For pioneering genetic and molecular studies that revealed the universal machinery for regulating cell division in all eukaryotic organisms, from yeasts to frogs to humans.
Lee Hartwell is a yeast man—a connoisseur of Saccharomyces cerevisiae, or budding yeast, that are essential for brewing beer and baking bread. But Hartwell sees neither brew nor bread in these simple organisms. Rather, he sees something even closer to the core of life itself. By studying yeast, Hartwell has seen the cell cycle up close and has identified genes that are crucial to controlling the intricate program of instructions by which a cell grows, rests, and divides to replicate itself.
Paul Nurse is also a yeast man—a scientist whose work with fission yeast, or Schizosaccharomyces pombe, also revealed previously unknown things about how genes regulate the lives of cells. Among Hartwell’s discoveries in budding yeast is a gene called CDC28 that cells need in order to progress through their various stages of division. Nurse and his colleagues discovered a nearly identical gene in fission yeast, cdc2 , that performs a similar regulatory role. Then Nurse not only showed that the CDC28 and cdc2 genes make proteins that are functionally like one another; he also identified the first protein in humans whose role in the cell is analogous to the role of the proteins in yeast.
Meanwhile, Yoshio Masui, whose experimental work has focused on frogs, discovered a protein, called maturation promoting factor (MPF), in the cytoplasm of cells that control cell division in the fertilized eggs of frogs.
Award presentation by Ira Herskowitz
One of the simplest but also one of the most profound questions to ask about biology is “How do you make a cell?” By that I mean, “How does one cell produce two cells?” A human skin cell divides to produce two cells like itself in about ten hours. A bacterial cell produces two bacterial cells in about 30 minutes, and a yeast cell produces two yeast cells in about ninety minutes.
In an intellectual feat as exciting as the athleticism displayed by the dynamic duo of Sosa and McGwire, Watson and Crick explained how the genetic instructions of the original cell are copied so that each of the daughter cells receives a precise replica of the original genetic information—a DNA double helix. That’s why each of the daughter cells looks like the original cell: they both get the identical genetic information.
As breathtaking as Watson and Crick’s explanation was, it didn’t answer another fundamental question about cells: how do the daughter cells manage to receive the new set of instructions? Do the newly replicated DNA molecules, the chromosomes, just float into the daughter cells or get distributed randomly to these cells? No, of course not. Cells have precise machinery to distribute the genetic information so that each cell gets exactly one copy of each chromosome.
So, now we can see some of the richness of a deep problem in biology: How do cells choreograph not only copying their genetic information but distributing this information? The cells had better do the copying before the distribution, or there will be a mess. How do cells know in what order to carry out such processes? Studies by Lee Hartwell, Paul Nurse, and Yoshio Masui identified the molecular machinery and the logic of how this machinery works to program the sophisticated events involved in duplicating cells.
Interview with Lee Hartwell and Rochelle (Shelly) Esposito
In an October 1998 interview with Dr. Rochelle (Shelly) Esposito, a professor of molecular genetics and cell biology and chair of the Committee on Genetics at the University of Chicago, Dr. Leland (Lee) Hartwell discusses how he developed a fascination with science and cellular research. He talks about his work and its value to medicine, his teaching philosophy, and what genetic developments he believes will occur in the not-so-distant future.
Part 1: From a Non-academic Beginning to the Halls of Cal Tech
After early work studying mammalian cell biology, Dr. Hartwell sought a new focus. Frustrated with the prevailing models framing mammalian cell research, he realized yeast cells presented the ideal environment for investigating mutant cells and DNA replication.
Esposito: On behalf of all of us who have been impacted by your work, I want to convey our warmest congratulations on this wonderful honor and award. We’re really pleased and delighted, and it’s very richly deserved. I’d like to ask you, can tell us what this award means to you and what you feel it’s recognizing?
Hartwell: Yes. It’s, of course, very exciting and rewarding to me. It’s always terrific in your career to feel like you’ve made a contribution, and that’s the gift the Lasker committee is giving me. I think they’re recognizing the whole field of cell cycle research and yeast genetics. I feel fortunate to have been in on some of the very early phases of that work, but it’s really the work from hundreds of labs and thousands of students that have brought it to the stage where it’s deserves this kind of recognition.
Esposito: Can you tell me what, from your perspective, are the most significant contributions that you think your lab has made to this field?
Hartwell: I think it was perhaps in seeing that a study of cell division, even though it was motivated by an interest in human cells and medical problems like cancer, needed to be explored in a much simpler system using genetics as a powerful tool. It was in attempting to place the groundwork there, that’s probably one of the major things we contributed at the beginning.
