- SCIENCE NEWS This Week

already have enough defenses against pests, for example, or the gene may exact a meta- bolic cost.

So far, no transgenic sunflowers have hit the U.S. market. Snow and her colleagues worked with an experimental variety and its wild relatives. Following strict containment procedures, the researchers planted their selected second-generation hybrids out- doors.

In a high-pest zone in Nebraska, sun- flowers carrying the borrowed Bt gene set 55 percent more seeds than hybrid descen- dants without the gene did. Even in the less- insect-infested site in Colorado, the trans- genic hybrids beat the others by 14 percent in seed setting. Also, the Bt-producing off- spring suffered fewer attacks from insects.

In the greenhouse, there was no evidence that the transgenic descendants paid a price for the Bt advantage, even under drought or low-nutrient regimens, say the researchers.

The project shows that the transgene adds an edge, says Ellstrand, but now he asks whether that advantage will boost the weed’s invasion power. -s. MILIUS

Spinning Fine Threads Silkworms coerced to make better silk

The caterpillars that spin commercial silk can make much tougher or more elastic threads, depending on how fast they’re forced to spin.

If this research finding is translated into amarketable process for obtaining silk, the fibers could rival those of widely acclaimed but commercially impractical spider silk, says Fritz Vollrath of Oxford University.

Many scientists hold that spider silk is the ultimate material-strong and tough, yet elastic. If produced in large quantities, spider silk could replace synthetic materi- als in surgical sutures, seat belts, or even carpeting, suggests Carl Michal ofthe Uni- versity of British Columbia in Vancouver.

But harvesting spider silk is labor inten- sive. Spiders must be tied down and their silk reeled out using a small motor. What’s more, ”if you put many spiders in a box together, you tend to end up with only one big one,” says Michal. “So, you have to store them in different cages.”

In contrast, even children can easily har- vest silk from the caterpillars known as silk- worms, says Vollrath. The silkworms construct thumb-size cocoons, each

improved char- SILK SOURCE A acteristics. In silkworm‘s cocoon. the Aug. 15 Nature, Vollrath and Zhengzhong Shao of Fudan University in Shanghai, China, report that slow reeling-at 4 millimeters per second-produces silk with the same elasticity as spider silk. Fast reeling-at 13 mm per second-doesn’t improve elas- ticity but increases silkworm silk to three- fourths the toughness of spider silk. The silkworms normally spin at speeds varying from 4 to 20 mm per second.

Although not quite as good as spider silks, the improved silkworm silk could give them “a run for their money,” the researchers argue. Moreover, Vollrath suggests, silk pro- ducers might breed caterpillars that natu- rally spin silk faster or slower than normal and thus produce better silk threads in their cocoons.

The new work “is clever,” says David Kaplan of n f t s University in Medford, Mass.

“It really emphasizes the importance of the fiber-formation conditions,” notes Michal. Yet, he points out, “there is some- thing important in the genes of the vari- ous organisms that plays a role in deter- mining the properties of the different materials.” -J. GORMAN

Not a Turn-On Alleged X chromosome activator may be a dud

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Female mammals have two X chromo- somes, but males only have one. Early in development, the female embryo must shut down one X chromosome in every cell, or an overdose of the genes on those chromo- somes will kill her.

Scientists haven’t worked out all the details of X inactivation, and a new study prolongs the puzzlement. A gene that sci-

entists have found to regulate X chromo- some activity in mice doesn’t work in peo- ple, report researchers from the Johns Hop- kins Medical Institutions in Baltimore.

some remains silent. This specifica- tion is called imprinting.

Scientists understand the off-but not the on-half of a molecular switch that con- trols X chromosomes’ fates in mice and peo- ple (SN: 8/05/00, p . 92). The gene Xist (pronounced “exist”) is continually tran- scribed into RNAfrom all X chromosomes in both sexes. Unchecked, Xist RNA sets off a cascade of molecular events that com- pacts the X chromosome into inert mate- rial. Scientists have been searching for the gene that haltsxist expression on the active X chromosomes.

In 1999, scientists from Harvard Uni- versity discovered a mouse gene that could stop Xist activity. They aptly named this gene Tsix-Xist spelled backward-because Tsix RNA is complementary to, and so binds, Xist RNA and knocks it out of com- mission.

The Harvard researchers showed that Tsix controls imprinting in mouse placen- tal cells. They speculated that Tsix might also control the random X inactivation of women.

Not so, say Barbara R. Migeon and her colleagues in the August American Jour- nal of Human Genetics.

These scientists had suspected that Tsix might function differently in people than in mice because human Tsixis missing ele- ments found in mouse Tsix. Using color- coded RNA tags, they studied expression of Tsix RNA and Xist RNA in human fetal cells. They found that, unlike in mouse pla- cental cells, Tsix is expressed only on the inactive X chromosome and is thus unlikely to be stoppingxist.

Migeon speculates that Tsiz controls imprinted, but not random, X inactivation. “Human placenta is not imprinted, so the fact that we don’t have an effective Tsix mol- I

j ecule would make sense,” she says.

Tsix in people is probably just an evolu- 9 tionary vestige, Migeon concludes. A gene 8 from a nonsex chromosome might better 2 control random inactivation, she notes. 5

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Not everyone is willing to dismiss Tsiz so easily, however. The study looked at human cells that were far past the period of X inac- tivation, says Harvard researcher Jeannie T. Lee, who led the original Tsiz discovery in mice. Led restrictions make it diflicult to get human cells that are young enough, Lee says.

