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"Microtubules orient the mitotic spindle in yeast through dynein-dependent
interactions with the cell cortex."
Janet L. Carminati and Tim Stearns (1997) J. Cell Biol. 138:629-641. Also see: Carminati, J. and Stearns, T. (1998) Cytoskeletal dynamics in yeast. Meth. Cell Biol. 58:87-105.


Summary
Proper orientation of the mitotic spindle is critical to successful cell division in
budding yeast. To investigate the mechanism of spindle orientation we used a green
fluorescent protein (GFP)-tubulin fusion protein to observe microtubules in living yeast
cells. GFP-tubulin is incorporated into microtubules, allowing visualization of both
cytoplasmic and spindle microtubules, and does not interfere with normal microtubule
function. Microtubules in yeast cells exhibit dynamic instability, though they grow and
shrink more slowly than microtubules in animal cells. The dynamic properties of yeast
microtubules are modulated during the cell cycle. The behavior of cytoplasmic
microtubules revealed distinct interactions with the cell cortex that result in associated
spindle movement and orientation. Dynein mutant cells have defects in these cortical
interactions, resulting in misoriented spindles. In addition, microtubule dynamics are
altered in the absence of dynein. These results indicate that microtubules and dynein
interact to produce dynamic cortical interactions, and that these interactions result in the
force driving spindle orientation.

The following are Quicktime movies, which can be viewed by clicking on the image (you can get Quicktime here). In each, microtubules are visualized in living yeast cells using a green fluorescent protein-tubulin fusion. The fusion protein is incorporated into microtubules, resulting in fluorescent microtubules. The microtubules are imaged in time-lapse with a cooled-CCD camera. For each movie, the real elapsed time is indicated in parentheses.

Wild-type unbudded cells (10.2 min).

A wild-type budded cell with a short spindle (19.2 min).

A wild-type budded cell with a medium spindle, and a cytoplasmic microtubule in the bud exhibiting "sweeping" behavior (8 min).

A wild-type budded cell with a long spindle; a cytoplasmic microtubule in the mother shrinks at the cortex, resulting in spindle movement (20.2 min).

A dyn1::HIS3 budded cell with a misaligned spindle, and a long cytoplasmic microtubule in the bud (8 min).

Three dyn1::HIS3 budded cells with misaligned spindles, and long cytoplasmic microtubules (6.7 min).