Fluorescent latex microspheres as a retrograde neuronal marker for in vivo and in vitro studies of visual cortex

The use of retrograde axonal transport of various substances (for example, enzymes, lectins, synthetic fluorescent compounds) has yielded much information on the organization of neuronal pathways. Each type of retrograde tracer has its own set of attributes which define the scope of problems it can address. We describe here a new class of retrograde tracer, rhodamine-labelled fluorescent latex microspheres (0.02-0.2 micron diameter), which have distinct advantages over other available tracers for in vivo and in vitro applications. When injected into brain tissue, these microspheres show little diffusion and consequently produce small, sharply defined injection sites. Once transported back to neuronal somata, the label persists for at least 10 weeks in vivo and 1 yr after fixation. Microspheres have no obvious cytotoxicity or phototoxicity as assessed by intracellular recording and staining of retrogradely labelled cells in a cortical brain slice preparation. This approach was further used to visualize and compare, in cat visual cortex slices, neurones with different projection patterns, and revealed significant differences in patterns of intrinsic axons and dendrites. These properties of microspheres open new avenues for anatomical and physiological studies of identified projection neurones in slices as well as in dissociated cell cultures.     

Detection of an intermediate of photosynthetic water oxidation

The oxygen that we breathe is produced by photosystem II of cyanobacteria and plants. The catalytic centre, a Mn4Ca cluster, accumulates four oxidizing equivalents before oxygen is formed, seemingly in a single reaction step 2H2O<==>O2 + 4H+ + 4e-. The energy and cycling of this reaction derives solely from light. No intermediate oxidation product of water has been detected so far. Here, we shifted the equilibrium of the terminal reaction backward by increasing the oxygen pressure and monitoring (by absorption transients in the near-ultraviolet spectrum) the electron transfer from bound water into the catalytic centre. A tenfold increase of ambient oxygen pressure (2.3 bar) half-suppressed the full progression to oxygen. The remaining electron transfer at saturating pressure (30 bar) was compatible with the formation of a stabilized intermediate. The abstraction of four electrons from water was probably split into at least two electron transfers: mildly endergonic from the centre's highest oxidation state to an intermediate, and exergonic from the intermediate to oxygen. There is little leeway for photosynthetic organisms to push the atmospheric oxygen concentration much above the present level.     

Iron-sulfur proteins: Recent developments in the field

Summary Iron-sulfur clusters in proteins are now recognized as among the main types of electron-transferring groups in biological systems, besides heme and flavins. Recent developments have brought forth a better understanding about the ways the protein environment modulates the potential of the cluster by placing the cluster in a more or less hydrophobic surrounding. Refinement in models, extensive studies on the kinetics of electron transfer (e.g. by measurement of the electronic spin lattice relaxation time) and the introduction of novel spectroscopic methods (EXAFS, magnetic CD and others) in the elucidation of structures in various systems are among the main developments. Other advances include EPR studies of the spatial orientation of Fe−S centers in complex membraneous systems (e.g. in mitochondria) and the recent elucidation of the nature of center X in photosystem I by M?ssbauer-spectroscopy. M?ssbauer studies have also been described on a number of Fe−S proteins (nitrogenase, aconitase, some ferredoxins, etc.) and revealed the existence of novel structures that enlarged the number of known basic units of Fe−S centers. These advances include: 1. the discovery of a novel non-heme Fe-protein (called desulforedoxin) of the rebredoxin type, 2. the elucidation of the nitrogenase Fe−S centers and the nitrogenase cofactor and 3. the discovery of a three-iron cluster in several enzymes and some ferredoxins. The latter 3-Fe cluster seems capable of being converted into a classical 4-Fe cluster under appropriate conditions, a phenomenon that plays a role in activation-deactivation of some enzymes (e.g. aconitase). It is now recognized that some iron-sulfur clusters may be involved in systems devoided of any oxydation-reduction reaction and may act as sensors of the surrounding redox potential, triggering the activation/deactivation of an enzyme (cf. e.g. aconitase).     

