D.L. Riddle and Saad Hafez (President, Society of Nematologists, 2005)
Donald Lee Riddle received a B.S. in Chemistry and Biological Sciences from the University of California-Davis, in 1968, and in 1971 was awarded a Ph.D. in Genetics by UC-Berkeley. From 1972-73 Don was a Postdoctoral Fellow in the laboratory of Dr. John Carbon, UC-Santa Barbara, and from 1973-75, he worked with Nobel laureate Dr. Sydney Brenner as a Postdoctoral Fellow, at the Medical Research Council Laboratory of Molecular Biology, Cambridge, England. It was during this time that Dr. Riddle, already an accomplished molecular biologist (responsible for discovering the mechanism of nonsense mutation suppression in bacteria), began to work on nematode developmental genetics, which has been the focus of his startling research career ever since. Dr. Riddle joined the faculty of the University of Missouri, Columbia, as an Assistant Professor in 1975, and was promoted to Associate in 1981 and to full Professor of Biological Sciences in 1985, a position he currently holds. He also was recently (2004) appointed Chief Scientific Officer, Genome British Columbia, Vancouver, Canada. Throughout his tenure at the University Missouri, Don has held many influential posts, including serving as the Director of the Molecular Biology Program (1988-2003), Chair of the Genetics Area Program (1994-95, 1996-03) and the founding Chair of the University Research Board (1992-94). Don was Visiting Professor at Simon Fraser University, B.C., Canada (1989), University of British Columbia (2000-01), CSIRO Division of Horticulture, Adelaide, Australia (1983), and Visiting Editor, Cold Spring Harbor Laboratory Press, NY (11/95-3/96). He also serves as scientific advisor to Divergence Inc, St. Louis, Missouri (2001-present).
Don Riddle was one of the pioneers in developing Caenorhabditis elegans as a research model, and throughout his career has made remarkable contributions not only to basic biology, but also to understanding the biology of nematodes per se, especially in relation to their function as parasites. Dr. Riddle’s simple insight has been that C. elegans is indeed, truly a nematode.
Dr. Riddle’s research productivity is amply shown by his publication list, but two points are especially worth noting. First, Don has published in a broad range of journals, specifically targeting nematologists with papers in the Journal of Nematolology, Nematologica and International Journal of Parasitolology, and the entire scientific community with papers in Nature, PNAS and Science. Second, a remarkable number of Dr. Riddle’s publications have become highly-cited classics. In particular, as of December 2003, his 1997 book has received more than 300 literature citations. Significantly, four of his peer-review publications have been cited more than 200 times, and 13 peer-review publications and three book chapters have each been cited more than 100 times. This is a truly remarkable achievement.
The theme running through Dr. Riddle’s career has been the manner in which nematodes interact with their environment and process this information to make developmental decisions. The ability of nematodes to modulate their development via dauer entry and exit is a fundamental strategy used by parasitic and free-living species alike. In 1977, Dr. Riddle’s research demonstrated the phenomenon of genetic epistasis in C. elegans and he used epistatic gene interactions to construct a pathway for formation of the dauer larva. Although this pathway has been subsequently expanded by Dr. Riddle’s group (and many others), the original dauer pathway he established in 1981 remains one of the most elegant intellectual achievements in modern biology. During the 1980s, Dr. Riddle’s group discovered and characterized the C. elegans dauer-inducing pheromone, which was the first pheromone shown to affect nematode development. The developmental effects of the pheromone were characterized, and in particular he showed that certain mutants defective in formation of dauer larvae exhibit pleiotropic defects in sensory behavior and possess ultrastructural abnormalities in the dendritic processes of chemosensory neurons.
The cloning of genes in the dauer pathway during the 1990s revealed that the same machinery is shared with other animals, including humans. To use but one example, two dauer genes (daf-1 and daf-4) encode transmembrane receptor protein kinases. The DAF-1 protein was the first receptor serine/threonine kinase reported. Numerous other receptors in this family have been found subsequently, including mammalian receptors for activin, bone morphogenetic proteins and transforming growth factor-b. These ligands are cytokines that have profound effects on cell differentiation in vertebrate development. Other daf genes correspond to members of the insulin pathway in mammals, and certain daf genes control life-span and aging in animals. Dr. Riddle’s dauer pathway ultimately has spawned dozens of research programs around the world studying these questions of great human medical interest.
Collectively, these studies have revealed much about the basic biology of nematodes, and of animals in general. But much more than that, Dr. Riddle has actively engaged researchers studying important parasitic nematodes. For example, in collaboration with Alan Bird, he described the specific association between nematode cuticle and bacterial capsules that permits the nematode Anguina agrostis to act as the vector in “Annual Rye Grass Toxicity,” a disease lethal to livestock in Australia. He characterized the sensory responses of plant-parasitic nematodes to chemical attractants, and also to plant roots. Dr. Riddle’s book chapters and reviews provide numerous examples of his interest in exploiting C. elegans to better understand parasitic nematodes. He has trained 39 Ph.D. students, and numerous postdoctoral fellows and visiting scientists have worked in his lab, many of whom went on to work on parasitic nematodes.
Throughout his career, Don has been, and continues to be an active and long-standing member of SON, and presented papers (many as an invited symposium speaker) at numerous annual meetings. He has presented keynote and symposium talks at other agricultural gatherings, including: International Congress of Plant Pathology (1983); International Congress of Parasitology (1986); Keystone Symposium on Molecular Helminthology, (1993, 1996); American Phytopathology Society (1993); American Society of Parasitologists (1994); Gordon Conference on the Biology of Parasitism (1995). Dr. Riddle was Associate Editor for JON, he served on the SON Information Retrieval Committee, the Membership Committee, and the Committee on Plant-Parasitic Nematode Genetic Nomenclature. He also participated in the CSRS Study Committee on the Science of Nematology, 1992-93, and was an active member of the USDA NCR-172 Committee (molecular genetics of host-parasite relations involving sedentary endoparasitic nematodes).
Through the C. elegans community, nematodes have become the best understood animals, and Dr. Riddle has been directly responsible for some of the most important of those findings. But more than that, he has worked tirelessly to make sure that that information is accessible to researchers working on other nematode species. We all have been empowered by those efforts. For his pioneering research on the developmental biology of nematodes, the Society of Nematologists is proud to name Dr. Don Riddle as a Fellow of the Society.