Epithelial cell dynamics can be difficult to study in intact animals or tissues. Here we use the medusa form of the hydrozoan Clytia hemisphaerica, which is covered with a monolayer of epithelial cells, to test the efficacy of an orientation-independent differential interference contrast microscope for in vivo imaging of wound healing. Orientation-independent differential interference contrast provides an unprecedented resolution phase image of epithelial cells closing a wound in a live, nontransgenic animal model. In particular, the orientation-independent differential interference contrast microscope equipped with a 40x/0.75NA objective lens and using the illumination light with wavelength 546 nm demonstrated a resolution of 460 nm. The repair of individual cells, the adhesion of cells to close a gap, and the concomitant contraction of these cells during closure is clearly visualized.

All animals have mechanisms for healing damage to the epithelial sheets that cover the body and line internal cavities. Epithelial wounds heal either by cells crawling over the wound gap, by contraction of a super-cellular actin cable (“purse string”) that surrounds the wound, or some combination of the two mechanisms. Both cell crawling and purse string closure of epithelial wounds are widely observed across vertebrates and invertebrates, suggesting early evolution of these mechanisms. Cnidarians evolved ~600 million years ago and are considered a sister group to the Bilateria. They have been much studied for their tremendous regenerative potential, but epithelial wound healing has not been characterized in detail. Conserved elements of wound healing in bilaterians and cnidarians would suggest an evolutionary origin in a common ancestor. Here we test this idea by characterizing epithelial wound healing in live medusae of Clytia hemisphaerica.