THE OLFACTORY AND VISUAL SYSTEMS ARE CLOSELY-RELATED IN DROSOPHILA

The olfactory and visual systems of Drosophila have similar developmen tal origins: both derive from the eye-antennal imaginal disc. Moreover , there are commonalities in the cellular, molecular, and genetic unde rpinnings of their development. For example, the developmental program of bath systems entails cell death, which depends upon the irregular chiasm C-roughest gene, and both systems require the lozenge gene for normal pattern formation. The rdgB (retinal degeneration B) gene is re quired not only for the maintenance and physiology of the visual syste m, but also for olfactory physiology. This gene has been shown by othe rs to encode a phosphatidylinositol transfer protein; it is expressed both in visual and olfactory organs. The norpA gene, which encodes a p hospholipase C, is also required both for phototransduction and for od orant response in one olfactory organ. Thus some genes are required in both systems; in addition, at least one olfactory gene that is appare ntly not expressed in the visual system may have a visual system count erpart. These and other similarities are considered in terms of the ev olutionary relationship between the two systems. We conclude that anal ysis of the visual system is likely to provide insight into the develo pment and function of the olfactory system, and vice versa.