bluuebunny/crossref_metadata_2025_split huggingface dataset:
Stratigraphic and structural expression of the lateral growth of thrust fault‐propagation folds: results and implications from kinematic modelling
Authors: Cooper Kate A. , Hardy Stuart , Gawthorpe Rob 
Published: May 2003

AbstractIn order to better understand the development of thrust fault‐related folds, a 3D forward numerical model has been developed to investigate the effects that lateral slip distribution and propagation rate have on the fold geometry of pre‐ and syn‐tectonic strata. We consider a fault‐propagation fold in which the fault propagates upwards from a basal decollement and along‐strike normal to transport direction. Over a 1 Ma runtime, the fault reaches a maximum length of 10 km and accumulates a maximum displacement of 1 km. Deformation ahead of the propagating fault tip is modelled using trishear kinematics while backlimb deformation is modelled using kink‐band migration.The applicability of two different lateral slip distributions, namely linear‐taper and block‐taper, are firstly tested using a constant lateral propagation rate. A block‐taper slip distribution replicates the geometry of natural fold‐thrusts better and is then used to test the sensitivity of thrust‐fold morphology to varied propagation rates in a set of fault‐propagation folds that have identical final displacement to length (Dmax/Lmax) ratios.Two stratigraphic settings are considered: a model in which background sedimentation rates are high and no topography develops, and a model in which a topographic high develops above the growing fold and local erosion, transport and deposition occur. If the lateral propagation rate is rapid (or geologically instantaneous), the fault tips quickly become pinned as the fault reaches its maximum lateral extent (10 km), after which displacement accumulates. In both stratigraphic settings, this leads to strike‐parallel rotation of the syn‐tectonic strata near the fault tips; high sedimentation rates relative to rates of uplift result in along‐strike thinning over the structural high, while low sedimentation rates result in pinchout against it. In contrast, slower lateral propagation rates (i.e. up to one order of magnitude greater than slip rate) lead to the development of along‐strike growth triangles when sedimentation rates are high, whereas when sedimentation rates are low, offflap geometries result. Overall we find that the most rapid lateral propagation rates produce the most realistic geometries. In both settings, time‐equivalent units display both nongrowth and growth stratal geometries along‐strike and the transition from growth to nongrowth has the potential to delineate the time of fault/fold growth at a given location. This work highlights the importance of lateral fault‐propagation and fault tip pinning on fault and fold growth in three dimensions and the complex syn‐tectonic geometries that can result.
Alluvial storage and the long‐term stability of sediment yields
Authors: Phillips Jonathan 
Published: May 2003

AbstractSeveral recent studies have shown general consistency of fluvial denudation rates over long time periods, or historical and contemporary sediment yields of the same general magnitude as sediment yields or accumulation rates over geologic time. This consistency of fluvial sediment export from some drainage basins, despite substantial climate, hydrological, ecological, base level, and other environmental changes, suggests that long‐term sediment yields may be controlled by factors that are independent of and overwhelm environmental changes (e.g. tectonics), or that the fluvial sediment system is at some level dynamically stable. The latter is explored via a model based on the notion that all debris produced by weathering within a drainage basin over any time period is either retained as part of the regolith, transported out of the basin as solid or dissolved sediment yield, or stored as alluvium within the fluvial system. This system is dynamically stable if alluvium is always potentially available for transport; e.g. to be converted to yield, and if regolith development exerts a negative feedback on weathering rates. This supports the argument that the long‐term consistency of sediment yields (where it exists) may be attributable to the storage and remobilization of alluvium, which buffers the system against environmental change. Environmental changes are manifested primarily in reorganizations within the fluvial sediment system, such as variations between net increases and decreases in alluvial storage, and changes in the spatial locus of deposition. These ideas are illustrated and tested using data from the lower Trinity River in southeast Texas.
Activation of the Hypothalamic Arcuate Nucleus Predicts the Anorectic Actions of Ciliary Neurotrophic Factor and Leptin in Intact and Gold Thioglucose‐Lesioned Mice
Authors: Anderson K. D. , Lambert P. D. , Corcoran T. L. , Murray J. D. , Thabet K. E. , Yancopoulos G. D. , Wiegand S. J. 
Published: May 2003

