A transgenic reporter under control of an es1 promoter/enhancer marks wound epidermis and apical epithelial cap during tail regeneration in Xenopus laevis tadpole

Rapid wound healing and subsequent formation of the apical epithelial cap (AEC) are believed to be required for successful appendage regeneration in amphibians. Despite the significant role of AEC in limb regeneration, its role in tail regeneration and the mechanisms that regulate the wound healing and AEC formation are not well understood. We previously identified Xenopus laevis es1, which is preferentially expressed in wounded regions, including the AEC after tail regeneration. In this study we established and characterized transgenic Xenopus laevis lines harboring the enhanced green Fluorescent protein (EGFP) gene under control of an es1 gene regulatory sequence (es1:egfp). The EGFP reporter expression was clearly seen in several regions of the embryo and then declined to an undetectable level in larvae, recapitulating the endogenous es1 expression. After amputation of the tadpole tail, EGFP expression was re-activated at the edge of the stump epidermis and then increased in the wound epidermis (WE) covering the amputation surface. As the stump started to regenerate, the EGFP expression became restricted to the most distal epidermal region, including the AEC. EGFP was preferentially expressed in the basal or deep cells but not in the superficial cells of the WE and AEC. We performed a small-scale pharmacological screening for chemicals that affected the expression of EGFP in the stump epidermis after tail amputation. The EGFP expression was attenuated by treatment with an inhibitor for ERK, TGF-β or Reactive Oxygen Species (ROS) signaling. These treatments also impaired wound closure of the amputation surface, suggesting that the three signaling activities are required for es1 expression in the WE and successful wound healing after tail amputation. These findings showed that es1:egfp Xenopus laevis should be a useful tool to analyze molecular mechanisms regulating wound healing and appendage regeneration.