Organization of Keratin Filaments in Skin Keratinocytes
The indirect immunofluorescence preparation illustrates the organization of the keratin intermediate filament array in the cytoplasm of two neighboring epidermal keratinocytes in primary culture. Typically, the keratin filament network spans the entire cytoplasm in these two neighboring keratinocytes. The top left inset shows 10 nm keratin intermediate filaments reconstituted in vitro from purified proteins and viewed by negative staining and electron microscopy. Such preparations in which individual filaments are loosely aggregated are obtained when using standard in vitro assembly buffer conditions (low ionic strenght, pH 7.4). The bottom right inset shows large bundles of keratin filaments as seen by differential interference contrast (DIC) in the light microscope. The formation of such macro-assemblies in vitro can be promoted by small changes in buffer conditions (e.g., shift to pH 7.0 or addition of salt). [Note: Individual 10 nm filaments can not be seen using DIC imaging under the light microscope]. Bundles represent the preferred mode of organization of keratin filaments in epidermal keratinocytes, as is suggested by the immunofluorescence staining pattern. This image was created by So Yamada, a former graduate student in the laboratory now on the faculty at UC Davis in California.
