Structural information encoded in complex carbohydrates mediates interactions between cells, or between cells and the extracellular matrix (ECM). The information is decoded by highly specific carbohydrate-binding receptors including lectins. One such family of beta-galactoside-binding lectins, the galectins, are synthesized in the cytosol and released into the extracellular space. Unique expression patterns, tissue distribution, and their affinity for endogenous ligands (ECM glycoproteins) and exogenous ligands (bacterial pathogens) have led to propose that galectins are involved in multiple functions. However, their biological roles are yet to be unequivocally established in vivo, due in part to the highly diversified (and functionally redundant") galectin repertoire of mammalian models. Zebrafish is a model of choice for these studies because it offers advantages over mammalian models, such as external fertilization, a short development period, transparent embryos, a large collection of mutants, and, based on our preliminary results, a less diversified galectin repertoire. We have partially characterized selected zebrafish galectins, developed a useful suite of molecular tools, and initiated studies aimed at elucidating their biological roles. By a "loss-of-function" approach targeted to a zebrafish galectin, which is a homologue of the mammalian galectin-1 and displays a unique expression pattern, we identified a tentative phenotype with a defect in muscle cell organization. We propose that: (a) galectins play a critical role in tissue development and organization, possibly by mediating cell migration and adhesion, and are indirectly involved in cell differentiation; and (b) galectins are involved in inflammation by interacting directly with potential pathogens and/or recruiting phagocytic cells (macrophages and neutrophils) to the infection sites. To test these hypotheses we will specifically: (a) complete the molecular characterization of the zebrafish galectin repertoire, including the identification of their ligands, and their patterns of spatial and temporal expression; (b) experimentally modulate/disrupt galectin function to assess their biological roles. Expected benefits include novel molecular tools and resources (available through the Consortium for Functional Glycomics) for functional analysis of galectins, and novel information on their interactions with cells, ECM and pathogens, that modulate their multiple functions in vertebrates.