Epithelial-mesenchymal transition contrast in the amputated tail and limb of the northern house gecko, Hemidactylus flaviviridis.

Abstract

The northern house gecko Hemidactylus flaviviridis exhibits appendage-specific responses to injuries. The autotomized tail regenerates, whereas the severed limb fails to regrow. Many site-specific cellular processes influence tail regeneration. Herein, we analyzed the epithelial-mesenchymal transition contrast in the lizard's amputated appendages (tail and limb). Morphological observations in the healing frame indicated the formation of regeneration blastema in the tail and scar formation in limb. Histology of the tail showed that epithelial cells closer to mesenchyme appeared less columnar and loosely packed, with little intercellular matrix. Whereas in the limb, the columnar epithelial cells remained tightly packed. Collagen deposition was seen in the limb at the intersection of wound epithelium and mesenchyme, favoring scarring by blocking the epithelial-mesenchymal transition. Markers for epithelial-mesenchymal transition were assessed at transcript and protein levels. The regenerating tail showed upregulation of N-cadherin, vimentin, and PCNA, favoring epithelial-mesenchymal transition, cell migration, and proliferation, respectively. In contrast, the scarring limb showed persistently elevated levels of E-cadherin and EpCAM, indicating retention of epithelial characteristics. An attempt was made to screen the resident epithelial stem cell population in both appendages to check their potential role in the epithelial-mesenchymal transition (EMT), hence the differential wound healing. Upregulation in transcript and protein levels of Nanog and Sox2 was observed in the regenerating tail. Fluorescence-activated cell sorting (FACS) provided supporting evidence that the epithelial stem cell population in tail remained significantly higher than in limb. Thus, this study focuses on the mechanistic role of the epithelial-mesenchymal transition in wound healing, highlighting the molecular details of regeneration and scarring events.