Abstract
The formation and maintenance of subcellular structures and organelles with a well-defined size is a key requirement for cell function, yet our understanding of the underlying size control mechanisms is limited. While budding yeast cell polarization and subsequent assembly of a septin ring at the site of bud formation has been successfully used as a model for biological self-assembly processes, the mechanisms that set the size of the septin ring at the bud neck are unknown. Here, we use live-cell imaging and genetic manipulation of cell volume to show that the septin ring diameter increases with cell volume. This cell-volume-dependence largely accounts for modulations of ring size due to changes in ploidy and genetic manipulation of cell polarization. Our findings suggest that the ring diameter is set through the dynamic interplay of septin recruitment and Cdc42 polarization, establishing it as a model for size homeostasis of self-assembling organelles.
Highlights
The formation and maintenance of subcellular structures and organelles with a well-defined size is a key requirement for cell function, yet our understanding of the underlying size control mechanisms is limited
To determine how the septin ring diameter at the mother-bud neck depends on cell volume, we tagged the endogenous copy of the septin CDC10 with the fluorescent protein mCitrine and used a microfluidicsbased live-cell microscopy setup to image haploid cells growing on synthetic complete medium with 2% glycerol 1% ethanol as carbon source (SCGE) for several hours
In the asymmetrically dividing budding yeast, the Cdc42-based polarization machinery determines the site of bud formation and establishes the size of the septin ring at the bud neck connecting mother and future daughter cells
Summary
The formation and maintenance of subcellular structures and organelles with a well-defined size is a key requirement for cell function, yet our understanding of the underlying size control mechanisms is limited. Our findings suggest that the ring diameter is set through the dynamic interplay of septin recruitment and Cdc[42] polarization, establishing it as a model for size homeostasis of self-assembling organelles. While self-organization is ubiquitous in biology, focusing experimental and theoretical studies on a small number of well-defined and accessible model processes facilitates a deep mechanistic understanding of potentially general regulatory principles. One such a model system is the formation of the bud site in the budding yeast Saccharomyces cerevisiae.
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