Immunocytochemical study of the distribution of a 16-kDa galectin in the chicken retina

PURPOSE. To compare the distribution of a developmentally regulated 16-kDa galectin in the chicken retina at two different developmental stages: embry onic day 13 (ED13) and postnatal day 10 (PD10) retinas, by immunocytochemic al analysis using light and transmission electron microscopy. METHODS. Semi-thin and thin sections from ED13 and PD10 retinas were incuba ted with the IgG fraction purified from a rabbit antiserum raised against t he 16-kDa chicken galectin. After incubation with colloidal Sold particle-l abeled goat anti-rabbit IgGs, tissue sections were analyzed by light and tr ansmission electron microscopy. To improve the observation by light microsc opy, semi-thin immunostained sections were intensified by silver enhancemen t. RESULTS. In ED13 retinas a specific galectin labeling was detected in the r egion corresponding to the outer limiting membrane by light microscopy. Thi s labeling seemed to be associated with the apical villi of Muller glial ce lls and their specialized junctions, as judged by transmission electron mic roscopy. In PD10 retinas, the more relevant finding revealed by light micro scopy was the detection of a widespread immunostaining at the level of all retinal layers. The ultrastructural analysis indicated that the galectin la beling was detected at the cytoplasmic and nuclear compartments of Muller c ells throughout the different retinal layers. Moreover, the labeling was de tected in the inner limiting membrane in structures that resemble the end f eet of Muller cells. The apical villi, and the specialized junctions of the se glial cells, appeared more strongly stained in PD10 retinas than in ED13 retinas. Finally, highly intense labeling in a group of mitochondria local ized in the inner segments of cone cells was observed. CONCLUSIONS. The present study clearly supports the idea that the subcellul ar distribution of the 16-kDa galectin changes during the development of th e chicken retina. Morphologic changes associated with developmentally regul ated expression and subcellular compartmentalization of the retinal galecti n suggest that this lectin may be involved in the modulation of several pro cesses in the visual system. Its presence in the apical villi of Muller cel ls may be related by modulatory Functions between retina and pigment epithe lium, but its presence in the cytoplasm and nucleus of these glial cells su ggests a potential immunomodulatory role and its involvement in different m etabolic processes between Muller and the other retinal cells. Finally, alt hough the presence of galectins inside mitochondria has not been described before, this localization gives rise to the idea that this lectin may be in volved in the modulation of mitochondrial processes.