During craniofacial development, TGFA is expressed at the medial edge epithelium of fusing palatal shelves (18,19).
It subsequently revealed that TGFA was present at high levels in epithelial tissue of the medial edge of the palatal shelves at the time of shelf fusion (17).
The effects of epidermal growth factor, transforming growth factors alpha and beta and platelet-derived growth factor on murine palatal shelves in organ culture.
Asymmetry: usually there is an asymmetry in the alignment of palatal shelves
, the cleft side palatal half is collapsed and positioned at a lower level than non-cleft side.
Irf6 is expressed in the facial primordium prior to and during morphogenesis of the primary palate (Washbourne & Cox, 2006), and preliminary findings in mice have revealed Irf6 expression in the medial edge epithelia of fusing secondary palatal shelves
, tooth buds, hair follicles, and skin (Kondo et al., 2002).
The medial edge epithelia of the approximating palatal shelves fuse with each other developing cell adhesion molecules and desmosomes to form a midline epithelial seam.
In human embryos palatal shelves elevate simultaneously on day 43 (22-24 mm CRL), and the palate is closed by 55 days (33-37 mm CRL).
The mesenchymal obstruction of the tongue can delay the movement of one or both palatal shelves, so that opportunities for palatal fusion are lost (rev by Poswillo, 1988).
Palatal shelf elevation and fusion depends on fetal neuromuscular activity, growth of the cranial base and mandible, production of extracellular matrix and contractile elements in the palatal shelves, shelf adhesion, PCD of the midline epithelial seam and fusion of the ectomesenchyme between one shelf and another.
Differentiation of cultured palatal shelves
from Alligator, chick, and mouse embryos.