Fig. 5. Exu phosphorylation is required for proper formation of the Bicoid protein gradient. (A-C) Confocal sections through the middle of early cleavage stage embryos hybridised with a bicoid RNA probe. (A) In all wild-type embryos (n=20), bicoid mRNA was localised anteriorly. (B) In embryos from females expressing the exu^A+B transgene in an exu-null mutant background, only 70% of the embryos (n=32) show anteriorly localised bicoid mRNA, while the other 30% show no anterior signal. (C) In embryos from exu-null mutants (exu^XL/exu^VL) all embryos (n=19) lack anterior bicoid mRNA. (D-F) Blastoderm embryos stained for Bicoid protein (green) and DNA (red). Right panel shows Bicoid protein alone. All embryos were fixed and stained in parallel, and pictures were taken with the same setup with a digital camera and a light microscope. (D) In all wild-type embryos (n=27), a clear Bicoid gradient with similar extension was observed. (E) In embryos from females expressing the exu^A+B transgene in an exu null mutant background, no Bicoid was detected in 27% of the embryos, while in all of the remaining embryos the extension of the gradient is reduced compared with wild-type embryos (n=30). (F) In all exu-null mutants examined (n=34) no Bicoid protein was detectable.