Epidermal Growth Factor Impairs Palatal Shelf Adhesion and Fusion in the <b><i>Tgf-β</i></b>₃ Null Mutant

Abstract

The cleft palate presented by transforming growth factor-β3 (Tgf-β₃) null mutant mice is caused by altered palatal shelf adhesion, cell proliferation, epithelial-to-mesenchymal transformation and cell death. The expression of epidermal growth factor (EGF), transforming growth factor-β1 (Tgf-β₁) and muscle segment homeobox-1 (Msx-1) is modified in the palates of these knockout mice, and the cell proliferation defect is caused by the change in EGF expression. In this study, we aimed to determine whether this change in EGF expression has any effect on the other mechanisms altered in Tgf-β₃ knockout mouse palates. We tested the effect of inhibiting EGF activity in vitro in the knockout palates via the addition of Tyrphostin AG 1478. We also investigated possible interactions between EGF, Tgf-β₁ and Msx-1 in Tgf-β₃ null mouse palate cultures. The results show that the inhibition of EGF activity in Tgf-β₃ null mouse palate cultures improves palatal shelf adhesion and fusion, with a particular effect on cell death, and restores the normal distribution pattern of Msx-1 in the palatal mesenchyme. Inhibition of TGF-β₁ does not affect either EGF or Msx-1 expression.

TGFβ3 Regulates Periderm Removal Through ΔNp63 in the Developing Palate

“…But the timing and location of TGFβ3 during palatogenesis suggests that TGFβ3 may contribute in MEE differentiation and periderm degeneration. Evidence also supports the role of IRF6 and ΔNp63 in MEE differentiation and maintenance through several pathways, including Wnt, Ephrin, TGFβ1, and Notch/Jag2 (Richardson et al, ; Lee et al, ; Murillo et al, ; Richardson et al, ; Risley et al, ; Moretti et al, ; Thomason et al, ; Yu et al, ; Ferretti et al, ; Iordanskaia and Nawshad, ; Fakhouri et al, ; Barrio et al, ; Kurosaka et al, ). During palatogenesis, the MEE cell surface is covered with a periderm layer, which prevents MEE cells from premature adhesion to other tissues within the oral cavity (Fitchett and Hay, ).…”

“…The question then remains, what regulates IRF6, if not TGFβ3? There are several candidates that are known to regulate IRF6, such as Wnt, Ephrin, TGFβ1, and Notch/Jag2 (Richardson et al, ; Lee et al, ; Murillo et al, ; Richardson et al, ; Risley et al, ; Yu et al, ; Iordanskaia and Nawshad, ; Barrio et al, ; Kurosaka et al, ). We have previously reported that TGFβ1 induces cell cycle arrest in the palatal epithelia by activating the CDK inhibitor, p15 ink4b (Iordanskaia and Nawshad, ); and TGFβ signaling via TGFβ receptor 2 regulates IRF6 and cell cycle arrest (Iwata et al, ).…”

Glycoprotein A repetitions predominant (GARP) positively regulates transforming growth factor (TGF) β3 and is essential for mouse palatogenesis

“…In TGF␤3 KO mice, the expression of GARP in MEEs most likely ensures abundant TGF␤1 and TGF␤2 in this location. However, for reasons that are unclear, neither of these two molecules is able to compensate for the loss of TGF␤3 (28,29,37,38).…”

Spatiotemporal Evolution of Developing Palate in Mice

“…At the current resolution in our study, the cell type of MES is consistent with cells in the oral cavity (Epi_Krt14), yet we can observe region-specific transforming signaling, Tgfβ3, and Pthlh, at MES. The Tgfβ3 signal has been reported to play an important role in the process of palatal adhesion and fusion (Barrio et al 2014; Hu et al 2015), while the Pthlh gene has been implicated in the epithelial–mesenchymal transition and cancer metastasis in previous studies (He et al 2018; Pitarresi et al 2021). For the first time, we observed the specific expression of Tgfβ3 and Pthlh signaling in the MES triangle, suggesting that they may mediate the epithelial–mesenchymal transition in the palatal fusion zone.…”