bluuebunny/crossref_metadata_2025_split huggingface dataset:
Seasonal decline in clutch size in European starlings: a novel randomization test to distinguish between the timing and quality hypotheses
Authors: Christians Julian K. , Evanson Melissa , Aiken Jonathan J. 
Published: March 2003

Summary

The seasonal decline in clutch size observed in many avian populations may be due to (a) a causal effect of the timing of breeding or (b) variation in individual quality (i.e. lower quality individuals lay fewer eggs and lay later in the season).
To distinguish between these two hypotheses, we manipulated the timing of breeding of European starlings (Sturnus vulgaris L.) by removing first clutches to induce the production of replacement clutches. This experiment was performed at two sites over three breeding seasons.
To test whether the within‐individual trend in clutch size differed from the seasonal decline in clutch size observed in the population, we devised a novel randomization test that overcomes some of the potential limitations of previously used analyses.
We observed no within‐female decline in clutch size in any year at either site. Therefore, clutch removal did not appear to manipulate female quality (due to the costs of egg production), a potentially confounding factor in such experiments; only the timing of breeding was manipulated.
The within‐individual seasonal trend in clutch size differed significantly from the population decline in four of six cases (year–site combinations); there is good reason to believe that the lack of a significant difference in the two other cases was due to low statistical power. Thus, our data support the hypothesis that the season decline in clutch size in this species is due to variation in female quality.
The between‐year repeatability of clutch size was 0·47 and significantly different from zero, whereas that of relative laying date was much lower (−0·23) and non‐significant. The repeatability data are thus consistent with the quality hypothesis: clutch size is characteristic of individuals regardless of their timing of breeding.
Female body mass at the beginning of incubation was not related consistently to clutch size or laying date, and therefore does not appear to be an indicator of female quality in this context.
Fluorescence localization after photobleaching (FLAP): a new method for studying protein dynamics in living cells
Authors: Dunn G. A. , Dobbie I. M. , Monypenny J. , Holt M. R. , Zicha D. 
Published: March 2003

SummaryFLAP is a new method for localized photo‐labelling and subsequent tracking of specific molecules within living cells. It is simple in principle, easy to implement and has a wide potential application. The molecule to be located carries two fluorophores: one to be photobleached and the other to act as a reference label. Unlike the related methods of fluorescence recovery after photobleaching (FRAP) and fluorescence loss in photobleaching (FLIP), the use of a reference fluorophore permits the distribution of the photo‐labelled molecules themselves to be tracked by simple image differencing. In effect, FLAP is therefore comparable with methods of photoactivation. Its chief advantage over the method of caged fluorescent probes is that it can be used to track chimaeric fluorescent proteins directly expressed by the cells. Although methods are being developed to track fluorescent proteins by direct photoactivation, these still have serious drawbacks. In order to demonstrate FLAP, we have used nuclear microinjection of cDNA fusion constructs of β‐actin with yellow (YFP) and cyan (CFP) fluorescent proteins to follow both the fast relocation dynamics of monomeric (globular) G‐actin and the much slower dynamics of filamentous F‐actin simultaneously in living cells.
Automated high‐throughput electron tomography by pre‐calibration of image shifts
Authors: Ziese U. , Janssen A. H. , Murk J.‐L. , Geerts W. J. C. , Van der Krift T. , Verkleij A.J. , Koster A.J. 
Published: March 2003

SummaryElectron tomography is a versatile method for obtaining three‐dimensional (3D) images with transmission electron microscopy. The technique is suitable to investigate cell organelles and tissue sections (100–500 nm thick) with 4–20 nm resolution. 3D reconstructions are obtained by processing a series of images acquired with the samples tilted over different angles. While tilting the sample, image shifts and defocus changes of several µm can occur. The current generation of automated acquisition software detects and corrects for these changes with a procedure that incorporates switching the electron optical magnification. We developed a novel method for data collection based on the measurement of shifts prior to data acquisition, which results in a five‐fold increase in speed, enabling the acquisition of 151 images in less than 20 min. The method will enhance the quality of a tilt series by minimizing the amount of required focus‐change compensation by aligning the optical axis to the tilt axis of the specimen stage. The alignment is achieved by invoking an amount of image shift as deduced from the mathematical model describing the effect of specimen tilt. As examples for application in biological and materials sciences 3D reconstructions of a mitochondrion and a zeolite crystal are presented.
Calcium‐induced Cytochrome c release from CNS mitochondria is associated with the permeability transition and rupture of the outer membrane
Authors: Brustovetsky Nickolay , Brustovetsky Tatiana , Jemmerson Ronald , Dubinsky Janet M. 
Published: March 2003

