(A) Macroscopic views of tympanic membrane from wild-type (+/+) and Eya4^–/– (–/–) mice. Eya4^–/– mouse ears had air bubbles (asterisk), indicative of middle ear effusion, and dilated capillaries (black arrow) as well as tympanic membrane retraction (see also Figure 3). Scale bars: 1 mm. (B and C) PAS-stained paraffin sections of mice, age 3 weeks. (B) The mesotympanum of middle ear cavity shows inflammatory cells (red arrow) in Eya4^–/– mice, and the mucoperiosteum (black arrowheads) is thickened. A, stapedial artery; I, incus; M, malleus; OW, bony niche of the oval window; T, tympanic membrane. Scale bars: 200 μm. (C) The hypotympanum regions of Eya4^–/– mice show effusion (asterisk), inflammatory cells (red arrow), hyperplastic ciliated epithelial cells (black arrows), and expanded lamina propria connective tissue in the mucoperiosteum (arrowhead; corresponding regions denoted by gray arrow/arrowhead in wild-type). MEC, middle ear cavity.