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: Upon carbon source exhaustion, fission yeast cells leave the cell cycle and enter quiescence from interphase (Bostock, 1970; Costello et al., 1986). In these conditions, we have analyzed MT organization in wild-type (WT) cells expressing the α-tubulin 2 (Atb2) fused to GFP. As expected, proliferating interphase cells displayed two to five long cytoplasmic bundles composed of 4 ± 1 MTs (Fig. 1, A and B; Höög et al., 2007). Strikingly, we observed that after carbon exhaustion, the number of MT bundles progressively decreased (Fig. 1 A). Four days after carbon exhaustion, the majority of the cells displayed a single MT bundle (Fig. 1 A and Fig. S1 A) that we named Q-MT bundle, standing for quiescent cell MT bundle. This unique MT bundle was composed of more than 15 MTs (Fig. 1 B) that were not necessarily of the same length, as exemplified by the arrow shape of the bundle extremities (Fig. S1 B). In fact, in ∼15% of the cells, the Q-MT bundle could display internal thickness variations (Fig. S1 C). Importantly, by imaging cells coexpressing GFP-Atb2 with the SPB-associated protein Sfi1 fused to CFP and the nuclear membrane protein Cut11 fused to RFP, we observed that the Q-MT bundle was generally associated with the SPB (>70% of the cells; Fig. 1, C, D, and G), even when quiescence was prolonged (Fig. S1 D). Yet, MT bundles not associated with the SPB displayed the same length and intensity than the SBP-associated ones (Fig. S1, E and F). EM analysis of quiescent WT cells showed that within the Q-MT bundle MTs were regularly spaced (Fig. 1, D–G; and Fig. S1 G). Finally, the Q-MT bundle organization and localization within the cell were confirmed by 3D models constructed using serial section electron tomograms (Fig. 1 G).
Affiliation: Université de Bordeaux, Institut de Biochimie et Génétique Cellulaires, 33000 Bordeaux, France Centre National de la Recherche Scientifique, UMR5095 Bordeaux, 33077 Bordeaux, France.