Tail shape evolution dynamics of MDCK cells on fibronectin substrates

Cell migration plays an important role in many biological processes. Trailing main cell body motion, the cell tail can be formed and exhibits different shapes. In this work, we experimentally investigated the tail shape evolution dynamics of MDCK adherent epithelial cells on fibronectin substrates. We found that, tails can be formed, (1) actively by turning a protruding arm with lamellipodia into a tail after the cell body reverses its moving direction, or (2) passively starting from a small region at the tail edge anchored on the substrate to resist the forward motion of the cell. Depending on whether the tail is overstretched, a narrow tail similar to the overstretched giant vesicle, or a tent shape tail with a fat base, can be developed. Focal adhesion locations at the tail end determine the tail end width and shape symmetry. Tails mainly exhibit three stage retraction, with a higher speed middle stage sandwiched between two slower speed stages. The speed of the middle stage is determined by whether the focal adhesions at the tail end in the initial low speed gliding retraction stage can be released in time. The actin bundles formed on the tail edge affect tail width evolution. In the narrow tail fast retraction, the interplay of membrane-cortex and actin bundle tensions, actin filament polymerization/depolymerization, cytoplasmic pressure, retardation of cytoplasmic flow through the narrow tail neck, leads to the developments of observed tail shape instabilities: tail end bulging, pearling, and wiggling.