STUDIES ON THE STRUCTURE OF OCELLAR PHOTORECEPTOR CELLS OF DROSOPHILA-MELANOGASTER WITH SPECIAL REFERENCE TO SUBRHABDOMERIC CISTERNAE

We studied the structure of ocellar photoreceptor cells of Drosophila melanogaster; particularly the subrhabdomeric cisternae which our prev ious studies have shown to be essential structures for turnover of pho toreceptive membranes in compound eyes. Each ocellus contained elongat ed photoreceptor cells with rhabdomeres positioned distally. In the su brhabdomeric regions, endocytotic imaginations were frequently observe d, suggesting active turnover of photoreceptive membranes. In the vici nity of the photoreceptive microvilli, membranous structures similar t o the subrhabdomeric cisternae in compound eyes were observed. These m embranous structures were immunopositive for the rdgB protein, a phosp hatidylinositol transfer protein that is localized to the subrhabdomer ic cisternae in compound eyes. The ocellar photoreceptor cells of the retinal degeneration mutants (rdgA,B) were also studied. In these muta nts, retinal degeneration has been reported to start, in compound eyes , with the disappearance of the subrhabdomeric cisternae. We found tha t the ocellar subrhabdomeric cisternae also disappear during the initi al stage of retinal degeneration. From these observations, we conclude that the mechanism of photoreceptive membrane turnover in ocellar pho toreceptor cells involves the rdgB and probably the rdgA proteins whic h are associated with subrhabdomeric cisternae, as is the case for pho toreceptive membrane turnover in compound eyes.