Microtubules are involved in the establishment and maintenance of cell polarity in many cells, including those of fission yeast. In this organism, the normally cylindrical cells become bent or branched when microtubule function is impaired by mutations or chemicals, indicating that cell polarity has been disrupted. Kenneth Sawin and Hilary Snaith now define more exactly how microtubules regulate fission yeast polarity (see ). By use of combinations of drugs, environmental perturbations, and genetic mutations, they show that, once cell polarity is defined, microtubules are not needed to maintain the direction or rate of cell growth. Similarly, microtubules are not needed per se to re-establish disrupted polarity. Instead, say the authors, microtubules determine the site at which polarity is established or re-established by signalling to the cortex of the cell. This signalling process requires Tea1p, a protein that associates with the plus ends of growing microtubules. The researchers propose that continuous Tea1p targeting to cell tips by microtubules helps to promote polarity axes de novo and present a model to explain how Tea1p might be involved in re-establishing polarity if it is perturbed.
