Yeast cells place their nucleus in the center of the cell, where the nucleus helps define where the cell will later divide in half. Researchers now report evidence supporting a new theory for how the cell measures distance such that the nucleus ends up in the right place.
The cells discussed by Phong Tran (Columbia University, New York) and colleagues in the April 16 issue of The Journal of Cell Biology are Schizosaccharomyces pombe or fission yeast cells. Tran et al. find that large bundles of microtubules, proteins that resemble train tracks, extend from the nucleus to either end of these cells. Previously workers had believed that the nucleus might be shuttled along these train tracks at the direction of some unknown signal. But Tran et al. gather evidence that the microtubules themselves are being used as an intracellular ruler.
The microtubules push against the end of the cell, thus pushing the nucleus away from the end of the cell. The likelihood of a microtubule bundle reaching the end of the cell, and thus having the opportunity to push against the end of the cell, drops off as the distance from the nucleus to the end of the cell increases. Thus, on average, microtubules will push more if the nucleus is close to the end of the cell, and the nucleus will be pushed back into the center of the cell.
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