TGF-beta3-dependent SMAD2 phosphorylation and inhibition of MEE proliferation during palatal fusion.
Transforming growth factor (TGF) -beta3 is known to selectively regulate the disappearance of murine medial edge epithelium (MEE) during palatal fusion. Previous studies suggested that the selective function of TGF-beta3 in MEE was conducted by TGF-beta receptors. Further studies were needed to demonstrate that the TGF-beta signaling mediators were indeed expressed and phosphorylated in the MEE cells. SMAD2 and SMAD3 were both present in the MEE, whereas SMAD2 was the only one phosphorylated during palatal fusion. SMAD2 phosphorylation was temporospatially restricted to the MEE and correlated with the disappearance of the MEE. No phosphorylated SMAD2 was found in MEE in TGF-beta3(-/-) mice, although nonphosphorylated SMAD2 was present. The results suggest that TGF-beta3 is required for initiating and maintaining SMAD2 phosphorylation in MEE. Phospho-SMAD3 was not detectable in palate during normal palatal fusion. Previous results suggested TGF-beta-induced cessation of DNA synthesis in MEE cells during palatal fusion in vitro. The present results provide evidence that inhibition of MEE proliferation in vivo was controlled by endogenous TGF-beta3. The number of 5-bromo-2'-deoxyuridine (BrdU) -labeled MEE cells was significantly reduced in TGF-beta3(+/+) compared with TGF-beta3(-/-) mice when the MEE seam formed (t-test, P < 0.05). This finding suggests that TGF-beta3 is required for inhibiting MEE proliferation during palatal fusion. The inhibition of MEE proliferation may be mediated by TGF-beta3-dependent phosphorylation of SMAD2.
Cui
Xiao-Mei
XM
Center for Craniofacial Molecular Biology, School of Dentistry, University of Southern California, Los Angeles, California 90033, USA.
Chai
Yang
Y
Chen
Jucheng
J
Yamamoto
Tadashi
T
Ito
Yoshihiro
Y
Bringas
Pablo
P
Shuler
Charles F
CF
D000818:Animals; D015153:Blotting, Western; D001973:Bromodeoxyuridine / Q000494:pharmacology; D002455:Cell Division; D004268:DNA-Binding Proteins / Q000378:metabolism*; D018507:Gene Expression Regulation, Developmental; D007150:Immunohistochemistry; D051379:Mice; D010159:Palate / Q000196:embryology; D021362:Palate, Hard / Q000196:embryology*; D010766:Phosphorylation; D016133:Polymerase Chain Reaction; D018125:Receptors, Transforming Growth Factor beta / Q000378:metabolism; D051899:Smad2 Protein; D051900:Smad3 Protein; D013997:Time Factors; D015534:Trans-Activators / Q000378:metabolism*; D016212:Transforming Growth Factor beta / Q000096:biosynthesis*; D053782:Transforming Growth Factor beta3
D004268:DNA-Binding Proteins; D018125:Receptors, Transforming Growth Factor beta; D051899:Smad2 Protein; C497783:Smad2 protein, mouse; D051900:Smad3 Protein; C497791:Smad3 protein, mouse; C509045:Tgfb3 protein, mouse; D015534:Trans-Activators; D016212:Transforming Growth Factor beta; D053782:Transforming Growth Factor beta3; D001973:Bromodeoxyuridine