The warm temperature acclimation protein Wap65 as an immune response gene: its duplicates are differentially regulated by temperature and bacterial infections.

The warm temperature acclimation related 65kDa protein (Wap65) in teleost fish shares high structural similarities with mammalian hemopexins. Recent studies using microarray analysis indicated that this temperature acclimation protein may also be involved in immune responses. To provide evidence of its potential involvement in immune responses after bacterial infections, we have identified and characterized two types of Wap65 genes in channel catfish, referred to as Wap65-1 and Wap65-2, respectively. While Wap65-1 and Wap65-2 are both structurally similar to the mammalian hemopexins, they exhibit highly differential patterns of spatial expression. Wap65-1 was expressed in a wide range of tissues, whereas Wap65-2 was only expressed in the liver. Their regulation with warm temperature and bacterial infections was also highly different: Wap65-1 was constitutively expressed, whereas Wap65-2 was highly regulated by both warm temperature and bacterial infections, and warm temperature and bacterial infections appeared to synergistically induce the expression of Wap65-2. The great contrast of expression patterns and regulation of the two catfish Wap65 genes suggested both neofunctionalization and partitioning of their functions. Phylogenetic analysis indicated that the duplicated catfish Wap65 genes were evolved not only from whole genome duplication, but also from tandem, intrachromosomal gene duplications. Taken together, the results of this study suggest that Wap65 genes are not only important for its classical role as a warm temperature acclimation protein, but more importantly, may also function as an immune response protein.