Cleft palate, the most common craniofacial deformity in the USA, may caused by a failure of palatal medial edge seam (MES) cells to undergo complete disintegration, which is necessary in establishing confluence of the palatal stroma. While, Transforming Growth Factor (TGF) (-1, 2 and 3 are involved in palatogenesis, interestingly, TGF(3 is the only member of this family that is involved in palatal seam disintegration. TGF(3 signaling initiates and completes sequential phases of cellular differentiation that is required during MES disintegration, which progress between 14 to 17 embryonic days in the murine system. Understanding the cellular mechanism of palatal MES disintegration in response to TGF(3 signaling will result in new approaches to defining the causes of cleft palate and other facial clefts that may result from failure of seam disintegration. We have isolated MES primary cells to study the details of TGF(3 signaling mechanisms during palate development. To elucidate the mechanisms of MES disintegration by TGF(3, using several biochemical and genetic approaches, we demonstrated a novel mechanism of MES disintegration where MES undergoes cell cycle arrest, cell migration and apoptosis chronologically to generate immaculate palatal confluency during palatogenesis. We have shown that robust TGF(3 signaling induces both Smad dependent and Smad independent pathways to activate many transcription factors such as Snail, Slug, SIP1 and LEF1. It is unclear how these pathways and activated transcription factors promote cell cycle arrest, cell migration and apoptosis in the same cell type. We, therefore, wish to further study the mechanisms and diversity of TGF(3 signaling in MES cell function and how they are related to differential transcription factors and pathways to cause controlled MES disintegration. In this proposal, we would like to examine TGF(3 signaling towards these three individual cell functions. The broad objective of this grant is to understand the tissue transitions involved in the development of the palate and craniofacial mesenchyme in response to TGF( signaling.
Each specific aim i n the proposed study is designed to analyze the three phenotypical changes triggered by TGF(3, such as cell cycle arrest (Aim #1), migration (Aim #2) and apoptosis (Aim #3) required for MES disintegration to generate structural and functional component of the confluent palate. The rationale for this study is that successful completion of the proposed research will contribute to a missing, fundamental element to our base knowledge about the diverse functions of TGF(3 without which the cell cycle arrest, migration and apoptosis during MES disintegration cannot be understood. We believe that in some cases, knowledge of the basic cell biology will lead to more effective treatment of facial clefting.
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