Drosophila NinaB and NinaD act outside of retina to produce rhodopsin chromophore

The Drosophila ninaB gene encodes a beta,beta-carotene-15,15'-oxygenase responsible for the centric cleavage of beta-carotene that produces the retinal chromophore of rhodopsin. The ninaD gene encodes a membrane receptor required for efficient use of beta-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 beta, beta-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 beta-carotene family of C-40 carotenoids, are supplied to photoreceptors for rhodopsin biogenesis.