The Kinetics of Polyethylenimine-Mediated Transfection in Suspension Cultures of Chinese Hamster Ovary Cells

The kinetics of polyethylenimine (PEI)-mediated gene transfer at early times after transfection of Chinese hamster ovary (CHO) cell in suspension were investigated using a novel in vitro assay. Addition of an excess of competitor DNA to the culture medium at various times after the initiation of transfection inhibited further cellular uptake of PEI–DNA particles. Using this approach, a constant rate of particle uptake was observed during the first 60 min of transfection at a PEI:DNA ratio of 2:1 (w/w) and a cell density of 2 × 10⁶ cells/ml under serum-free conditions. The uptake rate declined considerably during the next 2 h of transfection. Both the rate and the level of PEI–DNA uptake in serum-free minimal medium were found to be dependent on the PEI–DNA ratio, the cell density at the time of transfection, and the extent of particle aggregation. These studies of the early phase of PEI-mediated transfection are expected to lead to further opportunities for optimization of gene transfer to suspension cultures of mammalian cells for the purpose of large-scale transient recombinant protein production.     

The differentiation of cytoskeletal structures in nematocytes of Hydra

Nematocytes of hydra feature a complex cytoskeleton consisting mainly of several bundles of actin filaments and a basket-like structure formed by microtubules. The aim of this study was to establish the sequence of appearance of cytoskeletal elements during nematocyte development using immuno-fluorescence and electron microscopical techniques. Our results are a first step in trying to understand developmental hierarchies and mechanisms which govern the synthesis and assembly of the cytoskeleton in nematocytes. The finger-shaped rods around the apex of the capsule are the first detectable elements of the cytoskeleton. Microtubules of the basket structure then follow and later, the actin filaments of microvilli which support the cnidocil. The actin filaments, however, do not show the highly ordered bundling pattern characteristic of filaments in functional nematocytes.     

Improving Environmental Sanitation, Health, and Well-Being: A Conceptual Framework for Integral Interventions

We introduce a conceptual framework for improving health and environmental sanitation in urban and peri-urban areas using an approach combining health, ecological, and socioeconomic and cultural assessments. The framework takes into account the three main components: i) health status, ii) physical environment, and iii) socioeconomic and cultural environment. Information on each of these three components can be obtained by using standard disciplinary methods and an innovative combination of these methods. In this way, analyses lead to extended characterization of health, ecological, and social risks while allowing the comprehensive identification of critical control points (CCPs) in relation to biomedical, epidemiological, ecological, and socioeconomic and cultural factors. The proposed concept complements the conventional CCP approach by including an actor perspective that considers vulnerability to risk and patterns of resilience. Interventions deriving from the comprehensive analysis consider biomedical, engineering, and social science perspectives, or a combination of them. By this way, the proposed framework jointly addresses health and environmental sanitation improvements, and recovery and reuse of natural resources. Moreover, interventions encompass not only technical solutions but also behavioral, social, and institutional changes which are derived from the identified resilience patterns. The interventions are assessed with regards to their potential to eliminate or reduce specific risk factors and vulnerability, enhance health status, and assure equity. The framework is conceptualized and validated for the context of urban and peri-urban settings in developing countries focusing on waste, such as excreta, wastewater, and solid waste, their influence on food quality, and their related pathogens, nutrients, and chemical pollutants.