Photo credit: Rod Morata
For her discoveries in neurogenetics
For a few months during medical school, Huda Zoghbi slept in a windowless closet inside a women’s bathroom at the American University of Beirut. Outdoors, the Lebanese civil war raged, making daily trips between home and lectures too dangerous. She and her classmates ate in the hospital cafeteria, which they accessed through an underground tunnel. At night, she fell asleep atop her sleeping bag, listening to the irregular blasts of exploding bombs.
Zoghbi had not always been so committed to studying medicine. In high school, she developed a passion for Shakespeare and English literature. Left to her own devices, she would have pursued writing as a career, but this possibility dismayed her mother, a full-time homemaker, who pressed Zoghbi to become a physician. Zoghbi was good at biology and liked the subject, her mother contended—and medicine would provide independence. Zoghbi pushed back repeatedly. Eventually, realizing that her mother had a point, she relented.
After Zoghbi’s first year of medical school, her parents sent her and her siblings to safety in the United States. Zoghbi intended to visit a sister for a few months and then return home, but the continuing war thwarted her plans. She wound up finishing medical school in the States, graduating in 1979. Zoghbi gravitated toward pediatrics. Of the possible specialties, neurology enticed her because she relished the detective work. Before touching her patients or running a medical test, she could engage her mind in the puzzle that confronted her. Interviews alone allowed her to map the problem to a particular part of the brain and develop a provisional diagnosis.
Although intellectually satisfying, this specialty soon became emotionally fraught. She grew frustrated at how often she had to tell her patients’ families that their child had a devastating disorder—but that no cure or treatment existed.
As this reality weighed on her, she saw a patient with a provocative disease. This girl had walked, begun to talk, and otherwise progressed typically until she was almost two years of age. She had enjoyed playing with toys, turning book pages, and singing E-I-E-I-O from “Old MacDonald Had a Farm.” Then she started losing words, wringing her hands, avoiding eye contact, and holding her breath or hyperventilating. Having just read a paper from Europe about an unusual condition called Rett syndrome—the first report of this illness in an American medical journal—Zoghbi recognized the hallmark symptoms. A week later, a different child walked into the exam room wringing her hands. Zoghbi quickly realized that this girl, too, had Rett syndrome. This strange ailment with its odd progression intrigued Zoghbi. How could a child develop normally and then lose skills—particularly as neurons did not disappear? What kind of havoc in the brain could propel people into this state?
Although the infirmity seemed to crop up sporadically rather than run in families, Zoghbi had a hunch that it arose because of a genetic mistake: The symptoms were extremely consistent from one person to the next and all of the reported patients were girls. If she could find the gene, she’d have a tool that would help her figure out why the disease takes so long to set in and how it triggers its characteristic neurological problems. With this eventual goal, she began collecting DNA samples. Before she could hunt down the hypothetical gene that underlies Rett syndrome, however, she needed to learn how to do research. Tracking down the genetic cause of a rare disease that does not cluster in families would pose massive challenges even to an experienced genetics investigator, which she was not. To learn the required skills, she signed on as a postdoc with Arthur Beaudet at Baylor College of Medicine, in Houston, and decided to study a different illness—an inherited progressive balance disorder called spinocerebellar ataxia type 1 (SCA1) that can eventually interfere with eating and breathing. She continued this work after she established her own lab at the same institution in 1988.
Zoghbi teamed up with Harry Orr at the University of Minnesota to isolate the gene responsible for SCA1. From patient histories, a curious feature of the disease jumped out at her. In some families, each subsequent generation produces younger affected individuals. As Zoghbi listened to a seminar about a different illness that shares this attribute, a particular point struck her. The other disorder results from expansion of a repeated triplet sequence in the genetic code—and it can lengthen as the gene is passed down. The expanding genetic stutter exacerbates symptom severity and decreases the age of onset. Zoghbi decided to look for a similar repeat inspinocerebellar ataxia patients. In 1993, she and Orr discovered exactly that kind of genetic mark, a finding that pinpointed the gene they sought. Furthermore, they found that the size of the repeat inversely correlates with the age at which symptoms appear.
Subsequent work on mice and flies by Zoghbi and her colleagues has probed the normal function of the gene and suggested that protein misfolding promotes SCA1’s destructive effects. These findings are opening new avenues toward potential therapeutics and have enhanced scientists’ understanding of other neurodegenerative problems, including Alzheimer’s and Parkinson’s diseases. In the meantime, Zoghbi had been banking DNA from Rett patients and their parents since her postdoc, and she had begun to stalk the hypothetical gene. In most cases, only one girl in a family had Rett syndrome—but in two families, sisters with different fathers came down with the disease. Although Zoghbi knew of only these two families with more than one affected individual each (four patients total), the apparent inheritance pattern suggested that the syndrome arose from a marred gene that resides on the X chromosome.
As a first step, Zoghbi excluded regions of the X chromosome that were not shared between half siblings. Although this process whittled down the suspect area, it left a vast stretch of DNA and a daunting experimental task. Funding agencies, reviewers at scientific journals, and colleagues were skeptical that she would succeed. Rett syndrome was rare, most families had only one affected member, and the malady did not likely result from a genetic glitch anyway. They told her she was wasting her time.
Weary of this response, Zoghbi stopped telling people that she was pursuing the project. Now in stealth mode and stuck with a sizable piece of the chromosome, she convinced members of her lab to undertake the tedious job of analyzing genes—one by one—in the DNA span of interest, looking for sequence changes carried by people with the disease but not by unaffected individuals. Along the way, two additional affected families emerged, which helped focus the search. Through a painstaking process over a period of seven years, the team ruled out 19 genes.
