Abstract
Cytokinesis in many organisms requires a plasma membrane anchored actomyosin ring, whose contraction facilitates cell division. In yeast and fungi, actomyosin ring constriction is also coordinated with division septum assembly. How the actomyosin ring interacts with the plasma membrane and the plasma membrane-localized septum synthesizing machinery remains poorly understood. In Schizosaccharomyces pombe, an attractive model organism to study cytokinesis, the β-1,3-glucan synthase Cps1p / Bgs1p, an integral membrane protein, localizes to the plasma membrane overlying the actomyosin ring and is required for primary septum synthesis. Through a high-dosage suppressor screen we identified an essential gene, sbg1+ (suppressor of beta glucan synthase 1), which suppressed the colony formation defect of Bgs1-defective cps1-191 mutant at higher temperatures. Sbg1p, an integral membrane protein, localizes to the cell ends and to the division site. Sbg1p and Bgs1p physically interact and are dependent on each other to localize to the division site. Loss of Sbg1p results in an unstable actomyosin ring that unravels and slides, leading to an inability to deposit a single contiguous division septum and an important reduction of the β-1,3-glucan proportion in the cell wall, coincident with that observed in the cps1-191 mutant. Sbg1p shows genetic and / or physical interaction with Rga7p, Imp2p, Cdc15p, and Pxl1p, proteins known to be required for actomyosin ring integrity and efficient septum synthesis. This study establishes Sbg1p as a key member of a group of proteins that link the plasma membrane, the actomyosin ring, and the division septum assembly machinery in fission yeast.
Highlights
Cytokinesis is the terminal step in the cell cycle during which two cells are formed starting from one
Cell division in many organisms requires the function of an actomyosin ring, an apparatus that resembles the force generating machinery in the muscle
This ring apparatus is attached to the cell periphery such that when it contracts, it brings the cell periphery together with it, leading to cell division
Summary
Cytokinesis is the terminal step in the cell cycle during which two cells are formed starting from one. Fungi and metazoans use a plasma membrane anchored actomyosin-based contractile ring to mark the cell division site and contraction of the actomyosin ring generates a part of the tension required to divide the cell [1,2,3]. Cell division is brought about by a membrane anchored actomyosin ring whose contraction is tightly coupled to septum synthesis. Growing evidence in this organism suggests that while the actomyosin ring generates tension, the rate of growth of the septum cell wall determines the rate of contraction of the actomyosin ring [12,13]. The mechanisms by which the actomyosin ring, plasma membrane, and septum wall synthesis are coordinated are a subject of major interest
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