Changes in keratin gene expression are closely associated with the commitment of mammalia epidermal cells to terminal differentiation. The induction of the differentiation-specific keratin genes (Kl and Kl0) is a very early event, since it can be observed by in situ hybridization and double-label immunofluorescence in some basal cells prior to migration away from the basement membrane. The induction of a new subset of keratin genes presumably has functional significance, but the exact role of these structural proteins in terminal differentiation of the epidermis remains to be determined. Alterations in the normal program of terminal differentiation have been observed in several inherited skin disorders and skin cancer. An understanding of the molecular mechanisms regulating expression of the differentiation-specific keratin genes could provide insight into mechanisms regulating normal epidermal differentiation. Classical approaches, consisting of the insertion of putative regulatory sequences into reporter constructs, followed by DNA-transfection into primary mouse epidermal cells are the induction of terminal differentiation by an increase in extracellular calcium, have not been successful. Therefore, the transgenic mouse model is the only alternative experimental system to address questions concerning gene expression during terminal differentiation. This system will be used to identify sequences important for tissue-, development- and differentiation-specific expression of keratin genes (Kl and Kl0) expressed during terminal differentiation of epidermal cells. Proteins that interact with sequences shown to be important for appropriate expression in transgenic mice will be characterized and eventually the genes encoding these proteins will be cloned. In addition, mutations suspected of impairing keratin filament assembly and/or function will be produced and introduced into the germ-line of mice to determine if inherited skin disorders can be mimicked by this approach. Finally, existing mouse and human mutations known to affect epidermal differentiation will be examined to determine if there is direct involvement of the keratin genes in these defects or whether these defects result from a failure of the epidermis to respond to normal differentiation signals.
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