News this Week

Science  13 Aug 1999:
Vol. 285, Issue 5430, pp. 990

    Deep Green Rewrites Evolutionary History of Plants

    1. Kathryn S. Brown*
    1. Kathryn S. Brown is a science writer in Columbia, Missouri.

    ST. LOUIS—Not long ago, scientists trying to sort out the evolutionary links among plants often worked alone on secret projects, racing to scoop other labs. “It was a dog-eat-dog world,” says University of California, Berkeley, botanist Brent Mishler. Fed up with this poisonous atmosphere, Mishler and several colleagues, over lunch at the Missouri Botanical Garden in 1992, hatched a plan for a botanical version of the Human Genome Project: an effort to merge molecular, fossil, and morphological data to build a family tree for all green plants. It was a “big-science solution for a field stuck in a laissez-faire mode,” says Mishler.

    The first fruits of their 5-year effort, dubbed Deep Green, ripened in time for the 16th International Botanical Congress, held here last week. Challenging long-held notions about the relationships among species, scientists reported that plants should be divided into three kingdoms rather than one, unveiled the most primitive living flowering species, and homed in on the “Eve,” or mother, of all 500,000 green plant species. Deep Green, involving 200 scientists from 12 countries, “is the biggest attempt at phylogeny ever,” says Mishler.

    As genetic data add branches and leaves to the new family tree, biologists should be able to tap it for information on how to engineer useful traits, fight invasive species, identify organisms, and find potential medicines. Deep Green scientists intend to publish a book later this year and have established a Web site* that will become a repository for links to findings as they accumulate in the peer-reviewed literature. “If we can perfect the green plant tree, its impact will be phenomenal,” says Sean Graham of the University of Alberta in Canada.

    Adding one intriguing branch was the lab of botanists Pamela and Douglas Soltis of Washington State University in Pullman, a husband-and-wife team that 5 years ago set out to plumb the murky beginnings of flowering plants. How flowers arose, adding brilliant colors to a green panorama, is a question that has bedeviled biologists since Charles Darwin, who called the emergence of flowers an “abominable mystery.” Studies had suggested that magnolias or water lilies—both built simply, with saucerlike flowers—could be the closest living relatives of the earliest flowering plants, or angiosperms. The Soltises, however, felt that the first flowering plants must have been even simpler—perhaps lacking either tissues that transport water efficiently or closed carpels, modified leaves that protect seeds.

    To turn back the clock, the Soltises and their colleagues constructed phylogenies, or evolutionary histories, of angiosperms based on their DNA. They compared three common sequences—in the chloroplast genes rbcL and atpB, and 18S ribosomal DNA—from 560 species. These DNA regions mutate rapidly, making them good tools for differentiating among species. When a computer program shuffled the DNA sequences into a rough time order based on their mutations, it came up with a surprise: A rare tropical shrub called Amborella appeared at the bottom, or root. About 135 million years ago, the researchers concluded, nonflowering plants—perhaps similar to today's pines—hit an evolutionary fork in the road, with some veering off toward Amborella and later angiosperms while others continued life sans petals.

    Found only on New Caledonia, an island in the South Pacific, Amborella, a diminutive plant with creamy flowers and red fruit, had gone unnoticed by most botanists, says Pamela Soltis. But as Deep Green ground on, three other research teams created flowering-plant phylogenies; each confirmed that Amborella is, indeed, the closest living relative of the first flowering plant. Such diverse support for a new phylogenetic finding is rare, says Christopher Haufler of the University of Kansas, Lawrence. Amborella, he says, “is a tiny remnant of a lineage that goes back millions of years.”

    Deep Green, a $285,000 project funded by three U.S. agencies—the National Science Foundation, the Department of Agriculture, and the Department of Energy—also threw its weight behind the idea that single-celled algae, living in the cracks of rocks and in soil along streams at least 450 million years ago, evolved into mosses that gradually crept out of the water and became the first land plants. New data from biologist Marvin Fawley of North Dakota State University in Fargo put Mesostigma, a scaly, unicellular alga, at the base of this freshwater algal line. In addition, DNA data from biologist Louise Lewis of Louisiana State University in Baton Rouge and others suggest that the Eve of the green plants that first took root on land must resemble either Chara or Coleochaete algae, which still thrive in lakes and streams today.

    For plant taxonomists, the new data strike a blow to the foundation of their discipline: the 250-year-old system, designed by botanist Carolus Linnaeus, which groups species by the number and arrangement of their reproductive organs, the stamens and pistils. At the meeting, a vocal band argued that the Linnaean system should be thrown out, or at least overhauled, because many plants presumed by their appearance to be closely related—such as the water lily and the lotus—are in fact quite different genetically.

    In crafting a phylogenetic tree, Deep Green scientists confirmed that classic categories like monocot (one seed leaf) and dicot (two seed leaves) often fail to group plants accurately; that fungi are more closely related to animals than plants; and that some green algae are more like land plants than algae. Moreover, Mishler says, the brown, red, and green plants each arose independently from a common single-celled ancestor and thus deserve their own kingdoms. Overall, he claims, at least half the Linnaean classifications are wrong.

    Mishler and others would prefer to name plants according to clade, or genetically related group—a system called the PhyloCode. For example, the herb Prunella vulgaris and hundreds of other plants might simply go by the name vulgaris, with a tag in some master directory that scientists could refer to for phylogenetic data. “When I first heard this, I thought it was crazy,” says Kathleen Kron, a botanist at Wake Forest University in Winston-Salem, North Carolina. “But it's not. A plant's rank is arbitrary, and naming it by clade is a far more relevant, practical way to go.”

    Not everyone agrees. “The new phylogenetic information is absolutely wonderful, but renaming all these plants is going too far,” says Richard Brummitt of the Royal Botanic Gardens in Kew, England. “A red oak is not a white oak, and without rank, we lose the ability to make that distinction easily.” Like it or not, Brummitt concedes that the push to revamp nomenclature is gaining ground. Not too long from now, he predicts, botanists will have to cope with two systems—one Linnaean, the other cladistic.

    As the green plant tree grows, scientists should be able to start to decode the genetic ciphers explaining how competitive advantages evolved in plants—for example, how mosses gained an ability to resist drought. And some Deep Green insights may offer a biomedical payoff. For example, Patrick Keeling of the University of British Columbia in Vancouver reported that Microsporidia, a parasite that can sicken people with weakened immune systems, evolved from a fungus—not an ancient, premitochondrial eukaryote, as many scientists believe. Thus, drugs that disable fungal proteins may also work against Microsporidia, Keeling says.

    Although Deep Green is finished, researchers say it has sown the seeds for future collaborations. “It's taken people by surprise that botanists have been so willing to share unpublished data so we could all work together,” says Pamela Soltis. Along the way, the green plant tree is sure to branch off in new directions. Says mycologist John Taylor of the University of California, Berkeley: “As more genes are added to these phylogenies, we're not going to be so smug that we've got it all figured out.”

    • *

  2. U.S. BUDGET

    Tax Cut Politics Could Swallow Research Gains

    1. David Malakoff

    An already uncertain year for science funding got even more complicated last week. In a last-minute flurry of votes before their summer recess, House and Senate lawmakers passed spending and tax cut bills that drew White House veto threats. That action/reaction is prelude to a legislative showdown when Congress returns to Washington next month that could extend beyond the start of the fiscal year on 1 October. For the major science agencies, appropriations bills now being considered by Congress fall several billion dollars short of the Administration's proposals. The critical issue will be whether that shortfall can be funded by breaking politically sensitive limits on domestic spending or diverting money from projected budget surpluses.

    Unlike in past years, the current debate is fueled by the prospect of a $1 trillion surplus over the next 15 years. The Republican tax cut, passed on 6 August, would return much of the money to taxpayers. But President Clinton has vowed to veto the tax cut, which won't arrive on his desk until next month, saying the funds should be used instead to pay down the national debt and shore up retirement and medical insurance funds. Some science lobbyists worry that the partisan bickering may drown out their campaign to boost the government's $78 billion research and development budget.

