Modelling coccidial infection in chickens: emphasis on vaccination by in-feed delivery of oocysts.

Trickle immunization of poultry by incorporating wildtype strains of coccidia in the feed has been shown to be an effective and practical means of controlling coccidiosis. Here we develop a mathematical model of the life cycle of Eimeria tenella and estimate the model parameters from extant experimental studies. Numerical solutions of the model compare well with experiment. The model provides quantitative estimates of the required trickle immunization hitherto only available after extensive time-consuming trials.     

The effects of “Cell age” upon the lethal effects of physical and chemical mutagens in the yeast, Saccharomyces cerevisiae

Summary SummaryYeast cultures progressing from the exponential to the stationary phase of growth showed changes in cell sensitivity to physical agents such as UV light, heat shock at 52° C and the chemical mutagens ethyl methane sulphonate, nitrous acid and mitomycin C.Exponential phase cells showed maximum resistance to UV light and minimum resistance to heat shock and the three chemicals. The increased resistance of exponential phase cells to UV light was shown to be dependent upon the functional integrity of the RAD ₅₀ gene.Treatment of growing yeast cultures with radioactively labelled ethyl methane sulphonate indicated the preferential uptake of radioactivity during the sensitive exponential stage of growth. The results indicated that the differential uptake of the chemical mutagens was responsible for at least a fraction of the variations in cell sensitivity observed in yeast cultures at different phases of growth.     

Ants impact the composition of the aquatic macroinvertebrate communities of a myrmecophytic tank bromeliad

In an inundated Mexican forest, 89 out of 92 myrmecophytic tank bromeliads (Aechmea bracteata) housed an associated ant colony: 13 sheltered Azteca serica, 43 Dolichoderus bispinosus, and 33 Neoponera villosa. Ant presence has a positive impact on the diversity of the aquatic macroinvertebrate communities (n = 30 bromeliads studied). A Principal Component Analysis (PCA) showed that the presence and the species of ant are not correlated to bromeliad size, quantity of water, number of wells, filtered organic matter or incident radiation. The PCA and a generalized linear model showed that the presence of Azteca serica differed from the presence of the other two ant species or no ants in its effects on the aquatic invertebrate community (more predators). Therefore, both ant presence and species of ant affect the composition of the aquatic macroinvertebrate communities in the tanks of A. bracteata, likely due to ant deposition of feces and other waste in these tanks.     

Dishevelled phosphorylation, subcellular localization and multimerization regulate its role in early embryogenesis

Dishevelled (Dsh) induces a secondary axis and can translocate to the membrane when activated by Frizzleds; however, dominant-negative approaches have not supported a role for Dsh in primary axis formation. We demonstrate that the Dsh protein is post-translationally modified at the dorsal side of the embryo: timing and position of this regulation suggests a role of Dsh in dorsal-ventral patterning in Xenopus. To create functional links between these properties of Dsh we analyzed the influence of endogenous Frizzleds and the Dsh domain dependency for these characteristics. Xenopus Frizzleds phosphorylate and translocate Xdsh to the membrane irrespective of their differential ectopic axes inducing abilities, showing that translocation is insufficient for axis induction. Dsh deletion analysis revealed that axis inducing abilities did not segregate with Xdsh membrane association. The DIX region and a short stretch at the N-terminus of the DEP domain are necessary for axis induction while the DEP region is required for Dsh membrane association and its phosphorylation. In addition, Dsh forms homomeric complexes in embryos suggesting that multimerization is important for its proper function.     

Spindle assembly defects leading to the formation of a monopolar mitotic apparatus

Mitotic spindle formation in animal cells involves microtubule nucleation from two centrosomes that are positioned at opposite sides of the nucleus. Microtubules are captured by the kinetochores and stabilized. In addition, microtubules can be nucleated independently of the centrosome and stabilized by a gradient of Ran—GTP, surrounding the mitotic chromatin. Complex regulation ensures the formation of a bipolar apparatus, involving motor proteins and controlled polymerization and depolymerization of microtubule ends. The bipolar apparatus is, in turn, responsible for faithful chromosome segregation. During recent years, a variety of experiments has indicated that defects in specific motor proteins, centrosome proteins, kinases and other proteins can induce the assembly of aberrant spindles with a monopolar morphology or with poorly separated poles. Induction of monopolar spindles may be a useful strategy for cancer therapy, since ensuing aberrant mitotic exit will usually lead to cell death. In this review, we will discuss the various underlying molecular mechanisms that may be responsible for monopolar spindle formation.     

Messinian palaeoenvironments and hydrology in Sicily (Italy): The dinoflagellate cyst record

Hydrological conditions prevailing before, during and after the Messinian salinity crisis in Sicily have been approached using dinoflagellate cyst records. The synthetic sequence considered is based on five classical sections from the Caltanissetta Basin. Our interpretations are based on the recognition of autochthonous, allochthonous and reworked population among the dinocyst assemblages. For the first time, sea-surface temperatures and seasonal salinity contrasts were tentatively reconstructed using a “Mutual Climatic Range Method”. Sicilian late Tortonian deposits correspond to marine environment with significant terrestrial inputs favourable to eutrophic dinocyst species. Immediately after the beginning of the Messinian Stage, euryhaline assemblages took place, followed by meso-hyperhaline taxa, within a general trend to shallowing. At the end of the Tripoli diatomitic Formation, environment appears confined, with regular oceanic inflows. Such marine inflows remain persistent during the deposition of the salt Member, witnessing the probable persistence of nearby normal marine sea-surface water conditions in the Mediterranean Sea but with possible reduced hydrological circulation and/or low nutrient component. Such inflows are slightly decreasing up to the top of the Sicilian Upper Evaporites. At the same time, river inputs appear weak during the salt deposition, as the consequence of a rather dry climatic context. As shown by reworking activity, terrestrial inputs increase progressively from the base of the Upper Evaporites. During the Lago Mare period, while climate remains rather dry (absence of freshwater algae inputs, very low amount in trees requiring humid conditions), local deposition environment is confined with mesohaline to hypohaline sea-surface waters, in a context with relatively high seasonal sea-surface salinity contrast (up to 6‰). The very high reworking observed in the Arenazzolo silts, in addition to slightly increasing water depth, led us to consider the presence of a discontinuity between the Lago Mare and the Arenazzolo Fms. We consider the Arenazzolo Formation as a transgressive facies following a deep downcutting period. The Arenazzolo Formation presents a two-step development. The first one, correlative with the presence of a G. etrusca (a species with Paratethyan affinities), corresponds to a relative high-stand sea-level with oceanic influxes, low seasonal sea-surface salinity contrast and probable more humid context, as revealed by the important freshwater algal inputs. During the second step, salinity becomes much more variable, with a clear increase of seasonal sea-surface salinity contrast, a possible slight mean sea-surface temperature increase (only few degrees) and a clear weakening of the river inputs. Taking the proposed Zanclean position of the Arenazzolo Fm. into consideration, we state that mean sea-surface temperature did not change significantly from the base of the Messinian to the earliest Zanclean. At 5.33 Ma, the suddenly achieved flooding restored a fair, deep oceanic environment characterized, at the beginning, by a clear mean sea-surface temperature cooling (up to 6-7 °C) and a nutrient depletion, associated with the basins starvation. Sea-surface salinities were normal, with very low seasonal contrast. Hydrodynamics then nutrient supply became then quite normal from c.a. 5.08 Ma. The status of the Sicilian Caltanissetta Basin as a marginal basin although fastly deepening and the stratigraphical location of the Messinian discontinuity at the base of the Arenazzolo is the scenario that best matches our dinocyst record.