bluuebunny/crossref_metadata_2025_split huggingface dataset:
Pyruvate-Phosphate Dikinase of Oxymonads and Parabasalia and the Evolution of Pyrophosphate-Dependent Glycolysis in Anaerobic Eukaryotes
Authors: Slamovits Claudio H. , Keeling Patrick J. 
Published: January 2006

ABSTRACT

In pyrophosphate-dependent glycolysis, the ATP/ADP-dependent enzymes phosphofructokinase (PFK) and pyruvate kinase are replaced by the pyrophosphate-dependent PFK and pyruvate phosphate dikinase (PPDK), respectively. This variant of glycolysis is widespread among bacteria, but it also occurs in a few parasitic anaerobic eukaryotes such as
Giardia
and
Entamoeba
spp. We sequenced two genes for PPDK from the amitochondriate oxymonad
Streblomastix strix
and found evidence for PPDK in
Trichomonas vaginalis
and other parabasalia, where this enzyme was thought to be absent. The
Streblomastix
and
Giardia
genes may be related to one another, but those of
Entamoeba
and perhaps
Trichomonas
are distinct and more closely related to bacterial homologues. These findings suggest that pyrophosphate-dependent glycolysis is more widespread in eukaryotes than previously thought, enzymes from the pathway coexists with ATP-dependent more often than previously thought and may be spread by lateral transfer of genes for pyrophosphate-dependent enzymes from bacteria.
Cdc42 Is Required for Proper Growth and Development in the Fungal Pathogen
Colletotrichum trifolii
Authors: Chen Changbin , Ha Young-sil , Min Ji-young , Memmott Stephen D. , Dickman Martin B. 
Published: January 2006

ABSTRACT

Cdc42 is a highly conserved small GTP-binding protein that is involved in regulating morphogenesis in eukaryotes. In this study, we isolated and characterized a highly conserved Cdc42 gene from
Colletotrichum trifolii
(Ct
Cdc42
), a fungal pathogen of alfalfa. CtCdc42 is, at least in part, functionally equivalent to
Saccharomyces cerevisiae
Cdc42p, since it restores the temperature-sensitive phenotype of a yeast Cdc42p mutant. Inhibition of CtCdc42 by expression of an antisense Ct
Cdc42
or a dominant negative form of CtCdc42 (DN Cdc42) resulted in appressorium differentiation under noninductive conditions, suggesting that CtCdc42 negatively regulates pathogenic development in this fungus. We also examined the possible linkage between CtCdc42 and Ras signaling. Expression of a dominant active Cdc42 (DA Cdc42) in
C. trifolii
leads to aberrant hyphal growth under nutrient-limiting conditions. This phenotype was similar to that of our previously reported dominant active Ras (DA Ras) mutant. Also consistent with our observations of the DA Ras mutant, high levels of reactive oxygen species (ROS) were observed in the DA
Cdc42
mutant, and proline restored the wild-type phenotype. Moreover, overexpression of DN Cdc42 resulted in a significant decrease in spore germination, virtually no hyphal branching, and earlier sporulation, again similar to what we observed in a dominant negative Ras (DN Ras) mutant strain. Interestingly, coexpression of DA Cdc42 with DN Ras resulted in germination rates close to wild-type levels, while coexpression of DN Cdc42 with the DA Ras mutant restored the wild-type phenotype. These data suggest that CtCdc42 is positioned as a downstream effector of CtRas to regulate spore germination and pathogenic development.
Integration of Transcriptional and Posttranslational Regulation in a Glucose Signal Transduction Pathway in
Saccharomyces cerevisiae
Authors: Kim Jeong-Ho , Brachet Valérie , Moriya Hisao , Johnston Mark 
Published: January 2006

