Three-dimensional structure of Chlamydomonas reinhardtii and Synechococcus elongatus photosystem II complexes allows for comparison of their oxygen-evolving complex organization

Electron microscopy and single-particle analyses have been carried out on negatively stained photosystem II (PSII) complexes isolated from the green alga Chlamydomonas reinhardtii and the thermophilic cyanobacterium Synechococcus elongatus. The analyses have yielded three-dimensional structures at 30-A resolution. Biochemical analysis of the C. reinhardtii particle suggested it to be very similar to the light-harvesting complex II (LHCII).PSII supercomplex of spinach, a conclusion borne out by its three-dimensional structure. Not only was the C. reinhardtii LHCII.PSII supercomplex dimeric and of comparable size and shape to that of spinach, but the structural features for the extrinsic OEC subunits bound to the lumenal surface were also similar thus allowing identification of the PsbO, PsbP, and PsbQ OEC proteins. The particle isolated from S. elongatus was also dimeric and retained its OEC proteins, PsbO, PsbU, and PsbV (cytochrome c(550)), which were again visualized as protrusions on the lumenal surface of the complex. The overall size and shape of the cyanobacterial particle was similar to that of a PSII dimeric core complex isolated from spinach for which higher resolution structural data are known from electron crystallography. By building the higher resolution structural model into the projection maps it has been possible to relate the positioning of the OEC proteins of C. reinhardtii and S. elongatus with the underlying transmembrane helices of other major intrinsic subunits of the core complex, D1, D2, CP47, and CP43 proteins. It is concluded that the PsbO protein is located over the CP47 and D2 side of the reaction center core complex, whereas the PsbP/PsbQ and PsbV/PsbU are positioned over the lumenal surface of the N-terminal region of the D1 protein. However, the mass attributed to PsbV/PsbU seems to bridge across to the PsbO, whereas the PsbP/PsbQ proteins protrude out more from the lumenal surface. Nevertheless, within the resolution and quality of the data, the relative positions of the center of masses for OEC proteins of C. reinhardtii and S. elongatus are similar and consistent with those determined previously for the OEC proteins of spinach.     

Detection of the oyster parasite Bonamia ostreae by fluorescent in situ hybridization

Bonamia ostreae is an economically significant protistan parasite of the flat oyster Ostrea edulis in Europe and North America. Management of this parasite depends partly upon its reliable identification in wild and aquacultured oyster populations, but B. ostreae is small and difficult to detect by traditional microscopic methods. We designed a fluorescent in situ hybridization (FISH) assay to sensitively detect B. ostreae in standard histopathological sections of B. ostreae-infected oysters using fluorescently labeled DNA oligonucleotide probes. Hybridization using a cocktail of 3 presumptively B. ostreae-specific, fluorescein iso(thio)cyanate (FITC)-labeled oligonucleotides produced an unambiguous staining pattern of small green rings inside infected oyster hemocytes that was easily distinguished from host tissue background. This pattern is diagnostic for B. ostreae. A negative control cocktail of oligonucleotides containing 2 mismatches relative to target sequences, on the other hand, failed to hybridize at all. B. ostreae-specific probes did not cross-react with a related protist, Haplosporidium nelsoni.     

Spiked Sediment Toxicity Testing of Hydrophobic Organic Chemicals: Bioavailability,Technical Considerations,and Applications

