Fig. 5. The morphology of mesodermal cells is defective in pbl mutant embryos. Control (A-C,E) and pbl²/pbl³ mutant (D,F) stage 8 embryos in which GFP-Actin was expressed in mesodermal cells using the twist-GAL4 driver and visualised with an anti-GFP antibody. (A) A UAS-GFP-Actin/twist-GAL4 control embryo typical of the stage used in this morphological analysis, between the first two waves of mitosis in the mesoderm. (B) Cross-section of a control embryo expressing GFP-Actin in mesodermal cells. Embryos were oriented so that the leading mesodermal cells were parallel to the plane of the microscope. The white line indicates the plane of focus seen in C,D. The black line indicates a deeper plane of focus seen in E,F. (C,D) Projections of 1 µm optical sections of mid-stage 8 control (C) and pbl²/pbl³ (D) embryos showing the morphology of migrating mesodermal cells at the leading front. (C) Cells in a control embryo exhibit numerous protrusions (arrows) in the direction of migration and appear dissociated from each other. (D) Cells in a pbl²/pbl³ embryo extend far fewer protrusions (arrow) and appear more tightly adhered to their mesodermal neighbours. (E) Mesodermal cells in a control embryo appear more rounded with numerous intercellular gaps (arrowhead) present. (F) Cells in a pbl²/pbl³ embryo appear more tightly packed and are less rounded, with fewer intercellular gaps. Scale bars: 10 µm.