FIG. 4.

Compound mutant embryos have a drastic early reduction in NCCs. Littermate control (a,c) and compound mutant (b,d) whole-mount embryos at 9.5 dpc labeled by X-gal staining to trace Pax3-lineage cells. In controls, blue Pax3-lineage cells fill the first three pharyngeal arches (PA1, PA2, and PA3) and more of the developing skull. In littermate compound mutant embryos, only PA1 contains Pax3-lineage cells; PA2 and PA3 appear devoid of Pax3-lineage cells. Both embryos are at identical developmental stages, each with 26 somites. (c) and (d) are enlarged regions from (a) and (b), respectively. PA, pharyngeal arch; ss, somite stage.