Niccoli, Teresa; (2002) Regulation of microtubular dynamics in response to pheromone in Schizosaccharomyces pombe. Doctoral thesis (Ph.D), UCL (University College London).

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Abstract

Schizosaccharomyces pombe cells have two polarised growth modes: an intrinsic vegetative growth mode, determined by an internal positioning mechanism and an extrinsic shmooing growth mode, activated by external pheromone. I have analysed the role of the cell end marker Tea1p, the CLIP170 like protein Tip1p, the kinesin like protein Tea2p and the Dyrk like kinase Pom1p, during the switch between the two growth patterns, with the intention of studying the switch away from the vegetative growth mode. In vegetative growth these morphological factors are concentrated at cell ends, whereas during shmooing growth they are delocalised from the cell ends. In the absence of Tea1p, Tip1p and Tea2p, vegetative cells display microtubule and cell polarisation defects, but shmooing cells are indistinguishable from wild type and shmoo more readily. These results suggest that Tea1p, Tip1p and Tea2p are not required for polarised growth during shmooing, but form part of the intrinsic vegetative growth mode which needs to be dismantled before cells can generate an extrinsic growth pattern. In contrast, Pom1p appears to have a role in the initial stages of the switch to the shmooing growth mode. I then went on to analyse factors which do play a role during growth in response to pheromone. During shmooing the nucleus oscillates back and forth in a characteristic horsetail movement. This movement is driven by microtubules. I analysed the role of Dhc1p, dynein heavy chain and Ssm4p, a dynactin homologue, in the regulation of this oscillatory movement. These two factors are specifically induced in response to pheromone and they interact with each other. Together with Tip1p they co-ordinate the dynamics of microtubules at opposite ends of the cell to generate the oscillations which drive the nuclear movement.

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