So Benzer’s first years in Church Hall, from the first run of his first countercurrent machine, were one long confirmation of Konopka’s Law. Benzer had hardly started his study of genes and behavior before he and his raiders found the time, love, and memory mutants, mutants that seem even more remarkable now than they did then, knowing what came afterward. If Benzer had tried to hoard the mutants, as many laboratory heads do, they might have died on the shelf. But Benzer chose instead to let his students and postdocs leave with them and build careers on them. As a result, each gene opened extraordinary views. By the end of the century they were helping to change our view of all behavior, including the behavior of the human family.
PART THREE
Pickett’s Charge
and thus beneath the web of mind I saw
under the west and east of web I saw
… the coiling down the coiling in the coiling
—CONRAD AIKEN,
“Time in the Rock”
CHAPTER ELEVEN
The Drosophila Arms
The flies, poor things, were a mine of observations.
—PRIMO LEVI,
“The Invisible World”
JEFF HALL left Benzer’s Fly Room in December 1973, and he opened a Fly Room of his own at Brandeis University, just outside Boston. There he hung a sign on the door: “The Drosophila Arms.” On the sign he pasted photomicrographs of the sex combs on the forelegs of the male fruit fly, which help him grasp the female. By the sign of the Drosophila Arms, Hall planned to study the savoir-faire mutants, the ones that are unlucky in love.
Hall’s breakthrough began serendipitously when he and one of his own first postdocs, Charalambos Panyiotis Kyriacou, decided to study the love songs of mutant flies. They planned to put pairs of flies inside a tiny recording studio, tape their love songs, and analyze what is known to students of fly behavior as the song’s interpulse interval, or ipi.
In the scientific literature on Drosophila behavior, D. melanogaster was reported to sing with an ipi of thirty-four pulses per second. D. simulans, a sibling species, was reported to sing with an ipi of about twenty pulses per second. To a human ear both these songs sound alike. But if a female melanogaster hears thirty pulses per second she says, “Aha, that’s a male of my species.” If she hears the slower version, she says, “Ahh, you’re a male of the wrong species, go away.”
Before Hall and Kyriacou began testing mutant fly songs, they decided to measure the normal ipi for themselves. So Kyriacou built a recording studio, two centimeters long, one centimeter wide, and a third of a centimeter high, with a microphone two millimeters beneath the floor. Then he taped a series of normal male fruit fly love songs and played each tape into a machine that transformed it into a long, scrolling paper graph of pen squiggles.
Kyriacou might have recorded each song for a few seconds and taken his measurements from that. But instead, to be thorough, he and Hall recorded a full five minutes of tape, which generated a staggering amount of nervous-looking paper. Kyriacou would lug these scrolls home in the evenings, unroll them across his living room floor, and measure the ipis of fly songs while American sports events roiled across his television screen. Kyriacou is Greek by ancestry and British by citizenship, but while living in Boston he had pledged some allegiances to the local teams.
He soon found that the ipis in his scrolls agreed neither with the scientific literature nor with one another. The ipis kept changing from one end of a scroll to the other. That is, the beat varied from one minute to the next. First the song seemed to be allegro, then largo, then allegro again. Eventually, staring at one of these erratic love songs, Kyriacou decided to quit trying to measure the intervals between pulses and instead measure the intervals between the tempo changes. He was astonished to discover that this interval was regular: the tempo of the fly’s song changed once every minute. “And I looked at another one, the same thing,” Kyriacou says now, “and another one, the same thing.” The tempo changes were not erratic: They were a secret rhythm in the song, a hidden pattern marked in time by every singing fly.
Over lunch the next day, Kyriacou told Hall what he had found. Together they wondered what the songs of Konopka’s time mutants must be like. What kind of tempo changes would a fly make if it had a warped sense of timer Hall wrote to Konopka and asked him to send him some of his mutants. Konopka had published very little about period since he and Benzer had announced their discovery in 1971, and Hall wondered briefly if he would let them study period at all. “These mutants in principle were pure gold,” Hall says. “So if he’d wanted he could easily have just withheld them and not permitted anybody else to work on them.” Fortunately, fly people still shared mutants freely, a tradition that Morgan had started in the first Fly Room (the tradition has eroded recently in the gold rush that Hall’s own work helped to start).
