Science
Notebook

Monday, November 13, 2006

Sea Urchins' DNA Code Mapped

An international team of nearly 250 scientists reported Friday that they had determined the exact order of all 814 million letters of DNA code that carry the instructions for making and maintaining a sea urchin.

If you think that's relevant only to scuba divers and sea otters, you're wrong. Among life-forms that lack backbones, these spiky critters -- which are kissing cousins of starfish and can live for more than 100 years -- are our closest relatives. They are more similar to us than fruit flies or worms, those classic laboratory workhorses that for decades have provided insights into human biology and genetics.

Sea urchins, it turns out, have 23,300 genes, only slightly fewer than humans have. Many are similar to genes that cause human diseases, including Huntington's disease and muscular dystrophy. That means urchins may provide a new venue for studying the molecular origins of those ailments.

Surprisingly, urchins have 979 genes that, by the looks of them, are involved in sensing light or odors -- not bad, considering they have neither eyes nor noses. Lots of those genes are most active in urchin "feet," suggesting those appendages are as important for vision and other senses as for movement.

"I've been looking at these organisms for 31 years, and now I know they were looking back at me," said Gary Wessel of Brown University, part of a group that was led by Richard Gibbs and George Weinstock of Baylor College of Medicine.

In reports in the Nov. 10 issue of the journal Science and the Dec. 1 issue of Developmental Biology, the team also anticipates learning from the urchin's spectacular array of immune system genes and the genes for making its dome-shaped skeleton -- which is made of different minerals than ours.

-- Rick Weiss

Massive Flare Noted in Pegasus

The most powerful solar flare ever detected -- a release of energy a hundred million times as powerful as a typical flare from our sun -- was observed late last year on a star in the constellation Pegasus. The explosion was so massive that, had it come from the sun, it would have wiped out most life on Earth.

Fortunately, our sun is a far more stable star than the one about 135 light-years away that sent out the flare -- an explosion picked up by NASA's Swift orbiting telescope. The satellite is used to detect gamma-ray bursts, but the flare from star II Pegasi was energetic enough that it triggered a false alarm. NASA said the energy released was equivalent to about 50 million trillion atomic bombs.

"The flare was so powerful that, at first, we thought it was a star explosion," said Rachel Osten of the University of Maryland and NASA Goddard Space Flight Center in Greenbelt. She and colleagues at the Italian Space Agency describe it in a paper to be published in the Astrophysical Journal.

Scientists believe solar flares occur when a shower of electrons rains down from a star's superheated corona -- the outermost part of its atmosphere -- to the photosphere, or "surface." The loosening of the electrons results from twisting and breaking of magnetic field lines lacing through the corona and heating the coronal gases to temperatures usually encountered only deep inside the sun.

The Swift satellite was designed to study the origins and nature of the mysterious gamma-ray bursts, thought to result from the collapse and explosion of massive stars.

-- Marc Kaufman

Plankton's Influence on Clouds

Phytoplankton, microscopic plants that live in the ocean in vast quantities, may play a role in cloud formation, which in turn may have an effect on how much sunlight reaches and warms Earth's surface, a surprising study has found.

Researchers from the Georgia Institute of Technology and North Carolina State University discovered the link between clouds and the biosphere as they were examining increases in cloud cover over part of the Southern Ocean that encircles Antarctica. Using satellite observations, they found that the increased cloudiness coincided with a large phytoplankton bloom.

The scientists theorize that oxidation of the chemical isoprene, which phytoplankton emit, produced airborne particles that helped double concentrations of cloud droplets in the region.

The team calculated that the increased cloudiness reduced the absorption of sunlight by the same amount that has been observed in the more polluted areas of Earth. The researchers, who reported their findings in the Nov. 2 online edition of the journal Science, suggest the study could point toward new ways to curb global warming.

"Studies like this one may help reshape the way we think about how the biosphere interacts with clouds and climate," said Georgia Tech assistant professor Athanasios Nenes, who co-authored the paper. "We can now see very strongly the influence of marine biology on oceanic clouds."

-- Juliet Eilperin