Precocious terminal differentiation of premigratory limb muscle precursor cells requires positive signalling.
The timing of myogenic differentiation of hypaxial muscle precursor cells in the somite lags behind that of epaxial precursors. Two hypotheses have been proposed to explain this delay. One attributes the delay to the presence of negative-acting signals from the lateral plate mesoderm adjacent to the hypaxial muscle precursor cells located in the ventrolateral lip of the somitic dermomyotome (Pourquié et al. [1995] Proc. Natl. Acad. Sci. USA 92:3219-3223). The second attributes the delay to an absence of positive-acting inductive signals, similar to those from the axial structures that induce epaxial myotome development (Pownall et al. [1996] Development 122:1475-1488). Because both studies relied principally upon changes in the expression pattern of mRNAs specific to early muscle precursor cell markers, we revisited these experiments using two methods to assess muscle terminal differentiation. First, injection of fluorescent dyes before surgery was used to determine whether ventrolateral lip cells transform from epithelial cells to elongated myocytes. Second, an antibody to a terminal differentiation marker and a new monoclonal antibody that recognises avian and mammalian Pax3 were used for immunohistochemistry to assess the transition from precursor cell to myocyte. The results support both hypotheses and show further that placing axial structures adjacent to the somite ventrolateral lip induces an axial pattern of myocyte terminal differentiation and elongation.
Department of Anatomy, University of California, San Francisco, California 94143, USA.
Sara J
SJ
Venters
Rebecca E
RE
Argent
Fiona M
FM
Deegan
Gina
G
Perez-Baron
Ted S
TS
Wong
William E
WE
Tidyman
Wilfred F
WF
Denetclaw
Christophe
C
Marcelle
Marianne
M
Bronner-Fraser
Charles P
CP
Ordahl
D000818:Animals; D002454:Cell Differentiation; D002465:Cell Movement; D002642:Chick Embryo; D003370:Coturnix; D004268:DNA-Binding Proteins / Q000378:metabolism; D005121:Extremities / Q000196:embryology*; D005456:Fluorescent Dyes / Q000494:pharmacology; D007150:Immunohistochemistry; D017403:In Situ Hybridization; D008856:Microscopy, Fluorescence; D008954:Models, Biological; D009132:Muscles / Q000166:cytology / Q000196:embryology*; D017570:MyoD Protein / Q000378:metabolism; D000072041:PAX3 Transcription Factor; D051761:Paired Box Transcription Factors; D012333:RNA, Messenger / Q000378:metabolism; D015398:Signal Transduction; D013997:Time Factors; D014157:Transcription Factors / Q000378:metabolism
D004268:DNA-Binding Proteins; D005456:Fluorescent Dyes; D017570:MyoD Protein; D000072041:PAX3 Transcription Factor; D051761:Paired Box Transcription Factors; D012333:RNA, Messenger; D014157:Transcription Factors; C068686:Pax3 protein, mouse