Desmosome-cytoskeleton dynamics

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Desmosomal intercellular adhesions and their associated keratin intermediate filaments are hallmarks of epithelial differentiation with profound contributions to epithelial mechanics and function. Crosstalk between desmosomes and keratin filaments determines epithelial plasticity in different functional contexts. Emphasis was on the consequences of desmosomes for keratin organization during the previous project phase. We found, quite surprisingly, that nascent desmosomes serve as nucleation sites for elongating keratin filaments. Subsequent keratin filament bundling and desmosome fusion were also co-ordinated generating a stable transcellular keratin-desmosome scaffold in a "rim-and-spoke" arrangement consisting of interdesmosomal cortical keratin filament bundles (rim) and radial keratin filament bundles connecting desmosomes with the perinuclear keratin cage (spokes). Our observations further suggested that the morphogenesis and maintenance of the keratin-desmosome scaffold is guided by the actin cytoskeleton. We now want to investigate this relationship with a focus on the subplasmalemmal keratin-enforced actin-rich cell cortex as a major mechanical component of epithelial cells with potential functions in mechanosensing. Based on the hypothesis that dynamic interaction of the keratin-desmosome scaffold with the actomyosin cortex is important for epithelial tissue integrity and tissue re-organization, we will pursue three major aims: (i) Investigate the morphogenesis and maintenance of the cortical desmosome-associated actomyosin- and keratin-based cytoskeleton after selectively inactivating each major component, (ii) investigate the consequences of desmosome splitting and keratin filament-desmosome dissociation on distribution patterns and function of the actin cytoskeleton, and (iii) investigate keratin-desmosome dynamics and function in epithelial sheet migration. We will use fluorescent reporters to monitor cytoskeletal dynamics and desmosomal components by high-resolution time-lapse fluorescence microscopy in cultured epithelial cells on coated glass slides or specifically-tailored microprints. Genetic and pharmacologic approaches will be employed to inactivate and modulate specific components. Our goal is to contribute to the understanding of the properties and the role of the keratin-desmosome scaffold as a functional unit in epithelial plasticity.