bluuebunny/crossref_metadata_2025 huggingface dataset:
Contramensal interactions between two collembolan species: effects on population development and on soil processes
Authors: THEENHAUS A. , SCHEU S. , SCHAEFER M.
Published: March 2003

1.In the laboratory, a microcosm experiment was set up to study (1) the interaction between two collembolan speciesOnychiurus furcifer(Börner) andHeteromurus nitidus(Templeton) during 24 weeks of incubation; (2) the influence of slug (Arion rufusL.) cast material on the outcome of this interaction; and (3) the influence of collembolan activity on microbial biomass, respiration and nutrient mobilization.

2.The CO2production was monitored every other week and NH4+, NO3–and PO43–contents of leachates were determined every 4 weeks. After 12 and 24 weeks of incubation, the number of collembolans, basal respiration (O2consumption), microbial biomass (substrate‐induced respiration method), specific respiration (qO2) and the content of NH4+, NO3–and PO43–in soil were determined.

3.Generally, the number of collembolans in microcosms with cast material exceeded that of microcosms without cast material considerably on average by factors of 20 and 26 forO.furciferandH. nitidus, respectively. This increase was attributed to the additional food supply provided with the cast material. Numbers of collembolans declined during the experiment.

4.At both sampling dates, the presence ofH. nitidusled to a reduction in the number ofO.furcifer, whereasH. nitidusbenefited from the presence ofO.furcifer. Either trophic or non‐trophic mechanisms, or both, may have caused this interaction (contramensalism,sensuArthur & Mitchell 1989).

5.Both collembola species caused a decrease in microbial respiration, decomposition rates and tentatively also microbial biomass at high densities, whereas at low densities microbial respiration was stimulated while decomposition rates and microbial biomass remained unaffected. These effects were more pronounced forO.furciferthan forH. nitidus.

6.In treatments with cast material N‐mobilization was increased by collembolan activity.
Parental investment and egg yolk lipid composition in gulls
Authors: Royle N. J. , Surai P. F. , Mccartney R. J. , Speake B. K.
Published: March 2003

1.Within‐clutch variation in parental investment of yolk lipid (including essential fatty acid composition and fat‐soluble vitamin content) was investigated in whole clutches of three eggs of Lesser Black‐backed Gulls,Larus fuscus.

2.Although there were no significant differences between years in egg size or yolk mass among eggs of the same laying order, eggs collected in 1996 had significantly lower lipid content than those collected in 1997.

3.In both years third‐laid c‐eggs were smaller, had a smaller mass of yolk and had significantly lower yolk lipid mass compared with earlier laid (a‐ and b‐) eggs.

4.Despite this lower lipid mass of c‐eggs, of the different lipid fractions only cholesterol content of c‐eggs was significantly lower than that of a‐ or b‐eggs.

5.Earlier laid eggs had greater amounts of arachidonic acid in the phospholipid and cholesterol ester fractions of yolk lipid, and considerably greater quantities of vitamin E and carotenoids.

6.Conversely, levels of linoleic acid and vitamin A were equalized among eggs of different laying sequence as both these essential nutrients have primarily systemic roles.

7.The probable effect of increased antioxidant (vitamin E and carotenoid) content of earlier‐laid eggs is to enhance embryonic and neonatal growth and development, reduce susceptibility to pathogens and increase the ability of the embryo to withstand the oxidative stress associated with hatching.

8.The results suggest that there is maternal bias of essential nutrients to offspring with the highest reproductive value in order to maximize reproductive success.
Adjustments to nitrogen metabolism during wing moult in Greylag Geese, Anser anser
Authors: Fox A. D. , Kahlert J.
Published: March 2003

1. This study examined the nitrogen balance of free‐living flightless moulting Greylag Geese, Anser anser, in relation to food quality, nitrogen absorption, food retention time and nitrogen excretion rates.

2. Food intake rates during moult were the same as those before and after the flightless period, but total daily time spent foraging fell by 58% from 9·45 h to 3·96 h. Dropping production during moult was 43%, and mean dropping mass 42% of that before and after moult, suggesting a considerable increase in food passage time through the gut during moult. Nitrogen absorption increased from 25% prior to moult to 47% during moult.

3. At the same time, excreted dry mass uric acid in faecal material fell by 68%, such that the proportion of nitrogen absorbed and retained in the body as a proportion of the nitrogen ingested in food rose from 16% prior to moult to 42% during moult.

4. Based on these significant increases in nitrogen absorption and decreases in nitrogen excretion, geese were able to compensate for reduced food intake and derive sufficient nitrogen from their diet to re‐grow flight feathers.
Reproductive significance of feeding on saprobic and arbuscular mycorrhizal fungi by the collembolan, Folsomia candida
Authors: Klironomos J. N. , Bednarczuk E. M. , Neville J.
Published: March 2003

1. Collembolans have often been credited with negatively affecting arbuscular mycorrhizal (AM) symbioses, mainly by grazing and severing the associated external fungal network from host roots. However, most previous experiments were performed using relatively ‘clean’ systems where other, non‐mycorrhizal, fungi were largely excluded. Yet, plant rhizospheres harbour a wide variety of highly palatable non‐AM fungi, most of which have saprobic lifestyles.

2. In this study we isolated and cultured several rhizosphere fungi, and the collembolan, Folsomia candida, from the Long‐Term Mycorrhiza Research Site, University of Guelph, Canada, to test the hypothesis that, given a choice, collembolans would prefer to feed on saprobic fungi and that such a choice is of adaptive significance to the animals.

