Boolean analysis of cell regulation networks

A comparison is made between the predictions of the Boolean and continuous analysis of a regulation model when the formation of two mediators interacting by cross-inhibition is stimulated by one or two specific signals. For such a system, the Boolean analysis reproduces the characteristics of behaviour previously predicted by continuous analysis (multiple stable states of opposite type, discontinuous transition, and associated hysteresis phenomenon). The qualitative agreement between the two methods allows a qualitative but rigorous treatment of regulation systems in which the Boolean analysis is applicable. From a general schematic representation of interaction in bidirectional control systems, we analyse by the Boolean method a large range of possible systems of increasing complexities which could theoretically apply. Previously unforeseen consequences of some systems are described. After that, we give a logical analysis of a well-known system (negative loop grafted with additional external controls) and discuss the application of such a system to explain certain oscillatory phenomena in the cell, showing the disrupting role of an additional control on the expected behaviour. Thus, when the analysis of a model including a negative loop does not indicate the possibility of experimentally suggested oscillations, we propose other simple logical structures which can predict this behaviour. Finally, we show a logical analysis of an opposite type of example of cell regulation where the biochemical observations can be accounted for simply by a negative loop grafted with one input variable.     

A Study of the Chronic Effects of Insecticides in Man

Signs of possible chronic intoxication due to insecticides were sought among 441 apple-growers. A group of 170 persons living in the same environment and 162 other persons having no contact with insecticides were used as controls. It was the first attempt to determine signs of chronic intoxication by organic phosphate and chlorinated hydrocarbon insecticides. The greater incidence of leukopenia and of neurologic manifestations found among the subjects suggest that insecticides may have some chronic effects in man. This assumption is reinforced by the similarities in the findings between the subjects and the environments, and by the parallelism between the duration of exposure to insecticides and the number of affected subjects. The repetition of this study at five-year intervals seems desirable until a sufficient number of apple-growers have been studied who have been exposed to large doses of insecticides for 10, 15 or 20 years.     

RFLP of RT-PCR products: Application to the expression ofCHS multigene family in poplar

A novel method for studying differential expression of multigene family members based on the high sensitivity of RT-PCR completed by restriction site polymorphism of DNA is described. This method allows the identification of specific patterns of expression of fourchalcone synthase genes in a Hunnegem poplar clone (Populus trichocarpa ×Populus deltoides).     

Until death do us part? In-depth insights into Dutch consumers’ considerations about product lifetimes and lifetime extension

Long-lasting electronic products contribute to a sustainable society; however, both expected and actual lifetimes are in decline. This research provides in-depth insights into consumers’ considerations about product lifetimes, barriers to extending lifetimes, and responses to a product lifetime label. Results of interviews (n = 22) with Dutch consumers suggest a positive view on long-lasting products. Nevertheless, their products’ value depreciated during their lifetimes. Consumers consider themselves unable to estimate how long products should last, which can be detrimental as low expectations tend to negatively influence actual lifetimes. Also, use intensity and consumers’ care(less) behavior influence the lifetime. To extend product lifetimes, consumers often disregard the option of repairing malfunctioning products. They have limited knowledge and ability, and believe repair provides poor value for money. Lifetime extension can also be hindered by market-related factors, such as convenient replacement services, new technological developments, and (attractive) deals. We suggest a product lifetime label should contain relevant and reliable information; furthermore, we recommend including (extended) warranty information. When information about repairability is included, potential negative responses should be considered. Finally, raising awareness about the environmental impact of short-lived products via a label may have a positive effect but requires more research attention.     

Parthenogenesis in an elasmobranch in the presence of conspecific males

Parthenogenesis has been observed in several elasmobranch species, primarily in public aquaria. The majority of cases of parthenogenesis have occurred either when females were held without males or once a male was removed from a female's habitat. Here we report a second instance of parthenogenesis in a zebra shark female that was housed with conspecific mature males. This study calls into question the conditions under which elasmobranch females undergo parthenogenesis.     

Importance of canopy structure on photosynthesis in single- and multi-species assemblages of marine macroalgae

Plant communities utilize available irradiance with different efficiency depending not only on their photosynthetic characteristics but also on the canopy structure and density. The importance of canopy structure are well studied in terrestrial plant communities but poorly studied in aquatic plant communities. The objective of this study was to evaluate macroalgal community photosynthesis in artificial constructed communities of one to four species with different morphologies along a range of leaf (i.e.=thallus) area densities. In a laboratory set-up we measured net photosynthesis and dark respiration in constructed assemblages of macroalgae, excluding effects other than photosynthesis of individual tissue and distribution of photons in the canopy from influencing metabolism. We hypothezised that 1) canopy structure determines the actual rates of photosynthesis relative to the optimal rates and 2) multi-species communities attain higher maximum photosynthetic rates than single species communities. We found that differences in canopy structure outweighed large differences in tissue photosynthesis resulting in relatively similar maximum community photosynthetic rates among the different single and multi-species assemblages (20.1–40.5 μmol O₂ m⁻² s⁻¹). Canopy structure influenced community photosynthesis both at low and high leaf area densities because it determines the ability of macroalgae to use the photosynthetic potential of their individual tissues. Due to an averaging effect the photosynthetic rate at high leaf area density was more similar among multi-species community than among single-species communities. Multi-species communities had, on average, a slightly higher photosynthetic production than expected from photosynthesis of single species communities. Moreover multi-species communities were capable of exposing new tissue to irradiance up to high densities thereby avoiding a decrease in net photosynthesis. This finding suggests that multi-species communities may be able to maintain higher biomass per unit ground area than single-species communities.     

Novel cyanoguanidines with potent oral antitumour activity

4-Pyridyl cyanoguanidines with hydrophobic aromatic side chains showed potent antiproliferative activity in the human breast and lung cancer cell lines MCF-7, NYH and H460. In vivo, treatment with N-(6-chlorophenoxyhexyl)-N′-cyano-N″-4-pyridylguanidine (18, 20 mg/kg/day po.), gave a complete remission of tumours in a model of NYH inoculated nude mice.     

The MUC5AC gene: RFLP analysis with the Jer58 probe

We have recently obtained evidence that the locus corresponding to three groups of partial tracheobronchial cDNAs (A=Jer47, B=Jer57, C=Jer58) which mapped to chromosome 11p15 and was given the symbol MUC5 corresponds to two distinct genes which we have provisionally called MUC5B and MUC5AC. Here we describe the detection, using the Jer58 probe, which contains a 24-bp tandem repeat, of polymorphism in the MUC5AC gene with seven different restriction enzymes.