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Gene Review

Pax9  -  paired box 9

Mus musculus

Synonyms: Paired box protein Pax-9, Pax-9
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Disease relevance of Pax9

  • Although the diastema regions of the two species differed, in both species the earliest difference that we found was weaker expression of mesenchymal Pax9 in the diastema region than in molar and incisor regions at the dental lamina stage [1].
  • Temporal and spatial expression of Pax9 and Sonic hedgehog during development of normal mouse palates and cleft palates in TGF-beta3 null embryos [2].
  • In this study, Pax9 mRNA expression was investigated in the palatal shelves during palatal morphogenesis to assess the correlation between secondary palatal morphogenesis and Pax9 expression of CL/Fr embryos with spontaneous cleft lip and palate [3].

High impact information on Pax9

  • Here we have identified Pax9 as a marker for prospective tooth mesenchyme prior to the first morphological manifestation of odontogenesis [4].
  • Pax9, a member of this transcription factor family, is expressed in somites, pharyngeal pouches, mesenchyme involved in craniofacial, tooth, and limb development, as well as other sites during mouse embryogenesis [5].
  • The mesenchymal transcription factors Msx1 and Pax9 are initially regulated by epithelial FGFs and BMPs, but subsequently they function upstream of these signaling molecules [6].
  • In addition, hypomorphic Pax9 mutants show defects in enamel formation of the continuously growing incisors, whereas molars exhibit increased attrition and reparative dentin formation [7].
  • Together, we conclude that changes of Pax9 expression levels have a direct consequence for mammalian dental patterning and that a minimal Pax9 gene dosage is required for normal morphogenesis and differentiation throughout tooth development [7].

Biological context of Pax9

  • In Pax1/Pax9 double homozygous mutants, formation and anteroposterior polarity of sclerotomes, as well as induction of a chondrocyte-specific cell lineage, appear normal [8].
  • The analysis of Pax9 expression in compound mutants indicates that both spatial expansion and upregulation of Pax9 expression account for its compensatory function during sclerotome development in the absence of Pax1 [8].
  • These results indicate that both Pax9 and -1 may act in parallel during morphogenesis of the vertebral column [9].
  • The missing molars are arrested at different developmental stages and posterior molars are consistently arrested at an earlier stage, suggesting that a reduction of Pax9 gene dosage affects the dental field as a whole [7].
  • In addition, synergistic transcriptional activation of the Bmp4 promoter was lost with coexpression of mutant Pax9 and wild-type Msx1 [10].

Anatomical context of Pax9

  • We have previously shown that the paired-box transcription factors Pax1 and Pax9 synergistically act in the proper formation of the vertebral column [11].
  • Pax9 is expressed in the entire pharyngeal endoderm, and its function is required for normal development of organs derived from pharyngeal pouches [12].
  • However, from embryonic day 14.5 onwards, the size of the Pax9 mutant thymus is severely reduced [12].
  • Thymopoiesis requires Pax9 function in thymic epithelial cells [12].
  • We show here that Pax9, which is expressed in the epithelium of the tongue but not in skin, regulates several aspects of tongue-specific epithelial differentiation [13].

Regulatory relationships of Pax9

  • Pax1 and Pax9 activate Bapx1 to induce chondrogenic differentiation in the sclerotome [11].

Other interactions of Pax9

  • Nevertheless, downstream events of the Pax1/Pax9 action and their target genes remain to be elucidated [11].
  • Pax9, which is expressed in the face, paws, and tail, once qualified as a possible candidate for the Adp locus [14].
  • These results strongly suggest that Bapx1 is a direct target of Pax1 and Pax9 [11].
  • From our results, we conclude that the Adp locus is distinct from either Pax9 or Tcf3a [14].
  • Uncx4.1 is required for the formation of the pedicles and proximal ribs and acts upstream of Pax9 [15].

Analytical, diagnostic and therapeutic context of Pax9


  1. Gene expression patterns associated with suppression of odontogenesis in mouse and vole diastema regions. Keränen, S.V., Kettunen, P., Aberg, T., Thesleff, I., Jernvall, J. Dev. Genes Evol. (1999) [Pubmed]
  2. Temporal and spatial expression of Pax9 and Sonic hedgehog during development of normal mouse palates and cleft palates in TGF-beta3 null embryos. Sasaki, Y., O'kane, S., Dixon, J., Dixon, M.J., Ferguson, M.W. Arch. Oral Biol. (2007) [Pubmed]
  3. Association between palatal morphogenesis and Pax9 expression pattern in CL/Fr embryos with clefting during palatal development. Hamachi, T., Sasaki, Y., Hidaka, K., Nakata, M. Arch. Oral Biol. (2003) [Pubmed]
  4. Antagonistic interactions between FGF and BMP signaling pathways: a mechanism for positioning the sites of tooth formation. Neubüser, A., Peters, H., Balling, R., Martin, G.R. Cell (1997) [Pubmed]
  5. Pax9-deficient mice lack pharyngeal pouch derivatives and teeth and exhibit craniofacial and limb abnormalities. Peters, H., Neubüser, A., Kratochwil, K., Balling, R. Genes Dev. (1998) [Pubmed]
  6. Teeth. Where and how to make them. Peters, H., Balling, R. Trends Genet. (1999) [Pubmed]
  7. Reduction of Pax9 gene dosage in an allelic series of mouse mutants causes hypodontia and oligodontia. Kist, R., Watson, M., Wang, X., Cairns, P., Miles, C., Reid, D.J., Peters, H. Hum. Mol. Genet. (2005) [Pubmed]
  8. Pax1 and Pax9 synergistically regulate vertebral column development. Peters, H., Wilm, B., Sakai, N., Imai, K., Maas, R., Balling, R. Development (1999) [Pubmed]
  9. Characterization and developmental expression of Pax9, a paired-box-containing gene related to Pax1. Neubüser, A., Koseki, H., Balling, R. Dev. Biol. (1995) [Pubmed]
  10. Functional consequences of interactions between Pax9 and Msx1 genes in normal and abnormal tooth development. Ogawa, T., Kapadia, H., Feng, J.Q., Raghow, R., Peters, H., D'Souza, R.N. J. Biol. Chem. (2006) [Pubmed]
  11. Pax1 and Pax9 activate Bapx1 to induce chondrogenic differentiation in the sclerotome. Rodrigo, I., Hill, R.E., Balling, R., Münsterberg, A., Imai, K. Development (2003) [Pubmed]
  12. Thymopoiesis requires Pax9 function in thymic epithelial cells. Hetzer-Egger, C., Schorpp, M., Haas-Assenbaum, A., Balling, R., Peters, H., Boehm, T. Eur. J. Immunol. (2002) [Pubmed]
  13. Pax9 is required for filiform papilla development and suppresses skin-specific differentiation of the mammalian tongue epithelium. Jonker, L., Kist, R., Aw, A., Wappler, I., Peters, H. Mech. Dev. (2004) [Pubmed]
  14. Fine genetic mapping defines the genetic order of Pax9, Tcf3a, and Acrodysplasia (Adp). Watanabe, T., Tarttelin, E., Neubüser, A., Kimura, M., Solter, D. Mamm. Genome (1994) [Pubmed]
  15. Uncx4.1 is required for the formation of the pedicles and proximal ribs and acts upstream of Pax9. Mansouri, A., Voss, A.K., Thomas, T., Yokota, Y., Gruss, P. Development (2000) [Pubmed]
  16. Pax genes and organogenesis: Pax9 meets tooth development. Peters, H., Neubüser, A., Balling, R. Eur. J. Oral Sci. (1998) [Pubmed]
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