太阳中心探秘

于1995年12月2日发射升空的“太阳及日光层天体探测”卫星（soho）朝着太阳中心作了一次令人惊异的旅行。太阳黑点下究竟蕴藏着什么？为什么围绕着太阳的日冕之内层温度远比其表面高？太阳风是怎么形成的？太阳磁场是一种什么现象？这些是人们想通过Soho号卫星收集到的最新资料来加以解决的问题。揭开太阳的面纱欧洲人研制的太阳探测器——Soho号卫星配备着极为完备的测量仪。科学家们通过先进的卫星得以探查太阳内部最深处，太阳黑子底下的秘密特被人类揭开。对太阳作深入细致探测已经开始。为推断出太阳内部究竟发生着什么，天文学家们一…     

Pyruvate kinase deficiency in mice protects against malaria

The global health impact of malaria is enormous, with an estimated 300-500 million clinical cases and 1 million annual deaths. In humans, initial susceptibility to infection with Plasmodium species, disease severity and ultimate outcome of malaria (self-healing or lethal) are under complex genetic control. Alleles associated with sickle cell anemia, beta-thalassemia and deficiency in glucose-6-phosphate dehydrogenase have a protective effect against malaria and may have been retained by positive selection in areas of endemic malaria. Likewise, genetic variations in erythrocyte antigens and levels of host cytokines affect type and severity of disease. A mouse model of infection with Plasmodium chabaudi was used to study the genetic component of malaria susceptibility. Segregation analyses in informative F2 crosses derived from resistant C57BL/6J and susceptible A/J, C3H and SJL strains using extent of blood stage replication of the parasite and survival as traits mapped three P. chabaudi resistance (Char) loci on chromosomes 9 (Char1), 8 (Char2) and 17 (Char3, MHC-linked). Recombinant congenic strains AcB55 and AcB61 are unusually resistant to malaria despite carrying susceptibility alleles at Char1 and Char2. Malaria resistance in AcB55 and AcB61 is associated with splenomegaly and constitutive reticulocytosis, is inherited in an autosomal recessive fashion and is controlled by a locus on chromosome 3 (Char4). Sequencing of candidate genes from the Char4 region identified a loss-of-function mutation (269T-->A, resulting in the amino acid substitution I90N) in the pyruvate kinase gene (Pklr) that underlies the malaria resistance in AcB55 and AcB61. These results suggest that pyruvate kinase deficiency may similarly protect humans against malaria.     

Controlled vesicle deformation and lysis by single oscillating bubbles

The ability of collapsing (cavitating) bubbles to focus and concentrate energy, forces and stresses is at the root of phenomena such as cavitation damage, sonochemistry or sonoluminescence. In a biomedical context, ultrasound-driven microbubbles have been used to enhance contrast in ultrasonic images. The observation of bubble-enhanced sonoporation--acoustically induced rupture of membranes--has also opened up intriguing possibilities for the therapeutic application of sonoporation as an alternative to cell-wall permeation techniques such as electroporation and particle guns. However, these pioneering experiments have not been able to pinpoint the mechanism by which the violently collapsing bubble opens pores or larger holes in membranes. Here we present an experiment in which gentle (linear) bubble oscillations are sufficient to achieve rupture of lipid membranes. In this regime, the bubble dynamics and the ensuing sonoporation can be accurately controlled. The use of microbubbles as focusing agents makes acoustics on the micrometre scale (microacoustics) a viable tool, with possible applications in cell manipulation and cell-wall permeation as well as in microfluidic devices.     

Palaeobiology: calcification of early vertebrate cartilage

Hagfish and lampreys are unusual for modern vertebrates in that they have no jaws and their skeletons are neither calcified nor strengthened by collagen the cartilaginous elements of their endoskeleton are composed of huge, clumped chondrocytes (cartilage cells). We have discovered that the cartilage in a 370-million-year-old jawless fish, Euphanerops longaevus, was extensively calcified, even though its cellular organization was similar to the non-mineralized type found in lampreys. The calcification of this early lamprey-type cartilage differs from that seen in modern jawed vertebrates, and may represent a parallel evolutionary move towards a mineralized endoskeleton.     

Positive interactions among alpine plants increase with stress

Plants can have positive effects on each other. For example, the accumulation of nutrients, provision of shade, amelioration of disturbance, or protection from herbivores by some species can enhance the performance of neighbouring species. Thus the notion that the distributions and abundances of plant species are independent of other species may be inadequate as a theoretical underpinning for understanding species coexistence and diversity. But there have been no large-scale experiments designed to examine the generality of positive interactions in plant communities and their importance relative to competition. Here we show that the biomass, growth and reproduction of alpine plant species are higher when other plants are nearby. In an experiment conducted in subalpine and alpine plant communities with 115 species in 11 different mountain ranges, we find that competition generally, but not exclusively, dominates interactions at lower elevations where conditions are less physically stressful. In contrast, at high elevations where abiotic stress is high the interactions among plants are predominantly positive. Furthermore, across all high and low sites positive interactions are more important at sites with low temperatures in the early summer, but competition prevails at warmer sites.     

Mitotic spindle organization by a plus-end-directed microtubule motor.

Intracellular microtubule motor proteins may direct the motile properties and/or morphogenesis of the mitotic spindle (reviewed in ref. 3). The recent identification of kinesin-like proteins important for mitosis or meiosis indicates that kinesin-related proteins may play a universal role in eukaryotic cell division, but the precise function of such proteins in mitosis remains unknown. Here we use an in vitro assay for spindle assembly, derived from Xenopus egg extracts, to investigate the role of Eg5, a kinesin-like protein in Xenopus eggs. Eg5 is localized along spindle microtubules, and particularly enriched near spindle poles. Immunodepletion of Eg5 from egg extracts markedly reduces the extent of spindle formation in extracts, as does direct addition of anti-Eg5 antibodies. We also demonstrate that Eg5 is a plus-end-directed microtubule motor in vitro. Our results suggest a novel mechanism for the dynamic self-organization of spindle poles in mitosis.