Esposito: What I’d like to do in the next series of questions is address how this all came about. Maybe on a personal note you could begin by telling us a little bit about your family background and how you first got interested in science? I know this is going back a bit, but it’s always interesting, I think, to others, to know what the motivating forces are that drive us to the discoveries that we make.
Hartwell: I came from a family that was very nonacademic, so I didn’t recognize at an early stage the clear interest that I had in science as a child. Looking back, it’s easy to see now. I always collected bugs and took things apart and spent time at the library trying to learn things about radios and astronomy and various stuff like that without noticing that my peers weren’t spending their time the same way.
I don’t think I would have ever gotten the opportunity to spend my career in science if it hadn’t been for a few key teachers along the way. [There were] a couple in high school that recognized my interest and ability in math and physics, and gave me extra work and encouragement, and a counselor I had in junior college—I went to Glendale Junior College for a year—who also took an interest in me and got me to interview with a professor from Cal Tech who was visiting. It was through that interview that I eventually ended up at Cal Tech and discovered a whole fabulous world of science that I really didn’t even know existed.
Esposito: I know that your undergraduate career at Cal Tech was a transforming experience for you. Can you tell us what the atmosphere there was like and how it really set the stage for the future directions that you wound up taking?
Hartwell: Cal Tech was just an unbelievable sort of fairy tale place for me. You were spending your time thinking about really interesting scientific issues, and the faculty there treated the undergraduates like they were colleagues rather than students. It just gave me a sense of involvement and the possibility of participating in science, sort of an invitation, I guess I would say, that I look back on and just cherish those years. A particularly influential individual to me was Bob Edgar, who worked in Max Delbruck’s group and, of course, did all the work with Bill Wood on phage morphogenesis. But I can still remember the afternoon when I was walking by Bob’s office, and he stepped out and pulled me in and explained to me a neat idea he had for determining how all the genes and phage function. To think that an undergraduate would warrant that kind of collegiality just made it a very, very special place.
Esposito: It sounds like a wonderful environment. You were an undergraduate working in his lab. How does that come about?
Hartwell: The neat thing about Cal Tech was that they really encouraged people to do research, and so as an undergraduate I did research the whole time I was there—I mean both during school and in summers. There were so few undergraduates compared to faculty that you could essentially work for anybody there you wanted. They were always happy to have a student come in and work. I felt pretty much like it was a graduate level experience because I did so much research as an undergraduate.
Esposito: Did you work in several different labs, or did you find your way to Edgar’s group early on?
Hartwell: I worked in several different labs. I worked for Hildegard Lamfrom for a while, who was trying to figure out what messenger RNA was. I worked in Renato Dulbecco’s group with Howard Temin for a while and then in Delbruck’s group.
Esposito: Did your interest in the cell cycle originate at Cal Tech or later when you went to do post-doctoral work?
Hartwell: It didn’t really come until I was doing post-doctoral work. As an undergraduate I guess I was interested in phage and then as a graduate student I was interested in gene regulation. Then when I was thinking about becoming a post-doc, it seemed like the appropriate thing to do was to pick a problem that you were going to spend your career working on, something that wasn’t understood yet. I decided to work on cancer and cell division, growth control sorts of things. I went to work with Renato Dulbecco and came to a tremendous interest in the problems there. I had another wonderful experience with a colleague, Marguerite Vogt, who is just a delightful scientist who is always interested in each new theory about cancer. She is a person who has developed a sort of artistic love for cell culture and what cells are. That was a big experience for me, too.
Esposito: I guess when you went to do your post-doctoral work you really had in mind by your choice that you wanted to work in cancer and maybe cell cycle and cell division. Did this stem from your studies on gene regulation when you were at MIT? Also, I kind of transited through your graduate work without asking how you wound up at MIT, and what were the problems that were being addressed when you were there? What were your thoughts and the influences on you at the time you were there?
Hartwell: At MIT, that was a pretty neat experience, too. The reason that I ended up there was because I went to Bob Edgar and said, where should I go to graduate school? He said MIT, and so I did. One of the things they encouraged undergraduates to do at Cal Tech was to read in areas that you wanted to study in. And so every quarter I took a reading course under a faculty member’s direction. I read a lot about gene regulation, so I knew when I went to graduate school I wanted to study gene regulation. And so when I went to MIT I knew I wanted to work with Boris Magasanik and was fortunate enough to be able to do so. I think the main thing I took away from that experience was how Boris just let you find your own way.