ABSTRACT

Expression of the
HXT
genes encoding glucose transporters in the budding yeast
Saccharomyces cerevisiae
is regulated by two interconnected glucose-signaling pathways: the Snf3/Rgt2-Rgt1 glucose induction pathway and the Snf1-Mig1 glucose repression pathway. The Snf3 and Rgt2 glucose sensors in the membrane generate a signal in the presence of glucose that inhibits the functions of Std1 and Mth1, paralogous proteins that regulate the function of the Rgt1 transcription factor, which binds to the
HXT
promoters. It is well established that glucose induces degradation of Mth1, but the fate of its paralogue Std1 has been less clear. We present evidence that glucose-induced degradation of Std1 via the SCF
Grr1
ubiquitin-protein ligase and the 26S proteasome is obscured by feedback regulation of
STD1
expression. Disappearance of Std1 in response to glucose is accelerated when glucose induction of
STD1
expression due to feedback regulation by Rgt1 is prevented. The consequence of relieving feedback regulation of
STD1
expression is that reestablishment of repression of
HXT1
expression upon removal of glucose is delayed. In contrast, degradation of Mth1 is reinforced by glucose repression of
MTH1
expression: disappearance of Mth1 is slowed when glucose repression of
MTH1
expression is prevented, and this results in a delay in induction of
HXT3
expression in response to glucose. Thus, the cellular levels of Std1 and Mth1, and, as a consequence, the kinetics of induction and repression of
HXT
gene expression, are closely regulated by interwoven transcriptional and posttranslational controls mediated by two different glucose-sensing pathways.
Cellular and Molecular Biology of
Candida albicans
Estrogen Response
Authors: Cheng Georgina , Yeater Kathleen M. , Hoyer Lois L. 
Published: January 2006

ABSTRACT

Candida albicans
is the most common etiological agent of vaginal candidiasis. Elevated host estrogen levels and the incidence of vaginal candidiasis are positively associated. Elevated estrogen levels may affect host and/or fungal cells. This study investigates the effect of 17-β-estradiol, 17-α-estradiol, ethynyl estradiol, and estriol on several
C. albicans
strains at concentrations ranging from 10
−5
to 10
−10
M. The addition of 17-β-estradiol or ethynyl estradiol to
C. albicans
cells caused an increase in the number of cells forming germ tubes and an increase in germ tube length in a dose- and strain-dependent manner. The addition of 17-α-estradiol or estriol did not have a significant effect on germ tube formation by the cultured cells. Exposure to exogenous estrogens did not significantly change the biomass of any
C. albicans
culture tested. The transcriptional profile of estrogen-treated
C. albicans
cells showed increased expression of
CDR1
and
CDR2
across several strain-estrogen concentration-time point combinations, suggesting that these genes are the most responsive to estrogen exposure. Analysis of strain DSY654, which lacks the
CDR1
and
CDR2
coding sequences, showed a significantly decreased number of germ tube-forming cells in the presence of 17-β-estradiol.
PDR16
was the most highly up-regulated gene in strain DSY654 under these growth conditions. The cell biology and gene expression data from this study led to a model that proposes how components of the phospholipid and sterol metabolic pathways may interact to affect
C. albicans
germ tube formation and length.
SST2, a Regulator of G-Protein Signaling for theCandida albicansMating Response Pathway
Authors: Dignard Daniel , Whiteway Malcolm 
Published: January 2006

ABSTRACTCandida albicanscontains a functional mating response pathway that is similar to the well-studied system ofSaccharomyces cerevisiae. We have characterized aregulator ofGproteinsignaling (RGS) homolog inC. albicanswith sequence similarity to theSST2gene ofSaccharomyces cerevisiae. Disruption of this gene, which had been designatedSST2, causes an opaqueMTLa/MTLaderivative of strain SC5314 to show hypersensitivity to theC. albicansα-factor. This hypersensitivity generates an enhanced cell cycle arrest detected in halo assays but reduces the overall mating efficiency of the cells. Transcriptional profiling of the pheromone-regulated gene expression in thesst2mutant shows a pattern of gene induction similar to that observed in wild-type cells, but the responsiveness is heightened. This involvement of an RGS in the sensitivity to pheromone is consistent with the prediction that the mating response pathway inC. albicansrequires the activation of a heterotrimeric G protein.
ATP Synthase Is Responsible for Maintaining Mitochondrial Membrane Potential in Bloodstream Form
Trypanosoma brucei
Authors: Brown Silvia V. , Hosking Paul , Li Jinlei , Williams Noreen 
Published: January 2006

