Compartmentalization of the somite and myogenesis in chick embryos are influenced by wnt expression.
Muscles of the body and bones of the axial skeleton derive from specialized regions of somites. Somite development is influenced by adjacent structures. In particular, the dorsal neural tube and the overlying ectoderm have been shown to be necessary for the induction of myogenic precursor cells in the dermomyotome. Members of the Wnt family of signaling molecules, which are expressed in the dorsal neural tube and the ectoderm, are postulated to be responsible for this process. It is shown here that ectopically implanted Wnt-1-, -3a-, and -4-expressing cells alter the process of somite compartmentalization in vivo. An enlarged dorsal compartment results from the implantation of Wnt-expressing cells ventrally between the neural tube/notochord and epithelial somites, at the expense of the ventral compartment, the sclerotome. Thus, ectopic Wnt expression is able to override the influence of ventralizing signals arising from notochord and floor plate. This shift of the border between the two compartments was identified by an increase in the domain of Pax-3 expression and a complete loss of Pax-1 expression in somites close to the ectopic Wnt signal. The expanded expression of MyoD and desmin provides evidence that it is the myotome which increases as a result of Wnt signaling. Paraxis expression is also drastically amplified after implantation of Wnt-expressing cells indicating that Wnts are involved in the formation and maintenance of somite epithelium and suggesting that Paraxis is activated through Wnt signaling pathways. Taken together these results suggest that ectopic Wnts disturb the normal balance of signaling molecules within the somite, resulting in an enhanced recruitment of somitic cells into the myogenic lineage.
Wagner
J
J
Institute of Anatomy, University of Freiburg, Freiburg, D-79001, Germany.
Schmidt
C
C
Nikowits
W
W
Christ
B
B
D000818:Animals; D051792:Basic Helix-Loop-Helix Proteins; D002460:Cell Line; D017690:Cell Transplantation; D002642:Chick Embryo; D004268:DNA-Binding Proteins / Q000378:metabolism; D003893:Desmin / Q000378:metabolism; D004627:Embryonic Induction; D004848:Epithelium / Q000378:metabolism; D018507:Gene Expression Regulation, Developmental; D053823:Hedgehog Proteins; D006651:Histocytochemistry; D017403:In Situ Hybridization; D051379:Mice; D018482:Muscle, Skeletal / Q000166:cytology / Q000196:embryology* / Q000378:metabolism; D017570:MyoD Protein / Q000378:metabolism; D009672:Notochord / Q000166:cytology / Q000378:metabolism; D009687:Nuclear Proteins; D000072041:PAX3 Transcription Factor; D051761:Paired Box Transcription Factors; D011506:Proteins / Q000378:metabolism; D011518:Proto-Oncogene Proteins / Q000235:genetics / Q000378:metabolism*; D016372:RNA, Antisense / Q000378:metabolism; D012333:RNA, Messenger / Q000235:genetics / Q000378:metabolism; D051381:Rats; D015398:Signal Transduction; D019170:Somites / Q000166:cytology / Q000378:metabolism*; D015534:Trans-Activators; D014157:Transcription Factors / Q000378:metabolism; D051153:Wnt Proteins; D051155:Wnt1 Protein; D029961:Zebrafish Proteins
D051792:Basic Helix-Loop-Helix Proteins; D004268:DNA-Binding Proteins; D003893:Desmin; D053823:Hedgehog Proteins; D017570:MyoD Protein; D009687:Nuclear Proteins; D000072041:PAX3 Transcription Factor; D051761:Paired Box Transcription Factors; D011506:Proteins; D011518:Proto-Oncogene Proteins; D016372:RNA, Antisense; D012333:RNA, Messenger; D015534:Trans-Activators; D014157:Transcription Factors; D051153:Wnt Proteins; D051155:Wnt1 Protein; D029961:Zebrafish Proteins; C093234:Tcf15 protein, mouse; C495246:Wnt1 protein, mouse; C495245:Wnt1 protein, rat; C489412:pax3a protein, zebrafish; C512784:tcf15 protein, zebrafish; C068686:Pax3 protein, mouse; C070835:PAX1 transcription factor