PNAS highlights for the week of May 16 - 20


Network Analysis Details Partisanship in House of Representatives

A mathematical network analysis of voting patterns and committee memberships in the 107th U.S. House of Representatives suggests that the Select Committee on Homeland Security is among the most partisan committees in the House and that it has close membership ties with the House Rules Committee rather than with the Permanent Select Committee on Intelligence, which is among the least partisan committees in the House.

Mason Porter and colleagues used network analysis to explore data of 101st-108th Houses (1989-2004) and provide detailed examples for the 107th House (2001-2002). The researchers determined a measure of the connection between pairs of House committees and subcommittees by looking at the number of members they share. They then clustered the committees according to strengths of those connections. This led to the finding of close ties between the House Rules Committee and the Select Committee on Homeland Security.

The researchers also analyzed the 990 House roll call votes of the 107th Congress and found that a simple mathematical tool called a singular value decomposition can identify Representatives' partisanship and their degree of cooperativity with the House as a whole.

Using these measures of Representatives' voting records, committees and subcommittees can be categorized according to the partisanship of their constituent members. The paper identifies "extreme" committees, or those whose members are highly partisan. Examples include the Judiciary, the House Rules, and the Homeland Security Committees.

Potential Diabetes Treatment with Transplanted Liver Cells

According to a newly published report, researchers have converted adult human liver (AHL) cells expressing the pancreatic and duodenal homeobox gene-1 (PDX-1) into insulin-producing cells that can be transplanted into mice to treat diabetes.

Cell replacement therapies for diabetes have been hindered by the limited availability of insulin-producing tissues, such as pancreatic ß-cells, and the need for lifelong immunosuppression. Previous research has shown that PDX-1 plays a central role in the development of the pancreas and in ß-cell function.

Sarah Ferber and colleagues demonstrated that PDX-1 activated the insulin promoter in up to 25% of treated AHL cells. The researchers observed that the insulin was stored in granules as in pancreatic ß-cells and was secreted in a glucose-regulated manner. The researchers transplanted the treated AHL cells into hyperglycemic mice with diminished serum insulin levels. The cells caused a gradual and prolonged decrease in the blood glucose levels of the mice.

The authors suggest that their work may lead to therapies that allow individuals with diabetes to be the donors of their own insulin-producing tissues.

Virus Emergence in African Bushmeat Hunters

The identification of two viruses among central African hunters of nonhuman primates reveals the need to regularly survey human populations in contact with animals, researchers report.

William Switzer and colleagues sampled blood from >900 people from 12 villages in Cameroon, who reported exposure to the blood and body fluids of nonhuman primates. Exposure occurred during hunting, butchering, and in some cases keeping primates as pets.

The researchers found two viruses, HTLV-3 and HTLV-4, both of which belong to a genus of viruses known as deltaretroviruses. Other deltaretroviruses like HTLV-1 cause leukemia and other inflammatory diseases, and HTLV-2 is known to cause neurological disease.

HTLV-3 is similar to the simian virus STLV-3, leading the researchers to believe that the individual carrying the virus was infected through direct contact with a primate.

HTLV-4 does not have a primate counterpart, making its origin less clear. The researchers suggest that HTLV-4 may have arisen through cross-species transmission from an animal carrying a highly divergent form of STLV not previously identified.

Subliminal Processing of Threatening Words

Researchers report that individuals can unconsciously process the meaning of subliminal words--addressinga long-standing question in cognitive psychology.

To measure brain activity during presentation of subliminal words, Lionel Naccache and colleagues studied three patients with epilepsy who had electrodes placed in their brains as part of a presurgical evaluation.

On a computer screen, the patients viewed words flashed too quickly to be seen consciously, as well as visible words shown long enough to be detected. Half of the words were threatening in nature (e.g., "danger", "kill"), and the other half were emotionally neutral (e.g., "cousin", "see"). During word presentation, the researchers recorded electrical activity in the amygdala, a brain structure that responds to fearful or threatening stimuli.

The researchers observed that the subliminal, threatening words were detected by the brain and elicited a more positive electrical response than neutral words. Differences in electrical activity evoked by threatening versus neutral words were similar, whether the words were consciously seen or subliminal. However, consciously seen words were processed more quickly and elicited a stronger, more sustained effect than subliminal words.

These findings indicate that the emotional meaning of words can be accessed subliminally, occurring in the same brain region as conscious processing.

GM Crops with Broader Insect Resistance

Researchers report the development of a genetically engineered crop providing long-term resistance against many insect species.

The Bt gene, which has already been incorporated into potatoes, cotton, and corn, enables a plant to produce an insecticide. But researchers fear that heavy use of commercial pesticides containing Bt will breed resistant bugs.

