Purification of galectin-3 from ovine placenta: developmentally regulated expression and immunological relevance

Galectins, beta-galactoside-binding lectins, are extensively distributed inthe animal kingdom and share some basic molecular properties. Galectin-3, amember of this family, is generally associated with differentiation,morphogenesis, and metastasis. In this study, galectin-3 was isolated fromovine placental cotyledons round the middle of the gestation period bylactose extraction followed by affinity chromatography on lactosyl-agarose,and separated from galectin-1 by size exclusion chromatography on aSuperose 12 column. Under native conditions this lectin behaved as amonomer with an apparent molecular weight of approximately 29,000 and anisoelectric point of 9.0. The partial amino acid sequence of the peptidesobtained by tryptic digestion of this protein followed by HPLC separationshowed striking homology with other members of the galectin-3 subfamily.Furthermore, ovine placental galectin-3 exhibited specific mitogenicactivity toward rat spleen mononuclear cells. Besides, this proteinstrongly reacted with a rabbit antiserum raised against a chicken galectin.Results obtained by Western blot analysis showed that its expression wasgreatly decreased in term placenta with respect to the middle of thegestation period, suggesting a regulated expression throughout development.