bluuebunny/crossref_metadata_2025_split huggingface dataset:
Differentiation of Trypanosoma brucei may be stage non‐specific and does not require progression of cell cycle
Authors: Li Yan , Li Ziyin , Wang Ching C. 
Published: June 2003

SummaryUbiquitination and proteasomal degradation of cell cycle regulatory proteins are known to play a pivotal role in controlling the progression of the eukaryotic cell cycle. Using the technique of RNA interference (RNAi) on the bloodstream form of Trypanosoma brucei, we were able to knock down expression of each of the 11 non‐ATPase regulatory subunit proteins (Rpns) in the 19S regulatory complex of the 26S proteasome. In each case, the knock‐down led to arrest of cells within the G1 and G2 phases, suggesting blockage of cell cycle progression at both G1/S and G2/M boundaries. This finding differs from that observed previously in the procyclic form of T. brucei, in which loss of individual Rpns blocks only passage across the G2/M boundary. Thus, proteasomal degradation of additional regulatory protein(s) may be required for exiting from G1 phase in the bloodstream form. In vitro differentiation of each of the 11 Rpn‐depleted bloodstream form cell lines into the procyclic form was monitored. Each cell line proceeded to completion of the differentiation process like the wild‐type cells with the total percentage of differentiated cells about equivalent to the sum of G1 and G2 cells. Thus, cells trapped in either G1 or G2 phase can apparently still enter and complete the process of differentiation, which is probably neither stage specific nor dependent on the progression of the T. brucei cell cycle. The process is probably a simple pattern change of gene expression in the trypanosome induced by a temperature decrease from 37°C to 26°C in the presence of citrate and cis‐aconitate.
Sip, an integrase protein with excision, circularization and integration activities, defines a new family of mobile Staphylococcus aureus pathogenicity islands
Authors: Úbeda Carles , Tormo Ma. Ángeles , Cucarella Carme , Trotonda Pilar , Foster Timothy J. , Lasa Íñigo , Penadés José R. 
Published: June 2003

SummaryWe report the complete sequence of Staphylococcal pathogenicity island bovine 2 (SaPIbov2), encoding the biofilm‐associated protein Bap. SaPIbov2 contains 24 open reading frames, including sip, which encodes a functional staphylococcal integrase protein. SaPIbov2 is bordered by 18 bp direct repeats. The integration site into the chromosome lies at the 3′ end of a gene encoding GMP synthase. SaPIbov2 has extensive similarity to previously described pathogenicity islands of Staphylococcus aureus. The principal difference is that toxin genes present in the other pathogenicity islands are exchanged for a transposon‐like element that carries the bap gene and genes encoding an ABC transporter and a transposase. Also, SaPIbov2 can be excised to form a circular element and can integrate site‐specifically and RecA‐independently at a chromosomal att site in a Sip‐dependent manner. This was demonstrated both in S. aureus and with plasmid substrates ectopically in Escherichia coli. Thus, SaPIbov2 encodes a functional recombinase of the integrase family that promotes element excision and insertion/integration. In addition, we demonstrated that the presence of SaPIbov2 facilitated the persistence of S. aureus in an intramammary gland infection model. Finally, different bovine isolates of S. aureus were found to carry islands related to SaPIbov2, suggesting the existence of a family of related pathogenicity islands.
In vivo evidence of TonB shuttling between the cytoplasmic and outer membrane in Escherichia coli
Authors: Larsen Ray A. , Letain Tracy E. , Postle Kathleen 
Published: June 2003