    White House science adviser Neal Lane has already begun beating the drums. This week Lane called a meeting of Washington science community leaders to rally opposition to the reductions by the House in a number of high-profile science programs within NASA, the National Science Foundation (NSF), and other agencies (see table). “This situation can be turned around if America's research community makes its strong voice heard,” he said in a 6 August statement. Republicans say the cuts, on bills passed generally on party-line votes, are required under a 1997 budget-balancing law that imposes strict caps on spending in 2000. “The White House is blaming us for obeying the law,” said one Republican House aide. In fact, neither side so far has been willing to take the political heat for suggesting that the caps be raised.

    Swipe at science?

    House members, either as a whole or in committee, pruned the president's 2000 budget request for several high- profile science projects.

    View this table:

    Other lawmakers, however, have called for using part of the surplus to restore the $18 billion or more that will be needed to prevent cuts in several major spending bills, including the one that funds the $16 billion National Institutes of Health (NIH), which biomedical lobbyists hope to keep on a pace to double its budget within 5 years. Last month, Republican leaders put off any votes on the NIH bill until September, partly in hopes that they could broker a deal with the White House to restore the shortfall in NIH's budget. Advocates of breaking the budget caps include Representative John Porter (R-IL), chair of the House appropriations subcommittee that oversees NIH, and Senator Ted Stevens (R-AK), chair of the Senate appropriations committee.

    Indeed, Stevens has suggested one possible route out of the impasse: a deal in which the White House agrees to a smaller tax cut bill in return for some surplus funds to raise 2000 budgets. Without a deal, however, “any hope that NIH will keep doubling its budget this year are gone with the wind—we'd be lucky to get a 3% increase,” says a Democratic House aide, in contrast to last year's 15% hike. Absence of a budget deal could also imperil efforts to restore funds to NASA and raise NSF's budget by the requested 6%, she says. Ironically, it also undermines the hard-fought House increases in the Pentagon's basic research accounts, which the White House had slated for cuts.

    The defense bill is already ensnarled in a debate that could prompt a veto. It centers on a congressional plan to reorganize the Department of Energy's (DOE's) nuclear weapons research program—which is largely funded by the defense bill—into an independent agency within DOE. Energy Secretary Bill Richardson, however, opposes the plan, complaining that it undermines his authority, and has recommended that Clinton veto the entire bill. Richardson supports a different plan passed by the Senate.

    Even a smaller tax cut has a downside for science: A proposed 5-year extension of the R&D tax credit, long sought by high-tech and pharmaceutical companies, is currently included in the tax bill. But its cost, estimated at $20 billion, could make it a casualty of this fall's expected political horse trading.


    Deep Space 1 Traces Braille Back to Vesta

    1. Richard A. Kerr

    Asteroids tend to wander far from home, but researchers can now reunite a wayward offspring with its “parent” in the main asteroid belt between Mars and Jupiter. At a press conference last week at the Jet Propulsion Laboratory (JPL) in Pasadena, California, researchers announced that observations of an asteroid called Braille, returned by the Deep Space 1 spacecraft last week, show that the 2-kilometer-long rock is probably a chip blasted off the 500-kilometer asteroid Vesta, the third largest in the solar system.

    Deep Space 1, launched in October 1998, is the first mission in NASA's New Millennium program, set up to test new space technologies. It boasts a xenon-fueled ion propulsion system, high-efficiency solar cells, and an automated navigation system, AutoNav, that enables it to find its way in interplanetary space by tracking stars and asteroids without help from ground controllers. The navigation system brought the spacecraft within 10 to 15 kilometers of the asteroid—the closest flyby ever achieved. The asteroid, discovered in 1992, was only recently named after the Frenchman Louis Braille (1809–1852), who invented the alphabet for the blind. It orbits the sun in an elongated path outside Earth's orbit.

    First reports suggested that Deep Space 1's encounter with Braille was a bust, because the spacecraft's camera was pointing into empty space and missed its target. However, some of the last data beamed back did provide images of a distant, lumpy, elongated body and “colors” of the asteroid in the infrared range. Apparently, Deep Space 1 lost sight of Braille as it approached the asteroid from its dark side, but reacquired its target soon after passing to the asteroid's daylit side, according to mission engineer Marc Rayman of JPL.

    Although scientific observations are seen as a mere bonus in the New Millennium Program, team members regretted losing what would have been the closest look at an asteroid so far. But the infrared spectra proved some consolation. Braille's distinctive absorption pattern is “a remarkably close match” both to the asteroid Vesta in the main belt and to a type of meteorite known as a eucrite, said team member Laurence Soderblom of the U.S. Geological Survey in Flagstaff, Arizona. The close resemblance of eucrite spectra to that of Vesta had persuaded most astronomers and meteoriticists that eucrite meteorites come from Vesta, the only strong meteorite-asteroid link anyone has been able to make. Now asteroid Braille looks to be a bigger chip off Vesta.

    Given the match with Vesta, planetary scientists have a plausible story of how Braille, as well as eucrite meteorites, were born. As impact specialist Eileen Ryan of New Mexico Highlands University in Las Vegas, New Mexico, explained, Braille and the eucrites could have been blasted off Vesta in the huge impact that left a 460-kilometer crater, which is visible in Hubble Space Telescope images of the asteroid. The likely debris can be seen as small, Vesta-colored asteroids near their parent and strewn across the asteroid belt to a point where Jupiter's gravity could fling it in toward Earth. Braille hasn't yet gotten as far as the eucrites, but Soderblom noted that it will be drifting across Earth's path in the next few thousand years, possibly making it the planet's “Y6K” problem.


    New Genes Boost Rice Nutrients

    1. Trisha Gura*
    1. Trisha Gura is a free-lance writer in Cleveland, Ohio.

    ST. LOUIS—The latest high-tech version of rice may look like the saffron rice of paella, but the pretty yellow color is far more than decoration. Described here last week at the 16th International Botanical Congress, the golden rice has been genetically engineered to contain β-carotene, the precursor to vitamin A, as well as a healthy dose of iron. This achievement, by plant molecular biologist Ingo Potrykus at the Swiss Federal Institute of Technology in Zurich and his colleagues, is not only a Herculean feat of gene transfer, but also a major leap on a more humanitarian front: It may offer improved nutrition for the billions of people in developing nations who depend on rice as a staple food.

    Many researchers have already slipped one or two foreign genes into everything from tomatoes to cotton, endowing them with traits such as resistance to herbicides, plant pests, or pathogens. But the rice strain created by the Potrykus team carries a total of seven foreign genes from two separate pathways: Four encode enzymes that give rice grains the ability to make β-carotene, and three more allow the kernels to accumulate extra iron in a form that the human body can better absorb. Gene transfer on this scale, says plant biochemist Dean DellaPenna at the University of Nevada, Reno, “is tremendously exciting and should have an enormous impact.”

    “This is the first kind of rice that is genetically engineered for nutritional enhancement,” adds Gurdev Khush, principal plant breeder at the International Rice Research Institute (IRRI) in Manila, Philippines, and the humanitarian payoff could be high. Vitamin A deficiency affects some 400 million people worldwide, leaving them vulnerable to infections and blindness. And iron deficiency—the number one micronutritional shortage, which a diet of rice can exacerbate—afflicts up to 3.7 billion people, particularly women, leaving them weakened by anemia and susceptible to complications during childbirth. In addition, because the endeavor was not industry-funded, Khush and Potrykus both point out, the poor farmers who most need the micronutrient-rich rice are likely to get it, free of charge.

    The roots of the project go back 7 years, when Peter Burkhardt in Potrykus's laboratory took on the daunting task of inducing rice to make β-carotene, which the body readily converts to actual vitamin A. Although rice kernels contain absolutely no β-carotene, they do make a molecule called geranylgeranyl pyrophosphate that can be converted to β-carotene by a sequence of four enzymes in the vitamin A pathway. The Swiss researchers had access to the genes for those enzymes, cloned from daffodils by Peter Beyer at the University of Freiburg in Germany. The problem would be getting all four genes into the rice kernel and working in sync.

