American Scientist

This roundup of notable recent items about scientific research, culled from news reports, were compiled from free electronic newsletters produced by Sigma Xi's Public Understanding of Science Program.

Ebola Traced to Bats

Scientists may have located the long-sought natural reservoir of the deadly Ebola virus. After combing through 1,000 species, a team working in Gabon and the Republic of Congo isolated the virus in three species of fruit bats, which are eaten by people in Central Africa. Genetic traces turned up in 22.6 percent of the bats tested, but the virus produced no symptoms in the infected bats, presumably allowing them to spread the disease efficiently. Ebola's cycles of emergence and disappearance have intrigued infectious disease specialists. The new study does not nail down the bats as Ebola's prime nesting spot between outbreaks—certainty would require scientists to plot all points on the natural cycle of the disease—but it does paint the bats as the best candidate yet.

Leroy, E. Fruit bats as reservoirs of Ebola virus. Nature 438:575–576 (December 1).

Obscured Starlight Defines Charon

Last summer, Pluto's moon Charon blocked light from a distant star and in the process lifted itself out of obscurity. An international team of astronomers were ready with three telescopes locked in to catch the momentary eclipse, called a stellar occultation. From that triangulated view of what happened to the starlight as it passed around Charon's edge, the astronomers determined many details about the moon. For instance, Charon is some 1,200 kilometers across, or about half Pluto's size. Its density is 1.71 times that of water, meaning close to half of its icy mass consists of rock. The light also suggested that Charon has the same atmosphere as Pluto, backing up the idea that Pluto and its three moons coalesced as a system when two objects collided.

Sicardy, B., et al. Charon's size and an upper limit on its atmosphere from a stellar occultation. Nature 439:52–54 (January 5) .

Catching Cancer's Spread

Cancers orchestrate the movement of bone marrow cells, then tap them for the oxygen and other nutrients that power metastasis, according to a study on mice. The finding answers key questions about how tumor cells take up residence in other parts of the body. Cellular envoys—normal bone marrow cells pressed into pernicious action by tumor cells—prime the organ in which the tumor cells will implant and turn into full-blown cancer. Once that colonization of another organ has occurred, cancer is extremely difficult to eradicate. New treatments might be developed by tracking the movement of the envoy cells which provide a map of metastasis targets.

Rafii, S., and Lyden, D. VEGFR1-positive haematopoietic bone marrow progenitors initiate the pre-metastatic niche. Nature 438:820–827 (December 8).

Snails Hasten Marsh Grass Die-Off

In the last five years, Louisiana and South Carolina have lost thousands of acres of salt marsh, the vital coastal wetlands that filter pollutants, blunt the force of storms and serve as nurseries for marine life. Marsh ecologists had blamed the die-off on salt-stressed soil, but now another culprit has come to light: snails. Typically content to live around the edges of a marsh, munching on dead grasses and fungus, snails quickly changed their grazing habits once the salt marshes became stressed by drought. Huge numbers of them colonized the drier ground, eating large swaths through the grasses. Ecologists who tracked the occurrence contend more marshes could be subjected to the snails' altered eating habits as climate change–related droughts become more frequent.

Silliman, B. R., et al. Drought, Snails, and Large-Scale Die-Off of Southern U.S. Salt Marshes. Science 310:1803–1806
(December 16).

Skyscraper Causes Earthquakes?

Taipei 101 juts more than 500 meters up into the sky, making it the tallest building in the world. And it's not just tall: The structure is big-boned and immense, weighing 700,000 tons. A Taiwanese geologist has claimed that the behemoth exerts so much pressure on the ground that it has triggered two earthquakes and may have reopened an ancient fault. Before construction, the Taipei basin averaged about one micro-quake, of less than magnitude 2.0, per year. But during the building's construction period that number increased to about two micro-quakes per year. Since the building was completed in 2004, two temblors large enough to be felt, of magnitudes 3.8 and 3.2, have struck directly beneath 101. Ironically, the hybrid of concrete and steel used in part to protect the building from earthquakes may help to create them.

Lin, Cheng-Horng. Seismicity increase after the construction of the world's tallest building: An active blind fault beneath the Taipei 101. Geophysical Research Letters 32:L22313 (November 30).

Plucking Gene Makes Mice More Plucky

Call it addition through subtraction: Laboratory mice got a full dose of courage after scientists took from them one simple gene. Fear is fundamental, cruising along similar neurological pathways in all mammals. Specifically, it takes hold in the amygdala, a primitive little region of the brain that becomes hyperactive when the going gets tense. Working in the amygdala, scientists found heavy concentrations of a protein called stathmin; that protein was not abundant elsewhere in the brain. So they genetically engineered the stathmin gene out of a line of mice. Those mice showed significantly less caution than a control group in two different experiments. This result suggests that the stathmin protein might play a role in the formation of unconscious memory and the fears those memories create, which are filed in the amygdala.

Shumyatsky, G. Stathmin, a Gene Enriched in the Amygdala, Controls Both Learned and Innate Fear. Cell 123:697–709. (November 18).