SummaryGram‐negative bacteria are able to convert potential energy inherent in the proton gradient of the cytoplasmic membrane into active nutrient transport across the outer membrane. The transduction of energy is mediated by TonB protein. Previous studies suggest a model in which TonB makes sequential and cyclic contact with proteins in each membrane, a process called shuttling. A key feature of shuttling is that the amino‐terminal signal anchor must quit its association with the cytoplasmic membrane, and TonB becomes associated solely with the outer membrane. However, the initial studies did not exclude the possibility that TonB was artifactually pulled from the cytoplasmic membrane by the fractionation process. To resolve this ambiguity, we devised a method to test whether the extreme TonB amino‐terminus, located in the cytoplasm, ever became accessible to the cys‐specific, cytoplasmic membrane‐impermeant molecule, Oregon Green® 488 maleimide (OGM) in vivo. A full‐length TonB and a truncated TonB were modified to carry a sole cysteine at position 3. Both full‐length TonB and truncated TonB (consisting of the amino‐terminal two‐thirds) achieved identical conformations in the cytoplasmic membrane, as determined by their abilities to cross‐link to the cytoplasmic membrane protein ExbB and their abilities to respond conformationally to the presence or absence of proton motive force. Full‐length TonB could be amino‐terminally labelled in vivo, suggesting that it was periplasmically exposed. In contrast, truncated TonB, which did not associate with the outer membrane, was not specifically labelled in vivo. The truncated TonB also acted as a control for leakage of OGM across the cytoplasmic membrane. Further, the extent of labelling for full‐length TonB correlated roughly with the proportion of TonB found at the outer membrane. These findings suggest that TonB does indeed disengage from the cytoplasmic membrane during energy transduction and shuttle to the outer membrane.
VFK1, a Vicia faba K+ channel involved in phloem unloading
Authors: Ache Peter , Becker Dirk , Deeken Rosalia , Dreyer Ingo , Weber Hans , Fromm Jörg , Hedrich Rainer 
Published: June 2003

SummaryIn search of a K+ channel involved in phloem transport we screened a Vicia faba cotyledon cDNA library taking advantage of a set of degenerated primers, flanking regions conserved among K+ uptake channels. We cloned VFK1 (for Vicia faba K+ channel 1) characterised by a structure known from the Shaker family of plant K+ channels. When co‐expressed with a KAT1 mutant in Xenopus oocytes, heteromers revealed the biophysical properties of a K+ selective, proton‐blocked channel. Northern blot analyses showed high levels of expression in cotyledons, flowers, stem and leaves. Using in situ PCR techniques we could localise the K+ channel mRNA in the phloem. In the stem VFK1 expression levels were higher in the lower internodes. There channel transcripts increased in the light and thus under conditions of increased photosynthate allocation. VFK1 transcripts are elevated in sink leaves, and rise in source leaves during the experimental transition into sinks. Fructose‐ rather than sucrose‐ or glucose‐feeding via the petiole induced VFK1 gene activity. We therefore monitored the fructose sensitivity of the sieve tube potential through cut aphid stylets. In response to an 1 h fructose treatment the sieve tube potential shift increased from 19 mV to 53 mV per 10‐fold change in K+ concentration. Under these conditions K+ channels dominated the electrical properties of the plasma membrane. Based on the phloem localisation and expression patterns of VFK1 we conclude that this K+ channel is involved in sugar unloading and K+ retrieval.
Prognostic factors in neonatal tetanus
Authors: Davies‐Adetugbo Anita A. , Davies‐Adetugbo Anita A. , Torimiro S. E. A. , Ako‐Nai K. A. 
Published: June 2003

objective

Neonatal tetanus (NNT) is the leading cause of neonatal deaths in developing countries. The objective of this study was to determine prognostic indicators in NNT.methods  We reviewed the clinical records of all neonates (n= 174) admitted to Ife State Hospital with the diagnosis of NNT from 1991 through 1995.results  Delivery had occurred at home in 73.3% of cases. Only 37/164 of the mothers had had adequate immunization with tetanus toxoid. The umbilical cord appeared to be the portal of entry in 58.6% of cases. Mean age of infants at presentation was 7.2 days. Mortality was 57.5%; non‐survivors succumbed after mean stay in the hospital of 5.0 days. Mortality was significantly associated with an incubation period of 6 days or less (P= 0.0026), infant's weight of less than 2.5 kg (P= 0.0113), lack of antenatal care in a health facility (P= 0.0279), birth at home (P= 0.0455), but not with lack of adequate maternal immunization (P = 0.2081; not significant). Multivariable analysis showed that a short (6 d) incubation period was the strongest predictor of mortality (OR = 3.11, P= 0.0030) while low infant weight (< 2.5 kg) was also a significant predictor (OR = 2.46, P= 0.0408).conclusions  Hygienic deliveries and adequate cord care are very important for the prevention of neonatal tetanus deaths, and universal prenatal care, including education programmes on appropriate perinatal and cord care, can significantly reduce NNT incidence and mortality in developing countries.
Intramuscular artemether vs intravenous quinine: an open, randomized trial in Malawian children with cerebral malaria
Authors: Taylor T. E. , Taylor T. E. , Wills B. A. , Courval J. M. , Molyneux M. E. , Molyneux M. E. 
Published: June 2003

