Michael Rosbash (Brandeis): Understanding Circadian Rhythms

So hi everybody, my name is Michael Rosbash, and I’m an investigator of the Howard Hughes Medical Institute, and a professor at Brandeis University in the department of biology, where I’ve been for 40 years. So, the friendship aspect of this title refers to the fact that I collaborated for more than 20 years with my colleague, Jeff Hall, who arrived at Brandeis at exactly the same time I did. And we formed a fast friendship. Jeff is almost exactly my age, and we had many interests in common. And Jeff had worked as a postdoc for Seymour Benzer, where he met Ron Konopka, where he became fluent with the circadian story and also worked on that himself in his own lab, before I got involved. So that’s really how this story began. And Jeff and I, as I indicated, had many interests in common. One — two of them are shown here, tobacco and alcohol. We also both were great sports fans, and also played basketball for a decade together in a religious-obsession with the noon-time basketball game during that decade. And it was after the basketball games I in the locker room where everyone cools down and showers that we would exchange scientific stories. And Jeff would tell me about his research in circadian rhythms that was ongoing. And it’s really that friendship and those tales which were the backdrop for this story. So to tell you just a little bit about circadian biology, as shown here is the wheel running activity of hamsters recorded on an old machine and then plotted as a function of time of day, from the top to the bottom. And all animals have some circadian rhythms, from fungi to man. And they’re commonly assayed in constant darkness. And the rhythms, the intrinsic rhythms of animals, are not precisely 24 hours — they’re about 24 hours, a little slower, a little faster. Hence, the term “circadian” or “circa dia,” about a day. And shown here, is the rhythm of these rodents in constant darkness, which is a little faster than 24 hours, as indicated by every day starts a little bit earlier than the day before. And in a light-dark cycle, however, shown at the bottom panel, where there’s 12 hours of light and 12 hours of darkness, then the animal locks on to the light-dark cycle in the incubator as we lock onto a light-dark cycle from the external world. The set rising and setting of the sun, and temperature cycles can also do this as they accompany the light-dark in the external light-dark cycle. You’ll notice here also, that these animals are nocturnal, their activity coincides with the night, they sleep during the daytime, and that’s a characteristic of any but not all rodents. Now the star of our show is Drosophila melanogaster, as shown here using a primitive counting apparatus to keep time. This is drawn by my daughter, who is a graphic designer. And here’s a picture of Drosophila locomotor activity rhythms, the analog if you like, of the hamster’s wheel running activity. And what’s shown are the fact that these animals, insects — most insects, in general, are active at dawn and dusk, with a morning peak and an evening peak of activity. In this case, in an incubator, so the morning peak coincides with the appearance of light, whereas the evening peak coincides with the transition from light to dark. And the arrows refer to the fact that the activity ramps up in advance of those discontinuous incubator transitions, indicating that there’s really a timing mechanism that can anticipate the change in the external world’s conditions. And anticipation is the name of the game in circadian rhythms. It’s more advantageous to know what’s going to happen than to know what has just happened. And so that’s really what the circadian system contributes to the animals, one of several things. So genetics, in terms of addressing this kind of problem, has had some negative history, especially in the first half of the 20th century. For example, the eugenics movement, in which people of low intelligence, handicapped, or even of some disfavored races at the time, were inhibited from procreating, in some cases exterminated as you all know from Nazi Germany. So this movement gave behavioral genetics, gave intrinsic properties of animals or people, a bad name. And similarly, the psychologist B.F. Skinner, who had a long and distinguished career at Harvard, had a tremendous amount of influence and believed that one could change the behavior of virtually every individual by simply subjecting them to constraining conditions, which would then change their behavior. Meaning that intrinsic behavioral features were not really, were not really fixed. And so, of course there’s positive history, especially in the latter half of the 20th century that offsets that preceding negative history. We know that we can breed plants in order to enhance certain characteristics, that’s also true for animals, cattle, dogs, etc … And of course, the 1973 Nobel Prize was awarded to three scientists who really worked on animal behavior as intrinsic to those particular species. So the landscape shifted, I would say, as the 20th century progressed. And so, the question for you and for me, is why use genetics to try and address the problem like circadian rhythms? And I want to emphasize that this is different from the nature/nurture problem, we’re not trying to debate how much of circadian biology is inherited, and how much can be environmental. Nor whether you’re rhythm is different from my rhythm because of genetic features or environmental features. We’re using genetics as an entree into this process. Can we figure out what keeps time by finding mutants which disrupt that process? And therefore will provide access to the genes and the proteins which underlie the process. And to emphasize this distinction, let me point out to you that even learning, the ultimate in nurture, if you like, relies on proteins and therefore, relies on genes. So genetics, genes, proteins are inherent in everything. So I turn now to the studies of Konopka and Benzer, who identified clock mutants of Drosophila melanogaster in this landmark paper published in 1971. So they fed fruit flies mutagens to increase frequency of mutations and then screened those flies for aberrant circadian properties. And they came up with three