Figure 3

Cyclin-dependent kinase inhibitor p27^Kip1 expression demarcates the expansion of the post-mitotic sensory domain within the developing utricle. Pregnant Atoh1/EGFP female mice were injected with EdU three times at 2-h intervals at E11.5 (A,D,G,J), E12.5 (B,E,H,K,M–P) or E13.5 (C,F,I,L), and utricle samples were harvested 6 h after the initial injections. Whole-mount (A–L) and cross-section (M–P) preparations of harvested utricles were stained for EdU and p27^Kip1. No p27^Kip1 expression was found at E11.5, while Atoh1/EGFP expression occurs early (A,D,G,J). The expression of P27^Kip1 marked the same domain of minimum EdU incorporation where the early formations of Atoh1/EGFP⁺ hair cells were located at E12.5 (B,E,H,K). The p27^Kip1 domain expanded, overlapping with the increased Atoh1/EGFP⁺ sensory domain, which was devoid of EdU incorporation at E13.5 (C,F,I,L). It appeared that the developing sensory domain expanded from the striolar region (outlined by white lines) toward the MES from E12.5 to E13.5 (B–L). Cross sections (M–P) revealed the developing sensory epithelia in the utricle, saccule and the lateral crista(LC). White and yellow brackets mark the striolar and MES regions of the utricle, respectively. Scale: 100 μm.