HIV preferentially infects HIV-specific CD4+ T cells

HIV infection is associated with the progressive loss of CD4(+) T cells through their destruction or decreased production. A central, yet unresolved issue of HIV disease is the mechanism for this loss, and in particular whether HIV-specific CD4(+) T cells are preferentially affected. Here we show that HIV-specific memory CD4(+) T cells in infected individuals contain more HIV viral DNA than other memory CD4(+) T cells, at all stages of HIV disease. Additionally, following viral rebound during interruption of antiretroviral therapy, the frequency of HIV viral DNA in the HIV-specific pool of memory CD4(+) T cells increases to a greater extent than in memory CD4(+) T cells of other specificities. These findings show that HIV-specific CD4(+) T cells are preferentially infected by HIV in vivo. This provides a potential mechanism to explain the loss of HIV-specific CD4(+) T-cell responses, and consequently the loss of immunological control of HIV replication. Furthermore, the phenomenon of HIV specifically infecting the very cells that respond to it adds a cautionary note to the practice of structured therapy interruption.     

A case of leucism in the western bluebird ( Sialia mexicana )

Leucism in the western bluebird ( Sialia mexicana ) is reported from La Plata County, Colorado.     

Inference to the best explanation and Norton's material theory of induction

I argue that we should consider Norton's material theory of induction as consisting of two largely independent claims. First, there is the claim that material facts license inductions - a claim which I interpret as a type of contextualism about induction. Second, there is the claim that there are no universal rules of induction. While a good case can be made for the first claim, I believe that Norton's arguments for the second claim are lacking. In particular, I spell out Norton's argument against the claim that all induction may be reduced to inference to the best explanation, and argue that it is not persuasive. Rejecting this part of Norton's theory does not however require us to abandon the first claim that material facts license inductions. In this way, I distinguish the parts of the material theory of induction we should happily accept from the parts about which we should be more skeptical.     

星系对选择的新方法讨论

了解星系对的空间分布和随时间的演化是研究星系的形成和演化的重要手段之一,而其中完备星系对样本的选择是研究的关键.比起光学波段,在红外波段选择和观测星系对有很多优势.介绍了利用红外望远镜Spitzer卫星的SWIRE(the Spitzer Wide-area Infra Red Extragalactic survey)数据选择完备星系对样本的新方法,比较分析了星系对选源标准,得到了初步星系对样本.     

三峡库区湿地研究进展 (三峡地区资源环境生态研究)

对当前三峡库区消落带新生湿地的相关研究进展进行了分类综述，主要包括三峡库区湿地植物生态学研究、湿地生态环境问题研究、湿地保护与可持续利用研究、湿地土壤理化性质研究等4个方面。然而，现有研究中存在的一些不足，主要包括：基础理论与实践研究不够深入；与周边环境耦合关系研究较少；动态研究不足；湿地的空间分布与类型划分不明确；与全球变化关系研究十分薄弱。最后指出，三峡库区湿地研究必将是多学科交叉研究；湿地生态系统的恢复与重构，生态系统演替的长期监测，湿地开发与利用在相当长一段时间内仍是热点；长期定位观测技术、“3S”技术、计算机模拟等技术与方法将会广泛应用于三峡库区湿地的研究。
     

Sodium-dependent uptake of inorganic phosphate by the intracellular malaria parasite

As the malaria parasite, Plasmodium falciparum, grows within its host erythrocyte it induces an increase in the permeability of the erythrocyte membrane to a range of low-molecular-mass solutes, including Na+ and K+ (ref. 1). This results in a progressive increase in the concentration of Na+ in the erythrocyte cytosol. The parasite cytosol has a relatively low Na+ concentration and there is therefore a large inward Na+ gradient across the parasite plasma membrane. Here we show that the parasite exploits the Na+ electrochemical gradient to energize the uptake of inorganic phosphate (P(i)), an essential nutrient. P(i) was taken up into the intracellular parasite by a Na+-dependent transporter, with a stoichiometry of 2Na+:1P(i) and with an apparent preference for the monovalent over the divalent form of P(i). A P(i) transporter (PfPiT) belonging to the PiT family was cloned from the parasite and localized to the parasite surface. Expression of PfPiT in Xenopus oocytes resulted in Na+-dependent P(i) uptake with characteristics similar to those observed for P(i) uptake in the parasite. This study provides new insight into the significance of the malaria-parasite-induced alteration of the ionic composition of its host cell.     

Graphene-based composite materials

Graphene sheets--one-atom-thick two-dimensional layers of sp2-bonded carbon--are predicted to have a range of unusual properties. Their thermal conductivity and mechanical stiffness may rival the remarkable in-plane values for graphite (approximately 3,000 W m(-1) K(-1) and 1,060 GPa, respectively); their fracture strength should be comparable to that of carbon nanotubes for similar types of defects; and recent studies have shown that individual graphene sheets have extraordinary electronic transport properties. One possible route to harnessing these properties for applications would be to incorporate graphene sheets in a composite material. The manufacturing of such composites requires not only that graphene sheets be produced on a sufficient scale but that they also be incorporated, and homogeneously distributed, into various matrices. Graphite, inexpensive and available in large quantity, unfortunately does not readily exfoliate to yield individual graphene sheets. Here we present a general approach for the preparation of graphene-polymer composites via complete exfoliation of graphite and molecular-level dispersion of individual, chemically modified graphene sheets within polymer hosts. A polystyrene-graphene composite formed by this route exhibits a percolation threshold of approximately 0.1 volume per cent for room-temperature electrical conductivity, the lowest reported value for any carbon-based composite except for those involving carbon nanotubes; at only 1 volume per cent, this composite has a conductivity of approximately 0.1 S m(-1), sufficient for many electrical applications. Our bottom-up chemical approach of tuning the graphene sheet properties provides a path to a broad new class of graphene-based materials and their use in a variety of applications.     

A dynamic role for the mushroom bodies in promoting sleep in Drosophila

The fruitfly, Drosophila melanogaster, exhibits many of the cardinal features of sleep, yet little is known about the neural circuits governing its sleep. Here we have performed a screen of GAL4 lines expressing a temperature-sensitive synaptic blocker shibire(ts1) (ref. 2) in a range of discrete neural circuits, and assayed the amount of sleep at different temperatures. We identified three short-sleep lines at the restrictive temperature with shared expression in the mushroom bodies, a neural locus central to learning and memory. Chemical ablation of the mushroom bodies also resulted in reduced sleep. These studies highlight a central role for the mushroom bodies in sleep regulation.