Abstract
Deposition of additional plasma membrane and cargoes during cytokinesis in eukaryotic cells must be coordinated with actomyosin ring contraction, plasma membrane ingression and extracellular matrix remodelling. The process by which the secretory pathway promotes specific incorporation of key factors into the cytokinetic machinery is poorly understood. Here, we show that cell polarity protein Spa2 interacts with actomyosin ring components during cytokinesis. Spa2 directly binds to cytokinetic factors Cyk3 and Hof1. The lethal effects of deleting the SPA2 gene in the absence of either Cyk3 or Hof1 can be suppressed by expression of the hypermorphic allele of the essential chitin synthase II (Chs2), a transmembrane protein transported on secretory vesicles that makes the primary septum during cytokinesis. Spa2 also interacts directly with the chitin synthase Chs2. Interestingly, artificial incorporation of Chs2 into the cytokinetic machinery allows the localisation of Spa2 at the site of division. In addition, increased Spa2 protein levels promote Chs2 incorporation at the site of division and primary septum formation. Our data indicate that Spa2 is recruited to the cleavage site to co-operate with the secretory vesicle system and particular actomyosin ring components to promote the incorporation of Chs2 into the so-called ‘ingression progression complexes’ during cytokinesis in budding yeast.
Highlights
Before the end of mitosis, eukaryotic cells need to redirect the secretory machinery towards the site of division to ensure cells deposit additional plasma membrane between the two daughter cells
Eukaryotic cells must build a physical barrier of plasma membrane, which is coupled with the remodelling of the extracellular matrix between the dividing cells
To understand how cells control the activity of the chitin synthase Chs2 at the division site during cytokinesis, we previously isolated proteins that were able to interact at the same time with Chs2 and one of its regulators, the protein Inn1 [14]
Summary
Before the end of mitosis, eukaryotic cells need to redirect the secretory machinery towards the site of division to ensure cells deposit additional plasma membrane between the two daughter cells. Secretory vesicles transport key factors to enable cells to perform cytokinesis successfully [1,2,3]. The exocyst complex tethers secretory vesicles to sites of active exocytosis and membrane expansion. The remaining exocyst components are associated with secretory vesicles [7,8,9]. It has recently been reported that the exocyst has an open-hand conformation, which explains how the complex tethers secretory vesicles to put them in contact with the plasma membrane [10]. The association between vesicle and plasma membrane proteins of the SNARE complex (soluble N-ethylmaleimide-sensitive factor attachment protein receptor) leads to the fusion of secretory vesicles with the plasma membrane [7,8,9, 11, 12]
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