec(-1) for the ncd335-tubulin and ncd335-microtubules complexes, respectively. Only the polymerized complex is fully functional, suggesting the presence of additional contacts between adjacent protofilaments. Moreover, the data reveal that the oligomeric state of microtubules is a potent regulator for the activity of kinesin related proteins.

Adenosine Triphosphatases↗

PubMed1999

A Generic Disjunctive/Conjunctive Decomposition Model for n-ary Relations.

This paper discusses a generic decomposition model that represents an arbitrary n-ary relation as a disjunctive or conjunctive combination of a number of n-ary component relations of a prespecified type. An important subclass of order-preserving decompositions is defined and its properties are derived. The generic model is shown to subsume various known models as special cases, including the models of Boolean factor analysis, hierarchical classes analysis, and disjunctive/conjunctive nonmetric factor analysis. Moreover, it also subsumes a broad range of new models as exemplified with a novel model for multidimensional parallelogram analysis and novel three-way extensions of nonmetric factor analysis. Copyright 1999 Academic Press.

Journal Article↗

PubMed1995

A model of chiasma reduction of closely formed crossovers.

A model of chiasma reduction is developed, evaluated by computer simulation and discussed in relation to the evolution of interference. The model assumes that adjacently formed crossovers can interact, if there is incomplete sister chromatid cohesion between them, and give rise to a reduced number of chiasmata. In the absence of crossover position interference this leads to a considerable risk of non-disjunction for an average sized chromosome. It is suggested that an important function of crossover interference is to reduce this effect. The question is raised whether chiasma reduction takes place today. Some available cytological data can be interpreted as showing that chiasma reduction occurs in normal meiosis. The possibility of chiasma reduction therefore needs further attention.

Animals↗

PubMed1999

Cytological, genetic and evolutionary functions of chiasmata based on chiasma graph analysis.

The nature of the chiasma as a cytological parameter for analysing cross-over was reexamined quantitatively by an improved chiasma graph method. It was reconfirmed in Mus platythrix (n =13) that interstitial chiasmata at diakinesis are distributed randomly and almost uniformly along bivalents except for the centromere and telomere regions. The size of these chiasma blank regions was consistently 0.8% of the total length of haploid autosomes in all chromosomes. There was a minimum value of chiasma interference distance between two adjacent chiasmata, which was constantly 1.8% in all chromosomes. The chiasma frequency at diakinesis was 20.1+/-2. 0 by the conventional method including terminal chiasmata. However, the primed in situ labeling technique revealed that terminal chiasmata were mostly telomere-telomere associations. From these data and also from recent molecular data we concluded that the terminal chiasma is cytologically functional for ensuring the normal disjunction of bivalents at anaphase I, but genetically non-functional for shuffling genes. The chiasma frequency excluding terminal chiasmata was 14.6+/-1.8. Reexamination of the chiasma frequency of 106 animal species revealed that the chiasma frequency increased linearly in proportion to the haploid chromosome number in spite of remarkable difference in their genome size. The increase in chiasma frequency would be evolution-adaptive, because gene shuffling is expected to be accelerated in species with high chromosome numbers.

Animals↗

PubMed2002

Construction of an associative memory using unstable periodic orbits of a chaotic attractor.

Unstable periodic orbits are the skeleton of a chaotic attractor. We constructed an associative memory based on the chaotic attractor of an artificial neural network, which associates input patterns to unstable periodic orbits. By processing an input, the system is driven out of the ground state to one of the pre-defined disjunctive areas of the attractor. Each of these areas is associated with a different unstable periodic orbit. We call an input pattern learned if the control mechanism keeps the system on the unstable periodic orbit during the response. Otherwise, the system relaxes back to the ground state on a chaotic trajectory. The major benefits of this memory device are its high capacity and low-energy consumption. In addition, new information can be simply added by linking a new input to a new unstable periodic orbit.

Algorithms↗

PubMed1995

Phylogenetic relationships of the Prodontria (Coleoptera; Scarabaeidae; subfamily Melolonthinae), derived from sequence variation in the mitochondrial cytochrome oxidase II gene.

