Spatial Coordination of Cytokinetic Events by Compartmentalization of the Cell Cortex

Abstract

During cytokinesis, furrow ingression and plasma membrane fission irreversibly separate daughter cells. How actomyosin ring assembly and contraction, vesicle fusion, and abscission are spatially coordinated was unknown. We found that during cytokinesis septin rings, located on both sides of the actomyosin ring, acted as barriers to compartmentalize the cortex around the cleavage site. Compartmentalization maintained diffusible cortical factors, such as the exocyst and the polarizome, to the site of cleavage. In turn, such factors were required for actomyosin ring function and membrane abscission. Thus, a specialized cortical compartment ensures the spatial coordination of cytokinetic events.

Some assembly required: yeast septins provide the instruction manual

“…For example, the membrane-associated septins at the isthmus between a mother cell and its bud form a physical barrier that is necessary to prevent diffusion of bud-specific proteins into the mother cell [29,30]. During cytokinesis, the tubular collar of septin filaments is split into two separate 'rings' that seem to serve as gaskets that confine and concentrate between them factors that are involved directly in cytokinesis, such as the exocyst component Sec3, an adaptor protein Spa2 and an isoform of chitin synthase Chs2 [31]. This compartmentalization function appears to be conserved in fission yeast, where a double ring of septin filaments encompasses the contractile apparatus and provides for efficient dissolution of the primary septum [32,33].…”

Rho GTPase activity zones and transient contractile arrays

“…For example, the septins act as barriers for lateral diffusion during bud formation in yeast. (41) However, while septins are associated with the cytokinetic apparatus in a variety of metazoan systems, and have been suggested to limit diffusion across the cleavage furrow, (42) a corral role would require that they border both sides of zones, but the available information suggests that, in metazoan systems, septins are localized to the middle of the cytokinetic apparatus. (42)(43)(44) …”

Drosophila Orc6 Facilitates GTPase Activity and Filament Formation of the Septin Complex

“…Identified originally in yeast, septins are now found in many fungi and animals (Kinoshita, 2003;Pan et al, 2007). Septins are essential for cytokinesis (Hartwell, 1971;Neufeld and Rubin, 1994;Kinoshita et al, 1997); however, they have also been implicated in other processes such as polarity establishment, cell cycle checkpoints, formation of diffusion barrier, spindle alignment, chromosome segregation, vesicle trafficking, and exocytosis (Gladfelter et al, 2001;Kusch et al, 2002;Dobbelaere and Barral, 2004;Martinez et al, 2004;Spiliotis et al, 2005;Spiliotis and Nelson, 2006).…”