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ublished online: 6 June 2007; | doi:10.1038/447618a / http://www.nature.com/news/2007/070604/full/447618a.html

Simple switch turns cells embryonic

Technique removes need for eggs or embryos.

David Cyranoski

Research reported this week by three different groups shows that normal skin cells can be reprogrammed to an embryonic state in mice. The race is now on to apply the surprisingly straightforward procedure to human cells.

If researchers succeed, it will make it relatively easy to produce cells that seem indistinguishable from embryonic stem cells, and that are genetically matched to individual patients. There are limits to how useful and safe these would be for therapeutic use in the near term, but they should quickly prove a boon in the lab.

The birth of this chimaeric mouse suggests that the cells used to generate it behave like embryonic stem cells. S. OGDEN

"It would change the way we see things quite dramatically," says Alan Trounson of Monash University in Victoria, Australia. Trounson wasn't involved in the new work but says he plans to start using the technique "tomorrow". "I can think of a dozen experiments right now - and they're all good ones," he says.

In theory, embryonic stem cells can propagate themselves indefinitely and are able to become any type of cell in the body. But so far, the only way to obtain embryonic stem cells involves destroying an embryo, and to get a genetic match for a patient would mean, in effect, cloning that person - all of which raise difficult ethical questions.

As well as having potential ethical difficulties, the 'cloning' procedure is technically difficult. It involves obtaining unfertilized eggs, replacing their genetic material with that from an adult cell and then forcing the cell to divide to create an early-stage embryo, from which the stem cells can be harvested. Those barriers may have now been broken down.

"Neither eggs nor embryos are necessary. I've never worked with either," says Shinya Yamanaka of Kyoto University, who has pioneered the new technique.

Last year, Yamanaka introduced a system that uses mouse fibroblasts, a common cell type that can easily be harvested from skin, instead of eggs. Four genes, which code for four specific proteins known as transcription factors, are transferred into the cells using retroviruses. The proteins trigger the expression of other genes that lead the cells to become pluripotent, meaning that they could potentially become any of the body's cells. Yamanaka calls them induced pluripotent stem cells (iPS cells). "It's easy. There's no trick, no magic," says Yamanaka.

The results were met with amazement, along with a good dose of scepticism. Four factors seemed too simple. And although the cells had some characteristics of embryonic cells - they formed colonies, could propagate continuously and could form cancerous growths called teratomas - they lacked others. Introduction of iPS cells into a developing embryo, for example, did not produce a 'chimaera' - a mouse carrying a mix of DNA from both the original embryo and the iPS cells throughout its body. "I was not comfortable with the term 'pluripotent' last year," says Hans Schöler, a stem-cell specialist at the Max Planck Institute for Molecular Biomedicine in Münster who is not involved with any of the three articles.

This week, Yamanaka presents a second generation of iPS cells, which pass all these tests. In addition, a group led by Rudolf Jaenisch at the Whitehead Institute for Biomedical Research in Cambridge, Massachusetts, and a collaborative effort between Konrad Hochedlinger of the Harvard Stem Cell Institute and Kathrin Plath of the University of California, Los Angeles, used the same four factors and got strikingly similar results.

"It's a relief as some people questioned our results, especially after the Hwang scandal," says Yamanaka, referring to the irreproducible cloning work of Woo Suk Hwang, which turned out to be fraudulent. Schöler agrees: "Now we can be confident that this is something worth building on."

The improvement over last year's results was simple. The four transcription factors used by Yamanaka reprogramme cells inconsistently and inefficiently, so that less than 0.1% of the million cells in a simple skin biopsy will be fully reprogrammed. The difficulty is isolating those in which reprogramming has been successful. Researchers do this by inserting a gene for antibiotic resistance that is activated only when proteins characteristic of stem cells are expressed. The cells can then be doused with antibiotics, killing off the failures.

The protein Yamanaka used as a marker for stem cells last year was not terribly good at identifying reprogrammed cells. This time, all three groups used two other protein markers - Nanog and Oct4 - to great effect. All three groups were able to produce chimaeric mice using iPS cells isolated in this way; and the mice passed iPS DNA on to their offspring.