AbstractSimilar to leptin, ciliary neurotrophic factor (CNTF) suppresses appetite and selectively reduces body fat in leptin‐deficient ob/ob mice. To assess the relative importance of specific regions of the hypothalamus in mediating these effects, we administered a CNTF analogue (CNTFAx15) or leptin to mice made obese by administration of gold thioglucose (GTG), which destroys a well‐defined portion of the medial basal hypothalamus. CNTFAx15 treatment reduced appetite and body weight in obese GTG‐lesioned C57BL/6 mice, whereas leptin failed to effect similar changes regardless of whether treatment was initiated before or after the lesioned mice had become obese. Because leptin does not reduce food intake or body weight in most forms of obesity (a condition termed ‘leptin resistance’), we also investigated the actions of leptin in GTG‐lesioned leptin‐deficient (ob/ob) mice. By contrast to C57BL/6 mice, leptin treatment reduced food intake and body weight in GTG‐lesioned ob/ob mice, although the effect was attenuated. To further compare the neural substrates mediating the anorectic actions of leptin and CNTF, we determined the patterns of neurone activation induced by these proteins in the hypothalamus of intact and GTG‐lesioned mice by staining for phosphorylated signal transducer and activator of transcription 3 (pSTAT3). CNTFAx15 stimulated robust pSTAT3 signalling in neurones of the medial arcuate nucleus in both intact and lesioned C57BL/6 and ob/ob mice. Leptin administration stimulated pSTAT3 signalling in only a few neurones of the medial arcuate nucleus in intact or lesioned C57BL/6 mice, but elicited a robust response in intact or lesioned ob/ob mice. By contrast to CNTFAx15, leptin treatment also resulted in prominent activation of STAT3 in several areas of the hypothalamus outside the medial arcuate nucleus. This leptin‐induced pSTAT3 signal was at least as prominent in intact and GTG‐lesioned C57BL/6 mice as it was in ob/ob mice, and thus was not correlated with appetite suppression or weight loss. These results indicate that the medial arcuate nucleus is a key mediator of appetite suppression and weight loss produced by CNTF and leptin, whereas GTG‐vulnerable regions play a role only in leptin‐induced weight loss. Other regions of hypothalamus in which pSTAT3 signal is induced by leptin may regulate energy metabolism through mechanisms other than appetite reduction.
Hypothalamic‐Pituitary‐Adrenal Responses to Centrally Administered Orexin‐A are Suppressed in Pregnant Rats
Authors: Brunton P. J. , Russell J. A. 
Published: May 2003

AbstractOrexins are hypothalamic neuropeptides that stimulate arousal and food intake but also activate the hypothalamic‐pituitary‐adrenal (HPA) axis. During late pregnancy in the rat, the responsiveness of the HPA axis to stressors is attenuated, and thus we investigated HPA axis responses to centrally administered orexin‐A during pregnancy. Intracerebroventricular injection of orexin‐A (0.5 µg, 140 pmol) significantly increased plasma adrenocorticotropic hormone and corticosterone concentration within 10 min in virgin female Sprague‐Dawley rats, but had no effect in day 21 pregnant rats. Orexin‐A significantly increased corticotropin‐releasing hormone (CRH) mRNA expression, measured by in situ hybridization, in the paraventricular nucleus (PVN) of the virgin group but not in the pregnant group. Thus, the responsiveness of PVN CRH neurones to orexin‐A, and hence the pituitary‐adrenal axis, is markedly reduced in pregnancy. This may favour anabolic adaptations in pregnancy.
Nitric Oxide Produced by a Novel Nitric Oxide Synthase Isoform is Necessary for Gonadotropin‐Releasing Hormone‐Induced Growth Hormone Secretion Via a cGMP‐Dependent Mechanism
Authors: Uretsky A. D. , Weiss B. L. , Yunker W. K. , Chang J. P. 
Published: May 2003

AbstractThe involvement of nitric oxide (NO) in the regulation of goldfish growth hormone (GH) secretion was further characterized using primary cultures of dispersed goldfish pituitary cells. Western blots revealed the presence of an inducible nitric oxide synthase (iNOS)‐like protein of approximately 120 kDa in cytosol/plasma membrane extracts. By contrast, brain NOS‐immunoreactive proteins of approximately 120–140 kDa were occasionally detected in a cytoskeleton/organelle fraction but were absent from cytosol/plasma membrane extracts. The NO donor sodium nitroprusside (SNP) acutely increased GH secretion but this response was not observed in the presence of either a NO scavenger (PTIO) or a soluble guanylate cyclase inhibitor (ODQ). SNP also significantly increased the levels of cyclic (c)GMP in somatotrope‐enriched cell populations. Treatments with 1400W (iNOS inhibitor), PTIO and rutin hydrate (NO scavengers) and ODQ abolished the acute GH‐release response to two endogenous gonadotropin‐releasing hormones (GnRH). 1400W, rutin hydrate, PTIO and ODQ alone did not significantly alter basal GH secretion. Together, these results establish that an iNOS‐like peptide is constitutively present in the pituitary of the goldfish. Furthermore, these data suggest that NO, most likely through the generation of cGMP, is a necessary signal transduction component of GnRH‐induced GH secretion.
Mitochondrial Benzodiazepine Receptors in the Ventral Tegmental Area Modulate Sexual Behaviour of Cycling or Hormone‐Primed Hamsters
Authors: Frye C. A. , Petralia S. M. 
Published: May 2003