ABSTRACT

The mitochondrion of
Trypanosoma brucei
bloodstream form maintains a membrane potential, although it lacks cytochromes and several Krebs cycle enzymes. At this stage, the ATP synthase is present at reduced, although significant, levels. To test whether the ATP synthase at this stage is important for maintaining the mitochondrial membrane potential, we used RNA interference (RNAi) to knock down the levels of the ATP synthase by targeting the F
1
-ATPase α and β subunits. RNAi-induced cells grew significantly slower than uninduced cells but were not morphologically altered. RNAi of the β subunit decreased the mRNA and protein levels for the β subunit, as well as the mRNA and protein levels of the α subunit. Similarly, RNAi of α subunit decreased the α subunit transcript and protein levels, as well as the β-subunit transcript and protein levels. In contrast, α and β RNAi knockdown resulted in a 60% increase in the F
0
complex subunit 9 protein levels without a significant change in the steady-state transcript levels of this subunit. The F
0
-32-kDa subunit protein expression, however, remained stable throughout induction of RNAi for α or β subunits. Oligomycin-sensitive ATP hydrolytic and synthetic activities were decreased by 43 and 44%, respectively. Significantly, the mitochondrial membrane potential of α and β RNAi cells was decreased compared to wild-type cells, as detected by MitoTracker Red CMXRos fluorescence microscopy and flow cytometry. These results support the role of the ATP synthase in the maintenance of the mitochondrial membrane potential in bloodstream form
T. brucei
.
Cell Cycle-Dependent Localization and Properties of a Second Mitochondrial DNA Ligase in
Crithidia fasciculata
Authors: Sinha Krishna Murari , Hines Jane C. , Ray Dan S. 
Published: January 2006

ABSTRACT

The mitochondrial DNA in kinetoplastid protozoa is contained in a single highly condensed structure consisting of thousands of minicircles and approximately 25 maxicircles. The disk-shaped structure is termed kinetoplast DNA (kDNA) and is located in the mitochondrial matrix near the basal body. We have previously identified a mitochondrial DNA ligase (LIG kβ) in the trypanosomatid
Crithidia fasciculata
that localizes to antipodal sites flanking the kDNA disk where several other replication proteins are localized. We describe here a second mitochondrial DNA ligase (LIG kα). LIG kα localizes to the kinetoplast primarily in cells that have completed mitosis and contain either a dividing kinetoplast or two newly divided kinetoplasts. Essentially all dividing or newly divided kinetoplasts show localization of LIG kα. The ligase is present on both faces of the kDNA disk and at a high level in the kinetoflagellar zone of the mitochondrial matrix. Cells containing a single nucleus show localization of the LIG kα to the kDNA but at a much lower frequency. The mRNA level of LIG kα varies during the cell cycle out of phase with that of
LIG kβ
. LIG kα transcript levels are maximal during the phase when cells contain two nuclei, whereas
LIG kβ
transcript levels are maximal during S phase. The LIG kα protein decays with a half-life of 100 min in the absence of protein synthesis. The periodic expression of the
LIG kα
transcript and the instability of the LIG kα protein suggest a possible role of the ligase in regulating minicircle replication.
Multigene Family Encoding 3′,5′-Cyclic-GMP-Dependent Protein Kinases in
Paramecium tetraurelia
Cells
Authors: Kissmehl Roland , Krüger Tim P. , Treptau Tilman , Froissard Marine , Plattner Helmut 
Published: January 2006

