Cell proliferation was determined by EdU (5-ethynyl-2′-deoxyuridine; Life Technologies, Eugene, OR, USA) incorporation. Mice were labeled with 100 μg EdU/g body weight by intraperitoneal injection for 4 hours following a debridement wound. Unwounded littermate control mice also received EdU injections, providing proliferation control sections. Thereafter, the mice were killed by CO2 inhalation and their eyeballs enucleated, fixed in 2% buffered paraformaldehyde, and treated for 15 minutes in 0.1% sodium borohydrate. The tissues were then embedded in Tissue-Tek embedding medium (Sakura Finetek USA, Inc., Torrance, CA, USA) for cryosectioning. Sections (10 μm) were cut using a CryoStar NX70 (Thermo Scientific, Waltham, MA, USA) cryostat and collected on Fisherbrand SuperfrostPlus Gold microscope slides (Thermo Scientific). Upon use, sections were incubated for 30 minutes at 37°C, and excess tissue embedding medium was removed with PBS. Unspecific protein binding sites were blocked with 5% fetal bovine serum (FBS). The incorporated EdU was developed using the Click-IT Alexa Fluor 647 kit (Life Technologies) to reveal the incorporated EdU. The nuclei were counterstained with DAPI. Images were captured using a Zeiss Observer Z1 inverted microscope or Zeiss LSM-710 confocal microscope and images analyzed using the Zeiss LSM Image Browser 3.2 software (Zeiss, Oberkochen, Germany).