Fig. 2.

A mesenchymal-to-epithelial transition leads to hair cell differentiation. (a–c) The utricle sensory epithelium fixed in situ. (d–f) Fixed 2D cell cultures. (g–j) Spheres of sensory epithelium produced by dissociation and aggregation of cells from 2D cultures under conditions that prevented adhesion to a substrate. Phalloidin labeled F-actin that was in cortical bands and hair bundles, and the hair cells expressed myosin VIIa in the epithelia of the utricle and the spheres (a and g in A, B, and D). F-actin was organized as stress fibers, and there was no expression of myosin VIIa in the 2D cultures (d in A, B, and D). Likewise, E- and N-cadherin were expressed in the epithelia (b and h in A and B) but were absent from the cells cultured on 2D substrates. The sensory epithelia also expressed the hair cell marker calretinin (b and h in C) but not the mesenchymal intermediate filament, vimentin, or the mesenchymal transcriptional factor, slug (b and h in D). Both vimentin (e in C) and slug (e in D) were expressed in the cells cultured and passaged in 2D culture, but those mesenchymal proteins were not detectable in the epithelia that formed via aggregation (h in C and D). (Scale bars: 10 μm.)