PARP‐mediated proteasome activation: A co‐ordination of DNA repair and protein degradation?

During the evolution of aerobic life, antioxidant defence systems developed that either directly prevent oxidative modifications of the cellular constituents or remove the modified components. An example of the latter is the proteasome, which removes cytosolic oxidised proteins. Recently, a novel mechanism of activation of the nuclear 20S proteasome was discovered: automodified poly-(ADP-ribose) polymerase-1 (PARP-1) activates the proteasome to facilitate selective degradation of oxidatively damaged histones. Since activation of the PARP-1 itself is induced by DNA damage and is supposed to play a role in DNA repair, these new results suggest a joint role of PARP-1 in the removal of oxidised nucleoproteins and in DNA repair. We hypothesise that PARP-1 could provide a co-ordinative link between two nuclear antioxidant defence systems, whose concerted activation would produce a fast and efficient restoration of the native chromatin structure following oxidative stress.     

What is the mechanism of ParA‐mediated DNA movement?

The stable maintenance of low‐copy‐number plasmids requires active partitioning, with the most common mechanism in prokaryotes involving the ATPase ParA. ParA proteins undergo intricate spatiotemporal relocations across the nucleoid, dynamics that function to position plasmids at equally spaced intervals. This spacing naturally guarantees equal partitioning of plasmids to each daughter cell. However, the fundamental mechanism linking ParA dynamics with regular plasmid positioning has proved difficult to dissect. In this issue of Molecular Microbiology, Vecchiarelli et al. report on a time‐delay mechanism that allows a slow cycling between the nucleoid‐bound and unbound forms of ParA. The authors also propose a mechanism for plasmid movement that does not rely on ParA polymerization.     

Accumbens Homer2‐mediated signaling: a factor contributing to mouse strain differences in alcohol drinking?

Alcohol‐induced increases in nucleus accumbens glutamate actively regulate alcohol consumption, and the alcohol responsiveness of corticoaccumbens glutamate systems relates to genetic variance in alcohol reward. Here, we extend earlier data for inbred mouse strain differences in accumbens glutamate by examining for differences in basal and alcohol‐induced changes in the striatal expression of glutamate‐related signaling molecules between inbred C57BL/6J and DBA2/J mice. Repeated alcohol treatment (8 × 2 g/kg) increased the expression of Group1 metabotropic glutamate receptors, the NR2a/b subunits of the N‐methyl‐d ‐aspartate receptor, Homer2a/b, as well as the activated forms of protein kinase C (PKC) epsilon and phosphoinositol‐3‐kinase within ventral, but not dorsal, striatum. Regardless of prior alcohol experience, C57BL/6J mice exhibited higher accumbens levels of mGluR1/5, Homer2a/b, NR2a and activated kinases vs. DBA2/J mice, whereas an alcohol‐induced rise in dorsal striatum mGluR1/5 expression was observed only in C57BL/6J mice. We next employed virus‐mediated gene transfer approaches to ascertain the functional relevance of the observed strain difference in accumbens Homer2 expression for B6/D2 differences in alcohol‐induced glutamate sensitization, as well as alcohol preference/intake. Manipulating nucleus accumbens shell Homer2b expression actively regulated these measures in C57BL/6J mice, whereas DBA2/J mice were relatively insensitive to the neurochemical and behavioral effects of virus‐mediated changes in Homer2 expression. These data support the over‐arching hypothesis that augmented accumbens Homer2‐mediated glutamate signaling may be an endophenotype related to genetic variance in alcohol consumption. If relevant to humans, such data pose polymorphisms affecting glutamate receptor/Homer2 signaling in the etiology of alcoholism.     

Lipopolysaccharide‐induced increase in signalling in hippocampus is abrogated by IL‐10 – a role for IL‐1β?

