SVTR

http://www.nature.com/news/2007/070226/full/070226-4.html Published online: 26 February 2007; | doi:10.1038/news070226-4
Ancient DNA solves milk mystery
Analysis of fossilized bones suggests milk-drinking mutations emerged after dairy herding.

Erika Check

When did ancient populations learn that drinking milk 'does a body good'? A team of scientists in Germany has tried to answer this question by studying ancient DNA extracted from skeletons thousands of years old.

Many adult humans can drink cow's milk - a rare feat among mammals, which usually lose the ability to digest the sugar in milk after they are weaned. Scientists have found the genetic mutations that allow many Europeans and some Africans to digest milk (see 'Human evolution: How Africa learned to love the cow'). Geneticists have estimated that these mutations first spread 3,000 to 7,000 years ago in eastern Africa, and slightly earlier than that in Europe.

But some researchers have posed a 'chicken-and-egg' question about milk drinking: was dairy herding adopted only by those populations who could already drink milk? Or did the invention of dairy herding favour those people who had the mutation, so that the mutation quickly spread throughout the population?

Joachim Burger of the University of Mainz, Germany, and colleagues worked with Mark Thomas of University College London, UK, to address this riddle by studying DNA from skeletons scattered throughout Europe. The team examined ten skeletons ranging in age from 3,800 to nearly 6,000 years old. The skeletons were discovered at archaeological sites in Germany, Hungary, Poland and Lithuania.

http://www.nature.com/news/2007/070226/full/070226-2.html

Published online: 26 February 2007; | doi:10.1038/news070226-2
Mars - worth a detour
Europe's Rosetta mission is still years from its cometary target, but has sent home some pretty pictures of Mars en route

The images sent back - such as this one taken the day before the close flyby at a distance of 240,000 kilometres - were used mainly to check Rosetta's onboard instruments. Mars Express, the European Space Agency's current Mars mission, was also taking measurements at the same time, allowing comparisons and calibrations to be made. Because Mars Express was built from spare parts some of its instruments are identical to Rosetta's, which helped the process. The ability to produce accurate pictures will be crucial once Rosetta finally reaches Churyumov Gerasimenko and finds a safe place to set down its lander, Philae. 

This image of clouds in the martian atmosphere was taken by Rosetta's OSIRIS (Optical, Spectroscopic and Infrared Remote Imaging System) camera. Most of the instruments on Rosetta itself were powered down during the closest parts of the flyby because the spacecraft was flying through Mars's shadow and its solar panels thus couldn't provide power.

http://www.nature.com/news/2007/070226/full/070226-8.html
Published online: 28 February 2007; | doi:10.1038/news070226-8
Electric switch could turn on limb regeneration
Tadpoles use a proton pump to direct tissue regrowth.

Heidi Ledford

Tadpoles can achieve something that humans may only dream of: pull off a tadpole's thick tail or a tiny developing leg, and it'll grow right back - spinal cord, muscles, blood vessels and all. Now researchers have discovered the key regulator of the electrical signal that convinces Xenopus pollywogs to regenerate amputated tails. The results, reported this week in Development, give some researchers hope for new approaches to stimulating tissue regeneration in humans1.

Researchers have known for decades that an electrical current is created at the site of regenerating limbs. Furthermore, applying an external current speeds up the regeneration process, and drugs that block the current prevent regeneration. The electrical signals help to tell cells what type to grow into, how fast to grow, and where to position themselves in the new limb.

To investigate, Michael Levin and his colleagues at the Forsyth Center for Regenerative and Developmental Biology in Boston, Massachusetts, sorted through libraries of drug compounds to find ones that prevent tail regeneration but do not interfere with wound healing. One such drug, they found, blocks a molecular pump that transports protons across cell membranes; this kind of proton flow creates a current.

Levin speculates that the current generated by this proton pump produces a long-range electric field that helps to direct what happens to nerve cells pouring into the site. "We can use this hydrogen pumping as a top-level master control to initiate the regeneration response," says Levin. "We didn't have to specifically say, 'put a little muscle over here, a little muscle over there'."

