Characterizing the architecture of reconstituted minimal septin and septin-actin cortices at high resolution

Abstract

In animal cells, cell shape is primarily regulated by the actin cortex, a thin filament network connected to the plasma membrane. The architecture of the cortex is considered a key regulator of its function. Visualising the cortex is difficult due to the high density of numerous small-sized proteins involved in its formation. Consequently, the structure of the cortex at the membrane remains poorly studied. This study aims to gain insight into the organisation at the membrane of two key cortical components, human septin and septin-recruited actin. To study these filament structures, we reconstitute minimal cortices on supported lipid layers as model-membranes, allowing for imaging with electron and atomic force microscopy. We show that membrane binding of human septin results in ordered organisations of filaments. However, we find septin organises into arrays of paired filaments when incubated on a lipid monolayer and networks of bundles when incubated on a lipid bilayer. In addition, we showed a proof of concept for actin cortex reconstitution on lipid monolayers, which allowed us to see actin recruitment by septin meshworks.