Konopka mailed Hall a few test tubes full of his clock mutants. (Fruit flies can survive for days in a test tube with food at the bottom and a cotton stopper at the top, cushioned in a well-padded envelope.) One by one, Kyriacou put the mutants into his recording studio, and in the evenings he unrolled their love songs one by one onto his living room floor. From the very first scrolls, he saw that these mutants’ warped sense of time also warps their songs. Konopka’s short mutant, the nineteen-hour one, for example, changes tempo much more quickly than normal. Konopka’s long mutant, the twenty-nine-hour one, changes tempo much more slowly than normal. And Konopka’s insomniac fly, the fly that has no sense of rhythm at all, changes tempo just as randomly as he sleeps and wakes.
These differences were obvious in the scrolls. Hall and Kyriacou also found by experiment that simulans females prefer a male that sings with a fast rhythm, the rhythm of their own species, whereas melanogaster females prefer the sixty-second rhythm. The female fly is listening closely.
Rhythm also commands attention in our own speech, of course, although we are usually no more conscious of it than is any other species on the planet. In Lincoln at Gettysburg, a book in Hall’s extensive Civil War library, the critic and historian Gary Wills notes that throughout Abraham Lincoln’s famous speech there is a strong repeating rhythm: “Triple phrases sound as to a drumbeat.” Wills prints these triple phrases in a kind of accidental poem that seems to echo through our memories:
we are engaged …
We are met …
we have come …
we can not dedicate …
we can not consecrate …
we can not hallow …
that from these honored dead …
that we here highly resolve …
that this nation, under God …
government of the people,
by the people,
for the people …
Orators and storytellers have this gift. Somehow they communicate in the rhythm of a speech or story a human urgency, a message: hear, attend, gather round. They have the gift of producing the rhythm, and most of us have the gift of hearing it. Apparently flies have these gifts too.
Since melanogaster and simulans sing with different rhythms, Kyriacou wondered what would happen if he crossed these two species of flies. So he bred them and put their young flies in his recording studio. He found that he got two kinds of hybrid males. If his mother was a melanogaster, a male sang with a melanogaster rhythm. But if his mother was a simulans, he sang with a simulans rhythm. Since each male fly got his X chromosome from his mother, the difference in the genes was somewhere on the X.
Hall, of course, had been in Benzer’s laboratory when Konopka mapped the period gene, the first piece of complex behavior ever mapped. So Hall knew what Kyriacou’s cross might mean. The two men now knew that the gene that affects the tempo changes in the fly’s love songs is on the X; and they already knew that the period gene is on the X. So they had to wonder if both pieces of behavior might be shaped by one and the same gene. Hall still gets excited when he talks about the moment when Kyriacou’s cross pointed to the X.
“Now,
where is the period gene of Konopka?” Hall shouts. “It’s on the X chromosome! Tah-dahm!”
HALL EXPLAINED their hunch to his best friend at Brandeis, a young molecular biologist named Michael Rosbash. In those days, Hall, Rosbash, and Kyriacou spent a lot of time together. “And not only because of science,” Hall says now, “but because of interest in Boston sports teams—all three of us being fanatic betrayees of our Boston sports teams, particularly the Red Sox.”
Hall and Rosbash also played basketball together in the campus gym. The regular players were faculty and a bunch of guys from the repair department at the phone company. They played together for years—only the grad students would come and go. Sitting in the locker room day after day, Hall would talk about behavior, Konopka’s gene period, and the secrets of the sense of time. Rosbash would talk about molecular biology.
By now the molecular revolution had begun the explosion that still continues today. A new generation of molecular biologists was doing work that was in the best sense derivative—derived from what had come before. They were adding story upon story to Occam’s Castle. They had now figured out how to turn Delbrücks starting point, a petri dish of E. coli, into such a sophisticated all-purpose laboratory tool that even some of the young molecular biologists themselves were alarmed at how much they could do.
