SPATIAL AND TEMPORAL EXPRESSION OF CONE OPSINS DURING MONKEY RETINAL DEVELOPMENT

The primate retina requires a coordinated series of developmental even ts to form its specialized photoreceptor topography. In this study, th e temporal expression of cone photoreceptor opsin was determined in Ma caca monkey retina. Markers for mRNA and protein that recognize short wavelength (S) and long/medium wavelength (L/M) opsin were used to det ermine (1) the temporal and spatial patterns of opsin expression, (2) the spatial relationship between S and L/M cones at the time of initia l opsin expression, and (3) the relative time of cone and rod opsin ex pression (Dorn et al. [1995] Invest. Ophthalmol. Vis. Sci. 36:2634-265 1). Adult cone outer segments were recognized by either L/M or S opsin antiserum. Of all adult cone inner segments, 88-90% contained UM opsi n mRNA, whereas 10-12% contained S opsin mRNA. Fetal cones initially s howed cell membrane as well as outer segment labeling for opsin protei n, but cell membrane labeling disappeared by birth. No cones at any ag e contained markers for both S and L/M opsin mRNA or protein. S and L/ M opsin protein appeared in the fovea at fetal day 75. Once opsin expr ession progressed beyond the fovea, both mRNA and protein for S opsin were consistently detected more peripherally than L/M opsin. Cones at the peripheral edge of S opsin expression had basal telodendria that a ppeared to reach toward neighboring cones. Because interactions betwee n cone populations could organize the cone mosaic, the spatial relatio nship between S cones and the first cones to express L/M protein was a nalyzed quantitatively by using double-label immunocytochemistry. No c onsistent relationship was found between these two cone populations. C ones are generated at least 1 week before rods across monkey retina. H owever, rod opsin protein appears in and around the fovea at fetal day 66, 1 week before cone opsin protein. This suggests that independent local factors control differentiation in these two photoreceptor popul ations. (C) 1997 Wiley-Liss, Inc.