    In the first stage of the work, Burkhardt attached the genes to regulatory sequences that would allow them to be turned on in rice kernels. But when he tried to shoot the four modified genes into rice plant cells with a “gene gun,” a standard way of introducing new genes into plants, he couldn't get all four to work properly: Most shut down after settling into the rice genome. The team didn't succeed until graduate student Xudong Ye entered the lab and tried new strategies.

    Ye switched the source of two of the four genes from daffodil to the bacterium Erwinia uredovora and used the plant-infecting microbe Agrobacterium tumefaciens to ferry in the genes. When Agrobacterium infects plants, it injects them with a circular piece of DNA called a plasmid. Ye put the two daffodil genes on the plasmid of one A. tumefaciens strain and the Erwinia genes on the plasmid of another, and then let the bacteria do the job of introducing the genes into plant cells. The strategy worked, yielding plants that produced rice grains literally golden with β-carotene.

    Meanwhile, Potrykus and graduate student Paolo Lucca were working on the iron supplementation project, which involved introducing three genes into rice plants. One was aimed at doing away with a molecule in rice that makes people on a high-rice diet prone to iron deficiency. Called phytate, this sugarlike molecule ties up 95% of dietary iron and so keeps the human body from absorbing it. The Swiss pharmaceutical giant Hoffmann-La Roche in Basel provided a fungal gene for an enzyme known as phytase, which breaks down phytate. Whereas most enzymes unfold and lose their activity when heated, the Hoffmann-La Roche enzyme carries a mutation so that it can withstand cooking temperatures. One of the other two genes introduced by Lucca comes from the French bean and encodes the iron-storage protein ferritin, which doubles iron levels in the rice grains. And the third gene, from basmati rice, makes a metallothionein-like protein, which is rich in cysteine, a sulfur-rich amino acid that helps in iron absorption in the human digestive system.

    In the final step of their 7-year odyssey, the Potrykus team crossbred their β-carotene- and iron-rich rice strains, producing hybrids that combined both improvements. As little as 300 grams of the cooked rice per day—a typical Asian diet—should provide almost the entire daily vitamin A requirement, Potrykus says. In addition, the experimental rice appears to be fertile and to grow normally in greenhouses.

    The success so far doesn't mean that the new crop is ready for market, however. Potrykus and his colleagues used the lab workhorse japonica strain of rice for their experiments, while indica rice is the most common commercial strain. So scientists at IRRI will now take on the task of crossbreeding the new strain with indica rice and field-testing the hybrids. If all goes well, Khush estimates, the golden rice could land in the fields of developing countries in 2 to 3 years—assuming, that is, that it doesn't meet with regulatory barriers such as those imposed by Britain, which currently has issued a moratorium on all genetically altered foods.

    Khush and Potrykus think that won't happen. Because the potential benefits seem great and the potential health and environmental risks small, the two researchers say, the new rice strain may draw less opposition from the critics of genetically engineered foods than other modified crop plants now being marketed (Science, 28 May, p. 1442). DellaPenna hopes they are right. These results, he says, “are wonderful and what needs to be done.”


    "Super-Iron" Comes to the Rescue of Batteries

    1. Alexander Hellemans*
    1. Alexander Hellemans is a writer in Naples, Italy.

    Georges Leclanché, the French chemist who developed the dry battery nearly 140 years ago, would probably recognize the basic elements of a flashlight battery today. Most such batteries still contain a zinc anode and a cathode made of a mixture of carbon and manganese dioxide. But now a team led by Stuart Licht at the Israel Institute of Technology, or Technion, in Haifa reports on page 1039 the development of a new class of batteries that have greater capacity, a faster discharge rate, and are rechargeable. The difference is in the cathode, which is made from unusual iron-based molecules known as iron(VI), or “super-iron,” compounds that absorb more electrons than manganese dioxide. “Their performance in a battery system is very astounding,” says Jeff Dahn of Dalhousie University in Halifax, Canada.

    When a battery discharges, electrons absorbed from the electrolyte by the zinc anode pass through an electric circuit and end up in the cathode, where two manganese dioxide (MnO2) molecules join to form a manganese sesquioxide (Mn2O3) molecule, absorbing two electrons in the process. In the new super-iron compounds—which contain oxygen, as well as potassium, barium, and other elements—each iron atom is missing six electrons. During discharge, the iron is converted into a form of ferric oxide (Fe2O3)—common rust—that is three electrons short of its normal complement. Each iron atom thus absorbs three electrons, one more than two manganese dioxide molecules absorb.

    This larger appetite for electrons translates directly into increased storage capacity. The Technion team has produced batteries with super-iron cathodes that have capacities up to 47% greater than standard manganese dioxide batteries of the same size. They also found that the batteries' performance at high discharge rates was better because super-iron compounds are also better conductors of electricity. Another advantage is rechargeability: The team reports some 400 charge-discharge cycles.

    The team searched a long time before settling on super-iron compounds. “Previously we looked at sulfur, hydrogen peroxide, and a variety of materials, each of which have very unusual electrochemical properties, but were not compatible with the existing systems,” says Licht. Some other possible compounds were also ruled out because “we specifically wanted to start with an [environmentally] ‘clean’ material,” says Licht. The rust generated by discharging this battery is preferable to the somewhat poisonous manganese compounds that remain in the batteries presently used, notes Licht.

    Even so, super-iron compounds were not an obvious choice, because they are considered too unstable. “When these [compounds] were made in the past and you put them in a solution, they disappeared within minutes, decomposing into rust,” says Licht. The team solved this problem by carefully eliminating two catalysts, nickel and cobalt, that usually contaminate these compounds. The researchers found that, even in very small quantities, they cause the super-irons to break down. “We have demonstrated lifetimes of the super-irons without any change on the order of a month and extrapolated lifetimes of years,” says Licht. Denis Dees of Argonne National Laboratory in Illinois says, however, that he would like to see evidence that such batteries can survive for 6 to 12 months on the shelf and still be discharged. Because of the questionable stability of iron(VI) compounds, he says, “it is interesting that they have made it work at all.”

    If the cathodes do prove durable, Licht says the batteries should not be difficult to make. “We have been able to take it from a concept very quickly to conventional-sized batteries, and that is very promising,” he says. Another plus is that the starting materials are inexpensive and more easily available than manganese compounds.


    Education Chief Quietly Steps Down

    1. Jeffrey Mervis

    Luther Williams, the head of the education and human resources directorate at the National Science Foundation (NSF), is stepping down after 9 years on the job. But the circumstances surrounding his departure are as murky as the results of his ambitious efforts to reform the way U.S. children are taught science and mathematics.

    On Monday, NSF announced that veteran administrator Judith Sunley has been named interim head of the $689 million directorate, the keystone of the government's effort to improve U.S. rankings on international measures of student achievement in science and math. The two-paragraph “personnel announcement” said that Sunley, trained as a mathematician, would take over in 6 days. It made no mention of Williams, prompting widespread puzzlement over his status and future plans.

    NSF director Rita Colwell told Science that Williams, a former biology professor, is taking a position with a new program at Tulane University in New Orleans called the Payson Center for International Development and Technology Transfer. The program is a pet project of Eamon Kelly, president emeritus of Tulane and current chair of the National Science Board, NSF's governing body. She said that Williams told her of his plans “a month or so ago” and that she expects him to overlap briefly with Sunley before leaving “by the end of August.”

    Williams spearheaded NSF's campaign for “systemic reform” of the nation's elementary and secondary school science and math education, a high-profile effort whose impact on student achievement has been hard to measure (Science, 4 December 1998, p. 1800). “He can leave with a sense of accomplishment,” Colwell said. “But it seemed like a good time for him to go. I think that 5 to 6 years is a good length of time in that job, and he's been doing it for nine. Even the director serves a fixed term of 6 years.”

