characterization and functional analysis of a tandemrepeat galectin9 in large yellow croaker larimichthys crocea galectins are a family of endogenous lectins with galactosides affinity playing significant roles in the innate immunity of vertebrates and invertebrates in this report a new galectin9 cdna was identified and characterized in large yellow croaker larimichthys crocea designated as lcgal9 the complete cdna sequence of lcgal9 was 1795 bp with an open reading frame orf of 1032 bp encoding 343 amino acids the putative lcgal9 protein contained two carbohydrate recognition domains crds connected by a linker peptide with each carrying two conserved galactoside binding motifs hnpr and wgee and it possessed neither a signal peptide nor a transmembrane domain lcgal9 protein shared 4374 identity with galectin9 sequences from other species the qrtpcr analysis revealed that lcgal9 mrna was constitutively expressed in all tissues examined predominately expressed in liver spleen gill kidney headkidney and intestine western blot analysis showed that lcgal9 protein was highly expressed in liver spleen intestine kidney headkidney skin gill and heart but not detected in muscle and plasma lcgal9 mrna transcripts were induced by poly ic in the liver from 6 h to 48 h spleen at 12 h and headkidney at 12 h and 24 h in contrast vibrio parahaemolyticus caused a significant downregulation in these three tissues except for in spleen of 48 h and headkidney of 3 h postinfection with cryptocaryon irritans the transcripts were dramatically upregulated in gill skin spleen and headkidney during initial infection period while significant downregulation afterward was also observed both in spleen and headkidney the recombinant lcgal9 named as rlcgal9 purified from escherichia coli bl21 de3 demonstrated hemagglutination against human rabbit and l crocea in a ca2independent manner which was inhibited by lactose and lps the results of bacterial agglutination assays showed that rlcgal9 was able to agglutinate gramnegative bacteria v alginolyticus and aeromonas hydrophila in a ca2independent manner by immunohistochemistry assay significant increases of lcgal9 protein appeared in the spleen stimulated with poly ic for 12 h and v parahaemolyticus for 48 h compared with the control based on the collective data lcgal9 might play an important role in innate immune responses especially defense against gramnegative bacteria in l crocea