Sean Morrison: A root and branch approach to stem cells

T hroughout life, stem cells maintain themselves by dividing to produce one or two daughter stem cells with an identical developmental potential. Although this self-renewal process is fundamental to all types of stem cells, the precise mechanism varies between different tissues and stages of development. Sean Morrison examines the self-renewal of different types of stem cells to understand how the process declines with age and how it is hijacked by cancer cells to drive tumorigenesis. After a brief stint running a biotech company in his native Canada, Morrison's interest in stem cells began as a graduate student with Irv Weissman at Stanford University, where he developed new techniques to purify and characterize hematopoietic stem cells (1). He then adapted these techniques to the nervous system and neural crest stem cells as a postdoc with David Anderson at Caltech (2). In his own lab at the University of Michigan, Morrison goes back and forth between the blood and nervous systems, identifying new regulators of stem cell self-renewal and studying how their actions change during development and aging (3, 4). Morrison's lab also investigates the self-renewal of cancer stem cells that are proposed to drive tumor growth (5), while demonstrating that not all cancers follow this model of tumorigenesis (6). Morrison has challenged other commonly held assumptions too, such as the immortal strand hypothesis that daughter stem cells always inherit older copies of chromosomes (7). In a recent interview, Morrison discussed what his work has taught him about cancer and aging, and the importance of explaining stem cell research to the general public. Where did you grow up and what were your earliest experiences of science? I'm from Nova Scotia in Canada. I did a lot of sports and a lot of science fair projects growing up. My senior year high school project won national awards. It was on fungi called Mycorrhizae that colonize plant roots and enhance their ability to take up nutrients from the soil. The fungus is used agriculturally, but it was very expensive and diffi cult to grow. My lab partner and I thought we could grow the fungus more effectively using hydroponics and we ended up starting a company. The university where I did my undergraduate work, Dalhousie, gave us lab space, and we'd work on it full-time over the summer and part-time during the academic year. I'd run back and forth between the lab and classes, …