Downloaded from rstb.royalsocietypublishing.org on February 15, 2011 The first long-lived mutants: discovery of the insulin/IGF-1 pathway for ageing Cynthia Kenyon Phil. Trans. R. Soc. B 2011 366, 9-16 doi: 10.1098/rstb.2010.0276 Supplementary data "Audio supplement" http://rstb.royalsocietypublishing.org/content/suppl/2010/11/30/366.1561.9.DC2.html "Video supplement" http://rstb.royalsocietypublishing.org/content/suppl/2010/12/13/366.1561.9.DC3.html References This article cites 50 articles, 13 of which can be accessed free http://rstb.royalsocietypublishing.org/content/366/1561/9.full.html#ref-list-1 This article is free to access Rapid response Respond to this article http://rstb.royalsocietypublishing.org/letters/submit/royptb;366/1561/9 Subject collections Articles on similar topics can be found in the following collections molecular biology (320 articles) Receive free email alerts when new articles cite this article - sign up in the box at the top Email alerting service right-hand corner of the article or click here To subscribe to Phil. Trans. R. Soc. B go to: http://rstb.royalsocietypublishing.org/subscriptions This journal is © 2011 The Royal Society Downloaded from rstb.royalsocietypublishing.org on February 15, 2011 Phil. Trans. R. Soc. B (2011) 366, 9–16 doi:10.1098/rstb.2010.0276 Review The first long-lived mutants: discovery of the insulin/IGF-1 pathway for ageing Cynthia Kenyon* University of California, San Francisco, CA 94158, USA Inhibiting insulin/IGF-1 signalling extends lifespan and delays age-related disease in species throughout the animal kingdom. This life-extension pathway, the first to be defined, was discovered through genetic studies in the small roundworm Caenorhabditis elegans. This discovery is described here. Keywords: daf-2; daf-16; FOXO; history; insulin; IFG-1 This article describes the discovery of a genetic path- never seen the worm, can recognize as ageing (see way that regulates ageing. In spite of the fascinating electronic supplementary material, online movie). I qualities of the ageing process, such as its remarkably remember realizing this for the first time in the early different pace in different species, until the last few 1980s when I was a postdoctoral fellow with Sydney decades ageing was not thought to be subject to any Brenner in Cambridge, UK, and I was cultivating a active regulation. Now we know that the rate of mutant strain that had very few progeny. Normal ageing is indeed subject to regulation, by classical sig- C. elegans hermaphrodites produce 300 self-progeny nalling pathways. These pathways link the ageing rate during their first week of life. So a single worm on a to environmental and physiological cues, and may culture dish soon disappears into a sea of progeny even underlie its diversification during evolution. and cannot be found. I left culture dishes with my At the heart of these pathways are stress and metabolic almost-infertile mutants in the incubator for several sensors such as insulin and IGF-1 hormones, TOR weeks, and then looked at them. With so few progeny, kinase and AMP kinase, whose up- or downregulation the original animals were still easy to find, and to my can trigger a variety of cell-protective mechanisms that surprise, they looked old. This concept, that worms extend lifespan. get old, really struck me. I sat there, feeling a little The first lifespan pathway to be discovered was sorry for them, and then wondered whether there the insulin/IGF-1/FOXO pathway. This pathway is were genes that controlled ageing and how one might evolutionarily conserved: mutations in many insulin find them. and IGF-1-pathway genes extend the lifespan of mam- In fact, around that time, Michael Klass was already mals and several have been linked to human longevity. screening for long-lived mutants. Klass was a postdoc- In particular, DNA variants in FOXO transcription- toral in David Hirsh’s laboratory at the University of factor genes have been linked to exceptional longevity Colorado, Boulder, USA. His elegant early work set in human cohorts from around the world. These and the stage for genetic studies. Klass showed, for other exciting findings grew out of basic genetic example, that C. elegans lives longer and has fewer research in the small nematode Caenorhabditis elegans, progeny when subjected to dietary restriction. This where the first long-lived mutants were isolated. In this phenomenon had first been observed in rodents in article, I describe how some of these discoveries came the 1930s and had remained unexplained. Klass also about. I am not a historian but rather a scientist showed that worms, which are ectotherms, live longer who played a role in these discoveries. Although the at low temperature than at high temperature (Klass literature I cite establishes an objective narrative of 1977) [1]. By doing temperature-shift experiments, these findings, I will describe the studies in which I he discovered that the animals carry a memory of participated from my own personal perspective, their childhood temperature that affects their adult being part of the story as it unfolded. lifespan, a phenomenon that has yet to be explained Caenorhabditis elegans lives for only a few weeks, but molecularly. Then, to find genes affecting ageing, during its lifetime it undergoes a physical and behav- Klass carried out a screen for long-lived mutants, ioural decline that anyone, even someone who has noting that ‘Because many mutations in vital genes will lead to a decrease in lifespan, it is potentially more interesting to obtain mutants with significantly *[email protected] increased life spans.’ (Klass 1983) [2, p. 279] (also Electronic supplementary material is available at http://dx.doi.org/ see Johnson & Wood 1982 [3]). Klass mutagenized a 10.1098/rstb.2010.0276 or via http://rstb.royalsocietypublishing.org. group of animals and looked among their second- One contribution of 15 to a Discussion Meeting Issue ‘The new generation descendants for mutants that lived long. science of ageing’. To curtail reproduction while also ensuring that any 9 This journal is # 2011 The Royal Society Downloaded from rstb.royalsocietypublishing.org on February 15, 2011 10 C. Kenyon Review. Discovery of a genetic pathway for ageing long-lived mutants could be propagated, he carried for example, that age-1(hx546) slows the exponential out his screen in animals harbouring a temperature- increase in mortality rate that occurs with age (Johnson sensitive fer-15 mutation, which prevented reproduc- 1990) [6]. Interestingly, later, in 1993, he crossed away tion at high temperature. He established little the fertility defect of the age-1 mutant, and it still lived families from several hundred individual potential long (Johnson et al. 1993) [7]. mutants at low (permissive) temperature, and then Around the time that Johnson first described age-1, tested members of each family at high temperature, I had become very interested in studying ageing. To where they could not reproduce, to ask which families, me, ageing seemed like unexplored territory likely to if any, were long lived. Eight of Klass’ families were be full of interesting surprises. I was fascinated by long-lived, but, after observing their additional pheno- the ‘Hayflick limit’ (Hayflick 1965, 1989) [8,9], types, he concluded that they probably did not which raised the possibility of an intrinsic life timer, harbour interesting lifespan mutations. For example, and by human progeria diseases (Thomson & Forfar several mutants were feeding-defective, and Klass con- 1950; Brown 1979) [10 ,11], which suggested that at cluded that these animals were probably long-lived least some aspects of ageing could be accelerated. because of dietary restriction. He wrote ‘The high cor- Because of my previous scientific experience, I had relation of the decreased rate of food ingestion of these come to think that there would be universal, evolutio- mutants with their increased longevity is interpreted as narily conserved regulatory mechanisms for ageing. indicating that the increased longevity is most likely This had recently been shown to be the case for devel- due to reduced caloric intake. These results appear opment, and my laboratory had played a role in this to indicate that specific lifespan genes are extremely realization, discovering that Hox (Antennapedia-like rare or, alternatively, lifespan is controlled in a homeotic) genes patterned the bodies of a much polygenic fashion’ (Klass 1983) [2, p. 279]. broader spectrum of species than had been anticipated Klass’ mutants were not abandoned, however. (Costa et al. 1988) [12]. In general, this was the time Another researcher, Tom Johnson, continued to study of a great paradigm shift in biology, when we all them. Previously, Tom had been exploring the genetic began to realize that organisms from yeast to humans basis of ageing in another way (Johnson & Wood used highly similar molecular mechanisms, albeit 1982; Johnson 1987) [3,4]. Working in Bill Wood’s with variation, to carry out the fundamental processes laboratory, which was also at the University of of life. Even if we did not know why we age, ageing is a Colorado, Tom had crossed two different strains of nearly ubiquitous phenomenon, and something so uni- worms, the normal laboratory strain Bristol and a versal seemed to me likely to be regulated. French strain with a similar lifespan called Bergerac, Furthermore, the remarkable differences in lifespan and established new ‘recombinant-inbred’ lines from that one sees between different species could poten- their descendants. These different lines should contain tially have arisen by changes in regulatory genes. new combinations of polymorphic alleles present in the There are long- and short-lived insects, birds and parental Bristol or Bergerac strains. Tom found some- mammals; thus, the rate of ageing appeared to be thing very interesting: some recombinant-inbred lines highly ‘evolvable’.