A mere forty years ago it was unclear what motor molecules exist in cells that could be responsible for the variety of nonmuscle cell movements, including the “saltatory cytoplasmic particle movements” apparent by light microscopy. One wondered whether nonmuscle cells might have a myosin-like molecule, well known to investigators of muscle. Now we know that there are more than a hundred different molecular motors in eukaryotic cells that drive numerous biological processes and organize the cell's dynamic city plan. Furthermore, in vitro motility assays, taken to the single-molecule level using techniques of physics, have allowed detailed characterization of the processes by which motor molecules transduce the chemical energy of ATP hydrolysis into mechanical movement. Molecular motor research is now at an exciting threshold of being able to enter into the realm of clinical applications. It is an honor to be sharing the E. B. Wilson Medal with two friends and outstanding scientists, Dick McIntosh and Gary Borisy. We were all introduced to cytoskeletal research at about the same time. In my case, I was introduced to actin and myosin as a postdoctoral fellow at the MRC Laboratory of Molecular Biology in Cambridge, England, working with Hugh Huxley, on whose shoulders all molecular motor researchers stand. Hugh shared the 1983 E. B. Wilson Medal with Joseph Gall. My work with Hugh in 1969 and 1970 on the actin-tropomyosin-troponin-myosin muscle complex led us to postulate the steric blocking mechanism of calcium regulation of skeletal muscle ( Spudich et al. , 1972 ) , more fully developed by Hugh elsewhere (Huxley, 1973). After leaving Cambridge in 1971, I started my laboratory at the University of California, San Francisco, where I spent my first 6 years as a faculty member. In 1977, I moved to Stanford University. Over the years, I have had the privilege of working with the very best students, postdoctoral fellows, research associates, sabbatical visitors, and collaborators. This essay is a tribute to their contributions, rather than a minireview of the field. As it is, due to space limitations, I have had to leave out important contributions by many of my talented lab members, but a complete list of their contributions can be found on our laboratory website ( http://spudlab.stanford.edu ). This is a story of how our research evolved from 1971 to the present day. To put things in perspective, two key questions about molecular motors around that time were: How does myosin transduce the chemical energy of ATP hydrolysis into mechanical movement?, and What kind of mole-cular motors are in nonmuscle cells? I decided to focus on two goals: first, to develop quantitative in vitro motility assays for myosin movement on actin, essential for understanding energy transduction in this system; and second, to try to unravel the molecular basis of the myriad nonmuscle cell movements made apparent by light microscopy. During the first year of my assistant professorship, we searched for an ideal model system to study cell movements. We grew Neurospora , Saccharomyces , Physarum , Dictyostelium, Nitella , and other organisms totally unfamiliar to me at the time and searched for a myosin-like motor. Dictyostelium proved to be perfect for this purpose. Margaret Clarke, one of my first postdoctoral fellows, identified a Dictyostelium myosin with properties similar to those of conventional muscle myosin ( Clarke and Spudich, 1974 ), and we then developed methods for visualizing the cytoskeleton in this and other nonmuscle cells ( Clarke et al. , 1975 ; Brown et al. , 1976 ). FIGURE 1: The first Spudich lab group photo, University of California, San Francisco, 1974. Regarding an in vitro motility assay, Dictyostelium , being a phagocytic organism, offered promise. Actin filaments were known to be in the cortex of nonmuscle cells, with their barbed ends at the cell membrane ( Ishikawa et al. , 1969 ; Schroeder, 1973 ). I fed Dictyostelium small polystyrene beads and isolated the phagocytic vesicles from cell lysates, and found that the vesicles had actin filaments emanating from the membrane-coated surfaces. With great excitement, I tried to establish in vitro motility of these vesicles along myosin-coated coverslips, but directed movements were not readily apparent, and a definitive in vitro motility assay would wait another decade.
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