A B S T R A C T Two genes inDrosophila, rdgA and rdgB, which when defective cause retinal degeneration, were discovered by Hotta and Benzer (Hotta, Y., and S. Benzer. 1970. Proc. Natl. Acad. Sci. U. S. A. 67:1156-1163. These mutants have photoreceptor cells that are histologically normal upon eclosion but subsequently degenerate. The defects in the rdgA and rdgB mutants were localized by the study of genetic mosaics to the photoreceptor cells. In rdgB mutants retinal degeneration is light induced. It can be prevented by rearing the flies in the dark or by blocking the receptor potential with a no-receptor-potential mutation, norpA. Vitamin A deprivation and genetic elimination of the lysosomal enzyme acid phosphatase also protect the photoreceptors of rdgB flies against light-induced damage. The photopigment kinetics of dark-reared rdgB flies appear normal in vitro by spectrophotometric measurements, and in vivo by measurements of the M potential. In normal Drosophila, a 1-s exposure to intense 470-nm light produces a prolonged depolarizing afterpotential (PDA) which can last for several hours. In dark-reared rdgB mutants the PDA lasts less than 2 min; it appears to initiate the degeneration process, since the photoreceptors become permanently unresponsive after a single such exposure. Another mutant was isolated which prevents degeneration in rdgB flies but which has a normal receptor potential. This suppressor of degeneration is an allele of norpA. It is proposed that the normal norpA gene codes for a product which, when activated, leads to the receptor potential, and which is inactivated by the product of the normal rdgB gene.

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Drosophila INAD, which contains five tandem protein interaction PDZ domains, plays an important role in the G protein-coupled visual signal transduction. Mutations in InaD alleles display mislocalization of signaling molecules of phototransduction which include the essential effector, phospholipase C-β (PLC-β), which is also known as NORPA. The molecular and biochemical details of this functional link are unknown. We report that INAD directly binds to NORPA via two terminally positioned PDZ1 and PDZ5 domains. PDZ1 binds to the C-terminus of NORPA, while PDZ5 binds to an internal region overlapping with the G box-homology region (a putative G protein-interacting site). The NORPA proteins lacking binding sites, which display normal basal PLC activity, can no longer associate with INAD in vivo. These truncations cause significant reduction of NORPA protein expression in rhabdomeres and severe defects in phototransduction. Thus, the two terminal PDZ domains of INAD, through intermolecular and/or intramolecular interactions, are brought into proximity in vivo. Such domain organization allows for the multivalent INAD-NORPA interactions which are essential for G protein-coupled phototransduction.

Lipofuscin granules (age pigments) emit yellow light under ultraviolet excitation in the fluorescence microscope. The reported blue emission maximum of extracts of lipofuscin-laden cells may result from instrumental bias. The major fluorescent components that accumulate with age in these lysosomal residual bodies of human retinal pigment epithelium are yellow-emitting fluorophores. Different age-related fluorophores, which do emit blue light, are derived from other intracellular sources. A reevaluation of the connection between blue-emitting lipid peroxidation products and the age-related lipofuscin granules of classical pathology is necessary.

Nona-2,6-dienal, non-2-enal, hex-2-enal, and three saturated aliphatic aldehydes were isolated from cucumbers.Quantitative and qualitative aspects of the flavor of nona-2,6-dienal and non-2-enal were examined.