At summer’s end in 1999—16 years after Zoghbi had seen her first Rett patient—she returned from a visit to her parents in Lebanon. Jetlagged, she put her key in the door as the phone rang. Her postdoc had been calling every few minutes to tell her the big news. The 20th gene contained DNA-sequence glitches in patients and not their unaffected relatives. Zoghbi finally had captured her prey. Work from other labs had pointed toward the Rett protein’s function. It likely quashes the activity of other genes by binding to a methyl chemical group on the DNA. Zoghbi subsequently found that the mature mouse brain depends on the continuous operation of this protein. She is now elucidating how it evokes the neurological symptoms of the disease and figuring out why brain cells take time to register its absence. Perturbations in the Rett gene can also cause symptoms of autism spectrum disorders. Clinical manifestations depend on the exact genetic flaw and the percentage of cells in which the normal copy of the gene is active.
Zoghbi has made seminal contributions not only to our understanding of the genetics and pathology of spinocerebellar ataxia type 1 and Rett syndrome, but also to the study of balance. She has demonstrated that even complex brain physiology—and the illnesses that surface when it goes awry—can be rendered approachable by a combination of basic genetics, molecular neuroscience, inspiration, and sheer determination.
Author: Evelyn Strauss, Ph.D.
Photo credit: Scott Rudd
Joan A. Steitz
For her revolutionary discoveries about the biological molecule RNA
Joan Steitz held out against a research career until she could resist no longer. Undergraduate stints as a lab technician in the early 1960s introduced her to the new and effervescent world of molecular genetics. The subject fascinated her, but she knew of no female biology professors. She decided to become a physician.
The summer before medical school, Steitz took another lab job—this time as an independent researcher. She relished the responsibility and the thrill of discovery. Even if she couldn’t run a lab, she could conduct her own experiments in someone else’s. In the fall, she entered a Ph.D. program.
By her postdoc, Steitz still did not foresee a future professorship, so she embarked on a risky and challenging project—one that numerous male colleagues had rejected. Unlike them, she did not need results that would ensure a strong academic job application.
Scientists knew that molecular machines called ribosomes translate genetic information from messenger RNAs (mRNAs) into protein—and that bacterial ribosomes somehow find their starting points in the middle of mRNA molecules. As a step toward understanding that homing process, researchers wanted to isolate and sequence the target stretch of mRNA. Relevant techniques were in their infancy, however, and no one had dared attempt the task. After a year, Steitz prevailed.
That 1969 triumph propelled her onto the international stage as the women’s movement began prying open university doors. Six years later, as a faculty member, she tackled the next issue: How do ribosomes pinpoint their start sites? She discovered that the same force that holds together the DNA helix—base pairing—recruits an RNA component of the ribosome to the correct spot on mRNAs. This revelation forced scientists to rethink ribosomal RNAs: They were not just scaffolds for ribosomal proteins, but key players in protein synthesis.
In the meantime, perplexing information was emerging. Ninety percent of mammalian RNA disappears as soon as it’s made. No one knew why cells expend energy producing RNA only to destroy it.
In 1977, researchers uncovered an unanticipated process that explained that conundrum. After mammals make an RNA copy of their DNA, they remove internal sequences, dubbed introns, to craft mature mRNAs that serve as protein templates.
Molecular machinery must splice the precursor RNA, and Steitz wanted to track it down. She recognized and developed a powerful tool for pursuing this endeavor: autoimmune antibodies that bind ill-defined nuclear conglomerations of RNA and protein. Given the location and abundance of these RNA/protein complexes, she speculated that they contribute to splicing. Using the antibodies, Steitz and her student Michael Lerner identified distinct entities, each of which contained a specific small nuclear RNA (snRNA) and common proteins. She named the particles small nuclear ribonucleoproteins (snRNPs).
She noticed that one snRNA contains a sequence that aligns with the splice sites of precursor mRNAs. This observation and others led to confirmation of her idea and fueled a burst of knowledge about the intricate system by which snRNPs and other molecules remove introns.
Steitz has unveiled secrets not only about splicing, but also about the ever-growing family of small RNAs that do not encode proteins. These unforeseen yet mighty molecules perform numerous essential physiological processes.
Author: Evelyn Strauss, Ph.D.
Photo credit: Jonathan Ziegler
For her study of memory which has revolutionized the way we understand the human brain
Before the age of three, Brenda Milner crawled around on her parents’ bed, reading snippets from the newspapers strewn there. Of course, she couldn’t understand the politics or economics, but she enjoyed the words. Her behavior presaged a driving curiosity about the people and events around her.
As an undergraduate at Cambridge University, she devoured the encyclopedic Handbook of Experimental Psychology the summer before she formally entered that field. Fearful of becoming a factory inspector, a fate that greeted mediocre psychology graduates, she dedicated herself to her studies. On her final exams, she earned the highest mark possible—one that was rarely given—a “starred first.”
In 1950, Milner began working with neurosurgeon Wilder Penfield. He was controlling his patients’ epilepsy by removing part of the temporal lobe region of the brain. They generally did well afterward, but when seizures persisted, Penfield performed a more extensive operation. In one such case, the patient could not cement new experiences after the second surgery. Initially, the medical team thought that his predicament was a quirk, but then another patient suffered a similar outcome.
