Figure 1

Proliferating cells are not observed in the developing joint region. (A, B, D, E, G, H) PCNA staining of sagittal sections through the middle ear. Proliferating cells stained brown against a blue background. (C, F, I) Anti-phosphohistone H3 immunohistochemistry of sagittal sections through the middle ear. Cells outlines by DAPI (blue). Proliferating cells label as bright red spots. Ossicles are outlined with white dashes. (A-C) E15.5. (D-F) E14.5. (G-I) E13.5. (A, D) Malleus and incus. Joint region marked by *. (B, E) High power view of the joint region, showing no positively stained cells compared to the adjacent malleus and incus. (C, F) H3 positive cells are located within and around the ossicles but not in the joint region (*). (G) United malleus and incus. Presumptive joint region marked by *. (H) High power view of the malleus and presumptive joint region, showing no positively stained cells in the presumptive joint (*) compared to the adjacent malleus. (I) H3 positive cells are located within the incus but not in the presumptive joint region (*). M = malleus and I = incus. Scale bars in (A, B, C) = 100 μm.