AbstractThe mechanisms of Ca2+‐induced release of Cytochrome c (Cyt c) from rat brain mitochondria were examined quantitatively using a capture ELISA. In 75 or 125 mm KCl‐based media 1.4 µmol Ca2+/mg protein caused depolarization and mitochondrial swelling. However, this resulted in partial Cyt c release only in 75 mm KCl. The release was inhibited by Ru360, an inhibitor of the Ca2+ uniporter, and by cyclosporin A plus ADP, a combination of mitochondrial permeability transition inhibitors. Transmission electron microscopy (TEM) revealed that Ca2+‐induced swelling caused rupture of the outer membrane only in 75 mm KCl. Koenig's polyanion, an inhibitor of mitochondrial porin (VDAC), enhanced swelling and amplified Cyt c release. Dextran T70 that is known to enhance mitochondrial contact site formation did not prevent Cyt c release. Exposure of cultured cortical neurons to 500 µm glutamate for 5 min caused Cyt c release into the cytosol 30 min after glutamate removal. MK‐801 or CsA inhibited this release. Thus, the release of Cyt c from CNS mitochondria induced by Ca2+in vitro as well as in situ involved the mPT and appeared to require the rupture of the outer membrane.
A link between maze learning and hippocampal expression of neuroleukin and its receptor gp78
Authors: Luo Yongquan , Long Jeffery M. , Lu Chengbiao , Chan Sic L. , Spangler Edward L. , Mascarucci Paolo , Raz Avraham , Longo Dan L. , Mattson Mark P. , Ingram Donald K. , Weng Nan‐ping 
Published: March 2003

AbstractNeuroleukin (NLK) is a multifunctional protein involved in neuronal growth and survival, cell motility and differentiation, and glucose metabolism. We report herein that hippocampal expression of NLK and its receptor gp78 is associated with maze learning in rats. First, mRNA levels of NLK and gp78 were significantly increased in hippocampi of male Fischer‐344 rats following training in the Stone T‐maze and the Morris water maze. Second, a parallel increase was found in hippocampal NLK and gp78 proteins after maze learning. Third, NLK and gp78 mRNA and protein expression in hippocampus was reduced in a group of aged rats that showed more errors during the acquisition of the Stone maze task as compared with young rats. Finally, application of recombinant NLK to hippocampal neurons significantly enhanced glutamate‐induced ion currents, functional molecular changes that have been correlated with learning in vivo. Taken together, our results identify a novel association of hippocampal expression of NLK and its receptor gp78 with rat maze learning. Interaction of NLK with gp78 and subsequent signaling may strengthen synaptic mechanisms underlying learning and memory formation.
Increased mitochondrial antioxidative activity or decreased oxygen free radical propagation prevent mutant SOD1‐mediated motor neuron cell death and increase amyotrophic lateral sclerosis‐like transgenic mouse survival
Authors: Liu Rugao , Li Baolin , Flanagan Shawn W. , Oberley Larry W. , Gozal David , Qiu Mengsheng 
Published: March 2003

AbstractThe molecular mechanisms of selective motor neuron degeneration in human amyotrophic lateral sclerosis (ALS) disease remain largely unknown and effective therapies are not currently available. Mitochondrial dysfunction is an early event of motor neuron degeneration in transgenic mice overexpressing mutant superoxide dismutase (SOD)1 gene and mitochondrial abnormality is observed in human ALS patients. In an in vitro cell culture system, we demonstrated that infection of mouse NSC‐34 motor neuron‐like cells with adenovirus containing mutant G93A‐SOD1 gene increased cellular oxidative stress, mitochondrial dysfunction, cytochrome c release and motor neuron cell death. Cells pretreated with highly oxidizable polyunsaturated fatty acid elevated lipid peroxidation and synergistically exacerbated motor neuron‐like cell death with mutant G93A‐SOD1 but not with wild‐type SOD1. Similarly, overexpression of mitochondrial antioxidative genes, MnSOD and GPX4 by stable transfection significantly increased NSC‐34 motor neuron‐like cell resistance to mutant SOD1. Pre‐incubation of cells with␣spin trapping molecule, 5′,5′‐dimethylpryrroline‐N‐oxide (DMPO), prevented mutant SOD1‐mediated mitochondrial dysfunction and cell death. Furthermore, treatment of mutant G93A‐SOD1 transgenic mice with DMPO significantly delayed paralysis and increased survival. These findings suggest a causal relationship between enhanced oxidative stress and mutant SOD1‐mediated motor neuron degeneration, considering that enhanced oxygen free radical production results from the SOD1 structural alterations. Molecular approaches aimed at increasing mitochondrial antioxidative activity or effectively blocking oxidative stress propagation can be potentially useful in the clinical management of human ALS disease.
Neurotoxic mechanisms triggered by Alzheimer's disease‐linked mutant M146L presenilin 1: involvement of NO synthase via a novel pertussis toxin target
Authors: Hashimoto Yuichi , Ito Yuko , Arakawa Erika , Kita Yoshiko , Terashita Kenzo , Niikura Takako , Nishimoto Ikuo 
Published: March 2003