Jaenisch also used a special embryo to produce fetuses whose cells were derived entirely from iPS cells. "Only the best embryonic stem cells can do this," he says.

"It's unbelievable, just amazing," says Schöler, who heard Jaenisch present his results at a meeting on 31 May in Bavaria. "For me it's like Dolly [the first cloned mammal]. It's that type of accomplishment."

The method is inviting. Whereas cloning with humans was limited by the number of available eggs and by a tricky technique that takes some six months to master, Yamanaka's method can use the most basic cells and can be accomplished with simple lab techniques.

But applying the method to human cells has yet to be successful. "We are working very hard - day and night," says Yamanaka. It will probably require more transcription factors, he adds.

If it works, researchers could produce iPS cells from patients with conditions such as Parkinson's disease or diabetes and observe the molecular changes in the cells as they develop. This 'disease in a dish' would offer the chance to see how different environmental factors contribute to the condition, and to test the ability of drugs to check disease progression.

But the iPS cells aren't perfect, and could not be used safely to make genetically matched cells for transplant in, for example, spinal-cord injuries. Yamanaka found that one of the factors seems to contribute to cancer in 20% of his chimaeric mice. He thinks this can be fixed, but the retroviruses used may themselves also cause mutations and cancer. "This is really dangerous. We would never transplant these into a patient," says Jaenisch. In his view, research into embryonic stem cells made by cloning remains "absolutely essential".

If the past year is anything to judge by, change will come quickly. "I'm not sure if it will be us, or Jaenisch, or someone else, but I expect some big success with humans in the next year," says Yamanaka.

Additional reporting by Heidi Ledford
For more on alternative stem-cell work, see 'Stem cells: Recycling the abnormal'; and see http://www.nature.com/stemcells

References Okita, K., Ichisaka, T. & Yamanaka, S. Nature doi:10.1038/nature05934 (2007). Wernig, M. et al. Nature doi:10.1038/nature05944 (2007). Maherali, N. et al. Cell Stem Cell doi:10.1016/j.stem.2007.05.014 (2007). Takahashi, K. & Yamanaka, S. Cell 126, 663-676 (2006).

Published online: 7 June 2007; | doi:10.1038/news070604-9

Transgenic crops relatively kind to insects

Study helps mollify one concern about pest-killing crops.

Heidi Ledford

Crops engineered to kill off corn borers don't seem to wipe out other insects. Getty

Crops modified to produce insecticides against pests are relatively kind to other insects, an analysis of 42 field experiments suggests. Fields of transgenic cotton and corn contain more non-target insects than those of traditional crops sprayed with insecticides, the study shows. But both have fewer such insects than traditional fields that aren't sprayed at all.

The finding eases worries that crops engineered to produce an insecticidal toxin made by the Bacillus thuringiensis (Bt) bacterium might kill more insects than intended, thus harming wildlife. The toxin is intended to target specific groups of plant pests, such as corn borers and cotton bollworms.

A debate about this effect has run since the first Bt crops were released in 1996. Recent field trials have found that Bt crops have little or no significant impact on non-target species. But lab studies showing that insects fed Bt-producing pollen are smaller and reproduce less have worried sceptics.

"This is such a controversial issue," says ecologist Michelle Marvier of Santa Clara University, California. "There's a lot of public fear, in part because there's not a lot of transparency in the testing process."

Pooling resources

Marvier and her colleagues used the US Freedom of Information Act to obtain the results of field trials submitted to the Environmental Protection Agency as part of the approval process for the engineered crops.

The field studies, she found, tended to use sample sizes that were too small to reveal small but statistically meaningful differences. So the researchers combined the data from field studies that measured invertebrate populations near Bt crops, in the hope of getting a large enough sample to spot small differences.

Overall, they report in Science¹, Bt fields contained more invertebrates than fields sprayed with insecticide. But both contained fewer bugs than fields containing no Bt crops that were not sprayed with insecticides.

The results' ecological significance is unclear, given the small differences in the invertebrate populations of different fields, says entomologist Yves Carrière of the University of Arizona, Tucson. But the meta-analysis approach can give a clearer picture of what's happening in the field.

"The data are only just becoming available to conduct meta-analyses," says Carrière. "I'm certain that many such studies will come out in the next few years."