3. A laboratory food preference experiment revealed that F. candida favours common saprobic fungi over a variety of AM fungi. Coincidentally, fecundity levels across two Folsomia generations were higher when animals fed exclusively on the preferred fungus, Alternaria alternata. When fed less palatable fungi, fecundity was greatly reduced; in fact animals from the F1 generation were unable to produce any eggs when placed on an exclusive diet of one of the following three AM fungi, Acaulospora spinosa, Scutellospora calospora and Gigaspora gigantea.

4. These results indicate that a strict diet of AM fungi by collembolans has reproductive consequences. Therefore, we propose that under natural conditions these animals spend more time feeding on common saprobic fungi rather than their AM counterparts. This suggests that previous ‘clean’ studies that investigated the interactions between collembolans and AM fungi may have reported exaggerated effects of animal grazing. The influence of collembolans on the functioning of AM symbioses, under more natural conditions, remains not well understood.
Evapotranspiration from Eucalypt open‐forest savanna of Northern Australia
Authors: Hutley L. B. , O'Grady A. P. , Eamus D.
Published: March 2003

1. Using three independent methods (eddy covariance, heat pulse and open‐top chambers), diurnal and seasonal measurements of evapotranspiration were made in a wet–dry Eucalypt savanna of the Northern Territory, Australia.

2. Total annual dry‐canopy water loss was estimated to be 870 mm and understorey evapotranspiration contributed 557 mm to this flux. Understorey evapotranspiration occurred predominantly during the wet season as bare soil evaporation and transpiration of Sorghum spp., a C4 grass.

3. Annual transpiration from trees was 313 mm, significantly less than the grassy understorey. Despite a very high degree of seasonality in distribution of rainfall and large changes to soil and atmospheric water content, water use by the trees did not differ between wet and dry seasons. This suggests that mature trees exploit a large soil volume and this may include extraction from the capillary fringe of the shallow water table (2–10 m below the ground surface).

4. The open canopy created an aerodynamically rough surface well coupled to the atmosphere with the coupling coefficient, Ω, ranging from 0·40 to 0·11 over a wet–dry cycle.

5. Leaf area index (LAI) of the overstorey was typically 1·0 in the wet season and 0·65 in the dry season. The decline in tree LAI occurred when evaporative demand showed a similar proportional increase. Consequently overstorey water use remained relatively unchanged throughout the year.

6. Given the very high rainfall intensities of the monsoonal climate and low LAI of the site, canopy interception was set at 5% of rainfall. Including this amount gives an annual evapotranspiration of 958 mm for this savanna.
Trade‐offs in phenotypic traits: endurance at birth, growth, survival, predation and susceptibility to parasitism in a lizard,Lacerta vivipara
Authors: Clobert J. , Oppliger A. , Sorci G. , Ernande B. , Swallow J. G. , Garland T.
Published: March 2003

Considerable within‐population variability of locomotor performance traits has been shown to exist in several species of squamate reptiles. In general, high values for speed and endurance are thought to have positive effects on the ability to capture prey, escape from predators, compete with conspecifics and acquire mates. On the other hand, variation in performance might trade‐off with other components of fitness such that the net effect on Darwinian fitness is unpredictable.

Gravid females of the common lizard (Lacerta vivipara) were captured and several phenotypic traits of their offspring measured immediately following birth. These were endurance, body length and body mass. Offspring were marked for individual identification, released into the field, and correlations between the phenotypic traits and their subsequent growth, activity and survival rate over the next months were then tested for. Parasitism by hematozoa was monitored and predation risk by tail losses estimated.

It was found that individuals with a low endurance at birth tended to have reduced activity and growth rate, and higher parasite load; on the positive side, however, they experienced lower predation risk as assessed by tail losses. Conversely, individuals with a high endurance at birth had high activity and growth rates, low parasite load, but higher incidence of broken tails. Finally, endurance at birth was not correlated with survivorship up to the age of sexual maturity. Thus, individuals with varying locomotor endurance seem to exhibit behaviours that may result in the same level of Darwinian fitness.

The possibility that our results reveal a trade‐off between the risk of becoming infected with parasites when lizards are less active (which is related to having lower endurance)vsthe risk of being predated when the lizards are more active (higher endurance) is discussed.
Does enemy‐free space for eggs contribute to a leaf beetle’s oviposition preference for a nutritionally inferior host plant?
Authors: Ballabeni P. , Wlodarczyk M. , Rahier M.
Published: March 2003

Natural enemies are likely to influence the interactions between herbivorous insects and their host plants. In particular, selection exerted by natural enemies could favour host‐plant switches and cause, or maintain, oviposition preference for a host species that is nutritionally inferior to another acceptable host.

In a previous study, it was shown that larvae of the leaf beetle Oreina elongata perform better on Adenostyles alliariae (Asteraceae) than on Cirsium spinosissimum (Asteraceae). Moreover, A. alliariae provides larval and adult beetles with sequestrable chemical defences. However, in the field, egg densities are much higher on C. spinosissimum than on adjacent A. alliariae.

In this study, it was investigated whether this oviposition pattern could be maintained by C. spinosissimum, providing the eggs of O. elongata with better protection from natural enemies. In a field experiment, the survival of eggs was quantified on plants of each of the two species, with and without enemy exclusion.