At the time, conventional wisdom about memory drew from the effects of brain surgery on maze learning in rats. The animals’ abilities depended on the amount of tissue loss, not its location. Although some neurologists suspected a more nuanced situation in humans, these experiments had a huge impact on the field.
The Penfield team’s report of its two case studies in 1955 caught the attention of neurosurgeon William Scoville, who recognized that one of his patients had met a similar fate. Milner began working with this individual, H.M., who would become the most famous patient in the field of neuroscience.
H.M. retained memories from childhood, but could not recollect what he ate for breakfast. He could recall new things—strings of numbers, for instance—if he continually repeated them to himself. But shifting his attention, even briefly, obliterated the numbers. He had lost the ability to commit new events to long-term memory.
Milner decided to check whether H.M. could learn a new skill. She asked him to trace a path between the two lines of a double-contoured five-pointed star. A screen blocked direct view of the star, and it was visible only in a mirror. At each of the points, people whose brains operate normally first choose the wrong direction. With practice, they move their pencil the correct way.
Given that H.M. could not consolidate new memories, Milner figured he would perform poorly. He underwent 30 trials in three days. From one session to the next, he did not remember her, nor did he recall having done the task. Much to Milner’s surprise, however, he gradually improved. One part of H.M.’s brain acquired a skill that he did not know he had practiced. Milner realized that multiple memory systems must exist—and that different parts of the brain handle each type.
Later, Milner challenged other dogma. For example, she was one of the first to demonstrate that the frontal lobes—thought to affect intelligence only moderately—strongly shape problem-solving flexibility.
Milner has contributed groundbreaking work that has extended into all areas of neuropsychology. Her imprint on the field is immeasurable.
Author: Evelyn Strauss, Ph.D.
Photo credit: Darren Ornitz
Janet Davison Rowley and Mary-Claire King
For their insights into cancer research
As a child stamp collector, Janet Rowley pored over intricate images, seeking an extra curlicue or letter that would enhance a stamp’s value. Her ability to discern perturbations in expected patterns prepared her to notice deviant human chromosomes
Logic and orderliness appealed to Rowley and lured her toward science, an interest that led to medicine. Medical school quotas for women—three out of a class of 65—excluded
Rowley from admission the first time she applied. She patiently waited an extra year.
The day after Rowley graduated, she married another medical student. Committed to having children and staying home with them, she decided to work part time. She would
pursue clinical medicine—and later, research—in this fashion while raising four sons. During that period, she made her first key discoveries.
Rowley went to Oxford for her husband’s sabbatical in 1961–1962. She couldn’t practice medicine there, so she decided to study chromosomes, which had snagged her interest when she learned that Down syndrome arises from an extra chromosome 21. By year’s end, she was hooked on research. She came home, dreamed up a $5000-per-year, part-time job that gave her access to a microscope and a darkroom, and convinced Leon Jacobson at the University of Chicago to provide these resources.
In 1960, Peter Nowell and David Hungerford had noticed an abnormally small chromosome in cells from patients with chronic myeloid leukemia (CML). Its consistent presence prompted them to speculate that the genetic peculiarity instigates the disease. This proposal met skepticism, as cancer triggers genetic havoc in cells: Many scientists thought that the odd chromosome resulted from—rather than caused—malignancy.
Before 1970, scientists could discern the approximate size and shape of human chromosomes, but many looked similar. Then cytologists developed methods that reveal dark and light bands that render chromosomes distinguishable. Rowley aimed
these techniques at white blood cells from CML patients and discovered that the missing material from the tiny chromosome, number 22, had not vanished as many scientists thought, but reappeared on the end of chromosome 9. This pattern emerged early in disease, which supported the theory that the aberration promotes cellular misbehavior. Based on this work and similar findings that linked a different chromosomal rearrangement to another cancer, Rowley championed the notion that particular translocations, as such DNA exchanges are called, cause specific malignancies, an idea that has earned wide experimental support.
Subsequent studies showed that chromosome 22 and chromosome 9 had swapped genetic material. More than a decade later, scientists demonstrated that the tail of a gene from chromosome 9 that fosters cell division had fused to the head of a gene on chromosome 22—and lost its molecular brakes in the process. Rowley’s work has transformed our understanding of many cancers, improving diagnosis and unleashing powerful new treatments.
Author: Evelyn Strauss, Ph.D.
While young Mary-Claire King and her father watched televised baseball games together, he pitched word problems, quizzing her about how that day’s strikeouts changed a rookie’s batting average or standing. Sometimes the Chicago Cubs and White
Sox played at the same time, and the split-screen coverage offered the possibility of simultaneous equations. When her dad wasn’t cheering the local teams, he and King’s mother tuned into the world around them. They often tried to fix injustices, and King learned that she should right wrongs that she encountered.
As a statistics graduate student in the late 1960s, she realized that people get paid to solve thought-provoking genetics puzzles with mathematics. After switching fields to genetics, King and her Ph.D. advisor, Allan Wilson, showed that humans and chimpanzees are much more closely related than traditional evolutionary theory held. The genetic resemblance seemed to contradict anatomical and behavioral distinctions. King and Wilson proposed that the discrepancies arose not from markedly divergent DNA sequences, but because genes in the two hominids turn on and off at different times.
Just as genetic changes send species down new evolutionary avenues, they also push cells closer to a malignant fate. The same tools that revealed DNA disparities between species could uncover peculiarities that predispose people in high-risk families to breast cancer, King reckoned. Genetic anomalies also accrue during an individual’s lifetime, and when one of these “hits” occurs in a vulnerable cell, it can trigger uncontrolled growth. King reasoned that such a scenario might unfold in breast cancer.
