bluuebunny/crossref_metadata_2025_split huggingface dataset:
Functional significance of sexual dimorphism in Wandering Albatrosses, Diomedea exulans
Authors: Shaffer S. A. , Weimerskirch H. , Costa D. P. 
Published: March 2003

Abstract1. The investigation covered whether sexual dimorphism could affect flight performance in a manner that is consistent with differences in at‐sea distribution of male and female Wandering Albatrosses, Diomedea exulans Linnaeus. Adult morphology was also compared to near‐fledged chicks to assess whether morphological differences are consistent with different at‐sea distributions of adults and fledglings.2. Body girth, mass, wing span and area were measured on 24 females (16 adults and 8 chicks) and 32 males (20 adults and 12 chicks) breeding in the Crozet Archipelago.3. On average, adult males had longer wings (4%, 311 ± 4 cm) with 6·8% more area (6260 ± 270 cm2), but were also 20·4% heavier (9·44 ± 0·59 kg) than adult females. As a result, wing loading in adult males was 12·1% greater than adult females.4. When compared with adults, total wing area of chicks was lower resulting in higher wing loading because of the incomplete growth of chicks at the time measurements were collected. However, projected chick growth to fledging indicates that wing loading would be lower in fledglings than adults.5. Because wing loading determines flight speed, it is conceivable that windier regions of the sub‐Antarctic/Antarctic are more optimal for male albatrosses because they have higher wing loading. Conversely, wing loading is lower in adult females and fledglings, which could make them better adapted to exploit lighter winds of the subtropical and tropical regions. Thus, size dimorphism may have a functional role in flight performance that influences the at‐sea distribution of adult and fledgling Wandering Albatrosses.
Relationships between physical and chemical attributes of congeneric seedlings: how important is seedling defence?
Authors: Hanley M. E. , Lamont B. B. 
Published: March 2003

Summary

While herbivory is considered a major selective force operating in mature vegetation, much less is known about how herbivores affect the expression of defence at the seedling stage. In this study we quantified several chemical and physical properties, usually considered to affect seedling palatability, of 14 Western Australian Hakea species. We also determined whether seedling defences were related to other plant life‐history attributes.
Of all of the attributes measured, chemical defence (phenolic content of shoots) exhibited the most significant correlations with other traits (six of a possible eight). We also detected an apparent trade‐off between chemical (phenolics) and physical (spinescence) defence.
Seed mass, relative growth rate and specific leaf area are traits commonly held to have the most predictive power in simplifying our understanding of plant ecological and evolutionary processes across species boundaries. Within this genus, however, these attributes were poorly correlated with other traits.
We conclude that more extensive studies of seedling defence attributes are needed for a fuller understanding of what governs the evolution of plant life‐history traits.
Visit larger displays but probe proportionally fewer flowers: counterintuitive behaviour of nectar‐collecting bumble bees achieves an ideal free distribution
Authors: Ohashi K. , Yahara T. 
Published: March 2003

Summary1. Patterns of pollinator responses to variation in floral display size have significance for pollen flow among plants. Here we test a theoretical model for explaining such patterns by simultaneously assessing bumble bee behaviour and nectar availability in two native stands of Cirsium purpuratum with different spatial densities.2. A bumble bee (Bombus diversus) foraging on a plant remembered and avoided only one or two flower heads that it had probed before, so that the flower‐head revisitation rate increased as it stayed longer on a plant. Moreover, the revisitation rate increased less rapidly on larger displays.3. The number of heads probed per plant increased less than proportionally with display size, and this increase was smaller at higher plant density. This pattern is consistent with our expectation that a bee leaves a plant when the cost of flower‐head revisitation exceeds that of interplant movement. However, bees left plants slightly earlier than predicted.4. As predicted, the visitation rate of bees per plant showed a decelerated increase with floral display size, and this increase was greater at higher plant density.5. As a result of these complementary changes in the number of heads probed per plant and visitation rate per plant across plant densities, nectar rewards per head were equalized among displays (an ideal free distribution was achieved).
Spatial variation in ant and rodent post‐dispersal predation of vertebrate‐dispersed seeds
Authors: Rey P. J. , Garrido J. L. , Alcántara J. M. , Ramírez J. M. , Aguilera A. , García L. , Manzaneda A. J. , Fernández R. 
Published: March 2003

