bluuebunny/crossref_metadata_2025_split huggingface dataset:
Changing nutritional status causes a shift in the balance of nocturnal to diurnal activity in European Minnows
Authors: Metcalfe N. B. , Steele G. I. 
Published: March 2003

Summary

For animals that have access to a predator‐free refuge, the daily timing of feeding activity should reflect temporal variation in both the risk of predation while foraging and the rate of food intake: the preferred period of activity should be that which minimizes the predation risk per unit of food obtained.
However, several species of freshwater fish show flexibility in the daily pattern of feeding activity. European Minnows Phoxinus phoxinus L. prefer to feed at night at low temperatures, spending the majority of the day hiding in refuges. Since their feeding efficiency is lower at night, this behaviour is thought to minimize exposure to diurnal predators. The fish become increasingly active in the day as the temperature increases, possibly because their food requirements cannot be met by only feeding at night.
Here, it is tested experimentally whether nutritional state can affect the daily activity schedule, by manipulating the energy reserves of over‐wintering minnows and recording their relative night‐ and daytime use of refuges.
Well‐nourished fish were often observed hiding in refuges, especially during the day. As their energetic reserves decreased, they were more likely to be seen out of the refuges both by day and by night. However, the change in activity was greater by day, so that the fish became increasingly diurnal as their nutritional reserves declined. This effect was independent of temperature.
The results support the hypothesis that the fish attempt to minimize their exposure to diurnal predators, but must balance this against the need to increase their level of daytime foraging activity when in energy deficit.
Respiratory carbon loss of calcareous grasslands in winter shows no effects of 4 years’ CO2 enrichment
Authors: Volk M. , Niklaus P. A. 
Published: March 2003

Summary

CO2 exchange measurements in long‐term CO2‐enrichment experiments suggest large net carbon gains by ecosystems during the growing season that are not accounted for by above‐ground plant biomass. Considerable amounts of C might therefore be allocated below ground.
Winter ecosystem respiration from temperate grasslands under elevated CO2 may account for the loss of a significant part of the extra C gained during the growing season. To test this hypothesis, dark respiration was assessed throughout the winter of the fourth year of CO2 enrichment in a calcareous grassland.
Using these data, a model was parameterized to estimate whole‐winter respiratory CO2 losses. From November to February, 154 9 g C m−2 were respired under elevated CO2 and 144 5 g C m−2 under ambient [CO2], with no significant difference between the CO2 treatments.
We conclude that (i) wintertime respiration does not constitute a larger C loss from the ecosystem at elevated CO2; and (ii) the absence of respiratory responses implies no extra growing‐season C inputs with month‐to‐year turnover times at elevated CO2.
Shade acclimation of rainforest leaves to colonization by lichens
Authors: Anthony P. A. , Holtum J. A. M. , Jackes B. R. 
Published: March 2003

Summary

Lichens that live epiphytically on leaves (foliicolous lichens) are one of the most abundant groups of epiphytes in tropical rainforests, with lichen cover on individual leaves often exceeding 50%. In this study we quantified the shading of host leaves by foliicolous lichens, and investigated the capacity of palm leaves growing under contrasting light regimes to photo‐acclimate to lichen colonization.
Spectral analyses of 11 lichen species with differing thallus colouring and morphology demonstrated that the lichens exhibited absorptance spectra similar to their host leaves. The lichens showed mean light interceptions of 50%, with some species reducing the photosynthetically usable light by up to 70%.
Despite such shading, our observations indicated that leaves photo‐acclimate to the cover of lichens. The rate of photosynthesis of leaf patches covered by lichens was saturated at lower irradiances, and these patches had higher chlorophyll concentrations than uncolonized leaf areas. Monte Carlo estimates of total daily carbon gain, based on assimilation–irradiance curves and continuous light records, indicated that leaf areas covered by lichens compensated fully for the shading by lichens.
These findings do not support the widely held opinion that shading by foliicolous lichens and other epiphylls generally reduces the rate of photosynthesis by their host leaves.
Phenological and morphological adaptations to the light environment in two woody and two herbaceous plant species
Authors: Kikuzawa K. 
Published: March 2003

