The ortho and para nuclear spin isomers of water have been separated by Tikhonov and Volkov (p. 2363) using a simple adsorption method.
When Life Got Hard
Biomineralization has been thought to have developed in a series of steps before a great jump in complexity near the base of the Cambrian. Wood et al. (p. 2383) now describe a fossil showing complex patterns of biomineralization from rocks dated to 548 million years ago, in the uppermost Precambrian. This organism, named Namapoikia reitogensis, may also have helped the formation of early reefs.
Caught in the Corners
Calixarenes are cyclic molecules designed to capture guest molecules in solution through numerous weak interactions. Atwood et al. (p. 2367) report that crystals of calixarene can play an additional host-guest trick—the interstitial sites between the molecules can trap molecules during crystallization with extraordinary thermal stability through nothing more than weak van der Waals interactions. A number of freon molecules as well as methane can be trapped at low pressures and held up to temperatures well in excess of their boiling points.
Controlling Molecules Through the Turns
Interactions between functional groups in more complex molecules can lead to numerous conformational minima that are separated by relatively low energetic barriers. Because energy tends to redistribute quickly in larger molecules, even ones as small as dipeptides, one might expect that it would be difficult to excite molecules with infrared radiation and interconvert specific conformations. Nonetheless, Dian et al. (p. 2369; see the Perspective by Pratt) used a combination of ultraviolet and infrared spectroscopies to show that in the gas phase, a methyl-capped dipeptide, N-acetyl-tryptophan methyl amide, can be interconverted between three distinct conformers, despite the presence of some 60 conformational minima that have similar energies. The selectivity comes from exciting specific vibrations (in this case, N-H stretches) in the dipeptide that then drive the molecules over a specific barrier.
Electron-electron repulsion should be detrimental to electron pairing in normal metal superconductors. However, some cuprate materials become superconducting near the Mott insulating regime, which brings this intuitive expectation into question. Capone et al. (p. 2364), working on a mechanism to explain the recent observation of superconductivity in fullerenes, show that there are similarities between the two materials. Their model calculations suggest that that the pairing is phonon mediated, as in the case of the normal superconductors, but that the correlations between electrons can actually enhance the superconducting transition temperature.
Arsenic Abatement via Nitrate
The problem of high levels of arsenic in surface and ground water is often compounded by a lack of understanding of the abundance, speciation, or even the source of the arsenic. Senn et al. (p. 2373), through a detailed study over several years of the chemistry of an urban lake near Boston, Massachusetts, show that nitrate, which is also at high levels from fertilizer use, greatly affects arsenic cycling under anoxic conditions. Nitrate helps oxidize As(III) to As(V), which is less toxic, and oxidizes Fe(II) to create hydrous ferric oxide particles that scavenge arsenic.
Ancient Slime Eaters
The sea floor of the eastern Mediterranean is characterized by stratified sediments. Layers of greenish-brown organic sludge, or sapropels, alternate with carbonate oozes that contain microfossils. The fatty acids found in the sapropels suggest that they have a bacterial origin, but large numbers of dividing cells have also been detected. Coolen et al. (p. 2407) have now observed hydrolytic enzyme activity and a slow but significant turnover of glucose in these ancient deposits. These results indicate that sapropel layers more than 200,000 years old are still being modified at a rate that may be relevant to the global carbon cycle. A 16S ribosomal RNA analysis shows that most of these microorganisms are green nonsulfur bacteria. These results have implications for the reconstruction of stable isotopic signatures and Mediterranean sea levels from sapropels.
The recovery of forest diversity after the bolide impact at the end of the Cretaceous occurred much more quickly than has been assumed. Johnson and Ellis (p. 2379), report that a tropical rainforest with diversity similar to modern forests existed in Colorado as soon as 1.4 million years after the impact. These findings suggest that diverse plant species survived the impact and that the North American climate was warm during this period.
Infection Protection During Inflammation
During microbial infection, neutrophils generate microbicidal agents through the release of myeloperoxidase (MPO). Eiserich et al. (p. 2391) report that MPO's actions during inflammation extend beyond generating antimicrobial oxidizing species. MPO permeates the mammalian vasculature and alters blood vessel function during acute inflammation by catabolizing nitric oxide (NO). NO is an endothelial-derived blood vessel relaxant that is produced in response to endotoxin. By reducing NO availability, MPO impairs vascular changes produced by infection. This finding may explain the increased susceptibility of humans deficient in MPO to infection.