Parenterally administered lipopolysaccharide (LPS) increases the concentration of the pro-inflammatory cytokine interleukin-1beta (IL-1beta) in the rat hippocampus and evidence suggests that this effect plays a significant role in inhibiting long-term potentiation (LTP). The anti-inflammatory cytokine IL-10, antagonizes certain effects of IL-1beta, so if the effects of LPS are mediated through an increase in IL-1beta, it might be predicted that IL-10 would also abrogate the effect of LPS. Here, we report that IL-10 reversed the inhibitory effect of LPS on LTP and the data couple this with an inhibitory effect on the LPS-induced increase in IL-1beta. LPS treatment increased hippocampal expression of IL-1 receptor Type I protein. Consistent with the LPS-induced increases in IL-1beta concentration and receptor expression, were downstream changes which included enhanced phosphorylation of IRAK and the stress-activated kinases, JNK and p38; these LPS-induced changes were reversed by IL-10, which concurs with the idea that these events are triggered by increased activation of IL-1RI by IL-1beta. We provide evidence which indicates that LPS treatment leads to evidence of cell death and this was reversed in hippocampus prepared from LPS-treated rats which received IL-10. The evidence is therefore consistent with the idea that IL-10 acts to protect neuronal tissue from the detrimental effects induced by LPS.     

Song and Sperm in Crickets: A Trade‐off between Pre‐ and Post‐copulatory Traits or Phenotype‐Linked Fertility?

When females mate multiply (polyandry) both pre‐ and post‐copulatory sexual selection can occur. Sperm competition theory predicts there should be a trade‐off between investment in attracting mates and investment in ejaculate quality. In contrast, the phenotype‐linked fertility hypothesis predicts a positive relationship should exist between investment in attracting mates and investment in ejaculate quality. Given the need to understand how pre‐ and post‐copulatory sexual selection interacts, we investigated the relationship between secondary sexual traits and ejaculate quality using the European house cricket, Acheta domesticus. Although we found no direct relationship between cricket secondary sexual signals and ejaculate quality, variation in ejaculate quality was dependent on male body weight and mating latency: the lightest males produced twice as many sperm as the heaviest males but took longer to mate with females. Our findings are consistent with current theoretical models of sperm competition. Given light males may have lower mating success than heavy males because females take longer to mate with them in no‐choice tests, light males may be exhibiting an alternative reproductive tactic by providing females with more living sperm. Together, our findings suggest that the fitness of heavy males may depend on pre‐copulatory sexual selection, while the fitness of light males may depend on post‐copulatory fertilization success.     

Where's my dinner? Adult neurogenesis in free‐living food‐storing rodents

Postnatal hippocampal neurogenesis in wild mammals may play an essential role in spatial memory. We compared two species that differ in their reliance on memory to locate stored food. Yellow-pine chipmunks use a single cache to store winter food; eastern gray squirrels use multiple storage sites. Gray squirrels had three times the density of proliferating cells in the dentate gyrus (determined by Ki-67 immunostaining) than that found in chipmunks, but similar density of young neurons (determined by doublecortin immunostaining). Three explanations may account for these results. First, the larger population of young cells in squirrels may increase the flexibility of the spatial memory system by providing a larger pool of cells from which new neurons can be recruited. Second, squirrels may have a more rapid cell turnover rate. Third, many young cells in the squirrels may mature into glia rather than neurons. The densities of young neurons were higher in juveniles than in adults of both species. The relationship between adult age and cell density was more complex than that has been found in captive populations. In adult squirrels, the density of proliferating cells decreased exponentially with age, whereas in adult chipmunks the density of young neurons decreased exponentially with age.     

Does scale‐dependent feedback explain spatial complexity in salt‐marsh ecosystems?

Complexity theory highlights scale-dependent feedback mechanisms as an explanation for regular spatial patterning in ecosystems. To what extent scale-dependent feedback clarifies spatial structure in more complex, non-regular systems remains unexplored so far. We report on a scale-dependent feedback process generating patchy landscapes at the interface of intertidal flats and salt marshes. Here, vegetation was characterized by Spartina anglica tussocks, surrounded by erosion gullies. To demonstrate the presence of a scale-dependent feedback, we determined if vegetation induced habitat modification resulted in local facilitation and large scale-inhibition of plant growth. Field surveys revealed that larger tussocks have deeper gullies, suggesting that gully erosion is caused by increased water flow around tussocks. This was confirmed by flume experiments, showing that feedback effects vary with current velocity and water depth. Transplantation of small Spartina units inside and just outside present tussocks revealed that the growth of Spartina transplants compared to transplant growth on bare sediment was higher within the raised Spartina tussocks, but lower in the gully just outside Spartina tussocks, providing clear evidence of scale-dependent feedback. Our results emphasize that scale-dependent feedback is a more general explanation for spatial complexity in ecosystems than previously considered.     

