Contact dynamics during keratocyte motility

Background: Keratocytes are specialised, rapidly moving cells that generate substantial contractile force perpendicular to their direction of locomoti on. Potential roles for contractile force in cell motility include cell-bod y transport, regulation of adhesion, and retraction of the cell's trailing edge. Results: To investigate contact dynamics, we used simultaneous confocal flu orescence and interference reflection microscopy to image keratocytes injec ted with fluorescent vinculin. We found that contacts formed behind the lea ding edge and grew beneath both the lamellipodium and the cell body. Contac ts in the middle of the cell remained stationary relative to the substrate and began to disassemble as the cell body passed over them. In contrast, co ntacts in the lobes of the cell grew continuously and more rapidly. incorpo rated more vinculin, and slid inwards towards the sides of the cell body. C ontact sliding often led to merging of contacts before their removal from t he substrate. Conclusions: We suggest a synthesis of two existing, apparently conflicting models for keratocyte motility, in which network contraction progressively reorients actin filaments using the contacts as pivots, forming bundles th at then generate lateral tension by a sliding-filament mechanism. Contact d ynamics vary between the middle of the cell and the lobes. We propose that laterally opposed contractile forces first enhance contact growth and stabi lity, but escalating force eventually pulls contacts from the substrate at the back of the cell, without interfering with the cell's forward progress.