Highlights from this week's NATURE (VOL.436 NO.7050)

Humans can learn without remembering; How the Earth's insides stay warm; Genes responsible for breast cancer metastasis identified; The age of the Amazon's breath; Hybridization throws up new animal species; Parasites give caterpillars a taste for revenge

* Neuroscience: Humans can learn without remembering
* Particle physics: How the Earth's insides stay warm
* Cancer: Genes responsible for breast cancer metastasis identified
* Earth science: The age of the Amazon's breath
* Evolution: Hybridization throws up new animal species
* Molecular biology: RNAi screening pinpoints synaptic proteins
* Infectious diseases: Bacteria hijack tick proteins to spread Lyme disease
* Security: Fingerprints for fighting fraud
* Astronomy: Extra neon could explain Sun's ringing
* And finally... Parasites give caterpillars a taste for revenge

[1] Neuroscience: Humans can learn without remembering (pp 550-553)

Humans can learn without even realizing what they are doing, according to a study of patients with severe memory loss. Such 'non-declarative' learning has been found in monkeys and rats, but it was unclear whether humans have the same capacity, or whether our tendency to learn consciously means that we have lost this ability. Conscious learning and memory depend on a brain area called the medial temporal lobe. People with damage to this region suffer severe amnesia. But they are still capable of learning simple discriminatory tasks, even though they don't realize it, report Larry Squire and his colleagues in this week's Nature.

The researchers tested two patients with severe medial temporal lobe damage by setting them a simple test in which they were asked to study pairs of random objects and pick the one that was previously designated as 'correct'. Unimpaired subjects learn this task within a matter of days. The study patients took weeks to master it, but nonetheless ultimately achieved high success rates, despite the fact that they were unable to recall why they thought a certain object was the right one to choose.

Larry R. Squire (University of California School of Medicine, San Diego, CA, USA)
Tel: +1 858 642 3628; E-mail: [email protected] <mailto:[email protected]>

[2] Particle physics: How the Earth's insides stay warm (pp 499-503; N&V)

Elusive subatomic particles called neutrinos produced by radioactive decay deep within the Earth have been detected by an international team of researchers. Such particles could one day help us to measure directly how much radioactivity keeps our planet's interior warm, as reported this week in Nature.

The team, led by Georgio Gratta and Atsuto Suzuki, analysed measurements of neutrinos by the Kamioka neutrino detector KamLAND in Japan. This underground detector, consisting of a 13-metre-wide balloon filled with about a thousand tons of liquid, is designed to probe questions about the fundamental physics of neutrinos and to look at their astrophysical sources - but can also be used to study geophysical problems, as in this research.

It is the first neutrino detector capable of spotting neutrinos (actually antineutrinos, the antimatter partners of neutrinos) produced from
radioactive decay of uranium and thorium in the deep Earth. Neutrinos are very light, and hardly interact with other kinds of matter, making them difficult to detect.

The heat that makes the Earth's rocky insides act like sluggish liquid - providing the energy source for volcanic activity and plate tectonics - comes from two sources. Some of it is left over from the planet's fiery formation, concentrated in particular in the iron core. But much of it comes from the decay of radioactive elements in the Earth's mantle. Both the total amount of heat in the deep Earth and the proportions contributed by these two sources are poorly known and hard to measure; but the best current estimates suggest that around half of the heat comes from radioactive decay.

The KamLAND measurements provide an independent means of checking that figure. The initial results now reported by Enomoto and colleagues suggest that it is about right. The researchers haven't yet recorded enough antineutrinos to constrain the amount of radioactive heating very tightly, but the measurements do seem consistent with standard models of the Earth's interior, and put an upper limit on what the radioactive contribution to heating can be.

Georgio G Gratta (Stanford University, Stanford, CA, USA)
Tel: +1 650 725 6509, or +1 650 387 9658; E-mail: [email protected]
<mailto:[email protected]>

Atsuto Suzuki (Tohoku University, Sendai, Japan)
Tel: +81 227956727; E-mail: [email protected]
<mailto:[email protected]>

William McDonough (University of Maryland, College Park, MD, USA)
Tel: +1 301 405 5561; E-mail: [email protected]
<mailto:[email protected]>

[3] Cancer: Genes responsible for breast cancer metastasis identified (pp 518-524)

Identifying the tumour subtypes that influence clinical outcome remains an important goal of medical researchers. Now, a study from Joan Massagué and colleagues helps to shed some light on the genes that mediate breast cancer metastasis to the lung but not other organs. The findings of their analysis appear this week in Nature.

Whereas one subset of the genes involved in lung metastases promote primary tumour growth, a second subset affects the cancer's virulence at the metastatic site. Gene expression analysis showed that these genes were overexpressed in breast tumours that later spread to the lung, but not in those that spread to the bone. The research team also found that patients with the gene signature for lung metastasis had a worse prognosis than other patients. The results of this work could help doctors to refine their prognosis of breast cancer and provide new targets for future treatments.

