Fig. 1.

Expression of pax7 and pax3 compared during neurulation in Xenopus laevis. (A) A bootstrap phylogenetic tree illustrates the clear grouping of pax7 and pax3 paralogs in vertebrates while the chordate have a single Pax3/7 gene. Accession numbers are given in Supplemental Fig. 1. (B) RT-PCR analysis on whole embryos shows the early onset of pax3 expression during gastrulation (i.e. at times of neural crest induction), whereas pax7 is detected at mid-neurulation, after muscle actin (MA) is detected. EF1α is used as a baseline control. (C) In situ hybridization on stage-matched sibling embryos confirms the late onset of pax7, in brain first (c) then in paraxial mesoderm, and the lack of expression in the neural crest progenitor area (c, d). In contrast, pax3 and snail2 label neural crest (e–h). Myod marks paraxial mesoderm (i, j).