Finer grain

One useful step, he adds, would be to focus on species, rather than lumping invertebrates together by family, as Marvier's study did. That focus might reveal differences that are missed when species are grouped together.

The approach may also address other concerns about transgenic crops, such as whether they promote new types of pests, or encourage weeds that have a knock-on effect on butterflies and other insects.

To facilitate future studies, Marvier has made a database of all of the trials her team found. US regulators should require petitioners to deposit data in a similar database, akin to a clinical-trial registry for drug tests, she says.

The database will soon need updating, Carrière warns. "This study covers transgenics that produce a single Bt toxin," he says. "But this first generation of transgenics is being replaced with plants that have two toxins with a broader mode of action. So this is not the end of the story."

Reference : Marvier M., McCreedy C., Regetz J. & Kareiva P. Science, 316 . 1475 - 1477 (2007).

http://www.nature.com/news/2007/070604/full/070604-9.html 

Published online: 7 June 2007; | doi:10.1038/news070604-10 / http://www.nature.com/news/2007/070604/full/070604-10.html

Marijuana skin cream could help allergies

Cannabinoids provide relief for a mouse's itchy skin.

Heidi Ledford

Ouch: the itch from poison ivy can be soothed by skin creams - maybe ones made from cannabis. Getty

The chemicals that give marijuana its mood-altering kick might also be an option for treating skin allergies, according to a study done in mice.

The compounds, called cannabinoids, have been credited with everything from stimulating the growth of new neurons to easing the symptoms of multiple sclerosis. Although they are best known for spicing up marijuana, the body also produces cannabinoids, which are thought to play a part in learning and in communications between the immune system and the nervous system. Now, researchers have shown that cannabinoids can relieve some of the swollen, itchy agony of allergic skin reactions in mice.

The team first noticed the effect when they created mice that lacked two proteins that usually recognize cannabinoids produced by the body. Some of the mutant mice scratched at the metal identification tags in their ears until the area around the tags became raw and covered with sores. "We thought at first it was just an itching phenotype," says Andreas Zimmer, a neurobiologist at the University of Bonn. "But then we switched to another brand of ear tags and all of a sudden the problem completely disappeared."

The first set of tags, it turned out, contained nickel, whereas the second set was made from non-allergenic brass. Zimmer and his colleagues realized that the mutant mice were allergic to the nickel. Mice that still had their cannabinoid receptors did not react in this way.

The results suggested that cannabinoids produced by the body might help protect the animals against skin allergies. To find out whether the compounds could produce the same effect when applied externally, Zimmer's research team applied a cannabinoid to the skin of mice before and after they were exposed to a chemical (called 2,4-dinitrofluorobenzene), which is known to produce an allergic response. Mice that had received the cannabinoid had a diminished allergic response, with about 50% less swelling, than did those that had not received the compound. The results are published this week in Science.¹

Swell treatment

No one knows precisely how cannabinoids diminish allergic reactions, but Zimmer and his colleagues did find that the compounds alter the expression of genes that encode small proteins called chemokines. And some chemokines are known to promote inflammation.

Zimmer's mice received their cannabinoid treatment both before and after their encounter with the allergen, so it wouldn't necessarily work after a chance encounter with, for example, poison ivy. The best defence against most contact allergies is simply to avoid contact with the allergens, says Thomas Tüting, a dermatologist at the University of Bonn and a co-author of the study.

But the treatment could be useful for treating patients with chronic dermatitis, says Thomas Klein, an immunologist at the University of South Florida in Tampa. People with this condition have recurrent patches of swollen, itchy, cracked skin, and they don't always know the cause. "It's very uncomfortable and the wounds carry the risk of secondary infections," says Klein. The usual treatment is steroids and immunosuppressants. But long-term use of steroids can cause the skin to thin and patients often become tolerant of the drugs, rendering the medication less effective. An alternative treatment would be a welcome addition, says Klein.

But no therapeutic application is certain until the experiments have been repeated in humans, cautions Roman Rukwied, who studies pain and inflammation at the University of Heidelberg in Germany. "We are far before the day when we could say 'oh, I have a nickel allergy. I will smoke marijuana and I won't have it anymore'," he says. "That is definitely not the case."

