Desmoplakin: an unexpected regulator of microtubule organization in the epidermis

Despite their importance in cell shape and polarity generation, the organization of microtubules in differentiated cells and tissues remains relatively unexplored in mammals. We generated transgenic mice in which the epidermis expresses a fluorescently labeled microtubule-binding protein and show that in epidermis and in cultured keratinocytes, microtubules stereotypically reorganize as they differentiate. In basal cells, microtubules form a cytoplasmic network emanating from an apical centrosome. In suprabasal cells, microtubules concentrate at cell-cell junctions. The centrosome retains its ability to nucleate microtubules in differentiated cells, but no longer anchors them. During epidermal differentiation, ninein, which is a centrosomal protein required for microtubule anchoring (Dammermann, A., and A. Merdes. 2002. J. Cell Biol. 159:255-266; Delgehyr, N., J. Sillibourne, and M. Bornens. 2005. J. Cell Sci. 118:1565-1575; Mogensen, M.M., A. Malik, M. Piel, V. Bouckson-Castaing, and M. Bornens. 2000. J. Cell Sci. 113:3013-3023), is lost from the centrosome and is recruited to desmosomes by desmoplakin (DP). Loss of DP prevents accumulation of cortical microtubules in vivo and in vitro. Our work uncovers a differentiation-specific rearrangement of the microtubule cytoskeleton in epidermis, and defines an essential role for DP in the process.