Biologists Reexamine Cause of the Black Death
What wiped out half the population of Europe in 1348? The Black Death, of course. But what exactly was the Black Death? Biologists have assumed for more than a century that the culprit was Yersinia pestis, or plague. Three years ago researchers at the University of the Mediterranean in France thought they had settled the matter when they examined three Black Death victims and found segments of Yersinia DNA in their teeth.
But this year Alan Cooper, head of the Ancient Biomolecules Centre at Oxford University, showed that the teeth were most likely contaminated with a modern—not a medieval—strain of Yersinia.
“It’s incredibly easy,” Cooper says, to test a long-dead corpse and find plague. “In fact, it’s almost impossible not to get a positive result when doing ancient DNA work because there’s so much contamination around. It’s incredibly difficult to get an authentic result.” Part of the problem, in Cooper’s view, is that the researchers are microbiologists, not “proper DNA researchers. They don’t have a laboratory set up appropriately, on the whole, and the very pathogen that they’re most interested in is probably already present in large amounts around the building.”
It’s not as if the French researchers hadn’t taken precautions. The biologists looked for a different segment of the Yersinia genome every time they examined a new tooth. “The main problem,” Cooper says, “is if you actually have Yersinia DNA in the building from any previous work in the lab—even 5, 10, 15 years before—it doesn’t matter what target you go for because the DNA from the actual bug itself will have all the genes that you might want to go looking for.”
To test his skepticism, Cooper examined 121 teeth from 66 Black Death victims. He used a technique in which the tooth is coated in silicone before it is sent to the lab. The coating, says Cooper, prevents “any nasties from getting off the tooth surface” and contaminating the interior when a sample is taken.
Cooper found no trace of Yersinia DNA. That doesn’t mean the bacteria didn’t cause the Black Death, however. “I’m still a traditionalist,” says Cooper. “I think it was Yersinia.” He simply doesn’t think the French have proved it.
Bygone Bull Birthed From Frozen DNA
When the calf struggled to his feet on April 1 and bellowed, “we all cheered like proud parents,” says geneticist Robert Lanza. That’s because the 40-pound male banteng is an animal like no other. It is the first healthy, viable clone of an endangered species and the first successful birth from a cross-species nuclear transfer.
Paradoxically, the reason for the cloning was to increase genetic diversity among the dwindling pool of surviving bantengs, a species of large, wild oxen once common in the forests and jungles of Southeast Asia. Lanza, vice president of medical and scientific development at Advanced Cell Technology in Worcester, Massachusetts, is one of the geneticists who proposed the idea. The genes came from the Zoological Society of San Diego’s Frozen Zoo, a collection of 35,000 preserved animal tissue samples, including skin cells from a male banteng that had been killed in a fight with another animal at the zoo in 1980.
“We didn’t know whether cells that old would even work,” says Lanza. Researchers transferred the banteng DNA to Angus cow eggs from which the nuclei had been removed. Using an activation protocol that required bathing the eggs in chemicals, thereby imitating the fertilization process, the team was able to generate 45 embryos. The embryos were sent overnight to Trans Ova Genetics in Sioux Center, Iowa, where they were implanted in 30 Angus cows. Of 16 pregnancies, two went full term, with cesarean births in early April. The first calf was normal; the second was born almost twice the normal size and euthanized after being judged unlikely to survive.
The surviving calf was transferred to the San Diego Zoo Wild Animal Park, where the staff has been hand-rearing it. Now weighing more than 350 pounds, it is nearing adulthood. At sexual maturity, it will be able to mate with female bantengs in the zoo. The offspring of that union, Lanza says, will be “100 percent banteng and not a hybrid at all.”
—Michael W. Robbins
Good Runners Have Good Proteins
What gives a great athlete superhuman speed? Genetics may make a crucial difference. Scientists at the Institute of Neuromuscular Research at Children’s Hospital in Sydney, Australia, have discovered a variant of a gene called alpha-actinin-3 that appears to help muscles contract faster and with greater force by making a protein called actinin in muscle fibers. Researchers took DNA samples of more than 300 athletes who represented Australia in the Olympics or other major competitions. Their DNA was compared with the genetic profiles of 400 randomly chosen people. Among elite sprinters, 95 percent were found to have the gene variant versus about 82 percent of the general population.
Long-distance runners seem to have a different kind of genetic edge. Athletes who excel in endurance sports are more likely to have another version of the gene—this one called the X variant—that does not produce actinin. Kathryn North, a neurologist and clinical geneticist who led the study, suspects that its absence may make muscles contract more slowly and absorb nutrients at a lower speed, which is better for endurance.
North cautions that genetics are only part of what makes a successful athlete. “It is still highly contentious whether we can use genetic markers to predict athletic performance,” she says. “There are any number of critical nongenetic factors that play a key role: coaching, equipment, competition, and serendipity. But every variable counts. And genetic information may help athletes make better-informed decisions about the likelihood of success in a particular sport.”
Horse Racing May Never Be the Same
A horse was born this year with a most unusual pedigree. Cesare Galli and his colleagues at the Laboratory of Reproductive Technology in Cremona, Italy, announced the delivery in July of a 79-pound foal that has the distinction of being her mother’s twin sister. Prometea is not only the first cloned horse but also the first widely reported case of a cloned mammal whose genetic donor is her surrogate mother. Biologists had previously assumed that a mother’s immune system would reject a genetically identical fetus.
If cloning a horse were scored for difficulty, the feat would rank well above the more familiar mouse, rabbit, sheep, or pig. And the difficulty of cloning a mule might rank even higher. Horses usually release only one egg during ovulation, and they have an 11-month gestation. Mules, from the union of a horse and a donkey, are usually sterile because of the mismatched chromosomes they inherit. But in May Gordon Woods, a professor of animal and veterinary science at the University of Idaho, reported the birth of Idaho Gem, the world’s first cloned mule.
Racing fans are excited by the arrival of both Prometea and Idaho Gem. Don Jacklin, president of the American Mule Racing Association, who helped finance Woods’s research team, hopes cloning will reproduce prizewinning animals. Still, if the poor health and short life of Dolly the sheep is an indication, cloned equines will have the odds stacked against them.
Decaffing Bean Genes
Nature puts caffeine in coffee beans, then humans go to great lengths to take it out. Before being roasted, green beans must be soaked in poisonous solvents, carbon dioxide, or repeated water baths to remove their jolt. But research teams around the world have been trying, through selective breeding or genetic manipulation, to coax the coffee plant into omitting the caffeine in the first place.
Last June researchers led by Shinjiro Ojita at the Nara Institute of Science and Technology in Japan announced they had created the first coffee plants genetically engineered to do just that. In a normal coffee plant, enzymes add methyl groups to a chemical called xanthosine, converting it into caffeine. Using a technique called RNA interference, Ojita’s team constructed transgenic coffee plants in which the gene that governs production of one of those enzymes is, in essence, turned off. The resulting plants have about 60 percent less caffeine. Beans from the plants are expected to show a similar decrease, but researchers won’t know for sure until this first crop matures and beans are harvested in about four years. Whether they will make a decent double chocolate latte is a different question entirely.
—Michael W. Robbins