[Expression of cytokeratins during embryogenesis and in pathologic epithelia]

Epithelial cell intermediate filaments, or cytokeratins, are excellent markers for cell differentiation. During embryogenesis, cytokeratins specific of a stage of differentiation step always become detectable before corresponding morphologic changes: for instance, cytokeratins 5 and 14 are found around the eight week, shortly before stratification of the epithelium occurs, and cytokeratins 1 and 10 are produced before morphologic evidence of keratinization becomes detectable. Among potential diagnostic applications, analysis of cytokeratin patterns of epidermal cells desquamated in the amniotic fluid may provide earlier and less invasive diagnosis than fetoscopic biopsies. Similarly, a review of cytokeratins expressed in a variety of epithelial diseases (involving the epidermis, digestive tract, respiratory tract, urogenital tract, or breast) demonstrated persistence of the original tissue pattern in some instances (this was the case for the majority of simple epithelia) but not in others (complex epithelia). This suggests that cytokeratins may prove valuable as markers for specific tumor stages or types and may provide earlier information than morphologic studies.