Conservation of early odontogenic signaling pathways in Aves.
Teeth have been missing from birds (Aves) for at least 60 million years. However, in the chick oral cavity a rudiment forms that resembles the lamina stage of the mammalian molar tooth germ. We have addressed the molecular basis for this secondary loss of tooth formation in Aves by analyzing in chick embryos the status of molecular pathways known to regulate mouse tooth development. Similar to the mouse dental lamina, expression of Fgf8, Pitx2, Barx1, and Pax9 defines a potential chick odontogenic region. However, the expression of three molecules involved in tooth initiation, Bmp4, Msx1, and Msx2, are absent from the presumptive chick dental lamina. In chick mandibles, exogenous bone morphogenetic protein (BMP) induces Msx expression and together with fibroblast growth factor promotes the development of Sonic hedgehog expressing epithelial structures. Distinct epithelial appendages also were induced when chick mandibular epithelium was recombined with a tissue source of BMPs and fibroblast growth factors, chick skin mesenchyme. These results show that, although latent, the early signaling pathways involved in odontogenesis remain inducible in Aves and suggest that loss of odontogenic Bmp4 expression may be responsible for the early arrest of tooth development in living birds.
Chen
Y
Y
Division of Genetics, Department of Medicine, Brigham and Women's Hospital and Harvard Medical School, Boston, MA 02115, USA.
Zhang
Y
Y
Jiang
T X
TX
Barlow
A J
AJ
St Amand
T R
TR
Hu
Y
Y
Heaney
S
S
Francis-West
P
P
Chuong
C M
CM
Maas
R
R
D000818:Animals; D055415:Bone Morphogenetic Protein 4; D019485:Bone Morphogenetic Proteins / Q000235:genetics; D002642:Chick Embryo; D002645:Chickens; D004268:DNA-Binding Proteins / Q000235:genetics; D051524:Fibroblast Growth Factor 8; D005346:Fibroblast Growth Factors / Q000235:genetics; D018398:Homeodomain Proteins / Q000235:genetics; D051957:MSX1 Transcription Factor; D008334:Mandible / Q000196:embryology; D051379:Mice; D008817:Mice, Mutant Strains; D009024:Morphogenesis; D009306:Natal Teeth / Q000196:embryology; D009687:Nuclear Proteins; D009805:Odontogenesis / Q000502:physiology*; D051764:PAX9 Transcription Factor; D051761:Paired Box Transcription Factors; D015398:Signal Transduction / Q000502:physiology*; D014157:Transcription Factors / Q000235:genetics; D000097577:Homeobox Protein PITX2
D055415:Bone Morphogenetic Protein 4; D019485:Bone Morphogenetic Proteins; D004268:DNA-Binding Proteins; D051524:Fibroblast Growth Factor 8; D005346:Fibroblast Growth Factors; D018398:Homeodomain Proteins; D051957:MSX1 Transcription Factor; D009687:Nuclear Proteins; D051764:PAX9 Transcription Factor; D051761:Paired Box Transcription Factors; D014157:Transcription Factors; D000097577:Homeobox Protein PITX2; C095587:Barx1 protein, mouse; C525810:Bmp4 protein, mouse; C084119:MSX2 protein; C101485:homeobox protein PITX1; C433629:homeobox protein PITX3