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 Drosophila phosphatidylinositol transfer protein, was studied in the photoreceptor cells of compound eyes of normal and rdgAPC47 mutant of Drosophila 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 subrhabdomeric cisternae (SRC) and adjacent plasma membranes at the bases of photoreceptive microvilli. In rdgAPC47 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 became labeled by the antibody. These results indicate that the rdgB protein is normally localized to the SRC membranes and probably adjacent photoreceptive membranes, suggesting the involvement of the rdgB protein in the phosphatidylinositol transfer between SRC and photoreceptive membranes.