    Science was unable to reach Williams, whose secretary said he was “on travel” and not available for comment. Tulane epidemiologist Bill Bertrand, director of the 1-year-old Payson Center, said on Tuesday that he had “been talking about the possibility” of Williams joining the center, which is beginning an effort to train university teachers in French-speaking Africa and is heavily involved in using information technology to improve education in the developing world. Williams has instituted several programs at NSF aimed at using technology to broaden educational opportunities for underserved populations. Other colleagues said Williams was also weighing other offers.

  7. JAPAN

    Panel Examines National Universities

    1. Dennis Normile

    TOKYO—A move to shrink the size and scope of the government is spreading to the country's national universities. This week a blue-ribbon panel assembled by Japan's education ministry began debating ways to loosen the government's grip on the 98 national universities. But the promise of greater independence is mixed with fears that the government's desire to cut costs may be stronger than its commitment to high-quality university education and research.

    The idea for “denationalizing” the universities grew out of a December 1997 report to the government on streamlining the entire federal bureaucracy. The Ministry of Education, Science, Sports, and Culture (Monbusho) initially paid little attention to the proposal, but in June the government indicated it was serious about pursuing reform when it pushed through a law to turn 54 national research institutes affiliated with ministries other than Monbusho into so-called “independent administrative institutions.” To study what a similar move might mean for universities and university-affiliated institutes, Monbusho assembled an advisory panel, which includes Leo Esaki, a Nobel laureate in physics who is currently president of the University of Tsukuba, and Hiroyuki Yoshikawa, an engineer and former president of the University of Tokyo. The panel held its first meeting on 10 August.

    The plan to transform the national research institutes is modeled after the Institute of Physical and Chemical Research (RIKEN) outside Tokyo, which has had similar quasi-independent status for over 40 years. RIKEN has great leeway in managing its day-to-day affairs and uses an international review board to assess its accomplishments. The new institutes law, which goes into effect in spring 2001, envisions similar deals for the 54 national institutes.

    But no such model exists for universities. Yoshikawa says that most academic administrators initially feared that any new status would be followed by budget cuts. “But now there is a recognition that there could be some good aspects [to the plan],” he adds. Greater independence, for example, could free the universities from government-wide restrictions on staffing that make it nearly impossible to hire lab technicians. It would also give administrators more discretion over how they spend appropriated funds.

    But Ikuo Amano, a professor emeritus of education at the University of Tokyo and a member of the University Council, a Monbusho advisory body, worries about the government's motives: “This discussion started not from the standpoint of how to improve the universities but from the standpoint of how to reduce government expenditures and slim government payrolls.” Claims of benefits to university operations, he notes, are “not based on any evidence.”


    50 Monkeys Taken From Indian Lab

    1. Pallava Bagla

    NEW DELHI—Armed with a government order and escorted by police, animal activists have released into the wild 50 rhesus monkeys that were being used for drug testing. The episode is the latest battle in a fight over the country's new animal welfare rules, which scientists fear could halt drug testing in India.

    The animals were being kept at the National Center for Laboratory Animal Sciences (NCLAS) in Hyderabad for use in testing a potential drug against immune disorders. On 9 August, the activists, brandishing a government order citing NCLAS's failure to adhere to new animal welfare rules, released the primates into a forest about 400 kilometers away.

    The crisis has been brewing since December, when a law went into effect that aims to safeguard animals used in 5000 labs across the country (Science, 11 December 1998, p. 1967). Among other things, the law requires facilities to gain approval for animal experiments from the Committee for the Purpose of Control and Supervision of Experiments on Animals. Last month the committee threatened NCLAS with closure for housing primates in cages that are too small and for conducting experiments on captured wild monkeys instead of lab-bred animals (Science, 9 July, p. 180). Half of India's facilities could be shut down if held to the same standards, says microbiologist Nirmal Kumar Ganguly, director-general of the Indian Council of Medical Research.

    News of the government-sanctioned action stirred up the annual meeting of the Indian National Science Academy (INSA) in New Delhi, which passed a resolution seeking to persuade Prime Minister A. B. Vajpayee to intervene. Warns INSA president Goverdhan Mehta, “India's national interests are going to suffer very badly if all drug testing is halted like this.”


    Mining the Genome for Drugs

    1. Ingrid Wickelgren

    Biotech companies hope that their efforts to use modern genomics to identify new therapies for human diseases are on the verge of paying off. That's still a big if, however

    The construction crews have put the finishing touches on the maze of rooms housing the tubes, ducts, and silver-colored vats needed for production to commence. In the foyer, the large bronze of Mercury carrying a caduceus, a symbol of healing, serves to announce the task at hand. This 7000-square-meter, state-of-the-art facility is being prepped to mass-produce what may be the first drugs to emerge from the rush to find all human genes.

    The company that built the $45 million factory, Human Genome Sciences Inc. (HGS) of Rockville, Maryland, plans to use it to manufacture two human proteins and one human gene now in clinical trials. The molecules are meant to heal severe wounds, grow new blood vessels to circumvent damaged ones, and protect the blood-forming cells from the often lethal effects of cancer chemotherapy. If all goes as HGS intends—and that's a big if—these molecules will help establish the credibility of a revolutionary new approach to drug development, one of several that makes use of the growing knowledge of genes.

    In the past, biotech company scientists looking to develop new therapies for human diseases had to start with a protein already known to be a key player in the disorder, insulin in diabetes, say, or human growth factor in dwarfism. They would then clone the corresponding gene, and with it manufacture the protein to use in therapy. Now, HGS and other companies are mining large databases of human gene sequences, looking for previously unknown proteins that might have therapeutic value. Once promising genes are identified—often by their structural similarity to known molecules—company scientists screen the genes' protein products in cells and animals for medically useful effects.

    HGS has a leg up in this game. “HGS was first out of the gate in amassing [genomic] information. It looks like they've built the scientific infrastructure for the next step—developing pharmaceuticals,” says Bill Boyle, a top genomics researcher at another biotech firm, Amgen Inc., in Thousand Oaks, California. But other companies, including Amgen, are also taking the plunge. Researchers at Amgen, for instance, have fingered a bone-building protein from their own gene database that is now in human trials as a potential treatment for osteoporosis and other bone-thinning ailments. At Seattle-based Immunex Corp., researchers have nabbed a tumor-killing compound from a public gene database that they, now in collaboration with Genentech Inc. of South San Francisco, plan to bring to the clinic next year. And plenty more genomics-derived drug candidates are very likely under wraps at those companies and others.

    The success of these efforts is not assured, however. The hope is that because proteins have been designed by nature to work in the body, they can be developed for clinical use years faster, and far more cheaply, than synthetic chemical drugs can. The human protein drugs identified by more conventional means do include some blockbusters: erythropoietin, a protein used to treat anemia, reaped more than $2 billion in sales last year. But some other protein drug candidates have not panned out. For one thing, proteins often have more widespread effects than the drug developers count on: Tumor necrosis factor (TNF), for example, was touted as a potential cancer cure, but turned out to kill many normal cells as well.

    And no one knows whether the genomics approach to finding potential therapeutic proteins will be any more successful than the more traditional approaches. “There is nothing magical about molecules derived from genomics methodologies,” says Doug Williams, head of discovery research at Immunex. “You still have to do the biology to find out if you have a product candidate.” Indeed, for all of the genomics-based drugs, the hardest biological tests are yet to come: the ones conducted in large numbers of people.

    View this table:

    Gathering genes

    One reason HGS leads the pack in the search for genomics-based drugs is its early association with The Institute for Genomic Research (TIGR), founded by biologist J. Craig Venter. In the early 1990s, Venter, then working at the National Institutes of Health, along with Mark Adams and their NIH colleagues, devised an efficient way of finding genes. Instead of taking the Human Genome Project's tack of spelling out every letter of DNA's code—97% of which is not genes—Venter's group simply plucked out the molecular footprints active genes leave in cells. These are messenger RNAs (mRNAs) copied from the genes as the first step in protein synthesis. Venter's team would copy the mRNAs back into DNAs and then spell out a part of each gene to create what are called expressed sequence tags (ESTs), which could be later used to find the entire gene.