Summary

Leaf emergence, leaf longevity, light regime and photosynthetic rates were investigated in order to clarify the morphological and phenological adaptations to light conditions by avoiding self‐shading in two herbaceous (Polygonatum odoratum and Polygonum sachalinensis) and two woody (Fagus crenata and Alnus sieboldiana) plants in artificially created open habitats in Japan.
Fagus and Polygonatum open their leaves simultaneously as a flush during a short period at the start of the growing season (simultaneous foliar phenology), while Alnus and Polygonum open their leaves one by one successively for a longer period (successive foliar phenology).
Light conditions at the level of single leaves, defined as photon flux density relative to that above the plant, were essentially the same throughout a growing season for simultaneous species. On the other hand, light conditions for the two successive species degraded with time. There were gradients of light from the distal to basal part of a shoot only in successive species.
Reflecting the abrupt decrease in irradiance with time, photosynthetic rates of individual leaves decreased quickly with time in successive species (Alnus and Polygonum), while those of simultaneous species (Fagus and Polygonatum) decreased slowly. Photosynthetic rates of the canopy as a whole, however, were maintained constant over the season in successive species by replacing leaves frequently. Canopy‐level photosynthesis decreased slowly with time in the two simultaneous species.
Successive leaf emergence is adaptive in open habitats such as flood plains and canopy gaps, while simultaneous leafing is adaptive in light‐limited habitats such as the forest understorey.
Reduced leaf expansion as a cost of systemic induced resistance to herbivory
Authors: Moore J. P. , Taylor J. E. , Paul N. D. , Whittaker J. B. 
Published: March 2003

Summary

We investigated whether increases in cell wall peroxidases link the benefits of induced resistance and the potential ecological costs of reduced leaf expansion.
Rumex obtusifolius is a host plant of the chrysomelid beetle Gastrophysa viridula. The effect of feeding by G. viridula on plant physiology and activity of cell wall‐bound peroxidase activity in the plant was measured under controlled conditions.
Gastrophysa viridula were applied to fully expanded leaf 4, and expansion of leaf 8 was measured over 22 days. Removal of leaf tissue by the herbivore delayed subsequent leaf emergence in treated plants and temporarily reduced the expansion rate of leaf 8, beginning 5 days after treatment. This reduction continued for 4 days when compared with non‐treated plants, and reduced final leaf area by approximately 37%.
Final epidermal cell areas in leaf 8 were reduced by approximately 13%, while epidermal cell numbers remained unchanged.
Cell wall‐bound peroxidase activity was measured in leaf 8 over a 7‐day period following attack. Activity increased within 24 h following the start of treatment and peaked at day 3.
We postulate a herbivore‐induced systemic mechanism linking reductions in cell expansion and subsequent leaf growth rates as a result of an increase in cell wall‐bound peroxidase activity.
Herbivore grazing commonly reduces subsequent host growth, and the assumption has been that this is largely due to the consequences of leaf area lost to grazing. This study suggests that reduced growth, and the associated ecological costs result from induced resistance, and are the consequence of a more subtle direct physiological effect in constraining leaf expansion.
DNA polymerase ε encoded by cdc20+ is required for chromosomal DNA replication in the fission yeast Schizosaccharomyces pombe
Authors: Sugino Akio , Ohara Takeshi , Sebastian Josef , Nakashima Naomi , Araki Hiroyuki 
Published: March 2003

Background:DNA polymerase II (PolII), the homologue of mammalian DNA polymerase ε, is essential for chromosomal DNA replication in the budding yeast Saccharomyces cerevisiae and also participates in S‐phase checkpoint control. An important issue is whether chromosomal DNA replication in other eukaryotes, including the fission yeast Schizosaccharomyces pombe—in which the characteristics of replication origins are poorly defined—also requires DNA polymerase ε. It has been shown that DNA polymerase ε is not required for the in vitro replication of SV40 DNA by human cell extracts.Results:We have cloned and sequenced S. pombepol2+, which is identical to the cell‐cycle gene cdc20+, encoding the catalytic polypeptide of DNA polymerase ε (Polε). The predicted amino acid sequence of Polε is highly homologous to that of S. cerevisiae PolII and human Polε. Consistent with this, the Polε polypeptide was recognized by polyclonal antibodies against S. cerevisiae PolII holoenzyme (PolII*). The terminal morphology of cells containing the disrupted pol2 gene was similar to that of DNA replication mutant cells and cdc20 mutant cells. Furthermore, the Polε activity from temperature‐sensitive S. pombecdc20 mutant cells was temperture‐sensitive, and chromosomal DNA replication in the mutant cells was inhibited at the restrictive temperatures.Conclusion:These data strongly suggest that Polε is required for normal chromosomal DNA replication in S. pombe, as is PolII in S. cerevisiae. Thus, eukaryotic chromosomal DNA is replicated differently from that of viral SV40 DNA.
Sequence elements that contribute to the degradation of yeast Gα
Authors: Schauber Cherylene , Chen Li , Tongaonkar Prasad , Vega Irving , Madura Kiran 
Published: March 2003

