Synthesis and characterization of three novel inorganic/organic hybrid materials based on polyoxomolybdate clusters: an investigation into the structural consequences of steric effect of the organoimine ligands

Hydrothermal means have been employed in isolating three new compounds, [Cu₂Mo₄O₁₃(C₅H₆N₂)₂·3H₂O] (1), [Cu₂Mo₄O₁₃(C₆H₈N₂)₂] (2) and [CuMo₆O₁₉(C₁₈H₂₄N₂)] (3) from mixtures of CuNO₃/CuSO₄, the corresponding ligands (methylpyrazine, dimethylpyrimidine and ditertiarybutyl-2,2′-bipyridine) and MoO₃ at temperatures from 120 to 160 °C. The structures of these compounds range from three-dimensional in the case of 1 to ‘zero-dimensional’ or molecular in the case of 3 in accordance with the extent of steric hindrance presented by the ligand.     

Quantitative aspects of endocytic activity in lipid-mediated transfections.

Variation in transfection efficiency observed in different cell-types is poorly understood. To investigate the influence of endocytic activity on lipid-mediated transfections, we have monitored both the processes in 12 different cell-types. The endocytic activity shows a strong positive correlation (P < 0.01), with transfection efficiency. Treatment with wortmannin resulted in cell-type-dependent inhibition of transfection. Studies on M-phase cells by confocal microscopy show that compared to interphase cells, uptake of cationic liposomes was substantially reduced. In addition, transfection efficiency of cells in mitotic phase was inhibited by >70% compared to controls. Our study based on several cell-types demonstrates for the first time that quantitative aspects of endocytosis have decisive influence on the overall process of lipid-mediated transgene expression.     

Factors Affecting Egg-ratio in Planktonic Rotifers

Edmondson’s egg ratio (number of amictic eggs per female) is an important life history variable, which has been in wide use to understand and predict patterns of population growth in planktonic rotifers under field conditions. It is also useful as an indicator of the health of rotifers under culture conditions. Generally, an inverse relationship exists between the egg ratio and the density of females in a population. A number of abiotic and biotic factors influence the egg ratio. For example, temperature can cause marked changes in the egg ratio by influencing the frequency of egg production and the hatching times of parthenogenetic eggs. Also, preferential feeding on ovigerous females of rotifers by invertebrate predators such as Asplanchna will lower the egg ratios of the population. The easy detachment of eggs, as may be the case in some members of the Brachionidae especially during enhanced reproduction when food levels are high, may also cause an underestimation of the egg ratio. In this review, we discuss the egg ratio of selected rotifer species in relation to the role of diel changes in egg production, the frequency or the intensity of feeding, the problems of distinguishing between different egg types and the negative effect of stressors such as toxicants and diet quality.     

Life history strategies of cladocerans: comparisons of tropical and temperate taxa

We review recent works on different life history variables of cladoceran taxa in tropical and temperate freshwater bodies, comparing the strategies that cladocerans have evolved to adapt to contrasting environmental conditions in the two geographical regions. These life-history parameters relate to age and size at maturity, survival, fecundity, life-expectancy at birth, lifespan, gross, and net reproductive rates, generation time, the rate of population increase, peak population density and day of peak abundance. We also discuss the role of photoperiod and temperature on some of these life history parameters. We found a general paucity of experimental work and field data in tropics on cladocerans. There is very limited information on the few Daphnia species found in the tropics. The misconception of low species diversity of cladocerans in the tropics arose due to several reasons including lack of extensive and intensive field collections. Higher water temperatures apparently promote permanent infestation of tropical waters with toxic cyanobacteria, which reduce the zooplankton diversity. In addition to higher temperatures in the tropics, the year-round high predation pressure of planktivorous fish probably causes the tropical species, particularly in pelagic habitats, to reach maturity earlier (< 3 days) than in temperate regions. Species of Daphnia in temperate regions are particularly adapted to living at food concentrations that are much lower and seasonably more variable than those for tropical genera such as Diaphanosoma. This is further corroborated by the more than an order of magnitude higher threshold food concentration (TFC) for tropical Cladocera than for their temperate counterparts. Fecundity patterns differ between tropical and temperate cladoceran taxa: cultured under optimal temperature regimes, tropical taxa have fewer eggs than temperate species of a comparable body size. Predation pressure may act differently depending on the size of the cladoceran neonates and thus on their population size structure. Global warming and climate changes seem to affect the behaviour (migration), distribution, and abundance of cladocerans. Apparently, in direct response to these changes, the possibility of encountering the tropical cladocerans in the northern, temperate hemisphere (bioinvasions) is on the rise.     