    In 1992, Venter received $70 million, to be paid over 10 years, from venture capitalist Wallace Steinberg to create TIGR as a nonprofit gene-finding research institute. Steinberg asked William Haseltine, then a Harvard virologist, to head a for-profit company—HGS—that would help find genes, patent and license promising ones, and spin some into drugs on its own. The partnership eventually soured, as the goals of the two companies diverged, and Haseltine and Venter's personal relations broke down (Science, 7 February 1997, p. 778). In the end, HGS and TIGR formally split (Science, 27 June 1997, p. 1959), but the collaboration helped HGS create its own enormous EST database, which Haseltine now estimates contains tags representing more than 95% of all human genes, although that figure is difficult to verify independently.

    To start with, Haseltine's team looked for membrane-bound proteins, including receptors for growth hormones, neurotransmitters, and the immune system regulators known as cytokines, that might serve as targets for chemical drugs to be developed by HGS's first corporate partner, SmithKline Beecham, and later by other partners. In addition, HGS scientists kept an eye out for proteins that might make good drugs themselves—proteins such as hormones, growth factors, and cytokines that are secreted by cells into the bloodstream. They identified such proteins by their structural similarity to known, secreted protein classes. By 1996, HGS scientists had found about 300 genes that appeared to encode new members of these classes. At that point, company researchers began making the proteins and testing them for activities that might help combat disease.

    Wound-healing was an inviting target. So-called “chronic wounds” fail to heal normally because of underlying medical problems such as poor blood circulation due to diabetes and other conditions. The only medication currently available to treat chronic wounds is Regranex, a gel containing platelet-derived growth factor that is marketed in the United States by Ortho-McNeil Pharmaceuticals Inc. Regranex is approved to treat persistent ulcers on the feet of diabetics. Although the drug clearly helps, it doesn't solve the problem. In a large clinical trial, Regranex completely healed the wounds of half the patients who received it, compared to 35% of patients who received a placebo treatment.

    In search of a better wound healer, HGS researchers tested the ability of their proteins to spur the growth of skin cells called keratinocytes in culture. Of those that did, only one didn't also cause other cell types, such as fibroblasts, to grow—a potential disadvantage because fibroblast growth is associated with scarring. The researchers began animal tests of that protein, called keratinocyte growth factor 2 (KGF-2), and this past February, HGS's Pablo Jimenez and Mark Rampy reported in the Journal of Surgical Research that in rats, it fosters the healing of linear cuts similar to wounds humans receive during surgery.

    Research in press in the Journal of Pathology by plastic surgeon Tom Mustoe at Chicago's Northwestern University Medical School and his colleagues suggests that KGF-2 also works on chronic wounds. They found, for example, that in animals it closes open wounds that, like many chronic wounds in humans, have an insufficient blood supply.

    Mustoe describes KGF-2 as “generally promising.” Still, no one knows yet whether it will work in humans. Clinical trials were launched several months ago to test KGF-2's potency against venous ulcers, persistent leg sores that afflict some patients with vascular disease. Results aren't expected until sometime early next year, and because these tests are small, and chronic wounds are highly variable from one person to another, experts won't have confidence in the compound until it's been successfully tested on hundreds of patients. They are all too aware that other proteins, such as epidermal growth factor, looked promising in animal tests of wound healing but later failed in human efficacy tests.

    KGF-2 isn't the only prospect HGS is testing, however. Also entering clinical trials is a chemokine, a protein that regulates immune cell function, called myeloid progenitor inhibitory factor (MPIF-1). In cell culture experiments published in 1997, an HGS team led by Vikram Patel found that the protein reversibly stops the proliferation of several types of bone marrow stem cells, the cells that give rise to mature blood cells, including those of the immune system. Thus, the researchers reasoned, the protein might help protect the bone marrow of cancer patients from the toxic effects of chemotherapy, which preferentially kills rapidly dividing cells. Available drugs can boost blood-cell numbers after a round of chemotherapy, but there are no approved ways to protect such cells from being killed in the first place.

    MPIF-1 does seem protective in mice. In as yet unpublished work, Patel and his HGS colleagues injected the protein into mice before administering repeated rounds of chemotherapy. After several rounds, they found, both clot-forming platelets and disease-fighting white blood cells rapidly returned to normal levels in the MPIF-treated mice but remained suppressed for several more days in the control mice.

    “It's a very exciting and important area,” says Hal Broxmeyer, an experimental hematologist at the Walther Oncology Center and Indiana University School of Medicine in Indianapolis who has studied MPIF-1 in cell culture. Broxmeyer cautions, however, that a related agent failed to provide much protection for blood cells in a trial of cancer patients conducted last year. “I'm just not sure one chemokine is going to work better than any other,” he says, adding that combining chemokines with other agents might ultimately be necessary to protect against anticancer drugs.

    A verdict should soon emerge about what MPIF-1 can do alone. After a successful safety study, doctors at several U.S. medical centers are now testing its ability to protect the stem cells of patients receiving chemotherapy for breast and ovarian cancers.

    A third prospect HGS is testing, as part of a joint venture called Vascular Genetics Inc. (VGI), is a gene, rather than a protein, that might provide help to patients whose severe atherosclerosis has resulted in blockage of blood vessels supplying their hearts or legs. About 4 years ago, HGS identified the gene for a protein called vascular endothelial growth factor 2 (VEGF-2) that promotes blood vessel growth. When company scientists presented a poster on VEGF-2 at a gene-therapy conference in 1997, it caught the eye of cardiovascular gene-therapy pioneer Jeffrey Isner of St. Elizabeth's Medical Center in Boston. Isner had seen vascular growth in rabbits after delivering the gene for VEGF-1, a previously discovered protein with similar effects, and he was interested in testing the VEGF-2 gene as well.

    Isner and HGS decided to collaborate, forming VGI, and so far the animal results look promising. In work described last August in the American Journal of Pathology, Isner's team injected the VEGF-2 gene into rabbits in a hindlimb that was deprived of blood by tying off one of the arteries that feeds it. They found that capillary density and other measures of vascular growth improved in the animals' legs as a result. They are using the gene because it's easier to produce than the protein and, because it's more stable, it may have longer lasting effects.

    Isner's team has recently begun testing the gene therapy in a small number of patients with critical limb ischemia, or persistent pain in their legs due to insufficient blood flow. Additional trials are now also under way in patients with coronary artery disease. The approach has many clinical hurdles to cross before it becomes therapy, and plenty of competition, too. Various companies are testing forms of the VEGF-1 gene, and scientists at Chiron Corp. in Emeryville, California, have just begun controlled human trials of fibroblast growth factor for fostering blood vessel growth in diseased hearts.

    HGS has a lot at stake in these trials. Although the Maryland Economic Development Corp. (MEDCO) floated a bond to finance the construction of the Rockville plant, including the equipment inside, the company must pay property taxes, as well as cover rent and the cost of operating the facility. And, of course, the company, presumably with the help of pharmaceutical and financial partners, must finance the clinical trials of each protein—which Haseltine estimates will cost up to $100 million per drug by the time they are through. Still, Haseltine feels the money will be well spent. “These drugs are designed to meet major medical needs,” he says. “Each and every one has the potential to be a blockbuster.”

    Saving bones

    HGS is not the only firm to find the risk worthwhile. In 1994, Amgen's team plucked out a gene from their company's cDNA database for a protein that looks like a receptor for TNF, the failed cancer therapy —except for one feature. It has no section that would allow the protein to stick into cell membrane, as a true receptor would. That indicated that it floats outside a cell. “That was really interesting,” Amgen's Boyle says. “It suggested the compound was acting as a sponge or a neutralizing factor” for whatever binds to it, which was then unknown.

    To find out what the protein does, Boyle and his colleagues engineered mice to make huge amounts of it. The mice appeared healthy, but x-rays revealed that their bones were virtually solid, lacking the marrow-filled core of normal bones. In contrast, mice in which the gene had been deleted developed severe osteoporosis that mimics the human form “right down to the hump in the spine,” Boyle says. “We concluded that the amount of [this protein] in the body correlated with bone density and strength.”

