Unlike mammalian GRIFIN, the zebrafish homologue (DrGRIFIN) represents a functional carbohydrate-binding galectin

Abstract

Galectins, a family of β-galactoside-binding proteins, participate in a variety of biological processes, such as early development, tissue organization, immune functions, tumor evasion, and cancer metastasis. However, the detailed mechanisms of their biological roles still remain unclear. As many as 15 galectins are known in mammals, excluding some galectin-like sequences such as lens crystallin protein GRIFIN (galectin related inter fiber protein) and the hematopoietic stem cell precursor, HSPC159. Although they have close similarity to galectin sequences, due to the lack of ligand (lactose) binding activity they are not considered to be members of the galectin family but possibly products of evolutionary co-option. We have identified a homologue of the GRIFIN in zebrafish ( Danio rerio) (designated DrGRIFIN), which is also expressed in the lens, particularly in the fiber cells, as evidenced from whole mount in situ hybridization and immunostaining of 2 dpf (days post fertilization) embryos. As evidenced by RT-PCR, it is weakly expressed in the embryos as early as 21 hpf (hour post fertilization) and strongly at all later stages tested (30 hpf and 3, 4, 6, and 7 dpf). In adult zebrafish tissues, however, DrGRIFIN is also expressed in oocyte, brain, and intestine. Unlike the mammalian equivalent, DrGRIFIN contains all amino acids critical for ligand-binding and thus may represent a functional carbohydrate-binding galectin. This notion has been confirmed as the recombinant DrGRIFIN was active and purified to homogeneity on a lactosyl-Sepharose column. DrGRIFIN is a novel galectin that may have also crystallin property other than carbohydrate-binding property.