Specific binding of peanut lectin to a class of retinal photoreceptor cells. A species comparison.

Although lectins have been used to study surface oligosaccharides of photoreceptor cells in intact retinas and dissociated retinal cells, the specificity of lectin binding to cones versus rods in a variety of species has not been examined closely. The authors previously found that application of fluorescein isothiocyanate (FITC)-conjugated peanut agglutinin (PNA), a lectin with high affinity for galactose-galactosamine disaccharide residues, to cryostat sections of unfixed mouse retina results in staining that is confined to synaptic regions and a subpopulation of photoreceptor cells. To further investigate the possibility that PNA binding is specific for cone photoreceptors, the authors extended their studies to include the duplex retinas of fish, rabbit, monkey, and human in addition to the cone-dominant retina of the chick. These studies show that PNA binding is specific for cone inner and outer segments and also is likely to be associated with the large synaptic pedicles of cone photoreceptor cells. In addition, the authors compared PNA binding with that of Ricinus communis agglutinin I (RCA), another lectin that preferentially binds terminal D-galactose moieties. While RCA does bind to cones in the species examined, it also binds to a lesser extent to rod photoreceptor inner segments. The pattern of binding of RCA in other regions of the retina differs markedly from that of PNA. Significantly, RCA serves as a specific marker for retinal vasculature in the human, monkey, and mouse. These results suggest that certain PNA-binding macromolecules may be important in defining the molecular and cellular specificity of cone photoreceptor cells and that PNA may provide a means for the isolation of cones and cone-specific molecules. RCA may prove to be of value in monitoring vascular changes associated with normal development and pathologic conditions.