Could explain failed response of the palatal mesenchyme in terms of gene expression to exogenous applied BMP induction [13]. The restricted ectopic domain of Smad1/5/8 phosphorylation along with activation of BMP noncanonical signaling regulators p38 and JNK and Msx1 and Shox2 expression in the posterior palate of Wnt1Cre;pMes-caBmprIa mice indicates a selective response of CNC-derived cells to BMP signaling. This ectopic expression of BMP canonical and noncanonical mediators (pSmad1/5/8, P-p38, P-JNK) and Msx1 and Shox2 appears to be responsible for the formation of ectopic cartilage in the posterior palatal shelf. The presence of ectopic cartilage seems to cause a deformed posterior palate structure (shorter and wider compared to control) and delayed palate elevation. This idea is supported by the correlation of the presence of an ectopic cartilage with dramatically reduced size in the palatal shelf and subsequent formation of an intact palate in Wnt1Cre;pMes-caBmprIa mice on a BmprIa haploinsufficient background. Nevertheless, these observations further confirm an absolute requirement of BMP signaling homeostasis in CNCderived tissue for palate development. Despite an elevated level of pSmad1/5/8 in the developing tooth germ in Wnt1Cre;pMes-caBmprIa mice, early tooth development, gene expression as well as cusp patterning appeared normal. However, the differentiation of odontoblasts and ameloblasts was delayed. These observations indicates that enhanced BMP signaling in the dental mesenchyme does not exert a detrimental effect on early tooth development and patterning, suggest that the developing tooth has a higher tolerance to overactive BMP signaling compared to the developing palatal shelves. This notion is consistent with phenotypes observed in Noggin mutant mice, analternative gain-of BMP signaling function model, in which a cleft palate formed, but the molars and lower incisors developed normally except an early fusion of upper incisors [11,36,44,45]. However, enhanced BMP activity in the dental mesenchyme has an effect at the late developmental stage, causing delayed odontogenic differentiation. Many studies have implicated a role of BMP signaling in the differentiation of odontoblasts and ameloblasts, as evidenced by the expression of multiple Bmp genes in the differentiating/differentiated odontoblasts and ameloblasts [46]. The facts that BMPs are able to induce odontoblasts to produce dentin and the lack of Smad4 Title Loaded From File Title Loaded From File prevents terminal odontoblast differentiation, as well as that overexpression of Follistatin, a BMP inhibitor, inhibits ameloblast differentiation support a positive role for BMP signaling in promoting odontogenic differentiation [47,48,49,50]. However, in our transgenic model, overactive BMP signaling appears to exert an opposite role in odontogenic differentiation. Several other signaling pathways are also involved in the regulation of odontogenic differentiation, including TGFb, Shh, and Wnt, forming a complicated regulatory network [51]. While the mechanism underlying the delayed odontogenic differentiation in Wnt1Cre;pMes-caBmprIa mice is currently unknown, and warrants future investigation, the enhanced BMP signaling in the dental mesenchymal component may disrupt the balance of this tightly regulated signaling network, leading to a delayed differentiation. Since caBmprIa is forced to be expressed in the dental mesenchymal cells but not in the dental epithelial cells and the differentiation of ameloblasts re.Could explain failed response of the palatal mesenchyme in terms of gene expression to exogenous applied BMP induction [13]. The restricted ectopic domain of Smad1/5/8 phosphorylation along with activation of BMP noncanonical signaling regulators p38 and JNK and Msx1 and Shox2 expression in the posterior palate of Wnt1Cre;pMes-caBmprIa mice indicates a selective response of CNC-derived cells to BMP signaling. This ectopic expression of BMP canonical and noncanonical mediators (pSmad1/5/8, P-p38, P-JNK) and Msx1 and Shox2 appears to be responsible for the formation of ectopic cartilage in the posterior palatal shelf. The presence of ectopic cartilage seems to cause a deformed posterior palate structure (shorter and wider compared to control) and delayed palate elevation. This idea is supported by the correlation of the presence of an ectopic cartilage with dramatically reduced size in the palatal shelf and subsequent formation of an intact palate in Wnt1Cre;pMes-caBmprIa mice on a BmprIa haploinsufficient background. Nevertheless, these observations further confirm an absolute requirement of BMP signaling homeostasis in CNCderived tissue for palate development. Despite an elevated level of pSmad1/5/8 in the developing tooth germ in Wnt1Cre;pMes-caBmprIa mice, early tooth development, gene expression as well as cusp patterning appeared normal. However, the differentiation of odontoblasts and ameloblasts was delayed. These observations indicates that enhanced BMP signaling in the dental mesenchyme does not exert a detrimental effect on early tooth development and patterning, suggest that the developing tooth has a higher tolerance to overactive BMP signaling compared to the developing palatal shelves. This notion is consistent with phenotypes observed in Noggin mutant mice, analternative gain-of BMP signaling function model, in which a cleft palate formed, but the molars and lower incisors developed normally except an early fusion of upper incisors [11,36,44,45]. However, enhanced BMP activity in the dental mesenchyme has an effect at the late developmental stage, causing delayed odontogenic differentiation. Many studies have implicated a role of BMP signaling in the differentiation of odontoblasts and ameloblasts, as evidenced by the expression of multiple Bmp genes in the differentiating/differentiated odontoblasts and ameloblasts [46]. The facts that BMPs are able to induce odontoblasts to produce dentin and the lack of Smad4 prevents terminal odontoblast differentiation, as well as that overexpression of Follistatin, a BMP inhibitor, inhibits ameloblast differentiation support a positive role for BMP signaling in promoting odontogenic differentiation [47,48,49,50]. However, in our transgenic model, overactive BMP signaling appears to exert an opposite role in odontogenic differentiation. Several other signaling pathways are also involved in the regulation of odontogenic differentiation, including TGFb, Shh, and Wnt, forming a complicated regulatory network [51]. While the mechanism underlying the delayed odontogenic differentiation in Wnt1Cre;pMes-caBmprIa mice is currently unknown, and warrants future investigation, the enhanced BMP signaling in the dental mesenchymal component may disrupt the balance of this tightly regulated signaling network, leading to a delayed differentiation. Since caBmprIa is forced to be expressed in the dental mesenchymal cells but not in the dental epithelial cells and the differentiation of ameloblasts re.
