Exploratory brain region pinpointed; Ovaries don't need help from circulating blood and bone cells; Night flights cause more global warming

Summaries of newsworthy papers from Nature Vol.441 No.7095 including Two become one, A glass from dry ice, Unhappy partners, Self-renewal understood, Sperm storage weakens immune system


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VOL.441 NO.7095 DATED 15 JUNE 2006

This press release contains:

* Summaries of newsworthy papers:

Neurobiology: Exploratory brain region pinpointed

Development: Ovaries don't need help from circulating blood and bone cells

Climate: Night flights cause more global warming

Evolution: Two become one

Materials science: A glass from dry ice

Quantum physics: Unhappy partners

Stem cells: Self-renewal understood

And finally… Sperm storage weakens immune system

* Mention of papers to be published at the same time with the same embargo
* Peer Review Commentaries
* Geographical listing of authors

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[1] Neurobiology: Exploratory brain region pinpointed (pp 876-879; N&V)

In an uncertain world we are sometimes faced with a dilemma: to stick with what we know or risk the unknown and explore unfamiliar territories with uncertain rewards. New work published in this week’s Nature now shows that exploratory decisions appear to be tightly linked to activity in the hitherto enigmatic frontal pole of the prefrontal cortex.

Nathaniel Daw and colleagues used functional magnetic resonance imaging to study human subjects as they played a carefully designed gambling task. The players had to balance the desire to select the richest option based on accumulated experience against the desire to choose a less familiar option that might have a larger payoff. The frontopolar cortex, a brain area known to be involved in cognitive control, was preferentially active during exploratory decisions.

Previous work has studied the neural substrates of exploitation behaviour, where participants chose to stick with and ‘exploit’ an already known resource. Combined with the new results, the authors suggest a model of decision making in uncertain environments that involves switching between exploratory and exploitative behaviours.


Nathaniel Daw (University College London, UK)
Tel: +44 20 7679 1176 wk; E-mail: [email protected]

Daeyeol Lee (University of Rochester, Rochester, NY, USA)
Tel: +1 585 275 8677; E-mail: [email protected]

[2] Development: Ovaries don't need help from circulating blood and bone cells (AOP)
DOI: 10.1038/nature04929

***This paper will be published electronically on Nature's website on 14 June at 1800 London time / 1300 US Eastern time (which is also when the embargo lifts) as part of our AOP (ahead of print) programme. Although we have included it on this release to avoid multiple mailings it will not appear in print on 15 June, but at a later date.***

Researchers have quashed the idea that cells from blood or bone marrow can be converted into new eggs through seeding of the ovary. Previous studies had led to hopes that cells from these sources could be used to treat ovarian damage, but research in mice now shows that ovaries produce their eggs only from local sources.

Amy Wagers and her colleagues made the discovery by surgically joining pairs of mice, one of which had been genetically engineered to produce a green fluorescent protein (GFP) in all of its cells. Once joined, the mice develop a shared circulatory system, meaning that if eggs can be produced from circulating germ cells, then the ovaries of GFP-producing mice would eventually develop non-fluorescent eggs, and vice versa.

But this did not prove to be the case, the researchers report in a paper published online by Nature, even when their ovaries were experimentally damaged to encourage regeneration. They conclude that, although recent research has called into question the dogma that ovaries cannot be replenished with fresh eggs during life, this replenishment seems to occur from germ cells within the ovary rather than from cells circulating around the body.


Amy Wagers (Harvard Medical School, Boston, MA, USA)
Tel: +1 617 732 2590; E-mail: [email protected]

[3] Climate: Night flights cause more global warming (pp 864-867)

Condensation trails (contrails) left by aircraft have the strongest impact on global warming for nighttime flights in the winter, according to Nicola Stuber and colleagues in Nature this week. Although there are far fewer flights in winter than in summer, their greater climate impact means that collectively they contribute equally overall to the warming caused by contrails.

Contrails exert two opposing effects on climate; trapping infrared radiation from the Earth’s surface prevents it from radiating into space and warms the atmosphere, but reflecting sunlight from their bright upper surface reduces the solar heating of the planet. On balance the warming effect exceeds the cooling, so contrails add to global warming - although the effect is small compared to other human activities.

The team looked at the formation of contrails over a site in southeast England, passed by aircraft heading for the North Atlantic. Measurements of atmospheric conditions enabled them to make accurate predictions of whether or not flights would create contrails. This depends strongly on the air humidity, which is higher on average during winter - so winter flights are roughly twice as likely as summer flights to create contrails.

Stuber’s team used flight schedule data to determine how much contrail formation occurred at different times during a day and over different seasons, and hence their climate model could indicate what the overall effect on heating of the Earth would be. They found that winter flights, while representing only 22 per cent of the yearly total, contributed 50 per cent of the annual warming. And night flights, between the hours of 6 pm and 6 am, also have a disproportionate effect, constituting only a quarter of the total air traffic but contributing between 60 and 80 per cent of the warming. The researchers say that this information could guide the reduction of such climate impacts by identifying the most effective ways of rescheduling flights.