She began a quest for the culprit gene, but the undertaking drew criticism. According to prevailing dogma, breast cancer arose from undefined interactions among multiple genetic and environmental mishaps. Furthermore, it usually cropped up sporadically, not in families. Perhaps the occasional clustering arose from shared conditions. No one would ever pin the disease to a single gene.
Aiming to test whether she could find evidence of a flawed gene whose presence correlates with breast cancer, she applied mathematical methods. Her analysis strongly supported the existence of a single gene with this effect in a small proportion of families. King began experimental work to find it. In late 1990—17 years after she began her mission—she identified a stretch of DNA that harbors a gene that predisposes people in some severely affected families to early-onset breast cancer. She named it BRCA1.
This finding instigated an international race to identify the gene, and four years later, scientists crossed the finish line. Glitches in BRCA1 and a second susceptibility gene, BRCA2, increase the lifetime risk of breast cancer from 12 percent in the general population to 80 percent.
King has also deployed her expertise beyond the realm of biomedicine. For example, she helped find the “lost children” of Argentina. Some babies born in prison or captured with their mothers during the military regime of the late 1970s and early 1980s were given to military families. By proving genetic connections, King enabled the reunion of more than 100 children with their relatives. She has since used the techniques she developed in that effort to expose human rights abuses in many countries throughout the world.
Author: Evelyn Strauss, Ph.D.
Photo credit: Star Black
For her insight into immunology and cancer biology
As a youngster, Suzanne Cory imagined her future self at a typewriter, concocting adventure stories. At age 12, she wrote Grey Gold, a novel in which children save their family from poverty when they discover ambergris on a beach. Although Cory loved language and the infinite worlds it could evoke, she moved toward biology, inspired in part by the opening moments of a university genetics lecture. The instructor charged into the room, electrified by what he had just learned: Each chromosome is made of a single DNA molecule. Cory absorbed his enthusiasm—and instantly fell in love with DNA. Eventually she headed to Francis Crick’s lab at the University of Cambridge, U.K. for her Ph.D. She needed financial support and learned that only one fellowship was available to women. She applied for it and got the award.
While in England, Cory met her future husband and scientific partner, Jerry Adams. After setting up their lab in Australia, they imported the then-new technology of genetic engineering. With it, they probed questions about antibody diversity and production. They demonstrated, for instance, that cells cut and paste antibody-gene segments to engineer the precise immune response the body needs at each point during an infection.
Around that time, crucial findings that captured Cory’s imagination were emerging from other labs. She learned that cancer-causing viral genes resemble DNA sequences from host cells—and that improper activation of these normal genes can provoke uncontrolled growth. Furthermore, she read that cells from Burkitt lymphoma—a malignancy of antibody-producing cells—carry a characteristic DNA swap, or translocation, between two chromosomes.
Knowing from her work on antibody-gene rearrangements that lymphocytes like those that give rise to Burkitt lymphomas excel at DNA reshuffling, she wondered whether sloppiness during that process had placed part of an antibody gene alongside one that can spur cell division. In 1983, she and Adams found exactly that situation in Burkitt tumors: A gene that provokes cancer when inappropriately triggered, myc, had moved next to antibody-gene sequences.
Eager to test whether such fusions can cause cancer, Cory, Adams, and collaborators engineered mice to carry myc linked to antibody-gene elements that turn on genes. In 1985, they reported that these animals develop lymphomas. This observation suggested that overzealous myc in Burkitt cells promotes malignant growth.
During these studies, Cory detected numerous hints that additional genes contribute as well. She went on to study several other cancer-causing genes that are roused by chromo chromosome translocations and—with Adams and Ph.D. student David Vaux—discovered that one, bcl-2, helps cells survive under conditions that normally incite death. Misbehaving cells usually self-destruct, which ensures the organism’s health. Overactive bcl-2 thwarts this process. By creating mice that carry a version of this gene that is always on, Cory and her colleagues showed that it speeds myc’s ability to cause cancer. Cory thus established that genes can foster malignancies not only by encouraging cell proliferation, but also by blocking cell death. Instead of killing themselves, marred cells that inappropriately stimulate bcl-2 and its kin persist long enough to accumulate additional genetic damage that sparks unrestrained duplication.
Author: Evelyn Strauss, Ph.D.
Photo credit: Star Black
Elizabeth Blackburn, Carol Greider, and Vicki Lundblad
For their insight into cellular aging and cancer
As a teenager, Elizabeth Blackburn refused to learn how to type. Tapping on the keyboard pointed toward the stereotypical life of a young woman in a menial office job—and she wanted to do something that she considered substantial. Biology always interested Blackburn, and two books steered her toward research. Madame Curie told how Marie grew up poor in Poland, hungered in a chilly Paris garret while studying at the Sorbonne, and teased out tiny quantities of radium from tons of pitchblende. These romantic images enchanted the suburban Australian youngster. Curie’s relentless pursuit of education and science, despite discrimination and other cultural barriers, conjured up an individual who relished her work—and this impression resonated with Blackburn. Later, George Gamow’s stories about Mr. Tompkins, who travels through his own body, convinced her that studying molecules would unveil biological mechanisms at a level that nourished her curiosity.
