Snail family members and cell survival in physiological and pathological cleft palates

Abstract

Palate fusion is a complex process that involves the coordination of a series of cellular changes including cell death and epithelial to mesenchymal transition (EMT). Since members of the Snail family of zinc-finger regulators are involved in both triggering of the EMT and cell survival, we decided to study their putative role in palatal fusion. Furthermore, Snail genes are induced by transforming growth factor beta gene (TGF-beta) superfamily members, and TGF-beta(3) null mutant mice (TGF-beta(3)-/-) show a cleft palate phenotype. Here we show that in the wild-type mouse at the time of fusion, Snail is expressed in a few cells of the midline epithelial seam (MES), compatible with a role in triggering of the EMT in a small subpopulation of the MES. We also find an intriguing relationship between the expression of Snail family members and cell survival associated to the cleft palate condition. Indeed, Snail is expressed in the medial edge epithelial (MEE) cells in TGF-beta(3)-/-mouse embryo palates, where it is activated by the aberrant expression of its inducer, TGF-beta(1), in the underlying mesenchyme. In contrast to Snail-deficient wild-type pre-adhesion MEE cells, Snail-expressing TGF-beta(3) mutant MEE cells survive as they do their counterparts in the chick embryo. Interestingly, Slug is the Snail family member expressed in the chick MEE, providing another example of interchange of Snail and Slug expression between avian and mammalian embryos. We propose that in the absence of TGF-beta(3), TGF-beta(1) is upregulated in the mesenchyme, and that in both physiological (avian) and pathological (TGF-beta(3)-/-mammalian) cleft palates, it induces the expression of Snail genes promoting the survival of the MEE cells and permitting their subsequent differentiation into keratinized stratified epithelium.

Regulation ofTwist,Snail, andId1is conserved between the developing murine palate and tooth

“…Snail and Twist have been implicated in this fusion process and our data, that Snail and Twist are intensely expressed in the palatal mesenchyme adjacent to the MEE immediately before and during the fusion process, would support this implication (Bloch-Zupan et al, 2001;Martinez-Alvarez et al, 2004). Snail, the closely related Slug and Twist are all known to induce EMT at many sites during development and invasive tumorigenesis (Nieto, 2002;Yang et al, 2004).…”

“…Snail proteins induce during mesoderm specification and emergence of neural crest from the neural tube. Snail may also play a role in EMT during fusion of the palatal shelves (Martinez-Alvarez et al, 2004). Twist has also been associated with EMT (Yang et al, 2004).…”

The mesenchymal cell, its role in the embryo, and the remarkable signaling mechanisms that create it

“…In vitro, inappropriate culture conditions are responsible for much of the reported basal cell death (Takigawa and Shiota, 2004). Palates express Snail (Martinez- Alvarez et al, 2004), which promotes cell survival, as well as EMT (Vega et al, 2004). Both the lip and palate midline epithelial seams transform into typical mesenchymal cells (Fig.…”

Jag2‐Notch1 signaling regulates oral epithelial differentiation and palate development

“…There is strong evidence that disruption of the palatal epithelial seam during palatal fusion results at least in part from apoptosis (Cecconi et al, 1998;Cuervo and Covarrubias, 2004;Martinez-Alvarez et al, 2004;Vaziri Sani et al, 2005). We carried out terminal deoxynucleotidyl transferasemediated deoxyuridinetriphosphate nick end-labeling (TUNEL) analysis to investigate the mechanism involved in the disruption of the epithelial seam between the palate and tongue in the Jag2 ⌬DSL/⌬DSL mutants and found that the palate-tongue seam contained numerous apoptotic cells, similar to the wild-type palate-palate seam during palatal fusion (Fig.…”