(A-C) Control (yw; Hand-GAL4, UAS-GFP-moe) embryos at stage 17 stained with anti-αSpectrin, which labels CB lateral and luminal membranes (A) and anti-GFP (B) in the heart region of the DV. Merged image is shown in (C). (D-O) Stage 17 embryos overexpressing wild type or dominant negative Rho1 or Rac1 in the Hand-GAL4, UAS-GFP-moe background and stained with anti-αSpectrin (D,G,J,M) and anti-GFP (E,H,K,N) in the heart region of the DV. (D) Rho1 overexpressing embryos appear to show stronger accumulation of αSpectrin at CB lateral membranes (arrowhead) as compared with wild type (A). (G-I) Overexpression of dominant negative Rho1 (Rho1N19) results in small holes (arrow) between Svp+ CBs, which can be identified by their elongated shape relative to the Tin+ CBs. (J-L) Rac1WT overexpressing embryos appear indistinguishable from wild type and overexpression of dominant negative Rac1 (Rac1N17) (M-O) produces in minor defects in CB positioning (arrowhead) (M) in the DV. See Table 1 for quantitative data. Scale bar is 20um.