The long range objective of this research is an understanding of the biochemical mechanisms that operate and regulate the expression of keratin genes during differentiation and development in human epithelial tissues. The human epidermis has been chosen as s model system, since we are able to serially cultivate these cells in vitro under conditions where many of their differentiative properties, including stratification are retained. The keratins are the major differentiation-specific proteins in these cells, They are a family of >20 fibrous proteins (MW 40-67K) that form 8 nm filaments in the cytoskeletons of all and only epithelial cells. They appear to be specifically tailored to suit the varied protective and structural needs of each epithelial cell. Keratins can be subdivided into two distinct groups, type 1 and type 11, and a member of each is essential for filament assembly. Type 1 and type 11 proteins are frequently expressed as specific pairs, and typically 1-3 pairs are expressed at any one time. During the course of differentiation in epidermis, this subset changes concomitantly with an increase in keratin synthesis, leaving the fully differentiated cell with 85% of its total protein as keratins. Additional changes in keratin patterns are observed during development, in wound-healing, and in a number of human skin diseases, As such, the pattern of keratins expressed by an epithelial cell may provide a powerful diagnostic tool for genetic diseases and cancers of epithelia, In order to assess the potential value of keratin expression in medicine, it is essential that we understand the functional and structural significance of the multiplicity of keratin sequences and their role in differentiation and development. We have isolated and characterized a number of the human genes encoding these keratins, and we have prepared specific cRNA probes to detect different keratin mRNAs, and monospecific antibody probes to detect different keratin proteins. We are currently using these tools to 1) examine the role of different keratin sequences in filament assembly; 2) examine the mechanism by which specific keratin pairs are selected from the repertoire of keratin genes, and how the two types are regulated in balance; 3) explore the function of keratins using an in vivo as well as an in vitro approach; and 4) examine the molecular basis of altered keratin expression in certain genetic skin diseases.