Giant magnetoresistance in organic spin-valves

A spin valve is a layered structure of magnetic and non-magnetic (spacer) materials whose electrical resistance depends on the spin state of electrons passing through the device and so can be controlled by an external magnetic field. The discoveries of giant magnetoresistance and tunnelling magnetoresistance in metallic spin valves have revolutionized applications such as magnetic recording and memory, and launched the new field of spin electronics--'spintronics'. Intense research efforts are now devoted to extending these spin-dependent effects to semiconductor materials. But while there have been noteworthy advances in spin injection and detection using inorganic semiconductors, spin-valve devices with semiconducting spacers have not yet been demonstrated. pi-conjugated organic semiconductors may offer a promising alternative approach to semiconductor spintronics, by virtue of their relatively strong electron-phonon coupling and large spin coherence. Here we report the injection, transport and detection of spin-polarized carriers using an organic semiconductor as the spacer layer in a spin-valve structure, yielding low-temperature giant magnetoresistance effects as large as 40 per cent.     

Historical phenology: grape ripening as a past climate indicator

French records of grape-harvest dates in Burgundy were used to reconstruct spring-summer temperatures from 1370 to 2003 using a process-based phenology model developed for the Pinot Noir grape. Our results reveal that temperatures as high as those reached in the 1990s have occurred several times in Burgundy since 1370. However, the summer of 2003 appears to have been extraordinary, with temperatures that were probably higher than in any other year since 1370.     

Interaction of volkensin with HeLa cells: binding,uptake, intracellular localization,degradation and exocytosis

Among two-chain ribosome-inactivating proteins (RIPs), volkensin is the most toxic to cells and animals, and is retrogradely axonally transported in the rat central nervous system, being an effective suicide transport agent. Here we studied the binding, endocytosis, intracellular routeing, degradation and exocytosis of this RIP. The interaction of volkensin with HeLa cells was compared to that of nigrin b, as an example of a type 2 RIP with low toxicity, and of ricin, as a reference toxin. Nigrin b and volkensin bound to cells with comparable affinity (approx. 10^-10 M) and had a similar number of binding sites (2 × 105/cell), two-log lower than that reported for ricin. The cellular uptake of volkensin was lower than that reported for nigrin b and ricin. Confocal microscopy showed the rapid localization of volkensin in the Golgi stacks with a perinuclear localization similar to that of ricin, while nigrin b was distributed between cytoplasmic dots and the Golgi compartment. Consistently, brefeldin A, which disrupts the Golgi apparatus, protected cells from the inhibition of protein synthesis by volkensin or ricin, whereas it was ineffective in the case of nigrin b. Of the cell-released RIPs, 57% of volkensin and only 5% of ricin were active, whilst exocytosed nigrin b was totally inactive. Despite the low binding to, and uptake by, cells, the high cytotoxicity of volkensin may depend on (i) routeing to the Golgi apparatus, (ii) the low level of degradation, (iii) rapid recycling and (iv) the high percentage of active toxin remaining after exocytosis.Received 21 April 2004; received after revision 26 May 2004; accepted 9 June 2004     

Sequential proteome alterations during genesis and progression of colon cancer

Changes in the proteome of colon mucosal cells accompany the transition from normal mucosa via adenoma and invasive cancer to metastatic disease. Samples from 15 patients with sporadic sigmoid cancers were analyzed. Proteins were separated by two-dimensional gel electrophoresis. Relative differences in expression levels between normal tissue, adenoma, carcinoma and metastasis were evaluated in both intra- and inter-patient comparisons. Up- and down-regulated proteins (<twofold) during development to cancer or metastasis were excised and submitted to peptide mass fingerprinting and MS/MS sequence analysis, facilitated by the use of a compact disc workstation. In total, 112 protein spots were found to be differentially regulated, of which 72 were determined as to protein identity, 46 being up-regulated toward the progression of cancer, and 26 down-regulated. Several of the identifications correlate with proteins of the cell cycle, cytoskeleton or metabolic pathways. The pattern changes now identified have the potential for design of marker panels for assistance in diagnostics and therapeutic strategies in colorectal cancer.Received 2 February 2004; received after revision 16 March 2004; accepted 18 March 2004     

Tonks-Girardeau gas of ultracold atoms in an optical lattice

Strongly correlated quantum systems are among the most intriguing and fundamental systems in physics. One such example is the Tonks-Girardeau gas, proposed about 40 years ago, but until now lacking experimental realization; in such a gas, the repulsive interactions between bosonic particles confined to one dimension dominate the physics of the system. In order to minimize their mutual repulsion, the bosons are prevented from occupying the same position in space. This mimics the Pauli exclusion principle for fermions, causing the bosonic particles to exhibit fermionic properties. However, such bosons do not exhibit completely ideal fermionic (or bosonic) quantum behaviour; for example, this is reflected in their characteristic momentum distribution. Here we report the preparation of a Tonks-Girardeau gas of ultracold rubidium atoms held in a two-dimensional optical lattice formed by two orthogonal standing waves. The addition of a third, shallower lattice potential along the long axis of the quantum gases allows us to enter the Tonks-Girardeau regime by increasing the atoms' effective mass and thereby enhancing the role of interactions. We make a theoretical prediction of the momentum distribution based on an approach in which trapped bosons acquire fermionic properties, finding that it agrees closely with the measured distribution.     

