18 | NewScientist | 25 February 2012

Enzyme extends the life of mice

FINALLY, a contender for the elusive fountain of youth: an enzyme found in humans appears to lengthen the life of mice.

Researchers hoping to slow the march of age were dealt a blow in 2010, when signs that an enzyme called sirtuin 2 extended the life of worms were shown to be false due to flawed experimental design.

Mammals have seven types of sirtuin, so Haim Cohen and Yariv Kanfi at Bar-Ilan University in Ramat Gan, Israel, turned to sirtuin 6 instead. They compared mice genetically engineered to have increased levels of SIRT6 with normal mice, engineering the mice in two different ways to control for genetic influences.

Male mice from both strains lived 15 per cent longer than normal mice or females. Older modified male mice metabolised sugar faster than normal mice and females, suggesting that SIRT6 might extend life by protecting against metabolic disorders such as diabetes.

Why SIRT6 didn’t affect females is a puzzle, but may be related to differences in genes that regulate ageing in males and females (Nature, DOI: 10.1038/nature10815).

Exquisite positioning turns single atom into a transistorTHE basic unit of matter could become the basic unit of computing. A transistor has been made from a single atom precisely embedded in a sheet of silicon.

A transistor is essentially two electrodes connected by a piece of conducting material that acts as a switch. A pulse of voltage is used to “open” the switch by allowing current to flow through the conductor.

Combining transistors on a chip produces logic circuits that can carry out computations. The more there are on a single chip the

greater its computational power. Transistors have been made with single-atom switches before, but their exact positions could not be determined, so combining them on a chip would be tough.

To dictate the exact position of their atomic transistor, Michelle Simmons at the University of New South Wales in Sydney, Australia, and colleagues covered a silicon sheet with hydrogen. Then they used the tip of a scanning tunnelling microscope to strip away some hydrogen atoms, exposing two

EvEr taken a dram of whisky to ward off a cold? Fruit fly larvae do something similar: they take alcohol to kill a parasitic wasp that lays its eggs in their blood. It’s a rare example of self-medication in insects.

Drosophila melanogaster larvae raised in rotting fruit can shrug off the toxic effects of alcohol. Todd Schlenke at Emory University in Atlanta, Georgia, and his team raised healthy and parasitised larvae in dishes containing normal food or food laced with alcohol. Eighty per cent of the parasitised larvae favoured the boozy food, compared

with just 30 per cent of healthy ones (Current Biology, DOI: 10.1016/j.cub.2012.01.045).

The parasites normally eat fly larvae from the inside out. But in Schlenke’s set-up, wasps avoided laying eggs in booze-soaked larvae. What’s more, infected larvae that consumed alcohol were more likely to survive than teetotallers.

Before you reach for the bottle, May Berenbaum of the University of Illinois at Urbana-Champaign cautions that flies are very different to us. The results say nothing about the health benefits of a hot toddy.

Flies self-medicate with a swig of booze

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perpendicular pairs of silicon strips plus a tiny central rectangle made of just six silicon atoms.

They then exposed the silicon sheet to phosphorus, which is conducting. Atoms of the element bound to silicon only in the exposed areas, with just one phosphorus atom inserting itself into the central rectangle. The result was two sets of phosphorus electrodes with a central phosphorus atom acting as the heart of the transistor (Nature Nanotechnology, DOI: 10.1038/nnano.2012.21).

Bipolar drug fixes damaged nerves

SOMETIMES salt is the good guy, in some forms anyway. Lithium chloride – a salt used as a mood stabiliser in bipolar disorder – appears to enhance the recovery of damaged neurons in mice. The drug may also help people with damaged nerves regain movement.

Charbel Massaad at Paris Descartes University in France and his colleagues recreated in mice the nerve damage that sports injuries and diabetes can cause in humans. When such damage occurs, neurons lose their myelin sheath – a coating that insulates the nerve, accelerating electrical impulses. People tend to lose the ability to move limbs as a result. After the mice’s facial nerves were damaged, their whiskers became paralysed.

The team put lithium chloride in the rodents’ drinking water. These mice completely recovered whisker movement within eight days, compared with mice who drank plain water, who had little movement at 20 days.

A closer inspection of the nerves revealed that myelin sheaths were much thicker in the treated mice (Proceedings of the National Academy of Sciences, DOI: 10.1073/pnas.1121367109).

Massaad hopes the drug will work as well in people: “Lithium could provide a novel, cheap therapy that stimulates myelination,” he says.

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