Fig. 3. The onset of Math1 expression in the cochlea. (A-C) Sections from E12.5 (A) and E13.5 (B) were stained with antibody to Math1 (Ab-Math1). No Math1 expression was visible in the cochlear epithelium (outlined in white) before E13.5, although cells in the vestibular system were stained by E12.5 (A,B). A section through the E13.5 cochlea, parallel to the cochlear duct was double labeled with antibodies against BrdU (green) and EGFP (red) (C). The apical to basal extent of the ZNPC is revealed by the BrdU-negative staining region (brackets) where no Math1/EGFP expression is detected, indicating the ZNPC is established prior to the onset of Math1/EGFP expression. (D-F) Sections through E14.5 cochlear epithelium. Sections were labeled with antibody to Math1 (D, red), double-labeled with antibodies to EGFP (E, red) and p27^Kip1 (E, green), or double-labeled with antibodies to EGFP (F, red) and BrdU (F, green). Math1 staining first appears on E14.5 as a column of cells spanning the cochlear epithelium (D, arrow). Math1/EGFP cells (arrows in E,F) appear at the medial border of the p27^Kip1-stained domain (E, bracket) or the ZNPC (F, bracket). Scale bars: in A, 50 µm in A-C; in D, 50 µm in D-F.