Joan Massagué (HHMI, Memorial Sloan-Kettering Cancer Center, New York, NY, USA)
Tel: +1 212 639 8975; E-mail: [email protected]
<mailto:[email protected]>

[4] Earth science: The age of the Amazon's breath (pp 538-541; N&V)

Amazonian rivers outgas a significant amount of carbon dioxide and an extensive survey in the Amazon basin has now found that it mostly originates from the breakdown of organic matter that is less than five years old. Emilio Mayorga and colleagues, writing in this week's Nature, suggest that this relatively young organic matter could come from vegetation found beside the rivers or streams. Even though most of the organic matter transported by these rivers is tens of thousands of years old, it contributes relatively little to the carbon dioxide output of the streams.

"The carbon dioxide degassing from the tropics thus simply represents the cyclical movement of the gas from the atmosphere, through land and rivers and then back to the atmosphere, and does not represent an additional input of greenhouse gas," explains Peter A. Raymond in a related News and Views article.

Emilio Mayorga (University of Washington, Seattle, WA, USA)
Tel: +1 206 295 5778; E-mail: [email protected]
<mailto:[email protected]>

Peter A Raymond (Yale University, New Haven, CT, USA)
Tel: +1 203 432 0817; E-mail: [email protected]
<mailto:[email protected]>

[5] Evolution: Hybridization throws up new animal species (pp 546-549)

Ecologists have found the first evidence that two animal species can interbreed and evolve into a new, distinct species by moving to a new habitat. The discovery demonstrates that two animal species can evolve to become one, as opposed to the more common mechanism in which a single species splits to form two.

Although the formation of new species through hybridization is know to occur among plants, researchers have doubted whether the same can happen in animals, because hybrid offspring are usually far less likely to survive and breed than pure-bred strains of the two parent species. For hybrid speciation to occur, therefore, the hybrids would need to be reproductively isolated from parent populations.

This has occurred among fruitflies that recently switched habitat to feed on non-native honeysuckle plants in the northeastern United States, report researchers led by Dietmar Schwarz in this week's Nature. The plant, called Lonicera, is thought to have invaded North America only in the last 250 years. These plants were colonized by fruitflies from a group of species called Rhagoletis pomonella, an initial founding population of hybrids that went on to become a genetically distinct species in their own right, which the authors christen the 'Lonicera fly' in honour of their host plant.

Dietmar Schwarz (The Pennsylvania State University, University Park, PA,
Tel: +1 814 863 3345; E-mail: [email protected] <mailto:[email protected]>

[6] & [7] Molecular biology: RNAi screening pinpoints synaptic proteins (pp 510-517 & 593-597; N&V)

For years, scientists have struggled to systematically identify the proteins that work at the synapse between neurons. An application of RNA interference (RNAi) has now yielded an unprecedented amount of information about the proteins that act to help pass on the intercellular signal. Using an RNAi screen Joshua Kaplan and his colleagues identified 185 genes involved in the function or development of neuromuscular junctions in the nematode worm Caenorhabditis elegans, 132 of which had not previously been recognized as playing a role in these processes. The results of their work and a companion paper from Gary Ruvkun and his team appear in this week's Nature.

Ruvkun's group had independently made the surprising discovery that retinoblastoma pathway genes negatively regulate RNAi in C. elegans. This finding allowed them to create worms with multiple mutant genes in their retinoblastoma and RNAi pathways. These multiple mutations had the benefit of making RNAi more efficient, and therefore more useful for approaches such as RNAi screens. It was with these genetically engineered worms that Kaplan and his fellow researchers were able to study neuronal signalling in such detail.

"This work raises the standard for future experiments in the field: it's not just a gene list from a screen, but a thorough and thoughtful
combination of genetics, molecular biology and data analysis," writes Cori Bargmann in a related News and Views article.

Joshua M. Kaplan (Harvard Medical School, Boston, MA, USA) Paper [6]
Tel: +1 617 726 5900; E-mail: [email protected]
<mailto:[email protected]>

Gary Ruvkun (Harvard Medical School, Boston, MA, USA) Paper [7]
Tel: +1 617 726 5959; E-mail: [email protected]
<mailto:[email protected]>

Cori Bargmann (Rockefeller University, HHMI, New York, NY, USA)
Tel: +1 212 327 7242; E-mail: [email protected]
<mailto:[email protected]>

[8] Infectious diseases: Bacteria hijack tick proteins to spread Lyme disease (pp 573-577)

Lyme disease can develop into a devastating illness: if left untreated it can cause joint swelling and brain inflammation. The disease appears in both mice and humans and is caused by the bacterial agent Borrelia burgdorferi, which infects the body through a tick host. Early signs of transmission include an expanding 'bull's-eye' rash that develops after a tick bite. In a paper to be published in Nature, Erol Fikrig and colleagues reveal an important aspect of Lyme disease transmission.