When a single bacterium divides in a dish, one becomes two, two become four. Within a day, by the implacable logic of exponential curves, the first bacterium has become several billion. Each cell is an identical twin of the one before. Each is what biologists call by the Greek word for a twig or a shoot: a clone.
When a particle of phage attacks a field of these clones, it injects its own strand of DNA into its victim like a hypodermic needle. (Phage particles actually look like hypodermic needles. The first time a phage watcher saw them in an electron photomicrograph, he slapped his forehead: “Mein Gott! They’ve got tails!”) Sometimes a bacterium is able to attack the incoming viral DNA with special enzymes, like sabers slashing tentacles. But if these enzymes fail, the viral DNA inserts itself into the bacterium’s ring of DNA, which is a circlet about a millimeter long. Once the cell receives that viral DNA, its behavior is transformed and it becomes a cloning machine at the service of the virus.
Bacterial cells also trade DNA peacefully among themselves. A bacterium will take in a smaller circlet of DNA, known as a plasmid, from a neighboring bacterium, cut out a few genes from the plasmid, and patch them into its own DNA. The secret formula for resistance to a drug such as penicillin may be carried on a single plasmid. If the cells are under attack by penicillin, a cell that carries that particular plasmid will survive and reproduce. Soon the whole petri dish has copies of the formula, some because they are clones of that surviving cell, some because they have received the formula on a plasmid and patched it into their own chromosome.
In the early 1970s, molecular biologists put this bacterial behavior to work. They figured out how to harvest a bacterium’s enzyme scissors or sabers and use the enzymes to cut any pure extract of DNA into ribbons of specified lengths. These bacterial tools are known as “restriction” enzymes. Whenever they encounter DNA they restrict it, or cut it, at certain specific points. Restriction enzymes are specialized or, to use one of the buzzwords of molecular biology, specific. A streptomyces bacterium, for instance, carries an enzyme known as SacI. SacI will cut DNA only if it finds the sequence GAGCTC, and it will make the cut only in one place, between the T and the last C.
Collecting a war chest of these enzymes, molecular biologists in the 1970s learned to cut DNA into snippets almost as deftly as the bacteria do. They also figured out how to copy phage behavior and inject snippets of DNA into a bacterium’s DNA. When their victim reproduced, it reproduced that extra bit of DNA along with its own. Then that cell’s children and its children’s children reproduced the gene. In the space of a few hours, a bacterium had become a colony of billions, containing billions of copies of the gene—cloned.
Benzer and his first disciples enjoyed working in what one of them calls “a carnival atmosphere.” These are some of the slides they showed at lectures. Benzer, going cross-eyed over flies. Benzer in front of a movie poster, doing his Jeff Goldblum imitation. Jeff Hall and Michael Rosbash ut a party at Brandeis University, wearing formal attire. (Illustrations credit 11.1)
Cloning genes turned molecular biologists into genetic engineers, a term that back in Morgan’s Fly Room would have sounded like pulp science fiction. Now they could excise a gene from one species, insert it into another species, and watch what it did. They could inject a human gene into a fly. First they cloned the human gene. Then they snipped it with a specialized restriction enzyme that left the DNA fragment with what are known as “sticky ends.” In a vial, they mixed a solution of these sticky DNA fragments (billions of clones of the sticky gene) with a second kind of DNA fragments called “P elements,” which would act as shuttles to carry the DNA of interest into the bacterial DNA. P elements are genes that do not stay in one place in chromosomes; they hop off a chromosome and reinsert themselves elsewhere. The existence of these jumping genes was first surmised by the geneticist Barbara McClintock, working with purple, white, and spotted kernels of maize, or Indian corn, at Cold Spring Harbor. McClintock spent several decades working in isolation. Most of her colleagues found her stories about jumping genes hard to understand and hard to believe. (Jim Watson used to trample through her cornfield, chasing softballs.) Then molecular biologists discovered jumping genes in E. coli, Drosophila, and human beings. Each one of us carries mariner, a jumping gene that was first discovered in the fruit fly. This gene mariner may have been injected by a virus into an egg or a spermatozoan of one of our distant ancestors before the evolution of the human species itself. The gene still passes from one generation to the next. We share whole families of these jumping genes with flies, including mariner, gypsy, and hobo. McClintock won a Nobel Prize in 1983, at the age of eighty-one.