AbstractHamsters are highly dependent upon the central actions of progesterone (P4) for facilitation of sexual behaviour. In the ventral tegmental area (VTA), P4 has actions through its neurosteroid metabolite 5α‐pregnan‐3α‐ol‐20‐one (3α,5α‐THP). The effects of enhancing or inhibiting neurosteroidogenesis (and thereby 3α,5α‐THP concentrations), through manipulations of mitochondrial benzodiazepine receptors, in the VTA on socio‐sexual behaviour of female hamsters were examined. Intact, naturally receptive hamsters and ovariectomized (OVX), hormone‐primed hamsters were unilaterally infused via chronic guide cannula to the VTA with the mitochondrial benzodiazepine receptor antagonist 1‐(2‐chlorophenyl)‐N‐methyl‐N‐(1‐methylpropyl)‐3‐isoquinolinecarboximide (PK‐11195) or the mitochondrial benzodiazepine receptor agonist, N,N‐dihexyl‐2‐(4‐fluorophenyl)indole‐30‐acetamide (FGIN 1‐27) and tested for sexual responsiveness and lordosis. PK‐11195 (5.6, 11.2 or 22.4 nm) to the VTA attenuated sexual responsiveness of naturally receptive or oestradiol benzoate (EB) + P4‐primed hamsters compared to vehicle. In addition, FGIN 1‐27 (11.4 nm) infusions to the VTA increased sexual responsiveness and lordosis of cycling or OVX, EB + P4‐primed hamsters, compared to vehicle infusions. In OVX, EB + P4‐primed hamsters, decrements in sexual responsiveness produced by VTA infusions of PK‐11195 (5.6 nm) were attenuated by VTA infusions of 3α,5α‐THP. VTA infusions of PK‐11195 (5.6 nm) or FGIN 1‐27 (11.4 nm), respectively, decreased and increased midbrain levels of 3α,5α‐THP compared to each other. Together, these findings indicate that manipulating actions of mitochondrial benzodiazepine receptors in the VTA can augment and inhibit neurosteroidogenesis and sexual responsiveness of hormone‐primed and naturally receptive hamsters.
Links Between the Appetite Regulating Systems and the Neuroendocrine Hypothalamus: Lessons from the Sheep
Authors: Henry B. A. 
Published: May 2003

AbstractThe hypothalamus is integral to the regulation of energy homeostasis and the secretion of hormones from the pituitary gland. Consequently, hypothalamic systems may have a dual purpose in regulating both neuroendocrine function and appetite. To date, most studies investigating the interface between appetite and hormone secretion have been performed in rats or mice that have been acutely fasted or baring a genetic abnormality causing either obesity or aphagia. By contrast, various physiological models, including chronic food‐restriction or photoperiodically driven changes in voluntary food intake, add further perspective to the issue. In this regard, sheep provide an innovative model whereby long‐term changes in body weight or extended feeding rhythms can be investigated. This review compares and contrasts data obtained in different species with regard to the neuroendocrinology of appetite, and discusses the benefits and knowledge gained from using various nonrodent models with a particular emphasis on a ruminant species.
The structure of the helically perturbed flagellar filament of Pseudomonas rhodos: implications for the absence of the outer domain in other complex flagellins and for the flexibility of the radial spokes
Authors: Cohen‐Krausz Sara , Trachtenberg Shlomo 
Published: May 2003