BackgroundGpa1 is the α subunit of the yeast G‐protein that regulates signal transduction during mating. The stability of Gα/Gpa1 is influenced by the ubiquitin‐dependent N‐end rule pathway, suggesting that the regulation of Gα levels may be important for effective mating response and recovery.ResultsThe Gα sequences that confer sensitivity to degradation by the N‐end rule pathway were identified. The insertion of this degradation signal (G1‐Deg) into the ordinarily stable Gpa2 protein conferred proteolytic targeting. We examined Gα degradation under different conditions and found that it was efficiently degraded in haploid and diploid cells, but was stable if it was synthesized prior to expression of the N‐end rule pathway. Interestingly, a specific mutation in Gα that is believed to promote the GTP‐bound form (N388K) caused accelerated degradation.ConclusionA region encompassing a putative effector‐binding domain (G1‐Deg) is required for Gα degradation via the N‐end rule pathway. Our studies have shown that Gα is susceptible to proteolysis soon after synthesis. These results are in agreement with the idea that Gα is more unstable in the GTP‐bound form, which is the predominant state of monomeric/free Gα soon after synthesis. It is likely that the signal transduced by Gβγ can be regulated by adjusting the levels of Gα through proteolysis.
Grb10/GrbIR as an in vivo substrate of Tec tyrosine kinase
Authors: Mano Hiroyuki , Ohya Ken‐ichi , Miyazato Akira , Yamashita Yoshihiro , Ogawa Wataru , Inazawa Johji , Ikeda Uichi , Shimada Kazuyuki , Hatake Kiyohiko , Kasuga Masato , Ozawa Keiya , Kajigaya Sachiko 
Published: March 2003

BackgroundTec is a member of the recently emerging subfamily among nonreceptor protein‐tyrosine kinases (PTKs). Although many members of this family have been shown to be involved in a wide range of cytokine‐mediated signalling systems, the molecular mechanism by which they exert in vivo effects remains obscure. To gain insights into the downstream pathways of Tec, we here looked for Tec‐interacting proteins (TIPs) by using the yeast two‐hybrid screening.ResultsOne of TIPs turned out to be Grb10/GrbIR, which carries one pleckstrin homology domain and one Src homology 2 domain. Grb10/GrbIR was known to bind receptor PTKs in a ligand‐dependent fashion, but not to be phosphorylated on tyrosine residues. In a transient expression system in human kidney 293 cells, however, Grb10/GrbIR becomes profoundly tyrosine‐phosphorylated by Tec, but not by Syk, Jak2 or insulin receptor. We also reveal that expression of Grb10/GrbIR suppresses the cytokine‐driven and Tec‐driven activation of the c‐fos promoter.ConclusionOur results indicate a novel role of Grb10/GrbIR as an effector molecule to a subset of nonreceptor PTKs.
Crm1 (XpoI) dependent nuclear export of the budding yeast transcription factor yAP‐1 is sensitive to oxidative stress
Authors: Kuge Shusuke , Toda Takashi , Iizuka Narushi , Nomoto Akio 
Published: March 2003

