Collective cell migration of primary zebrafish keratocytes.

Fish keratocytes are an established model in single cell motility but little is known about their collective migration. Initially, sheets migrate from the scale at ~145 µm/h but over the course of 24h the rate of leading edge advance decreases to ~23 µm/h. During this period, leader cells retain their ability to migrate rapidly when released from the sheet and follower cell area increases. After the addition of RGD peptide, leader cell lamellae are lost, altering migratory forces within the sheet, resulting in rapid retraction. Leader and follower cell states interconvert within minutes with changes in cell-cell adhesions. Leader cells migrate as single cells when they detach from the leading edge and single cells appear to become leader cells if they rejoin the sheet. Follower cells rapidly establish leader cell morphology during closing of holes formed during sheet expansion and revert to follower cell morphology after hole-closure. Inhibition of Rho associated kinase releases leader cells and halts advancement of the leading edge suggesting an important role for the intercellular actomyosin cable at the leading edge. In addition, the presence of the stationary scale orients direction of sheet migration which is characterized by a more uniform advance of the leading edge than in some cell line systems. These data establish fish keratocyte explant cultures as a collective cell migration system and suggest that cell-cell interactions determine the role of keratocytes within the migrating sheet.