Gene Flow in the Field
A field study of the extent of gene flow from genetically modified plants into surrounding crops through cross-pollination is presented by Rieger et al. (p. 2386; see the news story by Stokstad). A strain of canola (rapeseed oil) modified to be resistant to herbicides was first grown commercially in Australia in 2000. An analysis of surrounding fields across widely dispersed geographical samples revealed a low level of cross-pollination between canola fields. The range of long-distance pollination was more random than expected.
A Light Motif
Green algae move in response to light to find conditions that are optimal for photosynthetic growth, and this movement is mediated by photoreceptor currents. Nagel et al. (p. 2395) have identified an opsin-related protein, channelopsin-1, in Chlamydomonas reinhardtii that is likely to be the photoreceptor involved in phototaxis. Expression of channelopsin-1 in the presence of all-trans retinal in Xenopus oocytes produced light-induced proton currents. Characteristics of the conductance suggest that channelopsin-1 forms a light-gated proton channel.
Even a deleterious mutation rarely kills instantly and often persists and accumulates for some generations. McCune et al. (p. 2398) have estimated the frequency of such mutations through separate breeding experiments in two phylogenetically divergent teleost fishes, Lucania goodei and Danio rerio. When the results were compared with Drosophila species and with Xenopus laevis, it was found that animals with very different genome sizes and gene numbers have roughly the same number of lethal mutations.
Destroying Tumors by Special Delivery
Solid tumors do not grow well without a blood supply, and much effort has been directed toward designing drugs that selectively destroy actively growing blood vessels feeding tumors. Hood et al. (p. 2404; see the news story by Couzin) now show that cationic nanoparticles (NPs) can deliver a toxic gene to tumor blood vessels. Vascular targeting and internalization of the NPs was achieved by coupling them to an organic ligand for integrin αvβ3, and death of the target endothelial cells was achieved by coupling the NPs to a mutant Raf gene that blocks cell signaling. Systemic injection of these tailored NPs produced durable regressions of both primary and metastatic tumors in mice.
Genetic Clue to Mental Retardation
One of the receptors for angiotensin II, AGTR1, plays a key role in the regulation of blood pressure and water electrolyte balance. A second receptor, AGTR2, is expressed in a number of tissues including the brain, but its function is poorly understood. Vervoort et al. (p. 2401) identify AGTR2 as the causative gene in a family with X-linked mental retardation and find sequence changes in the gene in several unrelated patients with the disorder. These results suggest that AGTR2 plays a role in brain development, cognitive function, or both. Further study of signaling pathway of AGTR2 may provide insight into the pathogenesis of mental retardation, which affects 2 to 3% of the population.
The Right Conditioning for Gene Therapy
Severe combined immunodeficiency that is caused by a lack of adenosine deaminase has been an attractive target for gene therapy trials in humans. It was hoped that genetically engineered cells would have a growth advantage such that even low levels of correction would be effective in patients. Previous trials showed that low numbers of long-lived genetically corrected cells and low levels of transgene expression were not enough. Aiuti et al. (p. 2410) have worked out a conditioning regimen for patients and cells that provided room in the bone marrow for the growth of the transduced cells. High levels of transduced cells and clinical improvements 1 year after treatment were seen in two patients, who now no longer require enzyme replacement therapy. This approach may be useful in treating other congenital diseases involving the hematopoietic system.
One limitation to ambitious studies of the tree of life is a lack of bacterial fossils that could be used to calibrate timing. This problem is overcome for the intracellular bacterial symbiont, Buchnera, because its phylogeny mirrors that of insect hosts, for which there are fossils. In a comparative genome analysis, Tamas et al. (p. 2376) show that, unlike their close relatives, the more notorious Escherichia coli and Salmonella, the minimalist genomes of Buchnera aphidicola have stayed unchanged for 50 million years. Buchnera's isolation within its host may have allowed genetic drift to shed fragments of the genome and associated mobile elements until only the bare essentials are left.
Regulating Death by Hypoxia
Because of the high incidence of hypoxic disease processes such as heart attack and stroke, there is great need for a better understanding of the biological mechanisms that direct how an organism will respond to hypoxic conditions. Scott et al. (p. 2388; see the Perspective by Longo in SAGE) screened for hypoxia-resistant (Hyp) mutants in the worm Caenorhabditis elegans. Specific alleles of the DAF-2 insulin-like receptor confer a Hyp phenotype. Although DAF-2 mutant worms are known to be longer lived and resistant to various environmental stresses, the hypoxia pathway is distinct from the signaling pathways regulating life-span and stress resistance. In addition, the work shows that DAF-2 activity can be down-regulated prior to exposure to hypoxic conditions and provide a hypoxia-protective effect.