Low-Latitude CO2 Source
Several modeling studies suggest that increases in the concentration of CO2 in the atmosphere at the end of the last glacial period were caused by changes in high-latitude ocean processes. However, the equatorial Pacific is currently the area that transfers the largest amount of CO2 to the atmosphere. Palmer and Pearson (p. 480) have measured the boron isotopic composition of planktonic foraminifera from the western equatorial Pacific and find that this area was a strong donor of CO2 to the atmosphere 16,000 to 14,000 years ago. This observation suggests that there may have been a higher frequency of La Nina conditions during that interval.

The Y's of a Polymer Solution
When placed in dilute solution, amphiphilic diblock copolymers, in which hydrophilic and hydrophobic segments alternate, can form a variety of structural motifs, depending on the concentration, temperature, and block molecular weight. These motifs result from weak solvent-polymer and polymer-polymer interactions, and new examples are still being discovered. In an exploration of the phases, a polybutadiene-poly(ethylene oxide) diblock polmer in water, Jain and Bates (p. 460) observed a number of unusual motifs above a critical surfactant molecular weight, including Y-junctions, end caps, and fused loop networks.

Synthesizing Nanotubes in Nanotubes
The packing of spherical objects inside a cylindrical tube depends on the ratio of their diameters. Mickelson et al. (p. 467; see the cover) packed C60 fullerene molecules inside a boron nitride nanotube and found that the confinement of the tube forces the C60 closer together than they would naturally prefer, and leads to unusual packing formations. The C60 molecules can be fused together to form a conducting nanotube inside the insulating boron nitride outer casing.

Deep Fault Beneath Kilauea
Earthquakes at Kilauea Volcano, Hawaii, can be volcanic (caused by magma movement) or tectonic (caused by the volcanic load on the relatively thin oceanic crust). Wolfe et al. (p. 478) distinguished between volcanic and tectonic earthquakes below 13 kilometers depth using improved relocation and focal-mechanism analysis procedures. They find an active, low-angle, seaward dipping fault plane at about 30 kilometers depth that is laterally quite extensive and is related to tectonism in the lithosphere. Explaining this deep fault will refine our understanding of plate strength and deformation mechanics.
CREDIT: WOLFE ET AL.

DNA Methylation as Tumor Suppressor
Many human cancers show reduced levels of genome-wide DNA methylation, and this epigenetic alteration appears to play a causal role (see the Perspective by Lengauer). Gaudet et al. (p. 489) generated genetically altered mice with severely reduced levels of DNA methylation. Within 4 to 8 months of birth, the mutant mice developed aggressive T cell lymphomas that exhibited a high frequency of trisomy (the presence of extra chromosomes in cells). In a related study of a mouse model genetically predisposed to develop sarcomas, Eden et al. (p. 455) showed that reduced genomic methylation accelerates tumor development and that hypomethylated cells from these mice have a higher rate of chromosome loss than do normally methylated controls. Thus, genome-wide hypomethylation promotes cancer development, most likely by enhancing chromosomal instability.

Tough Titanium Alloys
By satisfying three "magic" criteria relating to the stability of body-centered cubic phases, Saito et al. (p. 464; see the Perspective by Shiflet) have designed titanium-based alloys that show a remarkable spectrum of "super" properties, which include high strength, elasticity, and plasticity as well as low modulus. They also exhibit temperature-invariant expansion ("Invar" behavior) and elasticity ("Elinvar" behavior). Deformation occurs along fault planes without the need for dislocations.
CREDIT: SAITO ET AL.

Come to the Point
Using a microwave plasma-assisted chemical vapor deposition technique, Zhang et al. (p. 472) synthesized highly tapered multiwall carbon nanotubes. The roots of the tubular cones are of micrometer size and taper to nanometer-scale tips. Because these tubes can be more readily mounted, they may prove useful as tips for atomic force microscopes or as field emitters.

