Figure 6: Cartoon illustrations of fluorescent footprint patterns due to isolated cell shape, receptor, and membrane morphology perturbations.

(a) A cell with uniform receptor distribution deforming due shear flow compression alone would produce uniform tracks without periodic patterns, much like those in a bead rolling assay (Supp. Figure S4A). (b) An undeformable cell with irregular cell shape but uniform surface receptor distribution would leave a periodic footprint that is uniform in intensity but variable in width. (c) Short elastic membrane tether formation does not alter periodicity of rolling as long as the cell maintains traction (the figure exaggerates the length of each tether to illustrate the concept; in reality, the tethers are only a few hundred nm in length). The tip of each tether (red and orange) forms adhesive contacts after each rotation cycle of the cell, regardless of the elastic tether history. (d) Recently discovered membrane ‘slings’ that are thought to stabilise cell rolling under high shear conditions⁴² would only produce contact adhesion points at discrete intervals, which is unlikely to produce periodicity, if any, that matches cell circumference. (e) A small fraction of cells that exhibit irregular membrane morphology such as small ruffles would introduce periodicity in the fluorescent footprint as repeating fine patterns that match the shape of the membrane irregularities. (f) Asymmetrically distributed receptors would produce periodic patterns with variable fluorescent intensity.