In the mid 1970s, Blackburn joined Joseph Gall’s laboratory as a postdoc, aiming to sequence the DNA at chromosomal ends. These regions interested her because they possess special characteristics. Chromosome breaks fuse with one another but their natural ends are stable. Unknown structures—which scientists had dubbed telomeres—must seal their tips. Furthermore, a quirk in the mechanism of DNA replication should nibble one strand’s terminus every time a cell divides, yet chromosomes in most cells don’t shrink. Something must replenish them.
For her experimental material, Blackburn exploited a creature from pond scum. This organism, Tetrahymena thermophila, accumulates large numbers of linear minichromosomes—and thus, telomeres. Using radioactive DNA subunits, Blackburn began sequencing. One day, a spot on her X-ray film—visible even in the darkroom’s red light—jumped out. She knew she’d see such a signal only if the same sequence recurred many, many times. She had discovered a string of Cs—part of what would turn out to be the telomeric repeat, CCCCAA, of Tetrahymena DNA.
By showing that the Tetrahymena sequences can protect linear yeast chromosomes from degradation and that a particular yeast sequence functions similarly, she and Jack Szostak demonstrated in 1982 that distantly related organisms cap their chromosomes with reiterated DNA. These observations and others presented new puzzles. Common models could not explain how an organism could attach its characteristic telomeric repeat to DNA ends from another creature, nor how the number of telomeric sequences varied among chromosomes and cells. No known molecular machine could perform these feats. Blackburn wondered whether an undiscovered enzyme constructs telomeres on DNA ends.
Graduate student Carol Greider joined Blackburn’s lab to begin in earnest the hunt for the hypothetical protein. Using a synthetic telomere in a test tube, she sought a substance from Tetrahymena cells that could add the distinctive repeated DNA sequence. With this approach, Greider and Blackburn identified the enzyme that creates telomeric DNA in 1985. They called it “telomerase” and established that it contains an RNA plus the expected protein component. Blackburn and her team then demonstrated that the RNA serves as the template for telomeric DNA.
Blackburn triggered an explosion in the study of telomeres and telomerase. This field now touches many biomedical arenas, including aging, cancer, and stem cells.
Author: Evelyn Strauss, Ph.D.
Carol Greider learned early to ignore obstacles. Her undiagnosed dyslexia landed her in remedial spelling classes as a child, and from the age of six—when her mother died—she had to find support in nontraditional places and chart her own course. Perhaps in part because she grew to expect impediments, Greider honed her ability to maneuver around them. In Germany for a year when she was 12 years old, she earned Fs in English class diction exercises because she spelled words backwards, yet she navigated the city bus system without knowing the language.
In college, Greider explored multiple areas of biological research before finding a home for how she thinks. With a biochemical approach, she could perturb a single experimental component and assess how that change affects the system. This method satisfied her mind’s yearning for decisive answers. Weak GRE scores brought automatic rejections from most graduate schools, but Greider’s research experience and stellar grades caught the attention of the admissions committee at the University of California, Berkeley. At the interview, faculty member Elizabeth Blackburn impressed Greider with her charisma and enthusiasm about an offbeat topic that Greider knew nothing about—telomeres, the protective caps at chromosome ends. Blackburn had proposed that an undiscovered molecular machine adds the repeated DNA sequences that characterize these structures. This idea challenged conventional wisdom. Unsure whether such an enzyme even existed, Greider set about tracking it down—an especially bold move for a graduate student, who might have wanted a safe project.
Greider sought a substance from Tetrahymena thermophila—a single-celled creature found in fresh water—that could add the telomeric sequences to an artificial telomere. After nine months, she came into the lab on Christmas Day 1984 and developed an X-ray film that identified the radioactively labeled DNA molecules in her experimental reaction. Emerging from the darkroom, she saw a ladder pattern that suggested the presence of the substance she sought: Each rung was exactly six DNA-subunits larger than the preceding one. Her heart raced because the result looked so promising, but she didn’t want to be fooled by hope. Over the next six months, she conducted dozens of experiments to rule out dull explanations for the data. Finally her results convinced her that she had unearthed an enzyme that repeatedly adds a particular sequence to the
ends of chromosomal DNA.
Greider and Blackburn discovered that the enzyme is composed not just of protein; it also contains an RNA component. In her own lab, Greider isolated the gene that encodes the RNA module and showed that it is essential for telomerase activity.
Greider and colleagues subsequently established that telomeres shorten progressively in cultured human cells, a process that triggers cell suicide or a state in which the cell neither divides nor dies. This observation led to the idea that telomere attrition contributes to age-related diseases—and that cancer cells owe their immortality in part to reactivation of telomerase. Greider now continues probing connections between telomeres, cancer, stem cells, and age-related human diseases.
Author: Evelyn Strauss, Ph.D.
In junior high school, Vicki Lundblad threw herself into science fair projects. Once she tested whether skin substances repel mosquitoes—and mistakenly released more than 100 insects into her house. Despite her initial enthusiasm for experimental work, she backed off from the pursuit in high school and immersed herself in music. She played the cello for hours each day, relishing the demands and creative opportunities. Lundblad holds a similar attitude toward research.
