Response of Daphnia to substances released from crowded congeners and conspecifics

The effects of chemicals released from crowded congeners andconspecifics on life history parameters of the freshwater zooplanktersDaphnia cucullata and Daphnia pulex were examined. Length andage at maturity of D. pulex were affected by crowding chemicals.Reproduction was lower in crowded medium, and ephippia wereproduced. Newborn D. pulex in crowded medium were significantlylonger than the controls. The intrinsic rate of population increaseof D. pulex was 14 and 25% lower than the control when exposedto crowded medium from D. cucullata and D. pulex, respectively.Neither urea nor ammonia (at 1 mg l^-1) seemed to be responsiblefor these effects in D. pulex. In D. cucullata, no significanteffect of crowding infochemicals on length and age at maturitywas found. However, crowding chemicals reduced reproduction.No ephippia were produced in crowded medium, but up to 83% non-developingeggs were observed in D. cucullata. Newborns were similarlysized in crowded and standard medium. The intrinsic rate ofpopulation increase of D. cucullata was 44 and 96% lower thanthe control when exposed to crowded medium from D. cucullataand D. pulex, respectively. Clearance rates of D. pulex weresignificantly reduced in crowded media compared with standardmedium, which could partly explain why the animals exposed tocrowding chemicals reacted as if they were food limited.     

A high risk phenotype of hypertrophic cardiomyopathy associated with a compound genotype of two mutated β-myosin heavy chain genes

Hypertrophic cardiomyopathy (HCM) is a genetically and clinically heterogeneous myocardial disease that is in most cases familial and transmitted in a dominant fashion. The most frequently affected gene codes for the cardiac (ventricular) β-myosin heavy chain. We have investigated the genetic cause of an isolated case of HCM, which was marked by an extremely severe phenotype and a very early age of onset. HCM is normally not a disease of small children. The proband was a boy who had suffered cardiac arrest at the age of 6.5years (resuscitation by cardioconversion). Upon screening of the β-myosin heavy chain gene as a candidate, two missense mutations, one in exon19 (Arg719Trp) and a second in exon12 (Met349Thr), were identified. The Arg719Trp mutation was de novo, as it was not found in the parents. In contrast, the Met349Thr mutation was inherited through the maternal grandmother. Six family members were carriers of this mutation but only the proband was clinically affected. Segregation and molecular analysis allowed us to assign the Met349Thr mutation to the maternal and the Arg719Trp de novo mutation to the paternal β-myosin allele. Thus, the patient has no normal myosin. We interpret these findings in terms of compound heterozygosity of a dominant (Arg719Trp) and a recessive (Met349Thr) mutation. Whereas a single mutated Arg719Trp allele would be sufficient to cause HCM, the concurrent Met349Thr mutation alone does not apparently induce the disease. Nevertheless, it conceivably contributes to the particularly severe phenotype. Received: 15 September 1997 / Accepted: 26 November 1997     

Interaction of RecBCD Enzyme with DNA at Double-Strand Breaks Produced in UV-Irradiated Escherichia coli: Requirement for DNA End Processing

The RecBCD enzyme has a powerful duplex DNA exonuclease activity in vivo. We found that this activity decreased strongly when cells were irradiated with UV light (135 J/m²). The activity decrease was seen by an increase in survival of phage T4 2⁻ of about 200-fold (phage T4 2⁻ has defective duplex DNA end-protecting gene 2 protein). The activity decrease depended on excision repair proficiency of the cells and a postirradiation incubation. During this time, chromosome fragmentation occurred as demonstrated by pulsed-field gel electrophoresis. In accord with previous observations, it was concluded that the RecBCD enzyme is silenced during interaction with duplex DNA fragments containing Chi nucleotide sequences. The silencing was suppressed by induction or permanent derepression of the SOS system or by the overproduction of single-strand DNA binding protein (from a plasmid with ssb⁺) which is known to inhibit degradation of chromosomal DNA by cellular DNases. Further, mutations in xonA, recJ, and sbcCD, particularly in the recJ sbcCD and xonA recJ sbcCD combinations, impeded RecBCD silencing. The findings suggest that the DNA fragments had single-stranded tails of a length which prevents loading of RecBCD. It is concluded that in wild-type cells the tails are effectively removed by single-strand-specific DNases including exonuclease I, RecJ DNase, and SbcCD DNase. By this, tailed DNA ends are processed to entry sites for RecBCD. It is proposed that end blunting functions to direct DNA ends into the RecABCD pathway. This pathway specifically activates Chi-containing regions for recombination and recombinational repair.     