Bottom‐up control in the benthos of ocean‐exposed sandy beaches?

Bottom‐up control is a fundamental structuring force in food webs. Food webs of ocean‐exposed sandy beaches are predicted to be bottom‐up controlled systems, underpinned by imported organic matter rather than in situ primary production. This ecological model of resource‐based regulation of biological assemblages is juxtaposed against a prevailing paradigm built around a dominance of physical drivers in sandy beach ecosystems. Surprisingly, given the apparently ubiquitous energetic subsidies of beach food webs, the central premise of bottom‐up control has not been tested. Here we experimentally manipulated in situ nutrient levels on a sandy beach to test food web responses at the levels of primary producers (benthic microalgae) and their grazers (meiofauna). The meiofauna community as a whole appeared most strongly influenced by the local physical environment, particularly changes in sediment grain size – this supports the traditional ‘environmental control paradigm’. We also detected a significant, positive response of two consumer groups of the meiofauna (nematodes, ostracods) to nutrient enrichment that supports a model of biological, bottom‐up control. Although the predicted response of elevated producer biomass following nutrient enrichment was not detected, intense grazing pressure on new, stimulated production may have masked positive responses by the primary producers. Multichannel regulation of food webs is likely for many exposed sandy beaches, albeit an often lower importance of in situ bottom‐up forces compared with stronger environmental control.     

Do weaver ants affect arthropod diversity and the natural‐enemy‐to‐pest ratio in horticultural systems?

High biodiversity is an important component of sustainable agricultural systems, and previous studies have found that increases in the diversity of the natural enemies of pests are associated with decreases in pest populations. Weaver ants are well known for their highly territorial and aggressive behaviour and for their control efficiency of many insect pests in tropical crop trees. Because of this, the ants have been used as a key component in integrated pest management (IPM) programmes for tropical crop trees. In implementing the IPM programmes, we received a number of enquiries related to whether weaver ants have negative effects on arthropod diversity and other natural enemies in orchard systems due to their aggressive behaviour. To answer these questions, we regularly sampled canopy arthropods in cashew and mango orchards in the Northern Territory of Australia in 1996, 2002 and 2003. We sampled, using a vacuum sampler, orchards with and without weaver ants. Cashew and mango plots with abundant weaver ants had similar or higher canopy arthropod and natural enemy diversity and similar ratios of natural enemies to insect pests, compared with plot where the weaver ant was absent. The study also showed that the application of insecticides reduced arthropod diversity and the ratio of natural enemies to insect pests in a mango orchard. However, insecticide spray did not affect natural enemy diversity and abundance, which may be related to a high immigration rate of natural enemies in small plots surrounded by areas that were not sprayed.     

How common is the funnel‐like energy landscape in protein‐protein interactions?

The goal of this study is to verify the concept of the funnel-like intermolecular energy landscape in protein-protein interactions by use of a series of computational experiments. Our preliminary analysis revealed the existence of the funnel in many protein-protein interactions. However, because of the uncertainties in the modeling of these interactions and the ambiguity of the analysis procedures, the detection of the funnels requires detailed quantitative approaches to the energy landscape analysis. A number of such approaches are presented in this study. We show that the funnel detection problem is equivalent to a problem of distinguishing between distributions of low-energy intermolecular matches in the funnel and in the low-frequency landscape fluctuations. If the fluctuations are random, the decision about whether the minimum is the funnel is equivalent to determining whether this minimum is significantly different from a would-be random one. A database of 475 nonredundant cocrystallized protein-protein complexes was used to re-dock the proteins by use of smoothed potentials. To detect the funnel, we developed a set of sophisticated models of random matches. The funnel was considered detected if the binding area was more populated by the low-energy docking predictions than by the matches generated in the random models. The number of funnels detected by use of different random models varied significantly. However, the results confirmed that the funnel may be the general feature in protein-protein association.     

Are nutrient availability and acidity‐alkalinity gradients related in Sphagnum‐dominated peatlands?