The beetle genus Prodontria is of importance to New Zealand conservation programs. All Prodontria species are brachypterous (having reduced wings), and the genus presents some interesting evolutionary and biogeographic questions that are testable using phylogenetic reconstruction. A phylogeny was produced for 14 flightless Prodontria species, 2 macropterous (fully winged) Odontria species, and single representatives of 2 outgroup genera using sequence data from the mitochondrial COII gene. The data support probable conspecificity of the morphologically similar P. modesta and P. bicolorata but do not support their hypothesized sister-species relationship with the geographically proximate P. lewisi. The alpine P. capito is found to be a paraphyletic group, with the most eastern population diverging after the western populations made their appearance. Many interesting biogeographic disjunctions are here proposed to be anomalous and the result of morphological convergence. The data do not support the idea of a common flightless ancester for Prodontria, but suggest that brachyptery has evolved numerous times. In some instances, this appears to have led to contemporaneous speciation resulting in little resolution of phylogenetic relationships in some parts of the tree. These data allow for a new interpretation of the origin and diversification of the southern New Zealand flightless melolonthine fauna. Multiple speciation events involving wing reduction are suggested to involve at least one widespread flighted ancestor that has given rise to brachypterous forms.

Amino Acid Sequence↗

PubMed1997

Phylogenetic relationships within genus Leuciscus (Pisces, Cyprinidae) in Portuguese fresh waters, based on mitochondrial DNA cytochrome b sequences.

To investigate phylogenetic relationships among Leuciscus species occurring in Portuguese inland waters, the cytochrome b gene was sequenced from representatives of the main rivers. This study supports the recognition of the species level for L. pyrenaicus, including populations from the southern Portuguese drainages (Tejo, Sado, and Guadiana drainages), and for L. carolitertii, including populations from the northern Portuguese drainages. The existence of two new species occurring in the extreme southwestern drainages of Mira and Arade is also suggested. The present results support the monophyly of the Mira and the Arade populations, as well as an early divergence of these two lineages. The present-day distribution of Leuciscus species is seen as a consequence of Pliocene and Pleistocene events, such as river disjunctions and posterior confluence in epicontinental seas and river captures. A mixture of haplotypes was observed in the Mondego and the Tejo drainages, which could be a consequence of ancient river captures, with a possible mitochondrial DNA introgression in the Tejo drainage and a recent introduction by man in the Mondego drainage. The pattern of differentiation among mtDNA haplotypes and their geographic distribution is discussed in terms of evolutionary aspects.

Animals↗

PubMed1999

Phylogeny, biogeography, and processes of molecular differentiation in Quercus subgenus Quercus (Fagaceae).

Quercus is one of the most abundant and economically important genera of woody plants in the Northern Hemisphere. To infer phylogenetic relationships within Quercus subgenus Quercus, chloroplast DNA (cpDNA) restriction sites and nucleotide sequences of the internal transcribed spacers (ITS) and the 5.8S coding region of the nuclear ribosomal DNA repeat were obtained for 44 individuals, including 25 species, intraspecific samples, and three outgroups. Separate parsimony analyses of each data set showed that individual gene trees were congruent and often complementary in supporting clades that generally corresponded to previously recognized taxonomic groups. Only one instance of strongly supported gene tree incongruence was detected and this anomalous pattern was explained best by ancient introgression of cpDNA across sectional boundaries. Simultaneous parsimony analysis of the pruned data sets supported the recognition of the strictly Eurasian section Cerris and resolved a novel hypothesis for the major infrageneric groups (Cerris- (Lobatae- (Protobalanus + Quercus sensu stricto))). The biogeographic hypothesis that all major oak lineages evolved locally at middle latitudes within the general distribution of their fossil ancestors was fully supported. This set of relationships also suggested a New World origin for the widespread white oaks of the Northern Hemisphere (section Quercus s. s.). For both data sets, inter- and intraspecific sampling within section Protobalanus showed little correspondence to morphological species. Greater cladistic structure among the samples was obtained by cpDNA restriction sites and two well-delimited plastomes types comprising a total of 15 distinct haplotypes were resolved. Haplotypes of 2 of the peripheral species in this species complex occupy terminal portions of one of the plastome clades, suggesting a more recent origin relative to those of more widespread species. The phylogeography of the two divergent plastome types suggested a north-south pattern, consistent with a Late Tertiary disjunction in the ancestral distribution of section Protobalanus.

Cell Nucleus↗