After college, where she vacillated between mathematics and biology, she decided to enter graduate school in biology. There, she heard a talk by Jack Szostak about his studies with Elizabeth Blackburn on telomeres, the caps that protect chromosome tips. Szostak and Blackburn had proposed the existence of an enzyme that adds DNA sequences to chromosome ends, thus enabling their maintenance, given that the cell-division process whittles down these termini. A year later, in 1983, Lundblad joined Szostak’s lab as a postdoc and strategized how to find this hypothetical molecular machine. She reasoned that telomeres of yeast with a faulty version of the enzyme, now called telomerase, would gradually shorten over many generations. Eventually this erosion would eat into sequences that signal DNA health; without that indicator of well-being, the cells would stop duplicating. By identifying yeast with those properties, she would unearth genes for constituents of the enzyme or its assistants.
In 1989, Lundblad found one such gene, which she named EST1 (for ever shorter telomeres), and we now know that the Est1 protein is a telomerase subunit that regulates its activity. Subsequent work extended Lundblad’s idea about the connection between short telomeres and cell-division capacity to mammals. Like yeast, many human cells fizzle in culture dishes when their telomeres have shrunk too far. This phenomenon underlies the body’s inability to rejuvenate particular tissues after injury or as we age.
Lundblad had noticed that a small proportion of yeast with flawed EST1 escape its lethal consequences. She and Blackburn discovered that these cells—despite inadequate Est1—rebuilt withering chromosome ends. They thus unveiled a telomere-replenishing system that did not rely on telomerase and predicted that similar schemes exist in mammalian cells. This idea proved correct. Some human cancers employ the telomerase-independent mechanism to refurbish telomeres, thus fostering unbridled proliferation.
Fueled by her success at identifying EST1, Lundblad sought additional genes involved in the chromosome-end reconstructing process when she established her own lab. She designed an approach that would expose not only participants in the bare-bones test-tube reaction, but also elements that govern telomerase’s behavior in living cells. This ambitious and painstaking project—as part of it, her team individually transferred 35,000 yeast colonies from petri dishes into culture broth—uncovered three additional genes involved in the telomerase pathway.
In parallel with Tom Cech, Lundblad found that the product of one of these genes resembles enzymes that copy RNA to make DNA—a hallmark of telomerase. The scientists had pinpointed the enzyme’s core.
As predicted, Est proteins also control telomerase’s conduct. For instance, Est1 recruits the enzyme to chromosome extremities. Lundblad is uncloaking additional essential roles the Est proteins play as she discerns how cells revitalize the crucial structures at their chromosome ends.
Author: Evelyn Strauss, Ph.D.
Photo credit: Eric Weiss
Gail Martin, Beatrice Mintz, and Elizabeth Robertson
For their contributions to the development of transgenic technologies
Unlike many scientists, Gail Martin was not feeding her curiosity when she took her fateful step into the lab. She wanted a bicycle.
Martin had landed as an undergraduate at the University of California, Berkeley, with a passion for culture. Her favorite course was Russian folklore. She applied for a lab-assistant job to make money for the bike so she could get around town.
As she prepared solutions and plated bacteria, she talked to postdoc Joan Sonneborn. The year was 1962. The women’s movement had not yet germinated, but Sonneborn encouraged Martin to pursue science, arguing that it would provide an interesting career. Inspired by Sonneborn and the interactive bustle of the lab, Martin decided to give biology a shot.
She struggled during graduate school, dropped research after earning her Ph.D., and moved to London. She almost took a low-level post at the British Museum, but it was a civil service position; because she was an American citizen, the offer fell through.
Martin drifted back toward the lab. As a postdoc, she joined Martin Evans, who was studying unusual testicular tumors in mice. These so-called teratocarcinomas consist of many tissues—hair, skin, muscle, teeth, and sometimes tiny appendages or organs. When cells from the cancers were cultured in lab dishes and reinjected into animals, growths similar to the original ones arose. This observation indicated that the cells that spawn the tumors—embryonal carcinoma (EC) cells—were pluripotent: They could develop into any of the body’s tissue types. They thus acted like cells from early embryos that scientists had not yet isolated.
Researchers wanted to use EC cells to investigate how specialization occurs. However, no one had observed EC cells undergoing this differentiation process in culture dishes, where it could be scrutinized more easily than during tumor formation in a mouse.
To tackle this challenge, Martin grew single cells from teratocarcinomas and observed their behavior. One night, hunched over the microscope, she saw something that made her sit up. In high-population areas, the cells were clumping and detaching from the dish. Moreover, the outsides of these bundles looked different from their insides. The conglomerations, Martin realized, resembled early embryos, with their two distinct layers.
By manipulating environmental conditions and aspects of the culture dish’s surface, she coaxed these “embryoid bodies” to develop further. Additional experiments confirmed that the process she was witnessing mirrored that of differentiation in mouse embryos.
After she established her own lab, Martin wanted to extract pluripotent cells from normal embryos. Reasoning that EC cells release goodies that would help their embryonic counterpart survive, she grew EC cells and collected the broth. Then she extracted the inside of mouse embryos and placed the cells into the pre-seasoned growth medium. This strategy worked: The cells proliferated. Furthermore, two-layered bundles again developed—but this time they derived from a normal embryo.
Wanting a moniker that distinguishes these pluripotent cells from EC cells, she coined the term embryonic stem cells when she published the results in 1981. The name stuck.
These findings and similar ones from Martin Evans offered new approaches for analyzing early mammalian development. They also provided tools for creating mice with specific genetic perturbations, an advance that has fueled tremendous biomedical progress.
Author: Evelyn Strauss, Ph.D.
While Elizabeth Robertson’s scientist father worked at an international research station in Nigeria’s jungle, she explored and learned. Swarming driver ants devoured her pet giant snail collection, and the legs of the family’s furniture sat in gas-containing cans so wood-eating insects couldn’t crawl up and demolish it. These observations provided Robertson with real-life biology lessons—and a fascination for the subject.
