Fig. 1

a Schemes representing a single auditory HC from the lateral/abneural (top) or medial/neural (bottom) side, and HC orientation (arrows) in the auditory epithelium and the utricular and saccular maculae. In the maculae, two HC populations of opposing orientations are separated by a virtual line of polarity reversal (LPR, yellow dashed line). Domains where HC orientation was quantified in e, f are indicated in blue (utricle: lateral extrastriolar (LES), LPR and medial (M) domains; saccule: anterior (ANT), LPR and posterior (POST) domains). b Phylogenetic tree of class C GPCRs adapted from⁶². c, d LPR region in P2 utricle (c) and saccule (d). Top panels show a low magnification view with SPTBN2 (βII-spectrin) labeling revealing HC orientation by the position of the off-center fonticulus devoid of signal. Bottom panels show a distinct region at higher magnification where PCNT (Pericentrin) labels the basal body below the fonticulus. The LPR can be traced in controls but not in mutants, where all HCs generally point laterally in the utricle and anteriorly in the saccule. e, f Circular histograms of HC orientation by region in the utricle (e) and saccule (f). Histograms show frequency distribution at P0-P2 (10° bins in a referential where 90° (top) is lateral in the utricle and anterior in the saccule; n indicates HC number in N = 4 animals; Watson U2 test of homogeneity; normalized difference (ND) value indicates how many standard deviations separate the circular means of each distribution). PTXa indicates the Cre-inducible R26-LSL-PTXa allele. Littermate controls for FoxG1-Cre; PTXa are Cre-negative PTXa animals. Arrows indicate HC orientation. Scale bars are 20 µm (c, d top), 5 µm (c, d bottom).