Figure 4(A) Scanning electron micrographs of cochlear tissue from P19 animals indicate no HC loss in the absence of Elp3 but illustrate some defects of polarity, as misaligned HCs and dysmorphic stereociliary bundles are visible (red arrows and white arrowheads, respectively). Scale bars=5µ(B) Surface view of P1 actin-stained organ of Corti confirms defective establishment of polarity in Elp3cKO as numerous stereociliary bundles are misaligned along the medio-lateral axis (M-L) or misshaped. Scale bars=5µm. Data information: #IHC; *OHC1; **OHC2; ***OHC3(C) Elp3cKOs exhibit a broader distribution of hair cell orientation. The angles of deviation between the stereociliary bundle and the medio-lateral axis are plotted in rose diagrams, for each OHC row. Whereas the majority of WT bundles are pointing to the most lateral region of the tissue (within a range of 10°), many Elp3cKO bundles of the two last rows of OHCs present increased angles of deviation (WT/Elp3cKO OHC1: n=99/99, p>0.1, DF=99; OHC2: n=99/100, p<0.001, DF=99; OHC3: n=99/98, p<0.001, DF=98; pooled data from 6 animals per genotype; Watson U2 test). Data information: #IHC; *OHC1; **OHC2; ***OHC3Elp3cKOs HCs harbour a flatter stereociliary bundle that is centrally shifted. (D) Scanning electron micrographs of HCs from P1 WT and Elp3cKO cochleae (scale bar=2µm) illustrating the misshaped stereociliary bundles and the shorter kinocilium (false coloured in pink) of Elp3cKO HCs. Data information: #IHC; *OHC1; **OHC2; ***OHC3Elp3cKOs HCs harbour a flatter stereociliary bundle that is centrally shifted. (E) Graph presents the mean angle of HC bundle (n=6 animals; one-way ANOVA, Tukey's multiple comparisons test; ***p<0.001, F=13.69, DF=7; mean±SD).Elp3cKOs HCs harbour a flatter stereociliary bundle that is centrally shifted. (F) Elp3cKO HCs possess a significantly larger bare zone (WT/KO IHC: n= 23/24 cells; OHC1: n=27/27; OHC2: n=27/29; OHC3: n=30/29; cumulative data collected from 3 animals per genotype; One-way ANOVA, Tukey's multiple comparisons test; ***p<0.001, *p<0.05 F=16.72, DF=7; mean±SD).Elp3cKOs HCs harbour a flatter stereociliary bundle that is centrally shifted. (G) Elp3cKO HCs possess a significantly smaller medial zone (WT/KO IHC: n= 23/24 cells; OHC1: n=27/27; OHC2: n=27/29; OHC3: n=27/29; cumulative data collected from 3 animals per genotype; One-way ANOVA, Tukey's multiple comparisons test; ***p<0.001, *p<0.05, F=63.3, DF=7; mean±SD).(H) Kinocilia are shorter in Elp3cKO HCs (WT/KO IHC: n=15/15; OHC1: n=30/32; OHC3: n=31/30; OHC3: n=27/30; data collected from 3 animals per genotype; One-way ANOVA, Tukey's multiple comparisons test, ***p<0.001, **p<0.01F=19.6, DF=7; mean±SD).(I) High magnification of representative HCs from P1 WT and Elp3cKO cochlea stained for F-actin and gamma-tubulin (white). The basal body of kinocilia is shifted centrally at the apical surface of Elp3cKO HCs. Scale bars=2µm. Polar plotting of kinocilium basal body position for each row of HCs of WT and Elp3cKO (WT/KO IHC: n= 42/32; OHC1: n= 47/48; OHC2: n= 47/45; OHC3: n= 44/44; cumulative data collected from 3 animals per genotype). Cellular orientations were tested using Watson U2 test (p<0.001 between WT/Elp3cKO, for all HC rows) and the mean vector lengths, determined from the cell centre to the basal body, were compared using t-tests (p<0.001 between WT/Elp3cKO, for all HC rows).The localization of apical polarity proteins is affected by Elp3 loss. Surface views of mid-basal turn of P1 cochleae from WT or Elp3cKO mice stained with LGN (J) and F-actin. The enrichment of these apical polarity regulators at the lateral edges of HCs is disrupted in Elp3cKO HCs. Scale bars=5µm (upper panels) and 2µm (lower panels). Data information: #IHC; *OHC1; **OHC2; ***OHC3The localization of apical polarity proteins is affected by Elp3 loss. Surface views of mid-basal turn of P1 cochleae from WT or Elp3cKO mice stained with Gαi3 (K) and F-actin. The enrichment of these apical polarity regulators at the lateral edges of HCs is disrupted in Elp3cKO HCs. Scale bars=5µm (upper panels) and 2µm (lower panels). Data information: #IHC; *OHC1; **OHC2; ***OHC3The localization of apical polarity proteins is affected by Elp3 loss. Surface views of mid-basal turn of P1 cochleae from WT or Elp3cKO mice stained with aPKC (L) and F-actin. The enrichment of these apical polarity regulators at the medial (L) edges of HCs is disrupted in Elp3cKO HCs. Scale bars=5µm (upper panels) and 2µm (lower panels). Data information: #IHC; *OHC1; **OHC2; ***OHC3