AbstractWhile it has been reported that familial Alzheimer's disease (FAD)‐linked mutants of amyloid precursor protein (APP) and presenilin (PS)2 induce neuronal cytotoxicity in a manner sensitive to antioxidant and pertussis toxin (PTX), little of the mechanism for PS1‐mediated neuronal cell death has been characterized. We previously found that multiple mechanisms, different in detail, underlie cytotoxicities by two FAD‐linked mutants of APP, using neuronal cells with an ecdysone‐controlled expression system. Here we report that this system revealed that (i) low expression of FAD‐linked M146L‐PS1 caused neuronal cell death, whereas that of wild‐type (wt)PS1 did not; (ii) mutation‐specific cytotoxicity by M146L‐PS1 was sensitive to antioxidant glutathione‐ethyl‐ester and resistant to Ac‐DEVD‐CHO; (iii) cytotoxicity by higher expression of wtPS1 was resistant to both; and (iv) cytotoxicity by M146L‐PS1 was inhibited by PTX. It was also highly likely that the involved superoxide‐generating enzyme was nitric oxide synthase (NOS), and that the PTX‐sensitive cytotoxic signal by M146L‐PS1 was mediated by none of the Gi/o proteins. We conclude that M146L‐PS1 activates a NOS‐mediated cytotoxic pathway via a novel PTX target.
PC12nnr5cells expressing TrkA receptors undergo morphological but not cholinergic phenotypic differentiation in response to nerve growth factor
Authors: Baskey Jacqueline C. , Kalisch Bettina E. , Davis Wanda L. , Meakin Susan O. , Rylett R. Jane 
Published: March 2003

AbstractWe investigated mechanisms underlying nerve growth factor‐mediated morphological differentiation and expression of cholinergic neuronal phenotype. In PC12, but not PC12nnr5cells, nerve growth factor induces neurite‐like outgrowths and enhances cholinergic phenotype; stable expression of TrkA receptors in nnr5 cells (called B5P cells) restores morphological differentiation but not expression of choline acetyltransferase. Transfection with an AP‐1 luciferase reporter gene revealed that PC12 but not B5P cells expressed nerve growth factor‐induced functional AP‐1 activity. RT‐PCR analysis of nerve growth factor‐mediated changes in AP‐1 transcription factors showed rapid increases inc‐fosandjunBmRNA in PC12 and B5P cells, while increases inc‐junwere small. Using DNA–protein gel shift assays we determined that nerve growth factor stimulates AP‐1 binding in both PC12 and B5P cells, and identified c‐Fos, FosB, Fra‐1, Fra‐2, c‐Jun, JunB and JunD in AP‐1 complexes. In Fos/Jun functional luciferase reporter assays, nerve growth factor stimulated phosphorylation of c‐Fos in both PC12 and B5P cells, but phosphorylation of c‐Jun only in PC12, and not in B5P cells. These data indicate that mechanisms relating to AP‐1 transcription factor complexes underlying nerve growth factor‐mediated enhancement of cholinergic gene expression may differ from those required for morphological differentiation.
Molecular determinants for the differential coupling of Gα16 to the melatonin MT1, MT2 and Xenopus Mel1c receptors
Authors: Lai Frank P. L. , Mody Sejal M. , Yung Lisa Y. , Kam Jason Y. M. , Pang Celia S. , Pang Shiu F. , Wong Yung H. 
Published: March 2003

