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To segregate the chromosomes faithfully during cell division, cells assemble a spindle that captures the kinetochores and pulls them towards opposite poles. Proper spindle function requires correct interplay between microtubule motors and non-motor proteins. Defects in spindle assembly or changes in spindle dynamics are associated with diseases, such as cancer or developmental disorders. Here, we compared mitotic and meiotic spindles in fission yeast. We show that, even though mitotic and meiotic spindles underwent the typical three phases of spindle elongation, they have distinct features. We found that the relative concentration of the kinesin-14 family protein Pkl1 is decreased in meiosis I compared to mitosis, while the concentration of the kinesin-5 family protein Cut7 remains constant. We identified the second kinesin-14 family protein Klp2 and microtubule dynamics as factors necessary for proper meiotic spindle assembly. This work defines the differences between mitotic and meiotic spindles in fission yeast Schizosaccharomyces pombe, and provides prospect for future comparative studies., We acknowledge the Cell and Tissue Imaging (PICT-IBiSA), Institute Curie, member of the French National Research Infrastructure France-BioImaging (ANR10-INBS-04). Ana Loncar is supported by a PhD fellowship from the European Union ITN-Divide Network (Marie Skłodowska-Curie grant agreement No 675737s). This work is supported by grants from INCa, Fondation ARC, and La Ligue National Contre le Cancer. The Tran lab is a member of the Labex CelTisPhyBio, part of IdEx PSL.

The fission yeast Schizosaccharomyces pombe has a cylindrical rod-shape that is organized and maintained by interactions between the microtubule, cell membrane, and actin cytoskeleton; i.e., microtubules deliver factors to the cell tips that subsequently recruit the actin machinery to direct localized cell growth [1]. Mutations affecting any components in this pathway lead to bent, branched, or round cells [2]. In this context, the cytoskeleton controls cell polarity and thus dictates cell shape. Here, we use soft-lithography techniques to construct microfluidic channels in order to control the shape of cells. We show that by physically forcing wildtype rod-shaped cells to grow bent, they will re-organize their cytoskeleton and re-direct cell polarity to make new ectopic cell tips. In addition, by physically forcing bent or round mutant cells to conform to the wildtype rod-shape, cells will reverse their mutational phenotypes by re-organizing their cytoskeleton to maintain proper wildtype-like microtubule, cell membrane proteins, and actin localizations. Our study provides direct evidence that the cytoskeleton controls cell polarity and cell shape and demonstrates that cell shape also controls the organization of the cytoskeleton, in a feedback loop. We present a model of the feedback loop which explains how fission yeast cells maintain a rod-shape, and how perturbation of specific parameters of the loop can lead to different cell shapes.