He would come by every afternoon and ask you how your experiments were going, so it sort of kept you at this feverish pace for having results every day. But he never told you what to do. He’d always just asked you how things were going, and he would make suggestions, but he made it clear that you were plotting your own course. That was very comfortable for me having already had so much research experience. But I think it also really helped me develop that sense of: I was the master of my research, and I had to find my own way.
Esposito: I had a similar experience. I wonder if when you look back and compare the way you were trained and the climate in which science was done to the way it is now, whether there was, in reality, more freedom to explore and follow your own instincts. What’s your thought on that?
Hartwell: My experience and my colleagues’ is that there is tremendous anxiety about getting grants and keeping your career going, so that there is much greater, often, direction of students to fill necessary goals, to get the right experiments done for the next grant and the paper out and that sort of thing. I never experienced that kind of pressure myself, and I must say I never put my students under it. I think I work with my students the same way I experienced science, where they’re in charge of what they do, and we hope for the best. Fortunately we have been lucky enough that that has worked. I do think the climate is very, very different now and not one that I would thrive in if I was a student and feeling like I was “doing project 17 on somebody’s RO1 grant.”
Yoshio Masui Interviewed by Joan Ruderman
Dr. Joan Ruderman, a professor of cell biology at Harvard Medical School, interviewed Dr. Yoshio Masui, whose research on cell division in frog oocytes led him to discover the mechanism that drives the division of all plant and animal cells; August 31, 1998.
Part 1: Starting with the Materials at Hand
As a junior high school student in Kyoto at the end of WW II, Dr. Masui was chosen for a special science class that offered him a good education and the opportunity to pursue his boyhood curiosity about living things using the research material he knew best: frogs.
Ruderman: I am very glad to have this time to talk to you about your life and your scientific journey.
Masui: Oh, thank you, yes.
Ruderman: You know, so much of your life has been devoted to explorations using amphibian eggs, even from your earliest days as a student.
Ruderman: I wanted to know what attracted you to biology as a young student?
Masui: Well, when I was around twelve years old, in grade six or so, I was subscribing to children’s science magazines. There were some stories about animals and medicine. Particularly, I was impressed by the history of medicine, very easy child-oriented stories about Pasteur and so forth. That fascinated me first, then I just started collecting frogs and that sort of thing to see their heart beating. It was a child’s hobby or a kind of play, first of all, and perhaps I was attracted to living things in nature. But I was not interested in a collection of insects, that sort of thing.
Ruderman: So you were not a naturalist?
Masui: No, no. I had no sort of inclinations to natural history kinds of things in my life. Next I was attracted by chemistry. So, when I went to the university, I chose natural science courses. But I wasn’t sure which way I should go, if I should go into chemistry, physics, or then biology.
I was also interested in physics, so it was a little bit difficult to chose. But then one of my high school senior [teachers] was a zoologist, and one night I talked with him in his office. He told me how interesting zoology was. But that still…that was not “real.” It was an attraction, yet I was still thinking which way I should go.
And then, one day I talked with my friend, who is now a real mathematician. But anyway, I was talking with him. I found that, you see, the homework…I could not finish it in one week. He finished it in two hours.
Ruderman: You got a message.
Masui: Yes, yes. So, that is the final thing that made me decide to go into biology or zoology, because, “if I go with these guys, I cannot do anything.”
Ruderman: Well, we’re all very glad you made this decision. That your homework took a long time.
Masui: Yes. I was so, so interested in medicine, but my father said that…you see, my sort of a character, is not sociable in a sense…that medical doctors need that kind of social skills, which I lacked. So my father recommended that maybe I’d better go into some pure science. So, I accepted his advice.
My father was not graduated from a university, so he said to me, “I don’t know anything about education, about the universities.” He said I could choose anything that I liked, but I should take all the responsibility myself.
He gave me quite a bit of freedom in a sense, so that I finally went to zoology, knowing that zoology is not a job that is well paid.
Ruderman: Yes. We are not known for our high salaries.
Masui: Right, right. So, I made up my mind that I could do something teaching in high school—that I wouldn’t mind to be a high school teacher, a biology teacher. I thought, at the worst, “perhaps, I can be a high school teacher and then, using the extra time, summer time or holidays, I can do small experiments, using a dissecting microscope and glass needles that you can get in a high school student lab.”
Ruderman: Right. So it was feasible to do this kind of experimentation.
