Archaeology: All that glitters
Archaeometry 48, 229–236 (2006)
Ceramicists have delighted in making lustrous, metallic glazes for far longer than we thought, according to findings from the Near East.
Metallic glazes are familiar in medieval pottery, but now Joris Dik of the Delft University of Technology in the Netherlands and his co-workers have found such material on fragments of a Levantine vessel at Deir ‘Alla in Jordan, dating from the Late Bronze Age (1550–1200 BC). The vessel is decorated with designs in a greyish, sparkly glaze containing natural chromite. The metallic lustre comes from crystals of a calcium–magnesium–iron silicate called augite, the formation of which is induced by chromite.
Cell biology: Nuclear history
Proc. Natl Acad. Sci. USA 103, 7077–7081 (2006)
Nuclear receptors — transcription factors that regulate genes in response to hormonal or metabolic signals — may have a much older heritage than previously thought.
Comparison of the sequences of different genomes has so far definitively identified nuclear receptors only in animals and sponges. But Didier Picard of the University of Geneva, Switzerland, and his colleagues have compared the predicted shapes of animal and fungus proteins to identify what may be a nuclear receptor in the yeast Saccharomyces cerevisiae. If confirmed, this suggests that fungal and animal lineages evolved nuclear receptors before their divergence in the distant past.
Earth science: Going up with a splash
Geology 34, 349–352 (2006)
Researchers have discovered a new type of mantle plume in computer simulations of convection in Earth's molten layers.
Huw Davies of Cardiff University, UK, and Hans-Peter Bunge of the Ludwig Maximilians University in Munich, Germany, observed ‘splash plumes’ forming when a stream of downward-flowing cold matter, which could come from a sinking plate, met a sheet of hot mantle. The structure created looked like the splash of a water droplet — with splash plumes rising from the rim of hot material thrown upwards.
It was previously thought that most plumes welled up from deep in Earth's mantle. Splash plumes may explain recent seismic images, which suggest that some plumes start in the middle of the mantle instead.
Circadian rhythm: CLOCK's surprising HAT
Cell 125, 497–508 (2006)
The body's master pacemaker — the circadian protein CLOCK — operates in the same way as enzymes known as HATs, says a study.
How CLOCK controls daily oscillations in the activity of a host of other circadian genes has been unclear. Paolo Sassone-Corsi at the the Institute of Genetics and Molecular and Cellular Biology in Strasbourg, France, noticed that portions of CLOCK look similar to enyzmes known as histone acetyltransferases, or HATs. These enzymes tag an acetyl group on to histone proteins, around which the DNA in chromosomes is coiled. The researchers confirmed that CLOCK has HAT activity, and showed that cells in which the CLOCK protein lacked its HAT function lost their daily rhythms.
Cosmology: Recycling space
Science doi:10.1126/science.1126231 (2006)
How did the cosmological constant (Λ) — a measure of the acceleration of the Universe's expansion — come to be close to zero, when theory predicts that it should be enormous?
Paul Steinhardt of Princeton University, New Jersey, and Neil Turok at Cambridge University, UK, say the solution might be that our Universe is cyclic. Such a universe would have expanded and contracted repeatedly on a trillion-year timescale, instead of having burst into existence only 13.7 billion years ago. This would have given Λ time to decay, avoiding the problem that cosmic expansion dilutes the Universe in the meantime — for matter is re-concentrated on each cycle.
Evolution: Tropical mix
Proc. Natl Acad. Sci. USA doi:10.1073/pnas.0510383103 (2006)
Is species richness in the tropics (pictured) fuelled by a faster rate of molecular evolution?
Shane Wright of the University of Auckland, New Zealand, and his colleagues compared 45 pairs of closely related plants from tropical and temperate climates. They found that the tropical species had more than double the average DNA mutation rate of their temperate cousins. They argue that increased mutation rate is the cause rather than effect of faster speciation, showing that tropical mutation rates were elevated even in a subset of genera whose temperate components were the more diverse.
The elevated metabolism associated with a warmer climate may be responsible for inducing mutations. However, the researchers could not completely rule out the possibility that genetic drift is simply more rapid in the smaller populations of the tropics.