Back in Oxford at age eight, she helped her dad with his investigations. In the garage, they soaked protein gels in a blue stain and then exchanged the dye for a liquid that leaches out the color. Proteins hang onto the tinted chemical, Robertson’s father explained, so as the blue washed away from most of the gel, bands that corresponded to particular proteins emerged. The magic of watching them appear enchanted Robertson, as did the suspense of discovering whether the experiment had worked.
After university, Robertson joined Martin Evans’s lab for her Ph.D. and stayed as a postdoc. The group studied peculiar cancers that arise from so-called embryonic carcinoma (EC) cells. Because these cells possess many potential fates, diverse tissues compose the tumors. When scientists injected EC cells that were cultivated in dishes into mouse embryos, the cells could contribute to the resulting “chimeric” animals, so named because of the creatures’ mixed genetic origins. Success varied, however, and researchers struggled to produce animals with the EC DNA in eggs or sperm—a necessity for transmitting the EC genome to subsequent generations. These problems occurred in part because the tumor cells often contained extra chromosomes.
Robertson and graduate student Allan Bradley showed that lab-grown cells from early embryos—embryonic stem (ES) cells, which similarly specialize into all tissue types— possess a normal number of chromosomes. Perhaps, they reasoned, ES cells would perform better than EC cells for constructing chimeric animals.
In 1984, the researchers reported that they could reliably incorporate ES cells into embryos—and the resulting chimeric animals carried eggs or sperm that descended from the introduced cell. Offspring produced by the union of such eggs and sperm held the ES cells’ chromosomes in every cell of their bodies. If scientists could manipulate a gene in cultured ES cells, this new technology would offer massive possibilities: the relatively efficient creation of animals that harbored any desired genetic perturbation in each of their cells.
As a step toward this goal, Robertson and her colleagues infected cultured ES cells with a virus whose DNA jumps into random spots on the genome. In 1986, they generated chimeric mice from these cells. She thus established that scientists could make animals from ES cells whose DNA had been altered in culture.
By this time, others had devised ways to direct incoming genetic changes to particular sites. These methods provided a way to modify specific genes at will. In 1989, having established her own lab, Robertson was among the first investigators to produce reproduction-competent mice that bore targeted mutations. Scientists have since created and studied innumerable “designer” animals, including many that mimic aspects of human disorders.
Author: Evelyn Strauss, Ph.D.
Photo credit: Eric Weiss
For her contributions to genetic research
Even in England’s mild climate, summer temperatures rise enough to make telephone wires sag—and young Mary Lyon wondered why. She soon realized that science explains such enigmas. At age ten, she won an essay contest in honor of King George V’s Silver Jubilee. The prize—a set of books about nature—ensnared her in biology. She learned about amoebae in pond water and marveled at the complex lives of butterflies and honeybees.
In college at Cambridge University, Lyon studied zoology. The notion that genes control embryonic development—a new idea in the mid 1940s—intrigued her. Her graduate work on mice led her to join a government project that explored the harmful effects of radiation. As part of this enterprise, Lyon studied mouse mutants—those that had acquired changes in their genetic blueprints. Occasionally, a so-called spontaneous mutant turned up in the control group.
In 1960, Lyon reported on such a mouse whose splotchy coat perplexed her. Its appearance typified females that carry particular coat-color genes on one of their two X chromosomes. The creature was male, however, and males with such X-linked traits typically died before birth or sported solid coats. In keeping with that trend, breeding studies showed that the gene carried by Lyon’s original dappled mouse killed would-be male descendants in utero. She puzzled over how the animal had survived and gotten his spots. Perhaps, she speculated, a genetic oddity arose in a single cell during early embryonic life. In Lyon’s scenario, the other—normal and healthy—cells divided and gave rise to most of the animal’s body. Fur from the perturbed cell differed in color from fur that came from the original cells. Because every cell spawns many others and the two cell types duplicated adjacent to each other, patches developed.
Lyon wondered whether this phenomenon might also create the coat patterns of females with X-linked pigment genes. She delved into the scientific literature and learned that female mice with a single X chromosome in each cell could survive and reproduce. Therefore, gene activity from only one X chromosome is needed. A second, even more tantalizing finding made her ideas coalesce. In 1960, researchers reported that the so-called Barr body, a structure that appears in the nuclei of female mammals, was a single X chromosome. This observation revealed that an X chromosome can behave differently from its partner. Furthermore, the Barr body stained darkly with certain dyes, suggesting a highly condensed and genetically silent state.
Lyon realized that the inactivation of one X chromosome might be the early event that produced the mottled coats of females with sex-linked coat-color mutations. In each cell, she proposed, the paternal or maternal X chromosome would randomly turn off and remain dormant. The blotchy pattern resulted because pigment-production genes on only one X chromosome fire in any given cell.
Lyon subsequently tested this 1961 hypothesis and extended it to humans. The discovery of X inactivation—also called “lyonization”—has established the cornerstone for insights into human sex-linked disorders, sex determination, and general health differences between men and women.
Author Profile: Evelyn Strauss, Ph.D.
Photo credit: Eric Weiss
In recognition of her numerous discoveries in the field of immunology
To many undergraduates, intermediary metabolism means late nights in the library, eyes glazed while trying to memorize the intricacies before the next morning’s exam. To Philippa Marrack, these biochemical pathways meant a gratifying cerebral jolt. Suddenly she understood how the body extracts energy from the food we eat.
