Nematostella wound healing is mediated by ERK signaling. Inhibition of ERK signaling by U0126 disrupts normal wound healing and regeneration. (A) Animals that underwent oral-aboral bisection regenerate oral structures by 72 hours, whereas (B) animals soaked for three days in 10 μM U0126 (MAPK inhibitor) did not regenerate lost heads. (C,D) Heads that had to regenerate lost aboral structures exhibited wound healing defects when soaked in 10 μM U0126 for three days. (E,F) Aboral view of phallacidin-stained animal tissue exposed to 10 μM U0126 for six hours after injury lacked proper wound closure. (G,H) Puncture wounds caused local activation of phosphorylated-ERK around the site of injury, where incubation with U0126 blocks phosphorylated activity of ERK around the site of injury. (I) Animals were pre-soaked in U0126 for one hour, injured, and analyzed with the DeadEnd tunnel assay for apoptosis. Exposure of injured animals to U0126 did not block the activation of apoptosis after injury. (J-L) Scanning laser confocal images of (J) injured animals that were soaked in U0126 for 12 hours; (K) injured animals that were soaked in U0126 for 12 hours before the U0126 removed, and then placed in 1/3× seawater for an additional six hours; and (L) wild-type injured animals at six hours. Animals exposed to U0126 for prolonged periods of time (J) remained in a compacted state as a result of wounds never healing. Removal of U0126 at 12 hours allowed animals to reinitiate wound healing (K) and the animals were morphologically similar to animals at six hours (L). (Red arrowhead in all images is used to identify the position of the wound). Black color in E and F and the white color in J to L are from phallacidin-FL, while the blue color in G and H and J to L is created from DAPI-labeled nuclei. wt, wild-type; UO, U0126.