 Egg survival was equal for both host species when enemies were excluded from the plants, but it was higher on C. spinosissimum than on A. alliariae when enemies were allowed to the plants. It was also experimentally tested whether the higher egg densities observed in the field on C. spinosissimum are actually due to oviposition preference by the beetle. In a no‐choice test, females laid more eggs on C. spinosissimum than on A. alliariae.

 It can thus be confirmed that C. spinosissimum is really preferred for oviposition and it is concluded that this preference is likely to be maintained, at least partly, by a higher egg survival on C. spinosissimum due to enemy‐free space provided by this host plant.
The energetics of Gentoo Penguins, Pygoscelis papua, during the breeding season
Authors: Bevan R. M. , Butler P. J. , Woakes A. J. , Boyd I. L.
Published: March 2003

The food consumption of an animal, both at the individual and the population level, is an essential component for assessing the impact of that animal on its ecosystem. As such, measurements of the energy requirements of marine top‐predators are extremely valuable as they can be used to estimate these food requirements.

The present study used heart rate to estimate the rate of energy expenditure of gentoo penguins during the breeding season. The average daily metabolic rate (ADMR) of penguins when one adult was necessarily present at the nest (incubating eggs or guarding small chicks; IG; 4·76 W kg−1) was significantly lower than that when both parents forage concurrently during the major period of chick growth (CR; 6·88 W kg−1).

The ADMR of a bird was found to be dependent on a number of factors, including the day within the breeding season and the percentage time that the bird spent foraging during that day.

When they were ashore, the estimated metabolic rate of IG birds (3·94 W kg−1) was significantly lower than that of CR birds (5·93 W kg−1). However, the estimated metabolic rates when the birds were at sea during these periods were essentially the same (8·58 W kg−1).

The heart rate recorded when the penguins were submerged (128 beats min−1) was significantly higher than that recorded from resting animals when ashore (89 beats min−1). However, it was lower than that recorded from birds that were swimming in a water channel (177 beats min−1). This might indicate that, although primarily aerobic in nature, there was an anaerobic component to metabolism during diving. An alternative interpretation is that the metabolic requirement during diving was lower than when the birds were swimming with access to air.

There was a significant decline in abdominal temperature, from 38·8 °C at the start of a diving bout to 36·2 °C at the end, which may indicate a reduction in overall metabolic rate during submersion. This in turn may explain the lowered heart rate.

In the present study, we have shown that the metabolic rate of the gentoo penguin varies during the breeding season. The relatively constant metabolic rate of the birds when at sea could represent an upper physiological limit that the birds are unable to exceed. If so, it will only be possible for the birds to increase foraging effort by diving more frequently and/or for longer periods thus reducing their foraging efficiency (the energy gained during foraging vs. energy spent gaining that food). During years when food is scarce, this reduction in foraging efficiency may have a profound influence on the reproductive productivity of the gentoo penguin.
Ecological correlates of endozoochory by herbivores
Authors: Pakeman R. J. , Digneffe G. , Small J. L.
Published: March 2003

1. Many plant species germinate from herbivore dung. However, there has been little assessment of how widespread this dispersal mechanism is.

2. A survey of the germinable seed in rabbit and sheep dung from 10 sites in the UK was used to identify the characteristics of species dispersed internally by animals.

3. A wide range of species germinated; the commonest species being ‘weeds’ of grazed communities.

4. Species that did germinate were characterized by small seed size and the capability of forming a persistent seedbank.

5. A substantial quantity and range of seeds are dispersed by herbivores in grazed ecosystems, and this could have a significant effect on the dynamics and species richness of these systems.
Does pregnancy affect swimming performance of female Mosquitofish, Gambusia affinis?
Authors: Plaut I.
Published: March 2003

1. The cost of reproduction due to limiting of the reproductive female’s locomotion capability has been suggested many times, but has rarely been directly examined, especially in fishes. Here, the effect of pregnancy on swimming performance in the viviparous Mosquitofish, Gambusia affinis, was studied.

2. Eight females of G. affinis were isolated, each in a separate aquarium, and critical swimming speed (Ucrit), body mass (BM) and cross‐section area were measured every 5 days from the beginning of the pregnancy until 2–4 days after parturition.

3. Swimming kinematics (tail beat frequency and amplitude) was measured in non‐pregnant and pregnant females at different swimming speeds.

4. BM increased during pregnancy from 0·47 ± 0·13 g to 0·72 ± 0·19 g, and the cross‐section area also increased during pregnancy from 0·21 ± 0·06 cm2 to 0·32 ± 0·07 cm2. Ucrit decreased from 25·0 ± 1·3 cm s−1 before pregnancy to 20·1 ± 1·5 cm s−1 just before parturition, and returned to 24·7 ± 1·4 cm s−1 2–4 days after parturition. Interindividual variation was repeatable and reflects real differences among individuals.

5. Swimming kinematics was not affected by pregnancy.

6. The results suggest that reductions in Ucrit are probably because of aerobic constraints and not necessarily due to hydrodynamic changes resulting from changing in body form or plasticity. Moreover, the reduction in Ucrit is, potentially, a ‘cost of reproduction’ owing to decrease in the ability to gain food during pregnancy in G. affinis females.
Patterns of yolk enrichment with dietary carotenoids in gulls: the roles of pigment acquisition and utilization
Authors: Blount J. D. , Surai P. F. , Houston D. C. , Møller A. P.
Published: March 2003

1. Carotenoid pigments are deposited into egg yolk by female birds, but little is known of the ecological regulation of this process. In particular, the relative importance of pigment acquisition and utilization (i.e. physiological discrimination: differential uptake, transport, deposition or metabolic conversions) is poorly understood.