Nicola Stuber (University of Reading, UK)
Tel: +44 118 378 6017; E-mail: [email protected]

Piers Forster (University of Leeds, UK) Co-author
Tel: +44 113 343 6476; E-mail: [email protected]

[4] Evolution: Two become one (pp 868-871)

Researchers have interbred two butterfly species and created a third, distinct species. The study, described in Nature, is the first definitive evidence that two animal species can evolve to form one, rather than the more common evolutionary scenario where a single species diverges to form two.

Jesús Mavárez and colleagues interbred Heliconius cydno, which is black with white and yellow marks, with H. melpomene, which is black with red, yellow and orange marks. The outcome was H. heurippa, a different species with a hybrid genome and intermediate wing pattern, which is known to occur naturally.

The creation of new species through hybridization is common amongst plants, but thought rare or absent in animals where, it’s argued, hybrid offspring would be less likely to survive and breed than the parent species. For hybrid speciation to be successful, the hybrids would need to be reproductively isolated.

Mavárez and colleagues demonstrate this by giving H. heurippa butterflies the opportunity to mate with their parent species or other H. heurippa individuals. Individuals were far more likely to mate with members of their own species, providing the clearest evidence so far that hybrid speciation can occur and cause reproductive isolation in animal species.


Jesus Mavarez (Smithsonian Tropical Research Institute, Panama)
Tel: +507 212 8842; E-mail: [email protected]

Mauricio Linares (Universidad de los Andes, Bogota, Colombia)
Tel: +571 332 4339; E-mail: [email protected]

[5] Materials science: A glass from dry ice (pp 857-860; N&V)

A team of European researchers has discovered a new form of solid carbon dioxide, quite different from the substance popularly known as ‘dry ice’ that provides the atmospheric smoke for corny stage shows. The new material, reported in Nature this week, is christened amorphous carbonia (a-CO2), and is more like window glass in its atomic-scale structure.

In its reactions with oxygen, carbon behaves very differently to the other elements in its column of the periodic table. Silicon forms crystalline silica - the mineral quartz - and amorphous silica glass - one of the main components of normal window glass, in which the atoms are linked into a disorderly network. Germanium is similar. But carbon combines with oxygen to form not hard, brittle solids but a gas, carbon dioxide (CO2), in which one carbon atom and two oxygens join into discrete molecules.

Carbon dioxide can be solidified into dry ice by cooling and squeezing it - but the atoms remain bound as separate molecules, rather than joining into the continuous networks of silica. It has been predicted theoretically that carbon and oxygen ought also to be able to form such networks - but only now have Federico Gorelli, Mario Santoro and colleagues succeeded in making it. They did so by squeezing normal solid carbon dioxide between diamond teeth to pressures of around 400,000 to 500,000 atmospheres. This transformed the material into a-CO2, which is no longer made up of molecules but has a disordered network structure like that of silica glass. The new substance is of interest because carbon dioxide is squeezed at high pressures in the interiors of gas-giant planets in the outer Solar System, and because a-CO2 might be expected, like diamond, to be very hard and stiff.


Federico Gorelli (University of Florence, Italy)
Tel: +39 055 457 2490; E-mail: [email protected]

Mario Santoro (University of Florence, Italy)
Tel: +39 055 457 2490/2515; E-mail: [email protected]

Paul F McMillan (University College London, UK)
Tel: +44 20 7679 4610; E-mail: [email protected]

[6] Quantum physics: Unhappy partners (pp 853-856; N&V)

Conventional wisdom says that to make two objects stick together; you have to make them attract one another. That, after all, is why the moon orbits the Earth and why electrons ‘orbit’ protons in atoms. But Johannes Hecker Denschlag and his colleagues show in Nature this week that binding atoms together does not always demand an attractive force - bizarrely, it can happen when they repel each other too.

Denschlag and colleagues created pairs of bound atoms of rubidium in an ultracold gas. They filled the space occupied by the atoms with ‘potential wells’ - dimples in which atoms can be trapped. This array of potential wells was created with light: wave interference between two crossed laser beams produces an ‘optical lattice’ of wells.

Although the rubidium atoms repelled one another, the researchers found that under the right circumstances they would all tend to sit in the potential wells in pairs. This is not simply a matter of the atoms getting reluctantly trapped together: in principle, each of them could escape to an adjacent well to get away from its repulsive partner, and yet they don’t do so.

Where does this seemingly perverse union of mutual enemies come from? It is a quantum-mechanical effect for which there isn’t really an everyday analogue: in order to escape into a neighbouring well, each lone atom would have to enter an energy state that is ‘forbidden’ by the laws of quantum physics. Thus, although escape seems to be in sight, the atoms are effectively sentenced to remaining together: they may move together from one well to another, like a pair of antagonistic convicts bound together by shackles, but can never do so alone.