The researchers found that B. burgdorferi can commandeer a tick salivary protein to facilitate the infection of mice. They explain that it is the first example of a complex pathogen-arthropod inter-relationship that enables a microbe to colonize a mammalian host. Additionally, they suggest that these proteins, which can influence the successful infection of the host organism, might serve as targets for vaccines and therapeutics to combat arthropod-borne diseases such as Lyme disease.

Erol Fikrig (Yale University School of Medicine, New Haven, CT, USA)
Tel: +1 203 785 2453 / +1 203 737 4080; E-mail: [email protected]
<mailto:[email protected]>

[9] Security: Fingerprints for fighting fraud (p 475)

Everyone has seen identity tags like holograms on credit cards or watermarks on documents that are meant to make it impossible to copy them. In a Brief Communication in this week's Nature, researchers report that they can measure the uniqueness of such items directly. The method would render any tagging unnecessary, at least with non-reflective plastic or paper surfaces. Such surfaces have unique imperfections that can be used as a 'fingerprint' to identify them.

Russell Cowburn and colleagues measured these imperfections on plastic, paper or coated paperboard surfaces with an inexpensive portable laser scanner. This scans the surface with a focused beam and measures the light scattered back from the surface. The resulting pattern in the scattered light, they found, is unique for every single surface - just like a fingerprint.

What's more, that fingerprint is pretty resistant to rough handling - for example, it survives even when the paper is screwed into a tight ball, submerged in cold water, baked at 180 degrees Celsius, scribbled upon heavily with a pen or scrubbed with an abrasive cleaning pad. The unique surface imperfections are so precise that there is no known manufacturing process to copy them, say the researchers.

Russell P. Cowburn (Imperial College, London, UK)
Tel: +44 20 75947586; E-mail: [email protected]
<mailto:[email protected]>

[10] Astronomy: Extra neon could explain Sun's ringing (pp 525-528)

Details of the Sun's internal structure and chemical composition can be inferred from its vibrations, which can be likened to the chiming of a bell. But the most recent estimates of the amounts of elements such as carbon, nitrogen and oxygen do not tally with the Sun's vibrations. Jeremy J. Drake and Paola Testa propose a solution to this mismatch in this week's Nature. They used NASA's orbiting X-ray telescope Chandra to measure the amount of neon in the atmospheres of nearby Sun-like stars, and found much more than was previously thought. The astronomers determine that if the Sun's neon abundance is similarly larger than has been thought, and the
other elemental abundances were scaled accordingly, the mismatch between its oscillations and its chemical composition would be resolved.

Jeremy J. Drake (Harvard-Smithsonian Center for Astrophysics, Cambridge, MA,
Tel: +1 617 496 7850; E-mail: [email protected]
<mailto:[email protected]>

[11] And finally... Parasites give caterpillars a taste for revenge (p 476)

When infected with potentially deadly parasites, a caterpillar's tastes change - literally. A Brief Communication in this week's Nature shows that the parasites affect the activity of taste-sensing cells in two different types of caterpillar, causing them to boost their intake of foods that help them to ward off the invaders.

Elizabeth Bernays and Michael Singer studied the caterpillars of two species of tiger moths - Grammia geneura and Estigmene acrea - that live in southern Arizona. These larvae defend themselves by eating plants that contain compounds called iridoid glycosides and pyrrolizidine alkaloids: chemicals that can kill off the parasites before they inflict a mortal wound on their host.

When exposed to these compounds, the taste cells that sense these medicinal agents were more responsive in infected caterpillars than in their parasite-free counterparts, the researchers report. Sensing of other plant components that are ineffective in warding off parasites was not boosted, suggesting that this is a specific mechanism by which caterpillars increase their intake of parasite-fighting foods when they need them most.

Elizabeth A. Bernays (University of Arizona, Tucson, AZ, USA)
Tel: +1 520 293 6132; E-mail: [email protected]
<mailto:[email protected]>


[12] Crossover from 'mesoscopic' to 'universal' phase for electron
transmission in quantum dots (pp 529-233)

[13] Unconventional critical behaviour in a quasi-two-dimensional organic
conductor (pp 534-537)

[14] A sharp lithosphere-asthenosphere boundary imaged beneath eastern
North America (pp 542-545)

[15] Molecular recycling within amyloid fibrils (pp 554-558)

[16] Action potential refractory period in ureter smooth muscle is set by
Ca sparks and BK channels (pp 559-562)

[17] Somatic control of germline sexual development is mediated by the
JAK/STAT pathway (pp 563-567)

[18] Temporal targeting of tumour cells and neovasculature with a
nanoscale delivery system (pp 568-572)

[19] T-cell receptor triggering is critically dependent on the dimensions
of its peptide-MHC ligand (pp 578-582)

[20] Functional coordination of intraflagellar transport motors (pp

[21] Optimality and evolutionary tuning of the expression level of a
protein (pp 588-592)

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Published: 27 Jul 2005

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