An Altered Distribution of the Medial Edge Epithelium Extracellular Matrix Contributes to the Cleft Palate Produced in the Absence of Tgf-Beta3

TGF-beta3 knockout mice present cleft palate due to the failure of palatal shelf adhesion. Previous work performed by our group has demonstrated the absence of chondroitin sulphate proteoglycan on these mice MEE surface and that its presence is crucial to palatal shelf adhesion. Objective: Our present aim was to determine whether changes in the presence/localization of other extracellular matrix molecules could also participate in this failure. Method: By using immunohistochemistry we have investigated the localization and distribution of fibronectin (FN), laminin (LN) and type IV collagen in the MEE of embryonic day 14 (E14) (when palatal shelves elevate) and E14,5 (just prior to palatal shelf adhesion) TGF-beta3 null and wild type mice. Results: Regarding FN and LN distribution, our results show no differences between the wild type and TGF-beta3 null palates at E14. However, at E14.5, FN is present on the apical surface of MEE cells in the wild type mice, but it is absent in this location in the TGF-beta3 null mutants. The distribution of LN is also altered is these mice. In the multilayered E14.5 wild type MEE, LN expression is regular and circumferentially located in the basal cells and basolaterally placed in the superficial cells. In contrast, the TGF-beta3 null MEE is monolayered and cells express LN all around. The presence of type IV collagen in the basal membrane is less intense at E14 in the TGF-beta3 null than in the wild type palates, but, at E14.5, this labelling is even fragmentary. Conclusion: We thus conclude that the absence of TGF-beta3 causes important changes in the MEE extracellular matrix, that are part of the alterations leading to the failure of palatal shelf adhesion and the production of the cleft palate observed in the TGF-beta3 null mutant mice. Granted by the Comunidad de Madrid, Ref. 08.6/0042/2000.