title: Regulation of BMP-dependent chondrogenesis in early limb mesenchyme by TGFbeta signals.
abstract: In the developing axial skeleton, sequential sonic hedgehog (SHH) and bone morphogenetic protein (BMP) signals are required for specification of a chondrogenic fate in presomitic tissue. A similar paradigm is thought to operate in the limb, but the signals involved are unclear. To investigate the nature of these signals, we examined BMP action in mesenchymal populations derived from the early murine limb bud (approximately embryonic day 10.5). These populations exhibited a graded response to BMPs, in which early limb mesenchymal cells (from the distal hind limb) displayed an anti-chondrogenic response, whereas BMPs promoted chondrogenesis in more mature cell populations (from the proximal fore limb). Under these conditions, multiple Gata genes were induced by BMPs and the extent of induction correlated with BMP anti-chondrogenic activity. A screen of limb-bud-expressed ligands revealed that prior short-term exposure to transforming growth factor beta1 (TGFbeta1) ameliorated the anti-chondrogenic response to BMP. Furthermore, brief activation of the TGFbeta pathway was found to be necessary for subsequent induction of chondrogenesis by BMPs. Our findings indicate that, similar to axial skeletogenesis, induction of chondrogenesis in the appendicular skeleton is a two-step process. However, the programs differ in the transient signals driving chondrogenic responsiveness to BMPs, with SHH operating in the former and TGFbeta activation in the latter.
authors.affiliation: Biomedical Research Centre, University of British Columbia, Vancouver, BC, Canada.
authors.forename: Konstantina
authors.initials: K
authors.lastname: Karamboulas
authors.forename: Helen J
authors.initials: HJ
authors.lastname: Dranse
authors.forename: T Michael
authors.initials: TM
authors.lastname: Underhill
mesh_terms: D000818:Animals; D055415:Bone Morphogenetic Protein 4 / Q000378:metabolism*; D002356:Cartilage / Q000196:embryology / Q000378:metabolism; D002454:Cell Differentiation; D002478:Cells, Cultured; D020219:Chondrogenesis; D005260:Female; D018507:Gene Expression Regulation, Developmental; D018878:Limb Buds / Q000196:embryology / Q000378:metabolism*; D008297:Male; D008648:Mesoderm / Q000196:embryology / Q000378:metabolism*; D051379:Mice / Q000196:embryology / Q000235:genetics / Q000378:metabolism*; D015398:Signal Transduction; D053773:Transforming Growth Factor beta1 / Q000378:metabolism*
chemical_list: C525810:Bmp4 protein, mouse; D055415:Bone Morphogenetic Protein 4; D053773:Transforming Growth Factor beta1