FGF8 and cleft palate: In our study, the mesenchymal cell proliferation drastically increased in both the medial and lateral sides by the over-expressed Fgf8 in mesenchyme, which in turn, altered the palate size and morphology, but cleft palate still happened due to the failure of elevation of the palatal shelves, indicating that the sole horizontal expansion of palatal shelves is insufficient to complete the palatal elevation.