    Other tests indicated that the protein, which the company named osteoprotegerin or OPG, meaning “protector of bone,” might be useful in treating or preventing osteoporosis. Osteoporosis risk rises in women at menopause or after removal of the ovaries, when estrogen levels drop. And company researchers found that in rats whose ovaries had been removed, OPG injections blocked the bone loss that would otherwise occur.

    Cell culture studies provided a mechanism for OPG's protective effects. They showed that the protein inhibits the maturation of cells called osteoclasts, which chew up bone, apparently because it blocks a molecule on other bone cells that are required for osteoclast development. Because osteoporosis is caused by too many osteoclasts, OPG seemed capable of directly attacking the cause of the disorder.

    Steven Teitelbaum, a bone cell biologist at Washington University School of Medicine in St. Louis, calls the OPG story “the most important thing that's happened in bone biology in the past decade.” But proteins such as OPG, he notes, are far from ideal treatments for osteoporosis because they must be injected, and many women won't tolerate shots to stave off a disease that has yet to produce any symptoms.

    Boyle agrees that a pill would be better, but says that if OPG shots are required only infrequently and the protein is safe and effective, it may be an option for women at risk for osteoporosis who experience unpleasant or dangerous side effects from oral drugs such as supplemental estrogen. Safety trials in people have just been completed successfully, and the company is gearing up for the next phase of clinical trials, which are likely to include women who already have osteoporosis.

    Immunex, meanwhile, has been investigating a possible cancer therapy based on a gene its computers picked out from a public database based on its similarity to the TNF gene. The Immunex team hoped this new protein would be more specific and thus less likely to cause the side effects that derailed TNF itself.

    It seems to be—both in cell culture and now in mice. In last February's issue of Nature Medicine, Henning Walczak, David Lynch, and their Immunex colleagues reported that the protein, called tumor necrosis factor apoptosis-inducing ligand (TRAIL), strongly suppresses the growth of tumors induced in mice. It also shrank and, in some cases, eliminated established tumors. Most remarkably, none of the treated mice showed any evidence of damage to the liver, brain, or any other tissue or organ. “With TNF, there wasn't a selective effect on tumor cells. With TRAIL, there seems to be,” says Immunex's Williams. It's not clear why TRAIL might be so selective, but one possibility is that normal cells, but not susceptible tumor cells, have proteins that suppress the cell-death programs TRAIL would otherwise trigger.

    Although TRAIL has not yet entered tests in people, the researchers hope it may someday be used along with chemotherapy to enhance tumor killing, or even used alone. But results in mice are often not replicated in people, so no one knows whether TRAIL will be a breakthrough in cancer treatment or another disappointment.

    Given such uncertainties, these companies are spreading their bets across a number of compounds. An HGS team led by David Hilbert, for instance, has just now reported finding a novel cytokine they call BLyS for B lymphocyte stimulator, which promotes the growth and activation of antibody-producing cells called B lymphocytes in cell culture and in mice. They suggest that the factor might be used to treat ailments of the immune system such as AIDS or autoimmune disorders (Science, 9 July, p. 260).

    In addition, over the past 2.5 years, HGS researchers have cloned some 14,000 genes for secreted proteins and others—up from hundreds in 1996—that they think might be good drugs or drug targets. Last year, HGS scientists began screening these proteins on a massive scale for their effects on many different cell types.

    At least some of these proteins should prove valuable, predicts Daniel Cohen, chief genomics officer at Genset SA in Evry, France, which has a secreted protein project of its own as part of a collaboration with Genetics Institute, a unit of American Home Products in Cambridge, Massachusetts. “There were 2000 secreted proteins known before genomics, and 10 of them were blockbuster [drugs],” he says. “So the assumption is that in the next 2000, there will be another 10.”

    For Haseltine, christening any of these new compounds as drugs would be a realization of plans laid long ago, when HGS was first founded. “For me, this is like a butterfly emerging from a cocoon. There is a deep sense of satisfaction in seeing this program unfurl,” he says.


    The Man Who Would Spin Genes Into Gold

    1. Ingrid Wickelgren

    A stoic young man in gilded black armor sits astride a white horse. The fists of the warrior, the young St. George, clench a long sword, ready to dispatch the snarling winged monster clawing at his feet. The tableau—painted some 500 years ago by Raphael—now symbolizes the modern ambitions of William Haseltine, CEO of Human Genome Sciences Inc. (HGS) of Rockville, Maryland, the company in the forefront of efforts to use modern genomics to develop new drugs (see main text). It appears in HGS's latest annual report. “We see St. George as human hope fighting the dragon of disease,” says Haseltine.

    This choice of symbol echoes Haseltine's own style—brash, aggressive, and vigorously self-promotional. His urgency was sparked long ago, he says, in part by his mother, Jean, who seemed constantly ensnared by the dragon's claws, suffering a chronic skin condition that made her hands blister and bleed and also from detached retinas. Doctors twice had to surgically remove her eyeball to repair it. And Bill himself developed a heart condition that left him bedridden for months as a child.

    Spurred by those illnesses, Haseltine enrolled at the University of California, Berkeley, planning to pursue a medical career until he was diverted by a passion for science. Berkeley chemist George Pimentel selected him and 14 other freshmen for a summer science program in which Haseltine read about, and met, several Nobel laureates. “It was fabulous,” he recalls. “What you could see from all those guys is that they really loved what they're doing. So I thought: ‘Well, I should be a scientist.’”

    As a scientist at Harvard, Haseltine conducted groundbreaking research on retroviruses and was one of the first to champion the idea that HIV, the AIDS virus, is a retrovirus. Another pioneer of that notion, Robert Gallo, who now directs the Institute of Human Virology at the University of Maryland Biotechnology Institute in Baltimore, remembers Haseltine as “brilliant” and a tremendous asset to the collaboration. “We went faster because of Bill Haseltine, and that's what I call a good scientist,” Gallo says.

    Indeed, Haseltine went on to discover many HIV genes and proteins and to start several biotech companies before being asked in 1992 to lead HGS. Now, his hopes rest on a stash of frost-covered vials inside tall freezers that occupy a room in one of HGS's cluster of red brick buildings. Together, these vessels may contain something close to all human genes. The genes, Haseltine believes, hold the secrets that will allow humanity to remake its own tissues when they become frail or diseased. HGS has three potential therapies based on those genes wending their way through clinical testing.

    Some attribute Haseltine's success to his practical bent as much as his scientific sense. He likes to explore potential uses for scientific advances, they say—and does so aggressively. “He goes after what he wants with great tenacity,” says his former collaborator, virologist John Coffin of Boston's Tufts University School of Medicine. Still, Coffin says he sometimes found Haseltine “challenging” to work with due to his hard-driving style. And Haseltine's eagerness to promote his own accomplishments has grated on a few nerves. Many people engage in self-promotion, Gallo points out, “but Bill does it with more pizzazz.”

    Haseltine has also ruffled feathers of fellow gene researchers. In addition to his difficulties with biologist J. Craig Venter during his company's partnership with Venter's institute (Science, 7 February 1997, p. 778), Haseltine has sharply criticized the stated goals of the Human Genome Project, describing the effort as “a technofolly” and “more about our aspirations to explore the unknown than about anything practical.” In May of last year, Haseltine argued in The New York Times that the $3 billion in federal funds devoted to sequencing the entire human genome —including the intervening “junk” DNA as well as the genes—should be spent in other ways. At a congressional meeting held shortly thereafter, Francis Collins, the project's director at the National Institutes of Health, said “not to consider that particular point of view as representative of the mainstream of scientific thought, either public or private.”

    Haseltine calls such statements “inappropriately dismissive,” considering his expertise in the area. But others, such as Harvard Nobel laureate Walter Gilbert, agree with Collins. “Bill is wildly wrong about that,” Gilbert says, referring to Haseltine's opinions about the federal project's limited medical value. Gilbert, who was Haseltine's thesis adviser at Harvard, nevertheless applauds his former student's efforts at HGS.

