title: Hensen's node provides an endogenous limb-forming signal.
abstract: Acquisition of limb-forming ability by discrete regions of the lateral plate of the chick embryo is thought to depend on a signaling cascade moving sequentially from the area of Hensen's node to the somitic mesoderm, the intermediate mesoderm, and then to the prospective limb-forming regions of the lateral plate (Stephens et al., 1991). In the present study it is demonstrated that grafts of Hensen's node can induce the formation of supernumerary rudimentary limbs from the non-limb-forming flank region of the lateral plate of stage 9-15 chick embryos. The rudimentary limbs that form from the flank in response to Hensen's node grafts often contain elongated, jointed cartilaginous elements arranged in three distinct proximodistal segments resembling the developing stylopod, zeugopod, and autopod and express the limb-characteristic genes Msx-2 and BMP-4. However, the rudimentary limbs are incomplete and nonpolarized in that they do not form girdles or paired skeletal elements and fail to express sonic hedgehog, FGF-4, and FGF-8, signaling molecules that have been implicated in regulating the patterning of the developing limb bud. These results indicate that Hensen's node can provide a limb-forming signal to the lateral mesoderm, but that other signals are necessary to promote the expression of genes required for the complete patterning and morphogenesis of the limb.
authors.affiliation: Department of Anatomy, University of Connecticut Health Center, Farmington, Connecticut 06030, USA.
authors.forename: C N
authors.initials: CN
authors.lastname: Dealy
mesh_terms: D000818:Animals; D055415:Bone Morphogenetic Protein 4; D019485:Bone Morphogenetic Proteins / Q000096:biosynthesis; D002356:Cartilage / Q000196:embryology; D002642:Chick Embryo / Q000502:physiology*; D004268:DNA-Binding Proteins / Q000096:biosynthesis; D004475:Ectoderm / Q000502:physiology; D004627:Embryonic Induction; D005121:Extremities / Q000196:embryology*; D016332:Fetal Tissue Transplantation; D051519:Fibroblast Growth Factor 4; D051524:Fibroblast Growth Factor 8; D005346:Fibroblast Growth Factors / Q000096:biosynthesis; D018507:Gene Expression Regulation, Developmental; D006133:Growth Substances / Q000096:biosynthesis; D053823:Hedgehog Proteins; D018398:Homeodomain Proteins; D008648:Mesoderm / Q000502:physiology*; D009024:Morphogenesis; D009420:Nervous System / Q000196:embryology*; D010012:Osteogenesis; D014176:Protein Biosynthesis; D011518:Proto-Oncogene Proteins / Q000096:biosynthesis; D011784:Quail; D012333:RNA, Messenger / Q000096:biosynthesis; D015534:Trans-Activators
chemical_list: D055415:Bone Morphogenetic Protein 4; D019485:Bone Morphogenetic Proteins; D004268:DNA-Binding Proteins; D051519:Fibroblast Growth Factor 4; D006133:Growth Substances; D053823:Hedgehog Proteins; D018398:Homeodomain Proteins; C084119:MSX2 protein; D011518:Proto-Oncogene Proteins; D012333:RNA, Messenger; D015534:Trans-Activators; D051524:Fibroblast Growth Factor 8; D005346:Fibroblast Growth Factors