Fig. 5. Spatiotemporal shroom2 distribution in the mouse auditory epithelia. (A-D) At E12, shroom2 colocalizes with ZO-1 at the apical surface of all the epithelial cells delineating the cochlear duct (cd) (A). As development proceeds, the shroom2 labeling becomes more intense in the sensory epithelium (organ of Corti) (B). At birth, a transient diffuse labeling is observed throughout the cytoplasm of the sensory inner (IHC), and outer (OHC) hair cells (^* over cell bodies), and pillar (p) cells (C). This cell body labeling decreases at later stages, and is not detected from P10 onwards (D). The bulk of shroom2 labeling is associated with the tightly joined apical domains of the hair cells and their adjacent supporting cells, forming the reticular lamina (D), and also at the apical cell-cell junctions of the marginal cells in the stria vascularis (arrowheads in E). The stria vascularis is a bilayer epithelium of the cochlear duct lateral wall, which secretes K⁺ in the endolymph (the fluid filing the cochlear duct) and produces the endocochlear potential. (F) Whole-mount preparation of a mouse organ of Corti at P2, illustrating the codistribution of shroom2 and myosin VIIa. (G) The absence of myosin VIIa in shaker-1 mutant mice does not alter the normal targeting of shroom2 in the hair cells. Stronger shroom2 labeling is observed in the reticular lamina, whereas weaker labeling is seen in other supporting cells (arrows). Bars, 10 µm.