PMID:9165115

Citation	Papatsenko, D, Sheng, G and Desplan, C (1997) A new rhodopsin in R8 photoreceptors of Drosophila: evidence for coordinate expression with Rh3 in R7 cells. Development 124:1665-73
Abstract	The photoreceptor cells of the Drosophila compound eye are precisely organized in elementary units called ommatidia. The outer (R1-R6) and inner (R7, R8) photoreceptors represent two physiologically distinct systems with two different projection targets in the brain (for review see Hardie, 1985). All cells of the primary system, R1-R6, express the same rhodopsin and are functionally identical. In contrast, the R7 and R8 photoreceptors are different from each other. They occupy anatomically precise positions, with R7 on top of R8. In fact, there are several classes of R7/R8 pairs, which differ morphologically and functionally and are characterized by the expression of one of two R7-specific opsins, rh3 or rh4. Here, we describe the identification of a new opsin gene, rhodopsin 5, expressed in one subclass of R8 cells. Interestingly, this subclass represents R8 cells that are directly underneath the R7 photoreceptors expressing rh3, but are never under those expressing rh4. These results confirm the existence of two subpopulations of R7 and R8 cells, which coordinate the expression of their respective rh genes. Thus, developmental signaling pathways between R7 and R8 lead to the exclusive expression of a single rhodopsin gene per cell and to the coordinate expression of another one in the neighboring cell. Consistent with this, rh5 expression in R8 disappears when R7 cells are absent (in sevenless mutant). We propose a model for the concerted evolution of opsin genes and the elaboration of the architecture of the retina.
Links	PubMed
Keywords	Amino Acid Sequence; Animals; Base Sequence; Biological Evolution; Chromosome Mapping; Conserved Sequence; DNA Primers; DNA, Complementary; Drosophila melanogaster/genetics; Gene Expression Regulation, Developmental; Genes, Insect; Genomic Library; Molecular Sequence Data; Photoreceptor Cells, Invertebrate/cytology; Photoreceptor Cells, Invertebrate/physiology; Polymerase Chain Reaction; Promoter Regions, Genetic; Protein Structure, Secondary; Rhodopsin/biosynthesis; Rhodopsin/chemistry; Rhodopsin/genetics; Rod Opsins/biosynthesis; Rod Opsins/chemistry; Rod Opsins/genetics; Sequence Homology, Amino Acid
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