Summary

Post‐dispersal predation of vertebrate‐dispersed seeds has received little attention in the Mediterranean region. We investigated the spatial variation in post‐dispersal seed predation of vertebrate‐dispersed plants and its potential implications for plant diversity in fleshy fruited plant communities of southern Spain.
An experiment was conducted in forests and open scrubland at mid‐ and high elevations to explore: (a) the possibility of differential seed predation by rodents and granivorous ants; (b) the spatial variation, between and within habitats, in post‐dispersal seed predation and predator abundance; and (c) whether the spatial distribution of predation covaries among plant species.
Rodents and granivorous ants proved to be important predators of vertebrate‐dispersed seeds, and showed significant variation in their preferences for different seed species. Granivorous ant preferences depended on seed size, as seeds heavier than 20 mg were hardly ever removed. Rodents were indifferent to seed size.
Sites safe from predators were more frequent at mid‐elevations. In contrast to other temperate communities, successional status (open scrubland vs forest) did not determine the probability of predation, probably because ants are more important as seed predators in the early successional stages of Mediterranean habitats than in other temperate communities. The large‐scale variations in the occurrence of safe sites for the seeds depended on resource abundance rather than on predator abundance.
We found a significant interaction in seed predation rates between microhabitat and seed species at mid‐elevations, but not in high‐elevation habitats, implying stronger covariance across plant species in the microhabitats adequate for recruitment (e.g. with lower predation risk) at high elevation. This pattern may contribute to the differential plant diversity at mid‐ and high elevations in Mediterranean fleshy fruited plant communities. Theoretical models predict that seed predators may contribute to the maintenance of species diversity if the spatial distribution of safe sites from predators is uncorrelated across plant species, as it was at mid‐elevations.
Competitive status influences tree‐growth responses to elevated CO2 and O3 in aggrading aspen stands
Authors: McDonald E. P. , Kruger E. L. , Riemenschneider D. E. , Isebrands J. G. 
Published: March 2003

Summary

Competition effects on growth of individual trees were examined for 4 years in aggrading, mixed‐clone stands of trembling aspen (Populus tremuloides Michx.) at the Aspen‐FACE free‐air CO2 and O3 enrichment facility in northern Wisconsin, USA. During each growing season stands received one of four combinations of atmospheric [CO2] (ambient vs∼56 Pa) and [O3] (ambient vs∼1·5 × ambient).
Non‐destructive measurements of annual tree growth were compared within and among clones and treatments in relation to an index of competitive status based on the difference between a tree's height and that of its four nearest neighbours. Competitive status strongly influenced tree growth, and the positive growth response to elevated [CO2] was greater for competitively advantaged individuals than for disadvantaged individuals of most clones.
The magnitude of O3 effects on growth depended on clone and competitive status: for some clones, negative O3 effects were stronger with competitive advantage while others showed stronger O3 effects with competitive disadvantage. The interactive effects of CO2 and O3 differed among clones, with negative effects of O3 amplified or ameliorated by elevated CO2, depending on clone and competitive status.
Treatments modified competitive interactions by affecting the magnitude of growth differences among clones. These modifications did not alter clone rankings of competitive performance, but when CO2 and O3 were both elevated, the differences in competitive performance among clones decreased.
Multivariate responses to flooding in Arabidopsis: an experimental evolutionary investigation
Authors: Kolodynska A. , Pigliucci M. 
Published: March 2003

Summary

Response to selection in different environments has been investigated in the model system Arabidopsis thaliana in order to determine the changes in heritabilities, reaction norms, relationships with reproductive fitness, and character correlations induced by the selection regimes and by alterations of environmental conditions (flood vs normal water levels).
Our artificial population responded to selection mostly by line sorting, where some of the initial genotypes increased significantly in frequency over three generations, while others went extinct. This is probably how selection works in natural populations of this species.
We observed changes in the heritabilities of various traits in response to selection and experimental treatments, with morphological characters exhibiting higher heritabilities than life‐history traits.
The selection process did not alter the overall shape of the reaction norms of various characters, but did lower the phenotypic means of several traits in the same direction of plasticity imposed by flooding. Most characters were under directional selection throughout the experiment, though in the opposite direction from the actual shift in their means at the end of the experiment.
The multivariate architecture of this plant was affected more by selection than by environmental changes.
Type I interferons are essential mediators of apoptotic death in virally infected cells
Authors: Tanaka Nobuyuki , Sato Mitsuharu , Lamphier Marc S. , Nozawa Hiroaki , Oda Eri , Noguchi Shigeru , Schreiber Robert D. , Tsujimoto Yoshihide , Taniguchi Tadatsugu 
Published: March 2003

