Embryonic Patterning of Cone Subtypes in the Mammalian Retina

Abstract

Vertebrate color vision is mediated by different subtypes of cones whose visual pigments or opsins are maximally sensitive to long (LWS cones), middle (MWS cones), or short (SWS cones) wavelengths of light (Dartnall et al., 1983). Quantitative assessment of the distribution of these wavelength-sensitive cones in several mammalian species has revealed dramatically different arrangements and combinations of cone subtypes across the retinal sheet that coincide with differences in color vision and photopic acuity. For example, in the retina of both rhesus monkey and man, opsin-specific cone subtypes are arranged into reiterative patterns, in which each SWS cone is surrounded by approximately ten L/MWScones (Szel et al., 1988; Curcio et al, 1991; Wikler and Rakic, 1990). In contrast, in the mouse cone subtypes are topographically segregated with ventral retina occupied exclusively by SWS cones and dorsal retina dominated by MWS cones (Szel et al., 1992; Rohlich et al., 1994; Calderone and Jacobs, 1995). Thus, the different adult cone arrangements in murine and primate retina suggest that color vision may be tightly linked to the specification of both the position and the relative ratios of wavelength-sensitive cone subtypes.