2. Carotenoids are antioxidants, capable of neutralizing reactive free radicals and thus preventing lipid peroxidation. But animals must ultimately obtain carotenoids in the diet, and metabolic conversion of carotenoids is inefficient and expends energy. It has therefore been suggested that carotenoid supply may be limiting to animals.

3. Prelaying, wild Lesser Black‐Backed Gulls (Larus fuscus L.) were given supplementary feed with a cocktail of four carotenoids, or a carotenoid‐free (control) supplement. The yolk carotenoid profile and susceptibility to lipid peroxidation were then compared in eggs that they laid.

4. In comparison with controls, there was an increase in the yolk concentrations of seven carotenoids, and also unidentified carotenoids in eggs produced by carotenoid‐supplemented females. However, the relative proportions of five classes of carotenoid did not differ significantly, and consequently the percentage profile of yolk carotenoids was positively correlated, between feeding treatments, possibly indicating metabolic transformations and differential transfer of carotenoids from maternal diet to yolk.

5. Moreover, in control eggs relatively few possible correlations between carotenoid concentrations were significantly positive, and some correlations between carotenoid proportions were significantly negative, suggesting physiological discrimination.

6. Egg yolk produced by carotenoid‐supplemented females was significantly less susceptible to lipid peroxidation in comparison with controls.

7. These results suggest that yolk enrichment with carotenoids involves physiological discrimination in gulls, highlighting a previously unstudied, potential cost of reproduction.
The effect of total immunoglobulin levels, mass and condition on the first‐year survival of Grey Seal pups
Authors: Hall A. J. , McConnell B. J. , Barker R. J.
Published: March 2003

1. A joint live‐recapture/live‐resighting/dead‐recovery mark–recapture model was used to investigate the effect of serum gammaglobulin (IgG) levels, sex, mass and condition (mass/length as a surrogate for total body fat) at weaning on the probability of survival from weaning to age 1, in Grey Seal (Halichoerus grypus Fabricius 1791) pups born at two different breeding colonies (Isle of May and Farne Islands) in two different years (1997 and 1998).

2. It was found that increased mass or condition at weaning had a positive effect on the first year survival of Grey Seal pups born at both colonies. Males had a lower probability of survival than females.

3. Higher postweaning circulating IgG concentrations also decreased the probability of survival. It is not known if those pups with high IgG were individuals with naturally higher circulating concentrations or because titres were elevated due to antigenic challenge.
Does flight morphology relate to flight performance? An experimental test with the butterflyPararge aegeria
Authors: Berwaerts K. , Van Dyck H. , Aerts P.
Published: March 2003

1. The relationship between maximal acceleration capacity and flight morphology was tested experimentally in the butterflyPararge aegeria. Such relations are often assumed but seldom tested.

2. In both sexes acceleration capacity was positively correlated with total body mass, thorax mass, forewing area, forewing length, wing loading, aspect ratio and centre of forewing area (centroid). Relationships with total body mass, forewing area, forewing length and wing loading were stronger in males. This can be explained by different mass allocation: males allocate proportionally more mass to the thorax, females more to the abdomen.

3. Evidence for the combined effect of morphological traits on acceleration capacity was found by multivariate analysis. In males and females, a more distant relative centroid and higher relative thorax mass were related to a higher flight capacity. In addition, aspect ratio was positively related to acceleration capacity in males only.

4. Our results support the assumed mechanism behind the relationship between flight morphology and mate‐locating behaviour.
Feeding methods, visual fields and vigilance in dabbling ducks (Anatidae)
Authors: Guillemain M. , Martin G. R. , Fritz H.
Published: March 2003

1. Visual fields were determined in two species of dabbling ducks (Anatini): Shoveler Anas clypeata L. (planktivore whose foraging is guided mainly by tactile cues) and Wigeon A. penelope L. (herbivore whose foraging is guided mainly by visual cues).

2. The binocular fields of Shoveler and Wigeon are of similar maximum width (20°), but they differ in their position and vertical extent. The bill of the Shoveler lies in the very periphery of its frontal binocular field, which extends through 220° thus providing comprehensive visual coverage about the head. In Wigeon the bill is positioned more centrally in the frontal binocular field, which extends through 150° and results in the birds having a narrow blind area behind the head.

3. The vigilance behaviour of Shoveler and Wigeon when foraging simultaneously was studied using a focal observation procedure at sites where the two species winter in sympatry. Focal Wigeon almost only fed by grazing. Only Shoveler feeding by dabbling (filtering the first centimetres of water) were used in the analyses. Wigeon spent significantly more time in head‐up vigilance than Shoveler (F1,75 = 14·70, P = 0·0003).

4. It is proposed that this interspecific difference in the proportion of time spent in vigilance behaviour may be an adaptive response to differences in the visual field topography of these species, particularly with respect to the presence/absence of a blind area to the rear of the head.

5. The ability of foragers to combine part of their vigilance behaviour with head‐down feeding has recently been recognized as influencing the trade‐offs related to vigilance while foraging. This study shows that this ability may vary significantly between species, even within the same genus, and that these variations are likely to be due to contrasted visual fields, themselves related to the type of feeding techniques employed by the different duck species.
Comparative elemental stoichiometry of ecologically diverseDrosophila
Authors: Jaenike J. , Markow T. A.
Published: March 2003

Chemical analyses of ecologically diverse species ofDrosophilareveal substantial variation among them in their nitrogen and phosphorus contents, determined as a percentage of adult dry mass. AcrossDrosophilaspecies, the nitrogen content of flies is positively correlated with phosphorus content.

