A stable microtubule array drives fission yeast polarity reestablishment upon quiescence exit.
Bottom Line: Astonishingly, MTs are also stabilized and rearranged into a novel antiparallel bundle associated with the spindle pole body, named Q-MT bundle.Finally and importantly, we reveal that Q-MT bundle elongation is involved in polarity reestablishment upon quiescence exit and thereby the efficient return to the proliferative state.Our work demonstrates that quiescent S. pombe cells assemble specific cytoskeleton structures that improve the swiftness of the transition back to proliferation.
Affiliation: Université de Bordeaux, Institut de Biochimie et Génétique Cellulaires, 33000 Bordeaux, France Centre National de la Recherche Scientifique, UMR5095 Bordeaux, 33077 Bordeaux, France.Show MeSH
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Mentions: In actively dividing S.pombe, MTs deposit polarity factors, such as Tea1, to the cell tip to allow polarized growth (Chang and Martin, 2009; Martin, 2009; Piel and Tran, 2009; Hachet et al., 2012). In quiescent S. pombe cells, Tea1 was no longer detected at the cell tips but was rather localized onto the Q-MT bundle (Fig. 6 A). Tip1, a MT plus end tracking protein of the CLIP170 family, was also lost from cell extremities but couldn’t be detected in quiescent cells (Fig. 6 A). We made a similar observation for active Cdc42 (CRIB domain), the exocyst components Exo70 and Sec8 (Fig. 6 B), the myosin V myo52, the polarity factor Pob1 (Fig. S5 A), and the formin For3 (not depicted). Interestingly, in quiescent S. pombe, no actin cable or patch were found. Instead, we observed a big cytoplasmic F-actin–containing structure (Fig. 6 C). This structure displayed all the characteristics described for actin bodies in quiescent S. cerevisiae (Sagot et al., 2006): they do not have a particular size or shape (Fig. 6 C), they are resistant to Latrunculin A (not depicted), and they contain a specific set of actin binding proteins such as fimbrin (Fim1; Fig. 6 C), capping protein (Acp2; Fig. 6 C), and drebrin (Aap1; Fig. S5 A), but not Bud6, Vrp1, Crn1, Arp5, or End4 (Fig. S5 A). These observations indicated that upon glucose exhaustion–induced quiescence entry, S. pombe cells lose their polarity and entirely reorganize their actin cytoskeleton.
Affiliation: Université de Bordeaux, Institut de Biochimie et Génétique Cellulaires, 33000 Bordeaux, France Centre National de la Recherche Scientifique, UMR5095 Bordeaux, 33077 Bordeaux, France.