Sex ratios and sex-biased infection behaviour in the entomopathogenic nematode genus Steinernema

In experimentally infected insects, the sex ratio of first generation nematodes of five species of Steinernema was female-biased (male proportion 0.35-0.47). There was a similar female bias when the worms developed in vitro (0.37-0.44), indicating that the bias in these species is not due to a lower rate of infection by male infective juveniles (IJs). Experimental conditions influenced the proportion of males establishing in insects, indicating that male and female IJs differ in their behaviour. However, there was no evidence that males are the colonising sex in any species, contrary to what has previously been proposed. Time of emergence from the host in which the nematodes had developed influenced sex ratios in experimental infections. In three species (Steinernema longicaudum, Steinernema glaseri and Steinernema kraussei), early emerged nematodes had a higher proportion of males than those that emerged later, with the reverse trend for Steinernema carpocapsae and Steinernema feltiae. In a more detailed in vitro study of S. longicaudum, the proportion of males was similar whether or not the nematodes passed through the developmentally arrested IJ stage, indicating that the female bias is not due to failure of males to exit this stage. The sex ratio in vitro was independent of survival rate from juvenile to adult, and was female-biased even when all juveniles developed, indicating that the bias is not explained by failure of males to develop to adults. The female-biased sex ratio characteristic of Steinernema populations appears to be present from at least the early juvenile stage. We hypothesise that the observed female bias is the population optimal sex ratio, a response to cycles of local mate competition experienced by nematodes reproducing within insect hosts interspersed with periods of outbreeding with less closely related worms following dispersal.     

cAMP inhibits bud growth in a yeast strain compromised for Ca2+ influx into the Golgi

Biochemical and physiological studies have implicated cAMP and cAMP-dependent protein kinase (PKA) in a plethora of essential cellular processes. Here we show that yeast cells partially depleted of PKA activity (due to atpk ^w mutation) and bearing a lesion in a Golgi-localized Ca²⁺ pump (Pmr1), arrest division with a small bud. The bud morphology of the arrestedtpk1 ^w pmr1 mutant cells is characteristic of cells in S phase; however, the terminal phenotype of processes such as DNA replication and nuclear division suggests arrest at the G2/M boundary. This small bud, G2-arrest phenotype is similar to that of strains with a defect in cell wall biosynthesis (pkc1) or membrane biogenesis (och1); however, the biochemical defect may be different since thetpk1 ^w pmr1 double mutants retain viability. The growth defect of thetpk1 ^w pmr1 mutant can be alleviated by preventing the increase in cellular cAMP levels that is known to be associated with a decrease in PKA activity, or by supplementing the medium with millimolar amounts of Ca²⁺. Although the biochemical consequences of this increase in cAMP concentration are not known, the small-bud phenotype of the double mutant and the known protein processing defect of thepmr1 lesion suggest that the localization or function of some membrane component might be compromised and susceptible to perturbations in cellular cAMP levels. One candidate for such a protein is the cAMP-binding membrane ectoprotein recently described in yeast.     

Antifouling substances of natural origin: Activity of benzoquinone compounds from Maesa Lanceolata against marine crustaceans

A screening of antifouling activity from plants extracts led to selection and further study of Maesa lanceolata Forssk. Two p‐benzoquinone compounds were isolated from the fruits and found to be active against Artemia salina. The anti‐crustacean activity of both p‐benzoquinones is reported for the first time.     

Tumor necrosis factor-alpha inhibits myogenesis through redox-dependent and -independent pathways

Muscle wasting accompanies diseases that are associated with chronic elevated levels of circulating inflammatory cytokines and oxidative stress. We previously demonstrated that tumor necrosis factor-alpha (TNF-alpha) inhibits myogenic differentiation via the activation of nuclear factor-kappaB (NF-kappaB). The goal of the present study was to determine whether this process depends on the induction of oxidative stress. We demonstrate here that TNF-alpha causes a decrease in reduced glutathione (GSH) during myogenic differentiation of C(2)C(12) cells, which coincides with an elevated generation of reactive oxygen species. Supplementation of cellular GSH with N-acetyl-l-cysteine (NAC) did not reverse the inhibitory effects of TNF-alpha on troponin I promoter activation and only partially restored creatine kinase activity in TNF-alpha-treated cells. In contrast, the administration of NAC before treatment with TNF-alpha almost completely restored the formation of multinucleated myotubes. NAC decreased TNF-alpha-induced activation of NF-kappaB only marginally, indicating that the redox-sensitive component of the inhibition of myogenic differentiation by TNF-alpha occurred independently, or downstream of NF-kappaB. Our observations suggest that the inhibitory effects of TNF-alpha on myogenesis can be uncoupled in a redox-sensitive component affecting myotube formation and a redox independent component affecting myogenic protein expression.     