Association of polyaminergic loci with anxiety, mood disorders, and attempted suicide

Background

The polyamine system has been implicated in a number of psychiatric conditions, which display both alterations in polyamine levels and altered expression of genes related to polyamine metabolism. Studies have identified associations between genetic variants in spermidine/spermine N1-acetyltransferase (SAT1) and both anxiety and suicide, and several polymorphisms appear to play important roles in determining gene expression.

Methodology/Principal Findings

We genotyped 63 polymorphisms, spread across four polyaminergic genes (SAT1, spermine synthase (SMS), spermine oxidase (SMOX), and ornithine aminotransferase like-1 (OATL1)), in 1255 French-Canadian individuals who have been followed longitudinally for 22 years. We assessed univariate associations with anxiety, mood disorders, and attempted suicide, as assessed during early adulthood. We also investigated the involvement of gene-environment interactions in terms of childhood abuse, and assessed internalizing and externalizing symptoms as endophenotypes mediating these interactions. Overall, each gene was associated with at least one main outcome: anxiety (SAT1, SMS), mood disorders (SAT1, SMOX), and suicide attempts (SAT1, OATL1). Several SAT1 polymorphisms displayed disease-specific risk alleles, and polymorphisms in this gene were involved in gene-gene interactions with SMS to confer risk for anxiety disorders, as well as gene-environment interactions between childhood physical abuse and mood disorders. Externalizing behaviors demonstrated significant mediation with regards to the association between OATL1 and attempted suicide, however there was no evidence that externalizing or internalizing behaviors were appropriate endophenotypes to explain the associations with mood or anxiety disorders. Finally, childhood sexual abuse did not demonstrate mediating influences on any of our outcomes.

Conclusions/Significance

These results demonstrate that genetic variants in polyaminergic genes are associated with psychiatric conditions, each of which involves a set of separate and distinct risk alleles. As several of these polymorphisms are associated with gene expression, these findings may provide mechanisms to explain the alterations in polyamine metabolism which have been observed in psychiatric disorders.     

Reaction of wild-type and Glu243Asp variant yeast cytochrome c oxidase with O2

We have studied internal electron transfer during the reaction of Saccharomyces cerevisiae mitochondrial cytochrome c oxidase with dioxygen. Similar absorbance changes were observed with this yeast oxidase as with the previously studied Rhodobacter sphaeroides and bovine mitochondrial oxidases, which suggests that the reaction proceeds along the same trajectory. However, notable differences were observed in rates and electron-transfer equilibrium constants of specific reaction steps, for example the ferryl (F) to oxidized (O) reaction was faster with the yeast (0.4 ms) than with the bovine oxidase (~ 1 ms) and a larger fraction Cu_A was oxidized with the yeast than with the bovine oxidase in the peroxy (P_R) to F reaction. Furthermore, upon replacement of Glu243, located at the end of the so-called D proton pathway, by Asp the P_R → F and F → O reactions were slowed by factors of ~ 3 and ~ 10, respectively, and electron transfer from Cu_A to heme a during the P_R → F reaction was not observed. These data indicate that during reduction of dioxygen protons are transferred through the D pathway, via Glu243, to the catalytic site in the yeast mitochondrial oxidase. This article is part of a Special Issue entitled: 18th European Bioenergetic Conference.     

Invasion of insect cells by Spiroplasma citri involves spiralin relocalization and lectin/glycoconjugate‐type interactions

Spiroplamas are helical, cell wall‐less bacteria belonging to the Class Mollicutes, a group of microorganisms phylogenetically related to low G+C, Gram‐positive bacteria. Spiroplasma species are all found associated with arthropods and a few, including Spiroplasma citri are pathogenic to plant. Thus S. citri has the ability to colonize cells of two very distinct hosts, the plant and the insect vector. While spiroplasmal factors involved in transmission by the leafhopper Circulifer haematoceps have been identified, their specific contribution to invasion of insect cells is poorly understood. In this study we provide evidence that the lipoprotein spiralin plays a major role in the very early step of cell invasion. Confocal laser scanning immunomicroscopy revealed a relocalization of spiralin at the contact zone of adhering spiroplasmas. The implication of a role for spiralin in adhesion to insect cells was further supported by adhesion assays showing that a spiralin‐less mutant was impaired in adhesion and that recombinant spiralin triggered adhesion of latex beads. We also showed that cytochalasin D induced changes in the surface‐exposed glycoconjugates, as inferred from the lectin binding patterns, and specifically improved adhesion of S. citri wild‐type but not of the spiralin‐less mutant. These results indicate that cytochalasin D exposes insect cell receptors of spiralin that are masked in untreated cells. In addition, competitive adhesion assays with lectins strongly suggest spiralin to exhibit glycoconjugate binding properties similar to that of the Vicia villosa agglutinin (VVA) lectin.     

