Splice variants of ALK5 regulate medial palatal seam cell morphogenesis

Objective: The broad objective of this study is to understand the tissue transitions involved in the development of the palate and craniofacial mesenchyme in response to TGF&beta3 signaling. TGF&beta3 signaling initiates and completes sequential phases of cellular differentiation that is required for complete disintegration of the palatal medial edge seam, that progresses between 14 and 17 embryonic days in the murine system, which is necessary in establishing confluence of the palatal stroma. Understanding the cellular mechanism of palatal MES disintegration in response to TGF&beta3 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. Method: We have isolated MES primary cells to study the details of MES disintegration mechanism by TGF&beta3 during palate development using several biochemical and genetic approaches. Results: Our results demonstrate a novel mechanism of MES disintegration where MES, independently yet sequentially, undergoes cell cycle arrest, cell migration and apoptosis to generate immaculate palatal confluency during palatogenesis in response to robust TGF&beta3 signaling. Moreover, here we report for the first time that palatal MEE cells possess two splice variants of ALK5 receptors (long and short forms with splicing of 12 nucleotides encoding Gly-Pro-Phe-Ser amino acids). In response to TGF&beta3, these variants switch and cause palatal MES cell migration and apoptosis chronologically. Conclusion: The results contribute to a missing fundamental element to our base knowledge of the diverse roles of TGF&beta3 in functional and morphological changes that MES undergo during palatal seam disintegration. We believe that our findings will lead to more effective treatment of facial clefting. This study was supported by RR018759 for the Nebraska Center for Cellular Signaling from the NIH