References : Karsak M., et al. Science, 316 . 1494 - 1497 (2007).

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http://www.futura-sciences.com/fr/sinformer/actualites/news/t/medecine/d/le-cannabis-soignerait-il-les-allergies_12039/

Published online: 8 June 2007; | doi:10.1038/news070604-13 / http://www.nature.com/news/2007/070604/full/070604-13.html

Scientists mourn devastation of Valley of Geysers

Mudslide in Kamchatka wipes out some study sites.

Narelle Towie

Wildlife in the Valley of Geysers (top) may be threatened by the rubble that has caused flooding (below). Igor Shpilenok (www.shpilenok.com)

Teams of scientists have been sent to the Valley of Geysers, on the Kamchatka Peninsula in the far east of Russia, to report on the condition of the World Heritage site after a massive landslide in the Kronotsky national reserve.

The slide, which lasted only seconds on 3 June, loosed an estimated 4.5 million cubic metres of rock, gravel, snow and ice. A deluge of material into the Geyser River created a dam the size of 30 football fields, officials estimated. This has since been breached by waters building up behind the dam, clearing some of the valley and allowing at least some of the geysers to spout again.

The extent of damage to the region is unclear, including to scientists contacted by Nature who have study sites in the area. Juergen Wiegel, a microbiologist at the University of Georgia in Athens, Georgia, says the slide will "definitely" affect future research. His group has been investigating the extremophiles living in the vents in that valley and in the nearby Uzon caldera. Losing one of those comparison sites "is very sad", he says.

The introduction of new minerals and organic material to the geysers is expected to change the microbial community, Wiegel notes, which in itself could be interesting to study.

Geologists are uncertain what will happen in the area next. If masses of mud continue to block some geysers it could force a build-up of pressure. "Mud is not very porous and it forms a nice trap. If there are many tonnes of material then I wouldn't expect explosions right away, but they could come later," says Jake Lowenstern, lead scientist at the Yellowstone Volcano Observatory, a similarly volcanically active region.

Fish food

Botanists are concerned that rare plants and insects being researched may have been washed away in the torrent. "In the smaller river where the slide came down there was an endemic plant that was found only on this river, and that river is now under a tonne of mud," says Laura Williams, director of the Russian branch of the conservation group WWF in Kamchatka.

Fortunately, the nature reserve is big enough that most of the animals, including thousands of brown bears, are thought to have simply escaped to other parts of the park. However, their main food source - salmon - may be in jeopardy, says Jack Paczkowski, Kamchatka field coordinator for the Wildlife Conservation Society. "Many of the invertebrates that the young salmon rely on for food will be destroyed," he says.

Researchers note that a dramatic change to tourism in the region could affect their access to the area, as well as having a major impact on the local economy. Shunting ecotourists away from the valley to alternative sites could simultaneously begin to spoil previously pristine sites and reduce the ability of scientists to 'piggyback' on tourist flights to gain access to the valley, they say.

Slip sliding away

The reserve is one of the most volcanically active regions in the world, located on the unstable 'ring of fire' circling the Pacific Ocean. "There are 29 active volcanoes, and eruptions and earthquakes happen constantly," says Williams.

Even so, such powerful landslides are uncommon. Some reports suggest unusually warm weather may have caused a snow-covered mound to melt, sparking the torrent. Others suggest a small earthquake the night before may have triggered the fall.

A paper published in the Journal of Volcanology and Geothermal Research in 2006 details the instability of the area and evidence of previous landslides, varying from small to catastrophic, occurring between 10,000 and 30,000 years ago. The authors highlighted the importance of stability studies to aid in the forecast of future collapses1.

Regional officials are now deciding if and how the area should be restored. Environmental groups such as the WWF are arguing for allowing the region to restore itself, rather than forcibly removing remaining mud with heavy machines or dynamite. "Many birds, bears and other animals would be disturbed if such drastic human alteration of the valley were to go forward," says Williams.

Additional reporting by Nicola Jones

References : Ponomareva V.V., Melekestsev I. V. & Dirksen O. V. J. Volcanol. Geotherm. Res., 158 . 117 - 138 (2006).