Fig. 5. rib mutants fail to complete dorsal closure and have ventral cuticle patterning defects. Dark-field images of the lateral cuticle of wild type (A) and rib mutant larvae (B,C) photographed at the same magnification. Of the mutant larvae with scorable cuticles, small anterior dorsal holes and puckering of the dorsal epidermis occur in 36% of rib mutants (B) and large dorsal holes occur in 64% of rib mutants (C; arrows indicate extent of dorsal opening). Lateral views of dpp RNA expression in the leading edge cells of the lateral epidermis (large arrow) and the midgut (arrowhead) of rib/CFL (D) and rib mutant (E) embryos are shown. In rib mutants, dpp staining at the leading edge is more disorganized and in some regions extends into the lateral epidermis (small arrows in E). This apparent increase may be due to an increase in the number of cells expressing dpp or the morphology of these cells and the leading edge at late stages. (F-J) Representative phase contrast images of ventral cuticles of first instar larvae of an allelic series of rib mutations. Anterior (A) is oriented up, and larvae were photographed at the same magnification. There is a prominent narrowing of the lateral extent of denticle belts relative to the ventral surface of the larva, increasing with allele severity. Loss of denticle diversity also increases with the allelic series. The most severe phenotype (rib¹/rib¹) is shown in J and is equivalent to rib1/Df(2R)P34 (not shown); in such embryos, only a few similarly shaped denticles form.