English: Bicoid mRNA is localized to the anterior pole of the Drosophila oocyte (St. Johnston et al., 1989). Bicoid protein enters the nuclei and forms a nuclear gradient from anterior to posterior (Driever and Nusslein-Volhard, 1988). The top photograph shows the nuclear Bicoid protein gradient in a fixed transgenic Drosophila embryo carrying a bicoid–GFP fusion gene. In these embryos the concentration of Bicoid protein could be accurately measured either by the intensity of the autofluorescence of the GFP protein itself (not shown) or by the intensity of fluorescence of an anti-GFP antibody tagged with a fluorescent dye, as shown in a surface view of the embryo here. The lower photograph shows the anterior tip of a fixed transgenic Drosophila embryo carrying a bicoid–GFP fusion gene labeled with fluorescently-tagged cDNA probes that bind bicoid mRNA molecules. Green color shows autofluorescence of the GFP protein in the nuclei, red color shows packages of multiple bicoid mRNA molecules in the anterior cytoplasm. Methods described in Little et al. (2011).

References:

Driever, W.; Nüsslein-Volhard, C. (1988). "The bicoid protein determines position in the Drosophila embryo in a concentration-dependent manner". Cell 54: 95. doi:10.1016/0092-8674(88)90183-3

St Johnston D, Driever W, Berleth T, Richstein S, Nusslein-Volhard C (1989). Multiple steps in the localization of bicoid RNA to the anterior pole of the Drosophila oocyte. Development 107 Suppl: 13–19.

Little SC, Tkačik G, Kneeland T, Wieschaus EF, Gregor T (2011). The formation of the Bicoid morphogen gradient requires protein movement from anteriorly localized mRNA. PLoS Biology 9(3), e1000596.