Microtubules and microscopes: how the development of light microscopic imaging technologies has contributed to discoveries about microtubule dynamics in living cells.

Abstract

Microtubules are dynamic components of the cell cytoskeleton that participate in many important cellular processes, including mitosis, cell motility, morphogenesis, and organelle transport (reviewed in Desai and Mitchison, 1997 ). Microtubules are made up of α/β-tubulin heterodimers that assemble into ∼25 nm cylindrical polymers. Immunofluorescent localization of tubulin has shown that microtubules in interphase tissue cells are for the most part arranged in a radial array with the “minus” end oriented toward a central microtubule organizing center, the centrosome, and the “plus” end radiating toward the cell periphery. Biochemical studies in the 1970s and early 1980s on the assembly–disassembly dynamics of tubulin culminated in the demonstration that microtubules exhibit an unusual form of assembly behavior known as dynamic instability, defined as the coexistence of microtubules in growing and shrinking populations that interconvert infrequently and stochastically (reviewed in Waterman-Storer and Salmon, 1997a ). However, corroboration of these studies with real-time microscopic data was difficult, because 25-nm microtubules are ∼10 times below the resolution limit of the light microscope. This Video Essay provides a review of the ingenious methods that have been developed and applied over the past 10–15 years to the study of microtubule dynamic behavior in living cells. I have not included the many unique microscopic approaches that have been used for the study of microtubule behavior in vitro (for review, see Scholey 1993 ). Furthermore, this review intends by no means to be exhaustive but summarizes a few highlights in the field of which primary data was generously made available to me from the original authors for digitization and conversion into QuickTime movies. Finally, important advances such as the expression of green fluorescent protein–coupled proteins to follow microtubule dynamics in the ∼6-μm-diameter budding yeast Saccharomyces cerevisiae cell (Shaw et al., 1998 ) and the use of polarized light microscopy for monitoring microtubule dynamics during mitosis (Inoue and Oldenbourg, 1998 ) have been omitted from this review, because these topics have been dealt with in detail in recent Video Essays in this series.