Sonic hedgehog is required for survival of both myogenic and chondrogenic somitic lineages.
In vertebrates, the medial moieties of the somites give rise to the vertebrae and epaxial muscles, which develop in close relationship with the axial organs, neural tube and notochord. The lateral moieties contribute to the ribs and to limb and body wall muscles (hypaxial muscles) after a phase of lateral and ventral migration. Surgical ablation of the neural tube and notochord in the chick embryo during segmentation and early differentiation of the somites (day 2 of incubation) does not affect primary development of the hypaxial muscles, but leads to a complete absence of epaxial muscles, vertebrae and ribs, due to cell death in the somites. Here we demonstrate that cell death, which occurs within 24 hours of excision of the axial organs, affects both myogenic and chondrogenic cell lineages defined, respectively, by the expression of MyoD and Pax-1 genes. In contrast, Pax-3 transcripts, normally present in cells giving rise to hypaxial muscles, are preserved in the excised embryos. Backgrafting either the ventral neural tube or the notochord allows survival of MyoD- and Pax-1-expressing cells. Similarly, Sonic hedgehog-producing cells grafted in place of axial organs also rescue MyoD- and Pax-1-expressing cells from death and allow epaxial muscles, ribs and vertebrae to undergo organogenesis. These results demonstrate that the ventral neural tube and the notochord promote the survival of both myogenic and chondrogenic cell lineages in the somites and that this action is mediated by Sonic hedgehog.
Teillet
M
M
Institut d'Embryologie Cellulaire et Moléculaire du CNRS et du Collège de France, 49 bis Avenue de la Belle Gabrielle, 94736 Nogent-sur-Marne Cedex, France.
Watanabe
Y
Y
Jeffs
P
P
Duprez
D
D
Lapointe
F
F
Le Douarin
N M
NM
D000818:Animals; D019521:Body Patterning; D002356:Cartilage / Q000196:embryology*; D019070:Cell Lineage; D002470:Cell Survival; D002490:Central Nervous System / Q000196:embryology / Q000601:surgery; D002642:Chick Embryo; D004268:DNA-Binding Proteins / Q000096:biosynthesis; D004627:Embryonic Induction; D005819:Genetic Markers; D053823:Hedgehog Proteins; D009132:Muscles / Q000196:embryology*; D017570:MyoD Protein / Q000096:biosynthesis; D009672:Notochord / Q000601:surgery; D051761:Paired Box Transcription Factors; D011506:Proteins / Q000378:metabolism*; D011784:Quail; D012272:Ribs / Q000196:embryology; D019170:Somites; D013131:Spine / Q000196:embryology; D016378:Tissue Transplantation; D015534:Trans-Activators; D014157:Transcription Factors / Q000096:biosynthesis
D004268:DNA-Binding Proteins; D005819:Genetic Markers; D053823:Hedgehog Proteins; D017570:MyoD Protein; D051761:Paired Box Transcription Factors; D011506:Proteins; D015534:Trans-Activators; D014157:Transcription Factors; C070835:PAX1 transcription factor