Correspondence of gradual developmental increases of expression of galectin-reactive glycoconjugates with alterations of the total contents of the two differentially regulated galectins in chicken intestine and liver as indication for overlapping functions

The duplication of genes for recognition molecules and the ensuing diversif ication of the members of such families generate complex groups of homologo us proteins. One example are galactoside-specific lectins whose sequences d isplay constant features related to sugar binding, the galectins. Based on the inverse abundance of the chicken galectins CG-14 and CG-16 in adult int estine and liver, these two lectins represent a model to comparatively stud y expression of the related proteins and the galectin-reactive sites (glyco proteins and glycolipids) biochemically and histochemically. Functional ove rlap and/or acquisition of distinct functions would be reflected in qualita tive and/or quantitative aspects of ligand display. Using five different st ages of embryogenesis, differential regulation of the two galectins was det ected in liver and intestine. The clear preference for one galectin (CG-14) was observed in intestine already at rather early stages, whereas equivale nce for both proteins was noted in liver from day 12 to day 18 prior to hat ching, as seen by ELISA assays and Western blot analysis. Presentation of g alectin-reactive glycoproteins showed a tendency for gradual increase in bo th organs. Galectin-blotting analysis revealed primarily very similar patte rns of positive bands at the different stages of development and only few q uantitative and qualitative changes. The reactivity of glycolipids in a sol id-phase assay was more variable, even surpassing the response of extracts of the adult organ at several embryonic stages. While the localization patt erns of the galectins and galectin-reactive sites were nearly indistinguish able in the liver, intestinal tissue differed with respect to the placement and accessibility of binding sites. Thus, the results suggest a differenti al regulation of galectin activities in the two organs. As a sum they resem ble the course of development of availability of glycoprotein ligands in vi tro. These findings support the notion for a partial functional redundancy in this family. The described approach to employ galectin-specific antibodi es and the labeled galectins as tools to assess presentation of ligands is suggested to be of general relevance to address the question of distinct vs . overlapping functions of related recognition molecules.