The proton pump could also be used to turn on limb regeneration in older tadpoles that would normally have lost this ability. When Levin and his colleagues activated the proton pump during this older phase, tadpoles were more than four times more likely to regrow a perfectly formed tail than their normal counterparts.

Chop and change

The notion of regenerating complex organs from adult cells hasn't always been popular, says David Stocum, director of the Indiana University Center for Regenerative Biology and Medicine in Indianapolis. "People used to pooh-pooh the idea," says Stocum, "but now there's renewed interest in it." That interest has been primarily focused on the regenerative power of stem cells. But there is also some interest in direct regeneration from adult cells at the wound site.

At first glance, dramatic limb and tail regenerations seem to be restricted to 'simpler' creatures, such as the humble planaria flatworm - chop it up into a hundred pieces and you'll soon have a hundred little worms on your hands - and salamanders, which can grow back limbs, tails, jaws, intestines and some parts of their eyes and hearts.

But there are impressive examples of tissue regeneration in mammals as well. Male deer can grow the bone, skin, nerves and blood vessels of their antlers at a millimetre a day. Humans can regenerate livers, and many children under the age of seven have regrown amputated fingertips. And then there are the odd medical journal case studies of patients who have lost, say, a kidney, only to find years later that they've sprouted a new one.

Simple switch

Changes in electrical current have been measured in regenerating fingertips, just as in a tadpole's regenerating tail. But converting humans into fully functioning regenerators will probably take more than directing bioelectrical signals. The formation of scar tissue, for example, could inhibit regeneration in some cases, says David Gardiner, a biologist at the University of California, Irvine.

But the complex networks needed to construct a complicated organ or appendage are already genetically encoded in all of our cells - we needed them to develop those organs in the first place. "The question is: how do you turn them back on?" Levin says. "When you know the language that these cells use to tell each other what to do, you're a short step away from getting them to do that after an injury."

The simplicity of the regeneration start signal is promising, says Stocum: it is just possible that a properly tuned electric signal is all humans need to jumpstart tissue regeneration.

http://www.la-croix.com/article/index.jsp?docId=2296179&rubId=4076

27/02/2007 20:40 par Anne-Bénédicte HOFFNER

Comment mettre de l'ordre dans le diagnostic prénatal
Réagissant aux propos alarmistes du président du Comité consultatif national d'éthique, Didier Sicard, "La Croix" a interrogé des médecins sur leur pratique du dépistage prénatal  

"Le dépistage vise à la suppression, et non au traitement" 

"Les parents seuls aptes à juger"

"Aujourd'hui on organise la sélection des personnes"

"Donner leur vraie place aux personnes handicapées"

http://www.la-croix.com/article/index.jsp?docId=2296278&rubId=788
28/02/2007 20:40 par Mathilde DAMGE
"La lutte contre la cigarette se poursuit sur les trottoirs
"Interdits dans les bureaux et les écoles, les accros à la nicotine créent de nouvelles nuisances dans les espaces publics ouverts
"Le problème de l'assurance de l'employé hors des locaux

"Au Ritz, la consigne a été très claire : les employés sont priés d'aller fumer devant l'entrée du personnel, discrètement, dans la rue Cambon : « Le tas de mégots qui s'envole sur le trottoir, résume la direction, ce n'est pas très classe. » 

"Les filtres sont biodégradables... mais le processus met entre dix et vingt ans.  

"Des amendes sont prévues : 38 € pour toute entreprise qui ne ramassera pas les montagnes de mégots devant son pas-de-porte et 183 € à un fumeur qui jette sa cigarette dans la rue. 

"faudra-t-il blâmer celui qui fume sur son balcon pour ne pas empoisonner ses enfants et dont les volutes entreront par les fenêtres ouvertes de son voisin ? Autant de questions à résoudre avec souplesse et intelligence. "