For both N and P, the concentration in the flies is correlated with that of their breeding sites. The variation in the elemental composition of breeding sites, and therefore of the flies themselves, may affect the ecology and life‐history variation ofDrosophila.

The range of variation in N and P contents and the N : P ratio is considerably less amongDrosophilathan among their breeding sites, indicating that there is substantial constancy for elemental composition acrossDrosophilaspecies. The N : P ratio varies somewhat among species, indicating that the nitrogen and phosphorus contents do not change in perfect proportion across species.

An important, but unanswered, question concerns the relation between intraspecific homeostasis and interspecific constancy for elemental composition. Three possible mechanisms by which such interspecific constancy is brought about are discussed.
Cold acclimation enhances cutaneous resistance to inoculative freezing in hatchling painted turtles, Chrysemys picta
Authors: Packard G. C. , Packard M. J.
Published: March 2003

Neonatal Painted Turtles, Chrysemys picta (Schneider 1783), typically spend the first winter of their life inside the shallow, subterranean nest where they completed incubation the preceding summer. This behaviour commonly causes hatchlings in northerly populations to be exposed in mid‐winter to life‐threatening conditions of ice and cold. Neonates apparently withstand such exposure by remaining unfrozen and becoming supercooled.

Recently hatched turtles are unable to resist freezing by inoculation (i.e. freezing that is induced by the penetration of ice crystals through the integument and into body compartments from frozen soil). Consequently, newly hatched animals that make contact with ice are highly susceptible to freezing when temperature goes below the equilibrium freezing point for their body fluids (c. −0·7 °C). Freezing is fatal, even when temperature does not go below −2 °C, so newly hatched turtles have only a very limited tolerance for exposure to ice and cold.

Acclimation (or acclimatization) by neonatal turtles to low temperatures in the interval between hatching and the start of winter elicits an increase in effectiveness of the cutaneous barrier to the penetration of ice into body compartments from the environment. Acclimated hatchlings coming into contact with ice in frozen soil usually remain unfrozen and supercooled, and survival by supercooled turtles is uniformly high. This thermally induced enhancement of the cutaneous barrier to inoculation is key to an overwintering strategy based on supercooling.
Are bacteria more like plants or animals? Growth rate and resource dependence of bacterial C : N : P stoichiometry
Authors: Makino W. , Cotner J. B. , Sterner R. W. , Elser J. J.
Published: March 2003

We examined the relative importance of resource composition (carbon : phosphorus molar ratios which varied between 9 and 933) and growth rate (0·5–1·5 h−1) to biomass carbon : nitrogen : phosphorus stoichiometry and nucleic acid content in Escherichia coli grown in chemostats, and in other heterotrophic prokaryotes using published literature.

Escherichia coli RNA content and the contribution of RNA‐P to total cellular P increased with increasing growth rate at all supply C : P ratios. Growth rate had a much stronger effect on biomass C : P than did supply C : P, and increased RNA content resulted in low biomass C : P and N : P ratios.

However, we observed only twofold variations in biomass C : P and N : P ratios in the experiments, despite a difference of two orders of magnitude in C : P and N : P supply. The response of biomass C : P and N : P ratios to alteration of the supply C : P and N : P ratios revealed that E. coli was strongly homeostatic in its elemental composition.

This result, and a literature survey, suggest that each heterotrophic bacterial strain regulates its elemental composition homeostatically within a relatively narrow range of characteristic biomass C : P and N : P ratios.

Thus shifts in the dominance of different bacterial strains in the environment are probably responsible for the large variation in bacterial biomass C : P, as has been suggested for crustacean zooplankton. These findings indicate that bacteria are more like animals than plants in terms of biomass C : P and N : P homeostasis.
Growth phase coupled modulation of Escherichia coli ribosomes
Authors: Wada Akira
Published: March 2003

Ribosomal modulation factor (RMF), a small basic protein, expresses transcriptionally in the stationary phase of Escherichia coli cells and binds to 50S ribosomal subunits. The RMF bound 70S ribosomes dimerize to form 100S particles that have no translational activity. In transferring the stationary cells to a fresh medium, the 100S particles release the RMF and dissociate to active 70S. The interconversion of ribosomes between active 70S and inactive 100S by RMF is a cellular mechanism controlling translation.
A new sigma factor, SigD, essential for stationary phase is also required for multicellular differentiation in Myxococcus xanthus
Authors: Ueki Toshiyuki , Inouye Sumiko
Published: March 2003

Background:

Myxococcus xanthus is a gram‐negative bacterium that undergoes spectacular development to form multicellular fruiting bodies under nutrient deprivation. Inside a fruiting body, vegetative cells differentiate into spores. A number of sigma factors have been shown to play roles in the regulation of gene expression in the M. xanthus life cycle. Additional sigma factors were searched to further explore the M. xanthus life cycle.