Many evaluations estimating safe levels of hydrophobic organic chemicals in sediments do not account for confounding factors such as physical habitat quality or covariance among chemicals. Controlled experiments demonstrating cause and effect can be conducted with spiked sediment toxicity tests, but application of this methodology has been limited in part by concerns about chemical bioavailability and challenges in achieving target concentrations. Relevant literature was reviewed to assess the utility of standardizing sediment equilibration times; hydrophobicity, complex sediment characteristics, and temperature were identified as potentially equally important factors. Disequilibrium appears likely following limited equilibration time but should yield conservative toxicity test results relative to aged field sediments. Nominal and measured concentrations in over 20 published studies were compared to assess spiked chemical recovery (i.e., measured concentration/nominal concentration). Recovery varied substantially among studies and was not readily predictable based on spiking or extraction method, chemical properties, or measured sediment characteristics, although unmeasured differences between sediments appeared to be important. Factors affecting specific studies included chemical adsorption to glassware, biodegradation, and volatilization. Pre- and post-toxicity test analyses are recommended to confirm exposure concentrations. Studies with 2,3,7,8-tetrachloro-dibenzo-p-dioxin (2,3,7,8-TCDD) and hexachlorobenzene (HCB) exemplify the utility of verifying results of field studies using spiked sediment tests. Sediments spiked with these chemicals at concentrations greatly exceeding those in associated field studies caused no adverse effects in test organisms, demonstrating that other chemicals co-occurring in test sediment samples caused toxicity initially attributed to 2,3,7,8-TCDD and HCB in the field studies. Another key application of spiked sediment tests has been the investigation of TOC as the primary factor affecting bioavailability of hydrophobic organic chemicals. A review of LC50s for nine chemicals reported in 12 studies shows that comparable LC50s derived in different sediments generally agree within a factor of five when concentrations are normalized to a constant TOC. Additionally, use of spiked sediment toxicity testing to investigate toxicological interactions among chemicals provides a promising approach to improving the ability to predict sediment toxicity in the field.     

Assessing and reporting heterogeneity in treatment effects in clinical trials: a proposal

Background

This paper presents the study protocol for a pragmatic randomised controlled trial to evaluate the impact of a school based program developed to prevent teenage pregnancy. The program includes students taking care of an Infant Simulator; despite growing popularity and an increasing global presence of such programs, there is no published evidence of their long-term impact. The aim of this trial is to evaluate the Virtual Infant Parenting (VIP) program by investigating pre-conceptual health and risk behaviours, teen pregnancy and the resultant birth outcomes, early child health and maternal health.

Methods and Design

Fifty-seven schools (86% of 66 eligible secondary schools) in Perth, Australia were recruited to the clustered (by school) randomised trial, with even randomisation to the intervention and control arms. Between 2003 and 2006, the VIP program was administered to 1,267 participants in the intervention schools, while 1,567 participants in the non-intervention schools received standard curriculum. Participants were all female and aged between 13-15 years upon recruitment. Pre and post-intervention questionnaires measured short-term impact and participants are now being followed through their teenage years via data linkage to hospital medical records, abortion clinics and education records. Participants who have a live birth are interviewed by face-to-face interview. Kaplan-Meier survival analysis and proportional hazards regression will test for differences in pregnancy, birth and abortion rates during the teenage years between the study arms.

Discussion

This protocol paper provides a detailed overview of the trial design as well as initial results in the form of participant flow. The authors describe the intervention and its delivery within the natural school setting and discuss the practical issues in the conduct of the trial, including recruitment. The trial is pragmatic and will directly inform those who provide Infant Simulator based programs in school settings.

Trial registration

ISRCTN24952438     

On the multiplicity of sugar transport systems in guinea pig jejunum.

A study has been made in everted sacs of guinea pig jejunum to see if the two transport systems of glucose analogues characterized at the brush border membrane vesicles are operative. The transport kinetics of D-galactose and alpha-methylglucoside up to 80 mM concentrations has been studied, as well as the mutual inhibitions between them at low and high concentrations of the substrate and at different concentrations of the inhibitor. Low temperature (20 degrees C) inhibits galactose transport at 0.1 mM (70%) and 40 mM (78%) concentrations. A mass transfer coefficient, KD, somewhat higher for galactose than for alpha-methylglucoside, was obtained when the transport component was abolished by phlorizin. The transport of D-galactose and alpha-methylglucoside seemed to be compatible with the function of one system shared by both substrates, which presents greater affinity for alpha-methylglucoside. The functional existence of two systems of active transport at the brush border of guinea pig was not evidenced in intestinal preparations of whole tissue, due perhaps to the effect of the unstirred water layers. However, differences in KD values and some results of the mutual inhibitions may suggest a second system.     

Turning cells red: signal transduction mediated by erythropoietin

Erythropoietin (EPO) is the crucial cytokine regulator of red blood-cell production. Since the discovery of EPO in 1985 and the isolation of its cognate receptor four years later, there has been significant interest in understanding the unique ability of this ligand-receptor pair to promote erythroid mitogenesis, survival and differentiation. The development of knockout mice has elucidated the precise role of the ligand, receptor and downstream players in murine erythroid development. In this review, we summarize EPO-mediated signaling pathways and examine their significance in vivo.     

