MY FAVOURITE PAPER Kepler could exist, a man so much a child of the dark ages (he narrowly Adam Rudner, Ramon Tabtiang and rescued his mother from being burned as (1993) a witch). How was it that he wandered A mutation which out of the medieval darkness? The history of science is pock- doubles C. elegans life marked with such sudden appearances of span (imagine being new fields of research. One such is the 140). Worm Breeder’s recent emergence of lifespan genetics – the topic of my own research. Perhaps at Gazette 12 (5): 94. some future time, when the biology of is long since fully elucidated, and Genetics Society News (2005) treatments for ageing-related diseases 52, 53-55 such as cardiovascular disease and ageing-related cancers and dementias is David Gems routine, historians will wonder how the process of understanding ageing really A source of fascination for historians is began. the way that particular cultural While the biology of the ageing movements or traditions, conflicts and so process remains largely mysterious, it forth spring onto the scene, seemingly has always been obvious that longevity out of nowhere. I remember wondering is largely under genetic control: different as a boy during the 1960s where rock species have very different and roll music had come from. From lifespans, even when protected from watching television it seemed to me that external causes of mortality. This has to after a long pre-history of Bing Crosby be a function of their genome. If lifespan and Frank Sinatra, by some is genetically determined in the same extraordinary process there had suddenly way as, say development, morphology, appeared, ex nihilo, the Beatles and behaviour, why is it that classical genetic Herman’s Hermits. studies of lifespan only really began in Such miraculous births are a the 1990s? After all, ageing is an popular topic for scientific historians. interesting topic, since for most of us it Arthur Koestler, for example, wondered represents our death. On the face of it, in about the renaissance of cosmology after failing to examine the genetics of ageing the dark ages, and the origins of modern sooner, geneticists seem guilty of a physics: how did the process begin that serious failure of imagination. led to Isaac Newton and Albert Einstein? I first became aware of the Koestler dismissed Copernicus as a possibility of a classical genetics of medievalist who just happened to be ageing by accident. One day in 1989, as right with his heliocentric theory. For graduate student at the University of Koestler the first recognisably modern Glasgow, I was eating a sandwich in the physicist was Johannes Kepler, who library on the top floor of the Institute of devised his three laws of planetary Genetics, and leafing through what I motion in the early 1600s. Much of thought was the latest issue of Genetics. Koestler's book The Sleepwalkers is I came across a paper with the title "A dedicated to exploring how someone like mutation in the age-1 gene in

1 elegans lengthens life the adult: the . This is a and reduces hermaphrodite fertility" developmentally arrested third stage from Tom Johnson's lab at the larva, a non-feeding dispersal stage. Yet University of Colorado (Friedman and dauers seemed uninteresting with respect Johnson, 1988). In fact, the issue of to ageing, since they appeared to Genetics was an old one… left there, I represent a dormant stage, akin to a seed suspect by Gordon Lithgow, another or spore. Their long lifespan was graduate student in the Institute at that attributed to their hypometabolic state. time (now also working on ageing in C. Subsequently, while working as a elegans, at the Buck Institute near San postdoc at Imperial College, I searched Francisco). the literature for a suitable model I was entranced by this paper: a organism, and settled on another single gene mutation could result in a : Strongyloides ratti. This major increase in lifespan, suggesting strange creature has two adult forms, one that one could apply classical genetics to free-living and the other parasitic. The study ageing. Yet it seemed that the important thing was that these two adult increase in lifespan had a relatively forms were reported to have very trivial explanation. Reproduction different lifespans. S. ratti would not be reduced lifespan, and the age-1 mutation a convenient to work also reduced reproduction, which with, but if it represented the only route appeared to explain the increase in to understand the biology of ageing, it lifespan. Nobody at that time expected a would be worth the effort. So, I applied single gene mutation to extend lifespan for a fellowship to develop S. ratti as a by acting on the ageing process itself, model for studying ageing – and it was since the evolutionary theory of ageing turned down. predicted that ageing should be It was at that point that I was controlled by a large number of genes. struck by a bombshell. In February 1993 But still, if ever there was a topic I was sitting in the communal office of for the future of biology, this surely was Rick Maizels's lab when Mark Blaxter it. Yet the problem was: How could one (then working on C. elegans) handed me study the genetics of a trait predicted to the latest issue of the Worm Breeder's be controlled by a very large number of Gazette (now sadly defunct). He pointed genes. It seemed that in this case the to an abstract from Cynthia Kenyon's lab obvious short-lived model , C. at UCSF. She had discovered that a elegans and Drosophila, would not be mutation in the gene daf-2 doubled adult suitable. What one needed was an lifespan. I realized that had my organism which had evolved more than fellowship application been approved, I one pattern of ageing, more than one would not have wanted it. lifespan. One could then use classical The gene daf-2 had been genetics to identify genes that regulated discovered a decade earlier by Don the switch between lifespans, and study Riddle at the University of Missouri. His differential gene expression to identify work focused on the genetic control of the large number of lifespan genes. But dauer larva formation. daf stands for such organisms are rare in (or so abnormal in dauer formation. Now, it seemed). In C. elegans there is a long- dauers normally form when food levels lived form, which lives much longer than are low and population density high.