BackgroundThe interferons (IFNs) have been extensively studied in the context of host defence against viral infection. In the established model of IFN action, virally infected cells secrete type I IFNs (IFN‐α/β) which induce an antiviral state in uninfected cells. However, it is not clear how IFNs function on the infected cells. It has been reported that cells infected by some viruses die by apoptosis.ResultsIn the present study, we found that three types of viruses commonly induce apoptosis in primary cell cultures. Importantly, we observed that virus‐induced apoptosis was inhibited by anti‐IFN‐α/β antibodies, and in cells lacking either the type I IFN receptor 1 (IFNAR1) or its downstream mediator, Stat1 (Signal transducer and activator of transcription 1). IFN‐α treatment by itself did not induce apoptosis unless it was combined with transfection by double‐stranded RNA (dsRNA), which is normally generated during the course of viral infection.ConclusionThese results indicate a novel antiviral function of the type I IFNs, i.e. the selective induction of apoptosis in virally infected cells. In effect, these IFNs have a bifunctional role in limiting the spread of virus; eliciting an antiviral state in uninfected cells while promoting apoptosis in infected cells. Our results may help explain why IFNs are sometimes useful in the treatment of viral diseases and will provide further insight into the mechanisms of virus‐induced pathogenesis
Differential roles of GATA‐1 and GATA‐2 in growth and differentiation of mast cells
Authors: Harigae Hideo , Takahashi Satoru , Suwabe Naruyoshi , Ohtsu Hiroshi , Gu Lin , Yang Zhouying , Tsai Fong‐Ying , Kitamura Yukihiko , Douglas Engel James , Yamamoto Masayuki 
Published: March 2003

BackgroundWhile mast cells have been previously shown to express both GATA‐1 and GATA‐2 mRNAs, individual functions for these related factors during their course of differentiation within the mast cell lineage have not yet been defined. To address this question, the expression of GATA‐1 and GATA‐2 mRNAs and proteins were examined in three mouse mast cell progenitor lines as well as in mast cells isolated from both wild‐type and GATA‐1‐deficient mice.ResultsBoth mast cell progenitor lines, as well as primary mouse bone marrow‐derived mast cells (BMMCs) and peritoneal mast cells (PMCs) were examined by RNA blotting and immunological analyses. GATA‐2 protein was abundantly expressed in all three mast cell lines and in BMMCs, but only weakly in some of PMCs. In contrast, GATA‐1 protein was expressed in PMCs and BMMCs after culture in the presence of IL‐3 and SCF. We also found the presence of Alcian blue staining‐positive but berberine staining‐negative mast cells in the skin of mice heterozygous to GATA‐1 knock‐down allele.ConclusionThese results suggest that the expression of GATA factor‐dependent genes is regulated by GATA‐2 during mast cell development and that GATA‐1 is required for the specification of differentiated mast cell phenotypes.
Rad52 forms ring structures and co‐operates with RPA in single‐strand DNA annealing
Authors: Shinohara Akira , Shinohara Miki , Ohta Tsutomu , Matsuda Shimako , Ogawa Tomoko 
Published: March 2003

BackgroundThe RAD52 epistasis group in Saccharomyces cerevisiae is involved in various types of homologous recombination including recombinational double‐strand break (DSB) repair and meiotic recombination. A RecA homologue, Rad51, plays a pivotal role in homology search and strand exchange. Genetic analysis has shown that among members of its epistasis group, RAD52 alone is required for recombination between direct repeats yielding deletions. Very little has been discovered about the biochemical roles and structure of the Rad52 protein.ResultsPurified Rad52 protein binds to both single‐stranded DNA (ssDNA) and double‐stranded DNA (dsDNA). Electron microscope observations revealed that Rad52 molecules form multimeric rings. An increase in the intensity of fluorescence when Rad52 is bound to εDNA showed an alteration of the structure of ssDNA. RPA was binding to Rad52 and enhanced the annealing of complementary ssDNA molecules. This enhancement was not observed in Escherichia coli SSB protein or T4 phage gp32 protein.ConclusionRad52 forms a ring‐like structure and binds to ssDNA. Its structure and DNA binding properties are different from those of Rad51. The interaction of Rad52 with RPA plays an important role in the enhancement of annealing of complementary ssDNAs. We therefore propose that Rad52 mediates the RAD51‐independent recombination through an ssDNA annealing, assisted by RPA.
Identification of sna41 gene, which is the suppressor of nda4 mutation and is involved in DNA replication in Schizosaccharomyces pombe
Authors: Miyake Sanae , Yamashita Shigeru 
Published: March 2003

