Cell polarity in the fission yeast ras1 mutant.
Alena Pichova (1), Karel Sigler (1), Kenji Tanaka (2), Masayuki Yamamoto (3)
(1) Cell and Mol. Microbiology, Institute of Microbiology, Videnska 1083, Praha, CZ 142 20, Czech Republic; (2) Department of Biotechnology, National Institute of Technology and Evaluation, 2-5-8, Kazusakamatari, Kisarazu-shi, Chiba 292-0818, Japan; (3) Department of Biophysics and Biochemistry, Graduate School of Science, University of Tokyo, 7-3-1 Hongo, Bunkyo-ku, Tokyo 113-0033, Japan
The single ras gene, ras1, of Schizosaccharomyces pombe exhibits significant homology to the mammalian ras protooncogenes and functions in a signal transduction pathway controlling sexual development and cellular morphology [1]. The normally highly polarized rod-like S. pombe cells become dumpy if the ras1 gene is disrupted, and become spherical and completely non-polar in the absence of nutrients. Also, the cell wall and the cytoskeletal arrays exhibit significant alterations. Under starvation, the mutant undergoes dramatic dislocation of the cell wall deposition, with the envelope being abnormal in essential structural patterns, mechanical properties and chemical composition. In addition, the cytoskeletal structures are rearranged and completely disorganized. F-actin forms strong cables and microtubules are completely depolymerized. A nutritional stimulus can largely restore the dumpy but polarized morphology in the ras1 mutant: Cells resume cell cycle-dependent cell wall growth and dynamics of F-actin and microtubules, and eventually perform aberrant cell division. These observations suggest an involvement of the nutrition-sensing pathway and the ras1 function in determining the cell shape and polarity in S. pombe. [1] Fukui Y., Kaziro Y.: EMBO J. 4, 687, 1985 This work was supported by GACR grant 301/03/0289; MSMT ME179/1998, Institutional Research Concept AVOZ 50200510 and by grants-in-aid from the Ministry of Education, Science and Culture of Japan.