objectives

To compare artemether (by intramuscular injection) and quinine (by intravenous infusion) as treatments for cerebral malaria in African children.methods  An open, randomized trial conducted at the Queen Elizabeth Central Hospital in Blantyre, Malawi. This trial was part of a multicentre study designed to determine if treatment with artemether would significantly lower mortality rates compared with quinine. Data from 83 artemether recipients and 81 quinine recipients are reported here.results  Overall mortality rates and coma resolution times were not significantly different in the two treatment groups. Parasite and fever clearance times were significantly more rapid in the artemether recipients. Analyses which took into account the possible confounding variables did not significantly alter the findings of these unadjusted analyses.conclusion  These results do not suggest that treatment with artemether would confer a survival advantage in children with life‐threatening malaria. The power and precision of the estimated treatment effects of artemether would be enhanced by a meta‐analysis of all relevant clinical trials.
Prevalence of intestinal parasites in rural Southern Indians
Authors: Kang Gagandeep , Mathew Mary S. , Prasanna Rajan D. , Daniel Jasper D. , Mathan Minnie M. , Mathan V. I. , Muliyil J. P. 
Published: June 2003

objective

To determine the prevalence of intestinal protozoal and helminthic infection in a rural population.method  Seventy‐eight members of 15 families from a village were studied. Stool samples from all subjects were examined on alternate days for one month.results  The overall prevalence rate of various parasitic infections was 97.4%, with only 2 of 78 subjects not excreting parasites in any of their 15 samples. Eighteen (23.1%) persons had only one type of parasite, while 58 (74.3%) excreted multiple parasites. Giardia and Cryptosporidium were the commonest protozoan infections, affecting 42/78 (53.8%) and 31/78 (39.7%), respectively. Hookworm infestations were the commonest helminthic infections, seen in 48/78 (61.5%). Based on excretion patterns, the asymptomatic individuals could be divided into 2 groups of infrequent and frequent excretors, indicating that the host response may determine the level of parasite replication in the gut.
Anthropogenic disturbance promotes hybridization between Banksia species by altering their biology
Authors: Lamont B. B. , He T. , Enright N. J. , Krauss S. L. , Miller B. P. 
Published: June 2003

Abstract
Putative hybrids between Banksia hookeriana and B. prionotes were identified among 12 of 106 populations of B. hookeriana located at or near anthropogenically disturbed sites, mainly roadways, but none in 156 undisturbed populations. Morphometrics and AFLP markers confirmed that a hybrid swarm existed in a selected disturbed habitat, whereas no intermediates were present where the two species co-occurred in undisturbed vegetation. Individuals of both species in disturbed habitats at 12 sites were more vigorous, with greater size and more flower heads than their counterparts in undisturbed vegetation. These more fecund plants also showed a shift in season and duration of flowering. By promoting earlier flowering of B. hookeriana plants and prolonging flowering of B. prionotes, anthropogenic disturbance broke the phenological barrier between these two species. We conclude that anthropogenic disturbance promotes hybridization through increasing opportunities for gene flow by reducing interpopulation separation, increasing gamete production and, especially, promoting coflowering.
Evolvability and genetic constraint in Dalechampia blossoms: components of variance and measures of evolvability
Authors: Hansen Thomas F. , Pélabon Christophe , Armbruster W. Scott , Carlson Matthew L. 
Published: June 2003