mutants in single gene, all three were alleles of one gene, which either gave rise to an absent clock, that is no rhythm what so ever, a short period clock, which ran fast, or a long period clock, which ran slow. And all three of those, as I said, were single mutations, single nucleotide changes in the same protein, which they named Period, which suggested of course that this protein had some important role in the timekeeping process. But it was really — and here’s an example of the wild type circadian pattern on the left, or the per short pattern on the right. And the vertical line refers to the fact that the lights were turned off. And you’ll notice that the wild type fly, on your left, keeps very good time during the course of the subsequent days, that is almost exactly 24 hours. Whereas the per short mutant strain, every day advances the period by several — advances the beginning of activity by several hours hours by comparison to the day before. Very similar to the hamster phenotype, as I said before, only more profound, since this animal has a 19 or 20 hour period as contrasted with the almost precise 24 hour period of the wild type. So, how does one get at this problem? And there was really almost a 15 years between the publication of Konopka and Benzer and the appearance of recombinant DNA, which could be applied to this problem where the Period gene could be cloned and sequenced to try to ask what might this gene be doing? And so I was working on recombinant DNA in my laboratory on studies on yeast gene expression, Jeff Hall had not yet adopted this technology. So during one of these basketball games, I suggested to Jeff that we get together, that we collaborate and that we try to clone this gene, our two laboratories, to see if we could figure out what it was doing. And we did that at the same time Mike Young’s laboratory at the Rockefeller University also accomplished the same task. And unfortunately, this protein was a pioneer protein, as the expression goes, it had no relatives in the database. These were early days for DNA sequencing, there were a limited number of proteins that had been sequenced and identified, and so we were left still with the question of what this protein did. And it was Paul Hardin in his explorations of the Period gene’s expression, where he discovered that the Period messenger RNA underwent strong circadian oscillations in time, so messenger RNA levels increased and decreased by about a factor of 10. With a precise 24 hour period even in constant darkness, and remarkably, shown in blue, the per short messenger RNA, different, I remind you by only one single nucleotide from the wild type or normal strain, had only 20 hours between their peaks, just like its behavior as compared to this 24 hour difference in the wild type. So the RNA reflected the behavior and we proposed that the protein must feed back onto its messenger RNA somehow, and that that was intrinsic and important for the timing process. But we didn’t know at what level this occurred. We didn’t know whether this was transcriptional in origin, yet the focus on gene expression was something I was very familiar with and knew that the half lives of mRNAs in higher organisms were generally in the hours or even tens of hours range. Something that was perfect for being related to circadian timing. And then a publication in 1988 by Steve Crews and colleagues identified a Drosophila transcription factor named Single Minded, which had homology with the period protein. And that set us off on an expedition to rapidly see if transcription was part of the story. And sure enough, within the next two years, we were able to show through several independent kinds of investigation, that the Period protein was nuclear and it affected transcription and therefore, we could propose that the feedback loop was direct and was transcriptional on origin. And over the subsequent six years or so, the circadian field really exploded. And both identified the positive transcription factor, responsible for the synthesis of these regulators, led by Takahashi and his colleagues in mammalian studies. Followed very quickly by genetic studies in my lab and others. And in addition, people made the leap between flies and mammals, showing for example, that the Period protein was conserved and had a relative, a very close relative in mammals which did very similar, if not identical job. So there was really a grand synthesis, if you’d like, and this story has held up for the 17 years since 1998. And so the question, the summary if you will, is what do I draw as a personal conclusion from this journey of mine? And I would say, both from the nature and nurture standpoint, I’ve been incredibly lucky, from the nurture point of view, I went to Brandeis almost by accident. It was not a very well-considered decision, and Brandeis has been a wonderful place to do work. I’ve had great people who have come to my lab. I met Jeff Hall, to collaborate and my colleagues in the administration have been remarkably supportive and allowed me to undertake this thrilling enterprise. The NIH and in particular, HHMI, which has funded me for the last 25 years, have really been a wonderful source of support. HHMI funds people and not projects. Meaning I could more or less do whatever I wanted. And was able to accomplish this. I’ve had a very supportive family, that despite my obsessions loved me and allowed me to pursue this. And finally, let me emphasize that even from the nature point of view, whatever talents we individually bring to a problem, those talents, what we inherit from our parents, as we say, those parents are not — those genes are not by choice, we are all victims of accident. In my case, a happy victim. And so it’s really good fortune that underlies this story. Thank you very much.

16 comments

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  2. Excellent presentation, also look at the circadian rhythm-studies from Satchin Panda for practical daily use.

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  5. So the BMAL1 and CLOCK genes that give rise to the PERiod and CRY proteins are both responsible for the circadian clock in each mammal cell?

    What was Michael W. Young's contribution?

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