Results:

A new sigma factor was identified, SigD, which consists of 297 amino acid residues. Two transcription initiation sites for the sigD gene were detected by primer extension analysis using total RNA from the vegetative and developmental cells, one of which was specific for development. The characterization of sigD‐lacZ fusion strains demonstrated that sigD expression increased during entry into stationary phase of vegetative growth and during early development. A deletion mutant of sigD exhibited growth defects during the late‐log phase and stationary phase, with dramatically reduced cell viability. The patterns of protein synthesis at late log phase of vegetative growth and at early development on CF agar plates were significantly different between the deletion mutant and the wild‐type strain. The deletion mutant was more sensitive to various stresses when compared with the wild‐type strain and did not accumulate trehalose in response to osmotic stress. The deletion mutant also showed a significant delay in fruiting body formation and sporulation and yielded fewer spores than the wild‐type strain.

Conclusions:

SigD shows characteristic features of the stationary phase sigma factors and also plays important roles in multicellular differentiation of M. xanthus.
In vitro assembly of the CENP‐B/α‐satellite DNA/core histone complex: CENP‐B causes nucleosome positioning
Authors: Yoda Kinya , Ando Satoshi , Okuda Asuko , Kikuchi Akihiko , Okazaki Tuneko
Published: March 2003

Background

We have studied the nucleosome structure formed from α‐satellite DNA bound with CENP‐B and core histones, in order to develop a previous proposal that the CENP‐B dimer may play a critical role in the assembly of higher order structures of the human centromere by juxtaposing CENP‐B boxes in long α‐satellite arrays.

Results

The dimeric structure of CENP‐B was sufficiently stable to bundle together two 3.5 kbp DNA fragments when each DNA contained a CENP‐B box. When the same length of DNA included two CENP‐B boxes, the intra–molecular interaction with the CENP‐B dimer predominated, resulting in the formation of loop structures. The in vitro assembly of CENP‐B/α‐satellite DNA/core histone complexes with the aid of nucleosome assembly protein‐1 (NAP‐1) permitted an investigation into the nucleosome arrangement in α‐satellite DNA with CENP‐B bound to CENP‐B boxes. Footprint analyses with micrococcal nuclease (MNase) revealed that CENP‐B causes nucleosome positioning between pairs of CENP‐B boxes with unique hypersensitive sites created on both sides.

Conclusion

We propose that CENP‐B functions as a structural factor in the centromere region in order to establish a unique, centromere specific pattern of nucleosome positioning.
Overcoming barriers in the study of tight junction functions: from occludin to claudin
Authors: Tsukita Shoichiro , Furuse Mikio
Published: March 2003

Tight junctions (TJs) are essential structures for the physiological functions of epithelial and endothelial cells, and have been suggested to have both barrier and fence functions. Tight junctions create a primary barrier to the diffusion of solutes through the paracellular pathway, and also function as a fence between apical and basolateral membrane domains, to create and maintain cell polarity of epithelial and endothelial cells. Several peripheral membrane proteins have been shown to be concentrated at the cytoplasmic surface of TJs. However, TJ‐specific integral membrane proteins had not been identified until recently, and the lack of information concerning TJ‐specific integral membrane proteins has hampered a more direct assessment of the function of TJs at the molecular level. Here, we present an overview of current progress in the identification of TJ‐specific integral membrane proteins.
Mutational analysis on structure–function relationship of a Holliday junction specific endonuclease RuvC
Authors: Ichiyanagi Kenji , Iwasaki Hiroshi , Hishida Takashi , Shinagawa Hideo
Published: March 2003

Background

Escherichia coli RuvC protein is a specific endonuclease that resolves Holliday junctions during homologous recombination. For junction resolution, RuvC undergoes distinct steps such as dimerization, junction‐specific binding and endonucleolytic cleavage. The crystal structure of RuvC has been revealed.

Results

To identify functionally important residues, we isolated a large number of mutant ruvC genes created by random mutagenesis and characterized their properties in vivo and in vitro. The mutations which were isolated most frequently were mapped to the four acidic residues constituting the catalytic centre. Amongst the several mutant proteins affected in the dimer interface, only one could not form a dimer. The others were able to form a dimer but were defective in cleavage. F69L and K118R mutant proteins could not cleave the junction, but they were able to form a dimer and bind the junction DNA.

Conclusions

Random mutagenesis highlighted many structurally and functionally important residues of RuvC, most of which are highly conserved among RuvC homologues. Dimer formation and also conservation of intact interface interactions between the subunits are important for junction binding and subsequent cleavage. Phe‐69 and Lys‐118 are critically important for the interactions which lead to junction cleavage.
Spatio‐temporally regulated expression of receptor tyrosine kinases, mRor1, mRor2, during mouse development: implications in development and function of the nervous system
Authors: Oishi Isao , Takeuchi Shigeto , Hashimoto Ryuju , Nagabukuro Akira , Ueda Takahiro , Liu Zhao‐Jun , Hatta Toshihisa , Akira Shizuo , Matsuda Yoichi , Yamamura Hirohei , Otani Hiroki , Minami Yasuhiro
Published: March 2003

Backgrounds

Drosophila neurospecific receptor tyrosine kinases (RTKs), Dror and Dnrk, as well as Ror1 and Ror2 RTKs, isolated from human neuroblastoma, have been identified as a structurally related novel family of RTKs (Ror‐family RTKs). Thus far, little is known about the expression and function of mammalian Ror‐family RTKs.