When these processes hooked her in the mid 1960s, Marrack was studying science and mathematics at Cambridge University. She stayed there for her Ph.D. and joined a lab
that investigated what would be named T cells. The subject matter didn’t yet compel her: These immune cells had been discovered only a few years earlier, so no one knew whether they’d do anything interesting. Rather, she made the thesis choice because her advisor worked at an exciting place. The scintillating intellectual environment of the U.K.’s biochemical hub, the Medical Research Council’s Laboratory of Molecular Biology, seduced her.
In the early 1970s as a postdoc, Marrack met John Kappler, who would become her husband and scientific partner. By the decade’s end, immunologists had realized that T cells recognize chunks of foreign proteins—or antigens—only if they simultaneously detect particular host cell-surface proteins that display the antigen. No one knew, however, whether each T cell carries two receptor molecules—one that binds each of these components—or whether a single receptor attaches to both elements. Resolution of this issue was crucial if scientists wanted to understand how T cells identify the microbial antigens that provoke them to do battle.
Marrack and Kappler tackled this question by fusing cells that sense different antigen/host-protein pairs. If two separate receptors join forces, the receptors would re-assort and the merged cells would respond to new antigen/host-protein combinations.
Such novel reactivity did not materialize, indicating that a single T-cell receptor “sees” both molecules. The insight fueled an intense hunt for the receptor, which Marrack and
Kappler found in 1983 (concurrently with two other groups).
Four years later, Marrack’s team produced the first direct evidence to explain how our immune systems accomplish an astounding feat of molecular discrimination. Somehow our bodies get rid of T cells that attack our own tissues, yet retain those that combat invaders.
Normally, only a few mature T cells respond to any particular trigger. In certain mice, Marrack noticed, a huge number of these cells stirred when they encountered a specific unfamiliar protein. She analyzed T cells from different mice—those that harbored the same protein while T cells developed in the thymus. A dramatic result emerged: Mature T cells that perceive the protein were missing. This observation supported the notion that T cells encounter material from the body while they’re developing; if they bind it strongly, they are obliterated. Self-reactive T cells don’t escape the thymus alive and therefore don’t damage tissues.
This work on immunological tolerance laid the foundation for Marrack’s subsequent discovery of so-called microbial “superantigens,” which can stimulate rampant T-cell proliferation and a devastating inflammatory response. These molecules underlie scourges that include food poisoning and toxic shock syndrome.
Marrack’s pivotal work continues to provide key knowledge about how T cells—lynchpins of the immune system—fight germs, foster vaccine effectiveness, and misbehave in autoimmune diseases.
Author: Evelyn Strauss, Ph.D.
Photo credit: Bruce Gilbert
Nicole le Douarin
For her groundbreaking research in developmental biology
Nicole le Douarin learned to read by overhearing other children’s lessons. Her mother, a public-school teacher, brought her to class when she was three or four years old. Le Douarin colored quietly, but couldn’t help absorbing the tutorials meant for others. Almost 80 years later, she still sounds like a child on the first day of kindergarten when she discusses science: Questions—and the drive to track down answers—bubble out of her.
Unlike typical parents from le Douarin’s village, hers assumed that she would attend university and pursue a career. After graduating from the Sorbonne, le Douarin taught high school, but the lack of intellectual stimulation drove her toward research. She had trouble obtaining a position, given her advanced age (28 years old) and family. Eventually she landed a spot with embryologist Etienne Wolff and volunteered in his lab part time. After two years, she left her teaching job and joined Wolff as a Ph.D. student, studying digestive-tract and liver development in chick embryos.
In 1966, she and her husband, Georges, applied for academic positions at the University of Nantes. The dean did not want couples on his faculty. Nicole could come, he said, but as an assistant, not a professor. Wolff successfully intervened. However, when le Douarin arrived, she received no laboratory space. Exasperated but committed to science, she set up experiments on one of her husband’s benches.
At the time, scientists who studied embryonic development in vertebrates wanted to map out which cells gave rise to specific body parts, but suitable tools did not exist. Marking individual cells was especially difficult.
In the early 1970s, le Douarin pioneered a research approach that would open unexplored and fruitful avenues for the entire enterprise of developmental biology. A geneticist who was working with quail had extra eggs, so he was giving them away. Le Douarin wondered whether quail tissue could trigger chick tissue to specialize normally. She combined material from the two birds in a culture dish and showed that the animals’ cells were physiologically interchangeable. They looked different though: The quail version of a nuclear structure appeared larger and darker than its chick counterpart.
Le Douarin then replaced certain portions of chick embryos with the analogous regions from quail. The chicks developed normally, and quail cells—which retained their distinguishing features—migrated to particular spots. Le Douarin realized that she could study cell fate by transplanting particular pieces of embryos from quail to chick, and then noting where the quail cells wound up.
She used this system to discover how a temporary part of the vertebrate embryo—the neural crest—contributes to adult tissues. She showed that this region is much more important and versatile than previously appreciated. Its cells give rise to the peripheral nervous system, brain, blood, skull, and other body parts.
Le Douarin’s work has allowed her and other researchers to dig into molecular mechanisms that underlie numerous aspects of embryonic development. Furthermore, she has laid a foundation for studying brain disorders and generated crucial knowledge about how the immune system avoids attacking the body’s own tissues.
Author: Evelyn Strauss, Ph.D.