BackgroundThe replication licensing factor limits DNA replication to once in a cell cycle and is thought to contain MCM proteins as its component parts. Six MCM subtypes have been identified in various species. These MCM proteins are thought to bind each other to make a heteromeric complex. The Nda4 protein of Schizosaccharomyces pombe is one of the MCM proteins and is involved in DNA replication.ResultsThe suppressor mutant of nda4 was isolated and the mutant gene was named sna41. The sna41‐912 mutant demonstrated the ts phenotype, with an elongated cell shape at the restrictive temperature. Cells with 1C DNA content accumulated 2 h after shifting up to the restrictive temperature. This result suggests that sna41 is also involved in DNA replication. The sna41 genomic clone was isolated by a complementation of the ts phenotype of the mutant strain and was sequenced. The sna41 gene encodes a protein of 638 amino acids, which has low homology with CDC45 in S. cerevisiae. The gene disruption analysis showed that sna41 gene is essential for viability.ConclusionsThe S. pombe sna41 mutation suppresses the nda4‐108 mutation. Sna41 is involved in DNA replication and may play some roles in the regulation of DNA replication by the MCM proteins.
Characterization of the C. elegans gap‐2 gene encoding a novel Ras‐GTPase activating protein and its possible role in larval development
Authors: Hayashizaki Seiji , Iino Yuichi , Yamamoto Masayuki 
Published: March 2003

BackgroundThe Ras signalling pathway plays several important roles in the development of the nematode Caenorhabditis elegans. So far, two types of Ras‐GTPase activating proteins (Ras‐GAPs) have been identified in this organism. To aid the study of the regulation and function of the Ras pathway, we set out to isolate a new GAP gene from C. elegans by transcomplementation of the fission yeast gap1 mutant.ResultsWe isolated a C. elegans cDNA that encoded a protein which was similar to, but not exactly homologous with mammalian p120 Ras‐GAP. This gene, named gap‐2, generated at least nine distinct mRNA species through transcription from different promoters and subsequent alternative splicing involving 25 exons. These isoforms were differentially expressed among tissues. A deletion of gap‐2 caused no obvious phenotype by itself, but a loss of gap‐2 function could suppress larval lethality in both let‐23 and let‐60 reduction‐of‐function mutants, in which the Ras activity was lowered.Conclusions C. elegans gap‐2 encodes a novel Ras‐GAP, which is similar to vertebrate p120 but which may constitute a new GAP subfamily. gap‐2 mRNA isoforms arise by an unusually extensive variation in initiation sites and associated alternative splicing, and each isoform may play a distinct role in specific tissues. GAP‐2 appears to function as a negative regulator of LET‐60 Ras during larval development.
Myosin II activation promotes neurite retraction during the action of Rho and Rho‐kinase
Authors: Amano Mutsuki , Chihara Kazuyasu , Nakamura Nao , Fukata Yuko , Yano Takeo , Shibata Masao , Ikebe Mitsuo , Kaibuchi Kozo 
Published: March 2003

