Fig. 8. Disturbed boundary formation between the otic capsule and otic fibrocytes in Tbx18^-/- mice. (A-H) Analyses of histology by Hematoxylin/Eosin (A,E) and Picro-Sirius Red collagen staining (B,F), and of marker gene expression by RNA in situ hybridization (C,D,G,H) on sagittal sections of E18.5 cochleae. Figures show the spiral ligament of the basal coil. Genotypes and probes used are as indicated in the figure. (I-N) Analyses of β-galactosidase reporter activity by X-Gal staining on sagittal sections of Tbx18^lacZ/Tbx18^GFP and Tbx18^lacZ/+ (control) mice at E12.5 (I,L), E13.5 (J,M) and E14.5 (K,N). (A,E) HE staining reveals a local expansion of the otic capsule in the basal coil (arrow in E) and altered fibrocyte appearance in the spiral ligament of the mutant (E). (B,F) Collagen staining reveals disturbed boundary formation between spiral ligament fibrocytes and the otic capsule in the Tbx18^-/- mice. Arrowhead in B marks the compartment boundary in the control. (C,D,G,H) Spiral ligament fibrocytes show ectopic Postn (G) and a severe reduction of Coch (H) expression in the mutant. White arrow in C,G marks Postn expression lining the outer border of the otic capsule. (I-N) β-Galactosidase activity assay detects (former) Tbx18-expressing cells in the outer compartment of the periotic mesenchyme (asterisk in M) and the otic capsule (asterisk in N). Dashed lines mark the outer boundary of the periotic mesenchyme and the otic capsule. For abbreviations, see Fig. 2.