Plant Survival Strategies
Plants lack a means by which they can escape environmental extremes, and thus must be well adapted to local environmental variation. To investigate how genotype is linked to environmental response in Arabidopsis, Wilczek et al. (p. 930, published online 15 January) planted multiple accessions and flowering time mutants across the native range of Arabidopsis in Europe. The laboratory accession, Columbia, which rapidly cycles to flowering in the laboratory, could only do the same in one location. Furthermore, mutations affecting flowering time response to the environment had only minor effects on life history outside a small window of sensitivity. A model was developed that explains most of the observed variation in flowering time across a wide range of seasonal environments and successfully predicts flowering time under simulated environmental conditions.
Network research is increasingly prevalent in a number of disciplines. Insights in the social sciences—from the spread of behaviors through a network of friends to the kinds of organizations that stimulate innovation—are generating considerable excitement. Borgatti et al. (p. 892) review the history of network research in the social sciences and identify some historical criticisms and current challenges facing the field.
Iron Isotope Idiosyncrasy
Iron isotope studies have shown that rocks on Earth have different properties from those of Mars or other meteorites. The origin of these differences has been unclear. Polyakov et al. (p. 912; see the Perspective by Poitrasson) has used recent data on the vibrations of deep mantle minerals to calculate how iron isotopes fractionate with pure iron as a function of pressure and temperature. The data imply, surprisingly, that at high pressures, and despite high temperatures, pure iron favors the light isotopes. Thus, the planetary differences can be explained by formation of Earth's core at higher pressures than for Mars or other planetesimals.
The Farside of the Moon
Because the Moon presents a constant face toward the Earth, we have much more information on its nearside than its farside. Indeed obtaining accurate gravity and topographic data on the farside have been difficult because spacecraft are hidden from Earth and are thus difficult to track. The geology of the farside of the Moon is different from the nearside. Results from the Japanese Kaguya (SELENE) spacecraft enhance our understanding of the of the Moon's evolution and, in particular, of the farside (see the Perspective by Neumann). SELENE includes a separate relay spacecraft to provide accurate tracking data on the farside. Using this setup, Namiki et al. (p. 900) provide an improved gravity map of the Moon, which shows a marked difference between the nearside and farside. In combination with a high-resolution lunar topographic map by Araki et al. (p. 897) the data indicate that the Moon has a rigid crust, particularly on the farside. Detailed imaging of volcanic deposits and craters by Haruyama et al. (p. 905, published online 6 November) shows that volcanism apparently continued for longer on the farside than the nearside. Ono et al. (p. 909) describe how radar signals from SELENE have penetrated some of the flows on the nearside and may be mapping hiatuses. Together, these data help clarify the volcanic history of the Moon. SELENE is the first of several spacecraft now orbiting or scheduled to arrive at the Moon this year, and these results set the stage for a renewed focus on lunar evolution.
Unveiling Spin Crystals and Textures
The complex interactions within correlated electron systems are expected to give rise to stable configurations of electronic charge and spin textures. The identification of these states has been experimentally challenging (see the Perspective by Zaanen). Mühlbauer et al. (p. 915) use neutron scattering to probe a pocket of the phase diagram of the chiral magnet MnSi to reveal a lattice of spin textures called skyrmions. Furthermore, the lattice of vortex-like spin states can be described theoretically, providing a recipe for seeking out other exotic electronic and spin crystal structures. Recent developments in condensed-matter physics have revealed the existence of topological insulators—quantum phases of matter where the properties are dependent on the spin structure of the electronic Fermi contours on the surface. Hsieh et al. (p. 919) use spin-polarized, angle-resolved photoemission spectroscopy to probe the spin texture in the momentum space of a topological insulator, a BiSb alloy. Mapping out spin textures revealed the topological class of the novel topological quantum spin Hall insulators and allowed numerical imaging of the topological quantum numbers.
Pinning Down Parasitic Particles
Parasitic wasps contain virus-like particles of unknown origin, which have been hypothesized to be either of wasp or viral origin. Bezier et al. (p. 926; see the Perspective by Stoltz and Whitfield) show that the particles come from a lineage of polydnaviruses derived from portions of a nudivirus genome integrated into a wasp genome. These viral genes encode proteins with similarity to nudivirus (baculovirus) structural proteins and are used for packaging wasp genes into virion-like particles. These particles are injected into lepidopteran host larvae, along with the eggs of the wasp, and the wasp genes are expressed and suppress the defense response of the host, allowing the wasp eggs to develop and parasitize the larva.
