IMMUNOLOCALIZATION OF A DROSOPHILA PHOSPHATIDYLINOSITOL TRANSFER PROTEIN (RDGB) IN NORMAL AND RDGA MUTANT PHOTORECEPTOR CELLS WITH SPECIAL REFERENCE TO THE SUBRHABDOMERIC CISTERNAE

Distribution of rdgB protein, which was recently shown to be a Drosoph ila phosphatidylinositol transfer protein, was studied in the photorec eptor cells of compound eyes of normal and rdgA(PC47) mutant of Drosop hila melanogaster by immunoelectron microscopy using (1) pre-embedding HRP staining, (2) pre-embedding NANOGOLD labeling followed by siliver enhancement, (3) and post-embedding colloidal gold labeling methods. In normal cells, immunoreactivity was localized to the membranes of su brhabdomeric cisternae (SRC) and adjacent plasma membranes at the base s of photoreceptive microvilli. In rdgA(PC47) mutant cells, whose SRC gradually degenerate, the immunoreactivity in the plasma membranes at the bases of microvilli disappeared in parallel with the degeneration of SRC. Instead, the abnormally proliferated membranous structures bec ame labeled by the antibody. These results indicate that the rdgB prot ein is normally localized to the SRC membranes and probably adjacent p hotoreceptive membranes, suggesting the involvement of the rdgB protei n in the phosphatidylinositol transfer between SRC and photoreceptive membranes.