Effects of parasites on fish behaviour: a review and evolutionary perspective

Fish serve as hosts to a range of parasites that are taxonomically diverse and that exhibit a wide variety of life cycle strategies. Whereas many of these parasites are passed directly between ultimate hosts, others need to navigate through a series of intermediate hosts before reaching a host in (or on) which they can attain sexual maturity. The realisation that parasites need not have evolved to minimise their impact on hosts to be successful, and in many cases may even have a requirement for their hosts to be eaten by specific predators to ensure transmission, has renewed interest in the evolutionary basis of infection-associated host behaviour. Fishes have proved popular models for the experimental examination of such hypotheses, and parasitic infections have been demonstrated to have consequences for almost every aspect of fish behaviour. Despite a scarcity of knowledge regarding the mechanistic basis of such behaviour changes in most cases, and an even lower understanding of their ecological consequences, there can be little doubt that infection-associated behaviour changes have the potential to impact severely on the ecology of infected fishes. Changes in foraging efficiency, time budget, habitat selection, competitive ability, predator-prey relationships, swimming performance and sexual behaviour and mate choice have all been associated with – and in some cases been shown to be a result of – parasite infections, and are reviewed here in some detail. Since the behavioural consequences of infections are exposed to evolutionary selection pressures in the same way as are other phenotypic traits, few behavioural changes will be evolutionarily neutral and host behaviour changes that facilitate transmission should be expected. Despite this expectation, we have found little conclusive evidence for the Parasite Increased Trophic Transmission (PITT) hypothesis in fishes, though recent studies suggest it is likely to be an important mechanism. Additionally, since the fitness consequences of the many behavioural changes described have rarely been quantified, their evolutionary and ecological significance is effectively unknown.Potential hosts may also change their behaviour in the presence of infective parasite stages, if they adopt tactics to reduce exposure risk. Such `behavioural resistance', which may take the form of habitat avoidance, prey selectivity or avoidance of infected individuals, can be viewed as behavioural change associated with the threat of being parasitised, and so is included here. Actually harbouring infections may also stimulate fishes to perform certain types of simple or complex behaviours aimed at removing parasites, such as substrate scraping or the visitation of cleaning stations, although the efficacy of the latter as a parasite removal strategy is currently subject to a good deal of debate.The effects parasites have on shoaling behaviour of host fish have attracted a good deal of attention from researchers, and we have provided a case study to summarise the current state of knowledge. Parasites have been shown to affect most of the antipredator effects of shoaling (such as vigilance, co-ordinated evasion and predator confusion) and can also impair an individual's foraging ability. It therefore seems unsurprising that, in a number of species avoidance of parasitised individuals has evolved which may explain the occurrence of parasite-assorted shoals in the field. Parasitised fish are found more often in peripheral shoal positions and show a reduced tendency for shoaling in some fish species. Given the array of host behaviours that may be changed, the fitness consequences of shoal membership for parasitised hosts and their parasites are not always easy to predict, yet an understanding of these is important before we can make predictions regarding the ecological impact of infections on host fish populations.Clearly, there remain many gaps in our knowledge regarding the effects of parasites on the behaviour of host fish. We believe that a much greater understanding of the importance of infection-associated behaviour changes in fish could be gained from high quality research in comparatively few areas. We have completed our review by highlighting the key research topics that we believe should attract new research in this field.     

In vitro dialyzability of zinc from different salts used in the supplementation of infant formulas

Seven zinc salts—acetate, chloride, lactate, sulfate, citrate, gluconate, and oxide—were added to milk—and soy-based infant formulas to estimate possible differences in zinc availability depending on the type of salt used. For this purpose, an in vitro method that estimates the dialyzability of the element (i.e., the fraction available for absorption) was applied. Zinc dialyzability is always higher in milk-based products than in soy products, even when the total zinc contents are higher in the latter. The salts can be classified according to the zinc dialyzability in the two types of formulas as follows: oxide>gluconate=chloride=lactate>citrate=acetate>sulfate. Therefore, according to the dialysis percentage, oxide and gluconate are the compounds of choice for zinc supplementation of infant formulas.