Elastic energies and morphologies of the first stages of the discoechinocyte transition

Abstract

Red blood cells are highly sensitive to changes in the relative areas of the two lipid leaflets of the cell membrane. Expansion of the outer leaflet forces the membrane to bend, leading to the deformation of the biconcave discocyte into increasingly spiculated shapes, in a well-defined series of cell shapes known as the discoechinocyte transition. We explore the first stages of this transition by means of an elastic membrane energy model that accounts for the bilayer and cytoskeleton contributions. The morphological evolution is explained in terms of the elastic response of these membrane components. Our results highlight the importance of the cytoskeleton as a stabilizing component and how it determines the strong sequential character of the development of different morphologies. In general, cells develop undulations around the cell contour prior to the growth of out-of-plane bumps; this was found to be due to the high energetic penalty relative to a limited area-difference benefit.