Fig. 6. Exu phosphorylation is required for bicoid mRNA localisation and embryonic patterning. (A-E) In situ hybridisation showing bicoid mRNA (red) in confocal sections of stage 9 (left) and stage 10b (right) egg chambers. DNA is shown in green. Wild-type (A) or mutant (B-E) Exu protein was expressed from transgenes in an exu-null mutant background (exu^XL/exu^VL). Sequences of site A and B are indicated, and mutations are shown in red. All mutations affect bicoid mRNA localisation at stage 9 (B-E). bicoid mRNA localisation defects recover at stage 10b when only site A or B is mutant (B,C), and partially recovers when serines 438, 440 and 457 are mutant (D). No recovery is observed when all relevant serines in site A and B are simultaneously mutated. (A'-E') Embryos in the right panel are derived from females of the same genotype as egg chambers in the left panel. Embryos were stained with anti-Eve antibody to visualise segmentation. Ten embryos from each genotype were randomly chosen for analysis with the light microscope. Those embryos that show maximal anterior extension of the first Eve stripe are shown. The average position of the first Eve stripe of the ten analysed embryos is indicated as percentage of egg length. The average position of the first Eve stripe in exu null mutants (exu^XL/exu^VL) is at 26.9% egg length. Black line indicates the position of first Eve stripe in embryos expressing wild type Exu. The extension of the anterior shift of the first Eve stripe in the mutants (B'-E') corresponds to the severity of the bicoid mRNA localisation defects during oogenesis (B-E). All females were grown at 18°C. Anterior is leftwards; posterior is rightwards.