1 - Defining the function(s) of K6, K16, and K17 in vivo
Two obvious questions spring to mind when looking at the family of keratin proteins: Why so many ? What is the relationship between keratin expression and epithelial structure and function ? To address those questions, we are attempting to define the properties and function of a subset of keratin genes, the type II K6 isoforms and the type I K16 and K17, which are remarkable by several criteria. We do so by various types of genetic manipulations in transgenic mice, ranging from gene knock-out to forced expression of particular keratin sequences in a tissue-specific or ectopic fashion. An important element of our approach is that we study these genes and their products relative to a host of other keratins expressed in the skin and in simple epithelia.

2 - The wound repair response in adult skin, and its relationship to other processes
While keratins 6,16 and 17 are probably best known for their expression during wound repair and in the context of diseases such as psoriasis and cancer, these genes are also constitutively expressed in specific epithelial cell types within adult skin appendages (hair, nail, glands, tooth, etc.) and in internal complex epithelia (additional information). The hair, in particular, undergoes a cycle throughout life, with a phase of active growth interspersed with periods of involution and rest. At another level, these genes are each expressed according to a unique spatio-temporal pattern in developing skin and internal complex epithelia. A few other genes (e.g., connexin 26, a gap junction-forming protein) are regulated in a similar pattern. Altogether, these observations reinforce the belief that there exist a significant relationship between these various types of events. Indeed, psoriasis has been likened by some researchers to a deregulated wound repair response, while the latter is believed to be a recapitulation of specific developmental events. We believe that K6 isoforms, K16 and K17 belong to a group of genes (akin to a bacterial operon without the contiguous genomic organization) which are co-regulated at the transcriptional level and whose products put the keratinocyte into a specific mindset that enables plasticity of "choices" and of cellular activities. Continued studies of the significance of keratin gene expression in complex epithelia by us and many other groups will undoubtedly contribute to expand our understanding of the biology of these fascinating tissues.

3 - The biochemical and biophysical bases for the function of keratin filaments
Several criteria distinguish keratin and other types of intermediate filaments from the other cytoskeletal polymers, F-actin and microtubules. We are interested in understanding the process of keratin polymerization and filament network organization insofar as they pertain to the biological processes that we study in complex epithelia. We are also interested in the contribution of the non-helical end domains to the properties and function of keratin filaments. Much of the diversity among IF sequences, including keratins, stems from variations within the so-called head and tail domains. It thus appears likely that these domains play an important role in adapting intermediate filament polymers to the needs of the cell they find themselves in.

The function of structural scaffolding has been shown to be shared by most types of keratin polymers. In the context of a fruitful collaboration with Denis Wirtz and his colleagues (Dept. Chemical Engineering, Johns Hopkins University), we are utilizing biophysical methods to characterize the mechanical properties of suspension of keratin filaments in an in vitro setting. Now that we have an idea of the mechanical potential of keratin assemblies and of the source of their solid-like features, we are particular interested in i) comparing various types of keratin polymers; ii) mapping specific biophysical traits to specific domains within keratin sequences; and iii) undertansding how inherited mutations in keratin sequences result in epithelial fragility disorders.