BackgroundThe Rho small GTPase regulates myosin II activity through the phosphorylation of the myosin light chain (MLC) by activating Rho‐kinase, which is a target of Rho. Several lines of evidence point to an important role of Rho in the action of lysophosphatidic acid (LPA) and thrombin in provoking neurite retraction in N1E‐115 neuroblastoma cells.ResultsHere we examined whether Rho‐kinase and myosin II are involved in neurite retraction in N1E‐115 cells. We showed that the expression of constitutively active forms of Rho‐kinase induced neurite retraction in N1E‐115 cells and MLC phosphorylation in NIH 3T3 cells, whereas the expression of dominant negative forms of Rho‐kinase inhibited the LPA‐induced neurite retraction in N1E‐115 cells and the serum‐induced MLC phosphorylation in NIH 3T3 cells. The expression of mutant MLCT18D,S19D (substitution of Thr and Ser by Asp), which is known to lead to the activation of myosin ATPase and a conformational change of myosin II when reconstituted with myosin heavy chains in vitro, also promoted neurite retraction.ConclusionThese results indicate that Rho‐kinase is involved in the LPA‐induced neurite retraction downstream of Rho, and that myosin II activation promotes neurite retraction downstream of Rho and Rho‐kinase.
recessive spotting: a linked locus that interacts with W/Kit but is not allelic
Authors: Bennett Dorothy C. , Trayner Ian D. , Piao Xianhua , Easty David J , Klüppel Michael , Alexander Warren S. , Wagner Erwin F. , Bernstein Alan 
Published: March 2003

BackgroundThe murine coat‐colour mutation recessive spotting (rs) maps very closely to the W/Kit locus, encoding the proto‐oncoprotein Kit, the protein tyrosine kinase receptor for stem cell factor. Kit is important in the development of melanocytes, germ cells, interstitial cells of Cajal (ICC) and haemopoietic lineages, including mast cells. rs has never been genetically separated from Kit, and interacts with Kit mutations, suggesting that it is a recessive allele of Kit. Here we have tested this possibility. We have shown previously that diploid rs/rs melanocytes proliferated more slowly than did +/+ melanocytes, as did an immortal line of rs/rs melanocytes, melan‐rs.ResultsThe Kit mRNA level in rs/rs melanocytes was indistinguishable from that of other melanocyte lines. The Kit cDNA sequence from rs/rs melanocytes and the kinase activity of Kit in rs/rs mast cells appeared to be normal. No deficiency of mast cells or ICC was observed in rs/rs mice. Moreover, following the overexpression of a normal Kit cDNA, proliferation of rs/rs melanocytes was retarded further, but that of +/+ melanocytes was increased, indicating an intracellular interaction between rs and Kit. Of other closely linked tyrosine kinase genes, melanocytes and melanoblasts did not express mRNA for Pdgfra, Flk‐1 or Txk, but both expressed Tec, encoding a nonreceptor kinase that interacts with Kit.Conclusions rs is not a mutation in Kit, although we have confirmed that rs interacts with Kit. It seems unlikely that rs affects Pdgfra, Flk‐1 or Txk, but Tec remains a candidate for rs.
Cell cycle dependent topological changes of chromosomal replication origins in Saccharomyces cerevisiae
Authors: Fujita Masako , Hori Yuji , Shirahige Katsuhiko , Tsurimoto Toshiki , Yoshikawa Hiroshi , Obuse Chikashi 
Published: March 2003

BackgroundThe ORC (Origin Recognition Complex) of Saccharomyces cerevisiae is a protein complex for the initiation of replication which interacts with a cis‐element, ACS (ARS Consensus Sequence), essential for DNA replication. The protein–DNA complex detected by the DNase I genomic footprinting method has been shown to vary depending on cell cycle progression. Further studies on topological changes of replication origin in vivo caused by ORC association are crucial for an understanding of chromosomal DNA replication in S. cerevisiae.ResultsTopological changes in the replication origins of the S. cerevisiae chromosome were studied by an in vivo UV photofootprinting method which is capable of detecting the change in the flexibility of DNA caused by protein binding. The footprinting method detected the inhibition and enhancement of UV‐induced pyrimidine dimer formation in A and B1 elements of a chromosomal origin, ARS1, depending on the activity of native ORC subunits. Furthermore, footprint patterns were reproduced in vitro with purified ORC. The inhibition regarding the A element was stronger during the S to late M phase than that during the progression through the G1 phase. Functional CDC6 and MCM5 were required for maintaining the weaker inhibition state in G1‐arrested cells.ConclusionThe application of in vivo UV photofootprinting in studies of topological changes of S. cerevisiae replication origins revealed the presence of two modes of topological ORC‐ACS interaction. The weaker footprint in the G1 phase represents a specific topology of ACS, resulting from an alteration of the ORC–ACS interaction aided by CDC6 and MCM5, and this topological change may make the replication origin competent for initiating DNA replication.