American Scientist

This roundup summarizes some notable recent items about scientific research, selected from news reports compiled in Sigma Xi’s free electronic newsletters.

The Chihuahua Gene

Dogs show greater variation in size than any other terrestrial vertebrate. Yet all breeds—from the tiny terrier to the massive mastiff—are comparatively recent descendants of wolves, having most likely been domesticated just a few tens of thousands of years ago. Now biologists may have discovered how such diversity of size could have arisen so quickly: Body size in dogs may be largely controlled by a single gene on canine chromosome 15, one encoding insulin-like growth factor 1. One form of this IGF1 gene is common to all small dog breeds and is nearly absent from giant breeds. Remarkably, the investigators were able to identify this gene without having to perform experimental crosses; instead they took advantage of the information available from dog breeders’ centuries of experience.

Sutter, N. B. et al. A single IGF1 allele is a major determinant of small size in dogs. Science 316:112–115 (April 6).

Tastes Like Chicken?

Since the first screenings of Jurassic Park, scientists and the lay public alike have been taken with the concept of reading the genetic code of extinct organisms. Gathering such information is, however, not so easy, because DNA normally degrades too quickly to preserve the genetic sequence of an organism in fossil material. But an animal’s genome is reflected also in the sequences of amino acids it uses to construct its various proteins, and such molecules may survive intact long after all traces of DNA have disappeared. That’s what seems to have happened at least to one Tyrannosaurus rex that lived 68 million years ago in what is now Montana. A team of paleontologists have extracted collagen protein from a T. rex femur that apparently preserved some of the animal’s soft tissue. Measurements revealed collagen protein sequences that could be compared with those from various extant animals. The closest match—with 58 percent sequence identity—was to modern chickens.

Asara, J. M., M. H. Schweitzer, L. M. Freimark, M. Phillips, L. C. Cantley. Protein sequences from Mastodon and Tyrannosaurus rex revealed by mass spectrometry. Science 316:280–285 (April 13).

Hurricanes and Global Warming

Specialists have been unable to come to consensus about whether hurricanes will become more frequent or more intense if the Earth’s climate warms as much as many expect it to do over the 21st century. But some meteorologists have expressed concern that higher sea-surface temperatures in the decades soon to come will indeed fuel ever-larger and more-frequent hurricanes. Now a new modeling study suggests that global warming may induce greater wind shear over the tropical Atlantic and east Pacific, which can be expected to lower hurricane activity, suggesting that a warmer planet does not necessarily mean a stormier one, at least as far as those areas of the world are concerned.

Vecchi, G. A., and B. J. Soden. Increased tropical Atlantic wind shear in model projections of global warming. Geophysical Research Letters 34:L08702 (April 18).

Down on the Farm

Corn-derived ethanol is often touted as a clean-burning fuel for vehicles, but a recent study from Stanford casts serious doubt on that claim. The new research modeled the effects of the widespread use of E85—a mixture of 85 percent ethanol and 15 percent gasoline—and found that switching to this supposedly clean fuel would increase cases of ozone-related mortality, hospitalization and asthma by 4 percent for the nation as a whole. For Los Angeles, the figure was 9 percent. Although the use of E85 does diminish the concentration of some other atmospheric pollutants, there is no reason to believe that using ethanol-rich fuels would improve air quality overall.

Jacobson, M. Z. Effects of ethanol (E85) versus gasoline vehicles on cancer and mortality in the United States. Environmental Science & Technology (Published online April 18).

New AIDS-Fighting Drug on the Horizon?

German investigators have identified a component of human blood, a relatively small peptide, that in cell culture inhibits the replication of many strains of HIV-1, the virus responsible for the vast majority of AIDS cases. What’s more, these researchers found that by changing some of the 20 amino acids that make up this peptide, dubbed VIRIP, they could increase its effectiveness in thwarting HIV’s entry into cells of the immune system by two orders of magnitude. The discovery of VIRIP and the ability to modify it into a highly effective form may one day lead to a whole new class of anti-HIV drugs.

Münch, J. L. et al. Discovery and optimitzation of a natural HIV-1 entry inhibitor targeting the gp41 fusion peptide. Cell 129:263–275 (April 20).

Mercury’s Molten Middle

Three decades ago, the Mariner 10 space probe determined that Mercury (unlike Venus and Mars) has a significant magnetic field. Planetary scientists have since speculated about the possibility that Mercury’s magnetic field, like that of Earth, is generated by turbulent motions of a liquid-iron core. Estimates of the overall density of Mercury had suggested that the interior must contain considerable quantities of iron, but until now, there was no way to judge whether that iron was solid or liquid. The new work uses radar reflections to determine subtle oscillations in Mercury’s rotation rate. This telltale “libration” indicates Mercury’s rocky mantle is not physically coupled to the planet’s solid inner core. Thus, like Earth, Mercury has a liquid outer core, which presumably creates a strong magnetic field as it churns.

Margot, J. L., S. J. Peale, R. F. Jurgens, M. A. Slade and I. V. Holin. Large longitude libration of Mercury reveals a molten core. Science 316:710–714 (May 4).