title: Freeze-fracture study of the Drosophila photoreceptor membrane: mutations affecting membrane particle density.
abstract: The photoreceptor membrane of Drosophila melanogaster (wild type, vitamin A-deprived wild type, and the mutants ninaAP228, ninaBP315, and oraJK84) was studied by freeze-fracture electron microscopy. The three mutations caused a decrease in the number of particles on the protoplasmic face of the rhabdomeric membrane. The ninaAP228 mutation affected only the peripheral photoreceptors (R1-6), while the ninaBP315 mutation affected both the peripheral (R1-6) and the central photoreceptors (R7). The oraJK84 mutation, which essentially eliminates R1-6 rhabdomeres, was found to drastically deplete the membrane particles in the vestigial R1-6 rhabdomeres but not in the normal rhabdomeres of R7 photoreceptors, suggesting that the failure of the oraJK84 mutant to form normal R1-6 rhabdomeres may be due to a defect in a major R1-6 photoreceptor-specific protein in the mutant. In all cases in which both the rhabdomeric particle density and rhodopsin content were studied, the mutations or vitamin A deprivation was found to reduce both these quantities, supporting the idea that at least the majority of the rhabdomeric membrane particles are closely associated with rhodopsin. Vitamin A deprivation and the mutations also reduced the number of particles in the plasma membrane as in the rhabdomeric membrane, suggesting that both classes of membrane contain rhodopsin.
mesh_terms: D000818:Animals; D002462:Cell Membrane / Q000648:ultrastructure; D004331:Drosophila melanogaster; D005614:Freeze Fracturing; D007425:Intracellular Membranes / Q000378:metabolism / Q000648:ultrastructure; D008854:Microscopy, Electron; D009154:Mutation; D010786:Photoreceptor Cells / Q000648:ultrastructure*; D012243:Rhodopsin / Q000378:metabolism; D014801:Vitamin A / Q000378:metabolism
chemical_list: D014801:Vitamin A; D012243:Rhodopsin