Paul Christou and colleagues modified the Bt gene to make it more difficult for insects to evolve resistance. The researchers fused the original Bt gene with a gene segment called RB, enabling the Bt toxin bind to more types of molecules in the insects' gut, making it more lethal.

Rice and corn plants with this BtRB fusion gene were shown to be more toxic to a wider range of insects than plants with Bt alone.

Corn plants producing low levels of BtRB killed 75% of stem borer larvae, compared with 17% in Bt-only plants. Bt-resistant cotton leaf worm was highly susceptible to BtRB plants; 90% of larvae died within 9 days.

BtRB was not toxic to all insects, with no effect on the cereal aphid Rhopalosiphum padi.

The authors say further tests are necessary to make certain BtRB crops are not toxic or allergenic in humans.

Bonding Amino Acids to Inorganic Surfaces

Researchers have measured the bonding strengths of amino acids to a variety of inorganic surfaces and designed combinations that bond to each other.

Robert Willett and colleagues measured how the 20 amino acids used in proteins adhere to nine different metals, semiconductors, and insulators. The researchers found that adhesion depended on the amino acid, material surface, pH, and the solvent between them.

In general, electrically charged amino acids bonded more strongly, while uncharged ones bonded less strongly. Some substrates were more adherent, especially the semiconductors and aluminum. The most adhesion occurred between charged amino acids and the semiconductors. The least occurred between uncharged amino acids and gold, platinum, and palladium.

The team used their results to predict and measure the adhesion of a short chain of amino acids to an etched semiconductor. The chain had nonadhesive leucine tips and an adhesive aspartate center, while the semiconductor had parallel veins with alternating strong and weak adherence properties. Adhesion dropped when the separation between the veins bonding the aspartate became so small that the leucine segments no longer fit between the veins.

The researchers suggest this precise spatial control of amino acids on inorganic surfaces could have many technological applications.

Tracing the Rise of Ants

In a perspective article, Edward O. Wilson and Bert Hölldobler explore the evolutionary history of ants, tracing their waves of expansion from the first appearance more than 100 million years ago.

Over the past two decades, fossil discoveries combined with studies of anatomy, behavior, and DNA have helped clarify the phylogeny of ants, the authors say. Yet some puzzles remain, such as how the important and ancient subfamily Ponerinae spread so widely while retaining relatively primitive social organization--a question the authors term "the ponerine paradox."

A full explanation will require further discoveries in paleontology and ecology, the authors note. Until then, Wilson and Hölldobler offer a combined phylogenetic and ecological "dynastic-succession" hypothesis that ties together existing knowledge.

Key events in this history include an initial adaptation to forest ground litter and soil coincident with a surge in flowering plants, then an advance to ecological dominance in tropical forests, and finally a broad expansion up into trees and outward into drier environments.

Fish Genitalia May Balance Attractiveness with Predatory Escape

Male genital size in some fish species may be driven by competing evolutionary mechanisms, reflecting a tradeoff between the capacity to attract mates and the ability to quickly evade predators, researchers report.

Diversity of male genitalia size in animals with internal fertilization has intrigued scientists. Most evolutionary explanations have centered on postmating sexual selection, such as sperm competition advantages. The roles of premating sexual selection and natural selection have been less well studied.

Brian Langerhans and colleagues studied female preference and swimming performance in western and Bahamas mosquitofish. Mosquitofish cannot retract their gonopodia--modified anal fins through which males transfer sperm to females--and they often display or swing them during courtship.

In laboratory experiments, females preferred to spend time with videos of males displaying digitally enlarged gonopodia rather than those with average-sized gonopodia, which implies sexual selection for increased gonopodium size. Yet the researchers also found that males with larger gonopodia were slower to escape potential predators through evasive swimming bursts, an effect perhaps due to greater drag in the water.

These results suggest that alternative mechanisms, such as mating selection favoring larger genitalia and natural selection favoring reduced size, may also drive genital diversification.


Rapid Identification of Respiratory Pathogens

Researchers describe a high-throughput method to identify and genotype the bacteria in respiratory samples.

Human-Modified Temperatures Induce Species Change

Human activities contribute to surface-air temperature changes, and these human-altered temperatures are associated with discernible changes in plant and animal traits.

Reducing Scarring Following Traumatic Brain Injury

Treating rats with the cell cycle inhibitor flavopiridol after inducing a brain injury results in decreased neuron death, reduced scar tissue formation, and improved motor and cognitive recovery.

Early History of Domesticated Plants from Mexico Cave

Radiocarbon dating of specimens from Coxcatlan Cave in Mexico provides insight into the initial appearance of three domesticated plants in the country's Tehuacan Valley.

Source: Eurekalert & others

Last reviewed: By John M. Grohol, Psy.D. on 21 Feb 2009
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