Oviposition deterring infochemicals in ladybirds: the role of phylogeny

Faced with an ephemeral prey, aphidophagous ladybirds rely on the hydrocarbons present in the tracks of their larvae to choose an unoccupied patch for egg laying. Although both conspecific and heterospecific larval tracks might deter females from oviposition, the response to the later is often less striking. Several explanations have been suggested to account for this. In this paper we tested the phylogeny hypothesis, which predicts that the chemical composition of the tracks of closely related species of ladybirds will be more similar to one another than to those of more distantly related species. Qualitative and quantitative information on the chemical nature of the larval tracks and a molecular phylogeny of seven species belonging to three different genera are provided, and the congruence between these two sets of results assessed. The results confirm the phylogeny hypothesis and infer a gradual mode of evolution of these infochemicals.     

Mouse Protocadherin-1 Gene Expression Is Regulated by Cigarette Smoke Exposure In Vivo

Protocadherin-1 (PCDH1) is a novel susceptibility gene for airway hyperresponsiveness, first identified in families exposed to cigarette smoke and is expressed in bronchial epithelial cells. Here, we asked how mouse Pcdh1 expression is regulated in lung structural cells in vivo under physiological conditions, and in both short-term cigarette smoke exposure models characterized by airway inflammation and hyperresponsiveness and chronic cigarette smoke exposure models. Pcdh1 gene-structure was investigated by Rapid Amplification of cDNA Ends. Pcdh1 mRNA and protein expression was investigated by qRT-PCR, western blotting using isoform-specific antibodies. We observed 87% conservation of the Pcdh1 nucleotide sequence, and 96% conservation of the Pcdh1 protein sequence between men and mice. We identified a novel Pcdh1 isoform encoding only the intracellular signalling motifs. Cigarette smoke exposure for 4 consecutive days markedly reduced Pcdh1 mRNA expression in lung tissue (3 to 4-fold), while neutrophilia and airway hyperresponsiveness was induced. Moreover, Pcdh1 mRNA expression in lung tissue was reduced already 6 hours after an acute cigarette-smoke exposure in mice. Chronic exposure to cigarette smoke induced loss of Pcdh1 protein in lung tissue after 2 months, while Pcdh1 protein levels were no longer reduced after 9 months of cigarette smoke exposure. We conclude that Pcdh1 is highly homologous to human PCDH1, encodes two transmembrane proteins and one intracellular protein, and is regulated by cigarette smoke exposure in vivo.     

Changes in the origin and quality of soil organic matter after pasture introduction in Rondônia (Brazil)

We examined the effects of the conversion of tropical forest to pasture on soil organic matter (SOM) origin and quality along a chronosequence of sites, including a primary forest and six pastures. Bulk soil samples received a physical size-fractionation treatment to assess the contribution of each compartment to total SOM pool. Besides a general increase in total C and N stocks along the chronosequence, we observed a reduction of the relative contribution of the coarser fractions to total soil C content, and an increased concentration in the finer fractions. The origin of the C in each size fraction was established from measurements of¹³C abundance. After 80 years about 93% of the C in the least humified fraction of the top 10 cm of soil was of pasture origin, while in the most humified it was 82%. Chemical analyses indicated that the fine silt and coarse clay fractions contained the most refractory carbon.     

Comparison of pelagic food webs in lakes along a trophic gradient and with seasonal aspects: influence of resource and predation

Composition and seasonal dynamics of phytoplankton, bacteria,and zooplankton (including heterotrophic flagellates, ciliates,rotifers and crustaceans) were studied in 55 lakes in NorthernGermany with different trophic status, ranging from mesotrophicto hypertrophic. Mean abundance and biomass of all groups increasedsignificantly with trophic level of the lake, but bacteria andmetazooplankton showed only a weak correlation and a slightincrease with chlorophyll concentration. Composition of phytoplanktonshowed a dominance of cyanobacteria in hypertrophic lakes, whereasthe importance of chrysophytes and dinophytes decreased withan increase in trophic status. Protozoans (heterotrophic flagellatesand ciliates) made up 24% (mesotrophic lakes) to 42% (hypertrophiclakes) of total zooplankton biomass on average, and were dominatedby ciliates (62–80% of protozoan biomass). Seasonally,protozoans can build up to 60% of zooplankton biomass in spring,when heterotrophic flagellates can contribute