Tgf-beta3-induced palatal fusion is mediated by Alk-5/Smad pathway.
Cleft palate is among the most common birth defects in humans, caused by a failure in the complex multistep developmental process of palatogenesis. It has been recently shown that transforming growth factor beta3 (Tgf-beta3) is an absolute requirement for successful palatal fusion, both in mice and humans. However, very little is known about the mechanisms of Tgf-beta3 signaling during this process. Here we show that putative Tgf-beta type I receptors, Alk-1, Alk-2, and Alk-5, are all endogenously expressed in the palatal epithelium. Activation of Alk-5 in the Tgf-beta3 (-/-) palatal epithelium is able to rescue palatal fusion, whereas inactivation of Alk-5 in the wild-type palatal epithelium prevents palatal fusion. The effect of Alk-2 is similar, but less pronounced. The induction of fusion by activation of Alk-5 or Alk-2 is stronger in the posterior parts of the palates at the embryonic day 14 (E14), while their activation at E13.5 also restores anterior fusion, reflecting the natural anterior-posterior direction of palate maturation in vivo. We also show that Smad2 is endogenously activated in the palatal midline epithelial seam (MES) during the fusion process. By using a mutant Alk-5 receptor that is an active kinase but is unable to activate Smads, we show that activation of Smad-independent Tgf-beta responses is not sufficient to induce fusion of shelves deficient in Tgf-beta3. Based on these observations, we conclude that the Smad2-dependent Alk-5 signaling pathway is dominant in palatal fusion driven by Tgf-beta3.
Dudas
Marek
M
Developmental Biology Program, Department of Pathology of University of Southern California, Childrens Hospital Los Angeles, Los Angeles, CA 90027, USA.
Nagy
Andre
A
Laping
Nicholas J
NJ
Moustakas
Aristidis
A
Kaartinen
Vesa
V
D030201:Activin Receptors, Type I / Q000502:physiology*; D000256:Adenoviridae / Q000235:genetics; D000818:Animals; D001483:Base Sequence; D002972:Cleft Palate / Q000209:etiology; D017931:DNA Primers; D004268:DNA-Binding Proteins / Q000502:physiology*; D005822:Genetic Vectors; D017403:In Situ Hybridization; D051379:Mice; D018345:Mice, Knockout; D009924:Organ Culture Techniques; D010159:Palate / Q000196:embryology*; D017346:Protein Serine-Threonine Kinases; D000077293:Receptor, Transforming Growth Factor-beta Type I; D018125:Receptors, Transforming Growth Factor beta / Q000502:physiology*; D020133:Reverse Transcriptase Polymerase Chain Reaction; D051785:Smad Proteins; D015534:Trans-Activators / Q000502:physiology*; D016212:Transforming Growth Factor beta / Q000235:genetics / Q000502:physiology*; D053782:Transforming Growth Factor beta3
D017931:DNA Primers; D004268:DNA-Binding Proteins; D018125:Receptors, Transforming Growth Factor beta; D051785:Smad Proteins; C509045:Tgfb3 protein, mouse; D015534:Trans-Activators; D016212:Transforming Growth Factor beta; D053782:Transforming Growth Factor beta3; D017346:Protein Serine-Threonine Kinases; D030201:Activin Receptors, Type I; D000077293:Receptor, Transforming Growth Factor-beta Type I; C000625841:TGFBR1 protein, human; C000625842:Tgfbr1 protein, mouse