Fig. 3. Expression of constitutively active Drac1 causes an increase in F-actin and myosin staining in the amnioserosa. Embryos were stained with phalloidin to detect F-actin (A,B) or anti-nonmuscle myosin heavy chain antibody (C,D). (A) Dorsal view of the amnioserosa of a stage 15 wild-type embryo late in dorsal closure. There is heavy accumulation of F-actin along the leading edge (arrowhead). (B) Dorsal view of the amnioserosa of a stage 15 Hs-GAL4^M-4/UAS-Drac1V12 embryo showing elevated F-actin staining as compared to the embryo in A. (C) Lateral view of a stage 14 wild-type embryo showing the boundary between the amnioserosa (top of micrograph) and the epidermis. There is accumulation of myosin along the leading edge (arrowhead). (D) Lateral view of a stage 14 Hs-GAL4^M-4/UAS-Drac1V12 embryo showing the boundary between the amnioserosa (top of micrograph) and the epidermis. Compared with the embryo in C, there is increased myosin staining in the amnioserosa and parts of the epidermis. In this embryo the amnioserosa has begun to contract and pull away from the epidermis, although points of adhesion between the two tissues remain (arrowhead).