2 VISUAL PIGMENTS IN A SINGLE PHOTORECEPTOR CELL - IDENTIFICATION ANDHISTOLOGICAL LOCALIZATION OF 3 MESSENGER-RNAS ENCODING VISUAL PIGMENTOPSINS IN THE RETINA OF THE BUTTERFLY PAPILIO-XUTHUS

This paper describes the localization of newly identified visual pigme nt opsins in the tiered retina of the Japanese yellow swallowtail Papi lio xuthus. We first cloned three cDNAs encoding visual pigment opsins , PxRh1, PxRh2 and PxRh3, and then carried out histological in situ hy bridization to localize their mRNAs in the retina. By combining the pr esent data with our previous electrophysiological results, we conclude d that both PxRh1 and PxRh2 correspond to visual pigments expressed in photoreceptor cells sensitive in the green wavelength region (green r eceptors), whereas PxRh3 corresponds to a pigment in red receptors, Th e in situ hybridization studies showed that some photoreceptor cells e xpress two opsin mRNAs, In the ventral half of the eye, all green rece ptors in the distal tier were labelled by both PxRh1 and PxRh2 probes. The labelling by the PxRh2 and PxRh3 probes was detected throughout t he eye in the proximal tier; in 18% of ommatidia, the probes labelled the same photoreceptor cell. These results suggest that the possible c o-localization of two different visual pigments will broaden the sensi tivity spectrum of the photoreceptor cells.