Abstract
Many evolutionary arguments are based on the assumption that quantitative characters are highly evolvable entities that can be rapidly moulded by changing selection pressures. The empirical evaluation of this assumption depends on having an operational measure of evolvability that reflects the ability of a trait to respond to a given external selection pressure. We suggest short-term evolvability be measured as expected proportional response in a trait to a unit strength of directional selection, where strength of selection is defined independently of character variation and in units of the strength of selection on fitness itself. We show that the additive genetic variance scaled by the square of the trait mean, IA, is such a measure. The heritability, h2, does not measure evolvability in this sense. Based on a diallel analysis, we use IA to assess the evolvability of floral characters in a population of the neotropical vine Dalechampia scandens (Euphorbiaceae). Although we are able to demonstrate that there is additive genetic variation in a number of floral traits, we also find that most of the traits are not expected to change by more than a fraction of a percent per generation. We provide evidence that the degree of among-population divergence of traits is related to their predicted evolvabilities, but not to their heritabilities.
Sexual selection promotes hybridization between Pecos pupfish, Cyprinodon pecosensis and sheepshead minnow, C. variegatus
Authors: Rosenfield J. A. , Kodric-Brown A. 
Published: June 2003

Abstract
Rapid and extensive genetic introgression has occurred between Pecos pupfish (Cyprinodon pecosensis) and sheepshead minnow (Cyprinodon variegatus) in the wild. We studied both female mate choice and male–male competition for mates among C. pecosensis, C. variegatus, and their F1 hybrids to determine what role these behaviours played in the formation of the hybrid swarm. Female C. pecosensis preferred male C. variegatus to conspecific males, C. variegatus females displayed no significant preference when given a choice between purebred males, and neither C. pecosensis nor C. variegatus females discriminated against F1 hybrid males. We found no evidence for female olfactory recognition of mates. Male F1 hybrids and C. variegatus were more aggressive than C. pecosensis males, achieving greater reproductive success under two different experimentally-induced mating systems. Hybrids were superior to C. variegatus when only two males competed (dominance interactions), but the two types were competitively equivalent in a territorial mating system. Our results indicate that active inter- and intra-sexual selection contributed to the accelerated hybridization between these two species. By including the possibility that some aspects of a hybridization and introgression event may be under positive selection, researchers may better understand the dynamics that lead to hybrid zone stability or the spread of introgressed genetic material.
Local mate competition with lethal male combat: effects of competitive asymmetry and information availability on a sex ratio game
Authors: Abe J. , Kamimura Y. , Ito H. , Matsuda H. , Shimada M. 
Published: June 2003

Abstract
We constructed a sex allocation model for local mate competition considering the asymmetry of competitive abilities among sons. This model assumes two females of a parasitoid wasp oviposit on the same host in sequential order. The evolutionarily stable strategy will be in either Stackelberg or Nash equilibrium, depending on whether the females can recognize their opponent's sex ratio or not, respectively. The Nash equilibrium predicts the second female produce more males than the first. If the second female is able to know and respond to the strategy of the first (a Stackelberg equilibrium), the first will decide an optimal sex ratio assuming that the second reply to it. Under such an assumption, our model predicts that not producing sons is adaptive for the second female when the sons she produces have low competitive ability. Males of parasitoid wasps Melittobia spp. are engaged in lethal male–male combat, indicating large asymmetry in mating success among sons. If females have the ability to recognize their opponent's sex ratio, our model suggests that the severe lethal male–male combat may be one factor explaining their extremely female-biased sex ratio that is unexplainable by pre-existent models.
Selective and genetic constraints on the evolution of body size in a stream-dwelling salmonid fish
Authors: Wilson A. J. , Hutchings J. A. , Ferguson M. M. 
Published: June 2003