Johannes Hecker Denschlag (University of Innsbruck, Austria)
Tel: +43 512 507 6340; E-mail: [email protected]

Massimo Inguscio (University of Florence, Italy)
Tel: +39 055 457 2465; E-mail: [email protected]

[7] Stem cells: Self-renewal understood (AOP)
DOI: 10.1038/nature04914

***This paper will be published electronically on Nature's website on 14 June at 1800 London time / 1300 US Eastern time (which is also when the embargo lifts) as part of our AOP (ahead of print) programme. Although we have included it on this release to avoid multiple mailings it will not appear in print on 15 June, but at a later date.***

A paper to be published online this week by Nature identifies a molecule that endows embryonic stem (ES) cells with their revered properties: the ability to self-renew and ‘pluripotency’, the ability to make numerous other cell types. Molecules such as this might one day be used to convert a patient’s regular, somatic cell into an ES cell, perhaps avoiding the ethically contentious extraction of ES cells from human embryos.

Stem-cell biologists know that fusing an ES cell with a somatic cell can bestow the latter with pluripotency. Austin Smith and his colleagues show that a protein called Nanog, which is manufactured in young embryos, is responsible: they showed that mouse ES cells making extra Nanog protein can convert neural stem cells into pluripotent cells at a much higher efficiency. They propose that Nanog directs the ES cell machinery to erase old patterns of gene activity and install new pluripotent ones.


Austin Smith (University of Edinburgh, UK)
Tel: +44 131 650 5890; E-mail: [email protected]

[8] And finally… Sperm storage weakens immune system (pp 872-875)

Storing large amounts of sperm can seriously damage your health, if you’re a queen leaf-cutting ant that is. Stockpiling sperm can weaken the immune system of some queens, demonstrating a trade-off between short-term survival and long-term reproductive success.

Queens of the leaf-cutting ant Atta colombica mate young, but live long. Young adult females have only a few hours to copulate and then have to store millions of live sperm for the rest of their lives. But storing large numbers of sperm comes at a cost.

Boris Baer and his colleagues show in this week’s Nature that the number of stored sperm has a strong negative effect on immune defence during colony founding, and there is an additional cost of multiple inseminations. This can be a problem for founding queens who are exposed to a variety of soil-borne pathogens before their first workers emerge and the nests mature, and explains why there is an upper limit on sperm storage.


Boris Baer (University of Western Australia, Nedlands, Australia)
Tel: +61 8 6488 1029; E-mail [email protected]


[9] Accretion of the Earth and segregation of its core (pp 825-833)

[10] A common mass scaling for satellite systems of gaseous planets (pp 834-839)

[11] Control of four stereocentres in a triple cascade organocatalytic reaction (pp 861-863)

[12] Interleukin-2 signals during priming are required for secondary expansion of CD81 memory T cells (pp 890-893)

[13] CRD-BP mediates stabilization of bTrCP1 and c-myc mRNA in response to b-catenin signalling (pp 898-901)


***These papers will be published electronically on Nature's website on 14 June at 1800 London time / 1300 US Eastern time (which is also when the embargo lifts) as part of our AOP (ahead of print) programme. Although we have included them on this release to avoid multiple mailings they will not appear in print on 15 June, but at a later date.***

[14] Atom-by-atom analysis of global downhill protein folding (AOP)
DOI: 10.1038/nature04859

[15] ATM stabilizes DNA double-strand-break complexes during V(D)J recombination (AOP)
DOI: 10.1038/nature04866


Five new contributions to the second week of Nature's peer review debate are to be published next Wednesday at 1800 London time. They will appear at: <http://www.nature.com/nature/peerreview/debate/index.html>

Interested readers are invited to join the debate in Nature's peer review comments blog at:

An open, two-stage peer-review journal
Thomas Koop and Ulrich Pöschl (Editors of Atmospheric Chemistry and Physics)

Statistics in peer review - Researchers need reviewers to check their stats
David Ozonoff (co-editor of Environmental Health and Boston University School of Public Health)

What is it for? Analysing the purpose of peer review.
Elizabeth Wager (Member of the ethics committees of the BMJ, the World Association of Medical Editors and the Committee On Publication Ethics Council)

Wisdom of the crowds
Scientific publishers should let their online readers become reviewers.
Chris Anderson (Editor in Chief of Wired magazine)

Should authors be told who their reviewers are?
Thomas DeCoursey (Rush University Medical Center, Chicago)


The following list of places refers to the whereabouts of authors on the papers numbered in this release. For example, London: 4 - this means that on paper number four, there will be at least one author affiliated to an institute or company in London. The listing may be for an author's main affiliation, or for a place where they are working temporarily. Please see the PDF of the paper for full details.


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Trieste: 5


Kanazawa: 13

Panama: 4


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Edinburgh: 4

Leeds: 3

London: 1

Reading: 3


Pasadena: 1


Boulder: 10


Philadelphia: 13


Seattle: 12


Madison: 13


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For Japan, Korea, China, Singapore and Taiwan

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Published: 15 Jun 2006

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