  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.