Abstract. Gradients in acidity‐alkalinity and nutrient availability were studied in 2 Sphagnum‐dominated peatlands on the southeastern Italian Alps. Decreasing concentrations of most mineral elements (Ca²⁺, Mg²⁺, Mn²⁺, Al³⁺ and Si⁴⁺) in pore water indicated a progressively lower influx of mineral‐soil water from the slightly minerotrophic conditions in the peatland margins to ombrogenous conditions in the central part of the peatlands. This was paralleled by decreasing concentrations of ash, bulk density, Ca, Fe and, partly, Mn in the peat. The nutrient gradient, as defined by pore water concentrations of N and P, was largely independent of the acidity‐ alkalinity gradient: NO^3‐ and PO₄^3‐ had similar concentrations throughout the gradient, whereas NH₄⁺ concentrations increased with increasing pore‐water pH. In contrast, the peat nutrient gradient coincided with the acidity‐alkalinity gradient, with total concentrations of N and P decreasing from the margin to the centre. Bryophytes and vascular plants had different responses along the acidity‐alkalinity gradient and the nutrient gradient. Bryophyte distribution reflected the acidity‐alkalinity gradient both in pore water and in peat. Vascular plant distribution was mainly influenced by variations in nutrient availability.     

α<Subscript>1A</Subscript>- adrenergic receptor mediated pressor response to phenylephrine in anesthetized rat

To determine which subtype of α_1-adrenergic receptors plays a role in the regulation of blood pressure, with α_1--adrenergic receptor-mediated vasoconstriction in perfused hindlimb as a control, we compared the inhibitory effects of various aradrenergic receptor selective antagonists on the vasopressure responses to phenylephrine between the mean arterial pressure and hindlimb perfusion pressure in anesthetized rats. In Normotensive Wistar rats, the results showed that the inhibitory effects (dose ratios of ED₅₀, Dr) of α_-1adrenoceptor selective antagonist (prazosin, Dr 13.5 ± 3.6 vs. 15.1 ± 4.3, n = 11), /ga_1A-adrenoceptor selective antagonist (5-methyl-urapidil, Dr 2.4 ± 0.9 vs. 3.7 ± 2.3, n = 12; RS-17053, Dr 3.2 ± 1.6 vs. 4.4 ± 3.3, n =12) and α_1D- adrenoceptor selective antagonist (BMY7378, Dr 1.9 ±0.9 vs. 2.2 ± 0.8, n = 8) on phenylephrineinduced increases of perfusion pressure in the autoperfused femoral beds were the same as that in the mean arterial blood pressure in normotensive Wistar rats. The inhibitory effects of antagonists (RS-17053, Dr 3.4 ± 0.6 vs. 4.3 ± 0.9, n = 5; BMY7378, Dr 1.7 ± 0.5 vs. 1.7 ± 0.5, n = 8) in spontaneous hypertensive rats were similar with the Wistar rats. These results suggest that the mean arterial pressure induced by phenylephrine was mainly mediated by α_1A-adrenergic receptor in both the anesthetized Wistar rats and spontaneous hypertensive rats.     

Bi‐parental vs. cooperative breeding in a passerine: fitness‐maximizing strategies of males in response to risk of extra‐pair paternity?

In socially monogamous species, males that risk cuckoldry more than others might gain inclusive fitness by yielding paternity to relatives. We tested this prediction in the Tibetan ground tit Pseudopodoces humilis , an unusual facultative cooperative breeder wherein most helpers (87% males) join a mated pair shortly before clutch completion. Extra-pair paternity among bi-parental broods occurred less often (26% of broods, 9% of young) compared with cooperative broods (68%, 25%). In the former, most extra-pair sires (88%) were pair breeders unrelated to the cuckolded males, whereas in the latter, sires (87%) were mainly helpers related to the dominant males. Brood productivity did not differ between the bi-parental and cooperative breeders, but helpers' partitioning over group paternity reduced the realized reproductive success of helped males. After taking inclusive fitness into account, however, there was no difference in success of dominant males between the two social systems. One possible explanation for the differences in the rates of cuckoldry in the two systems was body size, because pair-bond males in bi-parental situations were significantly larger than those in cooperative ones. We propose two alternative strategies for males to maximize fitness: breed as a pair if large to avoid cuckoldry from helpers, or breed cooperatively if small but compromise some paternity to relatives. Our results provide an unusual route to the incidence of cooperative groups, based on constraints imposed by low competitive ability of breeding males rather than some external ecological or demographic factors.     