SummaryBacterial flagella, the organelles of motility, are commonly divided into two classes: ‘plain’ and ‘complex’. The complex filaments are pairwise, helically perturbed forms of the plain filaments and have been reported to occur only in Rhizobium and Pseudomonas. Previously, we reconstructed and analysed the structure of the complex filaments of Rhizobium lupini H13‐3 and determined their unique symmetry and origin of the perturbations (Trachtenberg et al., 1986, J Mol Biol 190: 569–576; 1987, 195: 603–620; 1998, 276: 759–773; Cohen‐Krausz and Trachtenberg, 1998, J Struct Biol 122: 267–282). Here, we analyse the structure of the flagellar filament of the other known complex filament, that of Pseudomonas rhodos, as reconstructed from electron microscope images. Compared with the filament of R. lupini, the  filament of P. rhodos is more flexible, as implied from high‐intensity darkfield light microscopy and, although constructed from flagellins of higher molecular weights (59 versus 41 kDa), has similar symmetry. Using cryonegative stained specimens and low‐dose, field emission electron microscopy, we reconstructed and averaged 158 filaments each containing 170 statistically significant layer lines. The three‐dimensional density maps of P. rhodos clearly suggest, when compared with those of R. lupini and the right‐handed Salmonella typhimurium SJW1655, that R. lupini is missing the outer flagellin domain (D3), that the interior of the complex filament is rather similar to that of the plain filament and that the radial spokes (connecting domains D0 and D1), present in individual density maps, average out because of their variability and implied flexibility. Extending the three‐start grooves and ridges on the propeller's surface, in the form of an Archimedean screw, may further improve the motility of the cell in viscous environments.
The DNA excision repair system of the highly radioresistant bacterium Deinococcus radiodurans is facilitated by the pentose phosphate pathway
Authors: Zhang Y.‐M. , Liu J.‐K. , Wong T.‐Y. 
Published: May 2003

Summary Deinococcus radiodurans is highly resistant to radiation and mutagenic chemicals. Mutants defective in the putative glucose‐6‐phosphate dehydrogenase gene (zwf–) and the aldolase gene (fda–) were generated by homologous recombination. These mutants were used to test the cells’ resistance to agents that cause dimer formation and DNA strand breaks. The zwf – mutants were more sensitive to agents that induce DNA excision repair, such as UV irradiation and H2O2, but were as resistant to DNA strand break‐causing agents such as methylmethanesulphonic acid (MMS) and mitomycin C (MMC) as the wild‐type cells. Analysis of the cytoplasmic fraction of zwf– cells showed that the concentrations of inosine monophosphate (IMP) and uridine monophosphate (UMP) were only 30% of those found in the wild‐type cells. The fda– mutants were slightly more resistant to UV light and H2O2. Results suggested that the deinococcal pentose phosphate pathway augmented the DNA excision repair system by providing cells with adequate metabolites for the DNA mismatch repair.
Tracing pathways of transport protein evolution
Authors: Saier Milton H. 
Published: May 2003

SummaryWe have conducted bioinformatic analyses of integral membrane transport proteins belonging to dozens of families. These families rarely include proteins that function in a capacity other than transport. Many transporters have arisen by intragenic duplication, triplication and quadruplication events, in which the numbers of transmembrane α‐helical hydrophobic segments (TMSs) have increased. The elements multiplied may encode two, three, four, five, six, 10 or 12 TMSs and gave rise to proteins with four, six, seven, eight, nine, 10, 12, 20, 24 and 30 TMSs. Gene fusion, splicing, deletion and insertion events have also contributed to protein topological diversity. Amino acid substitutions have allowed membrane‐embedded domains to become hydrophilic domains and vice versa. Some evidence suggests that amino acid substitutions occurring over evolutionary time may in some cases have drastically altered protein topology. The results summarized in this microreview establish the independent origins of many transporter families and allow postulation of the specific pathways taken for their appearance.
The use of flow cytometry to detect expression of subunits encoded by 11 Salmonella enterica serotype Typhimurium fimbrial operons
Authors: Humphries Andrea D. , Raffatellu Manuela , Winter Sebastian , Weening Eric H. , Kingsley Robert A. , Droleskey Robert , Zhang Shuping , Figueiredo Josely , Khare Sangeeta , Nunes Jairo , Adams L. Garry , Tsolis Renée M. , Bäumler Andreas J. 
Published: May 2003

