Septin filament compaction into rings requires the anillin Mid2 and contractile ring constriction

Septin filaments assemble into high-order molecular structures that associate with membranes, acting as diffusion barriers and scaffold proteins crucial for many cellular processes. How septin filaments organize in such structures is still not understood. Here, we used fission yeast to explore septin filament organization during cell division and its cell cycle regulation. Live-imaging and polarization microscopy analysis uncovered that septin filaments are initially recruited as a diffuse meshwork surrounding the acto-myosin contractile ring (CR) in anaphase, which undergoes compaction into two rings when CR constriction is initiated. We found that the anillin-like protein Mid2 is necessary to promote this compaction step, possibly acting as a bundler for septin filaments. Moreover, Mid2-driven septin compaction requires inputs from the septation initiation network as well as CR constriction and the beta(1,3)-glucan synthase Bgs1. This work highlights that anillin-mediated septin ring assembly is under strict cell cycle control.

Automated summary

In this study, the organization of septin filaments during cell division and its cell cycle regulation were investigated using fission yeast. The findings suggest that an anillin-like protein Mid2 plays a crucial role in promoting septin filament compaction and assembly, which is tightly controlled by the cell cycle.