Fundulus deep cells: Directional migration in response to epithelial wounding

During the normal embryogenesis of the killifish Fundulus heteroclitus deep cells migrate in an apparently random fashion throughout the subepithelial space of the yolk sac. These cells migrate by blebbing locomotion, and individual cells show tendencies for persistence in the directionality of their movement. Immediately after the wounding of the yolk sac epithelium (the enveloping layer), these deep cells reorient and migrate directionally toward the site of wound closure. This directional migration results in the aggregation of a large number of cells at the wound site. The response is both rapid and widespread; cells as far away as 800 μm respond as quickly as those nearby, and by 100 min after wounding up to 90% of the blebbing deep cells within this radius have clustered about the wound site. Then, cells begin to disperse, and by 150 min after wounding, it is almost impossible to tell where the wound had been made. Because of the transparency of the Fundulus yolk sac, this phenomenon can be utilized as a model system for observing details of in vivo directional cell movements. Time-lapse video micrography has revealed that the modes, rates, and overall cell morphologies during locomotion are identical for cells migrating in both unwounded and wounded embryos. What is different in the wounded embryos is that a single directionality is imposed upon a large population of cells, resulting in aggregation. Several aspects of the aggregation phenomenon suggest that a possible attractant originating at the wound site may travel through the subepithelial space by diffusion.