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THE activity of stem cells, prized for their ability to differentiate into any cell type in the body, has been controlled by manipulating cellular electrical signals.

At present, researchers expose stem cells to nutrients and growth factors to trigger differentiation and control what type of cell they will become. But when Michael Levin of Tufts University, Boston, and colleagues discovered voltage changes in adult human stem cells as the cells naturally differentiated into fat and bone, they wondered if changing the voltage could control a cell’s fate.

Sure enough, when they blocked ion flow in a fresh batch of cells, differentiation was suppressed, while adding chemicals that increase the voltage across cell membranes sped up their transformation (PLoS ONE, DOI: 10.1371/journal.pone.0003737).

The group hopes to use this method to more precisely control stem cell differentiation, perhaps in future when using the cells to build organs for transplantation. As fat and bone cells produced different voltage patterns during differentiation, electricity might be used to produce these cell types.

Electricity guides fate of stem cells

WHAT does a drop of water have in common with a black hole and an atom? Well, levitating water droplets can now simulate the dynamics of both cosmological and subatomic objects.

Richard Hill and colleagues at the University of Nottingham, UK, turned to water droplets because the surface tension that holds the drops together can be used to model other forces. For example, the event horizon of a black hole is sometimes thought of as a “stretched” membrane with a surface tension . Similar

forces also prevent atoms from flying apart.

The team levitated the droplets using an effect called diamagnetism: when an external magnetic field was applied to the droplets, they created their own opposing magnetic field, initiating a repulsive force strong enough to counteract gravity. To set the droplets spinning, they implanted two tiny electrodes, which generated an electric field.

They found that once a droplet with a diameter of 1 centimetre reached about 3 revolutions per

second, its shape, when viewed from above, became triangular, an effect never seen before in the lab. Astronomical observations suggest that objects with this shape exist in the Kuiper belt beyond Neptune (Physical Review Letters, DOI: 10.1103/PhysRevLett.101.234501 ).

“The breakthrough in this work is the ability to reproduce, in a simple table-top experiment, 100 years of theoretical work in fluid dynamics,” says Vitor Cardoso of the University of Mississippi.

Why spinning water drops are like black holes

IT IS not often that cultural and religious persecution makes countries more diverse, but the Spanish Inquisition may have done just that. It now seems that many Spanish and Portuguese people have Jewish or North African ancestors.

In 1492 Catholic monarchs forced Muslims and Sephardic Jews to “convert, go, or die,” says Mark Jobling, a geneticist at the University of Leicester, UK. If they chose to convert, the groups were more likely to integrate into society by marrying Christian Europeans.

To gauge the extent of this social integration, Jobling and colleagues analysed the DNA of over 1000 Spanish and Portuguese men who aren’t themselves Jewish or Muslim. Focusing on the Y chromosome, which passes from father to son, Jobling’s team matched the DNA to that of modern Basques, North Africans, or Sephardic Jews. They found that 1 in 5 men had a Jewish ancestor, and in 1 in 10 a North African ancestor (American Journal of Human Genetics, vol 83, p 633).

Stephen Oppenheimer of the University of Oxford says Jewish migrations up to 10,000 years ago from the eastern Mediterranean might confound the results. But Chris Tyler-Smith of the Sanger Institute in Hinxton, UK, says that slight individual differences in genetic markers on the Y chromosomes suggest Iberians and Sephardic Jews share ancestry more recent than several millennia ago.

Spanish Inquisition left genetic legacy

PAY attention please, using as much of your brain as possible. When your mind wanders during a boring task, it may be because parts of your brain simply disconnect.

Knowing that activity in different brain regions changes when attention lapses, Daniel Weissman of the University of Michigan, Ann Arbor, wondered if there were also changes in the crosstalk between regions.

Weissman asked volunteers to spend a tedious hour in a functional-MRI brain scanner, identifying letters that flashed on a screen. At times, their reactions slowed, showing that

attention was wavering. During these lapses, communication between regions related to self-control, vision and language processing died down. This is equivalent to these regions disconnecting, says Weissman, who presented the results at a recent neuroscience meeting .

He says that attention is like a communication amplifier that only focuses on the connections between certain regions at certain times. When the amplifier switches to a new set of connections, existing ones weaken. Communication between those regions slows and attention lapses .

The researchers also noticed one particular region “lit up” during lapses, and used this to predict when the mind would switch its focus.

I’m bored: my brain is disconnecting

18 | NewScientist | 13 December 2008 www.newscientist.com

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