Experimental models to analyze differentiation functions of cultured keratinocytes in vitro and in vivo

In this chapter, we present technical details for the generation of in vitro skin equivalents consisting of collagen gels with incorporated fibroblasts covered by proliferating and differentiating keratinocytes. Epithelial-mesenchymal interactions are clearly manifest in these skin equivalents. Therefore, they have proven to be suitable experimental tools for a broad range of applications, e.g., for studies on the the paracrine regulation of keratinocyte differentiation and proliferation. On the other hand, in vivo assays cannot be abandoned totally, in particular, when such properties as malignant growth potential, disturbed differentiation control in carcinogenesis, and impact on angiogenesis are concerned. For that reason, we additionally describe xenotransplantation techniques to graft human keratinocytes and skin equivalents, respectively, onto the dorsal muscle fascia of thymus-aplastic mice.