TGF-β signaling inhibits canonical BMP signaling pathway during palate development

Abstract

During early palate development, gene expression and regulation exhibit heterogeneity along the anterior-posterior axis. Transforming growth factor-β (TGF-β) and bone morphogenetic protein (BMP) signaling pathways play essential roles in secondary palatal formation but the exact relationship between the TGF-β and BMP pathways in palate development remains unknown. Here, we demonstrate that, during early secondary palate development, phospho-(p)Smad1/5/8 is highly expressed in the anterior palate but relatively lowly expressed in the posterior palate. Conversely, pSmad2/3 has a lower expression level in the anterior palate than in the posterior palate. With the BRE-Gal reporter, we found that the canonical BMP signaling pathway was not activated in the anterior palate but exhibited a moderate level in the posterior palate. Co-immunoprecipitation revealed that Smad4 bound to pSmad1/5/8 only in the posterior palate and not in the anterior palate. Knocking-out of Tgfbr2 (Wnt1-Cre;Tgfbr2 ;BRE) in the palatal mesenchyme enhanced canonical BMP activity in the posterior palate but not in the anterior palate, because of decreased pSmad2/3. pSmad1/5/8-Smad4 complexes were found to be dramatically increased in posterior palatal mesenchymal cells at embryonic day 13.5 cultured in the presence of SB525334. Proximity ligation assay also showed pSmad1/5/8-Smad4 complexes were increased in the posterior palate of Wnt1-Cre;Tgfbr2 mice. Therefore, the reduction of pSmad2/3 level in the palatal mesenchyme of Wnt1-Cre;Tgfbr2 ;BRE mice contributes primarily to the increase of pSmad1/5/8-Smad4 complexes leading to enhanced canonical BMP activity in the posterior palate. Moreover, during early development, canonical BMP signaling operates in the posterior palate but is completely absent in the anterior palate. Canonical TGF-β signaling suppresses canonical BMP signaling activity in the posterior palate by competing limited Smad4.

Inappropriate cathepsin K secretion promotes its enzymatic activation driving heart and valve malformation

“…BMP activity in both regions was reduced (relative to myosin expression) ~50% in gnptab –/– morphants ( Figure 3F and Supplemental Figure 2 ). Due to significant crosstalk between the TGF-β and BMP signaling systems, high TGF-β activity has been shown to negatively impact BMP activity ( 46 , 47 ). To address this possibility, gnptab –/– morphants were treated at 52 hpf with the TGFBRI inhibitor SB505124 (10 μM).…”

TGF-β Signaling and the Epithelial-Mesenchymal Transition during Palatal Fusion

“…In several biological events related to the fate of MEE, the EMT process is enhanced by proteins such as BMP2/4, EGF, FGF, Ephrin, Wnt, Msx1, Runx1 and MMPs [ 36 , 37 , 38 , 39 , 40 , 41 , 42 , 43 , 87 , 88 , 103 , 104 , 105 , 106 , 107 , 108 , 109 , 110 , 112 , 113 ]. In addition, it is possible that the observed EMT during palatal fusion continues after palatal fusion has been completed.…”

“…Expression of both BMP2 and BMP4, as well as their signaling target Msx1, has been detected in the palate [ 102 ]. BMPs are members of the TGF-β superfamily, and growth/differentiation signaling by BMP is one of the key regulators for palatal development [ 36 , 37 , 38 , 96 , 103 , 104 ]. Among other things, BMP signaling regulates cell proliferation, apoptosis, epithelial-mesenchymal interactions, and stem/progenitor differentiation during craniofacial development [ 37 , 103 ].…”

“…Recently, TGF-β signaling has been shown to be regulated by both Smad-dependent and non-Smad dependent pathways ( Figure 2 ). Additionally, multiple other molecules have been shown to play an important role in regulating developmental events, including bone morphogenetic proteins (BMPs) [ 36 , 37 , 38 ], FGFs [ 39 , 40 , 41 ], Wnt [ 7 ], Ephrins [ 42 ] and extra cellar matrix components [ 43 , 44 ]. Here, we present recent advances in TGF-β signaling research as they relate to the fate of the MEE cells during palate development.…”

Genetics and signaling mechanisms of orofacial clefts

“…Smad6/7 are inhibitory Smads that antagonize signaling by competitively binding to the receptor complex (Weiss & Attisano, 2013). Inhibition of Tgf‐β signaling upregulates canonical Bmp activity in the posterior PS, likely because Tgf‐β‐specific Smad2/3 and Bmp‐specific Smad1/5/8 must compete for a binding partner within the same pool of Smad4, reflecting a mechanism of mutual antagonism that occurs between the two pathways (G. Yuan, Zhan, Gou, Chen, & Yang, 2018).…”