ABSTRACT

In the ciliate
Paramecium tetraurelia
, 3′,5′-cyclic GMP (cGMP) is one of the second messengers involved in several signal transduction pathways. The enzymes for its production and degradation are well established for these cells, whereas less is known about the potential effector proteins. On the basis of a current
Paramecium
genome project, we have identified a multigene family with at least 35 members, all of which encode cGMP-dependent protein kinases (PKGs). They can be classified into 16 subfamilies with several members each. Two of the genes,
PKG1
-
1
and
PKG2
-
1
, were analyzed in more detail after molecular cloning. They encode monomeric enzymes of 770 and 819 amino acids, respectively, whose overall domain organization resembles that in higher eukaryotes. The enzymes contain a regulatory domain of two tandem cyclic nucleotide-binding sites flanked by an amino-terminal region for intracellular localization and a catalytic domain with highly conserved regions for ATP binding and catalysis. However, some
Paramecium
PKGs show a different structure. In Western blots, PKGs are detected both as cytosolic and as structure-bound forms. Immunofluorescence labeling shows enrichment in the cell cortex, notably around the dense-core secretory vesicles (trichocysts), as well as in cilia. Immunogold electron microscopy analysis reveals consistent labeling of ciliary membranes, of the membrane complex composed of cell membrane and cortical Ca
2+
stores, and of regions adjacent to ciliary basal bodies, trichocysts, and trafficking vesicles. Since PKGs (re)phosphorylate the exocytosis-sensitive phosphoprotein pp63/pf upon stimulation, the role of PKGs during stimulated exocytosis is discussed, in addition to a role in ciliary beat regulation.
Intact Recollection Memory in High-performing Older Adults: ERP and Behavioral Evidence
Authors: Duarte Audrey , Ranganath Charan , Trujillo Celina , Knight Robert T. 
Published: January 2006

Abstract
Numerous behavioral studies have suggested that normal aging has deleterious effects on episodic memory and that recollection is disproportionately impaired relative to familiarity-based recognition. However, there is a wide degree of variability in memory performance within the aging population and this generalization may not apply to all elderly adults. Here we investigated these issues by using event-related potentials (ERPs) to measure the effects of aging on the neural correlates of recollection and familiarity in older adults with recognition memory performance that was equivalent to (old-high) or lower than (old-low) that of young adults. Results showed that, behaviorally, old-high subjects exhibited intact recollection but reduced familiarity, whereas old-low subjects had impairments in both recollection and familiarity, relative to the young. Consistent with behavioral results, old-high subjects exhibited ERP correlates of recollection that were topographically similar to those observed in young subjects. However, unlike the young adults, old-high subjects did not demonstrate any neural correlates of familiarity-based recognition. In contrast to the old-high group, the old-low group exhibited neural correlates of recollection that were topographically distinct from those of the young. Our results suggest that the effects of aging on the underlying brain processes related to recollection and familiarity are dependent on individual memory performance and highlight the importance of examining performance variability in normal aging.
Access to Lexical Information in Language Comprehension: Semantics before Syntax
Authors: Müller Oliver , Hagoort Peter 
Published: January 2006

Abstract
The recognition of a word makes available its semantic and syntactic properties. Using electrophysiological recordings, we investigated whether one set of these properties is available earlier than the other set. Dutch participants saw nouns on a computer screen and performed push-button responses: In one task, grammatical gender determined response hand (left/right) and semantic category determined response execution (go/no-go). In the other task, response hand depended on semantic category, whereas response execution depended on gender. During the latter task, response preparation occurred on no-go trials, as measured by the lateralized readiness potential: Semantic information was used for response preparation before gender information inhibited this process. Furthermore, an inhibition-related N2 effect occurred earlier for inhibition by semantics than for inhibition by gender. In summary, electrophysiological measures of both response preparation and inhibition indicated that the semantic word property was available earlier than the syntactic word property when participants read single words.
The Representation of Polysemy: MEG Evidence
Authors: Pylkkänen Liina , Llinás Rodolfo , Murphy Gregory L. 
Published: January 2006

AbstractMost words in natural language are polysemous, that is, they can be used in more than one way. For example, paper can be used to refer to a substance made out of wood pulp or to a daily publication printed on that substance. Although virtually every sentence contains polysemy, there is little agreement as to how polysemy is represented in the mental lexicon. Do different uses of polysemous words involve access to a single representation or do our minds store distinct representations for each different sense? Here we investigated priming between senses with a combination of behavioral and magnetoencephalographic measures in order to test whether different senses of the same word involve identity or mere formal and semantic similarity. Our results show that polysemy effects are clearly distinct from similarity effects bilaterally. In the left hemisphere, sense-relatedness elicited shorter latencies of the M350 source, which has been hypothesized to index lexical activation. Concurrent activity in the right hemisphere, on the other hand, peaked later for sense-related than for unrelated target stimuli, suggesting competition between related senses. The obtained pattern of results supports models in which the representation of polysemy involves both representational identity and difference: Related senses connect to same abstract lexical representation, but are distinctly listed within that representation.
Effects of Attention on Neuroelectric Correlates of Auditory Stream Segregation
Authors: Snyder Joel S. , Alain Claude , Picton Terence W. 
Published: January 2006

