BSCB Newsletter, Summer 2005 Dennis Summerbell 1947-2005 Dennis Summerbell, who performed pioneering experiments on the development of the chick limb, has died at the early age of 58. He had been suffering from pancreatic cancer for 19 months, and had borne his illness with characteristic courage, dignity and humour. By Jim Smith I first came across Dennis in 1976, when I started as a graduate student with Lewis Wolpert, just three years after Dennis had finished his own PhD in the same lab. Dennis had first gone on to do a postdoc in Grenoble with Philippe Sengel, and by now was working in the University of Otago, New Zealand. Dennis's location on the other side of the world enhanced his almost mythical status in Lewis's lab, for he had produced a PhD thesis that was so comprehensive, so magisterial, so brilliant, that my fellow students and I (including Nigel Holder, Geoff Shellswell and John McLachlan) despaired of finding any new experiment that he hadn't already done. In my own PhD thesis, first author papers by Summerbell would have occupied a whole page in the references had I not, to tease him, squeezed in a Szabo reference before starting a new sheet of paper. I sometimes wonder how Dennis managed to achieve so much in such a short time; it must have had something to do with the way he combined his great technical expertise with a deep interest in theoretical models for limb development. A rare combination then, and even more so now. The most significant parts of Dennis' PhD thesis helped us understand how positional information along the antero-posterior and proximo-distal axes of the developing limb is specified. The work was described in two articles in Nature, the first with Julian Lewis and Lewis Wolpert and the second with Cheryll Tickle and Lewis Wolpert, and they were of extraordinary importance. The papers are cited to this day, and their significance was illustrated recently by the intense excitement that surrounded the suggestion that the so-called 'progress zone' model (in his thesis Dennis called it the 'magic zone') might be wrong. Any developmental biologist would have been delighted, and proud, if their model had managed to last for over 30 years before being questioned in a serious manner, but Dennis had cause to be even prouder, because, the recent results notwithstanding, the progress zone model remains the best way to understand how positional information is specified along the proximo-distal axis of the limb. On returning from Otago, Dennis moved to Mike Gaze's Division in the National Institute for Medical Research in Mill Hill, where he teamed up with like-minded developmental biologists such as Jonathan Cooke, with whom he analysed cell division during limb development, Vicky Stirling, with whom he carried out some beautiful experiments on innervation of the limb, and Malcolm Maden. The partnership with Malcolm was particularly important, providing, as it did, some of the first insights into the roles of retinoic acid signalling during development. As I got to know Dennis, I came to see how this work, like all his work, was careful, meticulous and beautifully controlled. Dennis had a strong regard for the truth and would never make any assertion unless he knew beyond doubt that it was true. Not long after Malcolm left NIMR to go to King's College London, Dennis decided that he wanted to learn how to apply molecular biological techniques to development and he joined Peter Rigby, also at Mill Hill, to study the regulation of muscle gene expression in the mouse embryo. He worked on the Hox genes and on the skeletal muscle determination gene Myf5. His characteristically painstaking and beautiful analysis of the extraordinarily complex regulation of Myf5 has been highly influential in the field. He published regularly with Peter in journals such as Development and Genes and Development and moved with him to The Institute of Cancer Research in 2000, where he continued to work at a high level even after he was diagnosed with pancreatic cancer. He did it, in spite of the pain, because he just loved doing science. Dennis married Amata Hornbruch in 1971. Their house, close to NIMR, became a haven for PhD students and postdocs in developmental biology: for times of celebration, for when things were getting a bit stressful, and for when they (the younger scientists) fancied a good glass of wine; Dennis had an excellent cellar and he and Amata were superb hosts. Dennis was also a tremendous teacher and mentor of young scientists and was an important influence on many careers. He will be greatly missed by his colleagues at The Institute of Cancer Research, as well as by his many friends and admirers at Mill Hill and around the world. But no one will miss Dennis more than Amata, to whom we send our deepest sympathy. Jim Smith