Masui: I knew a little bit about classical experimental embryology from reading—some Spemann kind of work. I could do that in a high school.
Ruderman: I was very surprised to hear you say that as young as twelve years old, you started collecting frogs and looking at them.
Masui: Yes, yes.
Ruderman: So you’ve been with amphibians for a very long time. We’ll get to the penguins later; I want to ask you about that. But I want to ask you about collecting materials. So you were living in Kyoto at that time. And you were collecting frogs?
Masui: This is a perhaps a most important factor for me to have decided coming to biology. My teacher was a very dedicated biologist, who was teaching me in high school as sort of a teacher. But he also was using his extra time working with diatoms, using an electron microscope to look at diatom structure.
Masui: That was in junior high. He encouraged everybody to do something on a small project. My class was a little bit special, because during the war…Japan was just about to be defeated in 1945…when I entered junior high, that was 1944 or ’43….At that time the Japanese government belatedly realized that science is important for winning a war.
So, now we have to raise the next generation as scientists. They started a special class in Tokyo, Kyoto and Hiroshima—the three towns had special classes. I was then recruited to that class.
And in that special science class I was exempted from all sorts of duties or work. Other students had to do something like helping farmers or factory workers. But I was exempted.
Also, during the war they prohibited learning English. But I was also exempted from that rule. So I had sort of a good chance to learn English as well as science…
Masui: …rather than going to a factory or farmland to help. That was very lucky. That is a very important factor for me. Otherwise, I couldn’t have a good education.
Ruderman: Yes, I understand. And in those early days, did you have the opportunity to work with other material, like starfish eggs or fish eggs, which were at the time and still are very popular and useful material for many Japanese scientists?
Masui: Well, you see, Kyoto is sort of, as you know, surrounded by hills. There is no outlet to the sea or anything, only the big lake nearby. So I had no chance at all to do anything with marine animals.
Ruderman: So then what happened?
Masui: Well, the only materials I could get were insects and frogs and that sort of stuff. But, you see, there are a lot of things about physiology in the children’s magazines or junior high class books. They mostly picked up the materials from frog physiology and development of frogs, you know, tadpoles, that sort of stuff. So I think frogs became the most familiar materials.
Ruderman: Well it’s very wonderful experimental material. Large enough so you can see it under a simple microscope, and they’re very hardy. You can culture them in all sorts of circumstances.
Masui: Right, right. Particularly in Kyoto. At that time it was still a suburban area not well developed. So, still there were a lot of farmlands around. It was a walking distance to collect frogs in the rice field, so it was a very easy material for children to play with.
Ruderman: You were a high school teacher for several years, while you were working on your PhD research.
Masui: Yes, yes. I was finishing in 1953, or I think actually up to ’54. I was working on my Master’s thesis. I wasn’t sure about what job I could get. There was assistant professor, a very, very good professor, Dr. Takaya. He was an experimental embryologist. I really admired him when I was an undergraduate. Then he moved to Konan University, so I asked to be his assistant, research assistant.
As soon as I got the Master’s, I moved to Konan University as a research assistant for him. The real job that I was working at that time was a high school teacher, because Konan University had also Konan High School.
Masui: I was teaching eight to twelve hours a week in high school, and I taught high school students a general sort of biology. Meanwhile, I was working in his lab, as a research assistant on one hand, but also I did PhD research afterwards.
Several years later I submitted my PhD thesis to Kyoto University, where I graduated from, and I got that degree.
Ruderman: So did you like teaching high school?
Masui: Well, no. [both laugh] Not much. And perhaps I was not a very good teacher. I didn’t like…somehow, I am not a good teacher per se, but my enthusiasm about a subject I am teaching… somehow that sort of impressed the students.
Ruderman: I have to disagree with you. I remember when you were teaching in the embryology course. I think it was in 1983?
Ruderman: You were a very good teacher then.
Masui: Yes, it’s something I like. I just naturally, I kind of, sort of totally [get] involved in a subject.
Ruderman: Well, you know, you gave several wonderful lectures, and the auditorium was packed. People stayed on and took lots of notes. It was a wonderful time. So I think you should not be so modest.
Masui: Yes, thank you. You see, I was a little while a lecturer at Yale, because Markert told me that I should start practicing teaching. So he gave me a chance to teach Yale students. At that time my English was…well, even now [it’s] terrible…but anyway it was really, really terrible in 1969.
I was teaching, but that was team teaching, Frank Ruddle and Ian Sussex and myself. So anyway, Ian Sussex told me that…I said that I’m sorry my teaching was terrible and students perhaps had a lot of troubles to understand.