AbstractThe pineal neurohormone melatonin modulates a variety of physiological processes through different receptors. It has recently been reported that the cloned melatonin receptors (MT1, MT2 and Mel1c) exhibit differential abilities to stimulate phospholipase C (PLC) via G16. Here we examined the molecular basis of such differences in melatonin receptor signaling. Coexpression of MT1 or MT2 with the α subunit of G16 (Gα16) allowed COS‐7 cells to accumulate inositol phosphates in response to 2‐iodomelatonin. In contrast, Mel1c did not activate Gα16 even though its expression was demonstrated by radioligand binding and agonist‐induced inhibition of adenylyl cyclase. As Mel1c possesses an exceptionally large C‐terminal tail, we further asked if this structural feature prevented productive coupling to Gα16. Eleven chimeric melatonin or mutant receptors were constructed by swapping all or part of the C‐terminal tail between MT1, MT2 and Mel1c. All chimeras were fully capable of binding 2‐[125I]iodomelatonin and inhibiting adenylyl cyclase. Chimeras containing the full‐length Mel1c tail were incapable of activating Gα16, while those that contained the complete C‐terminal region of either MT1 or MT2 stimulated PLC. Incorporation of the extra portion of the C‐terminal tail of Mel1c to either MT1 or MT2 completely abolished the chimeras' ability to stimulate PLC via Gα16. In contrast, trunc‐	ation of the C‐terminal tail of Mel1c allowed interaction with Gα16. Our results suggest that Gα16 can discern structural differences amid the three melatonin receptors and provide evidence for functional distinction of Mel1c from MT1 and MT2 receptors.
The molecular and genetic basis of pollen–pistil interactions
Authors: Wheeler M. J. , Franklin‐Tong V. E. , Franklin F. C. H. 
Published: March 2003

SummaryOver the past decade or so, there has been significant progress towards elucidating the molecular events occurring during pollination in flowering plants. This process involves a series of complex cellular interactions that culminates in the fusion between male and female gametes. The process also regulates crucial events such as pollen adhesion, hydration, pollen tube growth and guidance to the ovules. Additionally, in many instances, incompatibility mechanisms that control the acceptance or rejection of pollen alighting on a recipient plant play a major role in the pollination process. In this article we aim to review our current understanding of the components that are implicated in enabling the pollen to deliver the male gametes to the ovary and the molecular mechanisms by which they are thought to act.

Contents

Summary
565

I.
Introduction
565

II.
Adhesion of pollen to the stigma
566

III.
Pollen hydration
567

IV.
Pollen germination and initial growth on the stigma surface
568

V.
Pollen tube growth through the style and pollen tube guidance
569

VI.
Control of pollen viability by incompatibility responses
572

1. Self incompatibility (SI)
573

Gametophytic SI
573

SI in the Solanaceae
573

SI in Papaver
575

Sporophytic SI
577

SI in Brassica
577

SI in Ipomoea
579

2. Interspecific incompatibility responses
579

VII.
Conclusions and perspective
580

References
580
Ozone exposure affects photosynthesis of pumpkin (Cucurbita pepo) plants
Authors: Castagna A. , Nali C. , Ciompi S. , Lorenzini G. , Soldatini G. F. , Ranieri A. 
Published: March 2003

Summary

Physiological and biochemical responses of the ozone (O3)‐sensitive pumpkin cultivar (Cucurbita pepo‘Ambassador’) to O3 exposure are reported here to determine critical O3 concentrations related to duration of pollutant exposure.
Pumpkin plants were exposed to 150 nl l−1 of O3 for 5 h d−1 for 5 d. Gas‐exchange, chlorophyll a fluorescence and pigment‐content measurements were determined on days 1, 3, 5 for young leaves and days 1, 3, 4 for the mature leaves of control and treated plants.
In both young and mature leaves, O3 induced a significant decrease in photosynthetic rate through impacts on stomata and photochemistry. A reduction in PSII photochemistry, photochemical quenching and quantum yield, accompanied by a parallel increase in nonphotochemical quenching was detected. Following O3 treatment the pool of xanthophyll cycle pigments and the de‐epoxidation index underwent a significant increase, whereas chlorophylls and β‐carotene were less affected.
The results showed that most of the parameters were affected by O3 after 1 d of exposure and indicated an overall effect of O3 and days of treatment, irrespective of leaf age.
Why is there so little research into the cell biology of the secondary vascular system of trees?
Authors: Chaffey Nigel 
Published: March 2003

SummaryDespite new techniques for studying the cell biology of plant development in recent years, the secondary vascular system has been neglected. Why is this? Here it is argued that some of the barriers that have prevented more widespread study of the tree secondary vascular system are no longer valid. Some of the more intriguing aspects of the secondary vascular system include the recent discovery of a putative plant muscle and identification of a cytoskeleton‐facilitated three‐dimensional symplasmic transport pathway that permeates the tree. There are great merits in the recently adopted model tree species, poplar, and a new model system – wood formation in Arabidopsis. The time is now right for much greater exploitation of the possibilities that exist for study of the secondary vascular system of trees.
Role of fluids in the metamorphism of the Alpine Fault Zone, New Zealand
Authors: Vry J. K. , Storkey A. C. , Harris C. 
Published: March 2003

