Analysis of cell migration, transdifferentiation and apoptosis during mouse secondary palate fusion

Abstract

Malformations in secondary palate fusion will lead to cleft palate, a common human birth defect. Palate fusion involves the formation and subsequent degeneration of the medial edge epithelial seam. The cellular mechanisms underlying seam degeneration have been a major focus in the study of palatogenesis. Three mechanisms have been proposed for seam degeneration:lateral migration of medial edge epithelial cells; epithelial-mesenchymal trans-differentiation; and apoptosis of medial edge epithelial cells. However,there is still a great deal of controversy over these proposed mechanisms. In this study, we established a [Rosa26↔C57BL/6] chimeric culture system, in which a Rosa26-originated `blue' palatal shelf was paired with a C57BL/6-derived `white' palatal shelf. Using this organ culture system,we observed the migration of medial edge epithelial cells to the nasal side,but not to the oral side. We also observed an anteroposterior migration of medial edge epithelial cells, which may play an important role in posterior palate fusion. To examine epithelial-mesenchymal transdifferentiation during palate fusion, we bred a cytokeratin 14-Cre transgenic line into the R26R background. In situ hybridization showed that the Cretransgene is expressed exclusively in the epithelium. However,β-galactosidase staining gave extensive signals in the palatal mesenchymal region during and after palate fusion, demonstrating the occurrence of an epithelial-mesenchymal transdifferentiation mechanism during palate fusion. Finally, we showed that Apaf1 mutant mouse embryos are able to complete palate fusion without DNA fragmentation-mediated programmed cell death, indicating that this is not essential for palate fusion in vivo.

Palatogenesis: morphogenetic and molecular mechanisms of secondary palate development

“…Different results, however, have been reported by a third group (Jin and Ding, 2006b), who showed that some mesenchymal -galactosidase activity was present during and immediately after regression of the MES in K14-Cre; R26R embryos. The authors suggested that the discrepancy might have resulted from differences in Cre expression levels and/or patterns in the palatal epithelium in the different K14-Cre transgenic mouse lines used (Jin and Ding, 2006b).…”

“…To address this issue, palatal shelves derived from wild-type embryos were recombined in culture with palatal shelves expressing lacZ in all cells (Jin and Ding, 2006b). lacZ-expressing epithelial cells migrated onto the wild-type palatal shelves, indicating that MES migration can occur during palatal fusion.…”

Microtubule disassembly prevents palatal fusion and alters regulation of the E-cadherin/catenin complex

“…Epithelial mesenchymal transition (EMT) plays a crucial role in MES degradation (Greene and Pisano, 2010, Griffith and Hay, 1992, Jalali et al, 2012, Jin and Ding, 2006, Shuler et al, 1992, Yu W, 2009. It is characterized by loss of epithelial cell morphology and acquisition of mesenchymal properties.…”

Molecular basis of cleft palates in mice

“…The most significantly enriched molecular function was the "transcription factor" (P = Funato N et al . Cleft palates in mice the fusion line by epithelial cell migration, apoptosis, and epithelialmesenchymal transdifferentiation [14] . Tgfb3 (transforming growth factor, beta 3) or Egfr (epidermal growth factor receptor) knockout mice lack the adhesive interactions between the palatal shelves because the fate of MEE cells is altered [1518] .…”