Abstract
Epithelial fusion is critical in palatogenesis, and incomplete fusion results in various type of facial cleft, depending on the region that fails to fuse. In mammalian palatogenesis, the bilateral secondary palatal processes fuse in the middle of the face to form the secondary palate. Later, the dorsal side of the secondary palatal shelves fuses with the nasal septum to complete palatogenesis. Importantly, the anterior border of the secondary palatal shelf fuses with the primary palate, which is located at the anterior and ventral border of the nasal septum. While numerous studies have investigated the mechanism of fusion between secondary palatal shelves, very little is known about how the primary palate touches and fuses with the secondary palatal shelves. In this study, we investigate the possible epithelial cell behaviors on the surface of the primary palate using palatal explant cultures of K14-GFP mice. A time-lapse observation of the GFP-labeled epithelium and an SEM analysis revealed that the extrusion epithelium appeared at the region corresponding to the fusing area and expanded rostrally on the nasal septum surface in the absence of the secondary palatal processes. Unlike on the secondary palate surface, cellular migration and subsequent autonomous mesenchymal exposure were not evident on the nasal septum or the primary palate. TUNEL staining revealed that these extrusion epithelia were undergoing apoptosis. These findings indicated that extrusion with apoptosis was autonomously initiated at the presumptive region of the fusion without contact with the opposing secondary palate.
Highlights
Palatal fusion is essential for obtaining tissue continuity of facial processes from different embryonic origins
We evaluated the cellular behavior of the epithelium on the primary palate and the nasal septum using K14-GFP mouse explant culture as a model (Vaezi et al, 2002)
A dashed line in the Figure 1A schematic shows the plane of dissection for exposing the nasal septum during maxillary explant culture
Summary
Palatal fusion is essential for obtaining tissue continuity of facial processes from different embryonic origins. In mice, fusion of the nasal septum to the palate only occurs in the most anterior region, and the posterior region would remain a common nasal passage (Ferguson, 1978; Yu et al, 2017). After these processes contact, the intervening epithelium between the growing shelves merges to form an epithelial seam, which must be removed to complete the fusion (Ferguson, 1988; Bush and Jiang, 2012). Most previous studies focused on palatal fusion between bilateral secondary palates; fewer studies have focused on the fusion between the secondary palate and the primary palate/nasal septum
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