BackgroundThe yAP‐1 transcription factor is crucial for the oxidative stress response of the budding yeast Saccharomyces cerevisiae; its activity is induced in response to oxidative stress, and as a consequence the expression of a number of target genes is enhanced. We have shown previously that yAP‐1 is mainly found in the cytoplasm, but that upon the imposition of oxidative stress it localizes to the nucleus. In this study, we addressed the mechanism through which yAP‐1 nuclear localization is regulated.ResultsHere we show that yAP‐1 localization is mediated by active export from the nucleus, resulting from the activity of Crm1 (XpoI), a conserved protein that functions as an export receptor which recognizes the nuclear export signal (NES). When Crm1 expression was repressed, yAP‐1 was localized in the nucleus and induced the expression of a yAP‐1 dependent target gene. Our results also suggest that the cysteine rich domain (CRD), at the C‐terminus of yAP‐1, functions as an export recognition sequence. yAP‐1 and Crm1 interact in vivo and this interaction is reduced in response to oxidative stress.ConclusionsThese results suggest a novel regulatory mechanism of nucleocytoplasmic transport which is dependent upon a redox sensitive nuclear export pathway.
Mice lacking smooth muscle calponin display increased bone formation that is associated with enhancement of bone morphogenetic protein responses
Authors: Yoshikawa Hideki , Taniguchi Shun‐ichiro , Yamamura Hisako , Mori Shigeki , Sugimoto Mizuo , Miyado Kenji , Nakamura Kenji , Nakao Kazuki , Katsuki Motoya , Shibata Nobuhiko , Takahashi Katsuhito 
Published: March 2003

BackgroundCalponin is a calmodulin‐and actin‐binding protein expressed in smooth muscle. It promotes actin polymerization and inhibits actin‐activated myosin ATPase activity. Despite the molecular and functional characterization of calponin in vitro, the physiological role of calponin in vivo has not been clarified.ResultsWe investigated the in vivo function of smooth muscle calponin (also called basic calponin or calponin h1) by generating mice carrying a targeted mutation in both alleles of the calponin gene. Mice lacking basic calponin expression displayed enhanced ectopic bone formation in vivo, induced by recombinant human bone morphogenetic protein‐2 (rhBMP‐2), and an augmentation of the degree of osteoblastic differentiation of embryonic mesenchymal cells when they were stimulated by rhBMP‐2. Basic calponin messenger RNA was shown to be expressed in developing and healing bone tissues, and in undifferentiated MC3T3‐E1 osteoblasts. An examination of the skeletons of mutated mice showed an early onset of cartilage formation and ossification, and increased postnatal bone formation characterized by an increase in the number of activated periosteal osteoblasts. Bone fracture healing was accelerated in mutated mice.ConclusionThis is the first demonstration of animals with enhanced BMP responsiveness in host cells, suggesting that endogenous basic calponin may play a negative role in an osteogenic programme.
Cytoskeletal reorganization by soluble Wnt‐3a protein signalling
Authors: Shibamoto  , Higano Keiichi , Takada Ritsuko , Ito Fumiaki , Takeichi Masatoshi , Takada Shinji 
Published: March 2003

Background:Wnt‐3a is an intercellular signalling molecule that is involved in a variety of morphogenetic events. However, the molecular mechanisms underlying Wnt‐3a signalling are poorly understood. We have sought to establish in vitro systems to assay the activity of this protein and investigate its biological roles.Results:We prepared mouse L cells transfected with Wnt‐3a cDNA, and found that their β‐catenin protein level was up‐regulated. When conditioned medium (CM) was collected from cultures of the transfectants and added to nontransfected L cells, the β‐catenin level of the latter was also increased. Approximately 50% of the Wnt‐3a proteins synthesized by the transfectants were secreted into the CM in a soluble form. These secreted Wnt‐3a proteins formed an activity gradient in the environment surrounding the transfectants. Then, we studied whether Wnt‐3a had any effect on cellular behaviour in vitro. When the CM containing Wnt‐3a (W3a‐CM) was added to cultures of C57MG mammary epithelial cells, their morphology was altered to exhibit closer intercellular contacts. Immunostaining for various adhesion and cytoskeletal proteins showed that the actin–microfilamental system was re‐organized by the W3a‐CM treatment. It induced a directional alignment of actin stress fibres and other actin‐associated proteins. Moreover, villin, localized only at the perinuclear regions in untreated C57MG cells, was re‐distributed to the leading edges of the cells, co‐localizing with F‐actin, in the presence of Wnt‐3a.Conclusion:Our findings suggest that Wnt‐3a protein, in the soluble form, can act to re‐organize cytoskeletal structures.
α2D/A‐adrenergic receptor gene induction in the retina by phorbol ester: involvement of an AP‐2 element
Authors: Venkataraman Venkateswar , Duda Teresa , Sharma Rameshwar K. 
Published: March 2003

