Fig. 1: A close look inside the inner ear: the balance organ and its sensory epithelium.
From: Revealing heterogeneity and damage response in the adult human utricle
a Anatomical illustrations of the human inner ear encasing the utricle, a vestibular organ responsible for detecting head tilt and sensing linear acceleration, located within the vestibular region of the temporal bone. The utricular sensory epithelium contains sensory hair cells (HCs) and non-sensory supporting cells (SCs). Type I HCs are characterized by a narrow neck leading to a flask-shaped cell body, while type II HCs exhibit a cylindrical shape with the nucleus positioned higher in the cytoplasm. b H&E-stained utricle shows the organ structural integrity: HCs (eosin-stained pink cytoplasm), supporting cells nuclei (hematoxylin-stained, dark purple), and a small area with missing cells (white space between cells). Sensory nerve fibres are visible in the mesenchyme, n > 3. Scale bar = 100 μm. c Image showing the intactness of a dissected patient-derived utricle, representing the entire balance organ; inset shows sagittal axis (A-P, anterior-posterior) and frontal axis (M-L, medial-lateral), n > 3. d SEM micrograph of flat epithelium showing complete loss of HCs. e–g New/nascent HCs in the supporting cell layer of adult human utricles, which were previously reported4,18. In (e) SEM image shows four sensory cells: HC-1 without stereocilia, HC-2 with stereocilia rootlets on the surface, and HC-3 with kinocilium and short hair bundles as well as a new HC; f nascent hair cells MYO7A+ (green)/SOX2− (magenta), counterstained with DAPI (blue), are located at the basal region of the sensory epithelium, see also (h); (g) SEM image shows a new HC with short stereocilia. N = 3 for all SEM micrographs. Progressive numbers in the images reflect the numbers in the anatomical illustration in (a). h Immunofluorescence of MYO7A (green) and SOX2 (magenta) in a human utricle cross-section, counterstained with DAPI (blue). Inset (63x magnification of area outlined in white) highlighting the three main cell types: HC type I (MYO7A+/SOX2-), type II (MYO7A+/SOX2+), and supporting cell (SOX2+), n > 3. Schematics (created in BioRender. Luca, E. (2025), https://BioRender.com/zejtybk) illustrate the morphology of HCs and the expression of the subtype-specific nuclear marker SOX2 alongside cytoplasmatic marker MYO7A. Scale bars = 100 μm (b, e, h), 25 μm (inset in h), 1 mm (c), 50 μm (d), 10 μm (f, g).
