Activation of Ras inhibits apoptosis during Drosophila development. Genetic evidence indicates that Ras antiapoptotic activity in the developing eye is regulated by the Drosophila EGF receptor and operates through the Raf/MAPK pathway. Decreased activity of this pathway enhances, and increased activity suppresses, apoptosis induced by ectopic expression of the cell death regulators reaper (rpr) and head involution defective (hid). In addition, ectopic activation of the Ras/MAPK pathway in the developing embryo and in the developing eye suppresses naturally occurring apoptosis and regulates the transcription of the proapoptotic gene hid. Null alleles of hid recapitulate the antiapoptotic activities of Ras/MAPK, providing genetic evidence that downregulation of hid is an important mechanism by which Ras promotes survival.

Dominant mutations of the Drosophila ninaE-encoded rhodopsin are described that reduce the expression of wild-type rhodopsin and cause a slow, age-dependent form of retinal degeneration. A posttranslational event subsequent to the requirement for the ninaA-encoded cyclophilin is disrupted by the dominant mutations. Most of these dominant mutations are missense mutations that affect the physical properties of one of the seven transmembrane domains; another affects the cysteine involved in a disulfide linkage. The results indicate that misfolded or unstable mutant rhodopsin can interfere with maturation of wild-type rhodopsin, and that these cellular conditions may trigger retinal degeneration. In addition, these dominant rhodopsin mutations suppress the rapid degeneration seen in rdgC and norpA flies, indicating that high levels of rhodopsin are required.

Rab6 is a GTPQ71L is a GTPase defective mutant, indicating that anterograde transport of rhodopsin requires Rab6 GTPase function. The three Drab6 strains had no effect on the expression of several other photoreceptor proteins. The Drab6 Q71L photoreceptors show marked histological defects at young ages and degenerate over a two week time span. These results establish that rhodopsin is transported via a Rab6 regulated pathway and that defects in trafficking pathways lead to retinal degeneration.

ninaE(D1), a dominant allele of the major Drosophila rhodopsin gene, expresses a rhodopsin that is predominantly recovered in a 80-kD complex that likely represents rhodopsin dimers. By driving either ninaE(D1) or ninaE+ expression from a heat-shock promoter, we show that the 80-kD rhodopsin complex forms immediately after gene activation. In wild type, but not ninaE(D1), rhodopsin monomeric forms are detected at later times. The generation of monomeric forms of wild-type rhodopsin is suppressed in vitamin A-deprived flies or in flies heterozygous for the dominant rhodopsin mutation. We also show that ninaE(D1) expression does not affect the maturation of another Drosophila visual pigment, Rh3. These results are consistent with the view that the ninaE(D1) rhodopsin antagonizes an early posttranslation process that is specific for maturation of the ninaE-encoded rhodopsin.