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Fig. 6. The defects in the mesodermal epithelial-mesenchymal transition and the subsequent loss of the EVE-positive mesodermal cells in pbl mutant embryos are independent of the cytokinetic defect. (A,C,E,G) UAS-myc-pbl, pbl3/prd-GAL4, pbl2 embryos. (B,D,F,H) UAS-pbl{Delta}BRCT, pbl3/prd-GAL4, pbl2 embryos. (J-L) UAS-GFP-Actin/twist-GAL4;UAS-pbl{Delta}BRCT, pbl3/pbl2 embryos. (A,B) Stage 11 embryos stained with anti-EVE and visualised using an alkaline phosphatase assay. (C,D) Stage 14 embryos stained with anti-EVE and visualised using fluorescence microscopy (white). (E-H) Anti-Spectrin (green) and Hoechst 33258 DNA stain (blue). (G,H) Merge of the fluorescent images above. Anti-EVE (red), Anti-Spectrin (green) and Hoechst 33258 DNA stain (blue). (A,C,E,G) Expression of a wild-type copy of a pbl cDNA in a pbl mutant background rescues the EVE-positive mesodermal cell formation and the cytokinetic defect. (A) EVE-positive mesodermal cells are evident in embryos rescued with the wild-type pbl cDNA. (C,E,G) EVE-positive mesodermal cells are evident at a higher magnification (C,G) and rescue of cytokinesis is seen in epidermal cells in alternating stripes corresponding to the prd-GAL4 induced wild-type pbl expression (E,G). (D,F,H) Pbl{Delta}BRCT expression rescues the EVE-positive mesodermal cell defect (D,H) but fails to rescue the cytokinetic phenotype in pbl mutants (F,H). Note that the EVE-positive mesodermal cells in C,D are imaged at a different focal plane than the epidermis shown in E,F. (I) Schematic representations of the PBL constructs used in the EVE-positive hemisegment rescue assay. (J-L) Expression of PBL{Delta}BRCT using the twist-GAL4 driver alters the cellular phenotype of GFP-Actin-expressing mesodermal cells. (J) Cells extend more protrusions (arrows) in the direction of migration. (K) Cell bodies in the central mass of mesodermal cells appear more rounded (compare with Fig. 5F) and intercellular gaps (arrowhead) are present. (L) Single optical slice of cells in J showing binucleate cells (arrowhead) more clearly. Scale bars: 10 µm.