The retina of Manduca sexta: rhodopsin expression, the mosaic of green-, blue- and UV-sensitive photoreceptors, and regional specialization.

Abstract

Spectral sensitivities of individual photoreceptors in the compound eye of Manduca sexta were verified by immunocytochemistry, and the retinal mosaic was mapped, using polyclonal antisera raised against amino-terminal sequences of three identified rhodopsins: P520, P450 and P357. Retinulae are composed of a small proximal cell and seven or eight elongate cells extending across the retina. In each retinula, one or two elongate dv cells oriented in the dorsal-ventral axis of the retinal lattice express either P450 or P357. Six elongate ap and ob cells in the anterior-posterior and oblique axes express P520. The small proximal pr cell also appears to express P520. The retinal mosaic is regionalized into three distinct domains: ventral and dorsal domains that divide the main retina, and a large dorsal rim area. The immunocytochemical data provide a high-resolution map of the Manduca retina that confirms and refines earlier low-resolution ERG spectral sensitivity measurements. The dorsal and ventral domains, separated at a well-defined equatorial border, are distinguished by differences in the proportion of blue-sensitive dv cells: these cells dominate the ventral retina but are less abundant in the dorsal retina. Green-sensitive ap and ob receptors are uniformly distributed across the dorsal and ventral domains, and UV-sensitive dv cells are fairly uniformly distributed because many retinulae in the dorsal domain contain only one dv cell. Similarly, dorsal rim retinulae contain only the ventral member of the dv pair of receptors, two-thirds of which express P357. Otherwise, dorsal rim receptors express none of the three sequenced Manduca opsins; they must express rhodopsins that have yet to be cloned.