Fig. 1. The expression pattern of the lacZ gene from the mutated Pax3 allele recapitulates the Pax3 expression pattern. Whole mount X-gal staining at different developmental stages. Embryos in A and B are heterozygous, embryos shown in E and F are homozygous for the mutation (A,E: E10; B,F: E10.75). Exencephaly and spina bifida are indicated in black arrows in E and F. The lateral dermomyotome in E and F is disorganized and limb muscle is detected only in A and B, as indicated by black arrows. The lack of limb muscle is also documented by transverse sections at the limb level in G and H (higher magnification of G) and corresponding sections of heterozygous embryos in C and D (higher magnification of C) (E10.5). In D, myoblasts are indicated by black arrows. DM, dermomyotome; NT, neural tube; sp, spina bifida; +/-, heterozygous; -/-, homozygous. Scale bars: 1 mm in A,B,E,F; 500 µm in C,G; 200 µm in D,H.