The Drosophila ninaB gene encodes a ␤,␤-carotene-15,15 -oxygenase responsible for the centric cleavage of ␤-carotene that produces the retinal chromophore of rhodopsin. The ninaD gene encodes a membrane receptor required for efficient use of ␤-carotene. Despite their importance to the synthesis of visual pigment, we show that these genes are not active in the retina. Mosaic analysis shows that ninaB and ninaD are not required in the retina, and exclusive retinal expression of either gene, or both genes simultaneously, does not support rhodopsin biogenesis. In contrast, neuron-specific expression of ninaB and ninaD allows for rhodopsin biogenesis. Additional directed expression studies failed to identify other tissues supporting ninaB activity in rhodopsin biogenesis. These results show that nonretinal sites of NinaB ␤,␤-carotene-15,15 -oxygenase activity, likely neurons of the central nervous system, are essential for production of the visual chromophore. Retinal or another C 20 retinoid, not members of the ␤-carotene family of C 40 carotenoids, are supplied to photoreceptors for rhodopsin biogenesis.Mutants in eight Drosophila genes, designated ninaA through ninaH, are characterized by reduced rhodopsin levels in photoreceptors and altered electroretinograms (1). The opsin protein component of rhodopsin is coded by the ninaE gene (2, 3). The low rhodopsin phenotypes observed in other nina mutants are caused by deficits in the post-translational rhodopsin maturation process. For example, ninaA encodes a molecular chaperone required for movement of newly synthesized rhodopsin from the endoplasmic reticulum to the photosensitive rhabdomeric membranes (4, 5). In the case of ninaB and ninaD, defective rhodopsin production is the result of a failure to generate the chromophore of rhodopsin, 3-OH retinal (6).Animal species usually obtain retinals in their food. Plants and microorganisms produce C 40 carotenoids such as ␤-carotene and zeaxanthin, which animals metabolize to C 20 retinoids. In Drosophila, the ninaD gene encodes a membrane "scavenger" receptor proposed to mediate the cellular uptake of carotenoids (7). The ninaB gene encodes a ␤,␤-carotene-15,15Ј-oxygenase (BCO) 1 responsible for the centric cleavage of ␤-carotene to form retinal (8). This enzyme was originally named as a ␤-carotene dioxygenase. It has now been renamed BCO (9) in light of recent data showing related enzymes act as monooxygenases (10).In vertebrates, vitamin A is essential for development and differentiation processes as well as its role in vision. The availability of vitamin A for metabolic processes is governed by multiple factors, including dietary absorption, transport, metabolism, and storage (11). A human BCO is expressed in the retinal pigment epithelium and also in the kidney, intestine, liver, brain, stomach, and testis (12, 13), suggesting that the processing of dietary carotenoids occurs in a variety of vertebrate tissues. Additional studies show that centric cleavage of ␤-carotene plays a major role in the processing of carote...

We examined the role of programmed cell death (PCD) pathways in retinal degeneration caused by a mutation in the norpA gene. norpA degeneration shows morphological hallmarks of programmed cell death, specifically cytoplasmic condensation and engulfment of the dying photoreceptor cells by neighboring retinal pigment cells. However, genetic mosaic analysis of adult photoreceptors lacking rpr, hid, and grim show that these PCD inducers are not required for norpA degeneration. We showed previously that ectopic expression of either rpr or hid triggers rapid PCD in adult photoreceptors, and this is completely suppressed by the coexpression of the baculoviral P35 caspase inhibitor. In contrast, expression of P35 does not suppress norpA retinal degeneration, although a small delay in the rate of degeneration is observed in low light-low temperature conditions. P35 does not alter the morphological characteristics of norpA cell death. Overexpression of the Drosophila inhibitor of apoptosis Diap1 or a dominant-negative form of the Dronc caspase, even when coexpressed with P35, does not dramatically alter the time course of norpA degeneration. These results establish that the pathways responsible for PCD in development do not play a major role in adult retinal degeneration caused by norpA.

Electrometers for gas chromatographic detection are, at least in our hands, prone to malfunction; and they are expensive to repair or replace. Faced with such a dilemma, we recently assembled a simple amplifier from readily available components. It served as an inexpensive electrometer substitute for use with our Shimadzu flame photometric detector (FPD).Due to the relatively high current output of the photomultiplier tube, the FPD lends itself well to low-cost amplification. This is possible through the use of inexpensive monolithic field-effect transistor (FET) operational amplifiers that became readily available after the mid 1970s. Futhermore, we are making use of the fact that, nowadays, many recorders have multirange capability. Of course, there is nothing fundamentally new in our approach; however, it is certainly not common knowledge that one can significantly reduce the high cost of a flame photometric detection system in this manner. The price one pays for doing this-in terms of detector performance as well as in terms of electronic components-is minimal.