Malaria: Resistant mozzies
Science 312, 577–579 (2006)
Researchers have honed in on the genes that make some mosquitoes resistant to the malaria parasite Plasmodium falciparum.
A group led by the University of Minnesota's Kenneth Vernick fed malaria-infected blood to more than 1,000 Anopheles gambiae mosquitoes captured in Mali. After seven days, the researchers grouped the insects by the number of parasites in their mid-gut. By comparing the DNA of mosquitoes in the different groups, they traced resistance to a single region of the genome. They also used RNA interference to pinpoint one immunity gene, known as APL1, that controls parasite number.
The researchers speculate that mosquitoes are naturally resistant to malaria, and that a small number — which could be targeted as part of a control strategy — become susceptible through defects in their immune system.
Nuclear physics: Extending the elements
Phys. Rev. Lett. 96, 142502 (2006)
Where does the Universe get its heavy metals from? The formation of elements heavier than iron happens in supernovae, where atoms absorb extra neutrons and protons. But this doesn't explain the observed abundances of all elements, such as some proton-rich isotopes of ruthenium and molybdenum.
Carla Fröhlich of the University of Basel, Switzerland, and her co-workers propose a new mechanism for how some of these elements form. They say that a supernova explosion produces a short-lived shell of proton-rich material. The protons aren't readily captured by large, proton-rich nuclei because of their mutual repulsion. But by combining with antineutrinos, which are also common in the debris, the protons may become neutrons. The neutrons are then easily absorbed by nuclei, building heavier elements.
Polar science: Wind of change
Geophys. Res. Lett. 33, L08605 (2006)
Fragmentation of sea ice may accelerate melting in the Arctic by strengthening wind-driven currents, say researchers in Japan, Canada and the United States.
During the late 1990s, sea-ice cover in the Pacific quadrant of the Arctic more than halved. The sudden and dramatic melting, following a period of slow decline, was linked to an increased inflow of warm, summer water from the Pacific. But it was unclear what had changed, and why the ice did not recover.
Koji Shimada of the Institute of Observational Research for Global Change in Yokosuka, Japan, and his colleagues blame a novel feedback mechanism. Field research (pictured) shows that the gradually shrinking ice sheet had become more mobile. They suggest that this allowed the prevailing winds to set up currents that washed in the warm water, pushing the system over a threshold.
Synthetic chemistry: Two more ways to Tamiflu
J. Am. Chem. Soc. doi:10.1021/ja0616433; 10.1021/ja061696k (2006)
Two new methods have been devised to synthesize the anti-influenza drug oseltamivir.
Demand for the drug, also known as Tamiflu, has soared amidst fears that bird flu might mutate to trigger a human flu pandemic. The new syntheses avoid one of the problems that has limited production so far: a difficult-to-obtain starting material known as shikimic acid.
One reaction scheme, from E. J. Corey's group at Harvard University in Cambridge, Massachusetts, begins with the simple molecules butadiene and acrylic acid. The second, more complex synthesis, designed by Masakatsu Shibasaki of the University of Tokyo, Japan, and his colleagues, uses compounds known as meso-aziridines as a starting material.
Immunology: Baby's first bacteria
J. Exp. Med. 203, 973–984 (2006)
When babies encounter bacteria in the birth canal, it may teach them that the body's bugs are harmless.
Mathias Hornef of the University Clinic of Freiburg and his colleagues show in mice that epithelial cells lining the gut react to a bacterial endotoxin and release inflammatory molecules before birth — but the same cells do not do so in newborns or adults.
The authors present evidence that endotoxin from the mother's microflora, possibly from the vaginal tract, passes through the mouths of babies. This briefly stimulates the gut cells and teaches them to tolerate certain bugs, something not seen in babies born by caesarean section. The process may help useful bacteria to set up shop in babies' intestines after birth.
Materials science: Modern alchemy
Science 312, 420–424 (2006)
Materials scientists have come up with a modern-day twist to the alchemists' dream of turning base metals into gold. They have turned gold and silver into diamond — or at least, diamond-like crystals.
