folded gastrulation, cell shape change and the control of myosin localization Materials and methods Drosophila strains and genetics Line mat67;mat15 is matα4- GAL-VP16 (Hacker and Perrimon, 1998) with inserts homozygosed on II and III. The sqhGFP stock is y w sqh AV 3 cv; [sqh-gfp 42 ] (Royou et al., 2004) . Fog stocks are y w f fog 114 /FM7[ftzLacZ]; In(1)sc 8 Df(1)mal 12 B/y + Ymal/C(1)Dx. fog 114 is FlyBase Df(1)fog-1 (Perrimon et al., 1989) and deletes the entire fogcoding sequence (Costa,

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... 994) . shibire ts is FlyBase shibire-1. Oregon R was used as wild type. Germline clones were produced from the following crosses using standard techniques (Chou and Perrimon, 1992 ). Arm: arm 043A01 FRT 101 /FM6 x ovo D1 FRT 101 /Y; hs-flp 138 produced heat shocked arm 043A01 FRT 101 /ovo D1 FRT 101 females used to collect embryos (Tolwinski and Wieschaus, 2001). DRhoGEF2: y w hs-flp;FRT42B G13 DRhoGEF2 1.1 /CyO virgin females ϫ FRT42B G13 ovoD1/CyO males produced heat shocked FRT42B G13 DRhoGEF2 1.1 /FRT42B G13 ovoD1 females that were crossed to w males to collect embryos (Barrett et al., 1997). Drok alleles (Winter et al. , 2001) were used to make the following stocks and crosses: w rok 1or2 FRT 18D /FM7 ϫ ovo D2 FRT 18D /Y; hs-flp138 produced heat shocked w rok 1or2 FRT 18D /ovo D2 FRT 18D females from which embryos were collected. UASfog expressing embryos are from mat67;mat15 virgins ϫ UASfog males. Three UASfog lines were used: UASfog 6 (III), UASfog 12 (II) and UASfog 18 /TM3Ser. UASnullo-expressing embryos are from mat67;mat15 virgins ϫ UASnullo N39 males (Hunter et al., 2002) . Embryos expressing UASmYFP-myosin II DN are from mat67;mat15 virgins ϫ w; UAS mYFP-myosin II DN males to produce w; mat67/ UAS mYFP-myosin II DN ;mat15/+ virgins backcrossed to w; UAS mYFP-myosin II DN to collect embryos. Embryology, histology and image analysis All embryos were heat-methanol fixed (Muller and Wieschaus, 1996) except those stained with anti-GFP or anti-Fog antibody, which were Development 132 (18) Research article Development