Figure 3

Delayed deletion of Sox2 results in the differentiation of some neurosensory cells in the basal cochlear turn and in the vestibular organs.

(a,b) Sox2⁺ cells in the Sox2 CKO cochlea are detected only in the base at the age of E14.5 and disappear later in development. (b) The strong Sox2 expression domain is shifted toward the GER. Similarly, Myo7a⁺ cells do not differentiate in the proper area of OC. Some weak Sox2 expression remains in the OC area of Sox2 CKO (dotted area). (c,d) Variable numbers of HCs (Myo7a⁺) and supporting cells (Sox2⁺) develop in the Sox2 CKO vestibular system. (d) HCs in the saccule also develop in the area that lacks supporting cells (arrow). (e–h) Some poorly differentiated Myo7a⁺ HCs are present in the utricle, saccule and basal turn of the cochlea of the Sox2 CKO at E17.5. (i–m) At E18.5, the innervation of mutant cochlea, saccule and utricle is severely reduced and shows an unusual pattern compared to controls. Fibers show mostly directional growth toward remaining HCs but also transient expansion into HC-free regions. (n) The quantification of Myo7a positive HCs after whole mount immunostaining shows a striking reduction of HCs in the Sox2 CKO inner ear compared to littermate controls for the utricle (U), saccule (S) and cochlea (Co). Myo7a⁺ HCs were counted after whole mount immunostaining using LAS AF Lite draw counter to avoid counting error. The total number of HCs was determined in the entire utricle and saccule, and in the entire Sox2 CKO cochlea. The number of HCs in the control cochlea represents the total number of HCs in 1.5 mm of the base. The values represent means ± SD (N = 4–7 individuals/group). *P < 0.0001, t-test. Scale bars: 50 μm (a–h), 100 μm (i–m). AC, anterior crista; GER, greater epithelial ridge; HC, horizontal crista; OC, organ of Corti; S, saccule; U, utricle.