Fig. 6. Regulation of skeletal myogenesis in Meox1;Meox2 double mutants. In situ hybridization analysis of gene expression at E9.5 for: Pax3 (A,B), Pax7 (C,D), Myf5 (E-H) and myogenin (I,J). Control embryos (A,C,E,I), Meox mutants (B,D,F,G,H,J). (A) Pax3 is expressed in the dermomyotome of differentiated somites (arrowheads) and the neural tube (arrow). In Meox1^-/-;Meox2^-/- embryos (B), however, Pax3 is expressed at very reduced levels in the ventrolateral region of the dermomyotome of somites (arrowheads), while neural tube expression remains normal (arrow). The dermomyotome Pax7 expression seen in control embryos (arrowheads) (C) is extinguished in Meox double mutants (D). Myf5 mRNA is localised to the ventrolateral dermomyotome of control embryos (arrowhead, E). In double mutant embryos, Myf5 expression is not detected in caudal somites, and only at reduced levels in rostral somites (F). Myf5 expression is limited along the dorsoventral axis in mutants, compared with controls. Embryos with only one wild-type Meox allele have an intermediate phenotype; those with one Meox1 allele (G), Meox1^+/-;Meox2^-/-, were less severely affected than those with one Meox2 allele (H), Meox1^-/-;Meox2^+/-. (I,J) In the absence of Meox gene function, the expression of myogenin was reduced and limited to inter-limb somites (J).