Fig. 1

(A-G) Flat preparations of embryos injected with various RNAs. Asterisks label the affected side. (A) 10-somite stage control embryo injected with lacZ RNA alone. (B,C) 10- somite-stage embryos injected with full-length deltaD (B) and with deltaD^(Pst) (C) and lacZ RNA. Both embryos have been stained for MyoD (blue, in situ hybridization) and β-galactosidase (brown, antibody staining) expression. Somites are irregularly shaped on the affected side, arrows point to somite fusions. (D) 10-somitestage embryo injected with full-length deltaC RNA and stained by in situ hybridization for MyoD expression. Somitic defects are similar to those in B and C. Arrows point to somite fusions. (E) 10-somite-stage embryo injected with notch1a-intra (nic) mRNA and lacZ RNA and stained for MyoD (blue, in situ hybridization) and β-galactosidase (brown, antibody staining) expression. Notice the poor somitic organization on the affected side, MyoD expression is diffuse and no somite boundaries can be distinguished in the territory labelled by the vertical line. (F) 22- h-stage embryo that had been injected with notch1a-intra (nic) mRNA and lacZ RNA, and stained for myosin heavy chain. Notice that the outlines of the somites appear blurred and muscle fibres are not packed into somitic groups. The arrows point to individual muscle fibres extending through regions in which somite borders should have developed