Cholesterol alters the interaction of glycosphingolipid GM3 with alpha5beta1 integrin and increases integrin-mediated cell adhesion to fibronectin

Integrins bind to their ligand in the extracellular matrix (ECM), such as fibronectin (FN), through a specific interaction between the amino acid motifs in the ligand, and binding sites in the extracellular domains of the integrin molecule generated jointly by its alpha and beta subunits. It has been proposed that membrane cholesterol and glycosphingolipids (GSLs) can regulate integrin-ECM interactions and it has been demonstrated that increased membrane cholesterol leads to increased cell adhesion to FN. Here, we have shown that a specific glycosphingolipid GM3 binds directly to alpha5beta1 integrin and an increase in membrane cholesterol results in the redistribution of GM3-associated alpha5beta1 integrin molecules specifically on the surface that is in contact with the substratum. Our results suggest that GM3-associated alpha5beta1 integrins bind less avidly to FN than GM3-free integrins and that cholesterol and GM3 play an interdependent role in the distribution of alpha5beta1integrin molecules in the membrane and regulation of cell adhesion.     

Early localization of NPA58, a rat nuclear pore-associated protein, to the reforming nuclear envelope during mitosis

We have studied the mitotic reassembly of the nuclear envelope, using antibodies to nuclear marker proteins and NPA58 in F-111 rat fibroblast cells. In earlier studies we have proposed that NPA58, a 58 kDa rat nuclear protein, is involved in nuclear protein import. In this report, NPA58 is shown to be localized on the cytoplasmic face of the envelope in interphase cells, in close association with nuclear pores. In mitotic cells NPA58 is dispersed in the cytoplasm till anaphase. The targeting of NPA58 to the reforming nuclear envelope in early telophase coincides with the recruitment of a well-characterized class of nuclear pore proteins recognized by the antibody mAb 414, and occurs prior to the incorporation of lamin B1 into the envelope. Significant protein import activity is detectable only after localization of NPA58 in the newly-formed envelope. The early targeting of NPA58 is consistent with its proposed role in nuclear transport.     

Responses of rotifers and cladocerans to Microcystis aeruginosa (Cyanophyceae): A demographic study

The response of selected rotifers and cladocerans to Microcystis aeruginosa, offered as colonies and single cells, was compared to that on a diet of Chlorella vulgaris using the life table demography approach. The test zooplankton species were Simocephalus vetulus, Daphnia carinata, Moina macrocopa, Scapholeberis kingi, Ceriodaphnia cornuta, Brachionus calyciflorus and Hexarthra mira. To detect the development of resistance to toxins from Microcystis in zooplankton, in addition to the laboratory cultured strain of Ceriodaphnia cornuta, another strain of the same species was also used (designated as C. cornuta 2, this was collected from a pond containing Microcystis and cultured in the laboratory on Chlorella for a few weeks prior to experimentation). Experiments were conducted at 20°C and 30°C. Survivorship was high on Chlorella in most species but low on diets of Microcystis. Except for C. cornuta 2, S. kingi and S. vetulus, all other test species were adversely affected by Microcystis. The ability to utilise Microcystis improved at 30°C in M. macrocopa, D. carinata and H. mira. The longest mean lifespan was recorded for C. cornuta 2 (25.3 ± 4.86 d) and the lowest for B. calyciflorus (0.58 ± 0.05 d). The highest net reproductive rate was observed for C. cornuta 1 (44.9 ± 4.88) and the longest generation time of 26.6 ± 2.13 d for S. vetulus. Among the cladocerans that showed positive values of population growth rate (r), M. macrocopa had the highest of 0.96 ± 0.04 per day.     

Bayesian Meta‐Analysis of the Accuracy of a Test for Tuberculous Pleuritis in the Absence of a Gold Standard Reference

Summary Absence of a perfect reference test is an acknowledged source of bias in diagnostic studies. In the case of tuberculous pleuritis, standard reference tests such as smear microscopy, culture and biopsy have poor sensitivity. Yet meta‐analyses of new tests for this disease have always assumed the reference standard is perfect, leading to biased estimates of the new test’s accuracy. We describe a method for joint meta‐analysis of sensitivity and specificity of the diagnostic test under evaluation, while considering the imperfect nature of the reference standard. We use a Bayesian hierarchical model that takes into account within‐ and between‐study variability. We show how to obtain pooled estimates of sensitivity and specificity, and how to plot a hierarchical summary receiver operating characteristic curve. We describe extensions of the model to situations where multiple reference tests are used, and where index and reference tests are conditionally dependent. The performance of the model is evaluated using simulations and illustrated using data from a meta‐analysis of nucleic acid amplification tests (NAATs) for tuberculous pleuritis. The estimate of NAAT specificity was higher and the sensitivity lower compared to a model that assumed that the reference test was perfect.