Cancer: Telomeres on a short leash

Cancer Cell 7, 25–37 (2005)

Treatments that throw a double punch at chromosome ends could kill off cancer cells, Hiroyuki Seimiya et al. suggest. DNA sequences known as telomeres, typically found at chromosome ends, help normal cells keep tabs on how many times they have divided. Chromosomes must be replicated before cells can divide, but the very tips of telomeres cannot be copied, so, with each division, these sequences get shorter and shorter. Eventually, they become so truncated that the DNA cannot be properly replicated, and the cell stops dividing.

Cancer cells, however, contain an activated enzyme called telomerase, which prevents telomeres from shortening and leads to uncontrolled proliferation. So researchers have been developing treatments that inhibit this enzyme. But these therapies do not always succeed, and can produce drug resistance.

To develop a better treatment option, Seimiya et al. investigated what happened when they inhibited both telomerase and another enzyme, tankyrase 1, that helps it gain access to telomeres. This enhanced the shortening of these chromosomal ends, and accelerated cancer-cell death. The authors suggest that tankyrase 1 inhibitors might significantly boost the efficacy of telomere-targeted therapies.

Roxanne Khamsi

Developmental biology: Switch of fate

Cell 120, 123–135; 137–149 (2005)

Neurons produce two very distinct types of projection: a single axon, which passes signals on to neighbouring cells, and numerous dendrites, which receive signals from axons. Two groups have now found that an enzyme called glycogen synthase kinase-3β (GSK-3β) helps to determine what a projection becomes.

Hui Jiang et al. and Takeshi Yoshimura et al. showed that GSK-3β blocks the formation of axons. When they boosted the activity of GSK-3β in cultured neurons, the cells often lacked axons completely. Conversely, when GSK-3β was inhibited, the cells sprouted several axons — or converted existing dendrites into axons.

The groups went on to identify molecules working upstream and downstream of GSK-3β. They showed that GSK-3β is tagged with phosphate groups and thereby activated by the enzyme Akt. GSK-3β then itself phosphorylates and inhibits a molecule called CRMP-2, which normally promotes the assembly of the neuron's internal ‘skeleton’ and hence axon growth.

The discovery raises the possibility that drugs that block GSK-3β could be used to promote axonal growth and so enhance the repair of neuronal injuries, although the researchers have not yet shown that the new axons would work normally in animals.

Helen Pearson

Astronomy: Dusty dwarfs

Astrophys. J. (in the press)

Brown dwarfs are the failed stars of the cosmos. With insufficient mass to fuse hydrogen atoms, they glow weakly by burning deuterium. Astronomers are still unsure whether the smallest brown dwarfs form like their larger cousins — by accreting matter from a swirling disk of dust particles.

K. L. Luhman and colleagues have found the smallest and coolest brown dwarf to date that is surrounded by a dusty disk. The dwarf, called OTS 44, is about 15 times the mass of Jupiter, right at the lower mass limit necessary for deuterium burning. The observation of a disk around such a small star implies that the accretion mechanism works for even the smallest stars.

The researchers used infrared measurements from the Spitzer Space Telescope to identify the disk around the dwarf star. It lies in the Chamaeleon I cloud complex, a nearby star-forming region about 554 light years from Earth.

The finding raises the possibility that planets could form from dust around brown dwarfs that have barely more mass than planets themselves. Further study will focus on the size and composition of the particles in the disk.

Mark Peplow

Zoology: Estimating the unknown

Proc. R. Soc. Lond. B doi:10.1098/rspb.2004.2955

Andrew R. Solow and Woollcott K. Smith have taken a fresh look at estimating the number of species in a particular category of animals, including those that are yet to be discovered.

A traditional approach is to take the cumulative historical record of discoveries of species, and extrapolate into the future. Solow and Smith propose a statistical model for the ‘discovery process’, which can be fitted to the data using the principle of maximum likelihood, based in probability theory. Central elements factored into the procedure are the animals' visibility, and a function to account for changes over time in the skill and effort applied in sighting new species.

The authors test their model against a previously published record of the dates when large marine animals (defined as 2 metres or more in length) were discovered, starting in 1828 and ending in 1996. That record comprises 117 species, with a further 100 having been identified before 1828.

The upshot of the calculations, say Solow and Smith, is that around 10 large marine animals remain to be discovered, and probably 16 at most. The most likely candidates are fish and cephalopods.

Tim Lincoln

Self-assembly: Pots of soap

Langmuir 21, 516–519 (2005)

Structures that look like earthenware spun on a wheel emerge spontaneously from a solution of a common cosmetics surfactant, Janhavi S. Raut et al. report. This ‘micro-pottery’ is built from aggregates of the surfactant sodium myristate, which self-assemble when a concentrated solution is cooled to room temperature.

For fast cooling rates, the fibres simply tangle into a gel-like mat. If cooling is slower than 2 °C per minute, the fibres begin to curl into rings; at 1 °C per minute they form bundles like thread wound on a bobbin. Air bubbles in the cooling solution become covered in bundles in which the fibres are spooled into appealing shapes (pictured), about 10–20 µm across.

Raut et al. think that the initial bending of the fibres into rings, which act as seeds for ‘spinning’ the micro-pots, is triggered by pressure gradients at the air–water interface of the bubbles. These gradients arise from differences in surfactant concentration across the surface, leading to variations in surface tension that drive liquid flow: the so-called Marangoni effect. The micro-pots represent a third level of structural hierarchy in the surfactant assemblies, which form sheets that then gather in layers to create the ribbon-like fibres.

Philip Ball