Imaging oxygen in neural cell and tissue models by means of anionic cell-permeable phosphorescent nanoparticles

Cell-permeable phosphorescent probes enable the study of cell and tissue oxygenation, bioenergetics, metabolism, and pathological states such as stroke and hypoxia. A number of such probes have been described in recent years, the majority consisting of cationic small molecule and nanoparticle structures. While these probes continue to advance, adequate staining for the study of certain cell types using live imaging techniques remains elusive; this is particularly true for neural cells. Here we introduce novel probes for the analysis of neural cells and tissues: negatively charged poly(methyl methacrylate-co-methacrylic acid)-based nanoparticles impregnated with a phosphorescent Pt(II)-tetrakis(pentafluorophenyl)porphyrin (PtPFPP) dye (this form is referred to as PA1), and with an additional reference/antennae dye poly(9,9-diheptylfluorene-alt-9,9-di-p-tolyl-9H-fluorene) (this form is referred to as PA2). PA1 and PA2 are internalised by endocytosis, result in efficient staining in primary neurons, astrocytes, and PC12 cells and multi-cellular aggregates, and allow for the monitoring of local O₂ levels on a time-resolved fluorescence plate reader and PLIM microscope. PA2 also efficiently stains rat brain slices and permits detailed O₂ imaging experiments using both one and two-photon intensity-based modes and PLIM modes. Multiplexed analysis of embryonic rat brain slices reveals age-dependent staining patterns for PA2 and a highly heterogeneous distribution of O₂ in tissues, which we relate to the localisation of specific progenitor cell populations. Overall, these anionic probes are useful for sensing O₂ levels in various cells and tissues, particularly in neural cells, and facilitate high-resolution imaging of O₂ in 3D tissue models.     

The importance of regional geology in the geological theories of Abraham Gottlob Werner: a contrary opinion

It has been and still is commonly believed by geologists and historians of geology alike that geological theory is an extrapolation from the empirical knowledge of the geology of a region. Abraham Gottlob Werner (1749–1817), whose theory concerning the origin of basalt and the minor role of volcanoes and the major role of water in the history of the earth's crust was eventually proven wrong in some respects, is usually cited as the prime example of a geologist who had not ventured beyond the confines of his native region, Saxony, and had developed a universal geological theory based almost entirely on his observations of that region. In this essay I show that the geology of Saxony played a relatively unimportant role in the development of Werner's universal geological theory; that he became a neptunist before he had closely examined the geology of Saxony; and that his explanation of the history of the earth's crust was as reasonable, if not more reasonable, than the explanations brought forth by those of his contemporaries who opposed his views.     

Substrate ambiguity among the nudix hydrolases: biologically significant, evolutionary remnant, or both?

Many members of the nudix hydrolase family exhibit considerable substrate multispecificity and ambiguity, which raises significant issues when assessing their functions in vivo and gives rise to errors in database annotation. Several display low antimutator activity when expressed in bacterial tester strains as well as some degree of activity in vitro towards mutagenic, oxidized nucleotides such as 8-oxo-dGTP. However, many of these show greater activity towards other nucleotides such as ADP-ribose or diadenosine tetraphosphate (Ap₄A). The antimutator activities have tended to gain prominence in the literature, whereas they may in fact represent the residual activity of an ancestral antimutator enzyme that has become secondary to the more recently evolved major activity after gene duplication. Whether any meaningful antimutagenic function has also been retained in vivo requires very careful assessment. Then again, other examples of substrate ambiguity may indicate as yet unexplored regulatory systems. For example, bacterial Ap₄A hydrolases also efficiently remove pyrophosphate from the 5′ termini of mRNAs, suggesting a potential role for Ap₄A in the control of bacterial mRNA turnover, while the ability of some eukaryotic mRNA decapping enzymes to degrade IDP and dIDP or diphosphoinositol polyphosphates (DIPs) may also be indicative of new regulatory networks in RNA metabolism. DIP phosphohydrolases also degrade diadenosine polyphosphates and inorganic polyphosphates, suggesting further avenues for investigation. This article uses these and other examples to highlight the need for a greater awareness of the possible significance of substrate ambiguity among the nudix hydrolases as well as the need to exert caution when interpreting incomplete analyses.     

High Temperature Properties and Microstructures of Si_3N_4 with AZ-Type Non-Toxic, Non-Oxide Additives

A new type of Si3N4 ceramics (ZAN) is developed in our laboratory. Densification of ZAN is promoted by non-toxic, non-oxide AZ-type additives. In this work high temperature (HT) properties and microstructures of ZAN are investigated.     

Old-growth forests as global carbon sinks

Old-growth forests remove carbon dioxide from the atmosphere at rates that vary with climate and nitrogen deposition. The sequestered carbon dioxide is stored in live woody tissues and slowly decomposing organic matter in litter and soil. Old-growth forests therefore serve as a global carbon dioxide sink, but they are not protected by international treaties, because it is generally thought that ageing forests cease to accumulate carbon. Here we report a search of literature and databases for forest carbon-flux estimates. We find that in forests between 15 and 800 years of age, net ecosystem productivity (the net carbon balance of the forest including soils) is usually positive. Our results demonstrate that old-growth forests can continue to accumulate carbon, contrary to the long-standing view that they are carbon neutral. Over 30 per cent of the global forest area is unmanaged primary forest, and this area contains the remaining old-growth forests. Half of the primary forests (6 x 10(8) hectares) are located in the boreal and temperate regions of the Northern Hemisphere. On the basis of our analysis, these forests alone sequester about 1.3 +/- 0.5 gigatonnes of carbon per year. Thus, our findings suggest that 15 per cent of the global forest area, which is currently not considered when offsetting increasing atmospheric carbon dioxide concentrations, provides at least 10 per cent of the global net ecosystem productivity. Old-growth forests accumulate carbon for centuries and contain large quantities of it. We expect, however, that much of this carbon, even soil carbon, will move back to the atmosphere if these forests are disturbed.