Establishment of photoreceptor cell polarity in culture revealed by mushroom lectin binding.

Differentiation of photoreceptor cells dissociated from chick embryo was investigated in a monolayer culture at low cell density and low serum concentration. The precursor cells were initially round and finally adopted the elongated and monopolar shape characteristic of such photoreceptor cells in vivo. They exhibited the primitive inner segment, and on its distal side showed a crest-like membrane expansion instead of the developed outer segment. The cell polarity of these cultured photoreceptor cells was examined using mushroom lectin, which has specific affinity for the D-galactose-beta(1,3)-N-acetylgalactosamine moiety. Rhodamine-labeled mushroom lectin uniformly initially stained the surface of early round photoreceptor cells, but with time the staining became restricted to the inner segment and its distal membrane expansion in all elongated photoreceptor cells at 12 days from the beginning of development. In semithin sections of 12-day-old chick embryo retina, mushroom lectin also stained the immature inner segment that had emerged at this stage. After hatching, light and electron microscopic observations revealed that the entire scleral surface of retinal plasma membranes as far as the outer limiting membrane, i.e. the inner and outer segments of all types of photoreceptor cells and also Müller cell processes, were stained with the mushroom lectin. These results clearly show that all photoreceptor cells can establish their inherent cell polarity even in culture, and that mushroom lectin is a valuable marker, for the investigation of photoreceptor cell polarity.