Association between palatal morphogenesis and Pax9 expression pattern in CL/Fr embryos with clefting during palatal development.

The CL/Fr mouse strain develops cleft lip and palate (CLP) spontaneously. In this study, Pax9 mRNA expression was investigated in the palatal shelves during palatal morphogenesis to assess the correlation between secondary palatal morphogenesis and Pax9 expression of CL/Fr embryos with spontaneous cleft lip and palate. The expression of Pax9 mRNA was characterised using whole mount in situ hybridisation with a digoxygenin-labelled probe. In the control strain of C57BL/6 and CL/Fr normal embryos, Pax9 was expressed in the palate, especially along the medial edge (ME), on embryonic day 13.5 (E13.5) and E14.5 when the palatal shelves grew vertically down the side of the tongue and subsequently elevated to a horizontal position, and was down regulated on E15.5 when the palatal shelves met and began fusing. In the cleft embryo, Pax9 was expressed in the ME region but was not down regulated on E15.5. Furthermore, whole mount in situ hybridisation was performed after organ culture, using CL/Fr-N and CL/Fr-BCL palatal shelves dissected and approximated by pairs on E13.5. This showed that Pax9 was still expressed in the ME region in separated palatal shelves of CL/Fr-N and CL/Fr-BCL embryos, while Pax9 expression was down regulated in paired palatal shelves. These expression patterns of Pax9 in normal and cleft embryos during palatal fusion indicate that Pax9 expression is altered in spontaneous cleft lip and palate, and concludes that there is a direct correlation between Pax9 expression and palatal fusion.