ABSTRACT
Failure of palatal shelf fusion results in cleft palate (CP) and may lead to malformation of palatal bones and undergrowth of the maxilla. It is not known whether defects in bone formation may contribute to this phenotype. We tested the hypothesis that impaired fusion of developing palatal shelves affects palatal bone development using palate organotypic cultures. Using two different approaches, we show that induction of cleft results in increased expression of pre-osteoblast and early osteoblast markers, Twist1, Snai1 and Runx2, and decreased expression of more mature markers of bone differentiation, collagen-1 and osteopontin, indicating delayed osteoblast differentiation in CPs. This, together with the increase in immature osteoblasts and proliferation observed in non-fused palatal shelves, suggests that palatal osteoblast differentiation is at least partly modulated by shelf fusion. Delayed osteoblast differentiation may therefore contribute to defects in gross morphology and function of the maxilla in CP patients.
Subject(s)
Bone Development , Cell Differentiation , Cleft Palate/embryology , Osteoblasts/physiology , Osteogenesis , Animals , Bone Development/drug effects , Bone Development/genetics , Cell Differentiation/genetics , Collagen Type I/genetics , Core Binding Factor Alpha 1 Subunit/genetics , Disease Models, Animal , Facial Bones/embryology , Gene Expression , Maxillofacial Development/drug effects , Maxillofacial Development/genetics , Maxillofacial Development/physiology , Mice , Nuclear Proteins/genetics , Organ Culture Techniques , Osteoblasts/metabolism , Osteogenesis/drug effects , Osteogenesis/genetics , Osteopontin/genetics , Palate/embryology , Palate, Soft/embryology , Reverse Transcriptase Polymerase Chain Reaction , Snail Family Transcription Factors , Transcription Factors/genetics , Transforming Growth Factor beta/genetics , Transforming Growth Factor beta/physiology , Twist-Related Protein 1/geneticsABSTRACT
UNLABELLED: Failure of secondary palate fusion during embryogenesis is a cause of cleft palate. Disappearance of the medial epithelial seam (MES) is required to allow merging of the mesenchyme from both palatal shelves. This involves complex changes of the medial edge epithelial (MEE) cells and surrounding structures that are controlled by several genes whose spatio-temporal expression is tightly regulated. We have carried out morphological analyses and used a semi-quantitative RT-PCR technique to evaluate whether morphological changes and modulation in the expression of putative key genes, such as twist, snail, and E-cadherin, during the fusion process in palate organ culture parallel those observed in vivo, and show that this is indeed the case. We also show, using the organotypic model of palate fusion, that the down-regulation of the transcription factor snail that occurs with the progression of palate development is not dependent on fusion of the palatal shelves. ABBREVIATIONS: dsg1, desmoglein1; EMT, epithelial-mesenchymal transition; MEE, medial edge epithelium; MES, medial epithelial seam; RT-PCR, reverse-transcriptase polymerase chain-reaction.