2 Riddle discovered several classes of daf series of branching pathways. The mutant… some that form dauers Kenyon lab began to test these genes, constitutively (Daf-c) even in non-dauer focusing in particular on the gene daf-16. inducing conditions, and others that were Here mutants are dauer defective, and dauer defective (Daf-d), i.e. unable for daf-16(-) suppresses the Daf-c form dauers under otherwise dauer- phenotype of daf-2. daf-16(-) also inducing conditions. It turned out that proved to suppress the extended lifespan Cynthia Kenyon had wanted to screen resulting from daf-2(-), suggesting that for long-lived mutants, and had wanted the effect of daf-2(+) on ageing involved to do this using a mutant which left no antagonism of daf-16 activity. Kenyon et fertile progeny. She had opted to use a al. surmised that the really interesting daf-2(e1370) mutant, since it has a gene here was daf-16, since it is a temperature-sensitive dauer constitutive powerfully promoter of longevity. phenotype. At the permissive Some daf-2 alleles showed slight temperature it develops normally, but at decreases in fertility. To test the the non-permissive temperature it forms possibility that this was the cause of their 100% dauer larvae. A necessary test increased lifespan, Kenyon et al. prior to her planned mutant screen was examined worms that were sterile either to check that the daf-2 mutant itself is due to surgical removal of their gonad, healthy and exhibits a normal wild-type or mutation of a gene called fem-3. In lifespan. To her surprise, daf-2(e1370) neither case was lifespan increased, doubled adult lifespan. suggesting that the increased lifespan of Kenyon at once saw this daf-2 was not attributable to any effects implications of this. The great longevity on fertility. In fact, it turned out that the of dauer larvae had been attributed to longevity of age-1 mutants was not the hypometabolism, and dormancy. But the result of reduced fertility either; instead fact that daf-2 mutant adults were long- age-1 mutants proved to be dauer lived, yet active and fertile, implied that constitutive and age-1 to act with daf-2. it was possible to switch on dauer larva The real importance of this study longevity processes in the adult – i.e. to is that it established that one could use uncouple the dauer developmental arrest classical genetics to understand the from their increased longevity. This genetic determinants of ageing and suggested that the C. elegans genome lifespan. Before it, to try to understand was able to specify two distinct ageing through the study of long-lived longevity programmes, that of the dauer mutant would have been considered larva and that of the adult. naïve. The biology of ageing seemed an These preliminary findings were unassailable, impregnable fortress. The developed in a paper entitled "A C. daf-2 finding let down the draw-bridge, elegans mutant that lives twice as long initiated a dazzling cascade of as wild type", published in Nature in discoveries (including many more from December 1993 (Kenyon et al., 1993). the Kenyon laboratory), and stimulated a The genetics of dauer larva formation rapid growth of the field of lifespan was already well characterized by the genetics. daf-2, age-1 and daf-16 proved labs of Don Riddle and, latterly, Jim to encode elements of an insulin/IGF-1 Thomas. Dauer control genes had been signalling pathway. It then transpired organized by epistasis analysis into a that the role of this pathway in ageing is

3 evolutionarily conserved, controlling ageing in fruitflies and rodents; there are hints that it may also control human ageing. Currently the processes regulated by daf-16 are the subject of intense investigation. Meanwhile numerous other genes and pathways have been identified which control lifespan in yeast, , fruitflies and mice. After reading the gazette abstract, I began to look for a job in one of the C. elegans labs in the U.S. that worked on ageing, to learn how to work with the Worm. Luck was on my side: I obtained a fellowship to work with Don Riddle at the University of Missouri-Columbia, and began work there in the Autumn of 1993.

Friedman, D.B. and Johnson, T.E. (1988) A mutation in the age-1 gene in lengthens life and reduces hermaphrodite fertility. Genetics 118, 75-86. Kenyon, C., Chang, J., Gensch, E., Rudener, A. and Tabtiang, R. (1993) A C. elegans mutant that lives twice as long as wild type. Nature 366, 461- 464.

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