Physical Mechanisms Redirecting Cell Polarity and Cell Shape in Fission Yeast

The cylindrical rod shape of the fission yeast Schizosaccharomyces pombe is organized and maintained by interactions between the microtubule, cell membrane, and actin cytoskeleton [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 to control cell shape. We show that when wild-type rod-shaped cells are physically forced to grow in a bent fashion, they will reorganize their cytoskeleton and redirect cell polarity to make new ectopic cell tips. Moreover, when bent or round mutant cells are physically forced to conform to the wild-type rod-shape, they will reverse their mutational phenotypes by reorganizing their cyloskeleton to maintain proper wild-type-like localization of microtubules, cell-membrane proteins, and actin. 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 to explain how fission yeast maintain a rod shape and how perturbation of specific parameters of the loop can lead to different cell shapes.