    Indeed, there is little that is understated about Haseltine, except perhaps his attire, which features dark fashionable suits, thin-rimmed circular glasses, and a simple wedding band. Beyond that, his taste is more elaborate. His condominium at the posh Pierre Hotel in New York City has the air of a palace—with its colorful, paisley couches, art from many cultures and eras, and ornamental furniture.

    His dreams may be even bolder than the decor. He looks beyond the kinds of gene-based therapies now being developed at HGS to an era when older tissues can be transformed into young ones by setting back their genetic clocks. “I think we can get to a stage, perhaps 100 years from now, where we can keep people young and dramatically extend human life,” says Haseltine, with a daring worthy of St. George.


    Small Asteroids Point to a Source for Meteorites

    1. Richard A. Kerr

    New observations of the commonest asteroids suggest that, beneath a reddish cloak, they are made of the same stuff as ordinary meteorites

    Rocks by the ton fall to Earth every year, and yet no one knows where most of them come from. The asteroids that swarm between Mars and Jupiter have long been the prime suspects, but 95% of meteorites don't match any particular asteroid or even any general asteroid type. Last week's flyby of asteroid Braille highlighted a rare exception (see p. 993), but efforts to link the most common meteorites—so-called ordinary chondrites, thought to be made of primordial solar system material—to the most common type of asteroid, the S-type, have come up dry (Science, 6 September 1996, p. 1337). At last month's Asteroids, Comets, and Meteors meeting in Ithaca, New York, however, astronomers presented the best evidence yet that S-type asteroids are just big chunks of ordinary chondrite after all, cloaked in some way that hides their true nature.

    Seen in the telescope, the subtle reddish cast of S-types looks nothing like the gray of chondrites. But at the meeting, astronomers Michael Hicks and David Rabinowitz of the Jet Propulsion Laboratory in Pasadena, California, reported that the smaller the S asteroid, the more its color resembles that of ordinary chondrites. Because smaller asteroids are also thought to be the youngest, the relation could mean that some kind of weathering process reddens the surface of larger, older asteroids.

    “The question now is not whether there is a connection between S asteroids and ordinary chondrites,” says astronomer Richard Binzel of the Massachusetts Institute of Technology. “There is a relation. The problem now is unraveling the process” that disguises ordinary chondrite asteroids. Not everyone is so sure, and no one has duplicated the cloaking process in the lab. Still, the S-type source is gaining support as it heads toward a major test early next year, when the Near Earth Asteroid Rendezvous (NEAR) probe will orbit and inspect an S-type asteroid.

    Asteroid specialists have long suspected that some kind of weathering process might be giving S asteroids a deceptive reddish tint. So they have aimed their telescopes at the smallest S-types, reasoning that because smaller asteroids are more likely to be blasted to smithereens in a collision with another asteroid, their life-spans should be shorter, giving the rigors of space little time to alter their surfaces.

    Last fall, Binzel reported evidence that these youngest asteroids also look the most chondrite-like. His ongoing survey of more than 1000 asteroids showed a whole range of colors. At one extreme was the reddish cast most common in larger bodies; at the other were neutral, ordinary chondrite-like colors. They were seen in up to 10% of the smallest bodies in his survey, roughly a kilometer across.

    Since 1996, Hicks and Rabinowitz have been focusing on even smaller asteroids, ranging from 10 kilometers down to 100 meters in size. The colors of such small objects are difficult or impossible to measure in the main asteroid belt, but they can be recorded among the so-called near-Earth asteroids, which have somehow escaped from the main belt (see sidebar). Of the more than 140 near-Earth asteroids Hicks and Rabinowitz have studied, those above a diameter of a kilometer or so mostly resemble S-types, while “a large number” (about 25%) of those smaller than a kilometer resemble ordinary chondrites in color.

    To planetary scientist Clark Chapman of the Southwest Research Institute in Boulder, Colorado, the findings clinch the case that S-type asteroids are the source of most meteorites. “It looks to me like the story is finished,” he says. But Chapman notes, “You do need a step between the observation of a continuum [of color] and making an interpretation of what's doing it.”

    What may be doing it, say Binzel, Chapman, and others, is a process called space weathering. Just as exposure to the elements alters rocks on Earth, the space elements—such as the solar wind and the impacts of micrometeorites—can alter the surface of freshly exposed asteroidal rock by vaporizing part of a mineral and redepositing it elsewhere on the surface. Just how it works is a mystery, though, says meteoriticist Harry McSween of the University of Tennessee, Knoxville. “I believe in space weathering,” he says, “but we don't really understand it.”

    As a result, some researchers hesitate to accept that S asteroids are chondrites in disguise. “I'm still skeptical, because space weathering [of asteroids] hasn't been proven,” says astronomer Lucy-Ann McFadden of the University of Maryland, College Park. “It's easy to invoke space weathering but difficult to prove” that it's behind the differing appearance of S-types and ordinary chondrites. Planetary scientist Carlé Pieters of Brown University agrees, but notes that, in the lab, simulated space conditions can give ordinary chondrites at least some resemblance to S-types. And she says that space scientists are also learning how the solar wind and micrometeorite impacts alter soils on the moon—a model for what may happen to S-type asteroids.

    Space weathering may not be the only process altering the look of larger S-types, Binzel adds. Because of their weak gravity, small asteroids may retain little of the finest debris generated by impacts, resulting in a coarser surface coating than is found on more massive asteroids. Particles of different sizes scatter light differently, which could contribute to the differences in color. With plenty of possible explanations at hand, Chapman and others aren't discouraged by the mystery of what reddens S-types. “There's been a major shift of opinion,” says Chapman. “It's just the details that remain to be cleaned up.”

    Some of the details could be cleaned up starting this Valentine's Day, when the NEAR spacecraft goes into orbit around the 33-kilometer-long S-type asteroid Eros. X-ray and gamma ray instruments on NEAR will for the first time determine the elemental composition of an asteroid's surface, something that no amount of space weathering should alter. NEAR's close look could prove crucial in understanding cloaking and pinning down the link between S-types and chondrites. But if not, the frustrations could persist until a future mission to an S-type—as yet unplanned—actually scoops a sample from an asteroid and brings it back to Earth.


    Escaping From the Asteroid Belt

    1. Richard A. Kerr

    Recent observations may have fingered the type of asteroid responsible for most meteorites (see main text). And thanks to progress in orbital dynamics, another mystery may also be yielding: how asteroid debris is slung toward Earth in the first place.

    Planetary scientist Clark Chapman of the Southwest Research Institute in Boulder, Colorado, explains that, unperturbed by external forces, an asteroid or any debris it sheds would never leave the main belt, beyond the orbit of Mars. In recent decades, however, dynamicists found two narrow zones in the main belt, so-called “escape hatches,” where Jupiter's powerful gravity can stir up orbital chaos and send rock careening toward Earth. But that meant only the handful of asteroids close to an escape hatch could conceivably contribute to meteorite falls on Earth.

    Computer simulations are now revealing other routes out of the asteroid belt. Last year, the late Fabio Migliorini of the Astronomical Observatory of Torino in Italy and his colleagues found that the gravity of Mars creates unexpectedly large amounts of orbital chaos in many zones of the asteroid belt. The chaos is powerful enough to nudge rocks out of the belt and toward the orbit of Mars, where martian gravity could hurl some of them toward Earth.

    And this spring, dynamicists Paolo Farinella of the University of Trieste in Italy and David Vokrouhlicky of Charles University in Prague resurrected the century-old Yarkovsky effect to shake things up further in the main belt. The Russian engineer I. O. Yarkovsky had recognized that the “afternoon” quadrant of a solar system body—the side that has been exposed to the sun for the longest—would be the hottest, generating the strongest thermal radiation. The resulting radiation pressure, he said, would slowly alter the body's orbit. Farinella and Vokrouhlicky showed that the Yarkovsky effect is strong enough to move small asteroids into chaotic zones for transport to Earth. Taken together, the two effects mean “we can get meteorites from a broader distribution of locations,” says astronomer Richard Binzel of the Massachusetts Institute of Technology—enough to keep Earth well supplied with falling rock.


