Tak1, Smad4 and Trim33 redundantly mediate TGF-β3 signaling during palate development

Abstract

Transforming growth factor-beta3 (TGF-β3) plays a critical role in palatal epithelial cells by inducing palatal epithelial fusion, failure of which results in cleft palate, one of the most common birth defects in humans. Recent studies have shown that Smad-dependent and Smad-independent pathways work redundantly to transduce TGF-β3 signaling in palatal epithelial cells. However, detailed mechanisms by which this signaling is mediated still remain to be elucidated. Here we show that TGF-β activated kinase-1 (Tak1) and Smad4 interact genetically in palatal epithelial fusion. While simultaneous abrogation of both Tak1 and Smad4 in palatal epithelial cells resulted in characteristic defects in the anterior and posterior secondary palate, these phenotypes were less severe than those seen in the corresponding Tgfb3 mutants. Moreover, our results demonstrate that Trim33, a novel chromatin reader and regulator of TGF-β signaling, cooperates with Smad4 during palatogenesis. Unlike the epithelium-specific Smad4 mutants, epithelium-specific Tak1:Smad4- and Trim33:Smad4-double mutants display reduced expression of Mmp13 in palatal medial edge epithelial cells, suggesting that both of these redundant mechanisms are required for appropriate TGF-β signal transduction. Moreover, we show that inactivation of Tak1 in Trim33:Smad4 double conditional knockouts leads to the palatal phenotypes which are identical to those seen in epithelium-specific Tgfb3 mutants. To conclude, our data reveal added complexity in TGF-β signaling during palatogenesis and demonstrate that functionally redundant pathways involving Smad4, Tak1 and Trim33 regulate palatal epithelial fusion.

Constitutively active mutation of ACVR1 in oral epithelium causes submucous cleft palate in mice

“…2F, J, arrow head), suggesting that caACVR1;K14-Cre mice have SMCP without cleft soft palate. Previous studies have demonstrated that one of the causes of SMCP in mice is MEE persistence (Dudas et al, 2006; Lane et al, 2014; Xu et al, 2006). To elucidate whether SMCP found in caACVR1;K14-Cre mice is due to the MEE persistence, we focused on MEE seam formation at E14.5 and E15.5.…”

“…Loss of TGFβ signaling in the basal epithelium in mice results in medial edge epithelium (MEE) persistence and complete cleft of the soft palate (Dudas et al, 2006; Lane et al, 2015; Xu et al, 2006). Palatal mesenchyme-specific deletion of Bmpr1a impairs palatal shelf growth and bone development, and causes submucous cleft of the hard palate (Baek et al, 2011).…”

Cellular and Molecular Mechanisms of Palatogenesis

“…In addition, Tgfβ signaling can activate Smad-independent pathways, including the Tgfβ-activated kinase-1 (Tak1) and p38 MAPK kinase cascade (Derynck and Zhang, 2003). Studies of mice with epithelium-specific inactivation of Smad4 , Tak1 , and Trim33, show that all three pathways act partly redundantly to mediate Tgfβ3 signaling in palatal MES breakdown (Xu et al, 2008; Lane et al, 2015). …”

The pivotal role of CCN2 in mammalian palatogenesis

“…(Bush and Jiang 2012;Mishina and Snider 2014;Smith et al 2012) Among the myriad of factors that have are expressed during development of the palate, transforming growth factor beta (TGF-β), fibroblast growth factor (FGF), and bone morphogenetic protein (BMP) signaling pathways have been shown to be essential for palate development. (Bush and Jiang 2012;Hill et al 2015;Lane et al 2015;Matsumura et al 2011;Parada and Chai 2012;Smith et al 2012;Yumoto et al 2013) Previous studies on the developmental deficits observed in the absence of CCN2 found craniofacial differences between CCN2 knockout (KO) compared to wild-type (WT) littermates. Allometric (size-based) and non-allometric shape differences were observed in CCN2 KO skulls, which were shorter and wider than their WT counterparts.…”