Network analysis of adhesion/growth-regulatory galectins and their binding sites in adult chicken retina and choroid.

The highly ordered multilayered organization of the adult chicken retina is a suitable test model for examining zonal distribution of the members of a bioeffector family. Based on the concept of the sugar code, the functional pairing of glycan epitopes with cognate receptors (lectins) is emerging as a means to explain the control of diverse physiological activities. Having recently completed the biochemical characterization of all seven adhesion/growth-regulatory galectins present in chicken, it was possible to establish how the individual characteristics of their expression profiles add up to shape the galectin network, which until now has not been defined at this level of complexity. This information will also have relevance in explaining the region-specific presence of glycan determinants in the retina, as illustrated in the first part of this study using a panel of nine plant/fungal agglutinins. The following systematic monitoring of the galectins yielded patterns for which quantitative and qualitative differences were detected. Obviously, positivity in distinct layers is not confined to a single protein of this family, e.g. CG-1A, CG-3 or CG-8. These results underline the requirement for network analysis for these proteins that can functionally interact in additive or antagonistic modes. Labeling of the tissue galectins facilitated profiling of their accessible binding sites. It also revealed differences among the galectin family members, highlighting the ability of this method to define binding properties on the level of tissue sections. Methodologically, the detection of endogenous lectins intimates that cognate glycans can become inaccessible, a notable caveat for lectin histochemical studies.