Cell biology: In three dimensions
Nature Meth. 3, 369–375 (2006)
Traditional two-dimensional cell cultures, grown in the Petri dish, poorly mimic the natural organization of cells. But three-dimensional cultures have been difficult to control, prompting researchers in the United States to develop a fresh approach.
Sangeeta Bhatia of the Massachusetts Institute of Technology and her colleagues used an electric field to organize cells growing in liquid hydrogel into clusters of specific size and shape. The cells were fixed in place when the hydrogel solidified, forming sheets that could be stacked to build three-dimensional structures.
They used the system to show that the three-dimensional organization of chondrocytes, cells found in cartilage, influences the rate of synthesis of molecules important for cartilage function.
Evolutionary ecology: Live fast, die young
Proc. R. Soc. B doi:10.1098/rspb.2006.3544 (2006)
It has been observed that birds or mammals that develop very quickly as embryos tend to have short lives, and vice versa.
Robert Ricklefs of the University of Missouri in St Louis has used simple mathematical models to explore why. He suggests that the risks to an embryo of spending a long time in the egg or womb and the related cost of extended parenting are weighed against the advantages of having a long life in which to reproduce.
For example, sea birds, which have few predators, invest in a long development because their eggs are at a low risk and they can make the most of a long life. By contrast, animals that are likely to be picked off young come into the world in a hurry, and, because their chances of survival are low, are not built to last.
Cancer biology: Off target
Proc. Natl Acad. Sci. USA 103, 7444–7449 (2006)
Resistance to the archetypal ‘targeted’ anticancer drug imatinib (Gleevec) can occur when its target gene BCR-ABL mutates. But mutations in the tumour-suppressor gene p53 can also reduce responsiveness to this drug, according to research.
Gleevec works by blocking the enzyme BCR-ABL kinase, which is encoded by its target gene. Scott Lowe, of Cold Spring Harbor Laboratory in New York State and his colleagues show that one effect of blocking this enzyme is to activate p53. They further show in a mouse model of leukaemia that inactivation of p53 through mutation can reduce the anticancer effectiveness of Gleevec, even when its inhibition of BCR-ABL kinase is unaffected.
Methods: Cut-price genes
Proc. Natl Acad. Sci. USA 10.1073/pnas.0602476103 (2006)
It currently costs about US$10 million to sequence 3 billion base pairs — roughly the size of the human genome — according to the US National Institutes of Health. New devices will help to cut the price. Richard Mathies of the University of California, Berkeley, and his co-workers present one option.
They have developed a ‘lab on a chip’ device that performs all three steps in an established DNA-sequencing technique, known as the Sanger method. The device should reduce costs by minimizing the amount of reagents needed and simplifying the process.
The researchers used the technique to sequence up to 556 continuous bases from a remarkably small sample of DNA — just 1 femtomole. The results (pictured) were 99% accurate.
University of Leeds, UK
A biomechanist wants to predict the energy cost of funny walks.
My main field of research is the mechanics of human and animal movement. I am not content to know how people and animals move: I also want to know why they move as they do.
Why do animals use particular, highly predictable stride frequencies, and exert particular patterns of force on the ground, when they walk or run at particular speeds? Why do people often lift things along curving trajectories, instead of directly vertically?
Questions such as these imply the further question, what would happen if the movement were done differently? But that is hard to discover experimentally. It is difficult enough to train people to perform funny walks, let alone animals. Therefore computer modelling often looks like the best way forward.
In many cases, the most promising hypothesis for why people and animals move as they do says that the chosen pattern of movement minimizes metabolic energy costs. To test this idea by modelling, we need to be able to predict the energy demands of muscles for possible patterns of movement that are not used.
I have tried to do this in studies of gait, with Alberto Minetti, now at the University of Milan, Italy, but have been concerned about the applicability of available data on muscle metabolism.
Now there is a paper that shows how muscular energy costs can be predicted with better accuracy (G. A. Lichtwark and A. M. Wilson J. Exp. Biol. 208, 2831–2843; 2005). The paper tests the improved model against experimental data from muscles oscillating smoothly between contracting and stretching.
For the research that I want to see done, the approach will need to be validated for less-regular movements, but this paper takes a valuable step in the right direction.