AbstractModels of fluid/rock interaction in and adjacent to the Alpine Fault in the Hokitika area, South Island, New Zealand, were investigated using hydrogen and other stable isotope studies, together with field and petrographic observations. All analysed samples from the study area have similar whole‐rock δD values (δDWR = −56 to −30‰, average = −45‰, n = 20), irrespective of rock type, degree of chloritization, location along the fault, or across‐strike distance from the fault in the garnet zone. The green, chlorite‐rich fault rocks, which probably formed from Australian Plate precursors, record nearly isothermal fluid/rock interaction with a schist‐derived metamorphic fluid at high temperatures near 450–500°C (δD of water in equilibrium with the green fault rocks (δDH2O, green) ≈ −18‰; δD of water in equilibrium with the greyschists and greyschist‐derived mylonites (δDH2O, grey) ≈ −19‰ at 500°C; δDH2O, green ≈ −17‰; δDH2O, grey ≈ −14‰ at 450°C). There is no indication of an influx of a meteoric or mantle‐derived fluid in the Alpine Fault Zone in the study area. The Alpine Fault Zone at the surface shows little evidence of late‐stage retrogression or veining, which might be attributed to down‐temperature fluid flow. It is probable that prograde metamorphism in the root zone of the Southern Alps releases metamorphic fluids that at some region rise vertically rather than following the trace of the Alpine Fault up to the surface, owing to the combined effects of the fault, the disturbed isotherms under the Southern Alps, and the brittle–ductile transition. Such fluids could mix with meteoric fluids to deposit quartz‐rich, possibly gold‐bearing veins in the region c. 5–10 km back from the fault trace. These results and interpretations are consistent with interpretations of magnetotelluric data obtained in the South Island GeopHysical Transects (SIGHT) programme.
Computer experiments to investigate complex fibre patterns in natural antitaxial strain fringes
Authors: Koehn D. , Aerden D. G. A. M. , Bons P. D. , Passchier C. W. 
Published: March 2003

AbstractAntitaxial non‐deforming strain fringes from Lourdes, France, show complex quartz, calcite and chlorite fibre patterns that grew around pyrite in a slate during non‐coaxial progressive deformation. Development of these fringes was modelled using a computer program ‘Fringe Growth 2.0’ which can simulate incremental growth of crystal fibres around core‐objects of variable shape. It uses object‐centre paths as input, which are obtained from fibre patterns in thin section. The numerical experiments produced fibre patterns that show complex intergrowth of displacement‐controlled, face‐controlled and intermediate fibres similar to those in the natural examples. The direction of displacement‐controlled growth is only dependent on the relative movement between core‐object and fringe, so that core‐object rotation with respect to the fringe influences the fibre patterns and produces characteristic asymmetric fibre curvature. Object‐centre paths should be used for kinematic analysis of strain fringes instead of single fibres since these paths represent the fringe as a whole. The length along the path can be interpreted in terms of finite strain and path curvature in terms of rigid body rotation of fringes with respect to an external reference frame.
Allozyme relationships among ten species of Rhodniini, showing paraphyly of Rhodnius including Psammolestes
Authors: Monteiro F. A. , Lazoski C. , Noireau F. , Solé‐Cava A. M. 
Published: March 2003

Abstract Genetic relationships among 10 species of bugs belonging to the tribe Rhodniini (Hemiptera: Reduviidae), including some important vectors of Chagas disease, were inferred from allozyme analysis of 12 enzyme loci (out of 21 enzyme systems examined), using agarose gel electrophoresis. These species formed two clusters: one comprising Rhodnius brethesi, R. ecuadoriensis, R. pallescens and R. pictipes; the other with Psammolestes tertius, Rhodnius domesticus and the Rhodnius prolixus group comprising R. nasutus, R. neglectus, R. prolixus and R. robustus.The resulting tree was [((R. ecuadoriensis, R. pallescens) R. brethesi) R. pictipes], [R. domesticus (P. tertius{(R. nasutus, R. neglectus) (R. prolixus, R. robustus)})]. Rhodnius nasutus and R. neglectus differed by only one locus, whereas no diagnostic loci were detected between R. prolixus and R. robustus (22 loci were analysed for these four species), despite considerable DNA sequence divergence between species in each of these pairs. Allozymes of the R. prolixus group showed greater similarity with Psammolestes tertius than with other Rhodnius spp., indicating that Rhodnius is paraphyletic and might include Psammolestes.