Fig. 5
A missense mutation in Tbx1 causes malformation of the semicircular canals and profound deafness. a Mean ABR thresholds from P28 mice homozygous (n = 6, red triangles), heterozygous (n = 10, blue circles) and wildtype (n = 4, black inverted triangles) for the Tbx1ttch allele (MDLY colony), p.D212N. Error bars are standard deviations. See Additional File 1: Fig. S9b for individual thresholds. b Sequence traces from an unaffected and an affected mouse showing the variant. c Clustal alignment showing conservation of the affected amino acid (red box). d P4 sections showing the cochlear duct (top, anti-MYO7A brown stain, blue counterstain, 43% of the distance along the organ of Corti from base to apex) and the maculae (bottom, trichrome staining) (n = 3 affected, 3 unaffected littermates). MYO7A is expressed in hair cells (arrowheads; red/black for inner/outer hair cells) and the intermediate cells of the stria vascularis. e Trichrome-stained sections from adult mice (n = 4 affected, 4 unaffected littermates) showing the cochlear duct (top, 72% of the distance along the organ of Corti from base to apex) and the maculae (bottom). Brackets mark the organ of Corti and the spiral ganglion area is circled. Square brackets indicate abnormal saccular hair cells. In d and e, main panel scale bars = 50 µm, high magnification panel scale bars = 20 µm. Asterisks mark Reissner’s membrane, twin open arrowheads the stria vascularis, and arrows the collapsed saccule. f Human TBX1 protein model [104], as a homodimer (silver, gold) bound to DNA (pale green). The Asp212 residue is marked in blue (top), with the nmf219 mutant residue [41] in cyan (middle) and the ttch mutant residue in magenta (bottom). g MicroCT scans of cleared inner ears from affected P28 mice (n = 3, middle) and compound heterozygotes (Tbx1tm1Bld/ttch) at P21 (n = 2, bottom). An unaffected P21 mouse is shown at the top (P21 n = 4; P28 n = 3). Dashed lines outline the semicircular canals, with twin arrowheads for comparison of their width. The middle ear side, with the round (RW) and oval (OW) windows (dotted lines) is on the left, and the brain side, where the cochlear nerve exits (CN, dotted lines), on the right. Brackets indicate the cochlea (Co) and vestibular region (Ve). LSC = lateral semicircular canal; SSC = superior semicircular canal; PSC = posterior semicircular canal, CC = common crus. Scale bar = 1 mm. Data underlying plots in this figure are in Additional File 3