Models of epithelial histogenesis.

Epithelial tissues emerge from coordinated sequences of cell renewal, specialization and assembly. Like corresponding immature tissues, adult epithelial tissues are provided by stem cells which are responsible for tissue homeostasis. Advances in epithelial histogenesis has permitted to clarify several aspects related to stem cell identification and dynamics and to understand how stem cells interact with their environment, the so-called stem cell niche. The development and maintenance of epithelial tissues involves epithelial-mesenchymal signalling pathways and cell-matrix interactions which control target nuclear factors and genes. The tooth germ is a prototype for such inductive tissue interactions and provides a powerful experimental system for the study of genetic pathways during development. Clonogenic epithelial cells isolated from developing as well mature epithelial tissues has been used to engineer epithelial tissue-equivalents, e.g. epidermal constructs, that are used in clinical practise and biomedical research. Information on molecular mechanisms which regulate epithelial histogenesis, including the role of specific growth/differentiation factors and cognate receptors, is essential to improve epithelial tissue engineering.