Mei-P26 regulates microRNAs and cell growth in the Drosophila ovarian stem cell lineage

Drosophila neuroblasts and ovarian stem cells are well characterized models for stem cell biology. In both cell types, one daughter cell self-renews continuously while the other undergoes a limited number of divisions, stops to proliferate mitotically and differentiates. Whereas neuroblasts segregate the Trim-NHL (tripartite motif and Ncl-1, HT2A and Lin-41 domain)-containing protein Brain tumour (Brat) into one of the two daughter cells, ovarian stem cells are regulated by an extracellular signal from the surrounding stem cell niche. After division, one daughter cell looses niche contact. It undergoes 4 transit-amplifying divisions to form a cyst of 16 interconnected cells that reduce their rate of growth and stop to proliferate mitotically. Here we show that the Trim-NHL protein Mei-P26 (refs 7, 8) restricts growth and proliferation in the ovarian stem cell lineage. Mei-P26 expression is low in stem cells but is strongly induced in 16-cell cysts. In mei-P26 mutants, transit-amplifying cells are larger and proliferate indefinitely leading to the formation of an ovarian tumour. Like brat, mei-P26 regulates nucleolar size and can induce differentiation in Drosophila neuroblasts, suggesting that these genes act through the same pathway. We identify Argonaute-1, a component of the RISC complex, as a common binding partner of Brat and Mei-P26, and show that Mei-P26 acts by inhibiting the microRNA pathway. Mei-P26 and Brat have a similar domain composition that is also found in other tumour suppressors and might be a defining property of a new family of microRNA regulators that act specifically in stem cell lineages.     

Moulting hormone inLocusta migratoria: Rate of Ecdysone 20-hydroxylation and excretion during the last larval instar

Zusammenfassung Der Titer von Ecdyson und Ecdysteron in Heuschrecken (Locusta migratoria) des V. Larvenstadiums wurde getrennt bestimmt. Ecdysteron herrscht zur Zeit des Titermaximums vor. Durch Injektion von radioaktivem Ecdyson wird gezeigt, dass dies durch ein Ansteigen der Steroid-20-Hydroxylase-Aktivität verursacht wird. Die Ausscheidung von Häutungshormonen mit dem Kot sorgt für das Sinken der Häutungshormon-Konzentration in den Tieren.     

A rapid and simple method for the isolation of pure eosinophilic leukocytes from horse blood

Summary An improved and short method is described for the isolation of intact eosinophilic leukocytes from horse blood with high yield (1–1.5 g/20 1). Viability and purity of the preparations were verified by light and electron microscopy and by the trypan blue exclusion test. Isolated eosinophils were 98–100% pure, intact and viable, and they could be shown to phagocytise immune-complexes.The authors are indebted to the Schweizerischer Nationalfonds zur Förderung der wissenschaftlichen Forschung for financial support.     

相变储能大体积混凝土的控温性能

提出相变控温储能材料机敏控制混凝土结构温度裂缝技术途径.在混凝土浇注过程中将相变材料掺入使之与混凝土结构一体化,利用相变材料在特定温度范围的热效应控制混凝土内部温度场,从而机敏控制温度应力防止温度裂缝.通过自行设计的温度测试系统,对相变控温混凝土控温性能进行实测研究,结果表明:相变材料不但可以降低大体积混凝土的最高绝热温升值,而且可以降低大体积混凝土升温速度和降温速度,从根本上防止了大体积混凝土温度裂缝的出现.     

Accurate whole-genome sequencing and haplotyping from 10 to 20 human cells

Recent advances in whole-genome sequencing have brought the vision of personal genomics and genomic medicine closer to reality. However, current methods lack clinical accuracy and the ability to describe the context (haplotypes) in which genome variants co-occur in a cost-effective manner. Here we describe a low-cost DNA sequencing and haplotyping process, long fragment read (LFR) technology, which is similar to sequencing long single DNA molecules without cloning or separation of metaphase chromosomes. In this study, ten LFR libraries were made using only ～100?picograms of human DNA per sample. Up to 97% of the heterozygous single nucleotide variants were assembled into long haplotype contigs. Removal of false positive single nucleotide variants not phased by multiple LFR haplotypes resulted in a final genome error rate of 1 in 10?megabases. Cost-effective and accurate genome sequencing and haplotyping from 10-20 human cells, as demonstrated here, will enable comprehensive genetic studies and diverse clinical applications.     

Electro-optical shift

Zusammenfassung Erzeugt man in einem flüssigen Dielektrikum, wie wasserfreiem Äthanol, Schwefelkohlenstoff, p-Tolylazetat oder Nitrobenzol, zwischen speziell gestalteten Elektroden ein elektrisches Feld von etwa 10000 V/cm, so wird ein Lichtstrahl, der die im Feld befindlichen Teile der Flüssigkeit durchsetzt, gekrümmt. Die Ablenkung des Strahls aus der geraden Richtung beträgt in manchen Fällen 1°.