SummaryThe Salmonella enterica serotype Typhimurium (S. Typhimurium) genome contains 13 putative fimbrial operons termed agf (csg), fim, pef, lpf, bcf, saf, stb, stc, std, stf, sth, sti and stj. Evidence for in vitro expression of fimbrial proteins encoded by these operons is currently only available for agf, fim and pef. We raised antisera against putative major fimbrial subunits of S. Typhimurium, including AgfA, FimA, PefA, LpfA, BcfA, StbA, StcA, StdA, StfA, SthA and StiA. Elaboration of StcA on the bacterial surface could be detected by flow cytometry and immunoelectron microscopy after expression of the cloned stcABCD operon from a heterologous T7 promoter in Escherichia coli. To study the expression of fimbrial antigens in S. Typhimurium by flow cytometry, we constructed strains carrying deletions of agfAB, pefBACDI, lpfABCDE, bcfABCDEFG, stbABCD, stcABC, stdAB, stfACDEFG, sthABCDE or stiABCDE. Using these deletion mutants for gating, expression of fimbrial antigens was measured by flow cytometry in cultures grown in vitro or in samples recovered 8 h after infection of bovine ligated ileal loops with S. Typhimurium. FimA was the only fimbrial antigen expressed by S. Typhimurium after static growth in Luria–Bertani (LB) broth. Injection of static LB broth cultures of S. Typhimurium into bovine ligated ileal loops resulted in the expression of BcfA, FimA, LpfA, PefA, StbA, StcA, StdA, StfA and StiA. These data show that in vivo growth conditions drastically alter the repertoire of fimbrial antigens expressed in S. Typhimurium.
A reporter gene system for the hyperthermophilic archaeon Sulfolobus solfataricus based on a selectable and integrative shuttle vector
Authors: Jonuscheit Melanie , Martusewitsch Erika , Stedman Kenneth M. , Schleper Christa 
Published: May 2003

Summary Sulfolobus solfataricus has developed into an important model organism for molecular and biochemical studies of hyperthermophilic archaea. Although a number of in vitro systems have been established for the organism, efficient tools for genetic manipulations have not yet been available for any hyperthermophile. In this work, we have developed a stable and selectable shuttle vector based on the virus SSV1 of Sulfolobus shibatae. We have introduced pUC18 for propagation in Escherichia coli and the genes pyrEF coding for orotidine‐5′‐monophosphate pyrophosphorylase and orotidine‐5′‐monophosphate decarboxylase of Sulfolobus solfataricus as selectable marker to complement pyrimidine auxotrophic mutants. Furthermore, the beta‐galactosidase gene (lacS) was introduced into this vector as a reporter under the control of the strong and heat‐inducible promoter of the Sulfolobus chaperonin (thermosome). After transformation of a S. solfataricus pyrEF/lacS double mutant, the vector was found to reside as a single‐copy vector, stably integrated into the host chromosome via the site‐specific recombination system of SSV1. Specific beta‐galactosidase activities in transformants were found to be fourfold higher than in wild‐type S. solfataricus cells, and increased to more than 10‐fold after heat shock. Greatly increased levels of lacS mRNA were detected in Northern analyses, demonstrating that this reporter gene system is suitable for the study of regulated promoters in Sulfolobus and that the vector can also be used for the high‐level expression of genes from hyperthermophilic archaea.
Ribosome bypassing elicited by tRNA depletion
Authors: Lindsley Dale , Gallant Jonathan , Guarneros Gabriel 
Published: May 2003

SummaryRibosome bypassing refers to the ability of the ribosome::peptidyl‐tRNA complex to slide down the message without translation to a site several or dozens of nucleotides downstream and resume protein chain elongation there. The product is an isoform of a protein with a ‘coding’ gap corresponding to the region of the message which was bypassed. Previous work showed that ribosome bypassing was strongly stimulated at ‘hungry’ codons calling for a tRNA whose aminoacylation was limited. We have now used the ‘minigene’ phenomenon to ascertain whether depletion of the pool of specific isoacceptors has a similar effect. High level expression of plasmid‐borne minigenes results in the sequestration as peptidyl‐tRNA of tRNA cognate to the last triplet of the minigene, thereby limiting protein synthesis for lack of the tRNA in question. We find that induction of a minigene ending in AUA stimulates bypassing at an AUA codon, but not in a control sequence with AGA at the test position; induction of a minigene ending in AGA stimulates bypassing at the latter but not the former. Induction of the AUA minigene also stimulates both leftward and rightward frameshifting at ‘shifty’ sequences containing an AUA codon. The normal, background frequency of bypassing at an AUA codon is markedly reduced by increasing the cellular level of the tRNA which reads the codon. Thus, the frequency of bypassing can be increased or decreased by lowering or raising the concentration of a relevant tRNA isoacceptor. These observations suggest that the occurrence of ribosome bypassing reflects the length of the pause at a given codon.