Fig. 5.

Enhanced apoptotic cell death in MEKK4-/- neural tube. (A) Whole-mount TUNEL staining of E8.5 MEKK4+/+ (Left) and MEKK4-/- (Right) mice. In MEKK4+/+ mice, TUNEL-positive cells were largely restricted to the leading edges (arrows) of the cranial neural tube. In MEKK4-/- mice, TUNEL positivity was observed in the entire neural folds. (B) E8.5 horizontal semithin sections stained with Toluidine blue. Higher magnification of the boxed areas revealed limited pyknotic nuclei in MEKK4+/+ embryos (arrows), whereas MEKK4-/- embryos showed more numerous pyknotic nuclei throughout the neuroepithelium. (C) TUNEL staining of E9.5 embryos showed increased TUNEL-positive cells (red; arrows) in MEKK4-/- HB neuroepithelium (Right) compared with MEKK4+/+ (Left). Apoptosis was also observed in adjacent neural crest tissue (asterisks) in both genotypes. Sections were counterstained with TOPRO-3 for all nuclei (blue). (Bars, 100 μmin A;50 μmin B.)