Death is the major fate of medial edge epithelial cells and the cause of basal lamina degradation during palatogenesis
ABSTRACT During mammalian development, a pair of shelves fuses to form the secondary palate, a process that requires the adhesion of the medial edge epithelial tissue (MEE) of each shelf and the degeneration of the resulting medial epithelial seam (MES). It has been reported that epithelial-mesenchymal transformation (EMT) occurs during shelf fusion and is considered a fundamental process for MES degeneration. We recently found that cell death is a necessary process for shelf fusion. These findings uncovered the relevance of cell death in MES degeneration; however, they do not discard the participation of other processes. In the present work, we focus on the evaluation of the processes that could contribute to palate shelf fusion. We tested EMT by traditional labeling of MEE cells with a dye, by infection of MEE with an adenovirus carrying the lacZ gene, and by fusing wild-type shelves with the ones from EGFP-expressing mouse embryos. Fate of MEE labeled cells was followed by culturing whole palates, or by a novel slice culture system that allows individual cells to be followed during the fusion process. Very few labeled cells were found in the mesenchyme compartment, and almost all were undergoing cell death. Inhibition of metalloproteinases prevented basal lamina degradation without affecting MES degeneration and MEE cell death. Remarkably, independently of shelf fusion, activation of cell death promoted the degradation of the basal lamina underlying the MEE ('cataptosis'). Finally, by specific labeling of periderm cells (i.e. the superficial cells that cover the basal epithelium), we observed that epithelial triangles at oral and nasal ends of the epithelial seam do not appear to result from MEE cell migration but rather from periderm cell migration. Inhibition of migration or removal of these periderm cells suggests that they have a transient function controlling MEE cell adhesion and survival, and ultimately die within the epithelial triangles. We conclude that MES degeneration occurs almost uniquely by cell death, and for the first time we show that this process can activate basal lamina degradation during a developmental process.
- SourceAvailable from: Kathy K H Svoboda
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- "The extension of the filopodia-like structures on the MEE cell's surface before or during fusion indicates that cell migration contributes to the palatal fusion (Martin-Blanco and Knust, 2001). Thus, it has been proposed that the epithelial cells migrate to the oral and nasal surface (Cuervo and Covarrubias, 2004). In addition, anterior-posterior migration of the cells has also been proposed (Jin and Ding, 2006). "
ABSTRACT: Palatal fusion is a tightly controlled process which comprises multiple cellular events, including cell movement and differentiation. Midline epithelial seam (MES) degradation is essential to palatal fusion. In this study, we analyzed the function of Snail1 during the degradation of the MES. We also analyzed the mechanism regulating the expression of the Snail1 gene in palatal shelves. Palatal explants treated with Snail1 siRNA did not degrade the MES and E-cadherin was not repressed leading to failure of palatal fusion. Transforming growth factor beta 3 (Tgfβ3) regulated Snail1 mRNA, as Snail1 expression decreased in response to Tgfβ3 neutralizing antibody and a PI-3 kinase (PI3K) inhibitor. Twist1, in collaboration with E2A factors, regulated the expression of Snail1. Twist1/E47 dimers bond to the Snail1 promoter to activate expression. Without E47, Twist1 repressed Snail1 expression. These results support the hypothesis that Tgfβ3 may signal through Twist1 and then Snail1 to downregulate E-cadherin expression during palatal fusion.Frontiers in Physiology 02/2013; 4:12. DOI:10.3389/fphys.2013.00012 · 3.50 Impact Factor
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- "The median frontonasal prominence (FNP) contributes the columella and the central region of the primary palate, and coalesces with the paired maxillary prominences in a Y-shaped seam, where Bmp and a Pbx-dependent Wnt-p63-Irf6 regulatory module acts (Tamarin and Boyde, 1977; Jiang et al., 2006; Depew and Compagnucci, 2008; Ferretti et al., 2011). The secondary palate forms from midline fusion of bilateral palatal shelves, which are derived from the maxillary prominences (MXP), where midline fusion is characterized by distinct palatal shelf movements, apoptosis and epithelial-mesenchymal transition (Cuervo and Covarrubias, 2004; Helms et al., 2005; Bush and Jiang, 2012). "
ABSTRACT: Development of the palate in vertebrates involves cranial neural crest migration, convergence of facial prominences and extension of the cartilaginous framework. Dysregulation of palatogenesis results in orofacial clefts, which represent the most common structural birth defects. Detailed analysis of zebrafish palatogenesis revealed distinct mechanisms of palatal morphogenesis: extension, proliferation and integration. We show that wnt9a is required for palatal extension, wherein the chondrocytes form a proliferative front, undergo morphological change and intercalate to form the ethmoid plate. Meanwhile, irf6 is required specifically for integration of facial prominences along a V-shaped seam. This work presents a mechanistic analysis of palate morphogenesis in a clinically relevant context.Development 11/2012; 140(1). DOI:10.1242/dev.080473 · 6.27 Impact Factor
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- "The fate of the MES cells during fusion has long been a source of controversy. One theory has the cells dying by apoptosis (Glücksmann, 1965; Martínez-Alvarez et al., 2000; Cuervo and Covarrubias, 2004), while another says they undergo epithelial-to-mesenchymal transition (EMT) and migrate into the surrounding mesenchyme (Fitchett and Hay, 1989; Shuler et al., 1991, 1992; Kang and Svoboda, 2002, 2005). Current evidence on the mechanism of MES degradation best fits a model in which the medial edge epithelial (MEE) cells undergo EMT, followed by apoptosis (Ahmed et al., 2007). "
ABSTRACT: Studies of palate development are motivated by the all too common incidence of cleft palate, a birth defect that imposes a tremendous health burden and can leave lasting disfigurement. Although, mechanistic studies of palate growth and fusion have focused on growth factors such as Transforming Growth Factor ß-3 (Tgfß3), recent studies have revealed that the ephrin family of membrane bound ligands and their receptors, the Ephs, play central roles in palatal morphogenesis, growth, and fusion. In this mini-review, we will discuss the recent findings by our group and others on the functions of ephrins in palatal development.Frontiers in Physiology 09/2012; 3:376. DOI:10.3389/fphys.2012.00376 · 3.50 Impact Factor