Video microscopy of organelle inheritance and motility in budding yeast

By adapting the time-lapse video microscopy techniques that were developed for larger, more complex cells, to living Saccharomyces cerevisiae cells, intracellular organelle movements were observed. Differential interference contrast optics revealed an organelle transport process in cells treated with mating pheromone. Small particles were observed to travel distances of up to 6 microns at rates of 0.11-0.17 (and in one case 0.80) micron/sec. Overall, the frequency of these motile events was quite low compared to what is observed in cell types traditionally studied by video microscopy. The ability to discern clearly the vacuole and nucleus in budding yeast revealed the dynamics of these organelles and the fact that their movements are carefully orchestrated during the cell cycle. Two types of vacuolar dynamics were observed: 1) interconversion between one large organelle and numerous smaller organelles and 2) the formation of projections that extend from the mother cell's vacuole into the bud. When applied to the study of the many available cytoskeletal and cell cycle mutants, the application of video microscopy to the study of organelle movements in living yeast cells will provide a unique opportunity to determine the molecular mechanisms of intracellular motility and to elucidate the temporal controls over these processes.