Other scientists found the study more convincing. Migeon’s finding may help explain why women don’t have imprinted X inactivation, says Andrew Feinberg, a biologist from Johns Hopkins who wasn’t involved in the study. The Tsiz gene in peo- ple is missing an element that is essential to imprinting, he says.

This paper reminds us that it’s impor- tant to study people, not just mice, Fein- berg concludes. -K. COBB

Killer Cocktails Drug mixes threaten aquatic ecosystems

Combinations of drugs that have been detected in trace amounts in waterways from Nevada to Switzerland could deform and kill native microscopic organisms, a new study finds.

Since the 1970s, scientists have discov- ered more and more rivers, lakes, and streams tainted with tiny amounts of common pharmaceuticals, including antibiotics, antidepressants, hormones, chemotherapy drugs, cholesterol-lowering medications, and over-the-counter pain killers such as ibuprofen (SN: 3/21/98, p . 187; 6/17/00,p. 338). Researchers have estimated that up to 80 percent of drugs taken by people and livestock emerge from the body intact, so mixtures of medications may pollute aquatic ecosystems.

“Nobody really knows whether these ambient concentrations are affecting the.. . environment" says Colleen Flaherty, a zool- ogist at University of Wisconsin-Madison. Flaherty set out to test some trace pharma- ceuticals on Daphnia magna, the tiny fresh- water crustacean that is food for many fish.

In laboratory tests, Flaherty exposed D. magna, more commonly called daph- nia, to low concentrations of either of two drugs: clofibric acid, used to lower peo- ple’s blood concentrations of cholesterol, and fluoxetine, an antidepressant. These drug concentrations-36 parts per billion of clofibric acid and 100 parts per billion of fluoxetine-are similar to those detected in aquatic environments, Fla- herty says.

Over periods up to 6 days, neither drug by itself ”had any apparent effects,” says Fla- herty.

“On a whim,” she says, she exposed the daphnia to a cocktail of both drugs at the concentrations she had just tested. To her

surprise, most of the tiny crustaceans-up to 90 percent in some trials-died. Mix- tures with less clofibric acid resulted in less mortality but cause some daphnia offspring to have malformed carapaces and appendages.

In further tests, she exposed daphnia to five common antibiotics at 10 parts per billion. Though they, too, had no detri- mental effect individually, a combination of three-triclosan, erythromycin, and trimethoprin-yielded generations of daphnia with abnormally large propor- tions of males.

Such a change in sex ratio can indicate that an organism is under environmental stress, says Flaherty, who presented her results last week in Tucson at the annual meeting of the Ecological Society of America.

Both experiments show the importance of testing combinations to get an accurate picture of drugs’ effects, says Flaherty. She notes that most research into pollutants has only examined the effects of single chemi- cals. “In reality, these critters are not being exposed to just one drug, one heavy metal, or one pesticide,” she says.

Though studies have shown drugs wide- spread in waterways, scientists know “next to nothing about their. . . potential for effects,” says Christian Daughton of the Environmental Protection Agency’s National Exposure Research Laboratory in Las Vegas. Although he commends Fla- herty’s research, Daughton argues that clofibric acid and fluoxetine haven’t been found in the environment in concentrations quite as high as she used.

He notes, “The big question is, Is there a reason for concern?)) -J. PICKRELL

LETHAL COCKTAIL Drug combinations have the potential to damage aquattc organisms such as Daphnia magna, which can grow as big as 5 millimeters across.

Budding Tastes Higher blood pressure in newborns links to salt preference

Babies who tolerate a salty flavor have higher blood pressure on average than their less tolerant counterparts do, a new study shows.

During the 30-month experiment, sci- entists measured blood pressures of 283 newborns at a Providence, R.I., hospital. The researchers also tested each baby’s taste preferences using a special nipple that deliv- ers tiny drops of fluids and then records the intensity and frequency of a baby’s sucking. Each newborn received several rounds of drops of sweet liquids, salt-flavored ones, and plain water. Researchers conducted the taste tests 3 hours after a feeding.

All the babies showed energetic sucking responses to the sugar-flavored fluid and slightly less enthusiasm for plain water. In contrast, most showed an aversion to the taste of salt; they sucked less when given salt-flavored fluids rather than sweet liq- uids or plain water. Some of the babies, however, were less put off by the salt flavor than others were.

On average, babies who had the highest diastolic blood pressure-the bottom num- ber on a blood pressure reading-tolerated salty flavor better than the babies with lower diastolic blood pressure did, the researchers report in the September Hypertension.

One month later, follow-up examinations of 234 of the babies revealed that those who had been more tolerant of salt flavor still averaged significantly higher blood pres- sure, compared to the other babies. This finding is reminiscent of research indicat- ing that elevated blood pressure begins early and “remains on a track” throughout life, says study coauthor Stephen H. Zinner, an internist at Harvard Medical School in Boston and Mount Auburn Hospital in Cambridge, Mass.

‘We know salt is related to blood pres- sure: says endocrinologist Myron H. Wein- berger of Indiana University Medical School in Indianapolis. “Developing tastes for salt may be something that occurs early in life and may then lead to high blood pressure later.” The new study, he says, “is a very important addition [to this field] because it suggests these differences in the aversion to the salt taste exist when the infants are born.”

Zinner suggests researchers could create risk profiles for children with elevated blood pressure and a salt taste preference so pediatricians could intervene “to keep them off salt.”

While the causes of high blood pressure are poorly understood, there’s evidence of a hereditary component. Indeed, in this study,

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