Fig. 4. Dorsal closure defects are seen following expression of dominant-negative Drac1 in the amnioserosa and in embryos homozygous for a hypomorphic allele of crb. Dorsal views of embryos stained with anti-ß-galactosidase antibodies to label amnioserosa cells (A,B) or anti-phosphotyrosine antibodies to show morphology (C-H). (A,C) A double-stained stage 15 UAS-lacZ^1-71;GAL4^332.3 control embryo late in dorsal closure showing amnioserosa in transition from an elliptical to tubular morphology. (B,E) A double-stained UAS-lacZ^1-71;GAL4^332.3;UAS-Drac1N17 embryo similar in age to that in A and C but in which the amnioserosa is still elliptical in shape. The hindgut has ruptured the amnioserosa in this embryo. (D) A wild-type embryo at the end of dorsal closure. (F) UAS-lacZ^1-71;GAL4^332.3;UAS-Drac1N17 embryo similar in age to that in D showing persistence of a small dorsal hole. (G) A stage 15 embryo homozygous for crb^S010409 showing germband retraction defect and impaired dorsal closure. There is robust phosphotyrosine staining along the leading edge. (H) An embryo homozygous for crb^S010409, similar in age to that in D, showing persistence of dorsal hole.