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Introduction: Crocodiles have a very high capacity for wound healing, notably of the skin. During skin wound healing, proliferation and differentiation of keratinocytes takes place together with alterations of molecules such as cytokeratins, which are important intermediate filaments of the cytoskeleton. The aim of this study was to establish a marker for cytokeratins in order to investigate the distribution of these molecules in the crocodilian skin and other tissues.
Materials and Methods: Estuarine Crocodile skin samples of head, neck, belly, dorsal trunk and tail as well as samples from most organs and tissues were taken at different developmental stages (in ovo day 14, juvenile, adult). Immunohistochemistry was done on paraffin sections using an antibody against epidermal keratins of human origin cross reactive to many species (mouse-anti-keratin, clone AE3, Chemicon International, Inc.). Clone AE3 recognizes the cytokeratins of the basic subfamily cytokeratins 1-8.
Results: AE3 was established successfully as a marker of cytokeratins in the crocodile. Positive staining was detected in the cytoplasm of the epidermal layer cells, except for the superficial cells, in prenatal and adult skin. Osteoderm and adipose tissue cells were strongly positive for the marker. Epithelial cells of the tongue (mucosal and glandular epithelium), liver (bile ducts), perineurium and dura mater also reacted positively. Conclusion: The positive staining for cytokeratins in both mesodermally derived adipose tissue and ectodermal epithelial cells of the skin were remarkable. Stem cells derived from adipose tissue can differentiate into epithelial cells (Chavez-Munoz et al. PLoS ONE 2013; e80587). We propose that the expression of cytokeratins may indicate the origin of these cells from a single stem cell type and that the very high wound healing capacity of crocodilians may be linked to the differentiation of adipose cells into epithelial cells.