The murine Bapx1 homeobox gene plays a critical role in embryonic development of the axial skeleton and spleen.
Our previous studies in both mouse and human identified the Bapx1 homeobox gene, a member of the NK gene family, as one of the earliest markers for prechondrogenic cells that will subsequently undergo mesenchymal condensation, cartilage production and, finally, endochondral bone formation. In addition, Bapx1 is an early developmental marker for splanchnic mesoderm, consistent with a role in visceral mesoderm specification, a function performed by its homologue bagpipe, in Drosophila. The human homologue of Bapx1 has been identified and mapped to 4p16.1, a region containing loci for several skeletal diseases. Bapx1 null mice are affected by a perinatal lethal skeletal dysplasia and asplenia, with severe malformation or absence of specific bones of the vertebral column and cranial bones of mesodermal origin, with the most severely affected skeletal elements corresponding to ventral structures associated with the notochord. We provide evidence that the failure of the formation of skeletal elements in Bapx1 null embryos is a consequence of a failure of cartilage development, as demonstrated by downregulation of several molecular markers required for normal chondroblast differentiation (&agr; 1(II) collagen, Fgfr3, Osf2, Indian hedgehog, Sox9), as well as a chondrocyte-specific alpha1 (II) collagen-lacZ transgene. The cartilage defects are correlated with failed differentiation of the sclerotome at the time when these cells are normally initiating chondrogenesis. Loss of Bapx1 is accompanied by an increase in apoptotic cell death in affected tissues, although cell cycling rates are unaltered.
Tribioli
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Brookdale Center for Developmental and Molecular Biology, Mount Sinai School of Medicine, One Gustave L. Levy Place, New York, NY 10029-6574, USA.
Lufkin
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D000818:Animals; D001846:Bone Development; D055415:Bone Morphogenetic Protein 4; D019485:Bone Morphogenetic Proteins / Q000235:genetics; D002358:Cartilage, Articular / Q000196:embryology; D003094:Collagen / Q000235:genetics; D050659:Core Binding Factor Alpha 1 Subunit; D004268:DNA-Binding Proteins / Q000235:genetics; D005260:Female; D018507:Gene Expression Regulation, Developmental; D018390:Gene Targeting; D005801:Genes, Homeobox; D053823:Hedgehog Proteins; D018398:Homeodomain Proteins / Q000235:genetics / Q000502:physiology*; D006801:Humans; D008297:Male; D051379:Mice; D008810:Mice, Inbred C57BL; D008822:Mice, Transgenic; D009363:Neoplasm Proteins; D051761:Paired Box Transcription Factors; D011505:Protein-Tyrosine Kinases; D011506:Proteins / Q000235:genetics; D051498:Receptor, Fibroblast Growth Factor, Type 3; D017468:Receptors, Fibroblast Growth Factor / Q000235:genetics; D013131:Spine / Q000196:embryology*; D013154:Spleen / Q000196:embryology*; D015534:Trans-Activators; D014157:Transcription Factors / Q000235:genetics
C525809:BMP4 protein, human; C525810:Bmp4 protein, mouse; D055415:Bone Morphogenetic Protein 4; D019485:Bone Morphogenetic Proteins; D050659:Core Binding Factor Alpha 1 Subunit; D004268:DNA-Binding Proteins; D053823:Hedgehog Proteins; D018398:Homeodomain Proteins; C491536:NKX3-2 protein, human; D009363:Neoplasm Proteins; C107965:Nkx3-2 protein, mouse; D051761:Paired Box Transcription Factors; D011506:Proteins; D017468:Receptors, Fibroblast Growth Factor; D015534:Trans-Activators; D014157:Transcription Factors; C070835:PAX1 transcription factor; D003094:Collagen; C496365:FGFR3 protein, human; C496366:Fgfr3 protein, mouse; D011505:Protein-Tyrosine Kinases; D051498:Receptor, Fibroblast Growth Factor, Type 3