Abstract

The generation of specialized patterns of microtubule polymers is essential for the correct growth and division of all eukaryotic cells, from neurons to fungi. Fission yeast (Schizosaccharomyces pombe) cells, for example, grow only from their tips in a way that depends upon a uniform organization (polarization) of their microtubules. Using quantitative live-cell microscopy and permeabilized cell approaches, we have been able to demonstrate that uniform microtubule organization in fission yeast cells during growth (interphase) requires microtubule-associated motor activities. In these cells, microtubules are organized in three or four bundles and are uniformly polarized within the bundles. This uniform polarization was thought to be imposed by their de novo formation (nucleation) strictly around the surface of cell nuclei, at the cells centres. Our work demonstrates that microtubules are actually nucleated everywhere in these cells and that their uniform polarization emerges instead from the transport of newly formed microtubules toward the cell centre along pre-existing microtubule bundles. Transport is mediated by the motor protein Klp2, a member of the evolutionarily conserved Kar3/Ncd family of kinesin motors. Furthermore, we show that cell nuclei are dispensable for microtubule pattern formation in those cells and that, instead, the patterns self-organize dynamically via association of microtubules with interacting factors, such as motors. In this manner, we find that motor-mediated self-organization secures the correct steady-state pattern of microtubules in spite of quantifiable variation in microtubule content within and between cells. Self-organization processes were so far thought to be important for generating spatial order only in higher eukaryotic cells, during cell division. Our work using fission yeast cells strongly suggests that exploiting such processes to create robust yet adaptable positional information may instead be widespread among many eukaryotic cell types.

http://science.cancerresearchuk.org/research/loc/london/lifch/nursep/nursepproj?version=4