Mechanisms of cortical microtubule organization in epidermal keratinocytes

Microtubules in many differentiated cell types are reorganized from a radial, centrosome-bound array into a cell type-specific, non-centrosomal network. In epidermal keratinocytes, cortical microtubules are organized from desmosomes (Lechler, T., and Fuchs, E. 2007. J. Cell Biol. 176:147-154). Details of this organization are poorly understood. We used immunofluorescence expansion microscopy to visualize directly the contact between cortical microtubules and desmosomes in murine skin tissue. Microtubule bound laterally to desmosomes, or with their ends at mixed polarity. Experiments including time-lapse microscopy of EB3-GFP, microtubule regrowth after depolymerization, and expression of ectopic ninein that was sequestered to the plasma membrane with a CAAX sequence motif, indicated that limited nucleation of microtubules can occur at the cortex, but mostly, cortical microtubules may accumulate by translocation from non-cortical sites and anchorage to desmosomes.