Changing Chromosome Separation for Meiosis
In meiosis, the process that produces gametes, two rounds of chromosome segregation follow one round of DNA replication; in the first meiotic division, homologs, rather than sister chromatids, segregate. The machinery that controls chromosome segregation must be modulated so that sister kinetochores can first undergo co-orientation (attachment to microtubules emanating from the same spindle pole) and can then lose the cohesin complexes that hold sister chromatids together. Lee and Amon (p. 482) report that the budding yeast Polo-like kinase Cdc5 is instrumental in phosphorylating and removing meiotic cohesin from chromosomes and is essential for sister kinetochore co-orientation during meiosis I. In addition, Mam1, a protein essential for co- orientation, depends on CDC5 function for its recruitment to the kinetochores.

Antibody Blocking of Amyloid Proteins
Increasing evidence suggests that the toxicity of b-amyloid (Ab), which is involved in Alzheimer's disease (AD), and of other amyloid proteins is associated with soluble oligomeric intermediates and not the resulting insoluble fibrils. Kayed et al. (p. 486) have raised an antibody against soluble oligomers of Ab peptides that blocks the toxicity of this species and also the toxicity of the soluble oligomers of many other amyloidogenic proteins, including a-synuclein and the prion peptide. Immunological staining of postmortem brain tissue from patients with early AD showed that the distribution of soluble Ab oligomers was different from that of amyloid plaques.

Flight Caught on the Fly
Most of the recent studies of insect flight have relied on data gathered from tethered animals. To study the aerodynamics of active maneuvers in free flight, Fry et al. (p. 495) used the natural search behavior of the fruit fly Drosophila. Fruit flies explore their environment using a series of straight flight sequences interspersed with rapid turns called saccades. During these maneuvers, the flies change heading by 90{degrees} in less than 50 milliseconds. These maneuvers were captured on infrared video cameras at 5000 frames per second by luring flies toward a visual target laced with vinegar. Replays show that the flies generate the torques required to turn using remarkably minor alterations in wing motion. In addition, the experiments indicate that inertia, and not friction, dominates the flight dynamics of insects.

The Early Effects of Noise Pollution
A considerable body of work in the visual system of higher animals has established that postnatal maturation and refinement of neuronal connections requires salient binocular stimuli as would be present in the normal environment. The parameters for the developing auditory cortex are less clear, and Chang and Merzenich (p. 498) present an intriguing situation. They find that rearing infant rats in a continuous noise environment has the effect of maintaining the immature status of the auditory cortex, in terms of neuronal tuning and overall size. Furthermore, adult rats raised in such surroundings appear to retain their plastic potential because reversion to a salient auditory environment triggers a largely similar process of maturation, many weeks after it would normally have occurred.
CREDIT: CHANG AND MERZENICH

Insulin Receptors
In Drosophila, the insulin receptor (DInR) is expressed throughout the animal. Song et al. (p. 502; see the Perspective by Dickson) now analyze how the DInR functions during visual system development. As axons make their way from the retina to their final targets in the brain, a well-organized mapping results in thorough distribution of retinal connections across the optic lobe. When DInR or its adaptor protein Dock are disrupted by mutation, the retinotectal axonal connections are also disrupted. Thus, in Drosophila, one of the myriad functions of the insulin receptor is to mediate, with the help of Dock, the normal development of neuronal connections from eye to brain.

Shedding New Light on Superradiance
Superradiance is normally described as a scattering process in which light is collectively emitted from an ensemble of excited atoms; the photons that are emitted spontaneously from each atom are in phase. However, Schneble et al. (p. 475) looked at the scattering of short pulses of light from a Bose-Einstein condensate and found that at these time scales, the amplification is attenuated. Thus, in this case, not only is light scattered from an atomic grating--atoms are also scattered from the light grating.

Phosphorylation of RNA Polymerase with Forkhead Proteins
Winged-helix forkhead (Fkh) proteins are transcription factors that function in several cellular processes such as cell cycle regulation, cell death, and cell differentiation. The Fkh proteins assemble with the promoter regions of genes and function in either transcription activation or repression. Morillon et al. (p. 492) report that the yeast forkhead proteins Fkh1p and Fkh2p are involved in transcription elongation but with opposing functions. By affecting the phosphorylation status of the carboxy-terminal domain of the RNA polymerase molecule, Fkh2p promotes elongation, whereas FKH1p promotes arrest of the polymerase and is involved in 3' end formation of pre-messenger RNA.

Copyright (c) 2003 by the American Association for the Advancement of Science.