title: The crosstalk between transforming growth factor-β1 and delta like-1 mediates early chondrogenesis during embryonic endochondral ossification.
abstract: Delta like-1 (Dlk1)/preadipocyte factor-1 (Pref-1)/fetal antigen-1 (FA1) is a novel surface marker for embryonic chondroprogenitor cells undergoing lineage progression from proliferation to prehypertrophic stages. However, mechanisms mediating control of its expression during chondrogenesis are not known. Thus, we examined the effect of a number of signaling molecules and their inhibitors on Dlk1 expression during in vitro chondrogenic differentiation in mouse embryonic limb bud mesenchymal micromass cultures and mouse embryonic fibroblast (MEF) pellet cultures. Dlk1/Pref-1 was initially expressed during mesenchymal condensation and chondrocyte proliferation, in parallel with expression of Sox9 and Col2a1, and was downregulated upon the expression of Col10a1 by hypertrophic chondrocytes. Among a number of molecules that affected chondrogenesis, transforming growth factor-β1 (TGF-β1)-induced proliferation of chondroprogenitors was associated with decreased Dlk1 expression. This effect was abolished by TGF-β signaling inhibitor SB431542, suggesting regulation of Dlk1/FA1 by TGF-β1 signaling in chondrogenesis. TGF-β1-induced Smad phosphorylation and chondrogenesis were significantly increased in Dlk1(-/-) MEF, while they were blocked in Dlk1 overexpressing MEF, in comparison with wild-type MEF. Furthermore, overexpression of Dlk1 or addition of its secreted form FA1 dramatically inhibited TGF-β1-induced Smad reporter activity. In conclusion, our data identified Dlk1/FA1 as a downstream target of TGF-β1 signaling molecule that mediates its function in embryonic chondrogenesis. The crosstalk between TGF-β1 and Dlk1/FA1 was shown to promote early chondrogenesis during the embryonic endochondral ossification process.
authors.affiliation: Endocrine Research Laboratory (KMEB), Department of Endocrinology and Metabolism, Odense University Hospital, Odense, Denmark.
authors.forename: Hanna
authors.initials: H
authors.lastname: Taipaleenmäki
authors.forename: Linda
authors.initials: L
authors.lastname: Harkness
authors.forename: Li
authors.initials: L
authors.lastname: Chen
authors.forename: Kenneth H
authors.initials: KH
authors.lastname: Larsen
authors.forename: Anna-Marja
authors.initials: AM
authors.lastname: Säämänen
authors.forename: Moustapha
authors.initials: M
authors.lastname: Kassem
authors.forename: Basem M
authors.initials: BM
authors.lastname: Abdallah
mesh_terms: D000818:Animals; D002135:Calcium-Binding Proteins; D002454:Cell Differentiation; D002478:Cells, Cultured; D020219:Chondrogenesis; D005347:Fibroblasts / Q000378:metabolism; D018507:Gene Expression Regulation, Developmental; D006801:Humans; D036341:Intercellular Signaling Peptides and Proteins / Q000235:genetics / Q000378:metabolism; D047908:Intracellular Signaling Peptides and Proteins / Q000235:genetics / Q000378:metabolism*; D018878:Limb Buds / Q000166:cytology / Q000378:metabolism; D008565:Membrane Proteins / Q000235:genetics / Q000378:metabolism*; D051379:Mice; D008810:Mice, Inbred C57BL; D008822:Mice, Transgenic; D010012:Osteogenesis; D010766:Phosphorylation; D015398:Signal Transduction; D051899:Smad2 Protein / Q000378:metabolism; D053773:Transforming Growth Factor beta1 / Q000494:pharmacology / Q000502:physiology*
chemical_list: D002135:Calcium-Binding Proteins; C512925:Dlk1 protein, mouse; C511877:Dll3 protein, mouse; D036341:Intercellular Signaling Peptides and Proteins; D047908:Intracellular Signaling Peptides and Proteins; D008565:Membrane Proteins; D051899:Smad2 Protein; C497783:Smad2 protein, mouse; D053773:Transforming Growth Factor beta1