Genome duplication in the teleost fish Tetraodon nigroviridis reveals the early vertebrate proto-karyotype

Tetraodon nigroviridis is a freshwater puffer fish with the smallest known vertebrate genome. Here, we report a draft genome sequence with long-range linkage and substantial anchoring to the 21 Tetraodon chromosomes. Genome analysis provides a greatly improved fish gene catalogue, including identifying key genes previously thought to be absent in fish. Comparison with other vertebrates and a urochordate indicates that fish proteins have diverged markedly faster than their mammalian homologues. Comparison with the human genome suggests approximately 900 previously unannotated human genes. Analysis of the Tetraodon and human genomes shows that whole-genome duplication occurred in the teleost fish lineage, subsequent to its divergence from mammals. The analysis also makes it possible to infer the basic structure of the ancestral bony vertebrate genome, which was composed of 12 chromosomes, and to reconstruct much of the evolutionary history of ancient and recent chromosome rearrangements leading to the modern human karyotype.     

A 'snowball Earth' climate triggered by continental break-up through changes in runoff

Geological and palaeomagnetic studies indicate that ice sheets may have reached the Equator at the end of the Proterozoic eon, 800 to 550 million years ago, leading to the suggestion of a fully ice-covered 'snowball Earth'. Climate model simulations indicate that such a snowball state for the Earth depends on anomalously low atmospheric carbon dioxide concentrations, in addition to the Sun being 6 per cent fainter than it is today. However, the mechanisms producing such low carbon dioxide concentrations remain controversial. Here we assess the effect of the palaeogeographic changes preceding the Sturtian glacial period, 750 million years ago, on the long-term evolution of atmospheric carbon dioxide levels using the coupled climate-geochemical model GEOCLIM. In our simulation, the continental break-up of Rodinia leads to an increase in runoff and hence consumption of carbon dioxide through continental weathering that decreases atmospheric carbon dioxide concentrations by 1,320 p.p.m. This indicates that tectonic changes could have triggered a progressive transition from a 'greenhouse' to an 'icehouse' climate during the Neoproterozoic era. When we combine these results with the concomitant weathering effect of the voluminous basaltic traps erupted throughout the break-up of Rodinia, our simulation results in a snowball glaciation.     

Compact sources as the origin of the soft gamma-ray emission of the Milky Way

The Milky Way is known to be an abundant source of gamma-ray photons, now determined to be mainly diffuse in nature and resulting from interstellar processes. In the soft gamma-ray domain, point sources are expected to dominate, but the lack of sensitive high-resolution observations did not allow for a clear estimate of the contribution from such sources. Even the best imaging experiment revealed only a few point sources, accounting for about 50% of the total Galactic flux. Theoretical studies were unable to explain the remaining intense diffuse emission. Investigating the origin of the soft gamma-rays is therefore necessary to determine the dominant particle acceleration processes and to gain insights into the physical and chemical equilibrium of the interstellar medium. Here we report observations in the soft gamma-ray domain that reveal numerous compact sources. We show that these sources account for the entirety of the Milky Way's emission in soft gamma-rays, leaving at most a minor role for diffuse processes.     

The RickA protein of Rickettsia conorii activates the Arp2/3 complex

Actin polymerization, the main driving force for cell locomotion, is also used by the bacteria Listeria and Shigella and vaccinia virus for intracellular and intercellular movements. Seminal studies have shown the key function of the Arp2/3 complex in nucleating actin and generating a branched array of actin filaments during membrane extension and pathogen movement. Arp2/3 requires activation by proteins such as the WASP-family proteins or ActA of Listeria. We previously reported that actin tails of Rickettsia conorii, another intracellular bacterium, unlike those of Listeria, Shigella or vaccinia, are made of long unbranched actin filaments apparently devoid of Arp2/3 (ref. 4). Here we identify a R. conorii surface protein, RickA, that activates Arp2/3 in vitro, although less efficiently than ActA. In infected cells, Arp2/3 is detected on the rickettsial surface but not in actin tails. When expressed in mammalian cells and targeted to the membrane, RickA induces filopodia. Thus RickA-induced actin polymerization, by generating long actin filaments reminiscent of those present in filopodia, has potential as a tool for studying filopodia formation.     

Netrin-1 controls colorectal tumorigenesis by regulating apoptosis

The expression of the protein DCC (deleted in colorectal cancer) is lost or markedly reduced in numerous cancers and in the majority of colorectal cancers due to loss of heterozygosity in chromosome 18q, and has therefore been proposed to be a tumour suppressor. However, the rarity of mutations found in DCC, the lack of cancer predisposition of DCC mutant mice, and the presence of other tumour suppressor genes in 18q have raised doubts about the function of DCC as a tumour suppressor. Unlike classical tumour suppressors, DCC has been shown to induce apoptosis conditionally: by functioning as a dependence receptor, DCC induces apoptosis unless DCC is engaged by its ligand, netrin-1 (ref. 3). Here we show that inhibition of cell death by enforced expression of netrin-1 in mouse gastrointestinal tract leads to the spontaneous formation of hyperplastic and neoplastic lesions. Moreover, in the adenomatous polyposis coli mutant background associated with adenoma formation, enforced expression of netrin-1 engenders aggressive adenocarcinomatous malignancies. These data demonstrate that netrin-1 can promote intestinal tumour development, probably by regulating cell survival. Thus, a netrin-1 receptor or receptors function as conditional tumour suppressors.