Advecting Scaffolds: Controlling The Remodelling Of Actomyosin With Anillin

We propose and analyse an active hydrodynamic theory that characterises the effects of the scaffold protein anillin. Anillin is found at major sites of cortical activity, such as adherens junctions and the cytokinetic furrow, where the canonical regulator of actomyosin remodelling is the small GTPase, RhoA. RhoA acts via intermediary 'effectors' to increase both the rates of activation of myosin motors and the polymerisation of actin filaments. Anillin has been shown to scaffold this action of RhoA - improving critical rates in the signalling pathway without altering the essential biochemistry - but its contribution to the wider spatio-temporal organisation of the cortical cytoskeleton remains poorly understood. Here, we combine analytics and numerics to show how anillin can non-trivially regulate the cytoskeleton at hydrodynamic scales. At short times, anillin can amplify or dampen existing contractile instabilities, as well as alter the parameter ranges over which they occur. At long times, it can change both the size and speed of steady-state travelling pulses. The primary mechanism that underpins these behaviours is established to be the advection of anillin by myosin II motors, with the specifics relying on the values of two coupling parameters. These codify anillin's effect on local signalling kinetics and can be traced back to its interaction with the acidic phospholipid phosphatidylinositol 4,5-bisphosphate (PIP2), thereby establishing a putative connection between actomyosin remodelling and membrane composition.