Abstract
Intracellular structures and organelles such as the nucleus, the centrosome, or the mitotic spindle typically scale their size to cell size [1]. Similarly, cortical polarity domains built around the active form of conserved Rho-GTPases, such as Cdc42p, exhibit widths that may range over two orders of magnitudes in cells with different sizes and shapes [2-6]. The establishment of such domains typically involves positive feedback loops based on reaction-diffusion and/or actin-mediated vesicle transport [3, 7, 8]. How these elements may adapt polarity domain size to cellular geometry is not known. Here, by tracking the width of successive oscillating Cdc42-GTP domains in fission yeast spores [9], we find that domain width scales with local cell-surface radii of curvature over an 8-fold range, independently of absolute cell volume, surface, or Cdc42-GTP concentration. This local scaling requires formin-nucleated cortical actin cables and the fusion of secretory vesicles transported along these cables with the membrane. These data suggest that reaction-diffusion may set a minimal domain size and that secretory vesicle transport along actin cables may dilute and extend polarity domains to adapt their size to local cell-surface curvature. This work reveals that actin networks may act as micrometric curvature sensors and uncovers a generic morphogenetic principle for how polarity domains define their size according to cell morphologies.
Highlights
To directly manipulate local curvature independently of cell size, we first deformed spores in microfabricated wells or linear microchannels [18,19,20]
Cdc42-GTP Polarity Domains Scale Their Width to Local Cell-Surface Curvature To understand how cells may control the size of a polarity domain, we exploited the oscillatory dynamics of active Cdc42-GTP polar domains/caps in the early development of fission yeast spores, which occurs within an extended G1 phase [9] (Movie S1)
In wild-type (WT) spores, which come with natural variations in shapes and sizes, we found an interesting positive correlation between domain width and cellular local radius of curvature (RC) measured around the domain (R2 = 0.59; Figures S1F and S1G)
Summary
To directly manipulate local curvature independently of cell size, we first deformed spores in microfabricated wells or linear microchannels [18,19,20]. Cdc42-GTP Polarity Domains Scale Their Width to Local Cell-Surface Curvature To understand how cells may control the size of a polarity domain, we exploited the oscillatory dynamics of active Cdc42-GTP polar domains/caps in the early development of fission yeast spores, which occurs within an extended G1 phase [9] (Movie S1). Given that the oscillatory dynamics of these domains is much faster than shape changes in those spores, these scaling relationships predominantly reflect an adaptation of domain size to cell geometry, rather than a change in local shape consequent to persistent growth around the site of Cdc42-GTP accumulation [4, 16] (Figure S1J; Movie S1).
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