He told me, “Oh, no, no. That’s all right because of the enthusiasm that you showed. [You are] the most enthusiastic instructor, and that impressed the students.” That made up my deficiencies in English and lecturing.
So, I think my strength is a kind of enthusiasm about the sort of subjects I’m teaching, you see.
Paul Nurse interviewed by Gerard Evan
Dr. Gerard Evan interviews Lasker Award winner Paul Nurse, September 1998. Dr. Evans is currently the Service Chief for the Infectious Diseases Service of the Southeastern Ontario Health Sciences Centre and has an interest in medical education, both at the undergraduate and postgraduate level, antimicrobial use, clinical trials in new anti-infective agents, and home parenteral antibiotic therapy. Active interests in the sphere of clinical infectious diseases include infective endocarditis, sexually transmitted diseases, fungal infections, and CAPD peritonitis.
Part 1: Interest in the Cell Cycle Sprang from Desire to Do Something ‘Important’
Paul Nurse describes his genetic approach to cell reproduction and tells interviewer Gerard Evan how a grueling night in the laboratory as a graduate student prompted him to search for something “interesting and important” to work on. Nurse then details why he chose to study the cell cycle in yeast.
Evan: Hi, my name is Dr. Gerard Evan, and I’m interviewing Dr. Paul Nurse, who is a joint recipient of the 1998 Lasker Award for his work on the cell cycle. Paul, can you describe to me what you work on?
Nurse: Yes, Gerard. I have been interested, in fact for many years, more years than I would like to remember, in the cell cycle—that’s the process by which cells reproduce themselves—from one to two. And I’ve taken a genetic approach to this problem, working with a very simple organism, yeast—that’s a single-celled fungus. And I’ve isolated mutants, which are altered in the cell cycle and its control, and then studied these mutants to find out what the basic process is that is underlying the cell cycle. And then used these mutants to clone the genes and then establish what the molecular basis of how they work might be. By using these various approaches, you can then work out exactly what molecules are controlling cell cycle progression and how they are regulated.
Evan: As you say, you’ve been working for a very long time on the cell cycle. So why is this? Is it because it is innately so interesting? Or does it tell us a lot about other aspects of biology, or is it relevant to particular diseases, or what?
Nurse: Well, I have to say, my interests in the cell cycle, they started when I was a graduate student. And I was working all night with a machine that was actually in the development stage, so it kept breaking down. I remember I had to keep putting rubber bungs in all the safety switches to keep the thing working. And this was extraordinarily tedious, and my mind drifted off into other things about what sort of better world might there be somewhere else outside of this room with this little machine. And I thought it’s very important, if you are going to suffer like this doing science, to actually work on something that’s interesting and important. And the cell cycle came to mind then for several reasons.
The first is that one of the basic properties of life is its ability to reproduce. And that is seen in its simplest and most basic form with the reproduction of a cell, during the cell cycle, the division from one to two.
In fact, the reproduction of all living things, including complicated organisms, such as human beings, can be understood in terms of the division of a cell from one to two. So, it was a process that was central to understanding life, of defining one of the major distinguishing characteristics of life. So that was one reason.
A second reason was that the cell cycle is an example of a simple developmental pathway. Now, lots of biology has got to do with development, but it’s usually quite complex. Whereas, the growth and division of a cell, although actually quite complicated, is relatively simple compared with most development that we’re trying to understand. I mean, working out how a frog is made is certainly much more difficult than working out how a cell is reproduced.
Evan: So this is the advantage of yeast as a single-celled organism, when doing this sort of thing?
Nurse: It is, indeed, because a yeast is so simple that it barely does very much more than actually reproduce itself…and make beer and bread, of course. Many of the genes that it has are really devoted towards this process of cell reproduction. And the point about this is this—that I felt this was an example of a simple developmental sequence which, in principle, we could perhaps one day completely understand. Whereas, I think it will be a very long time before we understand how, for example, a tadpole is made. So that was another reason—that we could understand a developmental sequence in detail.
And the final reason was that because cells are in all living organisms, because they all have to undergo cell division, there was the possibility that we were looking at a process that was likely to be universal across all of life. And that had its attractions because it meant that it was relevant to all different sorts of living things and situations. And also, that perhaps we could use a whole variety of different tools, exploiting the different advantages of different organisms, to actually work this problem out. So I think that was what originally attracted me to this. And I suppose it was mainly thinking well into the night whilst looking after this ghastly machine that prompted most of this.