The environmental toxicology community recently lost a greatly revered member, Distinguished Professor Emeritus Michael Denison, after an extended illness. A special friend to colleagues and a favorite of students, Mike made everyone feel special. He was an accomplished scientist with many accolades who is a legend in the Department of Environmental Toxicology (ETX) for many reasons, not least of which was his penchant for Hawaiian shirts, long hair, and brightly colored tennis shoes. Mike was a happy and optimistic person. The only thing he took seriously was science, which he loved. His typical day was spent conducting research and mentoring students, and then after the workday, making a wonderful dinner for his wife before retreating to his home office to work until the wee hours of the following morning. He maintained curiosity and wonder about the world around him. He loved to solve problems and figure out how things worked. He was generous with his friends and colleagues and always quick to offer his services to those in need. A celebration of his life was held on campus with colleagues from around the world providing their recollections of Mike’s outstanding scientific achievements and unique style. One key observation was that someone else in his position might have been a bitter rival, but Mike was always a valued collaborator instead.

After receiving a PhD in Environmental Toxicology from Cornell University in 1983, Mike developed a research program focused on understanding how the notorious environmental contaminant, tetrachlorodibenzo-p-dioxin or TCDD (commonly called dioxin) caused toxicity through activation of the aryl hydrocarbon receptor (AhR). Mike’s research was fundamental to elucidating the binding site of TCDD in the AhR. Mike leveraged this basic research to develop a receptor-based assay for TCDD, which became the widely acclaimed Chemical Activated LUciferase gene eXpression (CALUX) assay. Using this cell-based bioassay, Mike discovered numerous compounds that activated the AhR, including compounds derived from many everyday items, such as baby bottle nipples and newsprint. He showed the assay could be formatted to discover other potentially dangerous environmental chemicals that were not dioxin-like chemicals, including environmental hormones (endocrine disruptors). His concept of using a receptor as a biological monitor of potential toxicity has been widely adopted internationally. The CALUX assay was approved by the Organization of Economic Cooperation and Development (OECD) and the USEPA as an international standard for detecting environmental contaminants and is used worldwide to protect human health. He also made seminal contributions to understanding AhR biology and was a leader in advancing this field of study.

Despite negotiating a retention package at UCD that included a clause that he would never have to serve as Department Chair, Mike had excellent diplomatic and administrative skills. As the ETX representative in the reorganization of the College of Agricultural and Environmental Sciences into departmental clusters, he arranged for ETX to be in an ideal cluster that preserved departmental autonomy. He also served as the Assistant Director of the NIEHS T32 in Environmental Toxicology, and for many years, he was the Assistant Director of the NIEHS Superfund Program at UCD. His wife Grace became the assistant administrator of the Superfund program, generating ‘superfun’ interactions across the Davis Campus as Mike would put it. Even after his official retirement, Mike continued to run a cell biology core that screened chemicals for potential risks to environmental and human health.

One can only speculate how Mike’s early environment shaped his approach to science and to life. His father was a career drill sergeant in the US Army who expected his sons to be model recruits. However, Mike (and his twin brother Steve) rebelled. As a faculty member, Mike was not known for neat haircuts, conservative clothing, or respect for authoritarian administrators. On the other hand, he was easily approachable and gracious to colleagues and especially to the many students who sought him out as a mentor. His teaching style was direct and filled with easily understandable and humorous examples. As a result, he received effusive student evaluations. In team teaching, he was an excellent colleague - but a tough act to follow. He even taught his little dog to be an excellent frisbee catcher, documented in a popular demonstration on YouTube. Over a 20-year period, he mentored tens of dozens of students, serving as the Major Professor for 14 PhD and 3 MS students, as a committee member for 29 PhD and 15 MS students, and on the qualifying committee of 81 PhD students. Of those students who worked directly in his laboratory, most were supported by the NIEHS training grant in environmental toxicology, and many have gone on to important scientific and administrative positions including in government regulatory agencies.

Perhaps his early training at army bases around the world instilled in Mike a propensity to travel. He seemed always off to give another invited lecture or prestigious keynote address on TCDD or AhR biology. In 1990, he came back from a meeting in Germany proudly displaying a piece of concrete he had chipped off the Berlin Wall. Later, he spent a sabbatical in Italy and, upon his return, became known to colleagues as Michelangelo. His early training may have given him an appreciation for organization. He led the international Dioxin 2000 meeting in Monterey, CA, at the end receiving a standing ovation for his outstanding organizational skills. With support from the US Government, he also organized a scientifically and politically important international conference in Viet Nam analyzing the legacy of spraying the defoliant Agent Orange there during the Viet Nam War.

Mike was an inspiration, ensuring that the scientists with whom he interacted took science very seriously, yet had fun while doing so. His foresight and originality extended far beyond Davis to influence how environmental chemistry is done around the world. He set an example of never taking himself seriously, which was his secret sauce for continually stimulating creative thought, innovation and productivity among his peers and his students. He is dearly missed by all who were lucky enough to know him.   

Robert H. Rice
Bruce D. Hammock
Grace L. Bedoian
Pamela J. Lein