    Many Modes of Transport for an Embryo's Signals

    1. Gretchen Vogel

    Developing embryos may actively ship key signaling molecules from place to place, instead of relying on diffusion to carry the messages

    The developing embryo is a complex and ever-changing world, where landmarks quickly form and disappear and the entire geography shifts over time. Orchestrating these changes are protein messengers that constantly flow within and between cells, directing the next stage of shape change and cell division. But how do these messengers travel to their appointed destinations?

    The classic paradigm is that a developmental signaling molecule diffuses freely from its source, so that nearby cells get the biggest dose and feel the strongest effects. “People have been talking about gradients since the beginning of embryology,” says developmental geneticist Thomas Kornberg of the University of California, San Francisco (UCSF). But he notes that researchers have been unable to find these concentration gradients for a few key signaling molecules. And simple gradients can't explain the physical changes that accompany some crucial developmental events.

    Now, thanks to an increasingly popular method of tracking proteins in space—hooking a glow-in-the-dark marker to the protein of interest—researchers can watch signals traverse cells in real time. Experiments with such methods are beginning to suggest that cells may actively ship some proteins around rather than relying on diffusion to carry the message. For example, 2 weeks ago researchers reported that frog eggs apparently haul a key signaling protein across the egg on a sort of intracellular railroad. Once at its destination, the protein helps trigger a cascade of messages that transform that side of the egg into the back of the embryo. And Kornberg's recent work on developing fly wings has sparked a bold new theory of transport: Rather than waiting for instructions to reach them, target cells may themselves send out long, skinny extensions to pick up messages from the source cells. “It's a way-out unexpected wrinkle,” Kornberg says.

    These and other studies offer a first glimpse into what may be a complex transportation system within the developing embryo, says developmental biologist Sergei Sokol of Harvard Medical School in Boston. “We used to have this simplistic view that different proteins diffuse readily in the cytoplasm. Now, more and more people think of it as a compartmentalized process,” he says.

    Still, the work is preliminary, cautions developmental geneticist Clifford Tabin of Harvard Medical School, and few papers have sewn up the details of these new modes of transport. For example, although Tabin agrees that the cell extensions Kornberg has spotted “are in a great place to be transmitting all sorts of signals,” so far no one has proved that they actually do so. All the same, says developmental geneticist Andrew McMahon of Harvard University, these and other transport findings are giving development researchers “new food for thought.”

    Riding the egg's railroad

    One of the key tasks in the life of a just- fertilized egg is to tell its back from its belly. In frog eggs, this feat requires at least two types of developmental events. A protein called β-catenin, which turns on a host of genes, must be activated, and the egg must also undergo a major contortion: Its entire outer layer rotates 30 degrees around the cell's interior, tugged by an array of protein chains called microtubules. Now, in the 26 July Journal of Cell Biology, scientists link these two events, reporting that as microtubules move the outer cytoplasm, they also cart a signal in the β-catenin pathway to the embryo's future back side.

    Previous research had shown that the microtubules not only drive the egg's rotation but also carry intracellular compartments called vesicles—highly suggestive evidence of protein transport. Researchers also knew that disrupting the microtubules both blocks the rotation and prevents the embryo from distinguishing its front and back sides: It becomes a blob of disorganized gut and blood cells without head, tail, or nervous system, says Randall Moon of the University of Washington School of Medicine in Seattle. Blocking β-catenin produces similar results. But no one knew how the microtubule-driven rotation and the protein cascade were connected.

    To find out, Moon, postdoctoral fellow Jeffrey Miller, and their colleagues attached the gene for green fluorescent protein (gfp)—a small glowing protein originally found in jellyfish—to the gene for Dishevelled, a cytoplasmic protein in the β-catenin cascade. Developmental biologists Carolyn Larabell and Brian Rowning of Lawrence Berkeley National Laboratory in Berkeley, California, then inserted the RNA message for the composite protein, a fluorescent version of Dishevelled, into frog eggs, so that the eggs made the new protein. The researchers then pricked the cells with a needle, tricking the eggs into thinking that they had been fertilized and prompting them to start dividing.

    As the eggs prepared for their first cell division, the team took microscope images of them every few seconds. They combined those images into an embryo home movie,* showing that as the cytoplasm rotates, gfp—and therefore its Dishevelled partner—also “zips over at high velocity to the dorsal side,” says Moon.

    The Dishevelled particles move at about the same speed—28 micrometers per minute—and in the same direction as vesicles moved along the microtubules in previous studies. So the authors propose that vesicles rolling along the microtubule tracks carry Dishevelled and perhaps other proteins to one side of the egg. There, Dishevelled stabilizes β-catenin so that it can turn on the other key genes, creating a back side. It's “the nearest thing yet to the ‘missing link’” between the egg's rearrangement and the β-catenin cascade, says Jonathan Slack of the University of Bath in the United Kingdom.

    Rowning notes that the same kind of intracellular railway might govern development in other large eggs known to have microtubules, such as those of zebrafish. The implications might extend to adults as well, for Dishevelled is part of the Wnt signaling pathway, which is also involved in cancer and hair growth (Science, 4 September 1998, pp. 1438 and 1509; 27 November 1998, p. 1617), Larabell notes. Understanding the protein's mode of travel may help researchers unravel those events, too.

    Cells reach out

    Well after front and back, head and tail have been determined, the now many-celled embryo still relies on protein messengers to trigger distinct developmental steps. Another gfp study now presents a bold new alternative explanation for how these signals get around. In the 28 May issue of Cell, developmental geneticists Felipe-Andrés Ramírez-Weber and Kornberg of UCSF reported never-before-seen cell extensions they call cytonemes, for their threadlike appearance (neme means thread in Latin). Only about 0.2 micrometer wide, the cytonemes they saw extended from cells in the outer regions of a developing fly wing toward a region in the center known to produce key developmental signals called Hedgehog and Decantaplegic (DPP), which regulate growth and cell fate. Because the cytonemes carry vesicles, the researchers suspect that they reach out and pick up signals from other cells.

    The team has yet to prove that cytonemes play this role, but even so, these skinny cellular extensions are “really something amazing,” says developmental biologist Edward De Robertis of the University of California, Los Angeles. “It's going to change all the thinking” about how signals might be transported to distant cells.

    Kornberg describes the find as “pure luck,” saying, “We didn't know what we were looking for.” Ramírez-Weber had randomly inserted a copy of the gfp gene into the genomes of various fly strains, hoping that it might light up a gene of interest to wing development. In one genetically altered strain, the anterior and posterior regions of the embryonic wing lit up bright green, but the middle stayed dark. Upon closer inspection, Ramírez-Weber spotted long green threads stretching from the outer cells toward the center region. The delicate threads, several times the cells' length, disappeared when the researchers applied any fixative or even when they moved the microscope objective to try to follow the threads to their ends.

    But the researchers found they could culture cytonemes on demand: They grew small pieces of tissue from the outer wing next to tissue from the center, and within about an hour the outer cells sprouted cytonemes stretching toward the center cells. In a few of these cultured cytonemes, the scientists spotted a vesicle moving away from the cell body— implying that the extensions can transport proteins. Similar methods also yielded cytonemes in cultured mouse limb bud cells and chick embryo cells, and several researchers, including De Robertis, have now spotted them in their own labs.

    The researchers theorize that the vesicles in these cellular threads cart Hedgehog and DPP back to the outer cells. Such a system would transport these powerful signals efficiently and also limit their spread, fitting their observed effects, says Kornberg. But it's a challenge to current thinking. “When we draw cells, we draw them as little round spheres,” says McMahon. The idea that cells stretch several cell lengths away “changes the whole equation of how signaling interactions may occur,” he says.

    Of course, as Kornberg readily admits, he and his colleagues have a long way to go before they prove that the signaling proteins really are on or within the cytonemes. If this and other early findings hold up, however, cytonemes, intracellular railways, and other active transport systems could explain the long-standing mystery of how signaling molecules orchestrate development so precisely. “There's a lot more organization than we know about,” Kornberg says. “Almost nothing is left to chance.”

Log in to view full text

Via your Institution

Log in through your institution

Log in through your institution

Navigate This Article