Adhesion of high and low virulence Flavobacterium psychrophilum strains to isolated gill arches of rainbow trout Oncorhynchus mykiss

The ability of Flavobacterium psychrophilum to adhere to the gill tissue of rainbow trout Oncorhynchus mykiss was evaluated. A gill perfusion model was adopted, offering a number of advantages compared to other in vitro as well as in vivo models. A comparison between the adhesion capacity of a high and low virulence F. psychrophilum strain was made. Experiments were additionally carried out to assess the influence of water quality (organic material, nitrite) and temperature on the adhesion process of the bacterial cells. The high virulence strain attached more readily to the gill tissue than did the low virulence strain. Moreover, the adherence of the high virulence strain of F. psychrophilum was influenced by a number of factors. These were immersion of the gill arches in water to which organic material or nitrite were added, and elevated temperature. The former 2 increased the adhesion ability, while the latter had a negative influence on the adherence process.     

Interference competition in entomopathogenic nematodes: male Steinernema kill members of their own and other species

There is evidence of competition within and between helminth species, but the mechanisms involved are not well described. In interference competition, organisms prevent each other from using the contested resource through direct negative interactions, either chemical or physical. Steinernema spp. are entomopathogenic nematodes; they enter a living insect host which they kill and consume with the aid of symbiotic bacteria. Several studies have demonstrated intra- and interspecific competition in Steinernema, mediated by a scramble for resources and by incompatibility of the bacterial symbiont. Here we describe a mechanism by which male Steinernema may compete directly for resources, both food (host) and females, by physically injuring or killing members of another species as well as males of their own species. A series of experiments was conducted in hanging drops of insect haemolymph. Males of each of four species (Steinernemalongicaudum, Steinernemacarpocapsae, Steinernemakraussei and Steinernemafeltiae), representing three of the five phylogenetic clades of the genus, killed each other. Within 48 h, up to 86% of pairs included at least one dead male, compared with negligible mortality in single male controls. There was evidence of intraspecific difference: one strain of S. feltiae (4CFMO) killed while another (UK76) did not. Males also killed both females and males of other Steinernema spp. There was evidence of a hierarchy of killing, with highest mortality due to S. longicaudum followed by S. carpocapsae, S. kraussei and S. feltiae. Wax moth larvae were co-infected with members of two Steinernema spp. to confirm that killing also takes place in the natural environment of an insect cadaver. When insects were co-infected with one infective juvenile of each species, S. longicaudum males killed both S. feltiae UK76 and Steinernema hermaphroditum. Wax moths co-infected with larger, equal numbers of S. longicaudum and S. feltiae UK76 produced mainly S. longicaudum progeny, as expected based on hanging drop experiments.     

On a general model structure for macroscopic biological reaction rates

Macroscopic modelling of bioprocesses requires the determination of a biological reaction scheme and a kinetic model. The a priori selection of an appropriate kinetic model structure is usually made difficult by the lack of detailed bioprocess knowledge and the profusion of apparently similar biological kinetic laws. Moreover, parameter identification is made arduous and time-consuming by the strong non-linearities involved in kinetic laws. In most cases, these kinetic structures are non-linearizable and no first parameter estimation can be deduced easily. In order to avoid such identification problems, Bogaerts et al. [Bogaerts, Ph., Castillo, J., Hanus, R., 1999. A general mathematical modelling technique for bioprocesses in engineering applications. Syst. Anal. Model. Simul. 35, 87-113] have developed a general linearizable kinetic structure which allows the representation of activation and/or inhibition effects of each component in the culture. This paper further generalizes this structure in order to improve the way saturation effects are taken into account, and in turn, improve the biological interpretation of the model parameters. The main advantage of the proposed structure lies in an associated systematic estimation procedure. The usefulness of the proposed model is tested with simulated as well as with experimental data.     

Increased incidence of pregnancy complications in women who later develop scleroderma: a case control study

Introduction  

Studies have shown that fetal progenitor cells persist in maternal blood or bone marrow for more than 30 years after delivery. Increased trafficking of fetal cells occurs during pregnancy complications, such as hypertension, preeclampsia, miscarriage and intra-uterine growth restriction (IUGR). Women with these pregnancy complications are significantly more often HLA-class II compatible with their spouses. Women who later develop scleroderma also give birth to an HLA-class II child more often. From these prior studies we hypothesized that preeclampsia and other pregnancy complications could be associated with increased levels of fetal cell trafficking, and later be involved in the development of scleroderma.