Outer segment localization signal at the C terminus of the photoreceptor-specific retinol dehydrogenase and proximal and distal sequences control UV cone pigment gene expression in transgenic zebrafish

Photoreceptors are highly polarized neurons, and they have a very specialized structure, the outer segment (OS), responsible for light detection. Rhodopsin and other phototransduction proteins specifically localize there. Since all of the protein synthesis machinery is in the inner segment, there must be a very active OS transportation pathway.; Photoreceptor retinol dehydrogenase (prRDH) is a membrane-associated cytosolic protein in the OS of rods and cones. In this work, we found that the C-terminal 16 amino acids of prRDH confer membrane association as well as cone and rod OS targeting. Membrane association in transfected 293 cells and in transgenic Xenopus photoreceptors is mediated by fatty acylation at one or more evolutionarily conserved cysteines within the prRDH C-terminal tail. In bovine OS, native prRDH is similarly acylated. Efficient OS localization requires both membrane association and the prRDH sequence...(V/I)XPX at the extreme C-terminus, which closely resembles the C-terminal sequence that targets opsin/rhodopsin to the OS. Taken together, these data imply that the C-terminal...(V/I)XPX sequence is a general OS localization signal that can function in the context of both integral and peripheral membrane proteins.; Cones are responsible for color vision. In general, only one cone opsin gene is chosen to be expressed in a given cone. However, the molecular basis of cone photoreceptor-specific gene expression is largely unknown. In this work, we defined cis-acting DNA sequences that control the cell-type specific expression of the zebrafish ultraviolet (UV) cone pigment gene by transient expression of green fluorescent protein (GFP) in transgenic zebrafish embryos. These experiments show that 4.8 kb of 5' flanking sequences from the zebrafish UV pigment gene direct expression specifically to UV cones and that this activity requires both distal and proximal sequences. In addition, we demonstrate that a UV promoter proximal region located between -215 to -110 bp (with respect to the initiator methionine codon) can function in the context of a zebrafish rhodopsin promotor to convert its specificity from rod-only expression to rod and UV cone expression.