Abstract
A general assumption underlying auditory scene analysis is that the initial grouping of acoustic elements is independent of attention. The effects of attention on auditory stream segregation were investigated by recording event-related potentials (ERPs) while participants either attended to sound stimuli and indicated whether they heard one or two streams or watched a muted movie. The stimuli were pure-tone ABA-patterns that repeated for 10.8 sec with a stimulus onset asynchrony between A and B tones of 100 msec in which the A tone was fixed at 500 Hz, the B tone could be 500, 625, 750, or 1000 Hz, and was a silence. In both listening conditions, an enhancement of the auditory-evoked response (P1-N1-P2 and N1c) to the B tone varied with f and correlated with perception of streaming. The ERP from 150 to 250 msec after the beginning of the repeating ABA-patterns became more positive during the course of the trial and was diminished when participants ignored the tones, consistent with behavioral studies indicating that streaming takes several seconds to build up. The N1c enhancement and the buildup over time were larger at right than left temporal electrodes, suggesting a right-hemisphere dominance for stream segregation. Sources in Heschl's gyrus accounted for the ERP modulations related to f-based segregation and buildup. These findings provide evidence for two cortical mechanisms of streaming: automatic segregation of sounds and attention-dependent buildup process that integrates successive tones within streams over several seconds.
Effect of Language Switching on Arithmetic: A Bilingual fMRI Study
Authors: Venkatraman Vinod , Siong Soon Chun , Chee Michael W. L. , Ansari Daniel 
Published: January 2006

Abstract
The role of language in performing numerical computations has been a topic of special interest in cognition. The “Triple Code Model” proposes the existence of a language-dependent verbal code involved in retrieving arithmetic facts related to addition and multiplication, and a language-independent analog magnitude code subserving tasks such as number comparison and estimation. Neuroimaging studies have shown dissociation between dependence of arithmetic computations involving exact and approximate processing on language-related circuits. However, a direct manipulation of language using different arithmetic tasks is necessary to assess the role of language in forming arithmetic representations and in solving problems in different languages. In the present study, 20 English-Chinese bilinguals were trained in two unfamiliar arithmetic tasks in one language and scanned using fMRI on the same problems in both languages (English and Chinese). For the exact “base-7 addition” task, language switching effects were found in the left inferior frontal gyrus (LIFG) and left inferior parietal lobule extending to the angular gyrus. In the approximate “percentage estimation” task, language switching effects were found predominantly in the bilateral posterior intraparietal sulcus and LIFG, slightly dorsal to the LIFG activation seen for the base-7 addition task. These results considerably strengthen the notion that exact processing relies on verbal and language-related networks, whereas approximate processing engages parietal circuits typically involved in magnitude-related processing.
Automatic Drive of Limb Motor Plasticity
Authors: Magescas F. , Prablanc C. 
Published: January 2006

Abstract
The ability to perform accurate limb movements may require learning mechanisms that continually tune the motor system. In the current study, we isolate a form of pure limb motor plasticity. Participants reached to targets that were turned off just after the onset of an initial eye movement, reappearing at a new location at the end of the reaching movement. In contrast to classical prism or virtual reality paradigms, our task eliminated sensory adaptation by always maintaining a congruency between the seen and felt limb position. We also minimized awareness and potential adaptation processes on the basis of volitional strategies by progressively increasing the size of the target perturbations. In this manner, our adaptation procedure mimicked conditions used to study saccadic adaptation. The results indicated that adaptation under these conditions led to a robust after-effect that generalized to a large range of movements within the workspace. This fully natural, nonim-posed generalization of adaptation is not expressed in a spatial coordinate system, but more likely in a joint-centered coordinate space.