The Sigma-1 Receptor--Orphan No More
The sigma-1 receptor has long been fairly mysterious, originally identified as a molecule that binds opioid drugs and thought to be important in some psychiatric diseases and cocaine addiction. However, it has been an “orphan receptor” for years—lacking known endogenous ligands. Now Fontanilla et al. (p. 934) have used receptor binding, photoaffinity labeling and displacement, electrophysiology, and behavioral tests in knockout animals to demonstrate that the naturally-occurring hallucinogen, N,N-dimethyltryptamine is the endogenous ligand for sigma-1 receptors.
GPR3 and Alzheimer's Disease
Accumulation of the amyloid-β peptide (Aβ) is thought to represent a central problem in the pathogenesis of Alzheimer's disease. Aside from the two proteases responsible for the generation of this peptide, few additional potential drug targets for the treatment of Alzheimer's disease have emerged. Thathiah et al. (p. 946) describe an extensive high-throughput screen that sought to identify modulators of Aβ production. This functional genomics effort identified the G protein-coupled receptor, GPR3, as a modulator of Aβ production. GPR3 has been mapped to a chromosomal locus associated with increased risk for Alzheimer's disease; is highly expressed in hippocampus and cortex, regions of the brain that strongly correlate with Alzheimer's disease progression; and thus represents an attractive drug target.
Social Comparison and Negative Emotions
Envy and schadenfreude (pleasure at another's misfortune) are profoundly social emotions and, perhaps, uniquely human. The mechanisms and brain areas underlying these sentiments are unclear. Using brain imaging, Takahashi et al. (p. 937; see the Perspective by Lieberman and Eisenberger) found that the dorsal anterior cingulate cortex, where cognitive conflicts are processed, plays a central role in processing envy. Dorsal anterior cingulate activation was stronger when the envied person had superior and more self-relevant characteristics. In contrast, the ventral striatum, a central node for processing reward, was associated with schadenfreude. Ventral striatum activation was more intense when misfortune befell an envied person more so than a neutral person. The more dorsal anterior cingulate activation an envied individual triggered, the greater the ventral striatum activation when bad luck struck them.
In yeast, a secreted peptide modified by the lipid farnesyl is used to attract cells to mate with. This pheromone is directly exported from cells by a transporter of the Mdr family, rather than being secreted by the classical secretory pathway. Ricardo and Lehmann (p. 943; see the Perspective by Hla and Im) demonstrate that lipid modification and an Mdr export pathway are also used by Drosophila embryos to attract germ cells to the somatic gonad, most likely through the release of a geranylated peptide attractant. Components of this unconventional export pathway are highly conserved, suggesting that similarly lipid-modified chemoattractants act from yeast to man.
Gesture and Language Acquisition
A child's vocabulary affects how successful that child will be in school. Children from lower socioeconomic brackets tend to have smaller vocabularies than children from higher socioeconomic brackets, an effect related to how the parents talk to the child. Now Rowe and Goldin-Meadow (p. 951) show that how the parents gesture to the child also affects the child's vocabulary. Gestures precede speech development and, after speech development, continue to enrich the communication process. Comparing how young children and their parents used gesture in their communications with analyses of socioeconomic status and of the child's vocabulary at age 54 months showed disparities in gesture use that preceded vocabulary disparities.
Scattering from Vortices
Scanning tunneling spectroscopy and the interference of quasiparticles of high-temperature superconductors is being used to probe the local electronic interactions and excitations within the material. In zero magnetic field there are a number of factors that contribute to the scattering processes, the relative contributions of which are unknown. Hanaguri et al. (p. 923, published online 22 January) use a magnetic field to induce vortices in the material. Because the vortices are quantum entities with quantized units of magnetic field and phase associated with them, the authors argue that they provide a benchmark with which to compare the scattering processes. With some complex analysis of the spectroscopy, the momentum-dependent coherence factors of the scattering processes were extracted. Such data may provide insights into the pairing mechanism of the cuprate superconductors.
In the Flick of an Eye
Microsaccades are the involuntary, very small, fast eye movements that occur during fixation. The neural mechanisms underlying microsaccades are still not fully understood. Hafed et al. (p. 940) investigated the role of a brain area called the rostral superior colliculus in the generation of these eye movements. In electrophysiological recordings, rostral superior colliculus cells were “tuned” for microsaccades. This tuning was very similar to that observed in the rest of the colliculus for macrosaccades. Pharmacological inactivation of the rostral superior colliculus with the drug, muscimol, led to a marked reduction in the probability of microsaccade generation. Thus, microsaccades share the same neural mechanisms in the superior colliculus as voluntary saccades.