BackgroundThe α2‐adrenergic receptor (α2‐AR) expressed in the bovine retina has been demonstrated to be of the α2D subtype. The bovine α2D‐adrenergic receptor (α2D/A‐AR) gene has been cloned and characterized. This report describes the induction of this gene by phorbol‐ 12, 13‐myristate acetate (PMA), an activator of protein kinase C (PKC).ResultsTreatment of the bovine retina for 60 min with PMA (1 μm) resulted in significant and similar increases in α2D/A‐AR mRNA level and gene transcription. This indicates that PMA causes α2D/A‐AR gene induction and that this induction takes place directly at the transcriptional level. In C6 cells, treatment with PMA at a concentration which was as low as 0.1 μm induced endogenous α2D/A‐AR mRNA after 60 min. Luciferase reporter assays in C6 cells mapped the PMA‐responsive element to a region between −247 bp and −163 bp on the α2D/A‐AR promoter. Electrophoretic mobility shift assays showed an increased binding of nuclear factor(s) from PMA‐treated bovine retina to this promoter region. Competition assays indicate that an AP‐2 element may be involved in the PMA‐dependent induction.ConclusionThese findings demonstrate for the first time, the direct induction of the α2D/A‐AR gene by PMA and support a role for an AP‐2 element in the induction mechanism.
Regulation of DNA gyrase operon in Mycobacterium smegmatis: a distinct mechanism of relaxation stimulated transcription
Authors: Unniraman Shyam , Nagaraja Valakunja 
Published: March 2003

BackgroundThe topological state of DNA is a result of the diverse influences of various topoisomerases present in the cell. Amongst these, DNA gyrase is the only enzyme that is capable of supercoiling DNA. In all the eubacterial cells tested so far, DNA gyrase has proved to be essential for survival. We have earlier cloned gyr genes from Mycobacterium smegmatis. Unlike the situation in Escherichia coli, genes encoding the two subunits of gyrase are present as a contiguous stretch in the M. smegmatis genome.ResultsWe have demonstrated that the two subunits are encoded by a single dicistronic message, with the transcriptional start site mapping 57 base pairs upstream of the putative translational start of the gyrB ORF. The gyr promoter is specific to M. smegmatis and does not function in E. coli. We have shown that the synthesis of DNA gyrase in M. smegmatis is induced by novobiocin—a known inhibitor of gyrase. Short fragments encompassing the promoter region, when cloned in a promoter selection vector, do not show any response to changes in supercoil levels. Larger fragments show a supercoil sensitive behaviour, as seen in the genomic context.ConclusionsThe gene structure and the transcriptional organization of the gyr operon suggest an overall regulatory scheme that is unique to mycobacteria. In contrast to E. coli, promoter and regions in its vicinity are not sufficient to confer supercoil sensitivity. Promoter distal regions— 600 bp downstream of the promoter—appear to be necessary for relaxation‐stimulated transcription in M. smegmatis.
Association of Lyn tyrosine kinase to the GM‐CSF and IL‐3 receptor common βc subunit and role of Src tyrosine kinases in DNA synthesis and anti‐apoptosis
Authors: Dahl Martin E. , Arai Ken‐ichi , Watanabe Sumiko 
Published: March 2003

BackgroundAfter GM‐CSF or IL‐3 stimulation, the activation of JAK2 tyrosine kinase and members of the Src family of tyrosine kinases takes place, followed by phosphorylation of βc tyrosine residues and the recruitment of SH2 containing molecules to the receptor complex. The exact role of Src kinases such as Lyn in this and other downstream signal transduction events remains unclear.ResultsWe investigated the association of Lyn kinase with βc using synthetic peptides derived from the eight βc tyrosine residues and the Box 1 motif. We found that Lyn kinase GST fusion proteins bind to peptides corresponding to the membrane proximal region of βc and to peptides containing specific βc derived phosphorylated tyrosine residues. We also determined that βc tyrosine residues Y1,2 as well as Y7 and Y8 can act as substrates of Lyn. We further analysed the role of the Src kinases in DNA synthesis and anti‐apoptosis downstream of GM‐CSF by using the Src kinase inhibitor PP1 in murine BA/F3 cells stably expressing a series of mutant βc receptors.ConclusionsLyn binds to βc derived peptides through multiple interactions, and may play an important role in βc phosphorylation. Src family kinases also play an essential role in GM‐CSF mediated DNA synthesis, as well as an important role in anti‐apoptosis in response to GM‐CSF.