Science briefing: maize genome is decoded

The largest and most complex plant genome known to science – that of maize – has been decoded at last. Results of the $30m US-led project are published on Friday in the journals Science and PLoS Genetics.

Maize DNA contains 2.3bn chemical “letters”, including 32,000 genes. The human genome has 3bn letters and 20,000 genes.

Agricultural scientists say the completed genome will improve efforts to breed better maize varieties for human consumption, livestock feed and biofuel production. Economically, maize is the most important crop in the US – $47bn worth was harvested from 86m acres of farmland last year.

“The maize genome is a true maze – full of confusing repeats and dead-ends that have troubled would-be sequencers for years,” said David Schwartz of the University of Wisconsin, one of more than 100 researchers who have worked on the project since 2005.

Maize has been domesticated and improved in the past 10,000 years from a Central American grass called teosinte. In the process its genome has accumulated repeated DNA sequences and multiple copies of genes.

Sound sleep aids memory process

Sounds that we hear during deep dreamless sleep register on our brain and affect memory processing, according to a study at Northwestern University in Illinois.

Psychologists taught a dozen volunteers to associate each of 50 images and its characteristic sound (for example a cat and a meow) with a particular location on a computer screen. Then the subjects took a nap.

When electrodes on their heads showed that they were deeply asleep, the researchers played a random selection of sounds associated with half the images in the study – loudly enough to be audible but not to awaken the volunteers.

After they had woken, the subjects repeated the computer placing test. Although none of them remembered sounds being played during their naps, they placed images associated with the sounds more accurately than images for which no sounds were played.

“The research strongly suggests that we don’t shut down our minds during deep sleep,” said John Rudoy, lead author of the study, which is published in Science. “Rather this is an important time for consolidating memories.”

Spare skin grown from stem cells

Human embryonic stem cells could be a source of temporary skin substitutes for patients awaiting permanent skin grafts, French researchers have shown.

Scientists working for Inserm, France’s medical research agency, converted embryonic stem cells into skin cells through pharmacological treatment and seeding on to a special matrix. The cells were then grafted on to mice where they formed a structure very like human skin. (The animals had no immune defences and therefore did not reject the human cells.)

The ideal skin substitute for patients suffering from severe burns or other injuries is skin grown from their own cells, but this takes at least three weeks to produce. Although temporary coverings are available, all have disadvantages.

The Inserm researchers say that, if lines of human embryonic stem cells with various immune characteristics were available, the technology could provide temporary skin to suit a wide range of patients. Their study is published in the Lancet.