Bartosz Grzybowski of Northwestern University in Evanston, Illinois, and his colleagues started with an aqueous solution of gold or silver nanoparticles capped with a single layer of organic molecules. By evaporating the water from the solution, they grew crystals in which the particles were arranged like the carbon atoms in diamond. Binary superlattices containing both gold and silver nanoparticles also showed diamond-like packing.
The structure is unusual because the forces between such particles generally make them close-packed: here, weak attractive interactions allow for a more spacious arrangement. Each micrometre-sized crystal (pictured) contains millions of nanoparticles.
Microbiology: Parasitic rodeo
Cell 125, 261–274 (2006)
Researchers have found that the common food-borne parasite Toxoplasma gondii uses a cowboy trick to rustle nutrients from its host.
Isabelle Coppens of Johns Hopkins University in Baltimore, Maryland, and her colleagues show that the parasite co-opts the host cell's microtubule network to lasso nutrient-rich lysosomes. The parasite wraps the lysosome in a protein called GRA7 before engulfing it. The role of the protein is not clear, but parasites engineered to lack it could not corral the lysosomes, leading to their death.
Chemistry: No flop means less flip
J. Am. Chem. Soc. 128, 5332–5333 (2006)
Thanks to the violation of mirror symmetry, or parity, in processes involving the weak nuclear force, the two enantiomers of a chiral molecule — mirror-image molecules that cannot be superimposed — should have different vibrational energies. The difference is so tiny that it has never been detected, but Andrey Fokin of the Justus Liebig University in Giessen, Germany, and his co-workers are not ready to give up.
The researchers have made chiral molecules that they say are well suited to searching for the effect.The molecules have four different halogens at the corners of a carbon-cube (cubane) framework. The molecules' rigid framework would help to reduce noise in the measurement because, unlike the floppier molecules tested so far, the configuration is less likely to switch between enantiomers.
Immunology: A tale of betrayal
Nature Immunol. doi:10.1038/ni1336; 10.1038/ni1344; 10.1038/ni1346 (2006)
The flagellin protein that bacteria use to make their propellor-like filaments can betray the bugs when they infect cells. A trio of papers unpicks how this happens to Salmonella typhimurium (pictured).
It was already known that the host cell receptor ‘Toll-like receptor 5’ detects flagellin to trigger an immune response. Now two groups in the United States have shown that a second part of the immune response to Salmonella, mediated by the receptor Ipaf, also depends on flagellin.
Researchers at the National Institute of Immunology in New Delhi, India, show that Salmonella's production of flagellin is boosted by lipids in the host cell — which should make the bugs easier to detect.
Yoshinori Watanabe University of Tokyo, Japan
A geneticist reveals an unexpected pattern of chromosome segregation.
Recent experiments have reshaped my ideas about how chromosomes behave in the two types of cell division — mitosis and meiosis.
Chromosomes in cells exist in pairs. Human cells have 23 pairs, for example. One chromosome in each pair is derived from dad, the other from mum. When the cell divides, these chromosomes are copied and then shared out between the daughter cells.
Mitosis produces identical daughter cells — with one copy of each ‘mum’ chromosome and one of each ‘dad’. I had thought, wrongly as it turns out, that the way mum and dad chromosomes divide in mitosis was always independent of each other.
Sometimes, genetic material is shuffled between the mum and dad chromosomes in a pair. This process is known as recombination. Pentao Liu and his colleagues from the National Cancer Institute in Frederick, Maryland, showed that recombined chromosomes in mouse embryonic stem cells always segregated into different daughter cells (P. Lui et al. Nature Genet. 30, 66–72; 2002), whereas I had supposed it should be random.
A further blow to my preconceived notions came from Athanasios Armakolas and Amar Klar of the National Cancer Institute (A. Armakolas & A. Klar Science 311, 1146–1149; 2006). They found that the segregation pattern of recombined chromosomes changes as the stem cells differentiate into more specialized cells.
This hints to me how meiosis, which I study, evolved from mitosis. In meiosis, the chromosomes are divided so that one daughter cell gets both mum chromosomes, the other both dads. Recombination, which may take place even during the repair of an injured chromosome, seems to have an intrinsic ability to shift mitosis towards splitting mums and dads, the hallmark of meiosis.