Results

We have identified murine Ror‐family RTKs, mRor1 and mRor2. Both mRor1 and mRor2 genes are induced upon neuronal differentiation of P19EC cells. During neuronal differentiation in vitro, the expression of mRor2 is transiently induced, although that of mRor1 increases continuously. During embryogenesis, the mRor1 gene is expressed in the developing nervous system within restricted regions and in the developing lens epithelium. The expression of mRor1 is sustained in the nervous system and is also detected in non‐neuronal tissues after birth. In contrast, the expression of mRor2 is detected mainly in the developing nervous system within broader regions and declines after birth. Possible relationships of mRor1 and mRor2 genes with previously identified mutants have also been examined.

Conclusions

The developmental expressions of mRor1 and mRor2, in particular in the nervous system, are differentially regulated, reflecting their expression patterns in vitro. mRor1 and mRor2 may thus play differential roles during the development of the nervous system.
A mammalian ortholog of Drosophila timeless, highly expressed in SCN and retina, forms a complex with mPER1
Authors: Takumi Toru , Nagamine Yasuko , Miyake Shigeru , Matsubara Chiaki , Taguchi Kouji , Takekida Seiichi , Sakakida Yoko , Nishikawa Kazuko , Kishimoto Toshihiko , Niwa Shin‐ichiro , Okumura Ko , Okamura Hitoshi
Published: March 2003

Background:

It is now becoming clear that the circadian rhythm of behaviours and hormones arises from a rhythm at the level of gene expression, and that mammals and Drosophila essentially use homologous genes as molecular gears in the control of circadian oscillation. In Drosophila, the period and timeless genes form a functional unit of the clock and its autoregulatory feedback loop for circadian rhythm. However, in mammals, the counterpart of timeless has not been found.

Results:

We have isolated a mammalian homologue of timeless, mTim, from the mouse brain. mTim is highly expressed, with a weak or absent rhythm in the suprachiasmatic nucleus, the mammalian circadian centre. In the retina, mTim mRNA was found to be expressed with a circadian rhythm, and a particularly robust cycle was observed in the presence of light/dark cycles. We demonstrated that mTIM physically associates with mPER1 in vitro and in the nuclei of cultured COS7 cells.

Conclusions:

We have reported the isolation of the mouse timeless cDNA, the expression of the mTim mRNA and an interaction of mTIM with mPER1. These results indicate that the autoregulatory feedback mechanism of circadian oscillation of the period gene may also be conserved in mammals.
Nps1/Sth1p, a component of an essential chromatin‐remodeling complex of Saccharomyces cerevisiae, is required for the maximal expression of early meiotic genes
Authors: Yukawa Masashi , Katoh Soko , Miyakawa Tokichi , Tsuchiya Eiko
Published: March 2003

Background

The NPS1/STH1 gene of Saccharomyces cerevisiae is essential for mitotic growth, especially for the progression through the G2/M phase. It encodes a major component of the chromatin‐remodelling complex, RSC, of unknown function. We attempted to address the function of NPS1 in meiosis.

Results

The homozygote of the temperature sensitive nps1 mutant, nps1‐105, showed reduced and delayed levels of sporulation, accompanied with a notable decrease and delay of the expression of several early meiotic genes (IME2, SPO11 and SPO13). Deletion analysis of the IME2 promoter revealed that the defect in the gene expression occurred through the URS1 site. The sporulation defect of nps1‐105 was alleviated by the over‐expression of either IME1 or IME2. However, over‐expression of IME1 did not permit the full expression of IME2, SPO11 and SPO13 in nps1‐105. In addition, the expression of NPS1 itself increased transiently upon initiation of meiosis, before the appearance of the IME2 message but after that of IME1. The impaired increase in NPS1 transcription led to inefficient sporulation.

Conclusion

The results suggest that Nps1p/RSC is required for the activation of gene expression at the initiation of meiosis.
Cytokine‐inducible SH2 protein‐3 (CIS3/SOCS3) inhibits Janus tyrosine kinase by binding through the N‐terminal kinase inhibitory region as well as SH2 domain
Authors: Sasaki Atsuo , Yasukawa Hideo , Suzuki Asuka , Kamizono Shintaro , Syoda Takanori , Kinjyo Ichiko , Sasaki Mika , Johnston James A. , Yoshimura Akihiko
Published: March 2003

Background

The Janus family of protein tyrosine kinases (JAKs) regulate cellular processes involved in cell growth, differentiation and transformation through their association with cytokine receptors. We have recently identified the JAK‐binding protein, JAB that inhibits various cytokine‐dependent JAK signalling pathways. JAB inhibits JAK2 tyrosine kinase activity by binding to the kinase domain (JH1 domain) through the N‐terminal kinase inhibitory region (KIR) and the SH2 domain. The SH2 domain of JAB has been shown to bind to the phosphorylated Y1007 in the activation loop of JH1. We also identified another JAK‐binding protein, CIS3 (cytokine‐inducible SH2‐protein 3, or SOCS3) that inhibits signalling of various cytokines. However, the mechanism of JAK signal inhibition by CIS3 has not been clarified.

Results

We showed that endogenous CIS3 bound to JAK2 in intact cells. The CIS3‐SH2 domain bound to the phosphorylated Y1007 of JH1, and inhibited tyrosine kinase activity through the N‐terminal KIR. Therefore, CIS3 and JAB inhibit JAK2 tyrosine kinase activity by an essentially similar mechanism. However, we found that the affinity of the SH2 domain of CIS3 to Y1007 was weaker than that of JAB. In contrast, the KIR of CIS3 showed stronger potential for both binding to JH1 and inhibition of JAK kinase activity than that of JAB. Consistent with this notion, chimeras containing CIS3‐KIR and JAB‐SH2 domain inhibited JAK2 kinase activity more efficiently than the wild‐type CIS3 or JAB.