Mating in the pseudogamic apomictic Anemopaegma acutifolium DC: another case of pseudo‐self‐compatibility in Bignoniaceae?

Self‐compatibility in apomictic pseudogamic species is considered fundamental to assure reproduction by seeds in extreme situations, making apomictic species more advantageous than sexual ones in these scenarios. Anemopaegma acutifolium is a polyploidy, apomictic sporophytic species with no endosperm development in ovules of unpollinated pistils, which indicates obligate pseudogamy. Thus, the aim of the present work is to study the breeding system and post‐pollination events to test if there is similar pseudogamous development irrespective of pollination treatment. We analysed fruit and seed set obtained in controlled experimental pollinations, as well as embryo number per seed, and the progress of ovule penetration, fertilisation and early endosperm development between self‐ and cross‐pollinated pistils. We found that the species is self‐fertile and that spontaneous selfing fruit set is also possible, although emasculated flowers never form fruits. Selfed pistils were as efficient as crossed ones for all parameters analysed, except for a delay in endosperm development observed in the former that may be an effect of the late‐acting self‐incompatibility. Therefore, the avoidance of selfed pistil abortion seems to be promoted by the presence of adventitious embryos and a normal endosperm. We conclude that A. acutifolium shows apomixis‐related pseudo‐self‐compatibility, as in other self‐fertile apomictic species of Bignoniaceae, which confer reproductive assurance and increases fruit‐set and persistence ability in fast‐changing tropical habitats.     

Spontaneous succession in Central‐European man‐made habitats: What information can be used in restoration practice?

Abstract. The results of previous studies concerning spontaneous vegetation succession in various man‐made or disturbed habitats in Central Europe are discussed in relation to restoration ecology. An attempt is made to answer the main questions which are important to restoration programs. These concern the rate and direction of succession; participation of target species and communities, woody species, ruderals and aliens; arresting or diverting succession; changes in species diversity; variability of successional pathways and the role of abiotic environmental conditions. The great potential for using successional theory in restoration programs is emphasized.     

How do slow‐growing,fire‐sensitive conifers survive in flammable eucalypt woodlands?

Question: To what extent do low flammability fuel traits enhance the survival and persistence of fire‐sensitive (slowing‐growing, non‐serotinous, non‐resprouting) dominant trees in highly flammable landscapes, under varying fire‐weather conditions? Location: Mixed forests co‐dominated by flammable Eucalyptus species and fire‐sensitive Callitris glaucophylla in Pilliga State Forest, southeast Australia. Methods: The influence of vegetation composition (relative abundance of Callitris and flammable Eucalyptus) on fire intensity and survival of fire‐sensitive Callitris was assessed across gradients of Callitris abundance in mixed Eucalyptus–Callitris forests that burned under low‐moderate and extreme fire‐weather conditions. Results: In areas that burned under low‐moderate fire‐weather conditions, as Callitris abundance increased, fire intensity declined and Callitris survival increased (46%). By comparison, in extreme fire‐weather conditions, lower fire intensity at higher levels of Callitris abundance, was not sufficient to increase Callitris survival (4%). Callitris survival was also positively related to trunk diameter. Ground fuel type, but not biomass, varied with vegetation composition. Conclusions: These results demonstrate that flammable feedbacks, mediated by low flammability fuel traits of dominant trees, can provide an important mechanism for enhancing the survival and persistence of slow‐growing, non‐serotinous, non‐resprouting, fire‐killed trees in highly flammable landscapes. By modifying vegetation and fuel structure, patches of fire‐sensitive Callitris reduce fire intensity, and thereby reduce Callitris mortality, enhancing population persistence. However, this feedback loop is insufficient to ensure Callitris survival under extreme fire‐weather conditions, when fire intensity is greater. After burning, stands remain vulnerable to future fires, until trees grow large enough to modify fuel levels and reduce stand flammability.