Abstract
To examine constraints on evolution of larger body size in two stunted populations of brook charr (Salvelinus fontinalis) from a single river in Cape Race, Newfoundland, Canada, we measured viability selection acting on length-at-age traits, and estimated quantitative genetic parameters in situ (following reconstruction of pedigree information from microsatellite data). Furthermore we tested for phenotypic differentiation between the populations, and for association of high juvenile growth with early maturity that is predicted by life history theory. Within each population, selection differentials and estimates of heritabilities for length-at-age traits suggested that evolution of larger size is prevented by both selective and genetic constraints. Between the populations, phenotypic differentiation was found in length-at-age and age of maturation traits, whereas early maturation was associated with increased juvenile growth (relative to adult growth) both within and between populations. The results suggest an adaptive plastic response in age of maturation to juvenile growth rates that have a largely environmental basis of determination.
The evolution of plumage polymorphism in birds of prey and owls: the apostatic selection hypothesis revisited
Authors: Fowlie M. K. , Krüger O. 
Published: June 2003

Abstract
Co-evolution between phenotypic variation and other traits is of paramount importance for our understanding of the origin and maintenance of polymorphism in natural populations. We tested whether the evolution of plumage polymorphism in birds of prey and owls was supported by the apostatic selection hypothesis using ecological and life-history variables in birds of prey and owls and performing both cross taxa and independent contrast analyses. For both bird groups, we did not find any support for the apostatic selection hypothesis being the maintaining factor for the polymorphism: plumage polymorphism was not more common in taxa hunting avian or mammalian prey, nor in migratory species. In contrast, we found that polymorphism was related to variables such as sexual plumage dimorphism, population size and range size, as well as breeding altitude and breeding latitude. These results imply that the most likely evolutionary correlate of polymorphism in both bird groups is population size, different plumage morphs might simply arise in larger populations most likely because of a higher probability of mutations and then be maintained by sexual selection.
Sexual selection, antennae length and the mating advantage of large males in Asellus aquaticus
Authors: Bertin A. , Cezilly F. 
Published: June 2003

Abstract
In crustacean species with precopulatory mate-guarding, sexual size dimorphism has most often been regarded as the consequence of a large male advantage in contest competition for access to females. However, large body size in males may also be favoured indirectly through scramble competition. This might partly be the case if the actual target of selection is a morphological character, closely correlated with body size, involved in the detection of receptive females. We studied sexual selection on body size and antennae length in natural populations of Asellus aquaticus, an isopod species with precopulatory mate guarding. In this species, males are larger than females and male pairing success is positively related to body size. However, males also have longer antennae, relative to body size, than females, suggesting that this character may also be favoured by sexual selection. We used multivariate analysis of selection to assess the relative influences of body size and antennae length in five different populations in the field. Selection gradients indicated that overall body size was a better predictor of male pairing success than antennae length, although some variation was observed between sites. We then manipulated male antennae length in a series of experiments conducted in the laboratory, and compared the pairing ability of males with short or long antennae. Males with short antennae were less likely to detect, orient to and to pair with a receptive female compared to males with long antennae. We discuss the implications of our results for studies of male body size and sexual dimorphism in relation to sexual selection in crustaceans.
The evolution of inquilinism, host-plant use and mitochondrial substitution rates in Tamalia gall aphids
Authors: Miller D. G. , Crespi B. 
Published: June 2003

Abstract
We used mitochondrial DNA data to infer phylogenies for 28 samples of gall-inducing Tamalia aphids from 12 host-plant species, and for 17 samples of Tamalia inquilinus, aphid ‘inquilines’ that obligately inhabit galls of the gall inducers and do not form their own galls. Our phylogenetic analyses indicate that the inquilines are monophyletic and closely related to their host aphids. Tamalia coweni aphids from different host plants were, with one exception, very closely related to one another. By contrast, the T. inquilinus aphids were strongly genetically differentiated among most of their host plants. Comparison of branch lengths between the T. coweni clade and the T. inquilinus clade indicates that the T. inquilinus lineage evolves 2.5–3 times faster for the cytochrome oxidase I gene. These results demonstrate that: (1) Tamalia inquilines originated from their gall-inducing hosts, (2) communal (multi-female) gall induction apparently facilitated the origin of inquilinism, (3) diversification of the inquilines has involved rapid speciation along host-plant lines, or the rapid evolution of host-plant races, and (4) the inquilines have undergone accelerated molecular evolution relative to their hosts, probably due to reduced effective population sizes. Our findings provide insight into the behavioural causes and evolutionary consequences of transitions from resource generation to resource exploitation.