title: Smad4 is required to induce digit ray primordia and to initiate the aggregation and differentiation of chondrogenic progenitors in mouse limb buds.
abstract: SMAD4 is an essential mediator of canonical TGFβ/BMP signal transduction and we inactivated Smad4 in mouse limb buds from early stages onward to study its functions in the mesenchyme. While this Smad4 inactivation did not alter the early Sox9 distribution, prefiguring the chondrogenic primordia of the stylopod and zeugopod, it disrupted formation of all Sox9-positive digit ray primordia. Specific inactivation of Smad4 during handplate development pointed to its differential requirement for posterior and anterior digit ray primordia. At the cellular level, Smad4 deficiency blocked the aggregation of Sox9-positive progenitors, thereby preventing chondrogenic differentiation as revealed by absence of collagen type II. The progressive loss of SOX9 due to disrupting digit ray primordia and chondrogenesis was paralleled by alterations in genes marking other lineages. This pointed to a general loss of tissue organization and diversion of mutant cells toward non-specific connective tissue. Conditional inactivation of Bmp2 and Bmp4 indicated that the loss of digit ray primordia and increase in connective tissue were predominantly a consequence of disrupting SMAD4-mediated BMP signal transduction. In summary, our analysis reveals that SMAD4 is required to initiate: (1) formation of the Sox9-positive digit ray primordia; and (2) aggregation and chondrogenic differentiation of all limb skeletal elements.
authors.affiliation: Developmental Genetics, Department of Biomedicine, University of Basel, Mattenstrasse 28, Basel, Switzerland.
authors.forename: Jean-Denis
authors.initials: JD
authors.lastname: Bénazet
authors.forename: Emanuele
authors.initials: E
authors.lastname: Pignatti
authors.forename: Ashleigh
authors.initials: A
authors.lastname: Nugent
authors.forename: Erkan
authors.initials: E
authors.lastname: Unal
authors.forename: Frédéric
authors.initials: F
authors.lastname: Laurent
authors.forename: Rolf
authors.initials: R
authors.lastname: Zeller
mesh_terms: D000818:Animals; D055396:Bone Morphogenetic Protein 2 / Q000378:metabolism; D055415:Bone Morphogenetic Protein 4 / Q000378:metabolism; D002454:Cell Differentiation / Q000235:genetics; D002478:Cells, Cultured; D020219:Chondrogenesis / Q000235:genetics; D024043:Collagen Type II / Q000172:deficiency; D003238:Connective Tissue / Q000378:metabolism; D005121:Extremities / Q000196:embryology; D005346:Fibroblast Growth Factors / Q000378:metabolism; D018507:Gene Expression Regulation, Developmental; D053823:Hedgehog Proteins / Q000378:metabolism; D036341:Intercellular Signaling Peptides and Proteins / Q000378:metabolism; D018878:Limb Buds / Q000166:cytology / Q000196:embryology* / Q000378:metabolism; D051379:Mice; D055758:SOX9 Transcription Factor / Q000378:metabolism*; D015398:Signal Transduction / Q000235:genetics; D051901:Smad4 Protein / Q000235:genetics* / Q000378:metabolism*; D013234:Stem Cells; D016207:Cytokines
chemical_list: D055396:Bone Morphogenetic Protein 2; D055415:Bone Morphogenetic Protein 4; D024043:Collagen Type II; D005346:Fibroblast Growth Factors; D053823:Hedgehog Proteins; D036341:Intercellular Signaling Peptides and Proteins; D055758:SOX9 Transcription Factor; D051901:Smad4 Protein; C525719:Bmp2 protein, mouse; C525810:Bmp4 protein, mouse; C465570:Shh protein, mouse; C490810:Smad4 protein, mouse; C527933:Sox9 protein, mouse; C113178:Grem1 protein, mouse; D016207:Cytokines