Conclusion

CIS3 inhibits JAK2 kinase activity by binding to the activation loop through the SH2 domain, and KIR is necessary for kinase inhibition. Although the inhibitory mechanism by CIS3 is similar to that by JAB, the contributions of the SH2 domain and KIR for binding are different between JAB and CIS3. Our study defined the inhibitory mechanism of CIS3 and provides a useful information for creating a novel tyrosine kinase inhibitor.
Changes in nuclear morphology during apoptosis correlate with vimentin cleavage by different caspases located either upstream or downstream of Bcl‐2 action
Authors: Morishima Nobuhiro
Published: March 2003

Background

Upon Fas stimulation, procaspase‐8 is recruited to the death‐inducing signalling complex where autoactivation of caspase‐8 occurs. Active caspase‐8 can directly activate downstream caspases (e.g. caspase‐3, 6, and 7) for the execution of apoptosis (mitochondria‐independent pathway), while caspase‐8 can also lead to executioner caspase activation through mitochondrial damage (mitochondria‐dependent pathway). Caspase activation results in the dismantling of intracellular structure through specific proteolysis.

Results

We have found that an intermediate filament protein, vimentin, is cleaved at multiple sites by caspases at an early stage of apoptosis in Jurkat cells. The sequences of the two major cleavage sites in vimentin (IDVD/V and DSVD/F) suggested that these sites are cleaved by caspase‐8 and caspase‐3, respectively, or by close homologues of these proteases. The IDVD/V site can be cleaved by caspase‐8 in vitro, and its cleavage is less sensitive to DEVD‐CHO and Bcl‐2 over‐expression than that of the DSVD/F site in Jurkat cells. Over‐expression of a mutant vimentin which was insensitive to caspase cleavage at these sites delayed the appearance of apoptotic nuclei in Jurkat cells.

Conclusion

The specific cleavage of vimentin can be used as an apoptotic marker of both apical‐ and mitochondria‐dependent caspase activation. Apoptotic cleavage of vimentin most likely results in disruption of its filamentous structure, which may facilitate nuclear condensation and subsequent fragmentation through disruption of the cytoskeletal network.
The deubiquitinating enzyme Fam interacts with and stabilizes β‐catenin
Authors: Taya Shinichiro , Yamamoto Takaharu , Kanai‐Azuma Masami , Wood Stephen A. , Kaibuchi Kozo
Published: March 2003

Background

In the ubiquitin–proteasome pathway, the ubiquitinated substrates either undergo degradation by the proteasome or stabilization through the action of the deubiquitinating enzyme. We have previously found that the deubiquitinating enzyme Fam is colocalized with AF‐6, one of the effectors of the Ras small GTPase, at cell–cell contact sites in epithelial cells and interacts with AF‐6 in vivo and in vitro. Fam has deubiquitinating activity in vitro and prevents the ubiquitination of AF‐6 in intact cells. The degradation of β‐catenin, which accumulates at the cell–cell contact sites as a cadherin/catenin complex, is thought to be regulated by the ubiquitin–proteasome pathway. These observations prompted us to examine the possible Fam regulation of the stabilization of β‐catenin.

Results

We found that Fam interacted with β‐catenin both in vivo and in vitro. The Fam‐binding site of β‐catenin mapped to the region close to the APC or Axin‐binding site of β‐catenin. Over‐expression of Fam in mouse L cells resulted in an elevation of β‐catenin levels and in an elongation of the half‐life of β‐catenin. In these L cells, Fam was colocalized with β‐catenin at the dot‐like structures in the cytoplasm.

Conclusion

These results indicate that Fam interacts with and stabilizes β‐catenin in vivo, presumably through the deubiquitination of β‐catenin.
Mouse Ror2 receptor tyrosine kinase is required for the heart development and limb formation
Authors: Takeuchi Shigeto , Takeda Kiyoshi , Oishi Isao , Nomi Masashi , Ikeya Makoto , Itoh Kyoko , Tamura Shingo , Ueda Takahiro , Hatta Toshihisa , Otani Hiroki , Terashima Toshio , Takada Shinji , Yamamura Hirohei , Akira Shizuo , Minami Yasuhiro
Published: March 2003

Backgrounds

A mouse receptor tyrosine kinase (RTK), mRor2, which belongs to the Ror‐family of RTKs consisting of at least two structurally related members, is primarily expressed in the heart and nervous system during mouse development. To elucidate the function of mRor2, we generated mice with a mutated mRor2 locus.

Results

Mice with a homozygous mutation in mRor2 died just after birth, exhibiting dwarfism, severe cyanosis, and short limbs and tails. Whole‐mount in situ hybridization analysis showed that mRor2 was expressed in the branchial arches, heart and limb/tailbuds, in addition to the developing nervous system. The mutants had cardiac septal defects, mainly a ventricular septal defect. In addition, an examination of the skeletal systems revealed that the mutants had shorter limbs, vertebrae and facial structure, with a particular defect in their distal portions, and that almost no calcification was observed in their distal limbs. Histological examination showed abnormalities in the chondrocytes.

Conclusions

Our findings suggest that mRor2 plays essential roles in the development of the heart and in limb/tail formation, in particular cardiac septal formation and ossification of distal portions of limbs and tails.