Fig. 3. Actin polymerization directs the expansion of histoblast nests. (A) Bristles with morphogenetic defects (yellow arrowheads) and cuticular abdominal clefts (white arrowheads) in an adult escaper of Permanent-Esg-Gal4/UAS-Profilin genotype. (B) In wild-type histoblasts (22 hours APF), most polymerized actin organizes in cortical filaments. Phalloidin-rhodamine staining (red) is shown in the top and bottom panels. UAS-GFP expression (green) under the control of Permanent-Esg-Gal4 is shown in the bottom panel. (C) Actin in histoblasts overexpressing Profilin (22 hours APF) hyperpolymerizes and accumulates in intracellular clumps (arrowheads). Top and bottom panels are as in B. (D) Snapshots from Movie 7 in the supplementary material. Top panel, wild-type dorsal posterior nest (23 hours APF). Arrowheads point to expanding peripheral protrusions. Bottom panel, dorsal posterior nests from pupae (23 hours APF) overexpressing Profilin (Permanent-Esg-Gal4/UAS-GFP; UAS-Profilin). Note the absence of long terminal protrusions and the histoblast expansion delay.