The Role of Twist During Palate Development

In palatogenesis, the MEE (Medial Edge Epithelium) cells disappear when palates fuse. We hypothesize that the MEE cells undergo EMT (Epithelial-Mesenchymal Transition) to achieve mesenchyme confluence. Twist has an important role in EMT for tumor metastasis. The purpose of this study was to analyze Twist function during palatal fusion. Twist protein was expressed in palatal shelves and MEE both in vivo and in vitro just prior to fusion. Twist mRNA increased in chicken palates 3 and 6 hr after TGF beta 3 treatment. Palatal fusion was decreased when cultured palatal shelves were treated with 200 nM Twist siRNA and the subcellular localization of P-catenin was altered. Twist mRNA decreased in palatal shelves treated with TGF beta 3 neutralizing antibody or LY294002, a specific phosphatidylinositol-3 kinase (PI-3K) inhibitor. In summary, Twist is downstream of TGF beta 3 and PI-3K pathways during palatal fusion. However, decreasing Twist with siRNA did not completely block palate fusion, indicating that the function of Twist may be duplicated by other transcription factors. Developmental Dynamics 237:2716-2725, 2008. (C) 2008 Wiley-Liss, Inc.