Transport and diffusion of Tau protein in neurons

In highly polarized and elongated cells such as neurons, Tau protein must enter and move down the axon to fulfill its biological task of stabilizing axonal microtubules. Therefore, cellular systems for distributing Tau molecules are needed. This review discusses different mechanisms that have been proposed to contribute to the dispersion of Tau molecules in neurons. They include (1) directed transport along microtubules as cargo of tubulin complexes and/or motor proteins, (2) diffusion, either through the cytosolic space or along microtubules, and (3) mRNA-based mechanisms such as transport of Tau mRNA into axons and local translation. Diffusion along the microtubule lattice or through the cytosol appear to be the major mechanisms for axonal distribution of Tau protein in the short-to-intermediate range over distances of up to a millimetre. The high diffusion coefficients ensure that Tau can distribute evenly throughout the axonal volume as well as along microtubules. Motor protein-dependent transport of Tau dominates over longer distances and time scales. At low near-physiological levels, Tau is co-transported along with short microtubules from cell bodies into axons by cytoplasmic dynein and kinesin family members at rates of slow axonal transport.     

离子选择电极应用研究——乙醇-水混合溶剂中硝酸根对铅离子的配合平衡

本文用铅离子选择电极测定了乙醇-水混合溶剂中Pb-NO_3配合物的稳定常数.实验证明,铅和硝酸根可以形成PbNO_3~+和Pb(NO_3)_2两种配合物。所计算的热力学稳定常数表明溶剂中乙醇含量直到76%(w/w)lgβ_i°-1/ε都呈直线关系.     

Applied embryology: no surrogate British mothers

Beardsley reports on the British Medical Association's decision to caution its members against involvement in surrogate motherhood arrangements. The Association's recommendation, together with a House of Commons bill that would make it illegal for agencies to coordinate such arrangements, will likely prevent expansion of the surrogate mother industry in Britain. Concern for the well-being of children born as a result of surrogate pregnancies, as well as apprehension over potential legal difficulties, were behind the BMA's decision. The government's Warnock committee, studying this and other reproductive issues, could be influenced by the BMA's action.     

UK drug trials: row over student trial

The British Medicines Commission has undertaken an urgent review of arrangements for testing new drugs on healthy volunteers in the wake of charges that one company, Charterhouse Clinical Research Unit Ltd., was using London students in toxicity tests of an antitumor drug without having informed the volunteers' physicians of the risks involved and without plans for long-term monitoring of the participants' health. Under current British law, drug studies with healthy volunteers are regarded as a private matter between the volunteers and the drug companies, which vary in their practices on disclosure of risks and compensation for injuries.     

In vitro fertilization: MRC tests the climate

It is reported that Britain's Medical Research Council has published guidelines for MRC-supported research involving human embryos obtained through in vitro fertilization. In ethics committee-approved projects, researchers may use deliberately fertilized ova or, with parents' consent, fertilized ova left over from therapeutic programs. In vitro culture of human embryos is permitted only up to the implantation stage. Conditions are also set for experiments on interspecies fertilization and on freezing of embryos. Concern over physician and public reception of these guidelines has been expressed by the British Medical Association.     

Increasing risk of Amazonian drought due to decreasing aerosol pollution

The Amazon rainforest plays a crucial role in the climate system, helping to drive atmospheric circulations in the tropics by absorbing energy and recycling about half of the rainfall that falls on it. This region (Amazonia) is also estimated to contain about one-tenth of the total carbon stored in land ecosystems, and to account for one-tenth of global, net primary productivity. The resilience of the forest to the combined pressures of deforestation and global warming is therefore of great concern, especially as some general circulation models (GCMs) predict a severe drying of Amazonia in the twenty-first century. Here we analyse these climate projections with reference to the 2005 drought in western Amazonia, which was associated with unusually warm North Atlantic sea surface temperatures (SSTs). We show that reduction of dry-season (July-October) rainfall in western Amazonia correlates well with an index of the north-south SST gradient across the equatorial Atlantic (the 'Atlantic N-S gradient'). Our climate model is unusual among current GCMs in that it is able to reproduce this relationship and also the observed twentieth-century multidecadal variability in the Atlantic N-S gradient, provided that the effects of aerosols are included in the model. Simulations for the twenty-first century using the same model show a strong tendency for the SST conditions associated with the 2005 drought to become much more common, owing to continuing reductions in reflective aerosol pollution in the Northern Hemisphere.