ABSTRACT
Invertebrate and Protochordate Model Systems ...................................................... 88 7.2.2.1 Caenorhabditis elegans ............................................................................. 88 7.2.2.2 Drosophila melanogaster .......................................................................... 89 7.2.2.3 Ciona intestinalis ...................................................................................... 89 7.3 Vertebrates ........................................................................................................................... 90 7.3.1 Studies on Lectins from Vertebrate Species ............................................................ 90 7.3.2 Assessment of Galectin Function Using Genetically
Tractable Vertebrate Model Systems ....................................................................... 92 7.3.2.1 Studies on Murine Models ........................................................................ 92 7.3.2.2 Zebra sh (Danio rerio) as an Alternative Vertebrate
Model System ............................................................................................ 96 7.3.2.3 Experimental Infection and Disease ......................................................... 97 7.3.3 Zebra sh as a Model for Studies on Cancer ............................................................ 97 7.3.4 Zebra sh Cell Lines ................................................................................................. 98 7.3.5 Galectin Repertoires in Zebra sh ............................................................................ 98 7.3.5.1 Carbohydrate-Binding Speci cities and Structures of Zebra sh
Galectins Are Similar to Mammalian Galectins ...................................... 98 7.3.6 Current Approaches to Address Biological Roles of Galectins in Zebra sh ........... 101 7.3.6.1 Antisense Morpholino Knockdowns ......................................................... 101 7.3.6.2 Expression of Ectopic Galectin mRNA ..................................................... 101 7.3.6.3 Analyses of Notochord Mutants for Expression of Drgal1-L2 .................. 102 7.3.6.4 Roles of Galectins in Innate Immunity ..................................................... 102 7.4 Conclusions and Future Directions ...................................................................................... 103 Acknowledgments ......................................................................................................................... 103 References ..................................................................................................................................... 104
Cell surface glycans, such as glycocoproteins and glycolipids, encode information that modulates interactions between cells, or between cells and the extracellular matrix (ECM), by speci cally regulating the binding to cell surface-associated or soluble carbohydrate-binding receptors such as lectins. Since the time of their discovery in the late nineteenth century and beyond a strictly utilitarian role as useful reagents, lectins from numerous invertebrate and vertebrate species have been subject to a variety of studies aimed not only at the characterization of their biochemical, molecular and structural properties, but also to gain insight into their biological roles. In this regard, lectins have constituted an enigmatic group of proteins and it has long been deemed reasonable to postulate that their physiological roles in any particular cell or tissue relate in some way to their carbohydratebinding properties. Thus, detailed and useful descriptions of biochemical properties such as sugar speci city and requirement of cations for binding, as well as subcellular and tissue distribution are available for many animal lectins. For some animal lectin families, comparative approaches have made substantial contributions to the understanding of their evolution in their gene organization, structural aspects, and biochemical properties, and the early reports focused primarily on their possible roles in fertilization and immune responses. Although these studies provide a solid foundation for gaining a better understanding of these proteins, conclusions drawn in regard to their functional aspects have been mostly speculative. The modern era of research on animal lectins has seen a vast expansion on these foundations and a considerable body of experimental evidence from biochemical and structural approaches has led to fairly sound conclusions about their diverse roles within intracellular compartments, at the cell surface, and between cells or cells and the ECM, thereby mediating roles in intracellular traf cking, protein folding, and signaling in various aspects of development and immunity (see the appropriate chapters in later sections of this volume). It is only in the past decade, however, that the use of genetically tractable animal model systems and the availability of their fully sequenced genomes has allowed us to fully appreciate the diversity of their lectin repertoires and has enabled the rigorous demonstration of function for any given member.
