Fig 2: Immature type I and type II vestibular hair cells in IEOs(A) UMAP plot of annotated human inner ear atlas highlighting hair cells (HCs).(B) UMAP plot comparing reference hair cell population (left) and mapped IEO-derived hair cell population (right) using Symphony.(C) Density plots of reference hair cell population (left) for immature, type I, and type II vestibular markers, and density plots of mapped IEO-derived hair cells showing expression of immature markers.(D) Schematic depicting morphological differences between type I and type II vestibular hair cells.(E) Calyx-type synapse (TUBB3+) surrounding a hair cell (MYO7A+). Scale bar, 10 µm.(F) Expression of ANXA4 and OCM in hair cells of a D75 IEO, showing subsets with none, either, or both. Scale bar, 10 µm.(G) OCM expression in hair cells of human fetal utricle (FW10.6). Scale bar, 10 µm.(H) ANXA4 expression in human fetal utricle (FW10.6). Scale bar, 10 µm.(I) Methylene blue-azure II staining of a D74 IEO-vesicle containing hair cells (arrow and “HC”). Scale bar, 20 µm.(J) Hair bundle with stereocilia and kinocilium cross-section (arrow). Scale bar, 1 µm.(K) Apical region of a hair cell with cuticular plate (yellow) and stereociliary rootlets. Scale bar, 1 µm.(L) Basal region of a hair cell showing synaptic ribbons (arrow) and bouton-like synapses (“N”). Scale bar, 500 nm.(M) Transection of type I vestibular hair cell almost entirely surrounded by calyx-type synapse (in red). Scale bar, 500 nm.(N) OTOF expression in MYO7A+ hair cells. Scale bar, 10 µm.(O) H&E overview with CDH23 in stereocilia by IHC. Scale bars: H&E, 100 µm; IHC, 20 µm.(P) H&E overview with WHRN in stereocilia by IHC. Scale bars: H&E, 100 µm; IHC, 20 µm.H&E and IHC images are representative of n = 6 aggregates (=2 experiments) (E, F, and N–P) or n = 2 human inner ear tissues of matching fetal age (G and H). TEM images are representative of n R 3.