So drosophilists clone a human gene, give it sticky ends, and allow it to stick to a P element. They also add to the ribbon one of the classic genes from Morgan’s Fly Room, white. They always use the normal form of white—the form that confers red eyes. Then, with a hypodermic needle, a microsyringe, they inject this submicroscopic ribbon of DNA into the rear end of the early embryo of a white-eyed fly. The whole ribbon—including the human gene, the P element, and white—goes floating off invisibly through the embryo. For the experiment to succeed, the P element must insert itself into one of the embryo’s chromosomes—not just any chromosome, but a chromosome inside one of the cells that will eventually become a germ cell, which is a cell that makes eggs or sperm. If the P element fails to insert itself there, then the fly’s children will have white eyes. But if the P element does insert itself in the right chromosome, then the fly’s children will pop out of their eggs with red eyes, and they will carry the human gene. Delbrück celebrated some of these innovations in “A Valentine for NIH”:
We now use chemistry to shuffle genes,
Use plasmids to move man’s to beans,
Or rat’s to microbes, flies’ to fleas,
Or yeast’s to coli, bee’s to peas.
All this is based on Watson-Crick’s
Phantastic Double Helix, plus some tricks
That others added to this play
And add still more from day to day.
Brenner and Benzer observed these new developments with excitement and some regret. The new tools were thrilling but made working with genes almost too easy. “We had grown up in a tradition, both he and I, where it was important to try and use your brain in doing this work,” Brenner says. As pioneers, they had been forced to look into the machinery of life from a certain distance. They had devised Olympian experiments and then made inferences and deductions, climbing through cloud banks in their minds like theoretical physicists. “And, of course, that’s the great fun of it,” says Brenner, “when you can cross the bridge between the machinery and your obse
rvations by thought.” Today they feel that young biologists are spoiled. “The present generation—you know, to them, getting hold of a gene is what you do,” Brenner says. “You get hold of the gene. “You clone it.
HALL HAD NEVER learned cloning. His background was classical genetics. So Hall had the mutants and he had the scientific problem. His friend Michael Rosbash had the tools, and Rosbash thought the fly might be ready to go molecular. Rosbash also thought that if he were going to move in on the fly, he would want to focus on a gene somewhere near white, because geneticists had been mapping and remapping that terrain ever since Morgan’s Raiders. Now period, of course, is right next to white. If Hall was right about his gene, Rosbash would be able to use the tools of molecular biology to dissect an instinct: to explore for the first time the molecular links between genes and behavior.
In the locker room, after their basketball games, Hall predicted (at top volume) that period would turn out to be one of the most glamorous genes ever discovered. It affects everything about a fly’s sense of time, from the hour of its rising up to the hour of its lying down, including the intimate rhythms in the vibrato of a love song. It is the quintessential behavior gene. But Rosbash, who is as forceful and intense as Hall, was not convinced. Rosbash thought that in spite of Benzer’s, Konopka’s, Hall’s, and Kyriacou’s enthusiasm, it was still quite possible that period would turn out to have nothing to do with the clock, or with the love song either. “The cell has to get up and brush its teeth, have its O.J., and so forth,” Rosbash used to tell Hall in the locker room. Each cell requires vast quantities of mundane molecular machinery just to keep itself running. Rosbash thought the period gene might turn out to run some boring housekeeping chore without which the cell could not function smoothly. If so, a defect in the period gene might affect every aspect of the fly’s behavior without being central to the clock. A man with the flu may not rise and shine at his normal hour, and he may not sing in the shower with his normal vigor, but that does not mean that his clock is broken. It just means he has the flu. Rosbash was raising the same objection that Benzer and his students had heard from the beginning of their project. When they poisoned flies and found lines that acted strange, how did they know they were not just breeding sick flies?
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